Author name code: cliver
ADS astronomy entries on 2022-09-14
author:Cliver, Edward W.
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Title: Extreme solar events
Authors: Cliver, Edward W.; Schrijver, Carolus J.; Shibata, Kazunari;
Usoskin, Ilya G.
Bibcode: 2022LRSP...19....2C
Altcode: 2022arXiv220509265C
We trace the evolution of research on extreme solar and
solar-terrestrial events from the 1859 Carrington event to the rapid
development of the last twenty years. Our focus is on the largest
observed/inferred/theoretical cases of sunspot groups, flares on the
Sun and Sun-like stars, coronal mass ejections, solar proton events,
and geomagnetic storms. The reviewed studies are based on modern
observations, historical or long-term data including the auroral and
cosmogenic radionuclide record, and Kepler observations of Sun-like
stars. We compile a table of 100- and 1000-year events based on
occurrence frequency distributions for the space weather phenomena
listed above. Questions considered include the Sun-like nature of
superflare stars and the existence of impactful but unpredictable solar
"black swans" and extreme "dragon king" solar phenomena that can involve
different physics from that operating in events which are merely large.
Title: Limits of eruptive flare activity on the Sun
Authors: Cliver, Edward
Bibcode: 2022cosp...44.1390C
Altcode:
Eruptive flares pose a threat to technology-based society, primarily via
CME-driven disruption of the power grid and secondarily through solar
proton bombardment of satellite infrastructure. What is the worst case
scenario? Here we consider observed, inferred, and theoretical limits
of the strength of solar flares, solar energetic proton events, and
coronal mass ejections. The current standard for each of these types
of solar emission (electromagnetic, particle, plasma) is set by the
eruptive event in 774 AD that was discovered via cosmogenic nuclide
enhancements in tree rings and ice cores.
Title: Avril Hart and the discovery of solar supergranulation
Authors: Cliver, Edward W.; Knipp, Delores J.
Bibcode: 2021A&G....62.6.38C
Altcode:
Edward W Cliver and Delores J Knipp chart the emergence of solar
astonomer Avril Hart (1928-2011) and her unexpected discovery of a
"noisy" velocity field.
Title: Carrington's lost photograph
Authors: Cliver, E. W.; Fletcher, Lyndsay; Hudson, H. S.
Bibcode: 2021A&G....62.2.40C
Altcode:
Ed Cliver, Lyndsay Fletcher and Hugh Hudson are looking for a photograph
of Richard Carrington. Can you help?
Title: On the Size of the Flare Associated with the Solar Proton
Event in 774 AD
Authors: Cliver, E. W.; Hayakawa, H.; Love, Jeffrey J.; Neidig, D. F.
Bibcode: 2020ApJ...903...41C
Altcode:
The 774 AD solar proton event (SPE) detected in cosmogenic nuclides
had an inferred >1 GV (>430 MeV) fluence estimated to have been
∼30-70 times larger than that of the 1956 February 23 ground level
event (GLE). The 1956 GLE was itself ∼2.5 times larger at >430 MeV
than the episode of strong GLE activity from 1989 August-October. We use
an inferred soft X-ray (SXR) class of X20 ± 10 for the 1956 February
23 eruptive flare as a bridge to the source flare for the 774 SPE. A
correlation of the >200 MeV proton fluences of hard-spectra post-1975
GLEs with the SXR peak fluxes of their associated flares yields an
SXR flare class of X285 ± 140 (bolometric energy of ∼(1.9 ± 0.7)
× 1033 erg) for the 774 flare. This estimate is within
theoretical determinations of the largest flare the Sun could produce
based on the largest spot group yet observed. Assuming a single eruptive
flare source for the 774 SPE, the above estimate indicates that the Sun
can produce a threshold-level 1033 erg superflare. If the 774
event originated in two closely timed, equal-fluence SPEs, the inferred
flare size drops to X180 ± 90 (∼(1.4 ± 0.5) × 1033
erg). We speculate on favorable solar conditions that can lead to
enhanced shock acceleration of high-energy protons in eruptive flares.
Title: Solar Longitude Distribution of High-energy Proton Flares:
Fluences and Spectra
Authors: Cliver, E. W.; Mekhaldi, F.; Muscheler, R.
Bibcode: 2020ApJ...900L..11C
Altcode:
The distribution of the longitudes of solar flares associated with the
high-energy proton events called ground level events (GLEs) can be
approximated by a Gaussian with a peak at ∼W60, with a full range
from ∼E90 to ∼W150. The longitudes of flares associated with the
top third (24 of 72) of GLEs in terms of their >430 MeV fluences
(F430) are primarily distributed over E20-W100 with a
skew toward disk center. This 120° span in longitude is comparable
to the latitudinal spans of powerful coronal mass ejections
(CMEs) from limb flares. Only 5 of 24 strong GLEs are located
within the W40-80 zone of good magnetic connection to Earth. GLEs
with hard spectra, i.e., a spectral index SI30/200(=
log(F30/F200)) < 1.5, also tend to avoid
W40-80 source regions. Three-fourths of such events (16 of 21) arise in
flares outside this range. The above tendencies favor a CME-driven shock
source over a flare-resident acceleration process for high-energy solar
protons. GLE spectra show a trend, with broad scatter, from hard spectra
for events originating in eruptive flares beyond the west limb to soft
spectra for GLEs with sources near central meridian. This behavior can
be explained in terms of: (1) dominant near-Sun quasi-perpendicular
shock acceleration of protons for far western (>W100) GLEs; (2)
quasi-parallel shock acceleration for well-connected (W40-80) GLEs,
and (3) proton acceleration/trapping at CME-driven bow shocks from
central meridian (E20-W20) that strike the Earth.
Title: What Can Be Learned from Modern Data?
Authors: Kusano, K.; Cliver, E.; Hayakawa, H.; Kovaltsov, G. A.;
Usoskin, I. G.
Bibcode: 2019esps.book....2K
Altcode:
Our detailed knowledge about the Sun comes from instrumental
observations, the precision and sophistication of which have rapidly
increased over the last decades. The primary focus of this book lies in
solar eruptive events. This chapter provides a review of what we know
about solar eruptive events, especially about the strongest observed
ones, from precise modern data.
Title: Characterization of the Measured Events
Authors: Cliver, E.; Ebihara, Y.; Hayakawa, H.; Jull, T.; Mekhaldi,
F.; Miyake, F.; Muscheler, R.
Bibcode: 2019esps.book....6C
Altcode:
In this chapter we summarize the characterization of the known
historical extreme solar events.
Title: State-of-the-art Theory and Modeling
Authors: Sokoloff, D.; Cliver, E.
Bibcode: 2019esps.book....3S
Altcode:
The occurrence of eruptive events, in particular solar flares and
SEP events, is a complicated process that needs to be understand
theoretically. This chapter is devoted to a presentation of the
state-of-the-art theoretical models trying to explain the observed
phenomena.
Title: The ESPERTA Forecast Tool for Solar Proton Events
Authors: Laurenza, Monica; Alberti, T.; Cliver, E. W.; Vecchio, A.
Bibcode: 2019shin.confE.113L
Altcode:
The ESPERTA (Empirical model for Solar Proton Event Real Time Alert)
forecast tool was designed to provide warnings of Solar Proton Events
(SPEs, defined as those that meet or exceed a proton flux at >10 MeV
energies of 10 pfu, class ?S1 in the NOAA scale), within 10 minutes
of the associated flare soft X-ray (SXR) maximum (Laurenza et al.,
2009). Within this time constraint, ESPERTA is based on input flare
data (flare location, flare 1-8 Å SXR fluence, and flare 1 MHz radio
fluence) that are, or could be made, available in real time. These
three parameters provide information on proton propagation, solar event
energy, and particle escape, respectively. ESPERTA has also been adapted
for predicting SPEs from moderate to extreme intensities (i.e., ?100
pfu, class ?S2 in the NOAA scale) which produce the most significant
biological and space operation impacts, with increased effects on HF
propagation in the polar regions (Laurenza et al., 2018). We obtained
a POD of 63% (75%) and an FAR of 38% (24%) with a median WT of 4.8
hr ( 1.7 hr) for the prediction of ?S1 events (?S2 events, based on
predictions made at the time of the S1 threshold crossing) over the
1995-2014 time period. The improved performance of ESPERTA for ?S2
events is a reflection of the big flare syndrome, which postulates that
the measures of the various manifestations of eruptive solar flares
increase as one considers increasingly larger events. Here, we present
the model application for the three campaign SEP events (7 March 2012,
17 May 2012, and 10 September 2017), which were correctly forecasted by
ESPERTA, both for the S1 and S2 thresholds. Moreover, we present some
advances toward the ESPERTA tool implementation in operational mode.
Title: The Disappearing Solar Filament of 2013 September 29 and Its
Large Associated Proton Event: Implications for Particle Acceleration
at the Sun
Authors: Cliver, E. W.; Kahler, S. W.; Kazachenko, M.; Shimojo, M.
Bibcode: 2019ApJ...877...11C
Altcode:
We present observations of a notable example of a disappearing solar
filament (DSF) on 2013 September 29 that was associated with a large
solar proton event (SPE) and discuss this event in the context of
four recent studies that compare flare and SPE size parameters. The
DSF-associated flare was characterized by weak radio and soft X-ray
emissions and a low reconnection flux. It was accompanied by a fast
coronal mass ejection (CME) and a decametric-hectometric type II
burst. We assembled a list of eight such events that are outliers
in plots of SPE versus flare size parameters. These events were
characterized by weak magnetic field source regions (predominantly
DSFs but including one case of a transequatorial loop and another
of a decaying active region), fast CMEs, type II bursts with low
starting frequencies, high proton yields (ratio of proton intensity
to 1 MHz radio fluence), and low high-energy Fe/O ratios. The last
of these attributes suggests quasi-parallel shock acceleration. The
relationship between SPE and flare size parameters in large (gradual),
well-connected proton events can be illustrated by a schematic diagram
with three principal regions: (1) a DSF zone of weak flares and large
SPEs, (2) a big flare syndrome main sequence of loosely correlated flare
and SPE parameters, and (3) a zone of moderate to large flares with no
SPEs. The existence of regions 1 and 3 argues against a significant
role for flares in large proton events: region 1 implies that flares
are not necessary for such SPEs, and region 3 indicates that they are
not sufficient.
Title: The extreme space weather event in September 1909
Authors: Hayakawa, Hisashi; Ebihara, Yusuke; Cliver, Edward W.;
Hattori, Kentaro; Toriumi, Shin; Love, Jeffrey J.; Umemura, Norio;
Namekata, Kosuke; Sakaue, Takahito; Takahashi, Takuya; Shibata,
Kazunari
Bibcode: 2019MNRAS.484.4083H
Altcode: 2018MNRAS.tmp.3046H
We evaluate worldwide low-latitude auroral activity associated with the
great magnetic storm of September 1909 for which a minimum Dst value
of -595 nT has recently been determined. From auroral observations,
we calculate that the equatorward boundary of the auroral oval in
the 1909 event was in the range from 31°-35° invariant latitude
(assuming auroral height of 400 km) to 37°-38° (800 km). These
locations compare with satellite-based observations of precipitating
auroral electrons down to 40° magnetic latitude for the March 1989
storm with its comparable minimum Dst value of -589 nT. According
to Japanese auroral records, bluish colour started to appear first,
followed by reddish colour. The colour change can be attributed to
the transition from sunlit aurora to the usual low-latitude reddish
aurora. Telegraph communications were disrupted at mid/low latitudes,
coincidently with the storm main phase and the early recovery
phase. The telegraphic disturbances were caused by geomagnetically
induced currents associated with the storm-time ring current and
substorm current wedge. From the calculated CME energy - based on the
24.75 hr separation between the flare-associated magnetic crochet
and the geomagnetic storm sudden commencement and interplanetary
conditions inferred from geomagnetic data - and consideration of the
∼-40 nT crochet amplitude, we estimated that the soft X-ray class
of the 24 September 1909 flare was ≥X10. As is the case for other
extreme storms, strong/sharp excursions in the horizontal component
of the magnetic field observed at low-latitude magnetic stations were
coincident with the observation of low-latitude aurora.
Title: Forecasting solar proton events by using the ESPERTA model
Authors: Alberti, T.; Laurenza, M.; Cliver, E. W.
Bibcode: 2019NCimC..42...40A
Altcode:
The ESPERTA (Empirical model for Solar Proton Event Real Time Alert)
forecast tool has a Probability of Detection (POD) of 63% for all
> 10 MeV events with proton peak intensity ≥ 10 pfu (i.e., ≥
S1 events, S1 referring to minor storms on the NOAA Solar Radiation
Storms scale), from 1995 to 2014 with a false alarm rate (FAR) of
38% and a median (minimum) warning time (WT) of ∼ 4.8 ( ∼ 0.4)
hr. The ESPERTA model modified to predict ≥ S2 (i.e., ≥ 100 pfu)
has a POD of 75% and a FAR of 24% for the 1995 - 2014 interval with a
median (minimum) WT of ∼ 1.7 ( ∼ 0.2) hr based on predictions made
at the time of the S1 threshold crossing. Here, both versions of the
ESPERTA model have been applied to forecast recent solar proton events
from 2015 to 2017, yielding results consistent with model performance
for the 1995 to 2014 interval.
Title: Evolution of the Sunspot Number and Solar Wind BB Time Series
Authors: Cliver, Edward W.; Herbst, Konstantin
Bibcode: 2019sfsw.book...81C
Altcode:
No abstract at ADS
Title: Magnetic Flux Reconnection in Flaring Active Regions with
Sustained Gamma-Ray Emission
Authors: Kahler, S. W.; Cliver, E. W.; Kazachenko, M.
Bibcode: 2018ApJ...868...81K
Altcode:
Characteristics of sustained >100 MeV γ-ray emission (SGRE)
events observed by the Large Area Telescope on Fermi were recently
reported by Share et al. Their spectra are consistent with the decay
of pions produced by >300 MeV protons and appear spectrally and
spatially distinct from preceding associated flares. The source(s) of
the sustained production of the >300 MeV protons is uncertain, but
acceleration in coronal/interplanetary shock waves driven by coronal
mass ejections, followed by a return of the protons back to the Sun,
is favored. This scenario requires proton transport through converging
magnetic fields behind the shock, which might result in considerable
reflection of the protons back into space, and 1 au observations of the
associated solar energetic proton (SEP) events do not always include a
population of E > 300 MeV protons. Alternative source candidates that
involve trapping or continued acceleration of SEPs in coronal loops have
been considered. The energy release rates from magnetic reconnection in
flaring active regions (ARs) have been measured with a new technique,
and in this work we compare those measured flux reconnection rates
with emission profiles in 11 SGRE events. In general, the magnetic
reconnection event is nearly or completely finished before the bulk
of the γ-ray emission, which argues against scenarios of continued
proton acceleration in the flaring ARs.
Title: Size Distributions of Solar Proton Events and Their Associated
Soft X-Ray Flares: Application of the Maximum Likelihood Estimator
Authors: Cliver, Edward W.; D'Huys, Elke
Bibcode: 2018ApJ...864...48C
Altcode:
We use the maximum likelihood estimator to determine the slope (α)
of the power-law size distribution of the peak proton fluxes of a
subsampled set of 106 ∼ 25 MeV solar energetic proton (SEP) events
from 1997 to 2016 associated with western hemisphere soft X-ray (SXR)
flares: α = 1.28 ± 0.03. For the peak SXR fluxes of a subsample of
110 SEP-associated flares, we find α = 1.51 ± 0.05. In addition, we
obtained a slope of 1.61 ± 0.05 for the peak SXR fluxes of a sample
of 128 ≥M1 SXR flares from 1996 to 2005 that were associated with
coronal mass ejections (CMEs) with speeds ≥1000 km s-1. The
slopes of both of these SXR peak-flux distributions (∼1.5 and ∼1.6)
are closer to that for proton events (∼1.3) than to the α value
of ∼2.1 (2.09 ± 0.08) determined for a subsample of 177 western
hemisphere ≥M1 SXR flares considered from 1996 to 2005. These results
are consistent with those of a previous study, based on a less reliable
method (for small samples), in which it was argued that the flatter
size distribution generally found for SEP events versus those for
flare electromagnetic emissions was due to the fact that SEP flares
are an energetic subset of all flares, characterized by their ∼100%
association with fast/wide CMEs that drive coronal/interplanetary shock
waves. Shock formation in the corona requires CMEs with speeds ≳400
km s-1, a threshold effect that further distinguishes SEP
flares from the general population of all flares.
Title: A Short-term ESPERTA-based Forecast Tool for
Moderate-to-extreme Solar Proton Events
Authors: Laurenza, M.; Alberti, T.; Cliver, E. W.
Bibcode: 2018ApJ...857..107L
Altcode:
The ESPERTA (Empirical model for Solar Proton Event Real Time Alert)
forecast tool has a Probability of Detection (POD) of 63% for all
>10 MeV events with proton peak intensity ≥10 pfu (i.e., ≥S1
events, S1 referring to minor storms on the NOAA Solar Radiation
Storms scale), from 1995 to 2014 with a false alarm rate (FAR) of 38%
and a median (minimum) warning time (WT) of ∼4.8 (0.4) hr. The NOAA
space weather scale includes four additional categories: moderate
(S2), strong (S3), severe (S4), and extreme (S5). As S1 events have
only minor impacts on HF radio propagation in the polar regions, the
effective threshold for significant space radiation effects appears
to be the S2 level (100 pfu), above which both biological and space
operation impacts are observed along with increased effects on HF
propagation in the polar regions. We modified the ESPERTA model to
predict ≥S2 events and obtained a POD of 75% (41/55) and an FAR
of 24% (13/54) for the 1995-2014 interval with a median (minimum)
WT of ∼1.7 (0.2) hr based on predictions made at the time of the
S1 threshold crossing. The improved performance of ESPERTA for ≥S2
events is a reflection of the big flare syndrome, which postulates
that the measures of the various manifestations of eruptive solar
flares increase as one considers increasingly larger events.
Title: Evolution of the Sunspot Number and Solar Wind B Time Series
Authors: Cliver, Edward W.; Herbst, Konstantin
Bibcode: 2018SSRv..214...56C
Altcode:
The past two decades have witnessed significant changes in our
knowledge of long-term solar and solar wind activity. The sunspot
number time series (1700-present) developed by Rudolf Wolf during
the second half of the 19th century was revised and extended by the
group sunspot number series (1610-1995) of Hoyt and Schatten during
the 1990s. The group sunspot number is significantly lower than the
Wolf series before ∼1885. An effort from 2011-2015 to understand and
remove differences between these two series via a series of workshops
had the unintended consequence of prompting several alternative
constructions of the sunspot number. Thus it has been necessary to
expand and extend the sunspot number reconciliation process. On the
solar wind side, after a decade of controversy, an ISSI International
Team used geomagnetic and sunspot data to obtain a high-confidence time
series of the solar wind magnetic field strength (B) from 1750-present
that can be compared with two independent long-term (> ∼600 year)
series of annual B-values based on cosmogenic nuclides. In this paper,
we trace the twists and turns leading to our current understanding of
long-term solar and solar wind activity.
Title: Minimal Magnetic States of the Sun and the Solar Wind:
Implications for the Origin of the Slow Solar Wind
Authors: Cliver, E. W.; von Steiger, R.
Bibcode: 2018smf..book..227C
Altcode:
No abstract at ADS
Title: Solar Magnetic Fields
Authors: Balogh, André; Cliver, Edward; Petrie, Gordon; Solanki,
Sami; Thompson, Michael; von Steiger, Rudolf
Bibcode: 2018smf..book.....B
Altcode:
No abstract at ADS
Title: Minimal Magnetic States of the Sun and the Solar Wind:
Implications for the Origin of the Slow Solar Wind
Authors: Cliver, E. W.; von Steiger, R.
Bibcode: 2017SSRv..210..227C
Altcode: 2015SSRv..tmp..116C
During the last decade it has been proposed that both the Sun and
the solar wind have minimum magnetic states, lowest order levels
of magnetism that underlie the 11-yr cycle as well as longer-term
variability. Here we review the literature on basal magnetic states at
the Sun and in the heliosphere and draw a connection between the two
based on the recent deep 2008-2009 minimum between cycles 23 and 24. In
particular, we consider the implications of the low solar activity
during the recent minimum for the origin of the slow solar wind.
Title: Sunspot number recalibration: The 1840-1920 anomaly in the
observer normalization factors of the group sunspot number
Authors: Cliver, Edward W.
Bibcode: 2017JSWSC...7A..12C
Altcode:
We analyze the normalization factors (k'-factors) used to scale
secondary observers to the Royal Greenwich Observatory (RGO) reference
series of the Hoyt & Schatten (1998a, 1998b) group sunspot number
(GSN). A time series of these k'-factors exhibits an anomaly from
1841 to 1920, viz., the average k'-factor for all observers who began
reporting groups from 1841 to 1883 is 1.075 vs. 1.431 for those who
began from 1884 to 1920, with a progressive rise, on average, during
the latter period. The 1883-1884 break between the two subintervals
occurs precisely at the point where Hoyt and Schatten began to use a
complex daisy-chaining method to scale observers to RGO. The 1841-1920
anomaly implies, implausibly, that the average sunspot observer
who began from 1841 to 1883 was nearly as proficient at counting
groups as mid-20th century RGO (for which k' = 1.0 by definition)
while observers beginning during the 1884-1920 period regressed
in group counting capability relative to those from the earlier
interval. Instead, as shown elsewhere and substantiated here, RGO
group counts increased relative to those of other long-term observers
from 1874 to 1915. This apparent inhomogeneity in the RGO group count
series is primarily responsible for the increase in k'-factors from
1884 to 1920 and the suppression, by 44% on average, of the Hoyt
and Schatten GSN relative to the original Wolf sunspot number (WSN)
before 1885. Correcting for the early "learning curve" in the RGO
reference series and minimizing the use of daisy-chaining rectifies
the anomalous behavior of the k'-factor series. The resultant GSN time
series (designated GSN*) is in reasonable agreement with the revised WSN
(SN*; Clette & Lefèvre 2016) and the backbone-based
group sunspot number (RGS; Svalgaard & Schatten 2016)
but significantly higher than other recent reconstructions (Friedli,
personal communication, 2016; Lockwood et al. 2014a, 2014b, Usoskin
et al. 2016a). This result is substantiated by a "correction-factor"
(CF) time series defined as the ratio of annual group counts of the
Hoyt & Schatten (1998a, 1998b) series to the average raw (unscaled)
group counts of all observers, as well as by a comparison of the GSN
and GSN* time series with a recent reconstruction of solar wind B from
1845 to the present. The 1840-1920 k'-factor anomaly and its impact on
the Hoyt and Schatten GSN are discussed in the context of the ongoing
effort to recalibrate the sunspot number time series.
Title: Solar Activity from 2006 to 2014 and Short-term Forecasts of
Solar Proton Events Using the ESPERTA Model
Authors: Alberti, T.; Laurenza, M.; Cliver, E. W.; Storini, M.;
Consolini, G.; Lepreti, F.
Bibcode: 2017ApJ...838...59A
Altcode:
To evaluate the solar energetic proton (SEP) forecast model of Laurenza
et al., here termed ESPERTA, we computed the input parameters (soft
X-ray (SXR) fluence and ∼1 MHz radio fluence) for all ≥M2 SXR
flares from 2006 to 2014. This database is outside the 1995-2005
interval on which ESPERTA was developed. To assess the difference in
the general level of activity between these two intervals, we compared
the occurrence frequencies of SXR flares and SEP events for the first
six years of cycles 23 (1996 September-2002 September) and 24 (2008
December-2014 December). We found a reduction of SXR flares and SEP
events of 40% and 46%, respectively, in the latter period. Moreover, the
numbers of ≥M2 flares with high values of SXR and ∼1 MHz fluences
(>0.1 J m-2 and >6 × 105 sfu × minute,
respectively) are both reduced by ∼30%. A somewhat larger percentage
decrease of these two parameters (∼40% versus ∼30%) is obtained
for the 2006-2014 interval in comparison with 1995-2005. Despite
these differences, ESPERTA performance was comparable for the two
intervals. For the 2006-2014 interval, ESPERTA had a probability of
detection (POD) of 59% (19/32) and a false alarm rate (FAR) of 30%
(8/27), versus a POD = 63% (47/75) and an FAR = 42% (34/81) for the
original 1995-2005 data set. In addition, for the 2006-2014 interval
the median (average) warning time was estimated to be ∼2 hr (∼7 hr),
versus ∼6 hr (∼9 hr), for the 1995-2005 data set.
Title: On the Origin of Long-duration Solar Gamma-ray Flares and
Their Connection with SEPs
Authors: Bernstein, V.; Winter, L. M.; Cliver, E. W.; Omodei, N.;
Pesce-Rollins, M.
Bibcode: 2016AGUFMSH41B2537B
Altcode:
The mechanism producing long-duration solar gamma-ray events
(LDGREs) is unresolved. Such events are characterized by high-energy
(>100 MeV) pion-decay emission that can be detected for up to 10
hours after the flare impulsive phase. Candidate processes include:
(1) prolonged acceleration/trapping of high-energy (> 300 MeV)
protons in flare loops and (2) precipitation of energetic protons to
the Sun's surface from the CME-driven coronal shock waves. LDGREs,
or events with delayed/prolonged pion-dominated emission, have been
detected by the SMM GRS, GRO EGRET, and Fermi LAT. To gain insight on
their origin, we examine associated GOES X-ray bursts, LASCO CMEs,
Wind Waves low-frequency radio bursts, and GOES high-energy proton
events, and compare the properties of these various phenomena with
the intensities and durations of the observed LDGREs.
Title: Flare vs. Shock Acceleration of High-energy Protons in Solar
Energetic Particle Events
Authors: Cliver, E. W.
Bibcode: 2016ApJ...832..128C
Altcode:
Recent studies have presented evidence for a significant to dominant
role for a flare-resident acceleration process for high-energy
protons in large (“gradual”) solar energetic particle (SEP) events,
contrary to the more generally held view that such protons are primarily
accelerated at shock waves driven by coronal mass ejections (CMEs). The
new support for this flare-centric view is provided by correlations
between the sizes of X-ray and/or microwave bursts and associated SEP
events. For one such study that considered >100 MeV proton events,
we present evidence based on CME speeds and widths, shock associations,
and electron-to-proton ratios that indicates that events omitted from
that investigation’s analysis should have been included. Inclusion
of these outlying events reverses the study’s qualitative result
and supports shock acceleration of >100 MeV protons. Examination
of the ratios of 0.5 MeV electron intensities to >100 MeV proton
intensities for the Grechnev et al. event sample provides additional
support for shock acceleration of high-energy protons. Simply scaling
up a classic “impulsive” SEP event to produce a large >100
MeV proton event implies the existence of prompt 0.5 MeV electron
events that are approximately two orders of magnitude larger than are
observed. While classic “impulsive” SEP events attributed to flares
have high electron-to-proton ratios (≳5 × 105) due to a
near absence of >100 MeV protons, large poorly connected (≥W120)
gradual SEP events, attributed to widespread shock acceleration, have
electron-to-proton ratios of ∼2 × 103, similar to those
of comparably sized well-connected (W20-W90) SEP events.
Title: Preface to Topical Issue: Recalibration of the Sunspot Number
Authors: Clette, F.; Cliver, E. W.; Lefèvre, L.; Svalgaard, L.;
Vaquero, J. M.; Leibacher, J. W.
Bibcode: 2016SoPh..291.2479C
Altcode: 2016SoPh..tmp..184C
This topical issue contains articles on the effort to recalibrate
the sunspot number (SN) that was initiated by the Sunspot Number
Workshops. These workshops led to a revision of the Wolf sunspot number
(WSN) and a new construction of the group sunspot number (GSN),
both published herein. In addition, this topical issue includes
three independently proposed alternative SN time series (two Wolf
and one group), as well as articles providing historical context,
critical assessments, correlative analyses, and observational data,
both historical and modern, pertaining to the sunspot-number time
series. The ongoing effort to understand and reconcile the differences
between the various new sunspot number series is briefly discussed.
Title: The Discontinuity Circa 1885 in the Group Sunspot Number
Authors: Cliver, E. W.; Ling, A. G.
Bibcode: 2016SoPh..291.2763C
Altcode: 2016SoPh..tmp...14C
On average, the international sunspot number (RI) is 44 %
higher than the group sunspot number (RG) from 1885 to the
beginning of the RI series in 1700. This is the principal
difference between RI and RG. Here we show that
this difference is primarily due to an inhomogeneity in the Royal
Greenwich Observatory (RGO) record of sunspot groups (1874 - 1976)
used to derive observer normalization factors (called k -factors)
for RG. Specifically, annual RGO group counts increase
relative to those of Wolfer and other long-term observers from 1876
- 1915. A secondary contributing cause is that the k -factors for
observers who began observing before 1884 and overlapped with RGO for
any years during 1874 - 1883 were not based on direct comparison with
RGO but were calculated using one or more intermediary or additional
observers. We introduce RGC by rectifying the RGO group
counts from 1874 - 1915 and basing k -factors on direct comparison
with RGO across the 1885 discontinuity, which brings the RG
and RI series into reasonable agreement for the 1841 -
1885 interval (after correcting RI for an inhomogeneity from
1849 - 1867 (to give RIC)). Comparison with an independently
derived backbone-based reconstruction of RG (RBB)
indicates that RGC over-corrects RBB by 4 %
on average from 1841 - 1925. Our analysis suggests that the maxima of
Cycles 10 (in 1860), 12 (1883/1884), and 13 (1893) in the RIC
series are too low by ≈ 10 %.
Title: Comparison of New and Old Sunspot Number Time Series
Authors: Cliver, E. W.
Bibcode: 2016SoPh..291.2891C
Altcode: 2016SoPh..tmp..104C
Four new sunspot number time series have been published in this Topical
Issue: a backbone-based group number in Svalgaard and Schatten (Solar
Phys., 2016; referred to here as SS , 1610 - present), a group number
series in Usoskin et al. (Solar Phys., 2016; UEA, 1749 - present) that
employs active day fractions from which it derives an observational
threshold in group spot area as a measure of observer merit, a
provisional group number series in Cliver and Ling (Solar Phys.,
2016; CL , 1841 - 1976) that removed flaws in the Hoyt and Schatten
(Solar Phys.179, 189, 1998a; 181, 491, 1998b) normalization scheme
for the original relative group sunspot number (RG, 1610 -
1995), and a corrected Wolf (international, RI) number
in Clette and Lefèvre (Solar Phys., 2016; SN, 1700 -
present). Despite quite different construction methods, the four new
series agree well after about 1900. Before 1900, however, the UEA
time series is lower than SS , CL , and SN, particularly
so before about 1885. Overall, the UEA series most closely resembles
the original RG series. Comparison of the UEA and SS series
with a new solar wind B time series (Owens et al. in J. Geophys. Res.,
2016; 1845 - present) indicates that the UEA time series is too low
before 1900. We point out incongruities in the Usoskin et al. (Solar
Phys., 2016) observer normalization scheme and present evidence that
this method under-estimates group counts before 1900. In general,
a correction factor time series, obtained by dividing an annual group
count series by the corresponding yearly averages of raw group counts
for all observers, can be used to assess the reliability of new sunspot
number reconstructions.
Title: Near-Earth heliospheric magnetic field intensity since 1750:
2. Cosmogenic radionuclide reconstructions
Authors: Owens, M. J.; Cliver, E.; McCracken, K. G.; Beer, J.; Barnard,
L.; Lockwood, M.; Rouillard, A.; Passos, D.; Riley, P.; Usoskin, I.;
Wang, Y. -M.
Bibcode: 2016JGRA..121.6064O
Altcode:
This is Part 2 of a study of the near-Earth heliospheric magnetic field
strength, B, since 1750. Part 1 produced composite estimates of B from
geomagnetic and sunspot data over the period 1750-2013. Sunspot-based
reconstructions can be extended back to 1610, but the paleocosmic ray
(PCR) record is the only data set capable of providing a record of
solar activity on millennial timescales. The process for converting
10Be concentrations measured in ice cores to B is more
complex than with geomagnetic and sunspot data, and the uncertainties
in B derived from cosmogenic nuclides (~20% for any individual year)
are much larger. Within this level of uncertainty, we find reasonable
overall agreement between PCR-based B and the geomagnetic- and sunspot
number-based series. This agreement was enhanced by excising low values
in PCR-based B attributed to high-energy solar proton events. Other
discordant intervals, with as yet unspecified causes remain included in
our analysis. Comparison of 3 year averages centered on sunspot minimum
yields reasonable agreement between the three estimates, providing a
means to investigate the long-term changes in the heliospheric magnetic
field into the past even without a means to remove solar proton events
from the records.
Title: Near-Earth heliospheric magnetic field intensity since 1750:
1. Sunspot and geomagnetic reconstructions
Authors: Owens, M. J.; Cliver, E.; McCracken, K. G.; Beer, J.; Barnard,
L.; Lockwood, M.; Rouillard, A.; Passos, D.; Riley, P.; Usoskin, I.;
Wang, Y. -M.
Bibcode: 2016JGRA..121.6048O
Altcode:
We present two separate time series of the near-Earth heliospheric
magnetic field strength (B) based on geomagnetic data and sunspot number
(SSN). The geomagnetic-based B series from 1845 to 2013 is a weighted
composite of two series that employ the interdiurnal variability index;
this series is highly correlated with in situ spacecraft measurements
of B (correlation coefficient, r = 0.94; mean square error, MSE =
0.16 nT2). The SSN-based estimate of B, from 1750 to 2013,
is a weighted composite of eight time series derived from two separate
reconstruction methods applied to four different SSN time series,
allowing determination of the uncertainty from both the underlying
sunspot records and the B reconstruction methods. The SSN-based
composite is highly correlated with direct spacecraft measurements of B
and with the composite geomagnetic B time series from 1845 to 2013 (r =
0.91; MSE = 0.24 nT2), demonstrating that B can accurately
reconstructed by both geomagnetic and sunspot-based methods. The
composite sunspot and geomagnetic B time series, with uncertainties,
are provided as supporting information.
Title: Comparison of New and Old Sunspot Number Time Series
Authors: Cliver, Edward W.; Clette, Frédéric; Lefévre, Laure;
Svalgaard, Leif
Bibcode: 2016SPD....47.1101C
Altcode:
As a result of the Sunspot Number Workshops, five new sunspot series
have recently been proposed: a revision of the original Wolf or
international sunspot number (Lockwood et al., 2014), a backbone-based
group sunspot number (Svalgaard and Schatten, 2016), a revised group
number series that employs active day fractions (Usoskin et al., 2016),
a provisional group sunspot number series (Cliver and Ling, 2016) that
removes flaws in the normalization scheme for the original group sunspot
number (Hoyt and Schatten,1998), and a revised Wolf or international
number (termed SN) published on the SILSO website as a
replacement for the original Wolf number (Clette and Lefèvre, 2016; thttp://www.sidc.be/silso/datafiles).
Despite quite different construction methods, the five new series
agree reasonably well after about 1900. From 1750 to ~1875, however,
the Lockwood et al. and Usoskin et al. time series are lower than the
other three series. Analysis of the Hoyt and Schatten normalization
factors used to scale secondary observers to their Royal Greenwich
Observatory primary observer reveals a significant inhomogeneity
spanning the divergence in ~1885 of the group number from the original
Wolf number. In general, a correction factor time series, obtained
by dividing an annual group count series by the corresponding yearly
averages of raw group counts for all observers, can be used to assess
the reliability of new sunspot number reconstructions.
Title: Flare vs. Shock Acceleration of >100 MeV Protons in Large
Solar Particle Events
Authors: Cliver, Edward W.
Bibcode: 2016SPD....47.0606C
Altcode:
Recently several studies have presented correlative evidence for
a significant-to-dominant role for a flare-resident process in the
acceleration of high-energy protons in large solar particle events. In
one of these investigations, a high correlation between >100 MeV
proton fluence and 35 GHz radio fluence is obtained by omitting large
proton events associated with relatively weak flares; these outlying
events are attributed to proton acceleration by shock waves driven
by coronal mass ejections (CMEs). We argue that the strong CMEs and
associated shocks observed for proton events on the main sequence of the
scatter plot are equally likely to accelerate high-energy protons. In
addition, we examine ratios of 0.5 MeV electron to >100 MeV proton
intensities in large SEP events, associated with both well-connected
and poorly-connected solar eruptions, to show that scaled-up versions
of the small flares associated with classical impulsive SEP events
are not significant accelerators of >100 MeV protons.
