Author name code: leamon
ADS astronomy entries on 2022-09-14
author:Leamon, Robert J.
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Title: Uniting The Sun's Hale Magnetic Cycle and `Extended Solar
Cycle' Paradigms
Authors: McIntosh, Scott W.; Scherrer, Phillip H.; Svalgaard, Leif;
Leamon, Robert J.
Bibcode: 2022arXiv220809026M
Altcode:
Through meticulous daily observation of the Sun's large-scale magnetic
field the Wilcox Solar Observatory (WSO) has catalogued two magnetic
(Hale) cycles of solar activity. Those two (~22-year long) Hale cycles
have yielded four ($\sim$11-year long) sunspot cycles (numbers 21
through 24). Recent research has highlighted the persistence of the
"Extended Solar Cycle" (ESC) and its connection to the fundamental Hale
Cycle - albeit through a host of proxies resulting from image analysis
of the solar photosphere, chromosphere and corona. This short manuscript
presents the correspondence of the ESC, the surface toroidal magnetic
field evolution, and the evolution of the Hale Cycle. As Sunspot Cycle
25 begins, interest in observationally mapping the Hale and Extended
cycles could not be higher given potential predictive capability that
synoptic scale observations can provide.
Title: Deciphering Solar Magnetic Activity: The Solar Cycle Clock
Authors: Leamon, Robert J.; McIntosh, Scott W.; Title, Alan M.
Bibcode: 2022FrASS...9.6670L
Altcode:
The Sun's variability is controlled by the progression and interaction
of the magnetized systems that form the 22-year magnetic activity cycle
(the "Hale Cycle") as they march from their origin at ∼55° latitude
to the equator, over ∼19 years. We will discuss the end point of that
progression, dubbed "terminator" events, and our means of diagnosing
them. In this paper we expand on the Extended Solar Cycle framework to
construct a new solar activity "clock" which maps all solar magnetic
activity onto a single normalized epoch based on the terminations
of Hale Magnetic Cycles. Defining phase 0*2π on this clock as the
Terminators, then solar polar field reversals occur at ∼ 0.2*2π,
and the geomagnetically quiet intervals centered around solar minimum
start at ∼ 0.6*2π and end at the terminator, thus lasting 40% of the
cycle length. At this onset of quiescence, dubbed a "pre-terminator,"
the Sun shows a radical reduction in active region complexity and,
like the terminator events, is associated with the time when the solar
radio flux crosses F10.7 = 90 sfu. We use the terminator-based clock
to illustrate a range of phenomena that further emphasize the strong
interaction of the global-scale magnetic systems of the Hale Cycle: the
vast majority, 96%, of all X-flares happen between the Terminator and
pre-Terminator. In addition to the X-rays from violent flares, rapid
changes in the number of energetic photons—EUV spectral emission
from a hot corona and the F10.7 solar radio flux—impinging on the
atmosphere are predictable from the Terminator-normalized unit cycle,
which has implications for improving the fidelity of atmospheric
modelling.
Title: Interactions Among Magnetic Bands in Extended Solar Cycles
Authors: Belucz, Bernadett; Dikpati, Mausumi; McIntosh, Scott; Erdelyi,
Robertus; Leamon, Robert
Bibcode: 2021AGUFMSH55D1875B
Altcode:
The extended solar cycle, observationally revealed from the evolutions
of ephemeral regions, X-ray and EUV brightpoints, plages, filaments and
faculae, indicates the existence of oppositely-directed double magnetic
bands at the bottom dynamo-layer in each hemisphere. The band-pairs
in the North and South hemispheres migrate towards the equator and
plausibly evolve in amplitude as the cycle progresses. By studying
the MHD interactions of these band-pairs among themselves in each
hemisphere, as well as with their opposite-hemisphere's counterparts,
we show that the cross-equatorial interactions between the low-latitude
bands (which are essentially the active cycle's bands) in the North and
South effectively start when the band-separation across the equator is
less than 30 degrees (the bands are at 15-degree latitude or lower in
the North and South). Analyzing the properties of this interaction we
show how certain changes in the energy extractions by various stresses
from the magnetic fields can lead to the start of the declining phase
of the solar cycle.
Title: Deciphering Solar Magnetic Activity: 140 Years of the `Extended
Solar Cycle' - Mapping the Hale Cycle
Authors: McIntosh, Scott W.; Leamon, Robert J.; Egeland, Ricky;
Dikpati, Mausumi; Altrock, Richard C.; Banerjee, Dipankar; Chatterjee,
Subhamoy; Srivastava, Abhishek K.; Velli, Marco
Bibcode: 2021SoPh..296..189M
Altcode: 2020arXiv201006048M
We investigate the occurrence of the "extended solar cycle" (ESC) as it
occurs in a host of observational data spanning 140 years. Investigating
coronal, chromospheric, photospheric, and interior diagnostics, we
develop a consistent picture of solar activity migration linked to the
22-year Hale (magnetic) cycle using superposed epoch analysis (SEA)
and previously identified Hale cycle termination events as the key
time for the SEA. Our analysis shows that the ESC and Hale cycle,
as highlighted by the terminator-keyed SEA, is strongly recurrent
throughout the entire observational record studied, some 140
years. Applying the same SEA method to the sunspot record confirms
that Maunder's butterfly pattern is a subset of the underlying Hale
cycle, strongly suggesting that the production of sunspots is not
the fundamental feature of the Hale cycle, but the ESC is. The ESC
(and Hale cycle) pattern highlights the importance of 55∘
latitude in the evolution, and possible production, of solar magnetism.
Title: Prediction of the first and last X-Flares of Cycle 25 Active
Regions
Authors: Leamon, Robert; McIntosh, Scott
Bibcode: 2021AGUFMSH55D1881L
Altcode:
The Suns variability is controlled by the progression and interaction
of the magnetized systems that form the 22-year magnetic activity cycle
(the "Hale Cycle") as they march from their origin at ~55 latitude to
the equator, over ~19 years. Recently, we introduced the concept of
"Terminators," the endpoints of those activity bands' progress, and a
new, and more insightful, way of looking at timing solar cycles than
counting spots [McIntosh et al. 2019; Leamon et al. 2020]. Rather
than the canonical minimum number of sunspots (which is arbitrary,
and depends on sum of four decreasing and increasing quantities --
the number of new and old cycle polarity spots in each hemisphere),
consider a precise date -- when there is no more old cycle polarity flux
left on the disk. Expressed in this way, a Terminator is the end of
a Hale Magnetic Cycle. Based on these Terminators, we construct a new
solar cycle phase clock which maps all solar magnetic activity onto a
single normalized epoch. If the Terminators appear at phase 0 * 2, then
solar polar field reversals occur at ~0.2 * 2, and the geomagnetically
quiet intervals centered around solar minimum, which start at 0.6 * 2
and end at the Terminator are thus 40% of the normalized cycle. These
"pre-Terminators" show a radical reduction of complexity of active
regions and (like the Terminators) are well approximated by the time
when the solar radio flux, F10.7 = 90 sfu. We demonstrate that the
vast majority, 96%, of all X-flares happen between the Terminator and
pre-Terminator; the July 2021 event appears to fall just outside this
window, but it is highly possible, if not probable that the Cycle 24
Terminator occurs between the date of abstract submission and the Fall
Meeting itself. Further, sunspot max amplitude, the aa geomagnetic
index, and F10.7 and spectral irradiance are all predictable from a
normalized unit cycle from Terminator to Terminator.
Title: Response to "Limitations in the Hilbert Transform Approach
to Locating Solar Cycle Terminators" by R. Booth
Authors: Leamon, Robert J.; McIntosh, Scott W.; Chapman, Sandra C.;
Watkins, Nicholas W.