Title: The new Sunspot and Group Numbers: a full recalibration
Authors: Clette, Frédéric; Svalgaard, Leif; Cliver, Edward W.;
Vaquero, José M.; Lefèvre, Laure
Bibcode: 2015IAUGA..2249591C
Altcode:
After a 4-year research effort, we present here the first end-to-end
revision of the Sunspot Number since the creation of this reference
index of solar activity by Rudolf Wolf in 1849 and the simultaneous
re-calibration of the Group Number, which leads to the elimination of
the past incompatibility between those two independent data sets.Most
corrections relied entirely on original sunspot data, using various
approaches. Newly recovered historical sunspot records were added
and a critical data selection was applied for the 17th
and 18th century, confirming the low solar activity
during the Maunder Minimum. Over the 19th century, the k
scaling coefficients of individual observers were recomputed using
new statistical methodologies, like the "backbone" method resting on
a chain of long-duration observers. After identifying major changes
in the observing methods, two major inhomogeneities were corrected
in 1884 in the Group Number (~40% upward drift) and in 1947 in the
Sunspot Number (~20% overestimate). Finally, a full re-computation of
the group and sunspot numbers was done over the last 50 years, using
all original data from the 270 stations archived by the World Data
Center - SILSO in Brussels.The new Sunspot Number series definitely
exclude a progressive rise in average solar activity between the Maunder
Minimum and an exceptional Grand Maximum in the late 20th
century. Residual differences between the Group and Sunspot Numbers over
the past 250 years confirm that they reflect different properties of
the solar cycle and that the average number of spots per group varies
over time, as it just happened in the recent unexpected evolution of
cycles 23 and 24. We conclude on the implications for solar cycle and
Earth climate studies and on important new conventions adopted for
the new series: new unit scales (constant "heritage" factors 0.6 and
12.08 dropped for the Sunspot and Group Numbers respectively), new
SN and GN symbols and a new version-tracking
scheme implemented at the WDC-SILSO, as a framework open to future
improvements of those unique data series.
Title: Coronal Sources of Impulsive Fe-Rich Solar Energetic Particle
Events
Authors: Kahler, S.; Reames, D.; Cliver, E.
Bibcode: 2015ICRC...34...49K
Altcode: 2015arXiv150909260K; 2015PoS...236...49K
We review recent work on 111 Fe-rich impulsive solar energetic
($\sim$ 3 MeV/nuc) particle (SEP) events observed from 1994 to
2013. Strong elemental abundance enhancements scale with A/Q, the
ion mass-to-charge ratio, as (A/Q)$^{\alpha}$, where 2 $< \alpha
<$ 8 for different events. Most Fe-rich events are associated with
both flares and coronal mass ejections (CMEs), and those with larger
$\alpha$ are associated with smaller flares, slower and narrower CMEs,
and lower SEP event fluences. The narrow equilibrium temperature
range required to fit the observed A/Q enhancements is 2.5--3.2 MK,
far below the characteristic flare temperatures of $>$ 10 MK. Only
a small number of SEP events slightly outside this temperature range
were found in an expanded search of impulsive Fe-rich events. Event
characteristics are similar for events isolated in time and those
occurring in clusters. The current challenge is to determine the
solar sources of the Fe-rich events. Ambient coronal regions in the
2.5--3.2 MK range are broadly distributed both in and outside active
regions. We explore the possibility of acceleration from thermal plasmas
at reconnecting current sheets in the context of observed standard and
blowout jets. Recent current sheet reconnection modelling provides a
basis for the A/Q enhancements.
Title: Assessment of F200 fluence for major solar energetic particle
events on the multi-millennial time scale
Authors: Usoskin, I.; Kovaltsov, G.; Cliver, E.; Dietrich, W. F.;
Tylka, A.
Bibcode: 2015ICRC...34...18U
Altcode: 2015PoS...236...18U
No abstract at ADS
Title: Temperature of the Source Plasma for Impulsive Solar Energetic
Particles
Authors: Reames, Donald V.; Cliver, Edward W.; Kahler, Stephen W.
Bibcode: 2015SoPh..290.1761R
Altcode: 2015SoPh..tmp...81R; 2015arXiv150502741R
The steep power-law dependence of element abundance enhancements
on the mass-to-charge ratios [A /Q ] of the ions in impulsive solar
energetic-particle (SEP) events causes these enhancements to reflect
the temperature-dependent pattern of Q of the ions in the source
plasma. We searched for SEP events from coronal plasma that is hotter
or cooler than the limited region of 2.5 - 3.2 MK previously found to
dominate 111 impulsive SEP events. Fifteen new events were found, four
(three) originating in 2-MK (4-MK) plasma, but none from outside this
temperature range. Although the impulsive SEP events are strongly
associated with flares, this result indicates that these ions are
not accelerated from flare-heated plasma, which can often exceed
10 MK. Evidently the ions of 2 -20 MeVamu−1 that we
observe in space are accelerated from active-region plasma on open
magnetic-field lines near the flare, but not from the closed loops of
the flare. The power-law dependence of the abundance enhancements on
A /Q of the ions is expected from theoretical models of acceleration
from regions of magnetic reconnection.
Title: Solar Cycle in the Heliosphere and Cosmic Rays
Authors: Bazilevskaya, Galina A.; Cliver, Edward W.; Kovaltsov,
Gennady A.; Ling, Alan G.; Shea, M. A.; Smart, D. F.; Usoskin, Ilya G.
Bibcode: 2015sac..book..409B
Altcode:
No abstract at ADS
Title: Recalibrating the Sunspot Number (SN): The 3rd
and 4th SN Workshops
Authors: Cliver, E. W.; Clette, F.; Svalgaard, L.; Vaquero, J. M.
Bibcode: 2015CEAB...39....1C
Altcode:
At the XIIth Hvar Astrophysical Colloquium in 2012, we reviewed the
progress of an effort begun in 2011 to recalibrate the sunspot number
(SN). That work is now nearing completion and we review the motivation,
approach, and results of this process which was conducted via a series
of four international workshops. Previously we discussed the principal
results of workshops at Sunspot in 2011 and Brussels in 2012. These
involved the identification of discontinuities circa 1885 in the Hoyt
and Schatten Group SN and 1945 in the International SN. Subsequently,
workshops were held in Tucson (2013) and Locarno (2014). Key results
during the time of these two workshops included: (1) development of
an independent ''backbone'' method for determining the Group sunspot
number; (2) identification of post-1970 inhomogeneities in the
Group SN and the International SN; (3) construction of preliminary
revisions of the Group SN from 1610-present and the International
SN from 1700--present; (4) reassessment (ongoing) of the Hoyt and
Schatten Group SN data base from 1610-present; and (5) establishment
of a SN archive at the University of Extremadura. The release of the
new International and Group SN series is anticipated during the second
half of 2015 and procedures are being put in place both to maintain the
calibration of these two series and to produce subsequent revisions
should more historical data be unearthed or new inhomogeneities in
the series be uncovered or arise.
Title: The Extended Cycle of Solar Activity and the Sun's 22-Year
Magnetic Cycle
Authors: Cliver, E. W.
Bibcode: 2015sac..book..169C
Altcode:
No abstract at ADS
Title: Revisiting the Sunspot Number
Authors: Clette, Frédéric; Svalgaard, Leif; Vaquero, José M.;
Cliver, Edward W.
Bibcode: 2015sac..book...35C
Altcode:
No abstract at ADS
Title: Solar Cycle in the Heliosphere and Cosmic Rays
Authors: Bazilevskaya, Galina A.; Cliver, Edward W.; Kovaltsov,
Gennady A.; Ling, Alan G.; Shea, M. A.; Smart, D. F.; Usoskin, Ilya G.
Bibcode: 2014SSRv..186..409B
Altcode: 2014SSRv..tmp...44B
Manifestations of the 11-year solar cycle and longer time-scale
variability in the heliosphere and cosmic rays are considered. We
briefly review the cyclic variability of such heliospheric parameters
as solar wind speed and density and heliospheric magnetic field, open
magnetic flux and latitude variations of the heliospheric current
sheet. It is discussed whether the local in-situ observation near
Earth can represent the global 3D heliospheric pattern. Variability
of cosmic rays near Earth provides an indirect useful tool to study
the heliosphere. We discuss details of the heliospheric modulation
of galactic cosmic rays, as recorded at and near Earth, and their
relation to the heliospheric conditions in the outer heliosphere. On
the other hand, solar energetic particles can serve as probes for
explosive phenomena on the Sun and conditions in the corona and inner
heliosphere. The occurrence of major solar proton events depicts an
overall tendency to follow the solar cycle but individual events may
appear at different phases of the solar cycle, as defined by various
factors. The solar cycle in the heliosphere and cosmic rays depicts
a complex pattern which includes different processes and cannot be
described by a simple correlation with sunspot number.
Title: The Extended Cycle of Solar Activity and the Sun's 22-Year
Magnetic Cycle
Authors: Cliver, E. W.
Bibcode: 2014SSRv..186..169C
Altcode: 2014SSRv..tmp...52C
The Sun has two characteristic migrations of surface features—the
equatorward movement of sunspots and the poleward movement of
high-latitude prominences. The first of these migrations is a defining
aspect of the 11-yr Schwabe cycle and the second is a tracer of the
process that culminates in solar polarity reversal, signaling the
onset of the 22-yr magnetic cycle on the Sun. Zonal flows (torsional
oscillations of the Sun's differential rotation) have been identified
for both of these migrations. Helioseismology observations of these
zonal flows provide support for the extended (>11-yr cycle) of solar
activity and offer promise of a long-term precursor for predicting the
amplitude of the Schwabe cycle. We review the growth of observational
evidence for the extended and 22-yr magnetic cycles and discuss:
(1) the significance of latitude ∼50∘ on the Sun;
(2) the "over-extended" cycle; and (3) the outlook for solar cycle 25.
Title: Variations in Abundance Enhancements in Impulsive Solar
Energetic-Particle Events and Related CMEs and Flares
Authors: Reames, Donald V.; Cliver, Edward W.; Kahler, Stephen W.
Bibcode: 2014SoPh..289.4675R
Altcode: 2014arXiv1407.7838R; 2014SoPh..tmp..121R
We study event-to-event variations in the abundance enhancements of the
elements He through Pb for Fe-rich impulsive solar energetic-particle
(SEP) events, and their relationship with properties of associated
coronal mass ejections (CMEs) and solar flares. Using a least-squares
procedure we fit the power-law enhancement of element abundances as
a function of their mass-to-charge ratio A/Q to determine both the
power and the coronal temperature (which determines Q) in each of
111 impulsive SEP events identified previously. Individual SEP events
with the steepest element enhancements, e.g. ∼ (A/Q)6,
tend to be smaller, lower-fluence events with steeper energy spectra
that are associated with B- and C-class X-ray flares, with cooler (∼
2.5 MK) coronal plasma, and with narrow (< 100∘),
slower (< 700 km s−1) CMEs. On the other hand,
higher-fluence SEP events have flatter energy spectra, less-dramatic
heavy-element enhancements, e.g. ∼ (A/Q)3, and come from
somewhat hotter coronal plasma (∼ 3.2 MK) associated with C-, M-,
and even X-class X-ray flares and with wider CMEs. Enhancements in
3He/4He are uncorrelated with those in heavy
elements. However, events with 3He/4He≥0.1
are even more strongly associated with narrow, slow CMEs, with
cooler coronal plasma, and with B- and C-class X-ray flares than
are other Fe-rich impulsive SEP events with smaller enhancements of
3He.
Title: Fluence Ordering of Solar Energetic Proton Events Using
Cosmogenic Radionuclide Data
Authors: Kovaltsov, G. A.; Usoskin, I. G.; Cliver, E. W.; Dietrich,
W. F.; Tylka, A. J.
Bibcode: 2014SoPh..289.4691K
Altcode: 2014SoPh..tmp..129K
While data on the cosmogenic isotopes 14C and 10Be
made it possible to evaluate extreme solar proton events (SPEs) in
the past, their relation to standard parameters quantifying the SPE
strengths, viz. the integrated fluence of protons with energy above
30 MeV, F30, is ambiguous and strongly depends on the
assumed shape of the energy spectrum. Here we propose a new index,
the integral fluence of an SPE above 200 MeV, F200, which
is related to the production of the cosmogenic isotopes 14C
and 10Be in the Earth atmosphere, independently of the
assumptions on the energy spectrum of the event. The F200
fluence is reconstructed from past cosmogenic isotope data, which
provides an assessment of the occurrence probability density function
for extreme SPEs. In particular, we evaluate that extreme SPEs with
F200>1010 cm−2 occur no more
frequently than once per 10 - 15 kyr.
Title: Revisiting the Sunspot Number. A 400-Year Perspective on the
Solar Cycle
Authors: Clette, Frédéric; Svalgaard, Leif; Vaquero, José M.;
Cliver, Edward W.
Bibcode: 2014SSRv..186...35C
Altcode: 2014SSRv..tmp...38C; 2014arXiv1407.3231C
Our knowledge of the long-term evolution of solar activity and of
its primary modulation, the 11-year cycle, largely depends on a
single direct observational record: the visual sunspot counts that
retrace the last 4 centuries, since the invention of the astronomical
telescope. Currently, this activity index is available in two main
forms: the International Sunspot Number initiated by R. Wolf in 1849
and the Group Number constructed more recently by Hoyt and Schatten
(Sol. Phys. 179:189-219, 1998a, 181:491-512, 1998b). Unfortunately,
those two series do not match by various aspects, inducing confusions
and contradictions when used in crucial contemporary studies of the
solar dynamo or of the solar forcing on the Earth climate. Recently,
new efforts have been undertaken to diagnose and correct flaws and
biases affecting both sunspot series, in the framework of a series of
dedicated Sunspot Number Workshops. Here, we present a global overview
of our current understanding of the sunspot number calibration.
Title: Abundance Enhancements in Impulsive Solar Energetic-Particle
Events with Associated Coronal Mass Ejections
Authors: Reames, Donald V.; Cliver, Edward W.; Kahler, Stephen W.
Bibcode: 2014SoPh..289.3817R
Altcode: 2014SoPh..tmp...86R; 2014arXiv1404.3322R
We study the abundances of the elements He through Pb in Fe-rich
impulsive solar energetic-particle (SEP) events with measurable
abundances of ions with atomic number Z>2 observed on the Wind
spacecraft, and their relationship with coronal mass ejections
(CMEs) observed by the Large Angle and Spectrometric Coronagraph
(LASCO) onboard the Solar and Heliospheric Observatory (SOHO). On an
average the element abundances in these events are similar to coronal
abundances at low Z but, for heavier elements, enhancements rise as
a power law in the mass-to-charge ratio A/Q of the ions (at coronal
temperatures of 2.5 - 3 MK) to a factor of 3 at Ne, 9 at Fe, and 900
for 76≤Z≤82. Energy dependences of abundances are minimal in the 2
- 15 MeV amu−1 range. The 111 of these Fe-rich impulsive
SEP events we found, between November 1994 and August 2013 using the
Wind spacecraft, have a 69 % association rate with CMEs. The CMEs are
narrow with a median width of 75∘, are characteristically
from western longitudes on the Sun, and have a median speed of ≈
600 km s−1. Nearly all SEP onsets occur within 1.5 -
5 h of the CME onset. The faster (> 700 km s−1),
wider CMEs in our sample are related to SEPs with coronal abundances
indicating hot coronal plasma with fully ionized He, C, N and O and
moderate enhancements of heavier elements, relative to He, but slower
(< 700 km s−1), narrower CMEs emerge from cooler
plasma where higher SEP mass-to-charge ratios, A/Q, yield much greater
abundance enhancements, even for C/He and O/He. Apparently, the open
magnetic-reconnection region where the impulsive SEPs are accelerated
also provides the energy to drive out CME plasma, accounting for a
strong, probably universal, impulsive SEP-CME association.
Title: Development of a Current Sheet in the Wake of a Fast Coronal
Mass Ejection
Authors: Ling, A. G.; Webb, D. F.; Burkepile, J. T.; Cliver, E. W.
Bibcode: 2014ApJ...784...91L
Altcode:
A bright ray that developed in the wake of a fast coronal mass
ejection (CME) on 2005 September 7 presents a unique opportunity
to study the early development and physical characteristics of a
reconnecting current sheet (CS). Polarization brightness images from
the Mk4 K-Coronameter at the Mauna Loa Solar Observatory are used to
determine the structure of the ray along its axis low in the corona as
it progressed outward. Coverage of the early development of the ray out
to ~1.3 R ⊙ for a period of ~27 hr after the start of the
event enables for the first time in white light a measurement of a CME
CS from the top of the arcade to the base of the flux rope. Measured
widths of the ray are combined to obtain the kinematics of the upper
and lower "Y"-points described in reconnection flux-rope models such
as that of Lin & Forbes. The time dependence of these points are
used to derive values for the speed and acceleration of the growth of
the CS. We note the appearance of a large structure which increases
in size as it expands outward in the early development of the ray and
an apparent oscillation with a period of ~0.5 hr in the position angle
of the ray.
Title: Cyclic and Long-Term Variation of Sunspot Magnetic Fields
Authors: Pevtsov, Alexei A.; Bertello, Luca; Tlatov, Andrey G.;
Kilcik, Ali; Nagovitsyn, Yury A.; Cliver, Edward W.
Bibcode: 2014SoPh..289..593P
Altcode: 2013arXiv1301.5935P
Measurements from the Mount Wilson Observatory (MWO) were used to
study the long-term variations of sunspot field strengths from 1920 to
1958. Following a modified approach similar to that presented in Pevtsov
et al. (Astrophys. J. Lett.742, L36, 2011), we selected the sunspot
with the strongest measured field strength for each observing week and
computed monthly averages of these weekly maximum field strengths. The
data show the solar cycle variation of the peak field strengths
with an amplitude of about 500 - 700 gauss (G), but no statistically
significant long-term trends. Next, we used the sunspot observations
from the Royal Greenwich Observatory (RGO) to establish a relationship
between the sunspot areas and the sunspot field strengths for cycles 15
- 19. This relationship was used to create a proxy of the peak magnetic
field strength based on sunspot areas from the RGO and the USAF/NOAA
network for the period from 1874 to early 2012. Over this interval,
the magnetic field proxy shows a clear solar cycle variation with an
amplitude of 500 - 700 G and a weaker long-term trend. From 1874 to
around 1920, the mean value of magnetic field proxy increases by about
300 - 350 G, and, following a broad maximum in 1920 - 1960, it decreases
by about 300 G. Using the proxy for the magnetic field strength as the
reference, we scaled the MWO field measurements to the measurements of
the magnetic fields in Pevtsov et al. (2011) to construct a combined
data set of maximum sunspot field strengths extending from 1920 to early
2012. This combined data set shows strong solar cycle variations and no
significant long-term trend (the linear fit to the data yields a slope
of − 0.2±0.8 G year−1). On the other hand, the peak
sunspot field strengths observed at the minimum of the solar cycle show
a gradual decline over the last three minima (corresponding to cycles
21 - 23) with a mean downward trend of ≈ 15 G year−1.
Title: Solar Drivers of 11-yr and Long-Term Cosmic Ray Modulation
Authors: Cliver, E. W.; Richardson, I. G.; Ling, A. G.
Bibcode: 2014crh..book....3C
Altcode:
No abstract at ADS
Title: On a Solar Origin for the Cosmogenic Nuclide Event of 775 A.D.
Authors: Cliver, E. W.; Tylka, A. J.; Dietrich, W. F.; Ling, A. G.
Bibcode: 2014ApJ...781...32C
Altcode:
We explore requirements for a solar particle event (SPE) and flare
capable of producing the cosmogenic nuclide event of 775 A.D.,
and review solar circumstances at that time. A solar source for
775 would require a >1 GV spectrum ~45 times stronger than that
of the intense high-energy SPE of 1956 February 23. This implies a
>30 MeV proton fluence (F 30) of ~8 × 1010
proton cm-2, ~10 times larger than that of the strongest
3 month interval of SPE activity in the modern era. This inferred F
30 value for the 775 SPE is inconsistent with the occurrence
probability distribution for >30 MeV solar proton events. The best
guess value for the soft X-ray classification (total energy) of an
associated flare is ~X230 (~9 × 1033 erg). For comparison,
the flares on 2003 November 4 and 1859 September 1 had observed/inferred
values of ~X35 (~1033 erg) and ~X45 (~2 × 1033
erg), respectively. The estimated size of the source active region for a
~1034 erg flare is ~2.5 times that of the largest region yet
recorded. The 775 event occurred during a period of relatively low solar
activity, with a peak smoothed amplitude about half that of the second
half of the 20th century. The ~1945-1995 interval, the most active of
the last ~2000 yr, failed to witness a SPE comparable to that required
for the proposed solar event in 775. These considerations challenge
a recent suggestion that the 775 event is likely of solar origin.
Title: The 1859 space weather event revisited: limits of extreme
activity
Authors: Cliver, Edward W.; Dietrich, William F.
Bibcode: 2013JSWSC...3A..31C
Altcode:
The solar flare on 1 September 1859 and its associated geomagnetic
storm remain the standard for an extreme solar-terrestrial event. The
most recent estimates of the flare soft X-ray (SXR) peak intensity
and Dst magnetic storm index for this event are: SXR class = X45 (±5)
(vs. X35 (±5) for the 4 November 2003 flare) and minimum Dst = -900
(+50, -150) nT (vs. -825 to -900 nT for the great storm of May 1921). We
have no direct evidence of an associated solar energetic proton (SEP)
event but a correlation between >30 MeV SEP fluence (F30)
and flare size based on modern data yields a best guess F30
value of ~1.1 × 1010 pr cm-2 (with the ±1σ
uncertainty spanning a range from ~109-1011
pr cm-2) for a composite (multi-flare plus shock) 1859
event. This value is approximately twice that of estimates/measurements
- ranging from ~5-7 × 109 pr cm-2 - for the
largest SEP episodes (July 1959, November 1960, August 1972) in the
modern era.
Title: Solar Drivers of 11-yr and Long-Term Cosmic Ray Modulation
Authors: Cliver, E. W.; Richardson, I. G.; Ling, A. G.
Bibcode: 2013SSRv..176....3C
Altcode: 2011SSRv..tmp..343C; 2011SSRv..tmp..179C; 2011SSRv..tmp...21C;
2011SSRv..tmp..103C
In the current paradigm for the modulation of galactic cosmic rays
(GCRs), diffusion is taken to be the dominant process during solar
maxima while drift dominates at minima. Observations during the recent
solar minimum challenge the pre-eminence of drift at such times. In
2009, the ∼2 GV GCR intensity measured by the Newark neutron monitor
increased by ∼5% relative to its maximum value two cycles earlier even
though the average tilt angle in 2009 was slightly larger than that
in 1986 (∼20° vs. ∼14°), while solar wind B was significantly
lower (∼3.9 nT vs. ∼5.4 nT). A decomposition of the solar wind
into high-speed streams, slow solar wind, and coronal mass ejections
(CMEs; including post-shock flows) reveals that the Sun transmits its
message of changing magnetic field (diffusion coefficient) to the
heliosphere primarily through CMEs at solar maximum and high-speed
streams at solar minimum. Long-term reconstructions of solar wind B are
in general agreement for the ∼1900-present interval and can be used
to reliably estimate GCR intensity over this period. For earlier epochs,
however, a recent 10Be-based reconstruction covering the past
∼104 years shows nine abrupt and relatively short-lived
drops of B to ≲0 nT, with the first of these corresponding to the
Spörer minimum. Such dips are at variance with the recent suggestion
that B has a minimum or floor value of ∼2.8 nT. A floor in solar wind
B implies a ceiling in the GCR intensity (a permanent modulation of the
local interstellar spectrum) at a given energy/rigidity. The 30-40%
increase in the intensity of 2.5 GV electrons observed by Ulysses
during the recent solar minimum raises an interesting paradox that
will need to be resolved.
Title: Recalibrating the Sunspot Number (SSN): The SSN Workshops
Authors: Cliver, E. W.; Clette, F.; Svalgaard, L.
Bibcode: 2013CEAB...37..401C
Altcode:
The sunspot number (SSN) is the primary time series in solar and
solar-terrestrial physics. Currently there are two widely-used
sunspot numbers, the International SSN and the Group SSN, which
differ significantly before ∼1885. Thus the SSN is potentially a
free-parameter in models of climate change or solar dynamo behavior. To
reconcile the International and Group SSNs, we have organized a series
of workshops. The end goal of this effort is a community-vetted time
series of sunspot numbers for use in long-term studies. We are about
half way through the process, with the International and Group SSN time
series reconciled back to 1826. We hope to have the reconciliation
completed back to the beginning of the SSN time series (1610) by
mid-2014. We have learned or relearned some interesting things along the
way: (1) the International or Wolf SSN time series is not based solely
on sunspots; (2) the simple formula from Wolf for the SSN that is found
in all solar physics textbooks is not used in practice (all sunspots
are not equal); and (3) the Group SSN appears to be too low before
1885. When completed, the reconciled ∼400-yr SSN time series will
serve as a bridge to the millennia-scale record of solar variability
from cosmogenic nuclide concentrations in tree rings and ice cores.
Title: Historically Great Magnetic Storms
Authors: Cliver, E. W.
Bibcode: 2012AGUFMSM14A..02C
Altcode:
What was the largest geomagnetic storm ever recorded? The question
is of interest for both theoretical and practical reasons. The
available records of magnetic activity indicate that three of the
largest storms (in 1859, 1909, and 1921) occurred before the epoch
of systematic high-time-resolution indices initiated by Bartels in
1932. Recent efforts to extend such indices back in time enable us to
compare the 1909 and 1921 storms with modern giants such as the March
1989 event. Comparisons are made between early reports of auroras at
mid-latitudes and magnetic activity. Overhead aurora are associated
with particularly strong magnetic disturbances, e.g., the 3000 nT
deflection recorded for the 1859 event in Rome.
Title: A Comparison of Ground Level Event e/p and Fe/O Ratios with
Associated Solar Flare and CME Characteristics
Authors: Kahler, S. W.; Cliver, E. W.; Tylka, A. J.; Dietrich, W. F.
Bibcode: 2012SSRv..171..121K
Altcode: 2011SSRv..tmp..358K; 2011SSRv..tmp...54K; 2011SSRv..tmp...39K;
2011SSRv..tmp..122K; 2011SSRv..tmp..198K
Solar energetic particle (SEP) events reaching rigidities >1 GV are
observed at 1 AU as ground-level events (GLEs). They are considered
to be extreme cases of gradual SEP events, produced by shocks driven
by wide and fast CMEs that are usually associated with long-duration
(>1 hour) soft X-ray (SXR) flares. However, some large gradual SEP
events, including GLEs, are associated with flares of short-duration
(<1 hour) timescales comparable to those of flares seen with
impulsive, low-energy SEP events with enhanced charge states,
heavy-element abundances, and e/p ratios. The association of some
GLEs with short-duration SXR events challenges us to understand the
GLE event-to-event variation with SXR durations and whether it truly
reflects the nature of the particle acceleration processes or simply
the characteristics of the solar regions from which large, fast CMEs
arise. We examine statistically the associated flare, active region
(AR), and CME characteristics of ∼40 GLEs observed since 1976
to determine how the GLE e/p and Fe/O ratios, each measured in two
energy ranges, depend on those characteristics. The abundance ratios
trend weakly to lower, more coronal, and less scattered values with
increasing flare timescales, thermal and nonthermal peak fluxes,
and measures of source AR sizes. These results and the wide range of
solar longitude connections for GLEs with high abundance ratios argue
against a significant role for flare effects in the GLEs. We suggest
that GLE SEPs are accelerated predominately in CME-driven shocks and
that a coupling of flare size and timescales with CME properties could
explain the SEP abundance correlations with flare properties.
Title: Richard Christopher Carrington: Briefly Among the Great
Scientists of His Time
Authors: Cliver, Edward W.; Keer, Norman C.
Bibcode: 2012SoPh..280....1C
Altcode: 2012SoPh..tmp..161C
We recount the life and career of Richard Christopher Carrington (1826 -
1875) and explore his pivotal relationship with Astronomer Royal George
Biddell Airy. Carrington was the pre-eminent solar astronomer of the
19th century. During a ten year span, he determined the position
of the Sun's rotation axis and made the following discoveries: i)
the latitude variation of sunspots over the solar cycle, ii) the
Sun's differential rotation, and iii) the first solar flare (with
Hodgson). Due to the combined effects of family responsibilities,
failure to secure a funded position in astronomy (reflecting Airy's
influence), and ill health, Carrington's productive period ended when
he was at the peak of his powers.
Title: Size distributions of solar flares and solar energetic
particle events
Authors: Cliver, E. W.; Ling, A. G.; Belov, A.; Yashiro, S.
Bibcode: 2012ApJ...756L..29C
Altcode:
We suggest that the flatter size distribution of solar energetic proton
(SEP) events relative to that of flare soft X-ray (SXR) events is
primarily due to the fact that SEP flares are an energetic subset of all
flares. Flares associated with gradual SEP events are characteristically
accompanied by fast (>=1000 km s-1) coronal mass ejections
(CMEs) that drive coronal/interplanetary shock waves. For the 1996-2005
interval, the slopes (α values) of power-law size distributions of
the peak 1-8 Å fluxes of SXR flares associated with (a) >10 MeV
SEP events (with peak fluxes >=1 pr cm-2 s-1
sr-1) and (b) fast CMEs were ~1.3-1.4 compared to ~1.2 for
the peak proton fluxes of >10 MeV SEP events and ~2 for the peak 1-8
Å fluxes of all SXR flares. The difference of ~0.15 between the slopes
of the distributions of SEP events and SEP SXR flares is consistent
with the observed variation of SEP event peak flux with SXR peak flux.
Title: Abrupt Changes of the Photospheric Magnetic Field in Active
Regions and the Impulsive Phase of Solar Flares
Authors: Cliver, E. W.; Petrie, G. J. D.; Ling, A. G.
Bibcode: 2012ApJ...756..144C
Altcode:
We compared time profiles of changes of the unsigned photospheric
magnetic flux in active regions with those of their associated soft
X-ray (SXR) bursts for a sample of 75 >= M5 flares well observed by
Global Oscillation Network Group longitudinal magnetographs. Sixty-six
of these events had stepwise changes in the spatially integrated
unsigned flux during the SXR flares. In superposed epoch plots for
these 66 events, there is a sharp increase in the unsigned magnetic
flux coincident with the onset of the flare impulsive phase while
the end of the stepwise change corresponds to the time of peak SXR
emission. We substantiated this result with a histogram-based comparison
of the timing of flux steps (onset, midpoint of step, and end) for
representative points in the flaring regions with their associated
SXR event time markers (flare onset, onset of impulsive phase, time of
peak logarithmic derivative, maximum). On an individual event basis,
the principal part of the stepwise magnetic flux change occurred during
the main rise phase of the SXR burst (impulsive phase onset to SXR peak)
for ~60% of the 66 cases. We find a close timing agreement between
magnetic flux steps and >100 keV emission for the three largest hard
X-ray (>100 keV) bursts in our sample. These results identify the
abrupt changes in photospheric magnetic fields as an impulsive phase
phenomenon and indicate that the coronal magnetic field changes that
drive flares are rapidly transmitted to the photosphere.
Title: Estimating the frequency of extremely energetic solar events,
based on solar, stellar, lunar, and terrestrial records
Authors: Schrijver, C. J.; Beer, J.; Baltensperger, U.; Cliver,
E. W.; Güdel, M.; Hudson, H. S.; McCracken, K. G.; Osten, R. A.;
Peter, T.; Soderblom, D. R.; Usoskin, I. G.; Wolff, E. W.
Bibcode: 2012JGRA..117.8103S
Altcode: 2012arXiv1206.4889S; 2012JGRA..11708103S
The most powerful explosions on the Sun - in the form of bright
flares, intense storms of solar energetic particles (SEPs), and fast
coronal mass ejections (CMEs) - drive the most severe space-weather
storms. Proxy records of flare energies based on SEPs in principle
may offer the longest time base to study infrequent large events. We
conclude that one suggested proxy, nitrate concentrations in polar
ice cores, does not map reliably to SEP events. Concentrations of
select radionuclides measured in natural archives may prove useful in
extending the time interval of direct observations up to ten millennia,
but as their calibration to solar flare fluences depends on multiple
poorly known properties and processes, these proxies cannot presently be
used to help determine the flare energy frequency distribution. Being
thus limited to the use of direct flare observations, we evaluate the
probabilities of large-energy solar events by combining solar flare
observations with an ensemble of stellar flare observations. We conclude
that solar flare energies form a relatively smooth distribution from
small events to large flares, while flares on magnetically active,
young Sun-like stars have energies and frequencies markedly in excess
of strong solar flares, even after an empirical scaling with the mean
coronal activity level of these stars. In order to empirically quantify
the frequency of uncommonly large solar flares extensive surveys
of stars of near-solar age need to be obtained, such as is feasible
with the Kepler satellite. Because the likelihood of flares larger
than approximately X30 remains empirically unconstrained, we present
indirect arguments, based on records of sunspots and on statistical
arguments, that solar flares in the past four centuries have likely
not substantially exceeded the level of the largest flares observed
in the space era, and that there is at most about a 10% chance of a
flare larger than about X30 in the next 30 years.
Title: The floor in the solar wind: status report
Authors: Cliver, E. W.
Bibcode: 2012IAUS..286..179C
Altcode:
Cliver & Ling (2010) recently suggested that the solar wind had a
floor or ground-state magnetic field strength at Earth of ~2.8 nT and
that the source of the field was the slow solar wind. This picture has
recently been given impetus by the evidence presented by Schrijver
et al. (2011) that the Sun has a minimal magnetic state that was
approached globally in 2009, a year in which Earth was imbedded in
slow solar wind ~70% of the time. A precursor relation between the
solar dipole field strength at solar minimum and the peak sunspot
number (SSN MAX ) of the subsequent 11-yr cycle suggests
that during Maunder-type minima (when SSN MAX was ~0),
the solar polar field strength approaches zero - indicating weak or
absent polar coronal holes and an increase to nearly ~100% in the time
that Earth spends in slow solar wind.
Title: Direct Comparison Of A Moreton Wave, EUV Wave And CME
Authors: White, Stephen M.; Cliver, E.; Balasubramaniam, K.
Bibcode: 2012AAS...22020412W
Altcode:
The first period of major solar activity in the current cycle,
due to AR 11158 in mid February 2011, produced a sequence of solar
flares exhibiting both Moreton waves in H-alpha images and "EIT-waves"
seen in EUV images. Given the rarity of Moreton waves, this offers an
excellent opportunity to compare the properties of the two phenomena
with simultaneous observations. We focus on the event of 17:24 UT on
February 14, which was well-observed by a number of observatories. We
find a strong link between the Moreton wave, the EUV wave and the CME
in this event. The Moreton wave has the same speed as the EUV wave, but
it lags behind the leading edge of the EUV wave. A vertical signature
is seen in the H-alpha Doppler images. STEREO observations of the
CME indicate that initially the vertical speed of the disturbance was
not as high as the EUV wave speed, and the CME rapidly decelerates on
merging with a rising loop system. We interpret the results in light
of current models for such disturbances.
Title: The Solar Decimetric Spike Burst of 2006 December 6: Possible
Evidence for Field-aligned Potential Drops in Post-eruption Loops
Authors: Cliver, E. W.; White, S. M.; Balasubramaniam, K. S.
Bibcode: 2011ApJ...743..145C
Altcode:
A 1.4 GHz solar radio burst associated with a 3B/X6 eruptive flare
on 2006 December 6 had the highest peak flux density (~106
sfu) of any event yet recorded at this frequency. The decimetric event
characteristics during the brightest emission phase (numerous intense,
short-lived, narrow-band bursts that overlapped to form a continuous
spectrum) suggest electron cyclotron maser (ECM) emission. The peak 1.4
GHz emission did not occur during the flare impulsive phase but rather
~45 minutes later, in association with post-eruption loop activity
seen in Hα and by the Hinode EUV Imaging Spectrometer. During the
Waves/LASCO era, three other delayed bursts with peak intensities
>105 sfu in the 1.0-1.6 GHz (L-band) frequency range
have been reported that appear to have characteristics similar to the
December 6 burst. In each of these three cases, high-frequency type
IV bursts were reported in a range from ~150 to ~1500 MHz. Assuming
a common ECM emission mechanism across this frequency range implies
a broad span of source heights in the associated post-eruption loop
systems. Difficulties with an ECM interpretation for these events
include the generation of the lower frequency component of the type
IVs and the long-standing problem of escape of the ECM emission from
the loops. Magnetic-field-aligned potential drops, analogous to those
observed for Earth's auroral kilometric radiation, could plausibly
remove both of these objections to ECM emission.
Title: The Floor in the Solar Wind Magnetic Field Revisited
Authors: Cliver, E. W.; Ling, A. G.
Bibcode: 2011SoPh..274..285C
Altcode:
Svalgaard and Cliver (Astrophys. J. Lett.661, L203, 2007) proposed
that the solar-wind magnetic-field strength [B] at Earth has a
"floor" value of ≈4.6 nT in yearly averages, which is approached
but not broached at solar minima. They attributed the floor to a
constant baseline solar open flux. In both 2008 and 2009, the notion
of such a floor was undercut by annual B averages of ≈4 nT. Here
we present a revised view of both the level and the concept of the
floor. Two independent correlations indicate that B has a floor of
≈2.8 nT in yearly averages. These are i) a relationship between
solar polar-field strength and yearly averages of B for the last four
11-year minima (BMIN), and ii) a precursor relationship
between peak sunspot number for cycles 14 - 23 and BMIN
at their preceding minima. These correlations suggest that at 11-year
minima, B consists of i) a floor of ≈2.8 nT, and ii) a component
primarily due to the solar polar fields that varies from ≈0 nT to
≈3 nT. The solar polar fields provide the "seed" for the subsequent
sunspot maximum. Removing the ≈2.8 nT floor from BMIN
brings the percentage decrease in B between the 1996 and 2009 minima
into agreement with the corresponding decrease in solar polar-field
strength. Based on a decomposition of the solar wind (from 1972 -
2009) into high-speed streams, coronal mass ejections, and slow solar
wind, we suggest that the source of the floor in B is the slow solar
wind. During 2009, Earth was in slow solar-wind flows ≈70% of the
time. We propose that the floor corresponds to a baseline (non-cyclic
or ground state) open solar flux of ≈8×1013 Wb, which
originates in persistent small-scale (supergranular and granular) field.