Bibcode: 2021SoPh..296..151L
Altcode:
Booth (Solar Phys.296, 108, 2021; hereafter B21) is essentially
a critique of the Hilbert transform techniques used in our paper
(Leamon et al., Solar Phys.295, 36, 2020; hereafter L20) to predict
the termination of solar cycles. Here we respond to his arguments;
our methodology and parameter choices do extract a mathematically
robust signature of terminators from the historical sunspot record. We
agree that the attempt in L20 to extrapolate beyond the sunspot record
gives a failed prediction for the next terminator of May 2020, and we
identify both a possible cause and remedy here. However, we disagree
with the B21 assessment that the likely termination of Solar Cycle 24
is two years after the date predicted in L20, and we show why.
Title: The Sun's Magnetic (Hale) Cycle and 27 Day Recurrences in
the aa Geomagnetic Index
Authors: Chapman, S. C.; McIntosh, S. W.; Leamon, R. J.; Watkins, N. W.
Bibcode: 2021ApJ...917...54C
Altcode: 2021arXiv210102569C
We construct a new solar cycle phase clock which maps each of the last
18 solar cycles onto a single normalized epoch for the approximately 22
yr Hale (magnetic polarity) cycle, using the Hilbert transform of daily
sunspot numbers (SSNs) since 1818. The occurrences of solar maxima show
almost no discernible Hale cycle dependence, consistent with the clock
being synchronized to polarity reversals. We reengineer the Sargent
R27 index and combine it with our epoch analysis to obtain a high time
resolution parameter for 27 day recurrence in aa, ⟨acv(27)⟩. This
reveals that the transition to recurrence, that is, to an ordered
solar wind dominated by high-speed streams, is fast, with an upper
bound of a few solar rotations. It resolves an extended late declining
phase which is approximately twice as long on even Schwabe cycles as
odd. Galactic cosmic ray flux rises in step with ⟨acv(27)⟩ but then
stays high. Our analysis also identifies a slow-timescale trend in
SSN that simply tracks the Gleissberg cycle. We find that this trend
is in phase with the slow-timescale trend in the modulus of sunspot
latitudes, and in antiphase with that of the R27 index.
Title: Termination of Solar Cycles and Correlated Tropospheric
Variability
Authors: Leamon, Robert J.; McIntosh, Scott W.; Marsh, Daniel R.
Bibcode: 2021E&SS....801223L
Altcode:
The Sun provides the energy required to sustain life on Earth and drive
our planet's atmospheric circulation. However, establishing a solid
physical connection between solar and tropospheric variability has posed
a considerable challenge. The canon of solar variability is derived
from the 400 years of observations that demonstrates the waxing and
waning number of sunspots over an 11( ish) year period. Recent research
has demonstrated the significance of the underlying 22 years magnetic
polarity cycle in establishing the shorter sunspot cycle. Integral to
the manifestation of the latter is the spatiotemporal overlapping and
migration of oppositely polarized magnetic bands. We demonstrate the
impact of "terminators"—the end of Hale magnetic cycles—on the
Sun's radiative output and particulate shielding of our atmosphere
through the rapid global reconfiguration of solar magnetism. Using
direct observation and proxies of solar activity going back some
six decades we can, with high statistical significance, demonstrate
a correlation between the occurrence of terminators and the largest
swings of Earth's oceanic indices: the transition from El Niño to La
Niña states of the central Pacific. This empirical relationship is a
potential source of increased predictive skill for the understanding
of El Niño climate variations, a high stakes societal imperative given
that El Niño impacts lives, property, and economic activity around the
globe. A forecast of the Sun's global behavior places the next solar
cycle termination in mid 2020; should a major oceanic swing follow,
then the challenge becomes: when does correlation become causation
and how does the process work?
Title: A clock for the Sun's magnetic Hale cycle and 27 day
recurrences in the aa geomagnetic index
Authors: Chapman, Sandra; McIntosh, Scott; Leamon, Robert; Watkins,
Nicholas
Bibcode: 2021EGUGA..23.2555C
Altcode:
We construct a new solar cycle phase clock which maps each of the last
18 solar cycles onto a single normalized epoch for the approximately
22 year Hale (magnetic polarity) cycle, using the Hilbert transform
of daily sunspot numbers (SSN) since 1818. We use the clock to study
solar and geomagnetic climatology as seen in datasets available
over multiple solar cycles. The occurrence of solar maxima on the
clock shows almost no Hale cycle dependence, confirming that the
clock is synchronized with polarity reversals. The odd cycle minima
lead the even cycle minima by ~ 1.1 normalized years, whereas the
odd cycle terminators (when sunspot bands from opposite hemispheres
have moved to the equator and coincide, thus terminating the cycle,
McIntosh(2019)) lag the even cycle terminators by ~ 2.3 normalized
years. The average interval between each minimum and terminator is
thus relatively extended for odd cycles and shortened for even ones. We
re-engineer the R27 index that was orignally proposed by Sargent(1985)
to parameterize 27 day recurrences in the aa index. We perform an epoch
analysis of autocovariance in the aa index using the Hale cycle clock
to obtain a high time resolution parameter for 27 day recurrence,
<acv(27)>. This reveals that the transition to recurrence,
that is, to an ordered solar wind dominated by high speed streams,
is fast, occurring within 2-3 solar rotations or less. It resolves an
extended late declining phase which is approximately twice as long on
even Schwabe cycles as odd ones. We find that Galactic Cosmic Ray flux
rises in step with <acv(27)> but then stays high. Our analysis
also identifies a slow timescale trend in SSN that simply tracks the
Gleissberg cycle. We find that this trend is in phase with the slow
timescale trend in the modulus of sunspot latitudes, and in antiphase
with that of the R27 index.
Title: Solar Wind Helium Abundance Heralds Solar Cycle Onset
Authors: Alterman, Benjamin L.; Kasper, Justin C.; Leamon, Robert J.;
McIntosh, Scott W.
Bibcode: 2021SoPh..296...67A
Altcode: 2020arXiv200604669A
We study the solar wind helium-to-hydrogen abundance's (AHe)
relationship to solar cycle onset. Using OMNI/Lo data, we show that
AHe increases prior to sunspot number (SSN) minima. We
also identify a rapid depletion and recovery in AHe that
occurs directly prior to cycle onset. This AHe shutoff
happens at approximately the same time across solar wind speeds
(vsw) and the time between successive AHe shutoffs
is typically on the order of the corresponding solar cycle length. In
contrast to AHe's vsw-dependent phase lag with
respect to SSN (Alterman and Kasper, 2019), AHe shutofff's
concurrence across vsw likely implies it is independent of
solar wind acceleration and driven by a mechanism near or below the
photosphere. Using brightpoint (BP) measurements to provide context,
we infer that AHe shutoff is likely related to the overlap
of adjacent solar cycles and the equatorial flux cancelation of the
older, extended solar cycle during solar minima.
Title: Solar Wind Turbulence from 1 to 45 AU
Authors: Pine, Z. B.; Smith, C. W.; Hollick, S.; Argall, M. R.;
Vasquez, B. J.; Isenberg, P. A.; Schwadron, N.; Joyce, C.; Sokol,
J. M.; Bzowski, M.; McLaurin, M. L.; Hamilton, K. E.; Leamon, R. J.
Bibcode: 2020AGUFMSH0160014P
Altcode:
We review five recent publications that extend magnetic turbulence
studies that were pioneered using data from 1 AU to now include Voyager
observations from 1977 through 1990 and 1 to 45 AU. We examine the
spectral scale at which evidence of dissipation sets in and evaluate the
spectral indices, anisotropies, polarizations, and spectral transfer
of energy. We compare the latter to predictions from transport
theory and the rate of energy injection through wave excitation by
newborn interstellar pickup ions. While many of our results agree with
conclusions from 1 AU, we find that the magnetic spectral anisotropy
that relates to the underlying anisotropy of the wave vectors exceeds
theoretical predications for reasons we are unable to determine. We also
establish that wave energy excitation by newborn interstellar pickup H+
forms the dominant energy source driving the turbulence beyond 10 AU.
Title: The Hale Cycle Clock
Authors: Leamon, R. J.; McIntosh, S. W.; Chapman, S. C.; Watkins, N. W.
Bibcode: 2020AGUFMSH053..02L
Altcode:
The Sun's variability is controlled by the progression and interaction
of the magnetized systems that form the 22-year magnetic activity cycle
(the ``Hale Cycle'') as they march from their origin at ∼55 degrees
latitude to the equator, over some 19 years. We will discuss the end
point of that progression, dubbed ``terminator'' events [McIntosh et
al. 2019], and our means of diagnosing them [McIntosh et al. 2019,
Leamon et al., 2020]. Based on these terminations of Hale Magnetic
Cycles, we construct a new solar cycle phase clock which maps all
solar magnetic activity onto a single normalized epoch [Chapman et al,
2020]. If the Terminators appear at phase 0 * 2π , then solar polar
field reversals occur at ∼{}0.2 * 2π , and the geomagnetically
quiet intervals centered around solar minimum, which start at 0.6 * 2π
and end at the terminator are thus 40% of the normalized cycle. These
``pre-terminators'' show a radical reduction of complexity of active
regions and (like the terminators) are well approximated by the time
when the solar radio flux, F10.7=90 sfu. There is thus immediate
applicability for the Hale Cycle Clock to predict when the first and
last X-flares and other severe Space Weather events of Cycle 25 will be
(with the first possibly already happening before the meeting), and
we further will discuss the applicability for confirming the length
of Cycle 25 as early as its polar field reversal near maximum. McIntosh et al., "What the Sudden Death of Solar Cycles Can Tell Us
About the Nature of the Solar Interior," Solar Physics 294, 88 (2020)
Leamon et al., "Timing Terminators: Forecasting Sunspot Cycle 25
Onset," Solar Physics 295, 36 (2020)
Title: Overlapping Magnetic Activity Cycles and the Sunspot Number:
Forecasting Sunspot Cycle 25 Amplitude
Authors: McIntosh, Scott W.; Chapman, Sandra; Leamon, Robert J.;
Egeland, Ricky; Watkins, Nicholas W.
Bibcode: 2020SoPh..295..163M
Altcode: 2020arXiv200615263M
The Sun exhibits a well-observed modulation in the number of spots
on its disk over a period of about 11 years. From the dawn of modern
observational astronomy, sunspots have presented a challenge to
understanding—their quasi-periodic variation in number, first
noted 175 years ago, has stimulated community-wide interest to this
day. A large number of techniques are able to explain the temporal
landmarks, (geometric) shape, and amplitude of sunspot "cycles,"
however, forecasting these features accurately in advance remains
elusive. Recent observationally-motivated studies have illustrated a
relationship between the Sun's 22-year (Hale) magnetic cycle and the
production of the sunspot cycle landmarks and patterns, but not the
amplitude of the sunspot cycle. Using (discrete) Hilbert transforms on
more than 270 years of (monthly) sunspot numbers we robustly identify
the so-called "termination" events that mark the end of the previous
11-yr sunspot cycle, the enhancement/acceleration of the present cycle,
and the end of 22-yr magnetic activity cycles. Using these we extract
a relationship between the temporal spacing of terminators and the
magnitude of sunspot cycles. Given this relationship and our prediction
of a terminator event in 2020, we deduce that sunspot Solar Cycle 25
could have a magnitude that rivals the top few since records began. This
outcome would be in stark contrast to the community consensus estimate
of sunspot Solar Cycle 25 magnitude.
Title: Solar Wind Helium Abundance Heralds the Onset of Solar Cycle 25
Authors: Alterman, B. L.; Kasper, J. C.; Leamon, R. J.; McIntosh, S. W.
Bibcode: 2020AGUFMSH053..01A
Altcode:
We study the solar wind helium-to-hydrogen abundance's (Ahe)
relationship to solar cycle onset. We identify a rapid depletion
and recovery in Ahe immediately prior to sunspot number
(SSN) minima. This depletion happens at approximately the same time
across solar wind speeds, implying that it is formed by a mechanism
distinct from the one that drives Ahe's solar cycle scale
variation and speed-dependent phase offset with respect to SSN. As
Ahe's rapid depletion and recovery have already occurred
and Ahe is now increasing as it has following previous
solar minima, we infer that solar cycle 25 has already begun.
Title: Deciphering Solar Magnetic Activity. The Solar Cycle Clock
Authors: Leamon, Robert; McIntosh, Scott; Title, Alan
Bibcode: 2020arXiv201215186L
Altcode:
The Sun's variability is controlled by the progression and interaction
of the magnetized systems that form the 22-year magnetic activity cycle
(the "Hale Cycle'') as they march from their origin at $\sim$55 degrees
latitude to the equator, over $\sim$19 years. We will discuss the end
point of that progression, dubbed "terminator'' events, and our means
of diagnosing them. Based on the terminations of Hale Magnetic Cycles,
we construct a new solar activity 'clock' which maps all solar magnetic
activity onto a single normalized epoch. The Terminators appear at
phase $0 * 2\pi$ on this clock (by definition), then solar polar
field reversals commence at $\sim0.2 * 2\pi$, and the geomagnetically
quiet intervals centered around solar minimum, start at $\sim0.6 *
2\pi$ and end at the terminator, lasting 40% of the normalized cycle
length. With this onset of quiescence, dubbed a "pre-terminator,''
the Sun shows a radical reduction in active region complexity and (like
the terminator events) is associated with the time when the solar radio
flux crosses F10.7=90 sfu -- effectively marking the commencement of
solar minimum conditions. In this paper we use the terminator-based
clock to illustrate a range of phenomena that further emphasize the
strong interaction of the global-scale magnetic systems of the Hale
Cycle. arXiv:2010.06048 is a companion article.
Title: Solar Wind Turbulence from 1 to 45 au. II. Analysis of
Inertial-range Fluctuations Using Voyager and ACE Observations
Authors: Pine, Zackary B.; Smith, Charles W.; Hollick, Sophia
J.; Argall, Matthew R.; Vasquez, Bernard J.; Isenberg, Philip A.;
Schwadron, Nathan A.; Joyce, Colin J.; Sokół, Justyna M.; Bzowski,
Maciej; Kubiak, Marzena A.; Hamilton, Kathleen E.; McLaurin, Megan L.;
Leamon, Robert J.
Bibcode: 2020ApJ...900...92P
Altcode:
We examine both Voyager and Advanced Composition Explorer magnetic
field measurements at frequencies that characterize the inertial
range using traditional polarization techniques that are designed to
characterize plasma waves. Although we find good agreement with both
the anticipated spectral index of the power spectrum and the scaling
of magnetic power with heliocentric distance, we do not find that the
polarization analyses yield results that can be readily described by
plasma wave theory. The fluctuations are not circularly polarized and
there is a markedly reduced coherence between the components of the
fluctuation. The degree of polarization is also generally low, although
not as low as the coherence, and the minimum variance direction is
essentially random. We conclude that traditional plasma wave theory
may not offer a good description for inertial-range fluctuations.
Title: Solar Wind Turbulence from 1 to 45 au. III. Anisotropy of
Magnetic Fluctuations in the Inertial Range Using Voyager and ACE
Observations
Authors: Pine, Zackary B.; Smith, Charles W.; Hollick, Sophia
J.; Argall, Matthew R.; Vasquez, Bernard J.; Isenberg, Philip A.;
Schwadron, Nathan A.; Joyce, Colin J.; Sokół, Justyna M.; Bzowski,
Maciej; Kubiak, Marzena A.; Hamilton, Kathleen E.; McLaurin, Megan L.;
Leamon, Robert J.