Title: The Disappearing Solar Filament of 2003 June 11: A Three-body
Problem
Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Cliver, E. W.;
Martin, S. F.; Panasenco, O.
Bibcode: 2011ApJ...743..202B
Altcode:
The eruption of a large quiescent filament on 2003 June 11 was preceded
by the birth of a nearby active region—a common scenario. In this
case, however, the filament lay near a pre-existing active region
and the new active region did not destabilize the filament by direct
magnetic connection. Instead it appears to have done so indirectly
via magnetic coupling with the established region. Restructuring
between the perturbed fields of the old region and the filament
then weakened the arcade overlying the midpoint of filament, where
the eruption originated. The inferred rate (~11° day-1)
at which the magnetic disturbance propagates from the mature region
to destabilize the filament is larger than the mean speed (~5º-6°
day-1) but still within the scatter obtained for Bruzek's
empirical relationship between the distance from a newly formed
active region to a quiescent filament and the time from active region
appearance to filament disappearance. The higher propagation speed in
the 2003 June 11 case may be due to the "broadside" (versus ''end-on")
angle of attack of the (effective) new flux to the coronal magnetic
fields overlying a central section of the axis of the filament.
Title: Simultaneous Observations of Hα Moreton Waves and EUV Waves
Authors: White, Stephen M.; Balasubramanian, K. S.; Cliver, E. W.
Bibcode: 2011SPD....42.1307W
Altcode: 2011BAAS..43S.1307W
The first period of major solar activity in the current cycle,
due to AR 11158 in mid February 2011, produced a sequence of solar
flares exhibiting both Moreton waves in H-alpha images and "EIT-waves"
seen in EUV images. Given the rarity of Moreton waves, this offers an
excellent opportunity to compare the properties of the two phenomena
with simultaneous observations. We analyze several events and compare
the speeds and locations of the disturbances using high-cadence
H-alpha data from both the ISOON telescope at Sunspot, NM, and the
GONG network, together with EUV images in several wavelengths from
the SDO/AIA telescope, and interpret the results in light of current
models for such disturbances.
Title: The Great Decimetric Solar Spike Burst of 2006 December 6:
Possible Evidence for Field-aligned Potential Drops in Post-eruption
Loops
Authors: Cliver, Edward W.; White, S. M.; Balasubramaniam, K. S.
Bibcode: 2011SPD....42.2223C
Altcode: 2011BAAS..43S.2223C
A 1.4 GHz solar radio burst associated with a 3B/X6 eruptive flare
on 2006 December 6 had the highest peak flux density ( 106
sfu) of any event yet recorded at this frequency. The decimetric event
characteristics during the brightest emission phase (numerous intense,
short-lived, narrow-band bursts that overlapped to form a continuous
spectrum) suggest electron cyclotron maser (ECM) emission. The peak
1.4 GHz emission did not occur during the flare impulsive phase
but rather 45 minutes later, in association with post-eruption loop
activity seen in H-alpha and by Hinode EIS. During the Waves/LASCO era,
three other delayed bursts with peak intensities >105
sfu in the 1.0-1.6 GHz (L-band) frequency range have been reported
and appear to have characteristics similar to the December 6 burst. In
each of these three cases type IV bursts were reported in a range from
150 to 1500 MHz. Assuming a common ECM emission mechanism across this
frequency range implies a broad span of source heights in the associated
post-eruption loop systems. Difficulties with an ECM interpretation for
these events include the generation of the lower frequency component
of the type IVs and the long-standing problem of escape of the ECM
emission from the loops. Magnetic-field-aligned potential drops,
analogous to those observed for Earth's auroral kilometric radiation,
could plausibly remove both of these objections to ECM emission.
Title: End-to-End Observations and Modeling of the 17-21 January
2010 CME/ICME
Authors: Webb, D. F.; Cliver, E. W.; Nitta, N. V.; Attrill, G. D.;
Marubashi, K.; Howard, T. A.; Tappin, J.; Jackson, B. V.
Bibcode: 2010AGUFMSH41A1778W
Altcode:
On 17 January 2010, before it rotated onto the Earth-facing disk and
produced a series of M-class X-ray flares, active region 11041 was
associated with an energetic CME with a coronal wave and dimming, radio
type II and III emission. During launch the CME revealed an unusual
circular profile viewed from STEREO-B with EUVI and extending into
the COR1 field. It was also observed over the southeast limb from SOHO
EIT and LASCO from which it appeared as a partial halo. The views from
STEREO and SOHO near the Sun and HI-A and SMEI at 1 AU suggest that at
least part of the CME traveled toward STEREO-B, where a small magnetic
cloud was observed on 21 January. The importance of this event lies in
the multiwavelength observations with high time cadences of near-limb
observations of a CME, its manifestations in the low corona, its passage
through the heliosphere and its appearance as an ICME/magnetic cloud
in-situ at STEREO-B 3.5 days later. This event permits us to study the
origin and driving of the wave because the flanks of the CME and its
relationship to the wave can be studied in detail. Our interpretation
is that the wave is initially driven by the CME and then becomes freely
propagating after the CME lateral expansion ends. Several models are
used to understand the 3-D geometry and propagation of the CME, and
two flux rope models are compared with the launch observations and
magnetic field orientations.
Title: On the Origin of the Solar Moreton Wave of 2006 December 6
Authors: Balasubramaniam, K. S.; Cliver, E. W.; Pevtsov, A.; Temmer,
M.; Henry, T. W.; Hudson, H. S.; Imada, S.; Ling, A. G.; Moore, R. L.;
Muhr, N.; Neidig, D. F.; Petrie, G. J. D.; Veronig, A. M.; Vršnak,
B.; White, S. M.
Bibcode: 2010ApJ...723..587B
Altcode:
We analyzed ground- and space-based observations of the eruptive flare
(3B/X6.5) and associated Moreton wave (~850 km s-1 ~270°
azimuthal span) of 2006 December 6 to determine the wave driver—either
flare pressure pulse (blast) or coronal mass ejection (CME). Kinematic
analysis favors a CME driver of the wave, despite key gaps in coronal
data. The CME scenario has a less constrained/smoother velocity versus
time profile than is the case for the flare hypothesis and requires an
acceleration rate more in accord with observations. The CME picture is
based, in part, on the assumption that a strong and impulsive magnetic
field change observed by a GONG magnetograph during the rapid rise phase
of the flare corresponds to the main acceleration phase of the CME. The
Moreton wave evolution tracks the inferred eruption of an extended
coronal arcade, overlying a region of weak magnetic field to the west
of the principal flare in NOAA active region 10930. Observations of
Hα foot point brightenings, disturbance contours in off-band Hα
images, and He I 10830 Å flare ribbons trace the eruption from 18:42
to 18:44 UT as it progressed southwest along the arcade. Hinode EIS
observations show strong blueshifts at foot points of this arcade
during the post-eruption phase, indicating mass outflow. At 18:45
UT, the Moreton wave exhibited two separate arcs (one off each flank
of the tip of the arcade) that merged and coalesced by 18:47 UT to
form a single smooth wave front, having its maximum amplitude in
the southwest direction. We suggest that the erupting arcade (i.e.,
CME) expanded laterally to drive a coronal shock responsible for the
Moreton wave. We attribute a darkening in Hα from a region underlying
the arcade to absorption by faint unresolved post-eruption loops.
Title: Heliospheric magnetic field 1835-2009
Authors: Svalgaard, Leif; Cliver, Edward W.
Bibcode: 2010JGRA..115.9111S
Altcode: 2010arXiv1002.2934S; 2010JGRA..11509111S
We use recently acquired geomagnetic archival data to extend
our long-term reconstruction of the heliospheric magnetic field
(HMF) strength. The 1835-2009 HMF series is based on an updated and
substantiated InterDiurnal Variability (IDV) series from 1872 onwards
and on Bartels' extension, by proxy, of his u-series from 1835 to
1871. The new IDV series, termed IDV09, has excellent agreement
(R2 = 0.98; RMS = 0.3 nT) with the earlier IDV05 series,
and also with the negative component of Love's extended (to 1905)
Dst series (R2 = 0.91). Of greatest importance
to the community, in an area of research that has been contentious,
comparison of the extended HMF series with other recent reconstructions
of solar wind B for the last ∼100 years yields a strong consensus
between series based on geomagnetic data. Differences exist from
∼1900-1910 but they are far smaller than the previous disagreement
for this key interval of low solar wind B values which closely
resembles current solar activity. Equally encouraging, a discrepancy
with an HMF reconstruction based on 10Be data for the
first half of the 20th century has largely been removed by a revised
10Be-based reconstruction published after we submitted this
paper, although a remaining discrepancy for the years ∼1885-1905
will need to be resolved.
Title: Coronal Shock Waves and Solar Energetic Particle Events
Authors: Cliver, Edward
Bibcode: 2010cosp...38.1806C
Altcode: 2010cosp.meet.1806C
Recent evidence supports the view first expressed by Wild, Smerd, and
Weiss in 1963 that large solar energetic particle (SEP) events are a
consequence of shock waves manifested by radio type II bursts. Following
Tylka et al. (ApJ 625, 474, 2005), our picture of SEP acceleration at
shocks now includes the effects of variable seed particle population
and shock geometry. By taking these factors into account, Tylka and Lee
(ApJ 646, 1319, 2006; see also Sandroos Vainio, ApJ 662, L127, 2007; AA
507, L21, 2009) were able to account for the charge-to-mass variability
in high-Z ions first reported by Breneman and Stone in 1985. Recent
studies of electron-to-proton ratios, both in interplanetary space
(Cliver Ling, ApJ 658, 1349, 2007; Dietrich et al., in preparation,
2010) and in gamma-ray-line events (Shih et al., ApJ 698, L152, 2009),
also support the view that large SEP events originate in coronal shocks
and not in solar flares. Concurrent with the above developments,
there is growing evidence that coronal shocks are driven by coronal
mass ejections rather than by flare pressure pulses.
Title: The Role of Flare Characteristics in the Production of SEP
Ground Level Events
Authors: Kahler, Stephen; Cliver, Edward; Tylka, Allan J.; Dietrich,
William F.
Bibcode: 2010cosp...38.3008K
Altcode: 2010cosp.meet.3008K
Solar energetic particle events reaching the GeV energy range can by
observed by ground-based neutron monitors and are known as ground-level
events (GLEs). They are considered to be extreme cases of gradual SEP
events, produced by shocks driven by wide and fast CMEs. The CMEs
in turn are usually associated with long-duration X-ray flares of
several hours or more. It has been known that some large SEP events,
including GLEs, are associated with relatively impulsive flares and
that the flare X-ray time scale orders large SEP events in terms of
electron/proton ratios. Another SEP class are the impulsive SEP events,
in which SEP acceleration occurs in flares, producing SEPs with enhanced
charge states, heavy element abundances, and high e/p ratios. Those
events are generally associated with short-duration X-ray flares
and narrow or no observed CMEs. The association of short-duration
X-ray events with some GLEs, presumed to be gradual SEP events,
thus challenges our basic notions of separate acceleration processes
for the two kinds of SEP events. We examine the associated flare and
CME characteristics of GLEs observed since 1976 to determine how the
characteristics of the SEP abundances and spectra depend, if at all,
on the properties of the associated flares and CMEs. The goal is to
obtain a comprehensive picture of the roles of flares and CMEs in the
production of the high-energy GLEs.
Title: The Solar Moreton Wave Of 6 December 2006: Evidence For A
CME Driver
Authors: Pevtsov, Alexei A.; Balasubramaniam, K. S.; Cliver, E. W.;
Neidig, D. F.; Petrie, G. J. D.
Bibcode: 2009SPD....40.3703P
Altcode:
We analyze ground- and space-based observations of the major eruptive
flare and associated Moreton wave of 6 December 2006. The Moreton wave
spanned 270° in azimuth and exhibited a variable speed time profile
as it propagated away from the source region. The Hα wave traveled
1.2 Rsun from the S06E63 site of the eruption and white-light flare
toward the southwest in 15 minutes where it disrupted a large quiescent
filament. A preceding coronal wave was observed in a single He 10830 Å
image. Potential field analysis of the active region magnetic fields
and a comparison of ISOON images of the eruptive flare in line-center
Hα with off-band images of the wave indicate that the Moreton wave
was driven by a coronal mass ejection.
Title: Erupting Chromospheric Filaments
Authors: Balasubramaniam, K. S.; Cliver, E.; Pevtsov, A.; Martin,
S.; Panasenco, O.
Bibcode: 2009SPD....40.1010B
Altcode:
Erupting filaments are commonly associated with coronal mass
ejections. They represent the chromospheric structures most closely tied
to the underlying photospheric magnetic fields. We present an analysis
of the eruption of an unusually large filament on the SE quadrant of the
solar disc on 2003 June 11. The data are drawn from USAF/NSO Improved
Solar Observing Optical Network, Solar and Heliospheric Observatory,
and ground-based telescopes at NSO. The filament rises with an initial
slow speed of 6-7 km/s over a period of 2 hours and later erupts by
rapidly accelerating to 170 km/s second in the following 30 minutes. The
filament eruption is accompanied by a flare in a neighboring active
region. We trace morphological and topological changes in the filament
and overlying arcade before and during its eruption, and interpret
these changes in terms of physical structure of the filament and whole
filament system. The destabilization of the filament and its overlying
coronal arcade are related to interactions with a new emerging active
region, and adjacent active region.
Title: A Forecast for Cycle 24 Based on Fluctuations Above the Floor
in the Solar Wind
Authors: Cliver, Edward W.; Svalgaard, L.
Bibcode: 2009SPD....40.1106C
Altcode:
We find a close correlation between solar polar field strength (dipole
moment, DM) and the solar wind magnetic field strength (BMIN,
with CME contribution removed) for the last four solar minima, extending
over a range from 115-250 µT. This correlation gives BMIN
= 3.2 nT for DM = 0. We derive an empirical precursor relationship
between peak sunspot number (SSNMAX) for cycles 12-23 and
BMIN at their preceding minima, taking BMIN for
early cycles from our IDV-based time series of yearly B values. From
this relationship, we obtain SSNMAX = 74 for cycle 24. We
suggest that at solar minimum, after the contribution from CMEs is
removed, solar wind B consists of: (1) a floor component of 3.2 nT,
attributed to a constant baseline open solar flux ( 3 x 1014
Wb), and (2) a smaller component < 2 nT that varies from cycle to
cycle in concert with the solar polar field strength. A 3.2 nT floor,
in comparison with our previously reported value of 4.6 nT, accommodates
the Ulysses and near-Earth field measurements (BR = 2.3 nT
and B = 4.2 nT, respectively) during the current solar minimum, and
the predicted peak sunspot number of 74 for cycle 24 substantiates
our earlier SSNMAX forecast of 75 which was based on
fewer cycles.
Title: A technique for short-term warning of solar energetic particle
events based on flare location, flare size, and evidence of particle
escape
Authors: Laurenza, M.; Cliver, E. W.; Hewitt, J.; Storini, M.; Ling,
A. G.; Balch, C. C.; Kaiser, M. L.
Bibcode: 2009SpWea...7.4008L
Altcode:
We have developed a technique to provide short-term warnings of solar
energetic proton (SEP) events that meet or exceed the Space Weather
Prediction Center threshold of J (>10 MeV) = 10 pr cm-2
s-1 sr-1. The method is based on flare
location, flare size, and evidence of particle acceleration/escape
as parameterized by flare longitude, time-integrated soft X-ray
intensity, and time-integrated intensity of type III radio emission
at ∼1 MHz, respectively. In this technique, warnings are issued
10 min after the maximum of ≥M2 soft X-ray flares. For the solar
cycle 23 (1995-2005) data on which it was developed, the method has
a probability of detection of 63% (47/75), a false alarm rate of 42%
(34/81), and a median warning time of ∼55 min for the 19 events
successfully predicted by our technique for which SEP event onset
times were provided by Posner (2007). These measures meet or exceed
verification results for competing automated SEP warning techniques but,
at the present stage of space weather forecasting, fall well short of
those achieved with a human (aided by techniques such as ours) making
the ultimate yes/no SEP event prediction. We give some suggestions
as to how our method could be improved and provide our flare and SEP
event database in the auxiliary material to facilitate quantitative
comparisons with techniques developed in the future.
Title: On solar cycle predictions and reconstructions
Authors: Brajša, R.; Wöhl, H.; Hanslmeier, A.; Verbanac, G.;
Ruždjak, D.; Cliver, E.; Svalgaard, L.; Roth, M.
Bibcode: 2009A&A...496..855B
Altcode:
Context: Generally, there are two procedures for solar cycle
predictions: the empirical methods - statistical methods based on
extrapolations and precursor methods - and methods based on dynamo
models.
Aims: The goal of the present analysis is to forecast
the strength and epochs of the next solar cycle, to investigate proxies
for grand solar minima and to reconstruct the relative sunspot number
in the Maunder minimum.
Methods: We calculate the asymmetry of
the ascending and descending solar cycle phases (Method 1) and use this
parameter as a proxy for solar activity on longer time scales. Further,
we correlate the relative sunspot numbers in the epochs of solar
activity minima and maxima (Method 2) and estimate the parameters of
an autoregressive moving average model (ARMA, Method 3). Finally,
the power spectrum of data obtained with the Method 1 is analysed
and the Methods 1 and 3 are combined.
Results: Signatures of
the Maunder, Dalton and Gleissberg minima were found with Method 1. A
period of about 70 years, somewhat shorter than the Gleissberg period
was identified in the asymmetry data. The maximal smoothed monthly
sunspot number during the Maunder minimum was reconstructed and found
to be in the range 0-35 (Method 1). The estimated Wolf number (also
called the relative sunspot number) of the next solar maximum is in
the range 88-102 (Method 2). Method 3 predicts the next solar maximum
between 2011 and 2012 and the next solar minimum for 2017. Also, it
forecasts the relative sunspot number in the next maximum to be 90
± 27. A combination of the Methods 1 and 3 gives for the next solar
maximum relative sunspot numbers between 78 and 99.
Conclusions:
The asymmetry parameter provided by Method 1 is a good proxy for solar
activity in the past, also in the periods for which no relative sunspot
numbers are available. Our prediction for the next solar cycle No. 24
is that it will be weaker than the last cycle, No. 23. This prediction
is based on various independent methods.
Title: History of research on solar energetic particle (SEP) events:
the evolving paradigm
Authors: Cliver, Edward W.
Bibcode: 2009IAUS..257..401C
Altcode:
Forbush initiated research on solar energetic particle (SEP) events in
1946 when he reported ionization chamber observations of the first three
ground level events (GLEs). The next key development was the neutron
monitor observation of the GLE of 23 February 1956. Meyer, Parker and
Simpson attributed this high-energy SEP event to a short time-scale
process associated with a solar flare and ascribed the much longer
duration of the particle event to scattering in the interplanetary
medium. Thus “flare particle” acceleration became the initial
paradigm for SEP acceleration at the Sun. A more fully-developed picture
was presented by the Australian radio astronomers Wild, Smerd, and
Weiss in 1963. They identified two distinct SEP acceleration processes
in flares: (1) the first phase accelerated primarily ~100 keV electrons
that gave rise to fast-drift type III emission as they streamed outward
through the solar atmosphere; (2) the second phase was produced by an
outward moving (~1000 km s-1) magnetohydrodynamic shock,
occurring in certain (generally larger) flares. The second phase,
manifested by slow-drift metric type II emission, appeared to be
required for substantial acceleration of protons and higher-energy
electrons. This two-stage (or two-class) picture gained acceptance
during the 1980s as composition and charge state measurements
strengthened the evidence for two distinct types of particle events
which were termed impulsive (attributed to flare-resident acceleration
process(es)) and gradual (shock-associated). Reames championed the
two-class picture and it is the commonly accepted paradigm today. A
key error made in the establishment of this paradigm was revealed in
the late 1990s by observations of SEP composition and charge states at
higher energies (>10 MeV) than previously available. Specifically,
some large and therefore presumably “gradual” SEP events looked
“impulsive” at these energies. One group of researchers attributes
these unusual events to acceleration of high-energy SEPs by flares
and another school favors acceleration of flare seed particles by
quasi-perpendicular shocks. A revised SEP classification scheme is
proposed to accommodate the new observations and to include ideas
on geometry and seed particle composition recently incorporated into
models of shock acceleration of SEPs.
Title: Great geomagnetic storm of 9 November 1991: Association with
a disappearing solar filament
Authors: Cliver, E. W.; Balasubramaniam, K. S.; Nitta, N. V.; Li, X.
Bibcode: 2009JGRA..114.0A20C
Altcode: 2009JGRA..11400A20C
We attribute the great geomagnetic storm on 8-10 November 1991 to a
large-scale eruption that encompassed the disappearance of a ~25° solar
filament in the southern solar hemisphere. The resultant soft X-ray
arcade spanned ~90° of solar longitude. The rapid growth of an active
region lying at one end of the X-ray arcade appears to have triggered
the eruption. This is the largest geomagnetic storm yet associated with
the eruption of a quiescent filament. The minimum hourly Dst value of
-354 nT on 9 November 1991 compares with a minimum Dst value of -161
nT for the largest 27-day recurrent (coronal hole) storm observed
from 1972 to 2005 and the minimum -559 nT value observed during the
flare-associated storm of 14 March 1989, the greatest magnetic storm
recorded during the space age. Overall, the November 1991 storm ranks
15th on a list of Dst storms from 1905 to 2004, surpassing in intensity
such well-known storms as 14 July 1982 (-310 nT) and 15 July 2000
(-317 nT). We used the Cliver et al. and Gopalswamy et al. empirical
models of coronal mass ejection propagation in the solar wind to
provide consistency checks on the eruption/storm association.
Title: Low-Frequency Type III Bursts and Solar Energetic Particle
Events
Authors: Cliver, E. W.; Ling, A. G.
Bibcode: 2009ApJ...690..598C
Altcode:
We compare the ~1 MHz type III bursts of flares associated with samples
of "impulsive" and "gradual" solar energetic particle (SEP) events from
cycle 23. While large gradual SEP events had much higher > 30 MeV
proton intensities, the median-integrated intensities, peak intensities,
and durations of the two groups of radio bursts were comparable. Thus,
the median "proton yield" (peak > 30 MeV proton intensity of an SEP
event divided by its associated integrated ~1 MHz intensity) of type
III bursts associated with gradual SEP events was ~280 times larger
than that for impulsive SEP events. A similar yield difference of
~250 was observed for 4.4 MeV electron events. Only for extrapolated
electron energies ~5 keV, corresponding to the energy of the electrons
that excite type III emission, does the median yield converge to the
same value for both groups of events. The time profiles of ~1 MHz
bursts associated with impulsive SEP events are characteristically
shorter and simpler than those associated with the gradual SEP events,
reflecting the development of the second stage of radio emission in
large eruptive flares. The gradual SEP events were highly associated
(96%) with decametric-hectometric (DH) type II bursts versus only a 5%
association rate for the impulsive events. Large favorably located ~1
MHz type III bursts with associated DH type IIs had an ~60% association
rate with large (>= 1 pfu) > 30 MeV SEP events versus ~5% for
~1 MHz bursts without accompanying DH II emission. These results are
interpreted in terms of two distinct types of particle acceleration
at the Sun, a flare-resident process that produces relatively few >
30 MeV protons and ~4 MeV electrons in space and a shock process that
dominates the large gradual proton events.
Title: A Prediction for the 24th Solar Cycle
Authors: Brajša, R.; Wöhl, H.; Hanslmeier, A.; Verbanac, G.;
Ruždjak, D.; Cliver, E.; Svalgaard, L.; Roth, M.
Bibcode: 2009CEAB...33...95B
Altcode:
The aim of the present analysis is to forecast the strength of the
next solar maximum of the 24th cycle. We correlate the
relative sunspot numbers in the epochs of solar activity minima and
maxima. Using this method, the estimated relative sunspot number (also
called the Wolf number) of the next solar maximum is in the range 67-81,
i.e., about 40 % below the peak sunspot number of 121 for cycle No. 23.
Title: A Revised Classification Scheme for Solar Energetic Particle
Events
Authors: Cliver, E. W.
Bibcode: 2009CEAB...33..253C
Altcode:
We propose a revision of the standard ``impulsive/gradual"
classification scheme for solar energetic particle (SEP) events. In
the new scheme, SEP events are divided into two basic classes: ``Flare"
and ``Shock". The flare class corresponds to the old impulsive class,
or more specifically, the ^{3}He-rich subset of that class. The
shock class, which replaces the gradual class, consists of two
subclasses based on shock geometry and seed particle population,
either quasi-perpendicular (operating on flare particle seeds) or
quasi-parallel (coronal or solar wind suprathermals). Our revision
was motivated by recent observations of large and presumably gradual
events that had impulsive event composition and charge states at
high energies. The new classification scheme is based on the Tylka
et al. (2005) study linking shock geometry and seed populations to
Fe/O variation in large SEP events. We show that flare time scale,
the organizing parameter in the current two-class picture, can be
incorporated naturally into the revised SEP classification scheme,
and we review recent evidence that supports the proposed framework.
Title: Obituary: James N. Kile, 1958-2007
Authors: Cliver, Edward W.; Lang, Kenneth R.; Willson, Robert F.
Bibcode: 2009BAAS...41..570C
Altcode:
James N. Kile, of Needham Heights, Massachusetts, died on 17 August
2007, following a brave two-year battle with cancer. One of three
children of David R. Kile and Betty Jane Kile, Jim was born in Niagara
Falls, New York, on 20 April 1958 and lived in the nearby village of
Lewiston before his family settled in Alden, an hour east of Niagara
Falls, when Jim was nine. Jim's father worked for American Telephone
and Telegraph for 37 years, and his mother was a homemaker. Jim
earned his Bachelor's degree in Physics from Rensselaer Polytechnic
Institute in 1980, a Master's degree from Northwestern University in
1982, and a Doctorate from Tufts University in 1996 under the direction
of Robert Willson. His thesis involved comparison of radio data from the
Very Large Array and the Russian RATAN 600 telescope with Yohkoh soft
X-ray data, with an emphasis on understanding the relationship between
solar noise storms and coronal magnetic fields. While working on his
thesis, Jim collaborated with one of us (EWC) at the Air Force Research
Laboratory on an investigation of the 154-day periodicity in solar
flares. The resulting publication (ApJ 370, 442, 1991) is his most cited
work. Jim co-authored four other papers in refereed journals. Jim's
professional affiliations included the American Astronomical Society,
the American Institute of Aeronautics and Astronautics, the American
Geophysical Union, and the Astronomical Society of the Pacific. Jim worked as a contractor in the defense industry from 1982 until the
time of his death, settling in the Boston area in the early 1980s. He
worked for Calspan Corporation from 1982-1989, the Ultra Corporation
from 1989-1994, and the Riverside Research Institute from 1994-2007. He
was a highly-respected expert in radar systems, including radar data and
systems analysis, systems engineering, and planning support for radar
acquisition programs and technology development. The work entailed
frequent extended travel to Norway for system testing. During
the summer of 1997 Jim was an instructor for introductory physics
laboratories at Simmons College, and in 2002 he developed and taught
a synthetic aperture radar measurement and signature intelligence
course for the Air Force Institute of Technology in Dayton, Ohio,
where he was appointed Adjunct Assistant Professor of Physics in the
Department of Engineering Physics, a position he held until 2005. On
the local level, Jim assisted in astronomy education projects, such
as nighttime telescope viewing, in the Needham public schools and
stargazing/astronomy courses at several Massachusetts Audubon wildlife
sanctuaries. Jim met the love of his life in the mid-1980s, and
he and Elaine were married within the year, on 19 October 1985. They
shared a passion for birding and a love for nature witnessed up close
when hiking, kayaking, snowshoeing, and cross-country skiing. Jim
had a wide range of interests. He was an accomplished folk musician,
playing the guitar and ukulele. He was a devoted "Trekkie" who could
quote every line from early Star Trek episodes and was a life member
of the American Radio Relay League [ARRL]. Jim had the warm and
open personality characteristic of those raised in the snow-belt. He
was always good company. His courage as he was dying, much too soon,
was a great source of strength for his family. Jim is survived by
his wife Elaine C. (Smith) Kile, his father David R. Kile, his sister
Diane Kile and her husband David Galson, his brother David M. Kile and
his wife Susan Kile, and four nephews, one niece, and a great niece
and nephew. He was predeceased by his mother Betty Jane Kile.
Title: Towards a Consensus View of the Heliospheric Magnetic Field
Strength Since 1900
Authors: Cliver, E. W.; Svalgaard, L.
Bibcode: 2008AGUFMSH24A..01C
Altcode:
McCracken (2007) inverted the galactic cosmic ray record for the
interval 1428-2005 to estimate annual averages of the heliomagnetic
field (HMF) near Earth during this interval. Quoting from his abstract,
"There is good agreement with the results obtained by others using
two independent methodologies based upon the sunspot [Solanki et
al., 2002] and geomagnetic [Lockwood et al., 1999] records There
is disagreement with another method based on the geomagnetic record
[Svalgaard and Cliver, 2005] that needs to be resolved." We address
the reported disagreement of our long-term reconstruction of the HMF
strength with that obtained in the other three studies. We show that
a recent reconstruction of the HMF by Rouillard, Lockwood, and Finch
[2007] agrees much more closely with that of Svalgaard and Cliver
than that of Lockwood et al. to the point where a consensus seems
to be reached. We suggest that the discrepancy between McCracken's
cosmic-ray-based HMF reconstruction and those based on geomagnetic data
originates in the Forbush and Neher ionization chamber data (1933-1957)
used to bridge the time gap between the 10Be time series (1428-1930)
and the Climax neutron monitor record (1951-present).
Title: Origin of Coronal Shock Waves. Invited Review
Authors: Vršnak, Bojan; Cliver, Edward W.
Bibcode: 2008SoPh..253..215V
Altcode: 2008SoPh..tmp..142V
The basic idea of the paper is to present transparently and confront
two different views on the origin of large-scale coronal shock waves,
one favoring coronal mass ejections (CMEs), and the other one preferring
flares. For this purpose, we first review the empirical aspects of the
relationship between CMEs, flares, and shocks (as manifested by radio
type II bursts and Moreton waves). Then, various physical mechanisms
capable of launching MHD shocks are presented. In particular, we
describe the shock wave formation caused by a three-dimensional piston,
driven either by the CME expansion or by a flare-associated pressure
pulse. Bearing in mind this theoretical framework, the observational
characteristics of CMEs and flares are revisited to specify advantages
and drawbacks of the two shock formation scenarios. Finally,
we emphasize the need to document clear examples of flare-ignited
large-scale waves to give insight on the relative importance of flare
and CME generation mechanisms for type II bursts/Moreton waves.
Title: Book Review: The Sun Kings: The Unexpected Tragedy of Richard
Carrington and the Tale of How Modern Astronomy Began
Authors: Cliver, Edward W.
Bibcode: 2008SpWea...611003C
Altcode:
Stuart Clark's The Sun Kings, the story of the nineteenth-century
astronomers, natural philosophers, and magneticians who established
solar-terrestrial science, is a must read for members of the space
weather community. Designated the Best Professional/Scholarly Book
in Cosmology and Astronomy for 2007 by the Association of American
Publishers and shortlisted for the Royal Society General Prize for
Science Books for 2008, The Sun Kings recounts the heroic scientific
advances-of Alexander von Humboldt, Samuel Schwabe, Edward Sabine,
Richard Carrington, Edward Maunder, George Hale, and others-that showed
that Earth's magnetic storms originate at the Sun.
Title: Solar Radio Bursts and Energetic Particle Events
Authors: Cliver, Edward W.
Bibcode: 2008AIPC.1039..190C
Altcode:
The two basic types of particle acceleration at the Sun-a flare-resident
process (or processes) and acceleration at coronal shock waves-were
first identified in solar metric radio emissions through their
associated type III bursts and type II bursts, respectively. A key
question for solar energetic particle (SEP) physics today concerns the
relative contributions of flares and shocks to large gradual SEP events,
particularly at >30 MeV energies. We address this question by:
(1) comparing low-frequency (~1 MHz) radio emissions for samples of
the largest gradual and impulsive SEP events from cycle 23; and (2)
determining SEP associations for a sample of large favorably-located
low-frequency type III radio bursts. Our results indicate that a strong
shock, as commonly manifested by a low-frequency (<14 MHz) type II
burst, is a necessary condition for the occurrence of a large >30
MeV proton event. We propose a revision to the standard two-class
paradigm for SEP events in which we subdivide the current gradual
event class on the basis of shock geometry, i.e., quasi-parallel or
quasi-perpendicular.
Title: ~130 Years of Solar-Wind Data: The Floor and More
Authors: Cliver, E. W.
Bibcode: 2008AGUSMSH44A..02C
Altcode:
Long-term reconstructions of solar wind parameters have implications
for topics ranging from the operation of the solar dynamo to solar
variability and climate change. Such reconstructions of the solar wind
interplanetary magnetic field (IMF) strength, beginning with the seminal
work of Lockwood et al. (1999), have been varied and contentious but
appear to be converging along the following lines: an IMF floor of ~4.5
nT in the ecliptic plane on which solar cycle variations (closed flux
from coronal mass ejections) ride. A recent reconstruction based on
cosmic ray data by McCracken is at variance with this picture, however,
and the differences remain to be resolved. The average IMF strength
near Earth during 2007 was 4.5 nT (rotation averages from January
2007- present ranged from 4.1-5.2 nT). Annual averages approaching
this value were last inferred (via the IDV index) for 1901 and 1902
(both ~4.7 nT). During the last century, it appears that there has
been an increase, of unknown cause, in the solar wind speed of ~15%.
Title: Type III bursts and solar energetic proton (SEP) events
Authors: Cliver, Edward
Bibcode: 2008cosp...37..563C
Altcode: 2008cosp.meet..563C
To assess the relative importance of flare vs. shock acceleration
in large SEP events, we compiled a computer generated list of major
∼1 MHz type III bursts observed by the Waves experiment on the Wind
spacecraft for solar cycle 23 (1996-2004). We defined major ∼1
MHz events as those have peak intensities > 3 x 105 solar flux
units (sfu) and durations, at intensities > 2 x 103 sfu, of >
15 minutes. From this list of type III bursts, we identified events
associated with solar flares between W20-W89 solar longitude in order
to minimize radio occultation and SEP propagation effects. We then
separated the favorably-located type III bursts into those with and
without associated low-frequency Waves type II bursts and determined
the association of the two groups with large (> 1 proton flux unit)
> 30 MeV SEP events. Our preliminary result is that a strong shock
(as manifested by a Waves type II burst) is a necessary condition for
a large > 30 MeV proton event.
Title: Chromospheric observations of erupting filaments with the
Optical Solar Patrol Network (OSPaN) telescope
Authors: Cliver, Edward; Balasubramaniam, K. S.; Cliver, E. W.;
Engvold, O.; Pevtsov, A.; Martin, S.; Panasenco, O.
Bibcode: 2008cosp...37..562C
Altcode: 2008cosp.meet..562C
Using AFRL/NSO OSPaN telescope chromospheric images, we present movies
and analyses of the eruption of a quiescent filament (11 June 2003)
and an active region filament (13 May 2005). In both cases, widely
separated regions of the solar surface were affected by the eruptions,
either via the Moreton waves they generated (inferred from winking
filaments) or through direct magnetic connection (manifested by
sequential chromospheric brightenings). We investigate the topology
of the magnetic fields in which these eruptions occur and use Doppler
measurements to understand the dynamics of the eruptions.
Title: Origins of the Wolf Sunspot Number Series: Geomagnetic
Underpinning
Authors: Cliver, E. W.; Svalgaard, L.
Bibcode: 2007AGUFMSH13A1109C
Altcode:
The Wolf or International sunspot number (SSN) series is based on
the work of Swiss astronomer Rudolf Wolf (1816-1893). Following
the discovery of the sunspot cycle by Schwabe in 1843, Wolf culled
sunspot counts from journals and observatory reports and combined them
with his own observations to produce a SSN series that extended from
1700-1893. Thereafter the SSN record has been maintained by the Zurich
Observatory and, since 1981, by the Royal Observatory of Belgium. The
1700-1893 SSN record constructed by Wolf has not been modified since
his death. Here we show that Wolf's SSNs were not based solely on
reports of sunspots but were calibrated by reference to geomagnetic
range observations which closely track the sunspot number. Nor were
these corrections small; for example Wolf multiplied the long series
(1749-1796) of sunspot counts obtained by Staudacher by factors of
2.0 and 1.25, in turn, to obtain the numbers in use today. It is
not surprising then that a competing SSN series obtained by Hoyt and
Schatten based on group sunspot numbers is different, generally lower
than that of Wolf. Comparison of the International number with current
magnetic range observations indicates that, as Wolf found, the magnetic
range (specifically, the average annual Y-component of mid-latitude
stations) can be used as an independent check on the validity and
stability of the SSN series. Moreover, the geomagnetic range series,
which in itself is a long-term proxy of solar EUV emission, can be
used to resolve discrepancies between the Wolf and Group SSN series
during the 19th century.
Title: Interhourly variability index of geomagnetic activity and
its use in deriving the long-term variation of solar wind speed
Authors: Svalgaard, Leif; Cliver, Edward W.
Bibcode: 2007JGRA..11210111S
Altcode: 2007arXiv0706.0961S
We describe the detailed derivation of the interhourly variability (IHV)
index of geomagnetic activity. The IHV index for a given geomagnetic
element is mechanically derived from hourly values or means as the
sum of the unsigned differences between adjacent hours over a 7-hour
interval centered on local midnight. The index is derived separately
for stations in both hemispheres within six longitude sectors spanning
the Earth using only local night hours. It is intended as a long-term
index and available data allows derivation of the index back well into
the 19th century. On a timescale of a 27-day Bartels rotation, IHV
averages for stations with corrected geomagnetic latitude less than 55°
are strongly correlated with midlatitude range indices (R2
= 0.96 for the am index since 1959; R2 = 0.95 for the aa
index since 1980). We find that observed yearly averages of aa before
the year 1957 are ∼3 nT too small compared to values calculated from
IHV using the regression constants based on 1980-2004. We interpret
this discrepancy as an indication that the calibration of the aa index
is in error before 1957. There is no systematic discrepancy between
observed and similarly calculated ap values back to 1932. Bartels
rotation averages of IHV are also strongly correlated with solar
wind parameters (R2 = 0.79 with BV2). On a
timescale of a year combining the IHV index (giving BV2
with R2 = 0.93) and the recently developed interdiurnal
variability (IDV) index (giving interplanetary magnetic field magnitude,
B, with R2 = 0.74) allows determination of solar wind speed,
V, from 1890 to present. Over the ∼120-year series, the yearly mean
solar wind speed varied from a low (inferred) of 303 km/s in 1902 to
a high (observed) value of 545 km/s in 2003. The calculated yearly
values of the product BV using B and V separately derived from IDV
and IHV agree quantitatively with (completely independent) BV values
derived from the amplitude of the diurnal variation of the horizontal
component in the polar caps since 1926 (and sporadically further back).
Title: A Floor in the Solar Wind Magnetic Field
Authors: Svalgaard, L.; Cliver, E. W.
Bibcode: 2007ApJ...661L.203S
Altcode:
Long-term (~130 years) reconstruction of the interplanetary magnetic
field (IMF) based on geomagnetic indices indicates that the solar
wind magnetic field strength has a ``floor,'' a baseline value in
annual averages that it approaches at each 11 yr solar minimum. In the
ecliptic plane at 1 AU, the IMF floor is ~4.6 nT, a value substantiated
by direct solar wind measurements and cosmogenic nuclei data. At
high heliolatitudes, Ulysses measured a constant radial field with
a magnitude (normalized to 1 AU) of ~3.2 nT during solar minimum
conditions in ~1995 when the observed solar polar fields were ~100
μT and in 2006 when the polar fields were ~60 μT, as well as for
solar maximum conditions in 2001 when the polar fields were close to
zero. We identify the floor with a constant (over centuries) baseline
open magnetic flux at 1 AU of ~4×1014 Wb, corresponding
to a constant strength (~1011 A) of the heliospheric
current. Solar cycle variations of the IMF strength ride on top of the
floor. The floor has implications for (1) the solar wind during grand
minima-we are given a glimpse of Maunder minimum conditions at every 11
yr minimum; (2) current models of the solar wind-both source surface and
MHD models are based on the assumption, invalidated by Ulysses, that the
largest scale fields determine the magnitude of the IMF; consequently,
these models are unable to reproduce the high-latitude observations; and
(3) the use of geomagnetic input data for precursor-type predictions of
the coming sunspot maximum-this common practice is rendered doubtful
by the observed disconnect between solar polar field strength and
heliospheric field strength.
Title: Agnes Mary Clerke: Real-time historian of astronomy
Authors: Cliver, E. W.
Bibcode: 2007A&G....48c..25C
Altcode:
Agnes Mary Clerke chronicled the turbulent leading edge of astronomical
research. Her authoritative accounts and assessments of solar and
stellar science captured the attention of the leading astronomers of
her day and are essential sources for historians today. Here I briefly
recount the details of her life and achievements, drawing attention
especially to the precise and enjoyable quality of her writing.
Title: Calibrating the Sunspot Number Using "the Magnetic Needle"
Authors: Svalgaard, L.; Cliver, E. W.
Bibcode: 2007AGUSMSH54B..02S
Altcode:
The 400-year long sunspot series is our primary direct record of
Space Climate. Two series exist: the Zurich (now: International)
series compiled by Wolf and successors, and the Group series by Hoyt
and Schatten. The two series agree well back to ~1875, but before
that the Group SSNs are systematically lower than the Wolf SSN. Wolf
(and others) noticed that the amplitude, rD, of the daily variation
of the Declination of the geomagnetic field varied with the sunspot
number, R, and proposed a linear relationship: rD = a + bR. In fact,
he used this relationship to calibrate the sunspot number for times
before his own observations started (1849). Later researchers were less
enthusiastic about this procedure. We re-examine Wolf's relationship
using the range of the East component measured in force units [nT],
rY, instead. This range is directly related to the intensity of the
ionospheric SR currents, which in turn depends on the conductivity
of the ionosphere. Solar FUV radiation creates and maintains the
ionosphere, therefore the rY range (corrected for the secular decrease
of the Earth's main field) is a proxy of the FUV. We show that this
proxy reproduces the F10.7 radio flux and the International sunspot
number with a correlation coefficient of 0.985, and recalibrate the
sunspot number back to 1841 [Geomagnetic data exists that may allow
such recalibration back to the 1740s]. The main conclusion is that
there does not seem to be any secular increase in solar activity over
the last 165 years: cycles 11 and 10 were as active as the most recent
cycles 22 and 23.
Title: Electrons and Protons in Solar Energetic Particle Events
Authors: Cliver, E. W.; Ling, A. G.
Bibcode: 2007ApJ...658.1349C
Altcode:
A plot of 0.5 MeV peak electron intensity versus >10 MeV peak
proton intensity for well-connected solar energetic particle (SEP)
events from 1997 to 2003 reveals two distinct populations: (1) a group
of events with peak proton intensities <3 protons cm-2
s-1 sr-1 that have electron-to-proton (e/p) ratios
ranging from ~102 to 2×104 and (2) a well-defined
branch spanning peak proton intensities from ~3 to 104
protons cm-2 s-1 sr-1 with e/p ratios
ranging from ~101 to 2×102. Events with strong
abundance enhancements of trans-Fe elements form a prominent subset of
``population 1'' and are absent from ``population 2.'' For a sample
of poorly connected SEP events, population 1 largely disappears, and
population 2 is observed to extend down to low (<10-1
protons cm-2 s-1 sr-1) proton
intensities. Plots of 0.5 MeV peak electron intensity versus >30
MeV peak proton intensity yield comparable results. The SEP events in
population 2 are highly (~90%) associated with dekametric/hectometric
(DH) type II bursts versus only a ~20% association rate for population
1 events. Population 2 events have flatter electron (0.5-4.4 MeV) and
proton spectra (10-30 MeV) than those in population 1. Based on their
high e/p ratios, trans-Fe enhancements, poor association with DH type
IIs, and inferred small ``emission cones,'' population 1 events are
attributed to acceleration in solar flares. For population 2 events,
evidence for a dominant shock process includes their flatter spectra,
apparent widespread sources, and high association with DH type II
bursts.
Title: Validating the proton prediction system (PPS)
Authors: Kahler, S. W.; Cliver, E. W.; Ling, A. G.
Bibcode: 2007JASTP..69...43K
Altcode: 2007JATP...69...43K
The proton prediction system (PPS) is a program developed at the Air
Force Research Laboratory (AFRL) to predict solar energetic (E>5MeV)
proton (SEP) intensities at 1 AU following solar flares. It is based
on average observed SEP intensity-time profiles, peak intensities,
and event durations. The input parameters are solar flare peak or
time-integrated X-ray or radio fluxes and their times of onsets and
maxima, and solar flare locations. We do a limited validation of the
PPS using 78 GOES solar X-ray flares of peak intensity ⩾M5 with well
associated Hα flare locations. Predicted peak proton intensities
J(E>10MeV) and event onset and rise times are compared with SEP
events observed by GOES. We also select all GOES E>10MeV SEP events
above 10 proton flux units (pfu) during the same time period to compare
with those predicted by the PPS. With our M5 X-ray flare threshold
the PPS yields approximately equal numbers of correct predictions,
false predictions, and missed 10-pfu SEP events.
Title: Long-term geomagnetic indices and their use in inferring
solar wind parameters in the past
Authors: Svalgaard, L.; Cliver, E. W.
Bibcode: 2007AdSpR..40.1112S
Altcode:
We discuss three new geomagnetic indices [the Inter-Hour Variability
( IHV), the Inter-Diurnal Variability ( IDV), Svalgaard, L.,
Cliver, E.W. The IDV index: its derivation and use in inferring
long-term variations of the interplanetary magnetic field
strength. J. Geophys. Res. 110, A12103. doi:10.1029/2005JA011203,
2005; and the Polar Cap Potential ( PCP) index, Le Sager, P.,
Svalgaard, L. No increase of the interplanetary electric field since
1926. J. Geophys. Res. 109 (A7), A07106. doi:10.1029/2004JA010411,
2004], that are derivable from data available for a century or
more. Each of these indices responds directly to either the solar
wind magnetic field strength ( B) or to different combinations of B
and the solar wind speed ( V). This over-determined system permits
a reconstruction of these parameters for the past ∼150 years. The
variation of yearly averages of B can be described as a constant value
(4.6 nT) plus a component varying with the square root of the sunspot
number. Because the latter seems to exhibit a ∼100 year Gleissberg
cycle, B does as well. Since 1890, annual averages of V range from a
low of ∼300 km/s in 1902 to 545 km/s in 2003. The IHV-index fords a
way to check the calibration of other long-term geomagnetic indices. We
find that the ap-index tracks the variation of IHV, back to 1932 but
that the aa-index (extended back to 1844) is systematically too low
(3-6 nT) before 1957, relative to modern values.
Title: Shock Versus Solar Flare Production of Heliospheric
Relativistic Electron Events
Authors: Kahler, S. W.; Cliver, E. W.
Bibcode: 2006AGUFMSH42A..05K
Altcode:
Electrons with relativistic (E > 0.3 MeV) energies are often
observed as discrete events in the inner heliosphere. Their sharp
onsets and antisunward flows indicate that they are produced in solar
transient events. In general their origins can be associated in time
with both solar flares and coronal mass ejections (CMEs). Unlike
the solar energetic proton (SEP) and ion events, we do not have
the advantage of particle elemental abundances and charge states as
source diagnostics. We review the characteristics of the electron
events observed on the Helios, Venera, ISEE-3, Phobos, and other
inner heliospheric spacecraft to determine whether they are more
likely to be produced by broad coronal shocks driven by CMEs or by
solar flare processes associated with magnetic reconnection. Electron
intensity-time profiles and energy spectra are compared with properties
of flares and CMEs for this determination. Recent comparisons of peak
electron and SEP event intensities provide strong evidence for the
shock interpretation, but definitive results require the observations
provided by the Sentinels mission.
Title: The Disappearance of Large, Fe-Rich Solar Energetic Particle
Events in the Declining Phase of Cycle 23: Implications for the Role
of Flares
Authors: Dietrich, W. F.; Tylka, A. J.; Cliver, E. W.; Cohen, C. M.;
Mewaldt, R. A.; Reames, D. V.
Bibcode: 2006AGUFMSH41B..03D
Altcode:
Solar energetic particle (SEP) events are generally divided into two
categories, "gradual" and "impulsive". corresponding, respectively, to
acceleration by shocks driven by fast coronal mass ejections (CMEs) or
acceleration at sites associated with flares, probably through resonant
wave-particle interactions following magnetic reconnection. One of the
defining distinctions between the two types is the event-integrated
Fe/O ratio, with gradual events at a few MeV/nucleon exhibiting
typical coronal values while impulsive events generally show strong
enhancements. But the precise, comprehensive observations from a fleet
of new spacecraft at the start of Cycle 23 immediately challenged this
neat picture: Fe/O ratios generally varied with energy, and a large
fraction of the nominally "gradual" events, when observed at energies
above the few MeV/nucleon where the two categories were originally
developed, showed enhanced Fe/O ratios approaching those typically
associated with impulsive events. In 1997-2002, 13 out of the 38 very
large SEP events (identified by >30 MeV proton fluence above 2 x
105/cm2-sr) had an Fe/O ratio above 30 MeV/nucleon that was at least
four times the nominal coronal value. But in 2003-2005, zero out of the
20 events satisfying the same selection criterion displayed comparably
large Fe/O enhancements. This dramatic shift clearly indicates that
the condition(s) that allow flares to contribute to large SEP events
have changed in some fundamental way in the declining phase of Cycle
23. In particular, three hypotheses (direct-flare; shock- acceleration
of escaping suprathermals from the accompanying flare; or shock
acceleration of remnant suprathermals from previous flare activity)
have been proposed in order to explain the flare-like composition seen
at high energies in some large gradual events. Based on comparisons
of the reported flare, CME, and suprathermal characteristics in the
two time periods, we show that the third hypothesis appears to be most
likely to be able to accommodate the late-Cycle disappearance of the
large Fe-rich events. We also examine open issues surrounding this
explanation that Sentinels will be able to address.
Title: Reply to the comment by M. Lockwood et al. on ``The IDV index:
Its derivation and use in inferring long-term variations of the
interplanetary magnetic field''
Authors: Svalgaard, L.; Cliver, E. W.
Bibcode: 2006JGRA..111.9110S
Altcode: 2006JGRA..11109110S
From an analysis of geomagnetic and solar wind data, [1999] (hereinafter
referred to as LSW99) reported that the solar coronal magnetic field had
increased by more than a factor of two during the last century. If true,
this would be an important discovery. Recently, [2005] (hereinafter
referred to as SC05) reported an analysis based on our newly developed
interdiurnal variability (IDV) index of geomagnetic activity which
indicated that cycle averages of the solar field varied no more than
∼25% over the same time interval and are now decreasing. Here, we
answer the criticisms of [2006] (hereinafter referred to as LRFS06)
to our paper. In sum, we find their objections without merit. If our
prediction that the next solar cycle will be the smallest in 100 years
[, 2005] bears out, this debate may be settled by direct solar wind
measurements within the next few years. In the following sections we
respond to the various points raised by LRFS06: percentage change,
Br versus B, regression technique (including the effect of
missing data), and analysis procedure.
Title: Electrons and Protons in Solar Energetic Particle Events
Authors: Cliver, Edward W.; Ling, A. G.
Bibcode: 2006SPD....37.2902C
Altcode: 2006BAAS...38..255C
A plot of 0.5 MeV peak electron intensity vs. 10 MeV peak proton
intensity for well-connected (W20-90) solar energetic particle (SEP)
events from 1997-2003 reveals two distinct populations: (1) a group
of events with peak proton intensities < 3 pr cm-2
s-1 sr-1 that have electron to proton (e/p)
ratios ranging from 3 x 102 - 5 x 104,
and (2) a branch spanning peak proton intensities from 3 -
104 pr cm-2 s-1 sr-1 with
e/p ratios ranging from 102 - 3 x 102. Events with
strong trans-Fe enhancements form a prominent subset of "population 1"
and are absent from "population 2". The SEP events in population 2 are
highly ( 85%) associated with decametric/hectometric type II bursts
vs. only a 15% association rate for events with trans-Fe enhancements in
population 1. For a sample of poorly-connected (E40-W19 and W91-W150)
SEP events, population 1 largely disappears, and population 2 is
observed to extend down to low (< 10-1 pr cm-2
s-1 sr-1) proton intensities. These results are
discussed in terms of current thinking on particle acceleration at
the Sun.
Title: Interplanetary Magnetic Field Strength 1902-1906
Authors: Svalgaard, L.; Cliver, E. W.
Bibcode: 2006AGUSMSH51A..06S
Altcode:
Using geomagnetic measurements made by Robert F. Scott at Discovery
Hut in the Antarctic polar cap 1902- 1903 and by Roald Amundsen
at Gjøahavn in the Arctic polar cap 1903-1906 we determine the
strength of the cross polar cap equivalent current. This quantity
is controlled by the interplanetary electric field, E, (essentially
the product VB of solar wind speed V and IMF strength B). Comparison
with modern data from contemporary polar cap stations at similar
latitudes and locations and from spacecraft yields the conversion
factor from the variation measured on the ground to the electric field
E. Our geomagnetic activity indices IDV and IHV measure B and BV22,
respectively, thus allowing both B and V to be determined since at
least 1882. Their product VB agrees well with VB determined from the
early polar cap data, providing an important independent confirmation
of the validity of all three methods. We find that B during 1902-1906
was ~6 nT, comparable to present day values ~100 years later.
Title: The IGY Gold History Preservation Program
Authors: Thompson, B. J.; Cliver, E. W.; Gentile, L. C.; Sigsbee,
K. M.; Doel, R. E.
Bibcode: 2006AGUSM.U41D..08T
Altcode:
An important part of the 2007 International Year activities will be
preserving the history and memory of IGY 1957. The "IGY Gold" History
initiative has several goals: 1) identifying and recognizing planners
of and participants in the first IGY, 2) preserving memoirs, articles,
photographs, and all items of historical significance for the IGY,
3) making these items available to historians, researchers, etc.,
4) serving as a contact service for these activities, 5) spreading
awareness of the history of geophysics, and 6) planning special events
and "reunions." The IGY "Gold" Club identifies participants from
the first IGY (gold symbolizing the 50th anniversary). "Gold club"
participants will be rewarded with a special "IGY Gold Anniversary"
certificate of recognition and a special commemorative "IGY Gold"
lapel pin. Many IGY participants from around the globe have received
IGY Gold Club awards, and many have submitted valuable historical
material about the IGY activities. This is a joint program of the IHY,
eGY, IPY, IYPE and IUGG.
Title: The Great Geomagnetic Storm of 9 November 1991: Origin in a
Disappearing Solar Filament
Authors: Cliver, E. W.; Nitta, N.; Balasubramaniam, K.; Li, X.
Bibcode: 2006AGUSMSH43A..06C
Altcode:
The largest geomagnetic storms are characteristically associated with
major solar flares. The great storm of 9 November 1991 (Dst = -375 nT)
provides an exception to this rule of thumb. It is ranked tenth of the
largest Dst storms from 1932-2002, surpassing in intensity such well
known events as 14 July 1982 and 16 July 2000. The November 1991 storm
can be traced to a large disappearing solar filament from the southeast
quadrant late on 5 November. The filament was located outside of an
active region and its disappearance was well observed in both H-alpha
and soft X-rays. The associated long-duration 1-8 Angstrom event had a
C5 peak. This solar-terrestrial event indicates that neither a large
complex active region nor an intense solar flare is a requirement
for even first rank geomagnetic storms, thus providing insight to the
physics of such events while making their prediction more difficult.
Title: The Unusual Relativistic Solar Proton Events of 1979 August
21 and 1981 May 10
Authors: Cliver, E. W.
Bibcode: 2006ApJ...639.1206C
Altcode:
Sixty-nine ground level events (GLEs) caused by relativistic
solar protons have been observed from 1942 to 2005. GLEs are
characteristically associated with intense solar flares [having peak ~9
GHz flux densities SP(9 GHz)>103 sfu] and fast
(>1000 km s-1) coronal mass ejections (CMEs). The small
GLEs on 1979 August 21 and 1981 May 10 provide an exception to these
rules of thumb. In comparison with other GLEs, they were associated with
significantly weaker flares [SP(9 GHz)<30 sfu vs. a median
value of ~8000 sfu for all GLEs] and slower CMEs (plane-of-sky speeds
~800 km s-1 vs. a median of ~1600 km s-1). The
sunspot groups in which these two events originated ranked near the
bottom of GLE-parent regions in terms of sunspot area (~100 millionths
of a solar hemisphere [msh] vs. a median of ~850 msh). What enabled
these two otherwise commonplace solar eruptions to accelerate protons
to GeV energies? In both cases, intense, long-duration, metric type II
bursts were observed. In addition, both of these GLEs occurred when
the background ~10 MeV proton intensity at 1 AU was >1000 times
the normal background because of preceding SEP events originating in
active regions that were located in each case ~100° east of the active
region responsible for the GLE. We suggest that the relativistic solar
protons observed in these two events resulted from CME-driven shock
acceleration of an elevated coronal seed population, reflecting the
enhanced background proton intensity at 1 AU. For this scenario, the
timing onset of the relativistic protons in the two events indicates
that the shocks had access to the energetic seed particles within ~2-5
Rsolar of the solar surface. While an elevated ~10 MeV proton
background at Earth is a favorable/common condition for GLE occurrence,
it is not a requirement.
Title: The 1859 space weather event: Then and now
Authors: Cliver, E. W.
Bibcode: 2006AdSpR..38..119C
Altcode:
The 1859 space weather event, combining the first solar flare ever
reported with arguably the largest geomagnetic storm ever observed,
provided a dramatic opening to a new area of Sun Earth studies. Here
I describe solar science at the time of the discovery of the flare,
recount the observation, and trace the developments that led to the
correct interpretation of the 1859 solar-terrestrial event by Bartels in
1937. A “fast forward” takes us to the present time when advances
in modeling and increasing concern with space weather have prompted
renewed interest in a classic observation.
Title: Sunspot Cycle 24: Smallest Cycle in 100 Years?
Authors: Svalgaard, L.; Cliver, E. W.; Kamide, Y.
Bibcode: 2005ASPC..346..401S
Altcode:
Predicting the peak amplitude of the sunspot cycle is a key goal of
solar-terrestrial physics. The precursor method currently favored for
such predictions is based on the dynamo model in which large-scale
polar fields on the decline of the 11-year solar cycle are converted
to toroidal (sunspot) fields during the subsequent cycle. The strength
of the polar fields during the decay of one cycle is assumed to be an
indicator of peak sunspot activity for the following cycle. Polar fields
reach their peak amplitude several years after sunspot maximum; the time
of peak strength is signaled by the onset of a strong annual modulation
of polar fields due to the 7 1/4 ° tilt of the solar equator to the
ecliptic plane. Using direct polar field measurements, now available
for four solar cycles, we predict that the approaching solar cycle 24
(∼2011 maximum) will have a peak smoothed monthly sunspot number of
75±8, making it potentially the smallest cycle in the last 100 years.
Title: The IDV index: Its derivation and use in inferring long-term
variations of the interplanetary magnetic field strength
Authors: Svalgaard, Leif; Cliver, Edward W.
Bibcode: 2005JGRA..11012103S
Altcode:
On the basis of a consideration of Bartels' historical u index of
geomagnetic activity, we devise an equivalent index that we refer to as
the interdiurnal variability (IDV). The IDV index has the interesting
and useful property of being highly correlated with the strength of the
interplanetary magnetic field (B; R2 = 0.75) and essentially
unaffected by the solar wind speed (V; R2 = 0.01) as measured
by spacecraft. This enables us to obtain the variation of B from 1872
to the present, providing an independent check on previously reported
results for the evolution of this parameter. We find that solar cycle
average B increased by ∼25% from the 1900s to the 1950s and has
been lower since. If predictions for a small solar cycle 24 bear out,
solar cycle average B will return to levels of ∼100 years ago during
the coming cycle(s).
Title: Carrington, Schwabe, and the Gold Medal
Authors: Cliver, E. W.
Bibcode: 2005EOSTr..86..413C
Altcode:
The mid-nineteenth-century sunspot studies of Heinrich Schwabe
and Richard Carrington helped revitalize the then-lagging subject
of solar astronomy, ushered in the new field of solar-terrestrial
relations, and pointed astronomers toward a more modern view of
the Sun's interior. This article recounts a little-known connection
between these two astronomers. Both Schwabe (Figure 1) and Carrington
and were wealthy amateurs who pursued precise observational goals
to great effect. While Schwabe's monumental result, the discovery
of the 11 year sunspot cycle, required 18 years of labor before its
announcement and another seven before its acceptance, Carrington's key
discoveries were all made within the first six years of his sunspot
observations. Schwabe's solar observing career spanned 43 years
(1825-1867) Carrington's spanned less than a fifth of that (1853-1861).
Title: Introduction to violent Sun-Earth connection events of
October-November 2003
Authors: Gopalswamy, N.; Barbieri, L.; Cliver, E. W.; Lu, G.; Plunkett,
S. P.; Skoug, R. M.
Bibcode: 2005JGRA..110.9S00G
Altcode: 2005JGRA..11009S00G
The solar-terrestrial events of late October and early November 2003,
popularly referred to as the Halloween storms, represent the best
observed cases of extreme space weather activity observed to date and
have generated research covering multiple aspects of solar eruptions and
their space weather effects. In the following article, which serves as
an abstract for this collective research, we present highlights taken
from 61 of the 74 papers from the Journal of Geophysical Research,
Geophysical Research Letters, and Space Weather which are linked under
this special issue. (An overview of the 13 associated papers published
in Geophysics Research Letters is given in the work of Gopalswamy et
al. (2005a)).
Title: Sequential Chromospheric Brightenings beneath a Transequatorial
Halo Coronal Mass Ejection
Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Neidig, D. F.; Cliver,
E. W.; Thompson, B. J.; Young, C. A.; Martin, S. F.; Kiplinger, A.
Bibcode: 2005ApJ...630.1160B
Altcode:
Analyses of multiwavelength data sets for a solar eruption at ~21:30
UT on 2002 December 19 show evidence for the disappearance of a
large-scale, transequatorial coronal loop (TL). In addition, coronal
manifestations of the eruption (based on SOHO EIT and LASCO images)
include large-scale coronal dimming, flares in each associated active
region in the northern and southern hemispheres, and a halo CME. We
present detailed observations of the chromospheric aspects of this
event based on Hα images obtained with the ISOON telescope. The
ISOON images reveal distant flare precursor brightenings, sympathetic
flares, and, of most interest herein, four nearly cospatial propagating
chromospheric brightenings. The speeds of the propagating disturbances
causing these brightenings are 600-800 km s-1. The inferred
propagating disturbances have some of the characteristics of Hα
and EIT flare waves (e.g., speed, apparent emanation from the flare
site, subsequent filament activation). However, they differ from
typical Hα chromospheric flare waves (also known as Moreton waves)
because of their absence in off-band Hα images, small angular
arc of propagation (<30°), and their multiplicity. Three of
the four propagating disturbances consist of a series of sequential
chromospheric brightenings of network points that suddenly brighten in
the area beneath the TL that disappeared earlier. SOHO MDI magnetograms
show that the successively brightened points that define the inferred
propagating disturbances were exclusively of one polarity, corresponding
to the dominant polarity of the affected region. We speculate that
the sequential chromospheric brightenings represent footpoints of
field lines that extend into the corona, where they are energized in
sequence by magnetic reconnection as coronal fields tear away from
the chromosphere during the eruption of the transequatorial CME. We
report briefly on three other events with similar narrow propagating
disturbances that were confined to a single hemisphere.
Title: On the Origins of Solar EIT Waves
Authors: Cliver, E. W.; Laurenza, M.; Storini, M.; Thompson, B. J.
Bibcode: 2005ApJ...631..604C
Altcode:
Approximately half of the large-scale coronal waves identified in
images obtained by the Extreme-Ultraviolet Imaging Telescope (EIT) on
the Solar and Heliospheric Observatory from 1997 March to 1998 June
were associated with small solar flares with soft X-ray intensities
below C class. The probability of a given flare of this intensity
having an associated EIT wave is low. For example, of ~8,000 B-class
flares occurring during this 15 month period, only ~1% were linked to
EIT waves. These results indicate the need for a special condition that
distinguishes flares with EIT waves from the vast majority of flares
that lack wave association. Various lines of evidence, including the
fact that EIT waves have recently been shown to be highly associated
with coronal mass ejections (CMEs), suggest that this special condition
is a CME. A CME is not a sufficient condition for a detectable EIT wave,
however, because we calculate that ~5 times as many front-side CMEs
as EIT waves occurred during this period, after taking the various
visibility factors for both phenomena into account. In general, EIT
wave association increases with CME speed and width.
Title: Reexamination of the coronal index of solar activity
Authors: Rybanský, M.; Rušin, V.; Minarovjech, M.; Klocok, L.;
Cliver, E. W.
Bibcode: 2005JGRA..110.8106R
Altcode: 2005JGRA..11008106R
The coronal index (CI) of solar activity is the irradiance of the Sun
as a star in the coronal green line (Fe XIV, 530.3 nm or 5303 Å). It
is derived from ground-based observations of the green corona made
by the network of coronal stations (currently Kislovodsk, Lomnický
Štít, Norikura, and Sacramento Peak). The CI was introduced by
Rybanský (1975) to facilitate comparison of ground-based green
line measurements with satellite-based extreme ultraviolet and soft
X-ray observations. The CI since 1965 is based on the Lomnický
Štít photometric scale; the CI was extended to earlier years by
Rybanský et al. (1994) based on cross-calibrations of Lomnický
Štít data with measurements made at Pic du Midi and Arosa. The
resultant 1939-1992 CI had the interesting property that its value
at the peak of the 11-year cycle increased more or less monotonically
from cycle 18 through cycle 22 even though the peak sunspot number of
cycle 20 exhibited a significant local minimum between that of cycles
19 and 21. Rušin and Rybanský (2002) recently showed that the green
line intensity and photospheric magnetic field strength were highly
correlated from 1976 to 1999. Since the photospheric magnetic field
strength is highly correlated with sunspot number, the lack of close
correspondence between the sunspot number and the CI from 1939 to
2002 is puzzling. Here we show that the CI and sunspot number are
highly correlated only after 1965, calling the previously-computed
coronal index for earlier years (1939-1965) into question. We can use
the correlation between the CI and sunspot number (also the 2800 MHz
radio flux and the cosmic ray intensity) to recompute daily values
of the CI for years before 1966. In fact, this method can be used to
obtain CI values as far back as we have reliable sunspot observations
(∼1850). The net result of this exercise is a CI that closely tracks
the sunspot number at all times. We can use the sunspot-CI relationship
(for 1966-2002) to identify which coronal stations can be used as a
basis for the homogeneous coronal data set (HDS) before 1966. Thus
we adopt the photometric scale of the following observatories for the
indicated times: Norikura (1951-1954; the Norikura photometric scale
was also used from 1939 to 1954); Pic du Midi (1955-1959); Kislovodsk
(1960-1965). Finally, we revised the post-1965 HDS and made several
small corrections and now include data from Kislovodsk, Norikura,
and Sacramento Peak to fill gaps at Lomnický Štít.
Title: Validating the Proton Prediction System
Authors: Kahler, S.; Cliver, E.; Ling, A.
Bibcode: 2005AGUSMSH41A..03K
Altcode:
The Proton Prediction System (PPS) is an empirical model developed at
the Air Force Research Laboratory to generate solar energetic proton
(SEP) time-intensity profiles at 1 AU following solar flares. PPS was
designed to match statistical Earth-observed average intensity-time
profiles, peak intensities, and event durations. The input parameters
are solar flare peak or time-integrated X-ray or radio fluxes and
their times of onsets or maxima, and solar flare locations. We have
validated the PPS using 101 solar X-ray flares of peak intensity >
M5 from Ha disk flares during the period 1997 through 2001. We looked
for correlations between predicted and observed GOES E > 10 MeV
peak intensities, rise times, and event durations. There was little
correlation between the predicted and observed times from flare peak
to either SEP onsets or SEP peak times. When a SEP event was both
predicted and observed, the logs of the SEP peaks were correlated at
about the 0.5 level. However, the numbers of correctly predicted events
were similar to those of the false alarms and to those of unpredicted
events. We do a further comparison between the SEP events and those
solar flares with observed coronal shocks to look for a predictive
capability improvement in the PPS.
Title: Comparing the 11-yr and 22-yr cycles in cosmic ray modulation
Authors: Storini, M.; Laurenza, M.; Cliver, E. W.
Bibcode: 2005ICRC....2..259S
Altcode: 2005ICRC...29b.259S
No abstract at ADS
Title: Sunspot cycle 24: Smallest cycle in 100 years?
Authors: Svalgaard, Leif; Cliver, Edward W.; Kamide, Yohsuke
Bibcode: 2005GeoRL..32.1104S
Altcode: 2005GeoRL..3201104S
Predicting the peak amplitude of the sunspot cycle is a key goal of
solar-terrestrial physics. The precursor method currently favored for
such predictions is based on the dynamo model in which large-scale
polar fields on the decline of the 11-year solar cycle are converted
to toroidal (sunspot) fields during the subsequent cycle. The strength
of the polar fields during the decay of one cycle is assumed to be
an indicator of peak sunspot activity for the following cycle. Polar
fields reach their peak amplitude several years after sunspot maximum;
the time of peak strength is signaled by the onset of a strong annual
modulation of polar fields due to the 7$1\!\big/\!_{4°
tilt of the solar equator to the ecliptic plane. Using direct polar
field measurements, now available for four solar cycles, we predict
that the approaching solar cycle 24 (~2011 maximum) will have a peak
smoothed monthly sunspot number of 75 +/- 8, making it potentially
the smallest cycle in the last 100 years.
Title: Solar Flare Nuclear Gamma Rays and Energetic Particles in
Space, 1980-198
Authors: Cliver, E. W.; Vestrand, W. T.; Reames, D. V.
Bibcode: 2005ICRC....1...53C
Altcode: 2005ICRC...29a..53C
No abstract at ADS
Title: The Solar Energetic Particle Event of 16 August 2001: ~
400 MeV Protons Following an Eruption at ~ W180
Authors: Cliver, E. W.; Thompson, B. J.; Lawrence, G. R.; Zhukov,
A. N.; Tylka, A. J.; Dietrich, W. F.; Reames, D. V.; Reiner, M. J.;
MacDowall, R . J.; Kosovichev, A. G.; Ling, A. G.
Bibcode: 2005ICRC....1..121C
Altcode: 2005ICRC...29a.121C
No abstract at ADS
Title: Semiannual Variation of Geomagnetic Activity: Protons or
Photons?
Authors: Svalgaard, L.; Schulz, M.; Cliver, E. W.
Bibcode: 2004AGUFMSM42A..02S
Altcode:
The cause(s) of the semiannual variation (SAV) of geomagnetic activity
is a problem of long standard ( ∼100 years). The various mechanisms
put forward can be divided into 'excitations' and 'modulations'. Using
45 years of the am-index, we show that the SAV is a modulation of
existing activity. The modulation is a function of the angle between the
Earth's dipole moment and either (1) the aberrated solar wind velocity
and/or (2) the sun-Earth line, causing both time of year and time of day
(UT) variations. Here we examine the correlation of geomagnetic activity
with directions (1) and (2). Mechanisms involving interaction between
the solar wind and the magnetopause would correlate best with direction
(1). Mechanisms involving ionospheric conductance would correlate best
with direction (2).
Title: Association of Coronal Mass Ejections and Type II Radio Bursts
with Impulsive Solar Energetic Particle Events
Authors: Yashiro, S.; Gopalswamy, N.; Cliver, E. W.; Reames, D. V.;
Kaiser, M. L.; Howard, R. A.
Bibcode: 2004ASPC..325..401Y
Altcode:
We report the association of impulsive solar energetic particle (SEP)
events with coronal mass ejections (CMEs) and metric type II radio
bursts. We identified 38 impulsive SEP events using the WIND/EPACT
instrument and their CME association was investigated using white
light data from SOHO/LASCO. We found that (1) at least ∼ 28--39 % of
impulsive SEP events were associated with CMEs, (2) only 8--13 % were
associated with metric type II radio bursts. The statistical properties
of the associated CMEs were investigated and compared with those of
general CMEs and CMEs associated with large gradual SEP events. The
CMEs associated with impulsive SEP events were significantly slower
(median speed of 613 kmps) and narrower (49 deg) than those of CMEs
associated with large gradual SEP events (1336 kmps, 360 deg), but
faster than the general CMEs (408 kmps).
Title: Wind/WAVES and SMEI Observations of ICMEs
Authors: Reiner, M. J.; Jackson, B. V.; Webb, D. F.; Kaiser, M. L.;
Cliver, E. W.; Bougeret, J. L.