Bibcode: 2020ApJ...900...93P
Altcode:
We examine both Voyager and Advanced Composition Explorer magnetic
field measurements at frequencies that characterize the inertial range
and evaluate the anisotropy of the fluctuations as they relate to both
the compressive component and underlying wavevector anisotropy of the
turbulence. The magnetic fluctuation anisotropy as it relates to the
compressive component is directly dependent upon both the plasma beta
of the thermal proton component and the ratio of magnetic fluctuation
magnitude to the strength of the mean magnetic field. This has been
seen before at 1 au. The magnetic fluctuation anisotropy in the plane
perpendicular to the mean magnetic field, which is a measure of the
anisotropy of the underlying wavevector distribution, should depend on
the angle between the mean magnetic field and the radial direction and
should be confined to values between one and the index of the power
spectrum, which is typically 5/3. Our results show that the average
of this anisotropy exceeds the value of the spectral index and is out
of bounds with the theory. Although the results are suggestive of past
analyses, we find that spherical expansion of the turbulence may offer
at least a partial explanation of the apparent amplification of this
measured anisotropy.
Title: Advanced Composition Explorer Observations of Turbulence from
1998 through 2002: Data Intervals
Authors: Hamilton, Kathleen E.; Smith, Charles W.; Vasquez, Bernard
J.; Leamon, Robert J.
Bibcode: 2020ApJS..250...15H
Altcode:
We have published several papers describing solar wind turbulence at
1 au using data from the Advanced Composition Explorer spacecraft. In
an oversight that we regret, we never published the list of data
intervals that constitute the database of observations. As we have
recently returned to this database of observations in comparisons of
turbulent observations by the Voyager spacecraft against established
results from 1 au, we wish to now correct our oversight and publish the
list of intervals that constitute the 1 au observations. Along with
this, we show the distribution of some common solar wind parameters
as contained within the database.
Title: Solar Wind Turbulence from 1 to 45 au. I. Evidence for
Dissipation of Magnetic Fluctuations Using Voyager and ACE
Observations
Authors: Pine, Zackary B.; Smith, Charles W.; Hollick, Sophia
J.; Argall, Matthew R.; Vasquez, Bernard J.; Isenberg, Philip A.;
Schwadron, Nathan A.; Joyce, Colin J.; Sokół, Justyna M.; Bzowski,
Maciej; Kubiak, Marzena A.; Hamilton, Kathleen E.; McLaurin, Megan L.;
Leamon, Robert J.
Bibcode: 2020ApJ...900...91P
Altcode:
As part of a published effort to study low-frequency magnetic waves
excited by newborn interstellar pickup ions seen by the Voyager
spacecraft, we developed a set of control intervals that represent
the background turbulence when the observations are not dominated
by wave excitation. This paper begins an effort to better understand
solar wind turbulence from 1 to 45 au while spanning greater than one
solar cycle. We first focus on the diagnostics marking the onset of
dissipation. This includes an expected break in the power spectrum
at frequencies greater than the proton cyclotron frequency and a
resultant steepening of the spectrum at higher frequencies. Contrary
to what is established at 1 au, we only see the spectral break in
rare instances. The expected scaling of the spectral index with the
turbulence rate is seen, but it is not as clearly established as it
was at 1 au. We also find that both Voyager data from 1 to 45 au and
Advanced Composition Explorer data from 1 au show significant bias of
the magnetic helicity at dissipation scales when the dissipation-range
power-law spectral index steepens. We conclude that dissipation dynamics
are similar throughout the heliosphere in so far as we have examined
to date.
Title: Quantifying the Solar Cycle Modulation of Extreme Space Weather
Authors: Chapman, S. C.; McIntosh, S. W.; Leamon, R. J.; Watkins, N. W.
Bibcode: 2020GeoRL..4787795C
Altcode:
By obtaining the analytic signal of daily sunspot numbers since 1818
we construct a new solar cycle phase clock that maps each of the last
18 solar cycles onto a single normalized 11 year epoch. This clock
orders solar coronal activity and extremes of the aa index, which
tracks geomagnetic storms at the Earth's surface over the last 14
solar cycles. We identify geomagnetically quiet intervals that are 40%
of the normalized cycle, ±2π/5 in phase or ±2.2 years around solar
minimum. Since 1868 only two severe (aa>300 nT) and one extreme
(aa>500 nT) geomagnetic storms occurred in quiet intervals; 1-3%
of severe (aa>300 nT) geomagnetic storms and 4-6% of C-, M-,
and X-class solar flares occurred in quiet intervals. This provides
quantitative support to planning resilience against space weather
impacts since only a few percent of all severe storms occur in quiet
intervals and their start and end times are quantifiable.
Title: Timing Terminators: Forecasting Sunspot Cycle 25 Onset
Authors: Leamon, Robert J.; McIntosh, Scott W.; Chapman, Sandra C.;
Watkins, Nicholas W.
Bibcode: 2020SoPh..295...36L
Altcode: 2019arXiv190906603L
Recent research has demonstrated the existence of a new type of solar
event, the "terminator." Unlike the Sun's signature events, flares and
coronal mass ejections, the terminator most likely originates in the
solar interior, at or near the tachocline. The terminator signals the
end of a magnetic activity cycle at the Sun's equator and the start
of a sunspot cycle at mid-latitudes. Observations indicate that the
time difference between these events is very short, less than a solar
rotation, in the context of the sunspot cycle. As the (definitive)
start and end point of solar activity cycles the precise timing of
terminators should permit new investigations into the meteorology of
our star's atmosphere. In this article we use a standard method in
signal processing, the Hilbert transform, to identify a mathematically
robust signature of terminators in sunspot records and in radiative
proxies. Using a linear extrapolation of the Hilbert phase of the
sunspot number and F10.7 cm solar radio flux time series we can achieve
higher fidelity historical terminator timing than previous estimates
have permitted. Further, this method presents a unique opportunity
to project, from analysis of sunspot data, when the next terminator
will occur, May 2020 (+4 , −1.5 months), and trigger the growth of
Sunspot Cycle 25.
Title: Timing Terminators: Forecasting Sunspot Cycle 25 Onset,
Activity Levels and Overcoming Social Constraints That Hamper Progress
Authors: Leamon, R. J.; McIntosh, S. W.
Bibcode: 2019AGUFMSA11C3234L
Altcode:
Recent research has demonstrated the existence of a new type of
solar event, the ``terminator''. Unlike the Sun's signature events,
flares and Coronal Mass Ejections, the terminator takes place in
the solar interior. The terminator signals the end of a magnetic
activity cycle at the Sun's equator and the start of a sunspot cycle
at mid latitudes. Observations indicate that the time difference
between these events is very short, less than a solar rotation, in the
context of the sunspot cycle. As the (definitive) start and end point of
solar activity cycles the precise timing of terminators should permit
new investigations into the meteorology of our star's atmosphere. In
this letter we use a standard method in signal processing, the Hilbert
transform, to identify a mathematically robust signature of terminators
in sunspot records and in radiative proxies. Using this technique we
can achieve higher fidelity terminator timing than previous estimates
have permitted. Further, this method presents a unique opportunity to
project when the next terminator will occur, 2020.33(± 0.16), and
trigger the growth of sunspot cycle 25. We also will use this
method to show why Cycle 23 was unusually long, why the Cycle 23-24
minimum was unusually quiet, and why neither of these occurrences
will happen with the end of Cycle 24. Ignoring the wealth of
observational evidence and viewing the solar activity cycle as merely
the growth and decay of sunspot number is one ``social constraint that
hampers progress" to be overcome.