Bibcode: 2004AGUFMSH11A..05R
Altcode:
The low-frequency (kilometric) radio observations on Wind/WAVES
provide important spectral and directional information related to the
propagation of ICMEs through interplanetary space. However, up to now
there has been no white-light observations with which to compare these
low-frequency interplanetary radio observations, beyond the 30 Rs limit
of the LASCO field of view. The recently launched Air Force Coriolis
spacecraft that includes the Solar Mass Ejection Imager (SMEI), which
is the first all-sky camera designed to track ICMEs from the Sun to
1 AU, provides a unique opportunity of simultaneously tracking CMEs,
both in white light and in radio, all the way from the corona to 1
AU. 3D reconstruction techniques, utilizing multiple perspective views
of the ICME observed by SMEI, represent the propagation and evolution
of these density structures through the 3D heliosphere. There are two
general ways that the Wind/WAVES radio data can be directly related
to the SMEI heliospheric white-light observations. First, since
the observed radio frequency depends on the local plasma density in
the radio source region and since the interplanetary plasma density
falls off with the inverse of the heliocentric distance squared, the
observed radio frequency generated by the CME/shock decreases as the
type II radio source associated with the CME propagates farther from the
Sun. Thus the frequency characteristics of the type II radio emissions
provide information on the radial distance of the ICME. Secondly, the
low-frequency radio receivers on the Wind spacecraft have the unique
capability of providing information on the direction of arrival of the
radio emissions and of the size of the radio-emitting region. Both
of these results, obtained from analyses of the Wind/WAVES radio
observations, will be directly compared with the results from the
analyses of the SMEI white-light data for various ICME events.
Title: Coronal Shocks of November 1997 Revisited: The Cme Type II
Timing Problem
Authors: Cliver, E. W.; Nitta, N. V.; Thompson, B. J.; Zhang, J.
Bibcode: 2004SoPh..225..105C
Altcode:
We re-examine observations bearing on the origin of metric type
II bursts for six impulsive solar events in November 1997. Previous
analyses of these events indicated that the metric type IIs were due to
flares (either blast waves or ejecta). Our point of departure was the
study of Zhang et al. (2001) based on the Large Angle and Spectrometric
Coronagraph's C1 instrument (occulting disk at 1.1 R0) that
identified the rapid acceleration phase of coronal mass ejections (CMEs)
with the rise phase of soft X-ray light curves of associated flares. We
find that the inferred onset of rapid CME acceleration in each of the
six cases occurred 1-3 min before the onset of metric type II emission,
in contrast to the results of previous studies for certain of these
events that obtained CME launch times ∼25-45 min earlier than type
II onset. The removal of the CME-metric type II timing discrepancy in
these events and, more generally, the identification of the onset of
the rapid acceleration phase of CMEs with the flare impulsive phase
undercuts a significant argument against CMEs as metric type II shock
drivers. In general, the six events exhibited: (1) ample evidence
of dynamic behavior [soft X-ray ejecta, extreme ultra-violet imaging
telescope (EIT) dimming onsets, and wave initiation (observed variously
in Hα, EUV, and soft X-rays)] during the inferred fast acceleration
phases of the CMEs, consistent with the cataclysmic disruption of the
low solar atmosphere one would expect to be associated with a CME; and
(2) an organic relationship between EIT dimmings (generally taken to
be source regions of CMEs) and EIT waves (which are highly associated
with metric type II bursts) indicative of a CME-driver scenario. Our
analysis indicates that the broad (∼90° to halo) CMEs observed in
the outer LASCO coronagraphs for these impulsive events began life
as relatively small-scale structures, with angular spans of ∼15°
in the low corona. A review of on-going work bearing on other aspects
(than timing) of the question of the origin of metric type II bursts
(CME association; connectivity of metric and decametric-hectometric
type II shocks; spatial relationship between CMEs and metric shocks)
leads to the conclusion that CMEs remain a strong candidate to be
the principal/sole driver of metric type II shocks vis-à-vis flare
blast waves/ejecta.
Title: The 1859 Solar-Terrestrial Disturbance And the Current Limits
of Extreme Space Weather Activity
Authors: Cliver, E. W.; Svalgaard, L.
Bibcode: 2004SoPh..224..407C
Altcode: 2005SoPh..224..407C
It is generally appreciated that the September 1859 solar-terrestrial
disturbance, the first recognized space weather event, was exceptionally
large. How large and how exceptional? To answer these questions, we
compiled rank order lists of the various measures of solar-induced
disturbance for events from 1859 to the present. The parameters
considered included: magnetic crochet amplitude, solar energetic proton
fluence (McCracken et al., 2001a), Sun-Earth disturbance transit time,
geomagnetic storm intensity, and low-latitude auroral extent. While the
1859 event has close rivals or superiors in each of the above categories
of space weather activity, it is the only documented event of the last
∼150 years that appears at or near the top of all of the lists. Taken
together, the top-ranking events in each of the disturbance categories
comprise a set of benchmarks for extreme space weather activity.
Title: Preface
Authors: mursula, kalevi; usoskin, ilya; cliver, edward
Bibcode: 2004SoPh..224....3M
Altcode: 2005SoPh..224....3M
No abstract at ADS
Title: How big was the Carrington 1859 Flare?
Authors: Cliver, E. W.; Svalgaard, L.; Neidig, D. F.
Bibcode: 2004AGUSMSH43A..03C
Altcode:
The 1859 space weather event was distinguished by its great geomagnetic
storm, widespread low-latitude aurora, and intense solar energetic
particle event (inferred from the NO3 concentration in
polar ice cores). Arguably each of these three effects was the largest
ever observed. What can we say about the size of the associated solar
flare? We have two observations with which to make such an assessment:
(1) Carrington's and Hodgson's report of the white-light flare and (2)
the solar flare effect or magnetic crochet observed in the Kew and
Greenwich magnetograms. Estimates of the area, duration, spectrum,
and intensity of the white-light emission indicate a large (~2 x
1030 erg) but not unequalled event (the white-light emission
of the 24 April 1984 >X13 flare contained ~6 x 1030
erg). The magnetic crochet of 130 nT in the horizontal force,
however, exceeds that for all >X10 soft X-ray flares observed from
1984-2002 (we are presently compiling magnetic data for the recent
October-November 2003 activity for comparison with the 1859 event). Thus
at this point, we can conservatively say that Carrington's flare likely
had a soft X-ray classification >X10 and was at least comparable
to the largest flares recorded during the spacecraft era.
Title: R.C. Carrington and the 1859 Space Weather Event
Authors: Cliver, E. W.
Bibcode: 2004AGUSMSH51B..01C
Altcode:
R.C. Carrington (1826-1875) is remembered in this session as the
co-discoverer of the first solar flare ever reported - on 1 September
1859. The ensuing space weather event remains a "worst case scenario"
for solar-terrestrial interaction. Carrington was one of the most
accomplished solar astronomers of the 19th century and is credited
with the discovery of differential rotation and the variation of
sunspot latitude over the solar cycle. I will review Carrington's life,
which ended soon and sadly after a brief but brilliant career, and the
scientific times in which he worked. I will assess the contemporary
impact of Carrington's flare observation and will briefly recount how
the meaning of the tantalizing clue presented by this event gradually
came to light.
Title: Coronal Shocks and Solar Energetic Proton Events
Authors: Cliver, E. W.; Kahler, S. W.; Reames, D. V.
Bibcode: 2004ApJ...605..902C
Altcode:
From 1996 July through 2001 June, less than half (43/98) of all
favorably located (from solar western hemisphere sources) metric type
II radio bursts were associated with solar energetic proton (SEP)
events observed at Earth. When western hemisphere metric type IIs were
accompanied by decametric-hectometric (DH; 1-14 MHz) type II emission
(observed by Wind/WAVES) during this period, their association with
~20 MeV SEP events (with peak fluxes >=10-3 protons
cm-2 s-1 sr-1 MeV-1)
was 90% (26/29), versus only 25% (17/69) for metric IIs without a DH
counterpart. Overall, 82% (63%) of all SEP events with visible disk
origins were associated with metric (DH) type II bursts, with the
percentage associations increasing with SEP event size to 88% (96%) for
~20 MeV SEP events with peak intensities of >=10-1 protons
cm-2 s-1 sr-1 MeV-1. Our
results are consistent with the following possibilities (which are not
mutually exclusive): (1) large ~20 MeV SEP events result from strong
shocks that are capable of persisting well beyond ~3 Rsolar
(the nominal 14 MHz plasma level); (2) shock acceleration is most
efficient above ~3 Rsolar and (3) shocks that survive
beyond ~3 Rsolar are more likely to have broad longitudinal
extents, enabling less well connected shocks to intercept open field
lines connecting to Earth.
Title: Origins of the semiannual variation of geomagnetic activity
in 1954 and 1996
Authors: Cliver, E.; Svalgaard, L.; Ling, A.
Bibcode: 2004AnGeo..22...93C
Altcode:
. We investigate the cause of the unusually strong semiannual variation
of geomagnetic activity observed in the solar minimum years of 1954 and
1996. For 1996 we separate the contributions of the three classical
modulation mechanisms (axial, equinoctial, and Russell-McPherron)
to the six-month wave in the index and find that all three contribute
about equally. This is in contrast to the longer run of geomagnetic
activity (1868-1998) over which the equinoctial effect accounts for 70%
of the semiannual variation. For both 1954 and 1996, we show that the
Russell-McPherron effect was enhanced by the Rosenberg-Coleman effect
(an axial polarity effect) which increased the amount of the negative
(toward Sun) [positive (away from Sun)] polarity field observed during
the first [second] half of the year; such fields yield a southward
component in GSM coordinates. Because this favourable condition occurs
only for alternate solar cycles, the marked semiannual variation in
1954 and 1996 is a manifestation of the 22-year cycle of geomagnetic
activity. The 11-year evolution of the heliospheric current sheet (HCS)
also contributes to the strong six-month wave during these years. At
solar minimum, the streamer belt at the base of the HCS is located
near the solar equator, permitting easier access to high speed streams
from polar coronal holes when the Earth is at its highest heliographic
latitudes in March and September. Such an axial variation in solar
wind speed was observed for 1996 and is inferred for 1954.
Title: IHV: a new long-term geomagnetic index
Authors: Svalgaard, Leif; Cliver, Edward W.; Le Sager, Philippe
Bibcode: 2004AdSpR..34..436S
Altcode:
We derive a new daily index of geomagnetic activity, the Inter-Hour
Variability index (IHV), for investigations of the long-term variability
of the solar wind-magnetosphere system. The IHV index is used to
successfully reconstruct yearly-averages of the range indices am,
ap, and aa from 1959 through 2000. When we attempt to reconstruct
the aa index back to 1901, however, the reconstructed aa lies above
the observed aa for years before 1957, with the difference between
the two curves being the greatest (∼5-10 nT) during the first two
decades of the 20th century.
Title: New Geomagnetic Index (idv) Measuring Magnitude of
Interplanetary Magnetic Field
Authors: Svalgaard, L.; Cliver, E. W.
Bibcode: 2003AGUFMSH21B0108S
Altcode:
We present a new long-term geomagnetic index (the IDV index) which has
the property that it is a proxy of the magnitude of the interplanetary
magnetic field at the Earth. The index is constructed (for any given
station) as the monthly (or yearly) average of the differences (taken
without regard to sign) of the hourly mean values of the hour following
local midnight between two consecutive days. It is similar to the
classical u-measure except that the differences are between one-hour
values rather than daily means. The IDV index has a strong correlation
(r=0.88) with the magnitude, B, of the IMF, but is uncorrelated (r=0.09)
with the solar wind speed, V. Because other indices (e.g. aa and our
own IHV) are strongly correlated with BV**2, the IDV index fords a
way of separating the influence of B and V and thus determining both.
Title: Origins of Coronal Shock Waves Revisited
Authors: Cliver, E. W.
Bibcode: 2003AGUFMSH42E..03C
Altcode:
The origins of coronal shock waves manifested by metric type II radio
bursts has been, and remains, a controversial topic. Type II shocks
have been attributed to flare blast waves or identified as waves driven
by flare ejecta or coronal mass ejections (leading edge or flanks). It
has also been suggested that a type II shock occurs when a blast wave
moves through a preceding coronal mass ejection. I focus on a few key
events to highlight points of contention in the debate such as the
association of metric IIs with flares and CMEs, timing relationships
between the various phenomena, and the connectivity of metric and
decametric-hectometric type II bursts.
Title: Determination of interplanetary magnetic field strength,
solar wind speed and EUV irradiance, 1890-2003
Authors: Svalgaard, Leif; Cliver, Edward W.; Lesager, Philippe
Bibcode: 2003ESASP.535...15S
Altcode: 2003iscs.symp...15S
A newly constructed long-term geomagnetic index, the interdiurnal
variability (the IDV index; defined to be the unsigned difference
between hourly averages of the H-component of the field near local
midnight at a midlatitude station for consecutive days), has the useful
property that its yearly averages are highly correlated with the solar
wind magnetic field strength (B) and are independent of solar wind speed
(V). Existing geomagnetic records allow us to construct IDV since 1890
and thus to determine solar wind B over that period. Once B is known,
we use other long-term indices with known dependence on B and V to
determine the variation of V since 1890. Average B during 1872-2003
was 6.4 nT with no long-term trend (other than a general correlation
with the sunspot number) and average V for the interval 1890-2003
was 433 km/s also with no apparent trend. These results are confirmed
using polar cap data available from 1926 to the present and magnetic
observations of the Amundsen and Scott polar expeditions for years
near 1900. Focusing on geomagnetic activity at local midnight hours
cleanly separates the EUV-regulated regular variation (SR)
of geomagnetic activity from the solar wind driven component, allowing
us to determine EUV variability since 1901. Using older data, all
these time series might be extended possibly back to the 1780s.
Title: Reexamination of the coronal index of solar activity before
the year 1965
Authors: Rušin, Vojtech; Minarovjech, Milan; Rybanský, Milan;
Cliver, Edward W.
Bibcode: 2003ESASP.535..247R
Altcode: 2003iscs.symp..247R
The coronal green line intensity of the Sun is a useful parameter
to study activity in the corona. An coronal index of solar activity
(CI), was previously obtained for the period 1939-2002, based on the
photometric scale from Lomnický Štít where observations began in
1965. This earlier construction of CI was suspect because its solar
cycle maxima values did not closely track cycle peak sunspot numbers,
contrary to expectation. In the revised construction of the CI,
we use correlations of the Lomnický Štít based CI with the Wolf
(sunspot) number, the 2800 MHz solar radio flux, and galactic cosmic
ray intensity to derive CIs for years before 1965. The correlation
between the sunspot number and CI in the period 1965-2002 allows
reconstruction of CI back to 1818.
Title: Coronal Mass Ejections, the Tail of the Solar Wind Magnetic
Field Distribution, and 11 Year Cosmic-Ray Modulation at 1 AU
Authors: Cliver, E. W.; Ling, A. G.; Richardson, I. G.
Bibcode: 2003ApJ...592..574C
Altcode:
Using a recent classification of the solar wind at 1 AU into its
principal components (slow solar wind, high-speed streams, and coronal
mass ejections [CMEs]) for 1972-2000, we show that the monthly averaged
Galactic cosmic-ray intensity is anticorrelated with the percentage
of time that the Earth is embedded in CME flows. We suggest that this
anticorrelation results primarily from a CME-related change in the tail
of the distribution function of hourly averaged values of the solar
wind magnetic field (B) between solar minimum and solar maximum. The
number of high B-values (>=10 nT) increases by a factor of ~3
from minimum to maximum (from 5% of all hours to 17%), with about
two-thirds of this increase due to CMEs. On an hour-to-hour basis,
average changes of cosmic-ray intensity at Earth become negative for
solar wind magnetic field values >=10 nT.
Title: Source Regions of Major Solar Energetic Particle Events
Authors: Nitta, N. V.; Cliver, E. W.; Tylka, A. J.; Smit, P.
Bibcode: 2003ICRC....6.3363N
Altcode: 2003ICRC...28.3363N
We examine the source regions of the largest prompt solar energetic
particle (SEP) events (Jproton [>10 MeV] >100 pr/cm2 /s/sr)
occurring between 1992 and 2002. We find that the 25 such events
originated in a broad spectrum of solar regions, ranging from large
complex active regions with delta sunspot groups (e.g., 30 October 1992)
to a very weak active region in which the ma jor feature was a large
filament that erupted to produce the SEP event (12 September 2000). Most
source regions are less than two rotation old. In terms of recent work
to identify two types of large SEP events on the basis of composition,
spectra, and charge state, we find that large complex active regions
can give rise to both types, whereas simple and magnetically weak
regions are preferentially linked to one type.
Title: Coronal Shocks and Solar Energetic Proton Events
Authors: Cliver, Edward W.; Kahler, S. W.; Reames, D. V.
Bibcode: 2003ICRC....6.3331C
Altcode: 2003ICRC...28.3331C
From July 1996 June 2001, < 50% of favorably-lo cated metric type I I
radio bursts had associated solar energetic protons (SEPs). When western
hemisphere metric I Is were accompanied by decametric-hectometric (DH;
1-14 MHz) type I I emission, their association with ∼20 MeV SEP events
was 90% vs. only 25% for metric I Is without a DH counterpart. Overall,
82% (63%) of all SEP events with visible disk origins were associated
with metric (DH) type I Is, with percentage associations increasing
with SEP event size to 88% (96%), respectively, for ∼20 MeV SEP events
with peak intensities ≥ 10-1 pr cm-2 s-1 sr-1 MeV-1 . Our results are
consistent with the following (not mutually exclusive) possibilities:
(1) large ∼20 MeV SEP events result from strong shocks that can
persist well beyond ∼3 R ; (2) shock acceleration is most efficient
above ∼3 R ; (3) shocks that survive to ∼3 R are more likely to
have broad longitudinal extents.
Title: Signatures of Large Scale Coronal Eruptive Activity, Associated
Flares, and Propagating Chromospheric Disturbances
Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Neidig, D. F.;
Cliver, E. W.; Young, C. A.; Martin, S. F.; Kiplinger, A. L.
Bibcode: 2003SPD....34.0505B
Altcode: 2003BAAS...35..814B
Analyses of multi-wavelength data sets on 2002 December 19 at
approximately 2150 UT show evidence of a large-scale, transequatorial
coronal eruption associated with simultaneous flares in active
regions in both hemispheres. The coronal manifestations (based on
EIT, LASCO, and TRACE images) include a large coronal dimming,
an opening/restructuring of magnetic fields, the formation of a
transient coronal hole, and a halo CME. In the chromosphere, ISOON
H-alpha images show distant flare precursor brightenings and several
sympathetic flares. Originating near the main flare is a rapidly
propagating (800 km/s), narrowly channeled disturbance detectable as a
sequential brightening of numerous pre-existing points in the H-alpha
chromospheric network. This disturbance is not a chromospheric Moreton
wave, but it does produce a temporary activation of a transequatorial
filament. This filament does not erupt nor do any other filaments
in the vicinity. MDI magnetograms show that the brightened network
points are all of the same polarity (the dominant polarity among the
points in the disturbance's path), suggesting that the affected field
lines extend into the corona where they are energized in sequence
as the eruption tears away. Three other similar eruptive events
(non-transequatorial) that we studied, while they are less impressive,
show most of the same phenomena including distant sympathetic flares and
a propagating disturbance showing close adherence to the monopolarity
rule. Two of these events do include filament eruptions near the main
flare. We conclude that the observations of these four events are
consistent with large scale coronal eruptive activity that triggers
nearly simultaneous surface activity of various forms separated by
distances on the same scale as the coronal structures themselves. A
filament eruption at the main flare site appears not to be a necessity
in this type of eruptive activity.
Title: No doubling of the Sun's coronal magnetic field during the
last 100 years
Authors: Svalgaard, L.; Cliver, E.; Le Sager, P.
Bibcode: 2003EAEJA.....7616S
Altcode:
Various authors have conjectured that the interplanetary magnetic
field near the Earth (and by inference the Sun's magnetic field) has
more than doubled during the last 100 years. The primary evidence for
this is a similar increase in the geomagnetic activity index aa. We
discuss several lines of independent evidence that all indicate that
the aa-index does not have a constant calibration over time. While
it certainly is true that different solar cycles show different
amounts of geomagnetic activity due to variations of the sun and the
interplanetary environment, correcting the calibration of the aa-index
strongly suggests that there is no persistent upward trend over the last
100 years. We call for a concerted effort to re-calibrate the aa-index.
Title: Real-Time Specifications of the Geospace Environment
Authors: Kamide, Y.; Kihn, E. A.; Ridley, A. J.; Cliver, E. W.;
Kadowaki, Y.
Bibcode: 2003SSRv..107..307K
Altcode:
We report the recent progress in our joint program of real-time mapping
of ionospheric electric fields and currents and field-aligned currents
through the Geospace Environment Data Analysis System (GEDAS) at the
Solar-Terrestrial Environment Laboratory and similar computer systems
in the world. Data from individual ground magnetometers as well as from
the solar wind are collected by these systems and are used as input for
the KRM and AMIE magnetogram-inversion algorithms, which calculate the
two-dimensional distribution of the ionospheric parameters. One of the
goals of this program is to specify the solar-terrestrial environment
in terms of ionospheric processes, providing the scientific community
with more than what geomagnetic activity indices and statistical
models provide.
Title: Low Coronal Signatures of Large Solar Energetic Particle Events
Authors: Nitta, Nariaki V.; Cliver, Edward W.; Tylka, Allan J.
Bibcode: 2003ApJ...586L.103N
Altcode:
We report on the low coronal signatures of major solar energetic
particle (SEP) events. Because large SEP events are highly
associated with both flares and coronal mass ejections, we focused on
flare-associated motions in soft X-rays. In a sample of a half-dozen
well-observed flares associated with SEP events, we identified two basic
types of motions or ejections. For one class of events including those
of 2001 November 4 and 1998 April 20, the ejections occur on active
region or larger scales. They have an extended ``preeruption'' phase
in which the involved structures slowly rise or expand on timescales
of tens of minutes. For the second class of events, including those on
1997 November 6 and 2001 April 15, the large-scale preeruption phase
is absent. In these events, ejecta appear explosively at the onset of
the flare impulsive phase. The observed differences in ejections appear
to correlate with spectral/compositional/charge state characteristics
of large SEP events, suggesting that flare ejecta are diagnostic of
shock properties/environment.
Title: Working Group on Solar and Interplanetary Nomenclature
(Groupe de Travail pour la Nomenclature Solaire et Interplanétaire)
Authors: Cliver, Edward W.
Bibcode: 2003IAUTA..25...76C
Altcode: 2003IAUTr..25A..76C
No abstract at ADS
Title: Commission 10: Solar activity (Activité solaire)
Authors: Cliver, Edward W.
Bibcode: 2003IAUTA..25...77C
Altcode:
No abstract at ADS
Title: Intense Flares Without Solar Energetic Particle Events
Authors: Nitta, N. V.; Cliver, E. W.; Hudson, H. S.
Bibcode: 2002AGUFMSH61A0437N
Altcode:
We study favorably located (western hemisphere) X-class flares that were
not associated with solar energetic particle (SEP) events. Three of the
four such flares that occurred during the present cycle lacked coronal
mass ejections (CMEs), consistent with the current paradigm. Soft X-ray
data for these three events show either outward moving loops above
the main flare loop or a much slower rise of the flare loop itself,
as predicted in bipolar reconnection models. However, unlike fully
eruptive events, the outward moving loops appear to stop at a certain
distance. We speculate that they are held back by overlying magnetic
field, as implied in soft X-ray images. The flare that was associated
with a CME (but not an SEP event) produced metric and decametric type
III bursts, but those without CMEs did not. Other characteristics for
the flares not associated with SEP events include relatively short
decay times of hard X-ray emission at 30--50 keV. We are extending
our study to include additional (somewhat smaller) events to try to
identify key parameters that keep intense flares from erupting and
accompanying SEP events.
Title: Evidence for a Dominant Russell-McPherron/Rosenberg-Coleman
Origin of the Semiannual Variation of Geomagnetic Activity in 1954
and 1996
Authors: Cliver, E. W.; Svalgaard, L.; Ling, A. G.
Bibcode: 2002AGUFMSM72B0614C
Altcode:
Occasionally, the semiannual variation of geomagnetic activity is so
pronounced that one can readily identify it in daily averages of the
aa index during the year. The solar minimum years of 1954 and 1996 were
two such intervals. Using solar eclipse data and the Svalgaard polarity
index for 1954 and solar magnetic field and solar wind data for 1996,
we show that the six-month wave in geomagnetic activity during these
years was primarily due to a flattened current sheet resulting in a
strong Rosenberg-Coleman effect (an axial polarity effect), which
in turn produced a strong Russell-McPherron response in aa. When
we normalize the aa data for these years for the equinoctial effect
(based on the angle between the solar wind flow direction and Earth's
dipole), we remove approximately 30% of the amplitude of the semiannual
variation, implying a dominant axial/Russell-McPherron origin. When
we perform this normalization for the entire 1868-1998 aa data set,
we remove 75% of the six-month wave, indicating that, in general,
the equinoctial effect is primarily responsible for the semiannual
variation of geomagnetic activity.
Title: Long-term trends in interplanetary magnetic field strength
and solar wind structure during the twentieth century
Authors: Richardson, I. G.; Cliver, E. W.; Cane, H. V.
Bibcode: 2002JGRA..107.1304R
Altcode:
[1999] have recently reported a ∼ 40% increase in the radial component
of the interplanetary magnetic field (IMF) at Earth between 1964
and 1996. We argue that this increase does not constitute a secular
trend but is largely the consequence of lower than average fields
during solar cycle 20 (1964-1976) in comparison with surrounding
cycles. For times after 1976 the average IMF strength has actually
decreased slightly. Examination of the cosmic ray intensity, an
indirect measure of the IMF strength, over the last five solar cycles
(19-23) also indicates that cycle averages of the IMF strength have
been relatively constant since ∼ 1954. We also consider the origin
of the well-documented increase in the geomagnetic aa index that
occurred primarily during the first half of the twentieth century. We
surmise that the coronal mass ejection (CME) rate for recent solar
cycles was approximately twice as high as that for solar cycles 100
years ago. However, this change in the CME rate and the accompanying
increase in 27-day recurrent storm activity reported by others are
unable to account completely for the increase in aa. Rather, the CMEs
and recurrent high-speed streams at the beginning of the twentieth
century must have been embedded in a background of slow solar wind
that was less geoeffective (having, for example, lower IMF strength
and/or flow speed) than its modern counterpart.
Title: Secular change in geomagnetic indices and the solar open
magnetic flux during the first half of the twentieth century
Authors: Cliver, E. W.; Ling, A. G.
Bibcode: 2002JGRA..107.1303C
Altcode:
We examined several long-term geomagnetic indices (u, Ci,
and Hm) to substantiate the secular increase in the aa
index during the first half of the twentieth century. The long-term
increase in aa and other geomagnetic indices was accompanied by a
corresponding rise in the envelope of the sunspot number (∼130%
increase of cycle averages). We used a correlation between solar cycle
averages of sunspot number and solar open magnetic flux for recent
cycles to infer a 140 ± 80% increase in the open flux between ∼1900
and ∼1950, comparable to the ∼130% increase in this parameter during
the twentieth century deduced by [1999] from solar wind measurements
during the space age. While the uncertainty in our result is large,
our method, which is not based on aa, provides independent support for a
substantial increase in the open magnetic flux during the last century.
Title: Sources of geomagnetic activity during nearly three solar
cycles (1972-2000)
Authors: Richardson, I. G.; Cane, H. V.; Cliver, E. W.
Bibcode: 2002JGRA..107.1187R
Altcode:
We examine the contributions of the principal solar wind components
(corotating high-speed streams, slow solar wind, and transient
structures, i.e., interplanetary coronal mass ejections (CMEs), shocks,
and postshock flows) to averages of the aa geomagnetic index and the
interplanetary magnetic field (IMF) strength in 1972-2000 during nearly
three solar cycles. A prime motivation is to understand the influence
of solar cycle variations in solar wind structure on long-term (e.g.,
approximately annual) averages of these parameters. We show that
high-speed streams account for approximately two-thirds of long-term
aa averages at solar minimum, while at solar maximum, structures
associated with transients make the largest contribution (~50%),
though contributions from streams and slow solar wind continue to be
present. Similarly, high-speed streams are the principal contributor
(~55%) to solar minimum averages of the IMF, while transient-related
structures are the leading contributor (~40%) at solar maximum. These
differences between solar maximum and minimum reflect the changing
structure of the near-ecliptic solar wind during the solar cycle. For
minimum periods, the Earth is embedded in high-speed streams ~55% of
the time versus ~35% for slow solar wind and ~10% for CME-associated
structures, while at solar maximum, typical percentages are as follows:
high-speed streams ~35%, slow solar wind ~30%, and CME-associated
~35%. These compositions show little cycle-to-cycle variation, at
least for the interval considered in this paper. Despite the change
in the occurrences of different types of solar wind over the solar
cycle (and less significant changes from cycle to cycle), overall,
variations in the averages of the aa index and IMF closely follow those
in corotating streams. Considering solar cycle averages, we show that
high-speed streams account for ~44%, ~48%, and ~40% of the solar wind
composition, aa, and the IMF strength,, respectively, with corresponding
figures of ~22%, ~32%, and ~25% for CME-related structures, and ~33%,
~19%, and ~33% for slow solar wind.
Title: The semiannual variation of great geomagnetic storms
Authors: Svalgaard, L.; Cliver, E. W.; Ling, A. G.
Bibcode: 2002GeoRL..29.1765S
Altcode: 2002GeoRL..29p..12S
The occurrence frequency of the largest geomagnetic storms from
1868-1998 exhibits a well-defined semiannual modulation with more
than twice as many storms occurring during equinoctial months than
at the solstices. To examine the cause of this seasonal imbalance, we
empirically obtained a new geomagnetic index aam that has the
same seasonal and Universal Time variation as the am index. In effect,
this extends the am index backward in time to 1868. By normalizing the
aam time series for Ψ, the angle between the solar wind
flow direction and Earth's dipole, we removed 75% of the amplitude of
the six-month wave in monthly averages of aam and ~75% of
the seasonal discrepancy in the numbers of great storms. We obtained
similar percentages for the (unmodified) am index over the shorter
1959-1998 interval. These results indicate that most, though not all,
of the discrepancy in storm counts between the equinoxes and solstices
is due to an equinoctial effect.
Title: Solar Wind Structural and Magnetic Field Changes Associated
With 11-yr Cosmic Ray Modulation at 1 AU
Authors: Cliver, E. W.; Richardson, I. G.; Ling, A. G.
Bibcode: 2002AGUSMSH32A..07C
Altcode:
Using a recent classification of the solar wind at 1 AU into its
principal components (slow solar wind, high-speed streams, and
coronal mass ejections (CMEs; including shocks and post shock flows))
for 1972-2000, we show that the galactic cosmic ray intensity is
anti-correlated with the percentage of time (each month) that the Earth
is imbedded in CME flows. We suggest that this correlation results
primarily from a CME-related change in the tail of the distribution
function of hourly-averaged values of the solar wind magnetic field (B)
between solar minimum and solar maximum. The number of high-B values
(> 10 nT) increases by a factor of three from minimum to maximum,
with 70% of this increase due to CMEs. On an hour-to-hour basis, average
changes of cosmic ray intensity become negative for solar wind magnetic
field values > 10 nT. These findings indicate a central role for
CMEs for 11-yr modulation at 1 AU. Strong (> 10 nT) fields in the
interaction regions between high and low speed streams appear to have
been responsible for the cosmic ray "mini-cycles" in 1973 and 1974.
Title: An independent assessment of solar wind conditions circa 1900
based on data obtained by the Roald Amundsen Gjoea expedition
Authors: Svalgaard, L.; Cliver, E.
Bibcode: 2002cosp...34E1833S
Altcode: 2002cosp.meetE1833S
Utilizing geomagnetic data obtained by the Roald Amundsen Gjoea
Expedition, 1903-1906, we deduce the interplanetary magnetic field
sector structure from the variation of magnetic activity, separately
for away polarity and toward polarity. From this we determine the
merging electric field in the solar wind via the Russell- McPherron
effect. This gives an independent assessment of long-term change in the
solar wind parameters and illustrates the importance of the long-term
solar-terrestrial record.
Title: Researchers discuss role of flares and shocks in solar
energetic particle events
Authors: Cliver, E.; Klecker, B.; Kallenrode, M. -B.; Cane, H.
Bibcode: 2002EOSTr..83..132C
Altcode:
Sixty participants gathered at a workshop last 5-7 August in Lüneburg,
Germany just prior to the 27th (Hamburg) International Cosmic Ray
Conference to discuss the relative importance of flares and shocks
as sources of solar energetic particle (SEP) events. In the current
two-class paradigm for SEP events [Reames, 1999], the flare process
accounts for acceleration in "impulsive" events, while Coronal Mass
Ejection (CME)-driven coronal and interplanetary shock acceleration
dominates "gradual" events. (For more on SEP terminology see Cliver
and Cane [2002].)
Title: The last word
Authors: Cliver, E. W.; Cane, H. V.
Bibcode: 2002EOSTr..83...61C
Altcode:
This is the second in a series of essays on terms used in
solar-terrestrial physics that are thought to be in need of
clarification. Terms are identified and essays are commissioned by
a committee chartered by Division II (Sun and Heliosphere) of the
International Astronomical Union. Terminology Committee members include:
Ed Cliver (chair), Jean-Loius Bougeret, Hilary Cane, Takeo Kosugi, Sara
Martin, Rainer Schwenn, Lidia van-Driel Gesztelyi, and Joe Borovsky
(Eos SPA Editor). Writers are asked to review the origins of a given
term and its current usage/misusage. The main point is to open a
discussion and inform the community. We solicit feedback (to Eos) on
the following article by Ed Cliver and Hilary Cane on the use of the
terms "impulsive" and "gradual" to describe solar energetic particle
events. In addition, we welcome suggestions (to any Committee member)
on other terms to address in this forum.
Title: The semiannual variation of geomagnetic activity: phases and
profiles for 130 years of /aa data
Authors: Cliver, E. W.; Kamide, Y.; Ling, A. G.
Bibcode: 2002JASTP..64...47C
Altcode: 2002JATP...64...47C
We determined the phases of the maxima (spring, fall) and minima
(summer, winter) in the curve of smoothed daily averages of the
/aa geomagnetic index, available from 1868 to 1998. The dates we
obtained are consistent with the equinoctial hypothesis which has
aberration-adjusted theoretical maxima, for a ~440kms-1
(modern epoch) average solar wind speed, on 25 March (experimentally
determined to be 27 March, with an uncertainty of /+/-2 days)
and 27 September (27 September) and minima on 25 June (26 June)
and 26 December (27 December). We also show that the overall shape
of the 30-day smoothed modulation curve throughout the year (broad
minima, narrow peaks) bears greater fidelity (/|r|=0.96) to the
aberration-shifted solar declination /δ (the controlling angle, on
average, for the seasonal variation under the equinoctial hypothesis)
than to the solar B0 angle (/r=0.76; axial hypothesis)
or the solar /P angle (/r=0.86; Russell-McPherron effect). Lastly, a
three-parameter fit of the smoothed annual variation of the /aa data
with a function consisting of the sum of the smoothed yearly curves
for the /δ, B0, and /P angles yielded an amplitude of
/0.58+/-0.07 for the /δ component vs. /0.16+/-0.03 for B0
and /0.20+/-0.04 for /P. Thus, the phases and profiles of the 6-month
wave in the long-running mid-latitude /aa range index are consistent
with control by a dominant equinoctial mechanism.
Title: CMEs: How do the puzzle pieces fit together?
Authors: Cliver, E. W.; Hudson, H. S.
Bibcode: 2002JASTP..64..231C
Altcode: 2002JATP...64..231C
This review consists of questions to participants in the S-RAMP
Symposium (S3) on CMEs and Coronal Holes, as well as to a few others,
and their responses in a ``town meeting'' format (originally conducted
on Hugh Hudson's website). Here we deal only with CMEs. The questions we
ask aim at probing the weaknesses of existing models and highlighting
controversies, thereby providing guidance toward a more complete view
of solar eruptions. Topics covered include: the ``solar flare myth'',
flux ropes, new phenomena (EIT waves, dimmings, global brightenings),
helicity and sigmoids, and transequatorial loops (as sources of
CMEs). Although this is a review, we're more concerned here with
what is not known than what is already agreed upon. We asked people
to speculate freely in advance of the observational, analytical, and
theoretical work that will provide definitive answers-this is not the
standard Scientific Method at work!
Title: The Semiannual Variation of Great Geomagnetic Storms
Authors: Svalgaard, L.; Cliver, E. W.; Ling, A. G.
Bibcode: 2001AGUFMSM31B0778S
Altcode:
The occurrence frequency of the largest geomagnetic storms as
measured by the aa index from 1868-present exhibits a well-defined
semiannual modulation with 2.4 times as many great storms occurring
during equinoctial months than at the solstices. We show that most,
but not all, of this variation can be attributed to an equinoctial
hypothesis whereby energy transfer from the solar wind to the
magnetosphere is modulated by psi, the angle between the solar wind
flow direction and Earth's dipole axis. After normalizing aa for the
seasonal/daily variation of psi, the imbalance in great storm counts
between equinoctial and solstitial months is reduced to a factor of 1.4.
Title: Solar Energetic Particle Events: Flares and CME-Driven
Shock Waves
Authors: Cliver, E. W.