Title: What the Sudden Death of Solar Cycles Can Tell Us About the
Nature of the Solar Interior
Authors: McIntosh, Scott W.; Leamon, Robert J.; Egeland, Ricky;
Dikpati, Mausumi; Fan, Yuhong; Rempel, Matthias
Bibcode: 2019SoPh..294...88M
Altcode: 2019arXiv190109083M
We observe the abrupt end of solar-activity cycles at the Sun's
Equator by combining almost 140 years of observations from ground and
space. These "terminator" events appear to be very closely related to
the onset of magnetic activity belonging to the next solar cycle at
mid-latitudes and the polar-reversal process at high latitudes. Using
multi-scale tracers of solar activity we examine the timing of these
events in relation to the excitation of new activity and find that the
time taken for the solar plasma to communicate this transition is of
the order of one solar rotation - but it could be shorter. Utilizing
uniquely comprehensive solar observations from the Solar Terrestrial
Relations Observatory (STEREO) and Solar Dynamics Observatory (SDO)
we see that this transitional event is strongly longitudinal in
nature. Combined, these characteristics suggest that information
is communicated through the solar interior rapidly. A range of
possibilities exist to explain such behavior: for example gravity
waves on the solar tachocline, or that the magnetic fields present
in the Sun's convection zone could be very large, with a poloidal
field strengths reaching 50 kG - considerably larger than conventional
explorations of solar and stellar dynamos estimate. Regardless of the
mechanism responsible, the rapid timescales demonstrated by the Sun's
global magnetic-field reconfiguration present strong constraints on
first-principles numerical simulations of the solar interior and,
by extension, other stars.
Title: Terminators: Predicting the end of sunspot cycle 24 and its
impacts on space weather, weather and climate.
Authors: Leamon, Robert; McIntosh, Scott W.
Bibcode: 2019AAS...23430503L
Altcode:
Recent research has demonstrated the existence of a new type of solar
"event." Unlike the signature events in the corona, flares and Coronal
Mass Ejections, this event, the Terminator, takes place in the solar
interior (at the Sun's equator), signalling the end of a magnetic
activity cycle and the start of a sunspot cycle at mid latitudes -
all at the same time. Observations indicate that the hand-over between
the termination of the magnetic activity cycle and the blooming of the
next sunspot cycle could be very short, possibly much less than a solar
rotation. Here we demonstrate the impact of these terminators on
the Sun's radiative output and particulate shielding of our atmosphere
through the dramatically rapid reconfiguration of solar magnetism. Using
direct observation and proxies of solar activity going back six decades
we can, with high statistical significance, demonstrate an apparent
correlation between the solar cycle terminations and the largest swings
of Earth's oceanic indices - a previously overlooked correspondence. We then use a standard method in signal processing, the Hilbert
transform, to investigate the presence, and identify the signature, of
terminators in solar magnetic and radiative proxies. Using many decades
of such data we can achieve higher fidelity on terminator timing than
previous estimates have allowed. The distinct signature presents
a unique opportunity to project when the next terminator will occur,
April 2020 (± two months) and sunspot cycle 25 will commence its growth
phase. Further, April 2020 implies cycle 24 will only be 9.25 years
long; we offer an explanation as to why cycle 24 is short (or rather,
why cycle 23 and its "unusual solar minimum" was so long). Finally,
should a major ENSO swing follow next year, our challenge becomes:
when does correlation become causation and how does the process work?
Title: Signature of Extended Solar Cycles as Detected from Ca II K
Synoptic Maps of Kodaikanal and Mount Wilson Observatory
Authors: Chatterjee, Subhamoy; Banerjee, Dipankar; McIntosh, Scott
W.; Leamon, Robert J.; Dikpati, Mausumi; Srivastava, Abhishek K.;
Bertello, Luca
Bibcode: 2019ApJ...874L...4C
Altcode: 2019arXiv190303598C
In recent years there has been a resurgence of the study of extended
solar cycles (ESCs) through observational proxies mainly in extreme
ultraviolet. But most of them are limited only to the space-based era
covering only about two solar cycles. Long-term historical data sets
are worth examining for the consistency of ESCs. The Kodaikanal Solar
Observatory (KSO) and the Mount Wilson Observatory (MWO) are two major
sources of long-term Ca II K digitized spectroheliograms covering the
temporal spans of 1907-2007 and 1915-1985 respectively. In this study,
we detected supergranule boundaries, commonly known as networks, using
the Carrington maps from both KSO and MWO data sets. Subsequently
we excluded the plage areas to consider only the quiet Sun (QS) and
detected small-scale bright features through intensity thresholding
over the QS network. Latitudinal density of those features, which we
named “Network Bright Elements,” could clearly depict the existence
of overlapping cycles with equatorward branches starting at latitude
≈55° and taking about 15 ± 1 yr to reach the equator. We performed
a superposed epoch analysis to depict the similarity of those extended
cycles. Knowledge of such equatorward band interaction, for several
cycles, may provide critical constraints on solar dynamo models.
Title: Termination of Solar Cycles and Correlated Tropospheric
Variability
Authors: Leamon, Robert J; McIntosh, Scott W.; Marsh, Daniel R.
Bibcode: 2018arXiv181202692L
Altcode:
The Sun provides the energy required to sustain life on Earth and
drive our planet's atmospheric circulation. However, establishing a
solid physical connection between solar and tropospheric variability
has posed a considerable challenge across the spectrum of Earth-system
science. The canon of solar variability, the solar fiducial clock, lies
almost exclusively with the 400 years of human telescopic observations
that demonstrates the waxing and waning number of sunspots, over an
11(ish) year period. Recent research has demonstrated the critical
importance of the underlying 22-year magnetic polarity cycle in
establishing the shorter sunspot cycle. Integral to the manifestation
of the latter is the spatio-temporal overlapping and migration of
oppositely polarized magnetic bands. The points when these bands emerge
at high solar latitudes and cancel at the equator are separated by
almost 20 years. Here we demonstrate the impact of these "termination"
points on the Sun's radiative output and particulate shielding of
our atmosphere through the dramatically rapid reconfiguration of solar
magnetism. These events reset the Sun's fiducial clock and present a new
portal to explore the Sun-Earth connection. Using direct observation
and proxies of solar activity going back six decades we can, with
high statistical significance, demonstrate an apparent correlation
between the solar cycle terminations and the largest swings of Earth's
oceanic indices---a previously overlooked correspondence. Forecasting
the Sun's global behavior places the next solar termination in early
2020; should a major oceanic swing follow, our challenge becomes:
when does correlation become causation and how does the process work?
Title: The Extended Solar Cycle: Muddying the Waters of Solar/Stellar
Dynamo Modeling Or Providing Crucial Observational Constraints?
Authors: Srivastava, Abhishek K.; McIntosh, Scott W.; Arge,
N.; Banerjee, Dipankar; Dikpati, Mausumi; Dwivedi, Bhola N.;
Guhathakurta, Madhulika; Karak, B. B.; Leamon, Robert J.; Matthew,
Shibu K.; Munoz-Jaramillo, Andres; Nandy, D.; Norton, Aimee; Upton,
L.; Chatterjee, S.; Mazumder, Rakesh; Rao, Yamini K.; Yadav, Rahul
Bibcode: 2018FrASS...5...38S
Altcode: 2018arXiv180707601S
In 1844 Schwabe discovered that the number of sunspots increased and
decreased over a period of about 11 years, that variation became known
as the sunspot cycle. Almost eighty years later, Hale described the
nature of the Sun's magnetic field, identifying that it takes about 22
years for the Sun's magnetic polarity to cycle. It was also identified
that the latitudinal distribution of sunspots resembles the wings of
a butterfly showing migration of sunspots in each hemisphere that
abruptly start at mid-latitudes (about ±35(o) ) towards the Sun's
equator over the next 11 years. These sunspot patterns were shown
to be asymmetric across the equator. In intervening years, it was
deduced that the Sun (and sun-like stars) possess magnetic activity
cycles that are assumed to be the physical manifestation of a dynamo
process that results from complex circulatory transport processes in
the star's interior. Understanding the Sun's magnetism, its origin
and its variation, has become a fundamental scientific objective
the distribution of magnetism, and its interaction with convective
processes, drives various plasma processes in the outer atmosphere
that generate particulate, radiative, eruptive phenomena and shape the
heliosphere. In the past few decades, a range of diagnostic techniques
have been employed to systematically study finer scale magnetized
objects, and associated phenomena. The patterns discerned became
known as the ``Extended Solar Cycle'' (ESC). The patterns of the ESC
appeared to extend the wings of the activity butterfly back in time,
nearly a decade before the formation of the sunspot pattern, and to
much higher solar latitudes. In this short review, we describe their
observational patterns of the ESC and discuss possible connections
to the solar dynamo as we depart on a multi-national collaboration to
investigate the origins of solar magnetism through a blend of archived
and contemporary data analysis with the goal of improving solar dynamo
understanding and modeling.
Title: The Heliospheric Meteorology Mission: A Mission to DRIVE our
Understanding of Heliospheric Variability
Authors: McIntosh, Scott W.; Leamon, Robert J.
Bibcode: 2018FrASS...5...21M
Altcode:
To make transformational scientific progress with the space weather
enterprise the Sun, Earth, and heliosphere must be studied as
a coupled system, comprehensively. Rapid advances were made in the
study, and forecasting, of terrestrial meteorology half a century ago
that accompanied the dawn of earth observing satellites. Those assets
provided a global perspective on the Earth's weather systems and the
ability to look ahead of the observer's local time. From a heliospheric,
or space, weather perspective we have the same fundamental limitation
as the terrestrial meteorologists had - by far the majority of our
observing assets are tied to the Sun-Earth line - our planet's "local
time" with respect to the Sun. This perspective intrinsically limits
our ability to "see what is coming around the solar limb" far less to
gain any insight into the global patterns of solar weather and how they
guide weather throughout the heliosphere. We propose a mission concept
- the Heliospheric Meteorology Mission (HMM) - to sample the complete
magnetic and thermodynamic state of the heliosphere inside 1AU using
a distributed network of deep space hardened smallsats that encompass
the Sun. The observations and in situ plasma measurements made by the
fleet of HMM smallsats would be collected, and assimilated into current
operational space weather models. Further, the HMM measurements would
also being used in an nationally coordinated research effort - at the
frontier of understanding the coupled heliospheric system.
Title: The Longitudinal Evolution of Equatorial Coronal Holes
Authors: Krista, Larisza D.; McIntosh, Scott W.; Leamon, Robert J.
Bibcode: 2018AJ....155..153K
Altcode:
In 2011, three satellites—the Solar-Terrestrial RElations Observatory
A & B, and the Solar Dynamics Observatory (SDO)—were in a
unique spatial alignment that allowed a 360° view of the Sun. This
alignment lasted until 2014, the peak of solar cycle 24. Using extreme
ultraviolet images and Hovmöller diagrams, we studied the lifetimes
and propagation characteristics of coronal holes (CHs) in longitude
over several solar rotations. Our initial results show at least three
distinct populations of “low-latitude” or “equatorial” CHs
(below 65^\circ latitude). One population rotates in retrograde
direction and coincides with a group of long-lived (over sixty days)
CHs in each hemisphere. These are typically located between 30°
and 55^\circ , and display velocities of ∼55 m s-1
slower than the local differential rotation rate. A second, smaller
population of CHs rotate prograde, with velocities between ∼20 and
45 m s-1. This population is also long-lived, but observed
±10° from the solar equator. A third population of CHs are short-lived
(less than two solar rotations), and they appear over a wide range
of latitudes (±65°) and exhibit velocities between -140 and 80 m
s-1. The CH “butterfly diagram” we developed shows a
systematic evolution of the longer-lived holes; however, the sample
is too short in time to draw conclusions about possible connections
to dynamo-related phenomena. An extension of the present work to the
22 years of the combined SOHO-SDO archives is necessary to understand
the contribution of CHs to the decadal-scale evolution of the Sun.
Title: Terminator 2020: Get Ready for the "Event" of The Next Decade
Authors: McIntosh, S. W.; Leamon, R. J.; Fan, Y.; Rempel, M.;
Dikpati, M.
Bibcode: 2017AGUFMSH22B..06M
Altcode:
The abrupt end of solar activity cycles 22 and 23 at the Sun's
equator are observed with instruments from the Solar and Heliospheric
Observatory (SOHO), Solar Terrestrial Relations Observatory (STEREO),
and Solar Dynamics Observatory (SDO). These events are remarkable in
that they rapidly trigger the onset of magnetic activity belonging
to the next solar cycle at mid-latitudes. The triggered onset of new
cycle flux emergence leads to blossoming of the new cycle shortly
thereafter. Using small-scale tracers of magnetic solar activity we
examine the timing of the cycle ``termination points'' in relation
to the excitation of new activity and find that the time taken
for the solar plasma to communicate this transition is less than
one solar rotation, and possibly as little as a eight days. This
very short transition time implies that the mean magnetic field
present in the Sun's convection zone is approximately 80 kG. This
value may be considerably larger than conventional explorations
estimate and therefore, have a significant dynamical impact on the
physical appearance of solar activity, and considerably impacting
our ability to perform first-principles numerical simulations of the
same. Should solar cycle 24 [and 25] continue in their progression
we anticipate that a termination event of this type should occur in
the 2020 timeframe. PSP will have a front row seat to observe this
systemic flip in solar magnetism and the induced changes in our star's
radiative and partiuculate output. Such observations may prove to be
critical in assessing the Sun's ability to force short term evolution
in the Earth's atmosphere.
Title: Predicting the La Niña of 2020-21: Termination of Solar
Cycles and Correlated Variance in Solar and Atmospheric Variability
Authors: Leamon, R. J.; McIntosh, S. W.
Bibcode: 2017AGUFMSH42A..05L
Altcode:
Establishing a solid physical connection between solar and tropospheric
variability has posed a considerable challenge across the spectrum
of Earth-system science. Over the past few years a new picture
to describe solar variability has developed, based on observing,
understanding and tracing the progression, interaction and intrinsic
variability of the magnetized activity bands that belong to the Sun's
22-year magnetic activity cycle. The intra- and extra-hemispheric
interaction of these magnetic bands appear to explain the occurrence
of decadal scale variability that primarily manifests itself in the
sunspot cycle. However, on timescales of ten months or so, those bands
posses their own internal variability with an amplitude of the same
order of magnitude as the decadal scale. The latter have been tied to
the existence of magnetized Rossby waves in the solar convection zone
that result in surges of magnetic flux emergence that correspondingly
modulate our star's radiative and particulate output. One of the most
important events in the progression of these bands is their (apparent)
termination at the solar equator that signals a global increase in
magnetic flux emergence that becomes the new solar cycle. We look at
the particulate and radiative implications of these termination points,
their temporal recurrence and signature, from the Sun to the Earth,
and show the correlated signature of solar cycle termination events and
major oceanic oscillations that extend back many decades. A combined
one-two punch of reduced particulate forcing and increased radiative
forcing that result from the termination of one solar cycle and rapid
blossoming of another correlates strongly with a shift from El Niño to
La Niña conditions in the Pacific Ocean. This shift does not occur at
solar minima, nor solar maxima, but at a particular, non-periodic, time
in between. The failure to identify these termination points, and their
relative irregularity, have inhibited a correlation to be observed and
physical processes to be studied. This result potentially opens the door
to a broader understanding of solar variability on our planet and its
weather. Ongoing tracking of solar magnetic band migration indicates
that Cycle 24 will terminate in the 2020 timeframe and thus we may
expect to see an attendant shift to La Niña conditions at that time.