Bibcode: 2001AGUFMSH31C..01C
Altcode:
During the past 15 years, a new paradigm has been developed for solar
energetic particle (SEP) events in which the particles observed in
space following solar activity are thought to be accelerated either
in flares (small impulsive SEP events with high-Z abundance anomalies
and high Fe charge states) or at CME-driven coronal/interplanetary
shock waves (large gradual events with "normal" abundances and low Fe
charge states). Observations from the Advanced Composition Explorer
(ACE), however, have shown that at energies > 10 MeV/amu, certain
large gradual events have event-averaged abundances and charge
states that look remarkably impulsive (e.g., Cohen et al., GRL 26,
2697, 1999). Recently-analyzed large events observed by the IMP-8
spacecraft since 1973 exhibit similar behavior (Dietrich and Lopate,
Proc. 27th ICRC, 8, 3120, 2001). I review the various suggestions
that have been made to account for these "mixed" events in terms of
propagation effects and/or seed particle populations.
Title: Observing coronal mass ejections without coronagraphs
Authors: Hudson, H. S.; Cliver, E. W.
Bibcode: 2001JGR...10625199H
Altcode:
A coronal mass ejection (CME), strictly speaking, is a phenomenon
observed via a white-light coronal imager. In addition to
coronagraphs, a wide variety of other instruments provide independent
observations of CMEs, in regimes ranging from the chromosphere to
interplanetary space. In this paper we list the most important of these
noncoronagraphic signatures, many of which had been known even before
CMEs were first identified in coronagraph observations about 30 years
ago. We summarize the new aspects of CMEs discovered in the past several
years, primarily with instruments on the Yohkoh and SOHO satellites. We
emphasize the need for detailed statistically based comparisons
between SOHO CMEs and their noncoronagraphic manifestations. We discuss
how the various aspects of CMEs fit into the current standard model
(sigmoids, flux rope, double dimming, arcade). While a class of CMEs
follows this pattern, it does not appear to work for all events. In
particular, some CMEs involve extended dimming regions and erupting
transequatorial X-ray loops, indicating a more complex geometry than
a simple bipolar magnetic configuration.
Title: Semiannual variation of the geomagnetic Dst index: Evidence
for a dominant nonstorm component
Authors: Cliver, Edward W.; Kamide, Y.; Ling, A. G.; Yokoyama, N.
Bibcode: 2001JGR...10621297C
Altcode:
The geomagnetic Dst index exhibits a strong semiannual variation
with amplitude of 5.3 nT (on an average baseline of -16.4 nT) for
1957-1997. If we consider the five quietest Dst days for each month
during this interval, we find that while the average Dst baseline
shifts from -16.4 to +4.0 nT, the amplitude of the 6-month wave remains
relatively strong at 2.5 nT. Thus ~50% (2.5 nT/5.3 nT) of the seasonal
variation of the Dst index results from modulation of its quiet time
baseline. The seasonal modulation of Dst appears to consist of both a
storm component, resulting from rapid variations of the ring current
and other currents, and a slowly varying, nonstorm component. We
estimate that the storm component accounts for only ~30-50% of the
amplitude of the 6-month wave in Dst versus ~50-70% for the nonstorm
component. The classic equinoctial effect appears to dominate the
storm component, accounting for 20-40% of the amplitude of the 6-month
wave in Dst versus ~10% for the combined axial/Russell-McPherron
mechanisms. Candidate mechanisms for the nonstorm component of the
6-month wave in Dst include the Malin-Isikara effect (the seasonal
displacement of ring/tail currents by solar wind compression) and a
semiannual variation of magnetopause currents.
Title: Particle Injection in The Relativistic SEP Event of 6
November 1997
Authors: Cliver, E. W.; Falcone, A.; Ryan, J.; Aurass, H.; Gentile,
L. C.; Kallenrode, M. B.; Ling, A. G.; Reiner, M. J.; St. Cyr, O. C.;
Yoshimori, M.
Bibcode: 2001ICRC....8.3277C
Altcode: 2001ICRC...27.3277C
The 6 November 1997 solar energetic particle (SEP) event exhibited
charge state dependence on energy with Fe having a mean charge state of
∼ 18-21 at energies > 10 MeV amu-1 . We review the CME, radio, and
gamma-ray observations of the associated solar event to gain insight
into the origin of this behavior. The CME was rapidly accelerated
low in the corona (to speeds ∼ 2000 km s-1 within ∼ 4 x 105 km of
the solar surface), consistent with the proposed picture in which the
observed Fe ions are accelerated by a CMEdriven shock (indicated by a
metric type II burst) and further stripped as they propagate through
the low corona. The situation is ambiguous, however, in that the period
when the CME/shock is at the required altitude/density for the stripping
scenario to occur corresponds to the peak of the gammaray burst and low
frequency radio emission of the associated flare, providing evidence
for an alternative (or contributing) source of SEPs.
Title: Rogue SEP Events: Modeling
Authors: Kallenrode, M. -B.; Cliver, E. W.
Bibcode: 2001ICRC....8.3318K
Altcode: 2001ICRC...27.3318K
Rogue events (see Kallenrode and Cliver, 2001) are associated with
multiple shocks and CMEs. We present a numerical model based on
the focused transport equation that incorporates shocks as moving
particles sources and magnetic clouds as transient modifications of
the interplanetary focusing length. This model allows to simulate the
effect of pairs of CMEs/shock on particle populations. Special attention
is paid to pairs of converging shocks which are believed to play an
important role in the formation of large events such as the August
72 SPE or the Bastille day event. We find that (a) the magnetic cloud
following the leading shock is of utmost importance for the creation
of high particle intensities, (b) the shocks need not to converge to
create an intensity enhancement, and (c) the trailing cloud is required
to reduce intensities after the passage of the shock pair.
Title: Rogue SEP events: observational aspects
Authors: Kallenrode, M. B.; Cliver, E. W.
Bibcode: 2001ICRC....8.3314K
Altcode: 2001ICRC...27.3314K
About once in a solar cycle, a SEP event occurs whose fluence
dominates that for the entire cycle. We refer to such events as
'rogue' events, in analogy to rogue ocean waves having unusually
large amplitudes. Well-known examples of rogue SEP events at Earth
occurred on 14 July 1959, 4 August 1972, 19 October 1989, and 14 July
2000. Rogue events also have been observed in the inner heliosphere
(with Helios 1 on 4 November 1980 at 0.5 AU) and with Ulysses in March
1991 at 2.5 AU. In this paper we review the solar (multiple CMEs)
and interplanetary circumstances (converging shocks) that give rise
to these rare but, if observed at Earth, geophysically important events.
Title: Sources of geomagnetic storms for solar minimum and maximum
conditions during 1972-2000
Authors: Richardson, I. G.; Cliver, E. W.; Cane, H. V.
Bibcode: 2001GeoRL..28.2569R
Altcode:
We determine the solar wind structures (coronal mass ejection
(CME)-related, corotating high-speed streams, and slow solar wind)
driving geomagnetic storms of various strength over nearly three
solar cycles (1972-2000). The most intense storms (defined by Kp)
at both solar minimum and solar maximum are almost all (∼97%)
generated by transient structures associated with CMEs. Weaker storms
are preferentially associated with streams at solar minimum and with
CMEs at solar maximum, reflecting the change in the structure of the
solar wind between these phases of the solar cycle. Slow solar wind
generates a small fraction of the weaker storms at solar minimum and
maximum. We also determine the size distributions of Kp for each solar
wind component.
Title: Coronal Mass Ejections, Open Magnetic Flux, and Cosmic-Ray
Modulation
Authors: Cliver, E. W.; Ling, A. G.
Bibcode: 2001ApJ...556..432C
Altcode:
Recent work indicates that the open magnetic flux from coronal holes
may be a more important driver of cosmic-ray modulation than coronal
mass ejections (CMEs), which originate from closed-field regions on
the Sun. As evidence against this point of view, we find that the
correlation coefficient (r) between the solar open flux from coronal
holes and the Climax cosmic-ray intensity for the period 1967-2000 is
only -0.37. We show that, for similar values of the total open flux
from the Sun near solar maximum and minimum, the cosmic-ray intensity is
much lower at maximum. Thus, something in addition to the open magnetic
flux from coronal holes is acting to block incoming cosmic rays at solar
maximum. Because they drive shocks and contain enhanced magnetic fields,
CMEs are the leading candidate to play such a role. Over the 1967-2000
interval, the cosmic-ray intensity is highly anticorrelated (r=-0.80)
with the sunspot number, a measure of closed fields on the Sun. For
the 1979-1989 interval covered by the Solwind and SMM coronagraphs,
the correlation coefficient between the CME rate and the cosmic-ray
intensity is -0.61. For cycle 21, an analysis of solar wind data shows
that CMEs and related shock flows accounted for ~40% (2.9/7.0 nT) of the
average interplanetary magnetic field strength at 1 AU at solar maximum,
versus 10% (0.5/5.0 nT) at solar minimum. If we break the open flux
into that originating from low-latitude (<=45°) and high-latitude
(>45°) coronal holes on the Sun for this 34 yr interval, we find
that the low-latitude flux is highly anticorrelated with cosmic-ray
intensity (r=-0.76), while the open flux from high latitudes and the
Climax count rate are directly correlated (r=0.53). We suggest that
the anticorrelation between low-latitude open flux and the cosmic-ray
intensity occurs because CMEs open new flux to the interplanetary
medium.
Title: Long-Term Variations in Geomagnetic Indices
Authors: Cliver, E. W.
Bibcode: 2001AGUSM..SH51A01C
Altcode:
The geomagnetic aa index developed by Mayaud and available from
1868-present exhibited a remarkable increase during the 20th century,
such that recent 11-yr minima in this index are higher than maxima from
100 years ago. Is this long-term increase in aa due to a corresponding
change in solar/solar wind conditions or to something else? To address
this question, I review the derivation of the aa index and compare its
behavior with that of magnetic indices (Ap, am, Dst, and AE) available
for shorter periods of time as well as with the sunspot number. I also
review work on other potential contributors to the long-term increase
in aa such as the secular change of Earth's main field.
Title: The semiannual variation of geomagnetic activity: Phases and
profiles for 130 years of aa data
Authors: Cliver, E. W.; Kamide, Y.; Ling, A. G.
Bibcode: 2001AGUSM..SM52A01C
Altcode:
We determined the phases of the maxima (spring, fall) and minima
(summer, winter) in the curve of smoothed daily averages of the aa
geomagnetic index, available from 1868-1998. The dates we obtained are
consistent with the equinoctial hypothesis which has aberration-adjusted
theoretical maxima on 25 March (experimentally determined to be 27
March) and 27 September (27 September) and minima on 26 June (26 June)
and 26 December (27 December). We also show that the overall shape of
the modulation curve throughout the year (broad minima, narrow peaks)
bears greater fidelity (r = -0.96) to the solar declination D (the
controlling angle for the seasonal variation under the equinoctial
hypothesis) than to the solar B angle (r = 0.83; axial hypothesis)
or the solar P angle (r = 0.80; Russell-McPherron effect). Lastly,
a three-parameter fit of the smoothed annual variation of the aa data
with a function consisting of the sum of the smoothed yearly curves for
the D, B, and P angles yielded an amplitude of 0.58 for the D component
vs. 0.20 for B and 0.16 for P. Generally similar results for each of
these analyses (timing, shape, relative contributions) were obtained
for shorter intervals of data for the ap and am indices. We conclude
that the semiannual modulation of average values of mid-latitude range
indices such as aa and ap is primarily controlled by the equinoctial
hypothesis.
Title: Sources of Geomagnetic Activity and Geomagnetic Storms for
Solar Minimum and Maximum Conditions During 1972-2000
Authors: Richardson, I. G.; Cliver, E. W.; Cane, H. V.
Bibcode: 2001AGUSM..SH51A04R
Altcode:
Continuing our recent study of the solar wind sources of geomagnetic
activity over the solar cycle, we have determined the contribution
of solar wind structures (coronal mass ejection (CME) - related,
high-speed streams, and slow solar wind) to long-term averages of the
aa geomagnetic index over an interval of nearly three solar cycles. We
have also identified the structures responsible for geomagnetic
storms of various strength. The most intense storms (defined by
Kp) at both solar minimum and solar maximum are almost all ( ~97%)
generated by transient structures associated with CMEs. Weaker storms
are preferentially associated with streams at solar minimum and with
CMEs at solar maximum, reflecting the change in the structure of the
solar wind between these phases of the solar cycle. Slow solar wind
generates a small fraction of the weaker storms at solar minimum and
maximum. We also determine the size distributions of Kp for each solar
wind component. These results help to understand the physical processes
underlying geomagnetic activity indices which may be of significance
in understanding longer-term trends in these indices.
Title: 22 Year Patterns in the Relationship of Sunspot Number and
Tilt Angle to Cosmic-Ray Intensity
Authors: Cliver, E. W.; Ling, A. G.
Bibcode: 2001ApJ...551L.189C
Altcode:
A comparison of 27 day averages of the sunspot number with the Galactic
cosmic-ray intensity observed at Climax reveals a 22 yr pattern. The
11 yr cosmic-ray cycle appears to lag the sunspot cycle by ~1 yr for
odd-numbered cycles such as 19 and 21. During even-numbered cycles
the sunspot number and cosmic-ray intensity curves are essentially
in phase. A similar pattern is apparent in a comparison of the tilt
angle of the heliospheric current sheet (HCS) with cosmic-ray intensity
for the last three solar cycles (21-23). The tilt angle evolution on
the rise of the last three cycles was remarkably similar, while the
decline of the tilt angle from high values at the maximum of cycle 21
(~1980) was more gradual than that observed following the maximum of
cycle 22 (~1990) or that inferred from coronal hole areas for cycle 20
(~1970). The reduced responsiveness of cosmic rays to sunspot or tilt
angle increases on the rise of odd-numbered solar cycles is consistent
with a drift effect. A difference in the evolution of large-scale
fields on the decay of even- and odd-numbered cycles may contribute to
more gradual recovery of cosmic-ray intensity following the maxima of
odd-numbered cycles. The onset of modulation in odd-numbered cycles,
and of diffusion/convection-dominated modulation in even-numbered
cycles, appears to begin when the tilt angle of the HCS exceeds ~50°.
Title: Low-latitude auroras: the magnetic storm of 14-15 May 1921
Authors: Silverman, S. M.; Cliver, E. W.
Bibcode: 2001JASTP..63..523S
Altcode: 2001JATP...63..523S
We review solar//geophysical data relating to the great magnetic storm
of 14-15 May 1921, with emphasis on observations of the low-latitude
visual aurora. From the reports we have gathered for this event,
the lowest geomagnetic latitude of definite overhead aurora (coronal
form) was /40° and the lowest geomagnetic latitude from which auroras
were observed on the poleward horizon in the northern hemisphere was
/30°. For comparison, corresponding overhead//low-latitude values of
/48°/32° and /41°/20° were reported for the great auroras on 28-29
August and 1-2 September 1859, respectively. However, for the 1921
event, there is a report of aurora from Apia, Samoa, in the southern
hemisphere, within /13° of the geomagnetic equator. This report by
professional observers appears to be credible, based on the aurora
description and timing, but is puzzling because of the discrepancy with
the lowest latitude of observation in the northern hemisphere and the
great implied auroral height (~2000km, assuming overhead aurora at
Auckland, New Zealand). We discuss various possibilities that might
account for this observation.
Title: Solar Flare Classification
Authors: Cliver, E.
Bibcode: 2000eaa..bookE2285C
Altcode:
SOLAR FLARES are classified according to their size, duration,
morphology or magnetic topology and the composition of their associated
energetic particles. This article will cover the more enduring and
comprehensive of these various classification schemes....
Title: Solar flare photons and energetic particles in space
Authors: Cliver, E. W.
Bibcode: 2000AIPC..528...21C
Altcode: 2000atep.conf...21C
I review the evolution of research on solar energetic particle events,
beginning with Forbush's report of the ground level event of 1946,
through the most recent observations of the Advanced Composition
Explorer (ACE). The emphasis is on research that attempted to link solar
flare electromagnetic emissions with the solar energetic particles
(SEPs) observed in space following flares. The evolution of thought
on this topic is traced from the initial paradigm in which SEPs were
accelerated at the flare site (a δ-function in space and time) to the
current two-class picture accommodating both impulsive acceleration
at the flare site (small 3He-rich events) and prolonged
acceleration at extended shocks driven by coronal mass ejections
(large proton events). I conclude with some open questions; the most
prominent of these concerns the relative contributions of the flare
and shock acceleration processes to ``mixed'' or hybrid SEP events in
which the distinguishing characteristics of the impulsive and gradual
classes are blended. .
Title: Correction to “Coronal dimmings and energetic CMEs in
April-May 1998,”
Authors: Thompson, B. J.; Cliver, E. W.; Nitta, N.; Delannée, C.;
Delaboudinière, J. -P.
Bibcode: 2000GeoRL..27.1865T
Altcode:
No abstract at ADS
Title: Solar energetic particles: Acceleration and transport
Authors: Cliver, Edward W.
Bibcode: 2000AIPC..516..103C
Altcode: 2000ICRC...26..103C
This paper reviews highlights of the 26th ICRC in the area of
acceleration and propagation of solar energetic particles (SEPs). New
results on SEP charge state and composition, a lively topic during
the Conference, are covered in an accompanying paper by Klecker. I
begin with a brief historical review of the field to provide context
for the key advances/developments on SEP acceleration/propagation
presented in Salt Lake City. These include: (1) the use of gamma-ray
emissions as diagnostics of the acceleration process(es) and probes
of the interaction region; (2) the observation of ~10 GeV (or higher)
protons for the 6 November 1997 ground level event by the Milagrito
experiment; (3) observations of coronal Moreton waves as ``smoking
pistols'' of shock acceleration/injection of SEPs; (4) an investigation
of the role of proton event spectra in the current ``two-class'' picture
of SEP events; (5) an analysis of the Gnevyshev Gap in SEP activity;
(6) a Ulysses-based determination of the dependence of SEP mean free
path on radial distance from the Sun and on heliographic latitude, and
(7) an examination of the dissipation range in the power spectrum of
interplanetary magnetic field fluctuations. I conclude with a discussion
of new instrumentation (e.g., Milagro, HESSI) and a look to the expected
level of SEP activity for the approaching maximum of solar cycle 23. .
Title: Coronal dimmings and energetic CMEs in April-May 1998
Authors: Thompson, B. J.; Cliver, E. W.; Nitta, N.; Delannée, C.;
Delaboudinière, J. -P.
Bibcode: 2000GeoRL..27.1431T
Altcode:
We have analyzed the coronal dimmings for seven fast (> 600 km/s)
coronal mass ejections (CMEs) occurring between 23 April and 9 May which
were associated with flares from NOAA active region (AR) 8210. Each
of these CMEs had at least one group of interplanetary radio bursts
associated with them. These dimming regions were identified by their
strong depletion in coronal EUV emission within a half hour of the
estimated time of CME lift-off. They included areas which were as
dark as quiescent coronal holes as well as other regions with weaker
brightness depletions. While the location of the active region and
the associated flare did not correspond well with the coronagraph
observations, we found that the extended dimming areas in these events
generally mapped out the apparent “footprint” of the CME as observed
by white-light coronagraph. We briefly discuss the implications of
these results on models of CME topology.
Title: Relationship of halo coronal mass ejections, magnetic clouds,
and magnetic storms
Authors: Webb, D. F.; Cliver, E. W.; Crooker, N. U.; Cry, O. C. St.;
Thompson, B. J.
Bibcode: 2000JGR...105.7491W
Altcode:
Halo coronal mass ejections (CMEs) had been rarely reported in
coronagraph observations of the Sun before the Solar and Heliospheric
Observatory (SOHO) mission. Since mid-1996, however, the SOHO Large
Angle Spectrometric Coronagraph (LASCO) instruments have observed many
halo or partial-halo CMEs. A halo CME, especially when associated
with solar activity near sun center, is important for space weather
concerns because it suggests the launch of a potentially geoeffective
disturbance toward Earth. During the post-solar minimum period from
December 1996 to June 1997, we found that all six halo CMEs that were
likely Earthward-directed were associated with shocks, magnetic clouds,
and moderate geomagnetic storms at Earth 3-5 days later. The results
imply that magnetic cloud-like structures are a general characteristic
of CMEs. Most of the storms were driven by strong, sustained southward
fields either in the magnetic clouds, in the post-shock region,
or both. We discuss the characteristics of the halo events observed
during this period, their associated signatures near the solar surface,
and their usefulness as predictors of space weather at Earth.
Title: Mountains versus valleys: Semiannual variation of geomagnetic
activity
Authors: Cliver, E. W.; Kamide, Y.; Ling, A. G.
Bibcode: 2000JGR...105.2413C
Altcode:
The semiannual variation in geomagnetic activity is generally attributed
to the Russell-McPherron effect. In that picture, enhancements of
southward field Bs near the equinoxes account for the
observed higher geomagnetic activity in March and September. In a
contrary point of view, we argue that the bulk of the semiannual
variation results from an equinoctial effect (based on the ψ angle
between the solar wind flow direction and Earth's dipole axis) that
makes Bs coupling less effective (by ~25% on average)
at the solstices. Thus the semiannual variation is not simply due to
``mountain building'' (creation of Bs) at the equinoxes but
results primarily from ``valley digging'' (loss of coupling efficiency)
at the solstices. We estimate that this latter effect, which clearly
reveals itself in the diurnal variation of the am index, is responsible
for ~65% of the semiannual modulation. The characteristic imprint of
the equinoctial hypothesis is also apparent in hourly/monthly averages
of the time-differential Dst index and the AE index.
Title: Energy Injection Rate of the Ring Current Estimated from Dst
Authors: Yokoyama, N.; Kamide, Y.; Cliver, E. W.
Bibcode: 2000AdSpR..26..107Y
Altcode:
We have estimated the energy injection rate for geomagnetic storms
from the hourly Dst variation and an assumed decay constant for the
ring current. It is found that intense storms do not require both long
and strong energy injections to the ring current. Intense short-lived
injection as well as weaker energy inputs of longer duration can
produce storms of equal magnitude for any given Dst size range
Title: On the origin of solar metric type II bursts
Authors: Cliver, Edward W.; Webb, David F.; Howard, Russell A.
Bibcode: 1999SoPh..187...89C
Altcode:
The vast majority of solar flares are not associated with metric Type
II radio bursts. For example, for the period February 1980-July 1982,
corresponding to the first two and one-half years of the Solar Maximum
Mission, 95% of the ∼2500 flares with peak >25 keV count rates
>100 c s−1lacked associated Type II emission. Even the
∼360 largest flares, i.e., those having >25 keV peak count rates
>1000 c s−1, had a Type II association rate of only
24%. The lack of a close correlation between flare size and Type II
occurrence implies the need for a 'special condition' that distinguishes
flares that are accompanied by metric Type II radio bursts from those
of comparable size that are not. The leading candidates for this special
condition are: (1) an unusually low Alfvén speed in the flaring region;
and (2) fast material motion. We present evidence based on SMM and GOES
X-ray data and Solwind coronagraph data that argues against the first
of these hypotheses and supports the second. Type II bursts linked to
flares within 30° of the solar limb are well associated (64%; 49/76)
with fast (>400 km s−1) coronal mass ejections (CMEs);
for Type II flares within 15° of the limb, the association rate is 79%
(30/38). An examination of the characteristics of 'non-CME' flares
associated with Type IIs does not support the flare-initiated blast
wave picture that has been proposed for these events and suggests
instead that CMEs may have escaped detection. While the degree of Type
II-CME association increases with flare size, there are notable cases
of small Type II flares whose outstanding attribute is a fast CME. Thus
we argue that metric Type II bursts (as well as the Moreton waves and
kilometric Type II bursts that may accompany them) have their root
cause in fast coronal mass ejections.
Title: A prediction of geomagnetic activity for solar cycle 23
Authors: Cliver, E. W.; Ling, A. G.; Wise, J. E.; Lanzerotti, L. J.
Bibcode: 1999JGR...104.6871C
Altcode:
Using a database of 13 solar cycles of geomagnetic aa data, we obtained
correlations between cycle averages of geomagnetic activity (and sunspot
number) and the numbers of days with disturbance levels above certain
aa thresholds. We then used a precursor-type relation to predict an
average aa index of 23.1 nT for cycle 23 and inserted this average
aa value into the above correlations to forecast the integral size
distribution of geomagnetic activity for the new cycle. The predicted
size distribution is similar to that observed for cycles 21 and 22
but most closely resembles that of solar cycle 18 (1944-1954), which
was slightly smaller than cycles 21 and 22. Our prediction agrees
reasonably well with the ``climatology-based'' forecast made by the
intergovernmental panel tasked to predict geomagnetic activity for
the coming solar cycle and is significantly different from their
``precursor-based'' prediction.
Title: Comment on ``Origin of coronal and interplanetary shocks:
A new look with Wind spacecraft data'' by N. Gopalswamy et al.
Authors: Cliver, E. W.
Bibcode: 1999JGR...104.4743C
Altcode:
Abstract Available
from AGU
Title: Solar Eclipse Workshop: Closing Comments
Authors: Cliver, E.
Bibcode: 1999CoSka..28..300C
Altcode:
I want to thank Voyto Rusin, Pavel Kotrc, and Eva Markova for organizing
this excellent workshop in preparation for the 11 August 1999 total
solar eclipse. There is less than a year before a notable eclipse
will bisect Europe - - - a fitting last eclipse for this millenium
because (the first scientific eclipse expeditions were organized by
Europeans) during the middle of the 19th Century. To me the great
themes of this eclipse underline are: (1) the science (as always);
and (2) the unprecedented opportunity for public education. As we
close this pre-eclipse workshop, I would like to remind everyone of
the post-eclipse workshop that is being organized by Atila Ozguc to
be held in Istanbul from August 13-15. It will be an opportunity to
review `lessons learned' while they are still fresh in mind, and in
the spirit of eclipse observers, to begin thinking about the first
eclipse of the new millenium.
Title: Solar-Terrestrial and Terrestrial Science
Authors: Ryan, J. M.; Aikin, A. C.; Cliver, E. W.; Rieger, E.; Share,
G. H.
Bibcode: 1999mfs..conf..457R
Altcode:
SMM's Impact on Solar-Terrestrial Studies Paradigm Shift in
Solar-Terrestrial Physics Two Classes of SEP Events γ-Rays from the
Earth Galactic Cosmic Ray-Induced γ-Rays from the Earth Solar Cosmic
Ray-Induced γ-Rays from the Earth Transient Radiation Belts from
Orbiting Nuclear Reactors Mesospheric Chemistry Studies with UVSP
Ozone Measurements Molecular Oxygen Measurements
Title: The solar origin of the January 1997 coronal mass ejection,
magnetic cloud and geomagnetic storm
Authors: Webb, D. F.; Cliver, E. W.; Gopalswamy, N.; Hudson, H. S.;
St. Cyr, O. C.
Bibcode: 1998GeoRL..25.2469W
Altcode:
The magnetic cloud and geomagnetic storm on January 10-11, 1997 were
associated with a halo-type Coronal Mass Ejection (CME) observed by
the SOHO/LASCO coronagraphs near the sun on January 6. We summarize
the solar activity related to this CME and the subsequent storm at
Earth. This solar activity was remarkably weak and unimpressive. If
the wide CME had not been observed, the storm would not have been
forecast. Thus this case represents an extreme example of so-called
“problem” magnetic storms that lack obvious surface signatures of
eruptive solar activity. It supports the view that CMEs involve the
destabilization of large-scale coronal structures which may or may
not have associated surface activity, and that CMEs, not the surface
activity, are the key causal link between solar eruptions and space
weather at Earth.
Title: Solar variability and climate change: Geomagnetic aa index
and global surface temperature
Authors: Cliver, E. W.; Boriakoff, V.; Feynman, J.
Bibcode: 1998GeoRL..25.1035C
Altcode:
During the past ∼120 years, Earth's surface temperature is correlated
with both decadal averages and solar cycle minimum values of the
geomagnetic aa index. The correlation with aa minimum values suggests
the existence of a long-term (low-frequency) component of solar
irradiance that underlies the 11-year cyclic component. Extrapolating
the aa-temperature correlations to Maunder Minimum geomagnetic
conditions implies that solar forcing can account for ∼50% or more
of the estimated ∼0.7-1.5°C increase in global surface temperature
since the second half of the 17th century. Our analysis is admittedly
crude and ignores known contributors to climate change such as
warming by anthropogenic greenhouse-gases or cooling by volcanic
aerosols. Nevertheless, the general similarity in the time-variation
of Earth's surface temperature and the low-frequency or secular
component of the aa index over the last ∼120 years supports other
studies that indicate a more significant role for solar variability in
climate change on decadal and century time-scales than has previously
been supposed. The most recent aa data for the current solar minimum
suggest that the long-term component of solar forcing will level off
or decline during the coming solar cycle.
Title: Geomagnetic activity and the solar wind during the Maunder
Minimum
Authors: Cliver, Edward W.; Boriakoff, Valentín; Bounar, Khaled H.
Bibcode: 1998GeoRL..25..897C
Altcode:
We used a strong (r = 0.96) correlation between 11-year averages of
sunspot number (SSN) and the geomagnetic aa index to infer that the mean
level of geomagnetic activity during the Maunder Minimum (1645-1715)
was approximately a third of that observed for recent solar cycles (∼7
nT vs. ∼24 nT). We determined the variation of 11-year averages of
solar wind speed (v) and the southward component of the interplanetary
magnetic field (Bs) with cycle-averaged SSN for the two
most recent cycles and also compared cycle-averaged variations of
v²Bs and aa for the same interval. We then extrapolated
these observed solar wind variations to Maunder Minimum conditions
(mean SSN of ∼ 2 and mean aa value of ∼ 7 nT) to deduce that,
on average, the solar wind during that period was somewhat slower
(v = 340 ± 50 km s-1), and the interplanetary magnetic
field much smoother (Bs = 0.3±0.1 nT), than at present
(∼ 440 km s-1 and ∼ 1.2 nT). Various lines of evidence
(including 10Be data) suggest that, despite the virtual
absence of sunspots that characterized the Maunder Minimum, the 11-year
geomagnetic (solar wind) cycle persisted throughout this period.
Title: Geomagnetic Activity and the Solar Wind During the Maunder
Minimum
Authors: Cliver, E. W.; Bounar, K. H.; Boriakoff, V.
Bibcode: 1998ASPC..140..437C
Altcode: 1998ssp..conf..437C
No abstract at ADS
Title: Disappearances of High-Latitude Filaments as Sources of
High-Latitude CMEs
Authors: Cliver, E. W.; Webb, D. F.
Bibcode: 1998ASPC..150..479C
Altcode: 1998IAUCo.167..479C; 1998npsp.conf..479C
No abstract at ADS
Title: A Prediction of the Peak Sunspot Number for Solar Cycle 23
Authors: Bounar, Khaled H.; Cliver, Edward W.; Boriakoff, Valentín
Bibcode: 1997SoPh..176..211B
Altcode:
We use a precursor technique based on the geomagneticaa index during the
decline (last 30%) of solar cycle 22 to predict a peak sunspot number
of 158 (± 18) for cycle 23, under the assumption that solar minimum
occurred in May 1996. This method appears to be as reliable as those
that require a year of data surrounding the geomagnetic minimum, which
typically follows the smoothed sunspot minimum by about six months.
Title: The Solar Source of the January 1997 CME/Magnetic Cloud;
Recurrent Activity on a Polar Crown Filament Channel
Authors: Webb, David; Cliver, E.; McIntosh, P.; Gopalswamy, N.;
Hudson, H.
Bibcode: 1997SPD....28.1501W
Altcode: 1997BAAS...29..918W
The magnetic cloud and geomagnetic storm on 10-11 January 1997 was
associated with a halo-type CME observed by LASCO near the sun on 6
January. As part of the ISTP and SHINE collaboration on this event we
are studying the solar source region of the CME and its propagation
through the interplanetary medium to Earth. We summarize the rather
weak solar activity that apparently was associated with this CME, and
contrast it with the strong surface and coronal activity associated
with the 9-11 February 1997 magnetic cloud/storm. We present evidence
that the solar sources of both of these events occurred over an area
where the southern polar crown filament channel diverted sharply to
the north and in the decaying remnants of the first large-scale active
region to form during the new solar cycle. Our results also suggest
that this region was the site of earlier CMEs; i.e., it was a key site
of recurrent activity during 1996-97 which, when aimed toward Earth,
produced recurrent magnetic clouds and storms.
Title: Observations of Faint, Outlying Loop Systems in Large Flares
Authors: Neidig, Donald F.; Švestka, Zdeněk; Cliver, Edward W.;
Airapetian, Vladimir; Henry, Timothy W.
Bibcode: 1997SoPh..170..321N
Altcode:
Faintly visible, darkened regions in Hα lying outside but
adjacentto bright flare emissionwere found to occur in 10 of 31 major
flares investigated. Without exception, the darkenings occur over
`magnetically neutral' areas, and these are usually bordered by ridges
ofoppositely-poled field, where one border is shared in common with a
flare ribbon. Thedarkenings probably result from the formation of faint,
outlying loop systems, similar topost-flare loops seen in absorption,
but which are connected to magnetic features outsidethe flare and
are unresolved or only marginally resolved in patrol images. Simple
modelsfor post-flare loops incorporating the results of statistical
equilibrium calculations readilydemonstrate that darkenings of several
percent (consistent with our photometric measurements) can be produced
by loop structures of cross-sectional diameter ≈ 102 km
(unresolved by patrol instruments) and containing gas at densities 5 ×
1010-5 × 1011 cm-3 andtemperatures
8000-15000 K. Outlying loop systems might be formed by magnetic
fieldreconnection, analogous to the mechanism ascribed to eruptive
two-ribbon flares, butassociated with field structures adjacent to the
flare. Alternatively, these outlying loopsystems may not erupt but
become visible as a result of heating and chromospheric evaporation
at the footpoints shared with the flare ribbon. In either case, the
observations presented here have interesting implications for both
the spatial scale and the topology of thecoronal magnetic fields in
which eruptions occur.
Title: LASCO data dazzle Chapman conference
Authors: Cliver, E. W.; Webb, D. F.
Bibcode: 1997EOSTr..78..107C
Altcode:
Research on coronal mass ejections (CMEs)—giant bubbles of magnetized
gas blown into the heliosphere by the Sun (Figure 1)—has entered
a time of dramatic growth. The large angle spectrometric coronagraph
(LASCO) on the recently launched Solar and Heliospheric Observatory
(SOHO) spacecraft has revealed unexpected aspects of the beautiful and
puzzling CME phenomenon (see Figure 1), which was recently shown to be
a key element for space weather. Studies of LASCO and other SOHO data
combined with Yohkoh Soft X Ray Telescope observations are certain to
provide new insight on how CMEs are initiated at the Sun. Concurrently,
analyses of in situ plasma and field data from the Wind and Ulysses
spacecraft are elucidating the structure of CMEs in the interplanetary
(IP) medium.
Title: The 22-year cycle of geomagnetic and solar wind activity
Authors: Cliver, Edward W.; Boriakoff, Valentín; Bounar, Khaled H.
Bibcode: 1996JGR...10127091C
Altcode:
The 22-year cycle in geomagnetic activity is characterized by high
activity during the second half of even-numbered solar cycles and the
first half of odd-numbered cycles. We present new evidence for this
22-year cycle using the aa magnetic index for the years 1844-1994. Over
this 150-year interval, the 22-year cycle can be observed through
differences between the decay phases of even- and odd-numbered cycles
in (1) average values of a 27-day recurrence index; (2) the results
of a χ2 ``event'' analysis of 27-day recurrences of both
disturbed and quiet days; and (3) an apparent annual modulation of
the 27-day peak in the power spectrum of the aa index. Currently,
the 22-year variation is attributed to the Russell-McPherron solar
wind-magnetosphere coupling mechanism working in conjunction with
the Rosenberg-Coleman polarity effect. Contrary to this viewpoint, we
argue that an intrinsic 22-year solar variation (other than polarity
reversal), revealed in the systematic low-high alternation of even-odd
sunspot maxima within the last six complete Hale cycles, is the
dominant cause of the 22-year cycle in geomagnetic activity. This
sunspot and related coronal mass ejection variation should lead
directly to higher geomagnetic activity during the first-half of
odd-numbered solar cycles. Various lines of evidence (including 1-3
above) indicate that 27-day recurrent wind streams are more prominent
during the decline of even-numbered solar cycles, contributing to the
higher geomagnetic activity observed at those times. These stronger
recurrence patterns may be related to the more rapid expansion of
polar coronal holes (faster movement of the coronal streamer belt to
low latitudes) observed following the maxima of recent even-numbered
cycles. The amplitudes of the 22-year sunspot and geomagnetic activity
cycles over the last 150 years are shown to be highly correlated. The
22-year pattern of geomagnetic activity appears to be a reflection of
the solar dynamo coupling of poloidal magnetic fields on the decline of
one solar cycle to the toroidal fields at the maximum of the following
cycle. It seems likely that the 22-year variation in sunspot/solar wind
activity plays a role in the observed 22-year modulation of galactic
cosmic ray intensity.
Title: A Search for MeV Gamma-Ray Emission from the Quiet-Time Sun
Authors: Young, C. A.; McConnell, M. L.; Rank, G.; Ryan, J. M.;
Schonfelder, V.; Bennett, K.; Cliver, E.; Miller, R.; MacKinnon, A.