Title: Deciphering Solar Magnetic Activity: Spotting Solar Cycle 25
Authors: McIntosh, Scott W.; Leamon, Robert J.
Bibcode: 2017FrASS...4....4M
Altcode: 2017arXiv170204414M
We present observational signatures of solar cycle 25 onset. Those
signatures are visibly following a migratory path from high to
low latitudes. They had starting points that are asymmetrically
offset in each hemisphere at times that are 21-22 years after the
corresponding, same polarity, activity bands of solar cycle 23 started
their migration. Those bands define the so-called "extended solar
cycle." The four magnetic bands currently present in the system are
approaching a mutually cancelling configuration, and solar minimum
conditions are imminent. Further, using a tuned analysis of the daily
band latitude-time diagnostics, we are able to utilize the longitudinal
wave number (m=1) variation in the data to more clearly reveal the
presence of the solar cycle 25 bands. This clarification illustrates
that prevalently active longitudes (different in each hemisphere) exist
at mid-latitudes presently, lasting many solar rotations, that can be
used for detailed study over the next several years with instruments
like the Spectrograph on IRIS, the Spectropolarimeter on Hinode, and,
when they come online, similar instruments on the Daniel K. Inouye
Solar Telescope (DKIST) as we watch those bands evolve following the
cancellation of the solar cycle 24 activity bands at the equator late
in 2019.
Title: The detection of Rossby-like waves on the Sun
Authors: McIntosh, Scott W.; Cramer, William J.; Pichardo Marcano,
Manuel; Leamon, Robert J.
Bibcode: 2017NatAs...1E..86M
Altcode:
Rossby waves are a type of global-scale wave that develops in planetary
atmospheres, driven by the planet's rotation1. They propagate
westward owing to the Coriolis force, and their characterization enables
more precise forecasting of weather on Earth2,3. Despite
the massive reservoir of rotational energy available in the Sun's
interior and decades of observational investigation, their solar
analogue defies unambiguous identification4-6. Here we
analyse a combined set of images obtained by the Solar TErrestrial
RElations Observatory (STEREO) and the Solar Dynamics Observatory (SDO)
spacecraft between 2011 and 2013 in order to follow the evolution
of small bright features, called brightpoints, which are tracers of
rotationally driven large-scale convection7. We report the
detection of persistent, global-scale bands of magnetized activity
on the Sun that slowly meander westward in longitude and display
Rossby-wave-like behaviour. These magnetized Rossby waves allow us to
make direct connections between decadal-scale solar activity and that
on much shorter timescales. Monitoring the properties of these waves,
and the wavenumber of the disturbances that they generate, has the
potential to yield a considerable improvement in forecast capability
for solar activity and related space weather phenomena.
Title: Coronal Holes and Open Magnetic Flux over Cycles 23 and 24
Authors: Lowder, Chris; Qiu, Jiong; Leamon, Robert
Bibcode: 2017SoPh..292...18L
Altcode: 2016arXiv161207595L
As the observational signature of the footprints of solar magnetic
field lines open into the heliosphere, coronal holes provide a
critical measure of the structure and evolution of these lines. Using a
combination of Solar and Heliospheric Observatory/Extreme ultraviolet
Imaging Telescope (SOHO/EIT), Solar Dynamics Observatory/Atmospheric
Imaging Assembly (SDO/AIA), and Solar Terrestrial Relations
Observatory/Extreme Ultraviolet Imager (STEREO/EUVI A/B) extreme
ultraviolet (EUV) observations spanning 1996 - 2015 (nearly
two solar cycles), coronal holes are automatically detected and
characterized. Coronal hole area distributions show distinct behavior
in latitude, defining the domain of polar and low-latitude coronal
holes. The northern and southern polar regions show a clear asymmetry,
with a lag between hemispheres in the appearance and disappearance of
polar coronal holes.
Title: Driving the Heliospheric Jellyfish
Authors: Leamon, R. J.; Mcintosh, S. W.
Bibcode: 2016AGUFMSH31B2550L
Altcode:
Recent observational work has demonstrated that the enigmatic
sunspotcycle and global magnetic environment of the Sun which source
theeruptive events and modulate the solar wind, respectively,
can beexplained in terms of the intra- and extra-hemispheric
interaction ofmagnetic activity bands that belong to the 22-year
magnetic polaritycycle. Those activity bands appear to be anchored
deep in the Sun'sconvective interior and governed by the rotation of
our star's radiativezone. We have also observed that those magnetic
bands exhibit strongquasi-annual variability in the rotating convecting
system which resultsin a significant local modulation of solar surface
magnetism, forcingthe production of large eruptive events in each
hemisphere that mouldsthe global-scale solar magnetic field and the
solar-wind-inflatedheliosphere. Together with significant changes
in the Sun's ultraviolet(UV), extreme ultraviolet (EUV), and X-Ray
irradiance, these eruptivefluctuations ensnare all the Heliosphere
(all of Heliophysics) like thetentacles of a jellyfish, and can be
inferred in variations of suchwide-ranging phenomena as the South
Atlantic Anomaly, the thermosphere,the radiation belts, and the can
address ``Has Voyager left theHeliosphere?''
Title: Coronal Holes and Magnetic Flux Ropes Interweaving Solar Cycles
Authors: Lowder, Chris; Yeates, Anthony; Leamon, Robert; Qiu, Jiong
Bibcode: 2016usc..confE..67L
Altcode:
Coronal holes, dark patches observed in solar observations in extreme
ultraviolet and x-ray wavelengths, provide an excellent proxy for
regions of open magnetic field rooted near the photosphere. Through a
multi-instrument approach, including SDO data, we are able to stitch
together high resolution maps of coronal hole boundaries spanning
the past two solar activity cycles. These observational results
are used in conjunction with models of open magnetic field to probe
physical solar parameters. Magnetic flux ropes are commonly defined
as bundles of solar magnetic field lines, twisting around a common
axis. Photospheric surface flows and magnetic reconnection work in
conjunction to form these ropes, storing magnetic stresses until
eruption. With an automated methodology to identify flux ropes within
observationally driven magnetofrictional simulations, we can study
their properties in detail. Of particular interest is a solar-cycle
length statistical description of eruption rates, spatial distribution,
magnetic orientation, flux, and helicity. Coronal hole observations
can provide useful data about the distribution of the fast solar wind,
with magnetic flux ropes yielding clues as to ejected magnetic field
and the resulting space weather geo-effectiveness. With both of these
cycle-spanning datasets, we can begin to form a more detailed picture of
the evolution and consequences of both sets of solar magnetic features.
Title: Deciphering Solar Magnetic Activity: On Grand Minima in
Solar Activity
Authors: Mcintosh, Scott; Leamon, Robert
Bibcode: 2015FrASS...2....2M
Altcode: 2015arXiv150502326M
The Sun provides the energy necessary to sustain our existence. While
the Sun provides for us, it is also capable of taking away. The weather
and climatic scales of solar evolution and the Sun-Earth connection are
not well understood. There has been tremendous progress in the century
since the discovery of solar magnetism - magnetism that ultimately
drives the electromagnetic, particulate and eruptive forcing of our
planetary system. There is contemporary evidence of a decrease in solar
magnetism, perhaps even indicators of a significant downward trend,
over recent decades. Are we entering a minimum in solar activity that is
deeper and longer than a typical solar minimum, a "grand minimum"? How
could we tell if we are? What is a grand minimum and how does the Sun
recover? These are very pertinent questions for modern civilization. In
this paper we present a hypothetical demonstration of entry and exit
from grand minimum conditions based on a recent analysis of solar
features over the past 20 years and their possible connection to the
origins of the 11(-ish) year solar activity cycle.
Title: The Quasi-Annual Forcing of The Sun’s Eruptive, Radiative,
and Particulate Output: Pervasive Throughout The Heliosphere
Authors: Leamon, Robert J.; McIntosh, Scott W.