Bibcode: 1996AAS...189.1804Y
Altcode: 1996BAAS...28.1298Y
Until now, solar gamma -ray emissions have only been detected during
solar flares. However, there are several scenarios (e.g., microflares
or cosmic-ray albedo emission) in which gamma -ray emission might
be detectable when there is no significant solar activity. These
processes might be related to the general problem of solar coronal
heating and would likely vary as a function of solar cycle. We have
embarked on a systematic search for quiet-time gamma -ray emissions
using the unique imaging capabilities of the COMPTEL experiment on
the Compton Gamma-Ray Observatory. With its large ( ~ 1 steradian)
FoV, the Sun has been observed by COMPTEL on several ocassions since
its launch in April 1991. We are using these data to search for both
time-integrated and time-resolved gamma -ray emission, concentrating on
those periods when there was negligible solar activity. Our analysis
involves a search for both broad-band and narrow line emissions. Here
we report on the first results from this effort.
Title: Comment on ``Interplanetary origin of geomagnetic activity
in the declining phase of the solar cycle'' by B. T. Tsurutani et al.
Authors: Cliver, E. W.
Bibcode: 1996JGR...10127625C
Altcode:
No abstract at ADS
Title: The angular extents of solar/interplanetary disturbances and
modulation of galactic cosmic rays
Authors: Cliver, E. W.; Cane, H. V.
Bibcode: 1996JGR...10115533C
Altcode:
From comparisons of solar activity with galactic cosmic ray (GCR)
modulation events at 1 AU and in the outer heliosphere, we argue
against the suggestion that individual solar eruptions can give rise
to major cosmic ray modulation events that span the heliosphere. For
the inner heliosphere, we use a sample, covering a ~30-year period,
of eruptive flares and confidently associated interplanetary shocks
to show that the following three parameters, determined at 1 AU,
all decrease with increasing longitudinal distance from the flare:
probability of detecting a shock, shock transit speed, and magnitude of
any associated Forbush decrease (FD). In addition, we associate each
of the 18 large (>=10%) FDs observed at Earth from 1958 to 1991
with one or more eruptive flares located near solar central meridian
(E47-W31). For each of the six heliosphere-wide modulation events that
have been associated thus far by other investigators with individual
flares we are able to identify multiple powerful flares, with one or
more of these eruptive events generally occurring close in ecliptic
longitude to each affected spacecraft. Supporting evidence for the
limited longitudinal extent of major interplanetary effects from
single eruptions is provided by a remarkable outer heliosphere event
in late 1989. A large shock (ΔV~200 km/s) and Forbushlike decrease
(18%) at Pioneer 10 at ~50 AU was not preceded by a commensurate
disturbance at Voyager 1/Voyager 2/Pioneer 11 located at ~30-40 AU
on the opposite side of the heliosphere. We conclude that widespread
modulation events in the outer heliosphere result from systems of
solar/interplanetary disturbances that, only in aggregate, encompass
360° of ecliptic longitude, rather than from azimuthally symmetric
shocks associated with single eruptive flares. We point out that the
documented preference for coronal mass ejections to occur at low and
middle solar latitudes will naturally form the wedge-shaped barrier
proposed by Van Allen and Mihalov to account for the ``inside-out''
pattern of recovery of individual modulation events observed at
progressively greater distances in the heliosphere.
Title: Solar flare gamma-ray emission and energetic particles in space
Authors: Cliver, E. W.
Bibcode: 1996AIPC..374...45C
Altcode: 1996hesp.conf...45C
We expand Reames' tabular summary of the two-class picture of solar
energetic particle (SEP) events to include characteristics of the
particles that interact at the Sun to produce gamma-ray emission. This
addition underscores the contributions of gamma-ray observations to our
current understanding. The broad picture that is emerging is remarkable
for its simplicity: while SEP events come in two basic types depending
on the duration of the associated flare, the interacting particles
in impulsive and gradual flares appear to be indistinguishable and
resemble the SEPs observed in space following impulsive flares. The
expanded classification system includes hybrid events, i.e., flares in
which the gradual/impulsive distinction is blurred and for which the SEP
events contain a mixture of flare-accelerated and CME/shock-accelerated
particles. We argue that SEP events associated with long duration flares
can be expected to have a temporally and spatially confined ``core''
of flare-accelerated particles surrounded by a ``halo'' of CME/shock
particles. Thus SEP composition should be checked in comparative studies
of gamma-ray emission and particles in space to ensure that the SEPs are
flare-accelerated. We discuss how recently-discovered types of gamma-ray
flares (electron-dominated events, spatially and temporally extended
gamma-ray events) may fit into the expanded classification scheme. We
suggest that the acceleration process in the pion-rich phase of large
flares (e.g., 1982 June 3) is similar to that occurring earlier in the
flare, the main differences being the greater height of the acceleration
region and the presence of previously accelerated seed particles.
Title: Book reviews
Authors: Cliver, E. W.; Somov, B. V.; Ambrož, P.
Bibcode: 1995SoPh..160..401C
Altcode: 1995SoPh..160..401P
No abstract at ADS
Title: Evidence for magnetic disconnection of mass ejections in
the corona
Authors: Webb, David F.; Cliver, Edward W.
Bibcode: 1995JGR...100.5853W
Altcode:
Coronal mass ejections (CMEs) involve the expulsion of significant
amounts of mass and magnetic flux into the heliosphere, a process which
implies an unobserved continuous buildup of the net interplanetary
magnetic flux. Some form of disconnection of the flux near the Sun,
either directly associated with the CME or occurring elsewhere in the
corona, appears to be required to prevent this buildup. Field line
reconnection in the wake of CMEs is also a fundamental aspect of some
types of magnetically driven eruptive flare/CME models. However, to
date there have been very few reports of CMEs which exhibited evidence
for disconnection, despite the detection of several thousand CMEs
over nearly two decades of observations. We report on the results of
a systematic search for candidate magnetic disconnection features,
defined as transient large-scale, concave-outward bright regions
usually folowing the CME leading edge, using both ground-based solar
eclipse and spaceborne coronagraph data. We conclude that greater
than or equal to 10% of all CMEs observed in the corona have possible
disconnection structures. We propose a simple classification scheme
for these features based on their morphology. The most common type of
candidate disconnection feature (65% of all the features) had a circular
or ovoid shape; 35% of the features consisted of concave-outward
partial arcs. The average leading edge speed and latitudinal span of
these CMEs were slightly less than those of the typical CMEs. The
results are discussed in the context of recent studies of magnetic
disconnection and reconnection in the corona.
Title: Solar Flare Nomenclature
Authors: Cliver, E. W.
Bibcode: 1995SoPh..157..285C
Altcode:
The evolution of solar flare nomenclature is reviewed in the context
of the paradigm shift, in progress, from flares to coronal mass
ejections (CMEs) in solar-terrestrial physics. Emphasis is placed
on: the distinction between eruptive (Class II) flares and confined
(Class I) flares; and the underlying similarity of eruptive flares
inside (two-ribbon flares) and outside (flare-like brightenings
accompanying disappearing filaments) of active regions. A list of
research questions/problems raised, or brought into focus, by the
new paradigm is suggested; in general, these questions bear on the
interrelationships and associations of the two classes (or phases)
of flares. Terms such as `eruptive flare' and `eruption' (defined
to encompass both the CME and its associated eruptive flare) may be
useful as nominal links between opposing viewpoints in the `flares vs
CMEs' controversy.
Title: Flare-Associated Darkenings in H-Alpha: Possible Evidence
for Faint Outlying, Unresolved Loop Systems
Authors: Neidig, D. F.; Cliver, E. W.; Svestka, Z.; Airapetian, V.;
Henry, T. W.
Bibcode: 1995SPD....26.1215N
Altcode: 1995BAAS...27..986N
No abstract at ADS
Title: The Eruption of a Pre-Existing Post Flare Loop System and
Associated Noise Storm Disappearance
Authors: Kahler, S. W.; Cliver, E. W.; Chertok, I. M.; Gnezdilov,
A. A.; Aurass, H.
Bibcode: 1995SPD....26.1320K
Altcode: 1995BAAS...27..991K
No abstract at ADS
Title: Recounting the birth of solar terrestrial physics.
Authors: Cliver, E. W.
Bibcode: 1995E&S.....7...12C
Altcode:
In the 19th century scientists began to notice a relationship between
solar activity and geomagnetism. From these beginnings, the science
of space physics and aeronomy was born.
Title: Solar activity and geomagnetic storms: From M regions and
flares to coronal holes and CMEs
Authors: Cliver, E. W.
Bibcode: 1995EOSTr..76...75C
Altcode:
Two earlier articles published in the December 6 and December 27, 1994,
issues of Eos outlined the history of solar-terrestrial research from
Sabine's founding discovery in 1852 through Chapman and Ferraro's
landmark paper in 1931. This article deals with the development of
the field from 1930 to the present with a focus on the identification
of the solar sources of the two basic types of geomagnetic storms:
recurrent and sporadic.
Title: The Angular Extents of Solar/Interplanetary Disturbances and
Modulation of Galactic Cosmic Rays
Authors: Cliver, E. W.; Cane, H. V.
Bibcode: 1995ICRC....4..884C
Altcode: 1995ICRC...24d.884C
No abstract at ADS
Title: Extreme "Propagation" of Solar Energetic Particles
Authors: Cliver, E. W.; Kahler, S. W.; Neidig, D. F.; Cane, H. V.;
Richardson, I. G.; Kallenrode, M. B.; Wibberenz, G.
Bibcode: 1995ICRC....4..257C
Altcode: 1995ICRC...24d.257C
No abstract at ADS
Title: Postmodern view of M-regions
Authors: Crooker, N. U.; Cliver, E. W.
Bibcode: 1994JGR....9923383C
Altcode:
The discovery of coronal holes in the early 1970s was heralded as
the discovery of the mysterious M-regions responsible for recurrent
geomagnetic activity. High-speed flow from the holes, sweeping past
Earth on successive solar rotations, was directly correlated with
sustained increases in activity indices. We argue that this view of
M-regions as coronal holes is incomplete because it ignores work dating
from the 1960s demonstrating that peak recurrent activity coincides with
passage of corotating interaction regions between high- and low-speed
flows. Thus, in an important way, M-regions include the boundary between
coronal holes and coronal streamers, since streamers supply the slowest
flows. In addition, we suggest that coronal mass ejections propagating
through the streamer belt can contribute to the peak intensities of
recurrent storms. Finally, we demonstrate that both peak recurrent
activity and the following sustained activity that correlates with the
high-speed flows are controlled by the Russell-McPherron effect: They
are prominent only when the azimuthal component of the Parker spiral
field projects a southward component in Earth's tilted dipole frame.
Title: A correlation between 4-8 MeV gamma-ray-line fluence and
>~50 keV X-ray fluence in large solar flares
Authors: Cliver, E. W.; Crosby, N. B.; Dennis, B. R.
Bibcode: 1994AIPC..294...65C
Altcode: 1994hesp.conf...65C
For large flares observed by the Solar Maximum Mission (SMM) satellite
from 1980-1982, we find a reasonably good correlation between
4-8 MeV gamma-ray-line (GRL) fluences and >~50 keV hard X-ray
fluences. We find no compelling evidence for a distinct population
of large hard X-ray flares that lack commensurate GRL emission. Our
results are consistent with the acceleration of the bulk of the ~100
keV electrons and ~10 MeV protons (i.e., the populations of these
species that interact in the solar atmosphere to produce hard X-ray
and GRL emissions) of a common process in large flares of both long
and short durations.
Title: Are Solar Gamma-Ray--Line Flares Different from Other Large
Flares?
Authors: Cliver, E. W.; Crosby, N. B.; Dennis, B. R.
Bibcode: 1994ApJ...426..767C
Altcode:
We reevaluate evidence indicating that gamma-ray-line (GRL) flares are
fundamentally different from other large flares without detectable GRL
emission and find no compelling support for this proposition. For large
flares observed by the Solar Maximum Mission (SMM) from 1980 to 1982,
we obtain a reasonably good correlation between 4-8 MeV GRL fluences
and greater than 50 keV hard X-ray fluences and find no evidence for a
distinct population of large hard X-ray flares that lack commensurate
GRL emission. Our results are consistent with the acceleration of the
bulk of the approximately 100 keV electrons and approximately 10 MeV
protons (i.e., the populations of these species that interact in the
solar atmosphere to produce hard X-ray and GRL emission) by a common
process in large flares of both long and short durations.
Title: Suppresion of Solar Radio Noise Storms in Eruptive Flares
Authors: Kahler, S. W.; Cliver, E. W.; Chertok, I. M.
Bibcode: 1994scs..conf..271K
Altcode: 1994IAUCo.144..271K
The authors report four cases in which eruptive flares were accompanied
by sharp decreases in pre-existing radio noise storm intensity observed
by the IZMIRAN station at 169 and 204 MHz. They suggest that a noise
storm accompanying streamer reformation following an initial CME was
interrupted by the disruption of the streamer in the second CME.
Title: Solar activity and geomagnetic storms: The corpuscular
hypothesis
Authors: Cliver, E. W.
Bibcode: 1994EOSTr..75..609C
Altcode:
An earlier article published in the December 6, 1994, issue of Eos
traced the history of solar-terrestrial relations from 1852, when Sabine
discovered that the 11-year sunspot and geomagnetic activity cycles
waxed and waned in unison, to the early 1890s. The narrative here picks
up in 1892, a year of fomentation that led to the development of the
corpuscular hypothesis by Maunder, Birkeland, Chapman, Ferraro, and
others.Magnetism was “in the air” in 1892. This seminal year for
solar activity saw several remarkable developments, not all of which
were positive or bore immediate fruit, but each provided stimulus and
a basis for subsequent progress.
Title: Solar activity and geomagnetic storms: The first 40 years
Authors: Cliver, E. W.
Bibcode: 1994EOSTr..75..569C
Altcode:
This article is the first of a series of three that traces the
evolution of our understanding of the relationship between solar
and geomagnetic activity from the mid-19th century to the present
era.The origin of solar-terrestrial physics is generally traced to
Sabine's recognition in 1852 that geomagnetic activity paralleled the
recently discovered sunspot cycle. Perhaps less well appreciated is
the slow and uneven pace of progress since then in forging definite
links between solar and geomagnetic activity. Thus 50 years after the
initial excitement attending Sabine's discovery, the role of the Sun as
the fundamental cause of magnetic storms was a matter of contention,
and nearly a century would pass before statistics were sufficient to
make a convincing case for an association between large solar flares
and severe storms.
Title: Rotation-Averaged Rates of Coronal Mass Ejections and Dynamics
of Polar Crown Filaments
Authors: Cliver, E. W.; St. Cyr, O. C.; Howard, R. A.; McIntosh, P. S.
Bibcode: 1994scs..conf...83C
Altcode: 1994IAUCo.144...83C
The authors obtained Carrington-rotation-averaged daily rates of
coronal mass ejections (CMEs), corrected for duty cycle, for the period
1979 - 1989. The 27-day averages of CME rate and sunspot number are
correlated. The baseline CME rate exhibited quasi-discontinuities
in 1982 (decrease) and 1988 (increase) when the "tilt angle" of the
heliospheric current sheet passed through values of ≡50°. The
authors suggest that these quasi-discontinuities are related to the
dynamics of the belts of polar crown filaments that reside at ≡50°
north and south of the equator during solar minimum and move poleward
during the rise phase of the solar cycle.
Title: The shapes of galactic cosmic ray intensity maxima and the
evolution of the heliospheric current sheet
Authors: Cliver, E. W.
Bibcode: 1993JGR....9817435C
Altcode:
The observation of a triangular-shaped galactic cosmic ray (GCR)
intensity maximum during the mid-1980s solar minimum was successfully
predicted by drift models of cosmic ray modulation. The assumption
underlying this prediction was that the evolution of solar activity,
represented in drift models by the time development of the ``tilt''
angle of the heliospheric current sheet (HCS), does not vary greatly
from cycle to cycle. Tilt angles derived from coronal brightness
distributions in the 1970s show that this assumption, seemingly
supported by the successful prediction, may not be valid. The evolution
of the HCS during the 1970s, when the 11-year GCR maximum exhibited
a broad peak, may have been significantly different (with a broader
and less regular period of low tilt angles) from that inferred for
the preceding mid-1960s solar minimum and from that determined by the
Wilcox Solar Observatory during the following mid-1980s minimum. Had
the 1970s corresponded to an A<0 epoch (in the drift formulation),
it appears that the resultant GCR intensity maximum would have been
double peaked, with a deep rift corresponding to the 1974 minicycle. The
different sensitivities of GCR intensity to tilt angle changes in A
positive and A negative solar cycles, as demonstrated by other authors,
provide support for drift models of modulation. The point we make here
is that nonsystematic evolution of the HCS from one cycle to the next
can be an additional source of variation in the shapes of consecutive
GCR intensity maxima.
Title: Superevents and cosmic ray modulation, 1974-1985
Authors: Cliver, E. W.; Droege, W.; Mueller-Mellin, R.
Bibcode: 1993JGR....9815231C
Altcode:
Superevents are long-lived (~40 days at 1 AU) ~10-MeV proton events that
originate in episodes of intense solar activity characterized by major
coronal mass ejections (CMEs) and individual solar energetic particle
(SEP) events. Superevents exhibit only weak intensity variation
with heliolongitude. They propagate to the outer heliosphere at
speeds above that of the average solar wind, and, at Pioneers 10
and 11, prominent superevents are generally associated with strong
interplanetary shocks. For the period from 1974 to 1985, we find that
superevents are not reliable signatures of the onsets of long-term
steps in the modulation record of >1-GV galactic cosmic rays
(GCRs) at 1 AU. Of six intense superevents during this interval,
one occurred coincident with the onset of a step (June-July 1982),
two occurred midway through step decreases, and three occurred at the
ends of step decreases. Two step decreases during this period began
in conjunction with relatively weak SEP activity. Thus the largest
superevents occurring from 1974 to 1985 were neither necessary nor
sufficient conditions for long-term GCR intensity steps and therefore
were not closely related to the global merged interaction regions that
have been identified with such steps. In terms of convection/diffusion
models of cosmic ray modulation, the poor association of the largest
superevents with long-term GCR intensity decreases during this period
suggests that the background level of more frequently occurring, and
less energetic, CMEs is more important for establishing the 11-year
cycle than are the sporadic, and relatively short-lived, outbreaks of
major CME activity that give rise to superevents.
Title: Reply [to “Comment on “The semiannual variation of
great geomagnetic storms and the postshock Russell-Mcpherron effect
preceding coronal mass ejecta” By N. U. Crooker, E. W. Cliver and
B. T. Tsurutani”]
Authors: Crooker, N. U.; Cliver, E. W.
Bibcode: 1993GeoRL..20.1661C
Altcode:
No abstract at ADS
Title: A Seasonal Dependence for the Geoeffectiveness of Eruptive
Solar Events
Authors: Cliver, E. W.; Crooker, N. U.
Bibcode: 1993SoPh..145..347C
Altcode:
The pronounced seasonal variation of the occurrence rate of great
geomagnetic storms, attributed to in-ecliptic draping of interplanetary
magnetic fields and the Russell-McPherron effect, suggests that
the geoeffectiveness of the causative eruptive solar events has a
seasonal dependence. Thus an eruptive solar event of a given `size'
occurring near the equinoxes might be expected to give rise to a
larger geomagnetic storm than would a comparable event occurring near
the solstices. We present the following evidence for such a seasonal
dependence: (1) the great `problem' storms of the last four solar
cycles, i.e., severe storms lacking commensurate preceding solar
activity, occurred relatively near the equinoxes, (2) the few great
storms that occurred near the solstices were generally preceded by
truly outstanding flares, and (3) on average, central meridian proton
flares occurring near the equinoxes were followed by significantly
larger geomagnetic storms than were similar flares occurring near
the solstices. We conclude that the strong semi-annual variation of
great storms results from the virtual absence, near the solstices,
of great storms associated with disappearing solar filaments and with
moderately-sized eruptive solar flares.
Title: An Investigation of the Relationship Between the Microwave
Spectra of Solar Flares and the Delay to Maximum of Associated Proton
Events at 1 AU
Authors: Cliver, E. W.; Kahler, S. W.; Campbell, J. M.
Bibcode: 1993stp2.conf..113C
Altcode:
No abstract at ADS
Title: Coronal Mass Ejections, Polar Crown Filaments, and Cosmic
Ray Modulation 1979-1989
Authors: Cliver, E. W.; St. Cyr, O. C.; Howard, R. A.; McIntosh, P. S.
Bibcode: 1993ICRC....3..517C
Altcode: 1993ICRC...23c.517C
No abstract at ADS
Title: On the Origin of Gamma-Ray Emission from the Behind-the-Limb
Flare on 29 September 1989
Authors: Cliver, E. W.; Kahler, S. W.; Vestrand, W. T.
Bibcode: 1993ICRC....3...91C
Altcode: 1993ICRC...23c..91C
No abstract at ADS
Title: X-Class Soft X-ray Bursts and Major Proton Events During
Solar Cycle 22 (1987-1991)
Authors: Gentile, L. C.; Campbell, J. M.; Cliver, E. W.; Cane, H. V.
Bibcode: 1993stp2.conf..153G
Altcode:
No abstract at ADS
Title: Comment On "An Investigation of the Relationship Between
the Microwave Spectra of Solar Flares and the Delay to Maximum of
Associated Proton Events at 1 AU"
Authors: Cliver, E. W.; Kahler, S. W.; Chertok, J. M.; Campbell,
I. M.; Bazilevskaya, G. A.; Sladkova, A. I.
Bibcode: 1993stp2.conf..121C
Altcode:
No abstract at ADS
Title: Reply to Comment by I. M. Chertok, G. A. Bazilevskaya and
A. I. Sladkova
Authors: Cliver, E. W.; Kahler, S. W.
Bibcode: 1993stp2.conf..127C
Altcode:
No abstract at ADS
Title: A Seasonal Dependence for the Geoeffectiveness of Eruptive
Solar Events
Authors: Cliver, E. W.; Crooker, N. U.
Bibcode: 1993stp3.conf...98C
Altcode:
No abstract at ADS
Title: CME Rates from 1979-1989 and Correlations With Other Solar
Activity Indices
Authors: Cliver, E. W.; Cyr, O. C. St.; Howard, R. A.
Bibcode: 1992AAS...180.5207C
Altcode: 1992BAAS...24Q.816C
We combined coronagraph observations from Solwind and SMM to obtain
monthly averages of the daily rate of coronal mass ejections (CMEs),
corrected for duty cycle, for the years 1979-1989. We examined
correlations between the CME rate and the following equivalent indices
of solar activity: sunspot number, 10-cm quiet sun flux, and soft X-ray
background flux. The CME rate exhibits significant fluctuations when
compared to these other activity indices on a monthly basis; however,
long-term correlations are clearly evident in each case. In early
1982 the baseline CME rate changed rapidly from a value of 1.8/day to
0.8/day; in late 1988, the reverse occurred. We note that both of these
quasi-discontinuities occurred when the inclination of the heliospheric
current sheet, as deduced from Stanford maps, crossed 50 degrees.
Title: Composition and Azimuthal Spread of Solar Energetic Particles
from Impulsive and Gradual Flares
Authors: Kallenrode, M. -B.; Cliver, E. W.; Wibberenz, G.
Bibcode: 1992ApJ...391..370K
Altcode:
A list of 77 flare-associated solar energetic particle (SEP) parent
flares are classified as impulsive (25 cases) or gradual (52 cases)
on the basis of their soft X-ray durations. The intensities of the
prompt component of about 0.5 MeV electrons, about 10 MeV protons,
and about 10 MeV per nucleon helium for the two classes of SEP flares
are compared. SEPs from gradual flares have higher intensities than
SEPs from impulsive flares. These differences are most pronounced for
protons (about two orders of magnitude), and less for electrons (about
one order of magnitude), and helium (about a factor of 5). The SEPs
from impulsive flares have a 'cone of emission' of +/- 50 deg vs +/-
120 deg for gradual flares.
Title: The semiannual variation of great geomagnetic storms and the
postshock Russell-McPherron effect preceding coronal mass ejecta
Authors: Crooker, N. U.; Cliver, E. W.; Tsurutani, B. T.
Bibcode: 1992GeoRL..19..429C
Altcode: 1992STIN...9312506C
The occurrence rate of great geomagnetic storms displays a pronounced
semiannual variation. Of the forty-two great storms during the period
1940-1990, none occurred during the solstitial months of June and
December, and 40% (17) occurred during the equinoctial months of March
and September. This suggests that the semiannual variation found
by averaging indices is not the result of some statistical effect
superposed on the effects of random storm occurrence but rather is
dominated by the storms themselves. Recent results indicate that the
intense southward interplanetary magnetic fields (IMFs) responsible for
great storms can reside in the postshock plasma preceding the driver
gas of coronal mass ejections (CMEs) as well as in the driver gas
itself. Here we propose that strong southward fields in the postshock
flow result from a major increase in the Russell-McPherron polarity
effect through a systematic pattern of compression and draping within
the ecliptic plane. Differential compression at the shock increases the
Parker spiral angle and, consequently, the azimuthal field component
that projects as a southward component onto Earth's dipole axis. The
resulting prediction is that southward fields in the postshock plasma
maximize at the spring (fall) equinox in CMEs emerging from toward
(away) sectors. This pattern produces a strong semiannual variation
in postshock IMF orientation and may account at least in part for the
observed semiannual variation of the occurrence of great geomagnetic
storms.
Title: Superevents: Their Origin and Propagation through the
Heliosphere from 0.3 to 35 AU
Authors: Droege, Wolfgang; Mueller-Mellin, Reinhold; Cliver, Edward W.
Bibcode: 1992ApJ...387L..97D
Altcode:
Interplanetary particle fluxes between 1974 and 1986 are analyzed and
compared with Kiel neutron monitor data to determine whether other
less obvious 'superevents' may exist than the five events previously
identified by Mueller-Mellin et al. (1986). The solar activity
associated with the most prominent superevents is examined, and it is
found that these events originate in extended (0.5-2 mo) episodes of
coronal mass ejection (CME) activity from single active regions or
narrow ranges of active latitudes. Analysis of the variation of the
particle peak intensity as a function of time, ecliptic longitude, and
radial distance suggests that superevents result when systems of CMEs,
with their associated shocks and particle events, create an outward
propagating shell encompassing the sun. The relatively weak negative
radial intensity gradients of the superevents indicate that local
acceleration and trapping, as well as flare-accelerated particles,
are key factors in their formation.
Title: History and Basic Characteristics of Eruptive Flares
Authors: Svestka, Z.; Cliver, E. W.
Bibcode: 1992LNP...399....1S
Altcode: 1992esf..coll....1S; 1992IAUCo.133....1S
We review the evolution of our knowledge and understanding of the
eruptive (dynamic, two-ribbon) flare phenomenon. Starting with the
first observation of a white-light flare by Carrington and Hodgson in
1859, we cover in succession the highlights: Hale's invention of the
spectroheliograph in 1892 and the spectrohelioscope in 1926 started
flare observations in H. The institution of a world-wide flare patrol
brought significant advances in knowledge of flares in the 1930s and
1940s and new windows were opened to observe flares at short (SID) and
long (radio) wavelengths. In the 1950s and 1960s metric radio bursts
were related to trapped energetic electrons and shocks, and two-ribbon
flares were associated with energetic protons in space. Radio and X-ray
observations gave evidence for two basic types of flare processes:
an impulsive phase followed by a long-duration or gradual phase. It
was found that flares were often preceded by filament activations, and
growing loop prominence systems were recognized as the limb counterpart
of two-ribbon disk flares. The early 1970s brought Skylab observations
of coronal mass ejections (CMEs) and arcades of coronal soft X-ray
loops above two-ribbon flares. In the mid-1970s, the Kopp-Pneuman
reconnection model, based on configurations proposed earlier by
Carmichael, Sturrock, and Hirayama, provided a framework in which the
newly discovered CMEs could be related to the basic characteristics
of two-ribbon flares. The 1980s brought, key new results from SMM
and Hinotori including images of hard X-ray flares and large-scale
coronal structures associated with eruptive flares. In the conclusion,
we summarize the basic characteristics of eruptive flares.
Title: Solar Gamma-Ray-Line Flares, Type II Radio Bursts, and Coronal
Mass Ejections
Authors: Cliver, E. W.; Cane, H. V.; Forrest, D. J.; Koomen, M. J.;
Howard, R. A.; Wright, C. S.
Bibcode: 1991ApJ...379..741C
Altcode:
A Big Flare Syndrome (BFS) test is used to substantiate earlier
reports of a statistically significant association between nuclear
gamma-ray-line (GRL) flares and metric type II bursts from coronal
shocks. The type II onset characteristically follows the onset of
gamma-ray emission with a median delay of two minutes. It is found that
70-90 percent of GRL flares for which coronagraph data were available
were associated with coronal mass ejections (CMEs). Gradual and
impulsive GRL flares were equally well associated with CMEs. The CMEs
were typically fast, with a median speed greater than 800 km/s. possible
`non-BFS' explanations for the GRL-type II association are discussed.
Title: Solar Activity in May 1987 at the Onset of the New Cosmic
Ray Modulation Cycle
Authors: Cliver, E.; Kahler, S.
Bibcode: 1991ICRC....3..410C
Altcode: 1991ICRC...22c.410C
No abstract at ADS
Title: The Propagation of Super-Events from 0.3-35 AU
Authors: Droge, W.; Muller-Mellin, R.; Cliver, E. W.
Bibcode: 1991ICRC....3..300D
Altcode: 1991ICRC...22c.300D
No abstract at ADS
Title: Ground-Level Events from Impulsive Solar Flares
Authors: Kahler, S. W.; Shea, M. A.; Smart, D. F.; Cliver, E. W.
Bibcode: 1991ICRC....3...21K
Altcode: 1991ICRC...22c..21K
No abstract at ADS
Title: Solar Energetic Proton Events Without Type II Burst
Authors: Kallenrode, M. -B.; Cliver, E. W.; Kahler, S. W.; Hucke,
S.; Wibberenz, G.
Bibcode: 1991ICRC....3...17K
Altcode: 1991ICRC...22c..17K
No abstract at ADS
Title: Size Distributions of Solar Energetic Particle Events
Authors: Cliver, E.; Reames, D.; Kahler, S.; Cane, H.
Bibcode: 1991ICRC....3...25C
Altcode: 1991ICRC...22c..25C; 1991icrc...22....2C
NASA particle detectors on the IMP-8 are employed to determine the size
distributions of the peak fluxes of events related to solar-energetic
particles including protons and electrons. The energetic proton events
show a flatter size distribution which suggests that not all flares
are proton flares. Both the electron and proton events are classified
as either 'impulsive' or 'gradual', and the impulsive events tend to
have a steeper power-law distribution.
Title: The Scale Sizes of CMEs and Associated Surface Activity
Authors: Webb, D. F.; Harvey, K. L.; Cliver, E. W.; Kahler, S. W.
Bibcode: 1991BAAS...23.1062W
Altcode:
No abstract at ADS
Title: A Search for the 154 Day Periodicity in the Occurrence Rate
of Solar Flares Using Ottawa 2.8 GHz Burst Data, 1955--1990
Authors: Kile, J. N.; Cliver, E. W.
Bibcode: 1991ApJ...370..442K
Altcode:
The Ottawa 2.8 GHz burst record from 1955 January to 1990 February
has been examined for evidence of a periodicity near 154 days in
the occurrence rate of solar flares. This periodicity is found to be
statistically significant, at the 1-percent level, only for the years
from 1978 to 1983, corresponding to the activity maximum of solar
cycle 21. Through 1990 February, the Ottawa data show no evidence for
a 154 day period in the current 22d solar cycle that began in 1986
September. A spectral peak near 51 days is found in solar cycle 19
(1955-1964), as had been previously reported based on an examination
of CFI data, but its significance is low, at the 33-percent level. It
is concluded that, other than for the period in cycle 21 in which it
was first discovered, the evidence for the 154 day periodicity from
flare-related data sets is contradictory and not compelling. Stronger
evidence for the occurrence of the 154 day periodicity outside cycle
21 can be found in recent studies that examine parameters such as
sunspot counts and areas that characterize solar active regions.
Title: High Coronal Flares and Impulsive Acceleration of Solar
Energetic Particles
Authors: Cliver, E.; Kahler, S.
Bibcode: 1991ApJ...366L..91C
Altcode:
Evidence is reviewed which suggests that the source regions of high
coronal flares (HCFs) are hot. A scenario is considered in which
the source region of He-3 enhancement in solar energetic particle
events from impulse flares is distinct from the source region of the
enhanced abundances of high-Z ions. It is proposed that HCFs occur
due to reconnection in the neutral current sheets of coronal streamers.
Title: A 154 Day Periodicity in the Occurrence Rate of Proton Flares
Authors: Bai, Taeil; Cliver, E. W.
Bibcode: 1990ApJ...363..299B
Altcode:
We have analyzed periodicities in the occurrence rate of proton flares
for solar cycles 19 through 21 (1955 to 1986) and have identified two
epochs that exhibit a 154-day periodicity. These epochs are a 14-year
interval from 1958 January through 1971 December and a 5.5-year
interval from 1978 February to 1983 August. The best-determined
period is 154.6. We have found that the phase of this periodicity
changed between the above-mentioned two epochs by about one half of a
period. It appears that the occurrence rate of proton flares is more
sensitive to the 154-day periodicity than the occurrence rate of flares
selected by other criteria.
Title: An estimate of the maximum speed of the solar wind, 1938-1989
Authors: Cliver, E. W.; Feynman, J.; Garrett, H. B.
Bibcode: 1990JGR....9517103C
Altcode:
Beginning with a list of severe geomagnetic storms, we obtain an
estimate of the maximum solar wind flow speed at Earth during the
past ~50 years. We do this by (1) focusing on the subset of severe
storms that followed major proton flares (since large proton events are
strongly associated with fast coronal mass ejections), (2) calculating
the average speed of the associated interplanetary shocks from the time
intervals between the flares and the onsets of the storms, and (3)
using an empirical relationship between the average shock speed and
the maximum flow speed of the associated transient stream to infer a
peak flow velocity for each event. We find no evidence for bulk flow
velocities greater than the >2000-km/s value deduced from Prognoz
2 and and HEOS 2 in situ plasma measurements for the August 4, 1972,
event. The >2000-km/s speed for that event does not appear to be
anomalously high, however; there are other credible events, occurring
before 1960, with inferred flow speeds approaching this value. The
>2000-km/s value lies at the high-speed edge of a reasonable single
distribution of peak solar wind speeds for a representative sample of
the most energetic solar-terrestrial events observed from 1938 to 1989.
Title: A Search for the 154-Day Periodicity in the Occurrence Rate
of Solar flares in the Early Years of Cycle 22
Authors: Kile, J. N.; Cliver, E. W.
Bibcode: 1990BAAS...22R.873K
Altcode:
No abstract at ADS
Title: Solar Flare Hard X-Ray Events of March 1989 from Active
Region 5395
Authors: Desai, U. D.; Orwig, L. E.; Cliver, E. W.
Bibcode: 1990BAAS...22..817D
Altcode:
No abstract at ADS
Title: Particle Ratios in Impulsive and Gradual Flares
Authors: Kallenrode, M. -B.; Wibberenz, G.; Cliver, E.
Bibcode: 1990ICRC....5..104K
Altcode: 1989ICRC....5..104K; 1990ICRC...21e.104K
No abstract at ADS
Title: Was the eclipse comet of 1893 a disconnected coronal mass
ejection?
Authors: Cliver, E. W.
Bibcode: 1989SoPh..122..319C
Altcode:
A re-evaluation of observations of the 16 April, 1893 solar eclipse
suggests that the `comet' photographed during totality was, in fact,
a disconnected coronal mass ejection. Like the disconnection event
in 1980 reported by Illing and Hundhausen, the outward speed of the
convex (toward the Sun) surface for the 1893 event was relatively low
(∼90 km s−1). Candidate disconnection events were also
observed during solar eclipses in 1860 and 1980.
Title: Shock Associated Kilometric Radio Emission and Solar Metric
Type-II Bursts
Authors: Kahler, S. W.; Cliver, E. W.; Cane, H. V.
Bibcode: 1989SoPh..120..393K
Altcode:
We present statistics relating shock-associated (SA) kilometric bursts
(Cane et al., 1981) to solar metric type II bursts. An SA burst is
defined here to be any 1980 kHz emission temporally associated with
a reported metric type II burst and not temporally associated with
a reported metric type III burst. In this way we extend to lower
flux densities and shorter durations the original SA concept of
Cane et al. About one quarter of 316 metric type II bursts were not
accompanied by any 1980 kHz emission, another quarter were accompanied
by emission attributable to preceding or simultaneous type III bursts,
and nearly half were associated with SA bursts. We have compared
the time profiles of 32 SA bursts with Culgoora Observatory dynamic
spectral records of metric type II bursts and find that the SA emission
is associated with the most intense and structured part of the metric
type II burst. On the other hand, the generally poor correlation
found between SA burst profiles and Sagamore Hill Observatory 606
and 2695 MHz flux density profiles suggests that most SA emission is
not due to energetic electrons escaping from the microwave emission
region. These results support the interpretation that SA bursts are
the long wavelength extension of type II burst herringbone emission,
which is presumed due to the shock acceleration of electrons.
Title: Solar Flare Nuclear Gamma Rays and Interplanetary Proton Events
Authors: Cliver, E. W.; Forrest, D. J.; Cane, H. V.; Reames, D. V.;
McGuire, R. E.; von Rosenvinge, T. T.; Kane, S. R.; MacDowall, R. J.
Bibcode: 1989ApJ...343..953C
Altcode:
Gamma-ray line (GRL) and solar energetic proton (SEP) events observed
from February 1980 through January 1985 are compared in order to
substantiate and better characterize the lack of correlation between
GRL fluences and SEP event peak fluxes. The scatter plot of SEP event
peak flux vs. GRL fluence is presented, and the ratio of 'solar' to
'interplanetary', about 10 MeV protons, is presented. It is shown that,
while even large SEP events can originate in flares lacking detectable
GRL emission, the converse case of flares with a significant GRL line
fluence by lacking protons in space is rare. The ratio R of the number
of about 10 MeV protons that produce GRL emission at the flare site
to the number of about 10 MeV protons detected in space can vary from
event to event by four orders of magnitude. There is a clear tendency
for impulsive flares to have larger values of R than long-duration
flares, where the flare time scale is given by the e-folding decay
time of the associated soft X-ray emission.
Title: A Search for Periodicities in the Occurrence Rates of Ottawa
2. 8 GHz Solar Burst Data 1955-1986
Authors: Kile, J. N.; Cliver, E. W.; Fougere, P. F.
Bibcode: 1989BAAS...21..828K
Altcode:
No abstract at ADS
Title: The 154-Day Periodicity of Proton Flares
Authors: Bogart, R.; Bai, T.; Cliver, E. W.; Kile, J.
Bibcode: 1989BAAS...21..836B
Altcode:
No abstract at ADS
Title: The Spatial and Temporal Relationship of Major Solwind CMEs
to Solar Surface Activity
Authors: Cliver, E. W.; Koomen, M. J.; Howard, R. A.
Bibcode: 1989BAAS...21..856C
Altcode:
No abstract at ADS
Title: Evidence for Magnetic Disconnection of Mass Ejections in
the Corona
Authors: Webb, D. F.; Cliver, E. W.
Bibcode: 1989BAAS...21..857W
Altcode:
No abstract at ADS
Title: Solar Cycle Variation of Long Duration 10.7-CM and Soft
X-Ray Bursts
Authors: Kahler, S.; Cliver, E. W.
Bibcode: 1988SoPh..115..385K
Altcode:
Gradual rise-and-fall (GRF) microwave bursts and long duration soft
X-ray events (LDEs) are generally accompanied by solar coronal mass
ejections (CMEs). We use reports from the Ottawa and Penticton stations
to examine the annual variations from 1965 to 1985 of 10.7 cm GRF bursts
with total durations of at least 4 hr. The annual numbers of such bursts
are well correlated with the quiet-Sun 10.7 cm flux densities. This
result is in contrast with the finding of Koomen et al. (1985)
that the annual numbers of ≥ 4 hr GOES soft X-ray events are not
well correlated with sunspot numbers. We show that the latter result
is biased by the large variation of the quiet-Sun X-ray background
throughout the solar cycle. Four-hour events are more easily detected
in X-ray data than in 10.7 cm data at solar minimum, but, conversely,
these events are much more easily detected in 10.7 cm data around solar
maximum. About 70% of the most energetic CMEs are associated with ≥
4 hr X-ray or 10.7 cm bursts. A one-to-one relationship does not exist
between CMEs and either LDEs or GRF bursts viewed in full-Sun detectors.
Title: Coronal Mass Ejections, Type II Shocks, and Gamma-Ray-Line
Emission from Solar Flares
Authors: Cliver, E. W.; Cane, H. V.; Forrest, D. J.; Koomen, M. J.
Bibcode: 1988BAAS...20.1029C
Altcode:
No abstract at ADS
Title: Coronal Type II Shocks and Gamma Ray Line Emission From
Solar Flares
Authors: Cliver, E. W.; Cane, H. V.; Forrest, D. J.
Bibcode: 1988BAAS...20..748C
Altcode:
No abstract at ADS
Title: Are All Metric Type II Bursts Piston-Driven by Coronal Mass
Ejections?
Authors: Webb, D. F.; Cliver, E. W.
Bibcode: 1988BAAS...20R.745W
Altcode:
No abstract at ADS
Title: Solar Flare Nuclear Gamma Rays and Interplanetary Proton Events
Authors: Cliver, E. W.; Forrest, D. J.; McGuire, R. E.; von Rosenvinge,
T. T.; Reames, D. V.; Cane, H. V.; Kane, S. R.; MacDowall, R. J.
Bibcode: 1988BAAS...20..740C
Altcode:
No abstract at ADS
Title: Was the eclipse comet of 1893 a disconnected coronal transient?
Authors: Cliver, E. W.
Bibcode: 1987sici.symp...27C
Altcode:
The comet-like feature obsereved in the solar corona by the Lick
Observatory eclipse expedition to Chile in 1893 bears an interesting
resemblance to the disconnection coronal transient reported by Illing
and Hundhausen. Reports of possibly-related limb activity are reviewed
to see whether a pre-discovery observation of a relatively rare type
of coronal mass ejection was mis-interpreted. The goal of this study
is to learn more about the morphology of mass ejections by examining
observations that extend down to the low corona of a disconnection
event.
Title: Solar activity and heliosphere-wide cosmic ray modulation
in mid-1982
Authors: Cliver, E. W.; Mihalov, J. D.; Sheeley, N. R., Jr.; Howard,
R. A.; Koomen, M. J.; Schwenn, R.
Bibcode: 1987JGR....92.8487C
Altcode:
A major episode of flare activity in June and July 1982 was accompanied
by a pair of heliosphere-wide cosmic ray modulation events. In each
case, a large Forbush decrease (FD) at earth was followed in turn
by apparently related decreases at Pioneer 11 (P11) and Pioneer 10
(P10). The Pioneer spacecraft were separated by ~155° in ecliptic
longitude. We reviewed white light coronagraph and near-sun (<=1 AU)
satellite data to identify plausible solar origins of these modulation
events. The first widespread intensity decrease (FD 1) can be attributed
to the combined effects of a backside flare on June 3 from solar active
region 18382/18383, located 23° in ecliptic longitude from Pioneer 10,
and a visible disk flare from 18405 on June 6, when this region was
9° from Pioneer 11. The second widespread modulation event during this
period (FD 2) may be linked to flares from active region 18474 on July
12 and 22. The July 12 flare was located 34° in azimuth from Pioneer
11, and the July 22 flare was 24° from Pioneer 10. Since even fast
shocks would take ~1 month to propagate to Pioneer 11 (12 AU) and ~2
months to reach Pioneer 10 (28 AU) in mid-1982, these ``one-to-one''
associations must be regarded with caution. The processes of entrainment
and coalescence can cause a given traveling interplanetary disturbance
to lose its identify enroute to the outer heliosphere. The fact that
we were able to identify plausible solar flare candidates for each of
the four Forbushlike decreases observed at the Pioneer satellites (two
each at P10 and P11), however, removes the need to invoke a chock from
a single flare as the sole cause of either FD 1 (at both P10 and P11)
or FD 2. Such single-flare scenarios have recently been suggested by
several investigators to account for the widespread intensity decreases
in mid-1982. Instead, the heliosphere-wide modulation during this
period appears to result primarily from a sustained episode of powerful
flares from a relatively narrow range of active solar longitude. A
significant fraction (1/2 to 3/4) of the major coronal mass ejections
(CMEs) and near-sun shocks observed during June and July 1982 originated
in flares occurring in a 45° band of Carrington longitude. Because
of solar rotation these flares occur over the full range of ecliptic
longitude and can generate an outward propagating shell of CMEs and
shocks that encompasses the sun to produce the observed azimuthal
symmetry in the cosmic ray modulation. The prolonged high-speed wind
stream at P10 in the second half of 1982 may have resulted, at least
in part, from the coalescence of a series of fast transient streams
directed toward that distant spacecraft into an extended compound
stream.
Title: Solar Flare Nuclear Gamma-Rays and Interplanetary Proton Events
Authors: Cane, H. V.; Cliver, E. W.; Forrest, D. J.; Kane, S. R.;
McGuire, R. E.; Reames, D. V.; von Rosenvinge, T. T.
Bibcode: 1987ICRC....3...61C
Altcode: 1987ICRC...20c..61C
No abstract at ADS
Title: Solar Cycle Variation of Long Duration 10cm and Soft X-Ray
Bursts
Authors: Kahler, S.; Cliver, E. W.
Bibcode: 1987sowi.conf..278K
Altcode:
No abstract at ADS
Title: Solar Energetic Proton Events and Coronal Mass Ejections Near
Solar Minimum
Authors: Kahler, S. W.; Cliver, E. W.; Cane, H. V.; McGuire, R. E.;
Reames, D. V.; Sheeley, N. R., Jr.; Howard, R. A.
Bibcode: 1987ICRC....3..121K
Altcode: 1987ICRC...20c.121K; 1987ICRC....3..121C
No abstract at ADS
Title: Solar Gradual Hard X-Ray Bursts and Associated Phenomena
Authors: Cliver, E. W.; Dennis, B. R.; Kiplinger, A. L.; Kane, S. R.;
Neidig, D. F.; Sheeley, N. R., Jr.; Koomen, M. J.
Bibcode: 1986ApJ...305..920C
Altcode:
White-light coronagraph, H-alpha and radio data are presented as well
as hard X-ray data for a sample of 10 gradual hard X-ray bursts (GHBs)
in an attempt to better understand the nature of these events. It is
found that: (1) the hard X-ray photon energy spectrum began to harden
near the onset of the GHBs and continued in this fashion during the
decay phase; (2) a coronal mass ejection (CME) occurred in association
with at least nine of the GHBs; (3) the GHBs occurred in the late phase
of major flares; (4) the centimeter wavelength bursts associated with
the GHBs had relatively low frequency spectral maxima, and in relation
to the observed hard X-ray emission, they were microwave-rich; (5) the
associated decimetric bursts showed significant intensity variations
on time scales ranging from 0.1 to approximately greater than 1 minute;
and (6) the GHBs were most strongly associated with type IV events. It
is concluded that the acceleration and trapping of radiating electrons
occurs in the postflare loop systems following CMEs.
Title: Why P/OF should look for evidences of over-dense structures
in solar flare hard X-ray sources
Authors: Neidig, D. F.; Kane, S. R.; Love, J. J.; Cliver, E. W.
Bibcode: 1986sfcp.nasa..142N
Altcode:
White-light and hard X-ray (HXR) observations of two white-light flares
(WLFs) show that if the radiative losses in the optical continuum
are powered by fast electrons directly heating the WLF source, then
the column density constraints imposed by the finite range of the
electrons requires that the WLF consist of an over-dense region in the
chromosphere, with density exceeding 10 to the 14th power/cu cm. Thus,
we recommend that P/OF search for evidences of over-dense structures in
HXR images obtained simultaneously with optical observations of flares.
Title: Solar Filament Eruptions and Energetic Particle Events
Authors: Kahler, S. W.; Cliver, E. W.; Cane, H. V.; McGuire, R. E.;
Stone, R. G.; Sheeley, N. R., Jr.
Bibcode: 1986ApJ...302..504K
Altcode:
The 1981 December 5 solar filament eruption that is associated with an
energetic (E greater than 50 MeV) particle event observed at 1 AU. The
eruption was photographed in H-alpha and was observed by the Solwind
whitelight coronagraph on P78-1. It occurred well away from any solar
active region and was not associated with an impulsive microwave burst,
indicating that magnetic complexity and a detectable impulsive phase
are not required for the production of a solar energetic particle (SEP)
event. No metric type II or IV emission was observed, but an associated
interplanetary type II burst was detected by the low-frequency radio
experiment on ISEE 3. The December 5 and two other SEP events lacking
evidence for low coronal shocks had unusually steep energy spectra
(gamma greater than 3.5). In terms of shock acceleration, this suggests
that shocks formed relatively high in the corona may produce steeper
energy spectra than those formed at lower altitudes. It is noted that
the filament itself maybe one source of the ions accelerated to high
energies, since it is the only plausible coronal source of the He(+)
ions observed in SEP events.
Title: Solar gradual hard X-ray bursts: Observations and an
interpretation
Authors: Cliver, E. W.; Dennis, B. R.; Kiplinger, A.; Kane, S.;
Neidig, D. F.; Sheeley, N.; Koomen, M.
Bibcode: 1986AdSpR...6f.249C
Altcode: 1986AdSpR...6..249C
A recent study of solar gradual hard X-ray bursts is summarized. The
data are interpreted in terms of a model involving the acceleration
and trapping of electrons in post flare loop systems following coronal
mass ejections. A controversy about the classification of the metric
continuum that typically accompanies gradual hard X-ray events is
addressed.
Title: Why P/OF should look for evidences of over-dense structures
in solar flare hard X-ray sources.
Authors: Neidig, D. F.; Kane, S. R.; Love, J. J.; Cliver, E. W.
Bibcode: 1986NASCP2421..142N
Altcode:
White-light and hard X-ray (HXR) observations of two white-light
flares (WLFs) show that if the radiative losses in the optical
continuum are powered by fast electrons directly heating the
WLF source, then the column density constraints imposed by the
finite range of the electrons requires that the WLF consist of
an over-dense region in the chromosphere, with density exceeding
1014cm-3. Thus, the authors recommend that P/OF
search for evidences of over-dense structures in HXR images obtained
simultaneously with optical observations of flares.
Title: Peak-Flux-Density Spectra of Large Solar Radio Bursts and
Proton Emission from Flares
Authors: Cliver, E.; Gentile, L.; McNamara, L.
Bibcode: 1986stp..conf..212C
Altcode:
No abstract at ADS
Title: The relationship of shock-associated kilometric radio emission
with metric type II bursts and energetic particles
Authors: Kahler, S. W.; Cliver, E. W.; Cane, H. V.
Bibcode: 1986AdSpR...6f.319K
Altcode: 1986AdSpR...6..319K
Shock-associated (SA) events are a class of kilometric wavelength
solar radio bursts first observed with the ISEE-3 Radio Astronomy
Experiment. Cane et al. /1/ noted that these fast drift events are
typically associated with metric type II bursts and hypothesized that
the SA events were due to electrons accelerated by coronal shocks. We
compare SA events from 1978 to 1982 with metric type II bursts and
solar energetic particle (SEP) events. Most metric type II bursts
are not obviously associated with SA events at 1980 kHz. Metric type
II bursts associated with magnetically well connected flares and SA
emission are well correlated with SEP events; those without SA emission
are poorly correlated with SEP events. The largest SEP events from
flares at any longitude are well correlated with SAs. These results
are consistent with the hypothesis that the escaping electrons giving
rise to SA emission are accelerated in coronal shocks.
Title: Rapid spectral and flux time variations in a solar burst
observed at various dm-mm wavelengths and at hard X-rays.
Authors: Zodivaz, A. M.; Kaufmann, P.; Correia, E.; Costa, J. E. R.;
Takakura, T.; Cliver, E. W.; Tapping, K. F.
Bibcode: 1986NASCP2449..171Z
Altcode: 1986rfsf.nasa..171Z
A solar burst was observed with high sensitivity and time resolution
at cm-mm wavelengths by two different radio observatories; with high
spectral time resolution at dm-cm wavelengths by patrol instruments;
and at hard X-rays. The event appears to be build up by a first major
injection of softer particles followed by other injections of harder
particles. Ultrafast time structures were identified as superimposed
to the burst emission at the cm-mm high sensitivity data and at X-rays,
with predominant repetition rates ranging 2.0 - 3.5 Hz.
Title: Fast Drift Kilometric Radio Bursts and Solar Proton Events
Authors: Cliver, E. W.; Kahler, S. W.; Cane, H. V.; McGuire, R. E.;
von Rosenvinge, T. T.; Stone, R. G.
Bibcode: 1985ICRC....4...14C
Altcode: 1985ICRC...19d..14C
Initial results of a comparative study of major fast drift kilometric
bursts and solar proton events from Sep. 1978 to Feb. 1983 are
presented. It was found that only about half of all intense, long
duration ( 40 min above 500 sfu) 1 MHz bursts can be associated with F
20 MeV proton events. However, for the subset of such fast drift bursts
accompanied by metric Type 2 and/or 4 activity (approximately 40% of the
total), the degree of association with 20 MeV events is 80%. For the
reverse association, it was found that proton events with J( 20 MeV)
0.01 1 pr cm(-2)s(-1)sr(-1)MeV(-1) were typically (approximately 80%
of the time) preceded by intense 1 MHz bursts that exceeded the 500
sfu level for times 20 min (median duration approximately 35 min).
Title: Peak-flux-density spectra of large solar radio bursts and
proton emission from flares
Authors: Cliver, E. W.; McNamara, L. F.; Gentile, L. C.
Bibcode: 1985aifo.reptQ....C
Altcode:
We have reexamined the relationship between U-shaped peak-flux-density
microwave spectra and solar proton events for approx 200 large (Sp(>
or = 2GHz) > or = 800 solar flux units (sfu) microwave burst (1965 -
1979). The radio spectra fell into two basic classes: (1) U-shaped with
two maxima ( > or = 800 sfu) in the range from 200 MHz to > or =
10 GHz (59 percent of all events), and (2) cutoff spectra with a maximum
> or = 800 sfu at f > or = 2 GHz and Sp (200 MHz) < 100 sfu
(18 percent). Nine percent of the events had intermediate spectra with
a maximum > or = 800 sfu at f > or = 2 GHz and 100 sfu < or =
Sp (200 MHz) < 800 sfu. We were unable to classify 15 percent of
the events because of incomplete data. The associations of the three
classes of spectra with Type II (and/or Type IV) meter wavelenght
bursts and > 10 MeV proton events of any size (> or = 0.01 pr
per sq cm per sec per sr) are as follows: U-shaped Type II/IV (90
percent of large microwave bursts with U-shaped spectra are associated
with Type II/IV events), protons (77 percent); intermediate Type II/IV
(78 percent), protons (73 percent); and cutoff Type II/IV (22 percent),
protons (33 percent). These statistics affirm various lines of evidence
linking coronal shock waves and interplanetary proton events. They also
suggest that the meter wavelength branch of the U-shaped spectrum may
be attributable to second phase (vs flash phase) accelerated electrons.
Title: Energetic Protons from a Disappearing Solar Filament
Authors: Kahler, S. W.; Cliver, E. W.; Cane, H. V.; McGuire, R. E.;
Stone, R. G.; Sheeley, N. R., Jr.
Bibcode: 1985ICRC....4...94K
Altcode: 1985ICRC...19d..94K
A solar energetic (E 50 MeV) particle (SEP) event observed at 1 AU began
about 15000 UT on 1981 December 5. This event was associated with a fast
coronal mass ejection observed with the Solwind coronagraph on the P78-1
satellite. No metric type 2 or type 4 burst was observed, but a weak
interplanetary type 2 burst was observed with the low frequency radio
experiment on the International Sun-Earth Explorer-3 satellite. The mass
ejection was associated with the eruption of a large solar quiescent
filament which lay well away from any active regions. The eruption
resulted in an H alpha double ribbon structure which straddled the
magnetic inversion line. No impulsive phase was obvious in either
the H alpha or the microwave observations. This event indicates that
neither a detectable impulsive phase nor a strong or complex magnetic
field is necessary for the production of energetic ions.
Title: Peak flux density spectra of large solar radio bursts and
proton emission from flares
Authors: Cliver, E. W.; McNamara, L. F.; Gentile, L. C.
Bibcode: 1985JGR....90.6251C
Altcode:
We have reexamined the relationship between ``U-shaped'' peak flux
density microwave spectra and solar proton events for ~200 large
(Sp(>=2 GHz)>=800 solar flux units (sfu) microwave bursts
(1965-1979). The radio spectra fell into two basic classes: U-shaped,
with two maxima (>=800 sfu) in the range from 200 MHz to >=10
GHz (59% of all events), and cutoff spectra, with a maximum >=800
sfu at f>=2 GHz and Sp (200 MHz)<100 sfu (18%). Nine percent
of the events had ``intermediate'' spectra with a maximum >=800
sfu at f>=2 GHz and 100 sfu <=Sp (200 MHz)<800 sfu. We were
unable to classify 15% of the events because of incomplete data. The
associations of the three classes of spectra with type II (and/or type
IV) meter wavelength bursts and >10-MeV proton events of any size
(>=0.01 protons cm-2 s-1 sr-1) are
as follows: U-shaped: type II/IV (90% of large microwave bursts with
U-shaped spectra are associated with type II/IV events), protons (77%)
intermediate: type II/IV (78%), protons (73%) and cutoff, type II/IV
(22%), protons (33%). These statistics affirm various lines of evidence
linking coronal shock waves and interplanetary proton events. They
also suggest that the meter wavelength branch of the U-shaped spectrum
may be attributable to second-phase (versus flash phase) accelerated
electrons. We have examined this latter supposition and find that
it cannot be true in general. In our sample a type II event was in
progress at the time of the peak of the low-frequency branch for only
about half of the bursts with U-shaped spectrum (U bursts). For these
events we cannot rule out a possible contribution to the peak 200-MHz
flux from either the second harmonic of the type II burst or from
flare-continuum of the type FC II, provided that the starting frequency
of the fundamental type II burst is >100 MHz. The low-frequency
branch of the U burst appears to be more closely related to impulsive
phase type III emission. We note that the small sample of U bursts that
lacked type II/IV association is also poorly associated with proton
events. We conclude that the observed association between U bursts and
proton events probably results from the big flare syndrome rather than a
close physical link between these two phenomena. If the current National
Oceanic and Atmospheric Administration prediction threshold of J(>10
MeV)>=10 protons cm-2 s-1 sr-1 had
been in effect during the period covered by our data base (1965-1979),
the U burst ``yes or no'' forecast tool would have had a false alarm
rate of 50-70% and would have failed to provide warning for 40-50% of
the significant prompt proton events attributable to disk flares. We
note that several (eight of 46) of the prompt events with J(>10
MeV)>=10 protons cm-2 s-1 sr-1
observed from 1965 to 1979 originated in flares that had relatively weak
(<=300 sfu) burst emission at 200 MHz.
Title: Characteristics of the white-light source in the 1981 April
24 solar flare
Authors: Kane, S. R.; Love, J. J.; Neidig, D. F.; Cliver, E. W.
Bibcode: 1985ApJ...290L..45K
Altcode:
The large white-light flare on 1981 April 24 (≡1358 UT) was very well
observed at the hard X-ray, optical, and radio wavelengths. Energetic
particles escaping from the Sun were detected in the interplanetary
space and in the vicinity of the Earth. The flare had distinct impulsive
and gradual phases and provided the best available measurements of
the optical continuum in a solar flare. In this letter the authors
present these observations and discuss their interpretation in terms
of the energetics of the flare and the role of energetic electrons in
the production of optical continuum emission.
Title: Non-thermal Excitation of the White Light Source in the 24
April 1981 (~1358 UT) Solar Flare
Authors: Kane, S. R.; Love, J. J.; Neidig, D. F.; Cliver, E. W.
Bibcode: 1985BAAS...17..628K
Altcode:
No abstract at ADS
Title: Characteristics of coronal mass ejections associated with
solar frontside and backside metric type II bursts
Authors: Kahler, S. W.; Cliver, E. W.; Sheeley, N. R.; Howard, R. A.;
Koomen, M. J.; Michels, D. J.
Bibcode: 1985JGR....90..177K
Altcode:
We compare fast (v>=500 km s-1) coronal
mass ejections (CME's) with reported metric type II bursts to study
the properties of CME's associated with coronal shocks. We confirm
an earlier report of fast frontside CME's with no associated metric
type II bursts and calculate that 33+/-15% of all fast frontside CME's
are not associated with such bursts. Faster CME's are more likely to
be associated with type II bursts, as expected from the hypothesis
of piston-driven shocks. However, CME brightness and associated
peak 3-cm burst intensity are also important factors, as might be
inferred from the Wagner and MacQueen (1983) view of type II shocks
decoupled from associated CME's. We use the equal visibility of solar
frontside and backside CME's to deduce the observability of backside
type II bursts. We calculate that 23+/-7% of all backside type II bursts
associated with fast CME's can be observed at the earth and that 13+/-4%
of all type II bursts originate in backside flares. CME speed again
is the most important factor in the observability of backside type
II bursts.
Title: The Gle-Associated Flare of 21 August 1979
Authors: Cliver, E. W.; Kahler, S. W.; Cane, H. V.; Koomen, M. J.;
Michels, D. J.; Howard, R. A.; Sheeley, N. R., Jr.
Bibcode: 1984sii..conf..205C
Altcode:
No abstract at ADS
Title: The GLE-associated flare of 21 August, 1979
Authors: Cliver, E. W.; Kahler, S. W.; Cane, H. V.; Koomen, M. J.;
Michels, D. J.; Howard, R. A.; Sheeley, N. R., Jr.
Bibcode: 1983SoPh...89..181C
Altcode:
We use a variety of ground-based and satellite measurements to identify
the source of the ground level event (GLE) beginning near 06∶30 UT on
21 August, 1979 as the 2B flare with maximum at ∼06∶15 UT in McMath
region 16218. This flare differed from previous GLE-associated flares
in that it lacked a prominent impulsive phase, having a peak ∼9 GHz
burst flux density of only 27 sfu and a ≳20 keV peak hard X-ray flux
of ≲3 × 10-6 ergs cm-2s-1. Also,
McMath 16218 was magnetically less complex than the active regions in
which previous cosmic-ray flares have occurred, containing essentially
only a single sunspot with a rudimentary penumbra. The flare was
associated with a high speed (≳700 km s-1) mass ejection
observed by the NRL white light coronagraph aboard P78-1 and a shock
accelerated (SA) event observed by the low frequency radio astronomy
experiment on ISEE-3.
Title: The Occurrence Frequency of White Light Flares
Authors: Neidig, D. F.; Cliver, E. W.
Bibcode: 1983SoPh...88..275N
Altcode:
We derive an occurrence frequency for white-light flares (WLF) of 15.5
± 4.5 yr−1 during a 2.6 year period following the maximum
of solar cycle 21. This compares with a frequency 5-6 yr−1
derived by McIntosh and Donnelly (1972) during solar cycle 20. We
find that the higher frequency of the more recently observed WLFs is
due to the availability of patrol data at shorter wavelengths (λ ≲
4000 Å), where the contrast of the flare emission is increased; the
improved contrast has allowed less energetic (and hence more frequently
occurring) events to be classified as WLFs. We find that sufficient
conditions for the occurrence of a WLF are: active region magnetic
class = delta; sunspot penumbra class = K, with spot group area ≥
500 millionths of the solar hemisphere; 1-8 Å X-ray burst class ≥ X2.
Title: A catalog of solar white-light flares, including their
statistical properties and associated emissions, 1859 - 1982
Authors: Neidig, D. F.; Cliver, E. W.
Bibcode: 1983STIN...8424521N
Altcode:
This catalog of 57 solar white-light flares reported between 1859
and 1982 includes H-alpha, soft X-ray, and radio emissions associated
with the white-light flares. The following are among the conclusions
resulting from statistical examination of the listed flares and the
active regions in which they occurred: (1) The active regions that
produce white-light flares tend to have the following characteristics:
(a) magnetic class = Delta; (b) classification of the penumbra of the
largest spot = K; and (c) sunspot group area > 500 millionths of the
solar hemisphere. (2) Northern Hemisphere white-light flare activity
begins abruptly about 1 or 2 years before solar maximum, and declines
slowly thereafter. Southern hemisphere white-light flare activity
follows the same pattern, but begins approximately 1 year after solar
maximum. (3) White light flares have a mean latitude of 13 + or - 2 deg
in the Southern Hemisphere but a mean latitude of 18 + or - 1 deg in
the Northern Hemisphere. (4) White-light flares exhibit a north-south
asymmetry with 70% more events having been observed in the Northern
Hemisphere as compared to the southern (the current solar cycle is a
possible exception with southern hemisphere activity dominating) as of
December 1982. (5) There is no compelling evidence of preferred solar
longitudes for white-light flare active regions. Southern Hemisphere
activity during the current cycle is a possible exception.
Title: Nuclear gamma rays and interplanetary proton events.
Authors: Cliver, E. W.; Forrest, D. J.; McGuire, R. E.; von Rosenvinge,
T. T.
Bibcode: 1983ICRC...10..342C
Altcode: 1983ICRC...18j.342C
From February 1980 - February 1982, the Gamma Ray Spectrometer on
the Solar Maximum Mission satellite observed the impulsive phases of
sixteen western hemisphere flares that were associated with prompt
solar proton events. Six of these flares had a detectable excess in
the 4-8 MeV window and four others had detectable continuum emission
above 300 keV. As indicated in earlier studies based on fewer events,
a lack of correlation is found between the peak 10 MeV near-earth
proton fluxes and prompt gamma-ray-line fluences. The two largest
proton events in the sample did not have detectable emission above 300
keV. For the 9 December event, an upper limit for the density of the
ion acceleration region of 8 billion/cu cm or less is obtained for an
acceleration time constant of 1500 s.
Title: Nuclear Gamma Rays and Solar Proton Events
Authors: Cliver, E. W.; Forrest, D. J.; McGuire, R. E.; Rosenvinge,
T. T. V.
Bibcode: 1983ICRC....4...84C
Altcode: 1983ICRC...18d..84C
No abstract at ADS
Title: Secondary Peaks in Solar Microwave Outbursts
Authors: Cliver, E. W.
Bibcode: 1983SoPh...84..347C
Altcode:
Observations are presented for several large solar flares in which a
timing association is observed between late (≳ 30 min after the flash
phase) microwave peaks and late stationary decametric continua. It is
suggested that the late microwave peaks are a phenomenon of the post
flare loop (relaxation) stage of large flares and are caused by field
line reconnections occurring above the Hα and soft X-ray emitting
loops. A simple model to account for the association between the
secondary radio peaks observed at discrete frequencies and the late
decametric continua is proposed.
Title: Solar proton flares with weak impulsive phases
Authors: Cliver, E. W.; Kahler, S. W.; McIntosh, P. S.
Bibcode: 1983ApJ...264..699C
Altcode:
The current picture of a proton flare includes a well-defined impulsive
phase characterized by a prominent hard X-ray (or microwave) peak. Lin
and Hudson have argued that the correlation between intense flare hard
X-ray bursts and large proton events is evidence that the second stage
of particle acceleration is fueled by energy originally contained
in flash phase 10-100 keV electrons. In their examination of large,
prompt, proton events occurring between 1965-1979, however, the authors
found several events that originated in flares with relatively weak
impulsive phases. Various lines of evidence indicate that these flares
were associated with mass ejection events which appear to have been
magnetically driven.
Title: Injection onsets of 2 GeV protons, 1 MeV electrons, and 100
keV electrons in solar cosmic ray flares
Authors: Cliver, E. W.; Kahler, S. W.; Shea, M. A.; Smart, D. F.
Bibcode: 1982ApJ...260..362C
Altcode:
The data for all 32 ground-level cosmic-ray events (GLEs) observed from
1942 through 1978 are reviewed, and injection onset times for the 2 GeV
protons, 1 MeV electrons, and 100 keV electrons are inferred. Contrary
to previous investigations, no compelling evidence is found for a
systematic delay in GLE onset times. The most likely time of GeV
proton injection onset in these large flares appears to be near the
maximum of the first significant microwave peak. GLEs with long delays
to onset tend to be small in size. In addition, the data indicate a
systematic phase relationship among the injection onsets of the three
particle species considered, with the low-energy electron onset times
preceding those of the relativistic protons by not more than 5 min,
and the relativistic electrons following the GeV protons by not less
than 5 min. This phase relationship holds even when the inferred
injection times of all three species follow the flare flash phase
by more than 20 min. To account for these observations, a picture is
suggested in which the earliest observed particles are injected when
an outward moving acceleration region at a shock front intersects the
open field lines connecting to earth.
Title: Associations of Nuclear Gamma Rays with Other Flares Emissions
Authors: Cliver, E.; Share, G.; Chupp, E.; Matz, S.; Howard, R.;
Koomen, M.; McGuire, R.; von Rosenvinge, T.
Bibcode: 1982BAAS...14..874C
Altcode:
No abstract at ADS
Title: Peak-Flux-Density Spectra of Large Solar Radio Bursts
Authors: Cliver, E. W.; Gentile, L. C.; Fink, J. M.
Bibcode: 1982BAAS...14..607C
Altcode:
No abstract at ADS
Title: Sagamore Hill Radio Observatory, Air Force Geophysics
Laboratory, Hanscom Air Force Base, Massachusetts 01731. Report.
Authors: Cliver, E. W.; Eadon, E. J.
Bibcode: 1982BAAS...14..486C
Altcode:
No abstract at ADS
Title: Prompt injection of relativistic protons from the September 1,
1971 solar flare
Authors: Cliver, E. W.
Bibcode: 1982SoPh...75..341C
Altcode:
The September 1, 1971 flare in McMath region 11482 was projected to
have occurred ∼30° behind the west limb. An anisotropic Ground Level
Effect (GLE) began <30 min after the inferred explosive phase of
the flare. We attribute the rapid injection of relativistic protons
onto the earth spiral field line to a shock wave associated with an
observed type II burst.
Title: Observations of an unusual pair of homologous flares on March
17, 1970
Authors: Cliver, E. W.; Wefer, F. L.
Bibcode: 1981SoPh...71...39C
Altcode:
Correlated optical, radio and X-ray observations are presented for a
pair of `consequently' homologous flares which occurred on March 17,
1970. A rich complexity of behavior in a bright sub-flare with maximum
at 14∶44 UT is repeated in a flare of importance 1B with maximum
at 22:49 UT. The unusual and interesting aspect of these flares is
that the second flare developed at approximately half the rate of
the first. A difference in the trigger mechanism of the two flares is
suggested as a possible explanation.
Title: Solar Proton Flares with Weak Impulsive Phases
Authors: Cliver, E. W.; Kahler, S. W.; McIntosh, P. S.
Bibcode: 1981BAAS...13..861C
Altcode:
No abstract at ADS
Title: The Air Force RSTN System
Authors: Guidice, D. A.; Cliver, E. W.; Barron, W. R.; Kahler, S.
Bibcode: 1981BAAS...13Q.553G
Altcode:
No abstract at ADS
Title: Comments on the Duration-Peak-Flux-Density Diagram for 2800
MHz Solar Bursts
Authors: Cliver, E. W.
Bibcode: 1981JRASC..75...15C
Altcode:
The existence of an essentially two-pronged distribution in the
duration-peak-flux-density scatter plot for simple 2800 MHz solar
bursts (Covington and Harvey, 1958) was verified for a more recent data
set. An investigation was made of events that fall between the impulsive
and gradual rise and fall branches of the duration-peak-flux-density
diagram. Such events are rare, with only 51 observed at Ottawa during
the 11 year period studied. A relatively high percentage of these bursts
were associated with proton flares. (This fact may aid in the prediction
of some otherwise difficult-to-forecast proton events.) Smaller
subgroups in the sample include bursts from behind-the-limb flares
and events associated with 'spotless' flares (Dodson and Hedeman, 1970).
Title: Onset delay times of ground-level events
Authors: Cliver, E. W.; Kahler, S. W.; Shea, M. A.; Smart, D. F.
Bibcode: 1981ICRC...10...13C
Altcode: 1982ICRC...10...13C; 1981ICRC...17j..13C
Data are reviewed for all 32 ground-level cosmic ray events (GLEs)
observed from 1942 through 1978. Contrary to previous investigations,
no compelling evidence is found for a systematic delay in GLE onset
times. The data indicate that the delays observed in some events are
due, at least in part, to an observational threshold effect. The most
likely time of proton injection onset in the corona is found to be
either the onset of the Type II burst or the maximum of the first
significant microwave peak.
Title: Observations of Type IV Microwave Emission from Behind-the-Limb
Flares
Authors: Cliver, E. W.
Bibcode: 1980BAAS...12..912C
Altcode:
No abstract at ADS
Title: Sharp-Cutoff Short-Cm Wavelength Bursts from Proton Activity
Centers
Authors: Cliver, E. W.; Guidice, D. A.
Bibcode: 1980BAAS...12..480C
Altcode:
No abstract at ADS
Title: Quasi-periodic burst structure at 2.8 GHz and its relationship
to burst morphological parameters.
Authors: Cliver, E. W.; Hurst, M. D.; Wefer, F. L.; Bleiweiss, M. P.
Bibcode: 1976SoPh...48..307C
Altcode:
Fifteen examples of quasi-periodic 2.8 GHz burst emission observed at
the La Posta Astrogeophysical Observatory during the period December
1966 through May 1973 were identified. The periods of these events and
those of 22 additional events previously reported in the literature
were plotted against burst morphological parameters. The relationship
between period and event energy was found to be considerably weaker
than initially reported by Cribbens and Matthews.