Bibcode: 2015TESS....130806L
Altcode:
The eruptive, radiative, and particulate output of the Sun are modulated
by our star’s enigmatic 11-year sunspot cycle. Over the past year
we have identified observational signatures which illustrate the ebb
and flow of the 11-year cycle - arising from the temporal overlap of
migrating activity bands which belong to the 22-year magnetic activity
cycle. (At the 2012 Fall AGU Meeting, Leamon & McIntosh presented
a prediction of minimum conditions developing in 2017 and Cycle 25
sunspots first appearing in late 2019.) As a consequence of this work we
have deduced that the latitudinal interaction of the oppositely signed
magnetic activity bands in each hemisphere (and across the equator near
solar minimum) dramatically impacts the production of Space Weather
events such as flares and Coronal Mass Ejections (CMEs). The same set
of observations also permits us to identify a quasi-annual variability
in the rotating convecting system which results in a significant local
modulation of solar surface magnetism. That modulation, in turn, forces
prolonged periods of significantly increased flare and CME production,
as well as significant changes in the Sun's ultraviolet (UV), extreme
ultraviolet (EUV), and X-Ray irradiance. These fluctuations manifest
themselves throughout the Heliosphere (throughout Heliophysics)
and can be inferred in variations of such wide-ranging phenomena as
the South Atlantic Anomaly, the thermosphere, the radiation belts,
and the can address "Has Voyager left the Heliosphere?"
Title: Modified Rossby Waves in the Solar Interior
Authors: McIntosh, Scott W.; Title, Alan M.; Leamon, Robert J.
Bibcode: 2015TESS....110501M
Altcode:
Using a combination of STEREO/SECCHI/EUVI and SDO/AIA imaging we reveal
patterns in the imaging data that are consistent in appearance with
global scale rotationally driven waves on the activity bands of the
solar magnetic polarity cycle.
Title: The solar magnetic activity band interaction and instabilities
that shape quasi-periodic variability
Authors: McIntosh, Scott W.; Leamon, Robert J.; Krista, Larisza D.;
Title, Alan M.; Hudson, Hugh S.; Riley, Pete; Harder, Jerald W.; Kopp,
Greg; Snow, Martin; Woods, Thomas N.; Kasper, Justin C.; Stevens,
Michael L.; Ulrich, Roger K.
Bibcode: 2015NatCo...6.6491M
Altcode: 2015NatCo...6E6491M
Solar magnetism displays a host of variational timescales of which
the enigmatic 11-year sunspot cycle is most prominent. Recent work
has demonstrated that the sunspot cycle can be explained in terms of
the intra- and extra-hemispheric interaction between the overlapping
activity bands of the 22-year magnetic polarity cycle. Those
activity bands appear to be driven by the rotation of the Sun's
deep interior. Here we deduce that activity band interaction can
qualitatively explain the `Gnevyshev Gap'--a well-established feature
of flare and sunspot occurrence. Strong quasi-annual variability in the
number of flares, coronal mass ejections, the radiative and particulate
environment of the heliosphere is also observed. We infer that this
secondary variability is driven by surges of magnetism from the activity
bands. Understanding the formation, interaction and instability of
these activity bands will considerably improve forecast capability in
space weather and solar activity over a range of timescales.
Title: Grand Minima: Is The Sun Going To Sleep?
Authors: Mcintosh, S. W.; Leamon, R. J.
Bibcode: 2014AGUFMSH21C4128M
Altcode:
We explore recent observational work which indicate that the energetics
of the sun's outer atmosphere have been on a steady decline for the past
decade and perhaps longer. Futher, we show that new investigations into
evolution of the Sun's global magnetic activity appear to demonstrate a
path through which the Sun can go into, and exit from, a grand activity
minimum without great difficulty while retaining an activity cycle -
only losing sunspots. Are we at the begining of a new grand(-ish)
minimum? Naturally, only time will tell, but the observational
evidence hint that one may not be far off to what impact on the
Sun-Earth Connection.
Title: Solar Coronal Holes and Open Magnetic Flux
Authors: Lowder, C.; Qiu, J.; Leamon, R. J.; Longcope, D. W.
Bibcode: 2014AGUFMSH13A4081L
Altcode:
Using SDO/AIA and STEREO/EUVI EUV data in conjunction with an
instrument-specific adaptive intensity thresholding algorithm, we are
able to track coronal hole boundaries across the entire solar surface at
a cadence of 12 hours. SOHO/EIT provides earlier era data, allowing the
building EUV coronal hole maps over the course of a solar rotation. We
find that for solar cycle 23 the unsigned magnetic flux enclosed
by coronal hole boundaries ranges from (2-5)x10^{22} Mx, covering
5%-17% of the solar surface. For solar cycle 24 this flux ranges from
(2-4)x10^{22} Mx, covering 5%-10% of the solar surface. Using a surface
flux transport model, we compare observational coronal hole boundaries
and computed potential open field for solar cycles 23 and 24. From both
our observed coronal holes and modeled open magnetic field, we find that
low-latitude regions are significant in area, contributing to the total
open magnetic flux, and should be considered in more significant detail.
Title: On Magnetic Activity Band Overlap, Interaction, and the
Formation of Complex Solar Active Regions
Authors: McIntosh, Scott W.; Leamon, Robert J.
Bibcode: 2014ApJ...796L..19M
Altcode: 2014arXiv1410.6411M
Recent work has revealed a phenomenological picture of the how the
~11 yr sunspot cycle of the Sun arises. The production and destruction
of sunspots is a consequence of the latitudinal-temporal overlap and
interaction of the toroidal magnetic flux systems that belong to the 22
yr magnetic activity cycle and are rooted deep in the Sun's convective
interior. We present a conceptually simple extension of this work,
presenting a hypothesis on how complex active regions can form as a
direct consequence of the intra- and extra-hemispheric interaction
taking place in the solar interior. Furthermore, during specific
portions of the sunspot cycle, we anticipate that those complex active
regions may be particularly susceptible to profoundly catastrophic
breakdown, producing flares and coronal mass ejections of the most
severe magnitude.
Title: Deciphering Solar Magnetic Activity. I. On the Relationship
between the Sunspot Cycle and the Evolution of Small Magnetic Features
Authors: McIntosh, Scott W.; Wang, Xin; Leamon, Robert J.; Davey,
Alisdair R.; Howe, Rachel; Krista, Larisza D.; Malanushenko, Anna V.;
Markel, Robert S.; Cirtain, Jonathan W.; Gurman, Joseph B.; Pesnell,
William D.; Thompson, Michael J.
Bibcode: 2014ApJ...792...12M
Altcode: 2014arXiv1403.3071M
Sunspots are a canonical marker of the Sun's internal magnetic
field which flips polarity every ~22 yr. The principal variation of
sunspots, an ~11 yr variation, modulates the amount of the magnetic
field that pierces the solar surface and drives significant variations
in our star's radiative, particulate, and eruptive output over that
period. This paper presents observations from the Solar and Heliospheric
Observatory and Solar Dynamics Observatory indicating that the 11
yr sunspot variation is intrinsically tied to the spatio-temporal
overlap of the activity bands belonging to the 22 yr magnetic activity
cycle. Using a systematic analysis of ubiquitous coronal brightpoints
and the magnetic scale on which they appear to form, we show that the
landmarks of sunspot cycle 23 can be explained by considering the
evolution and interaction of the overlapping activity bands of the
longer-scale variability.
Title: Solar Coronal Holes and Open Magnetic Flux
Authors: Lowder, Chris; Qiu, Jiong; Leamon, Robert; Longcope, Dana;
Liu, Yang
Bibcode: 2014shin.confE..27L
Altcode:
Coronal holes are regions on the Sun"s surface that map the footprints
of open magnetic field lines. Using SDO/AIA and STEREO/EUVI EUV data
coupled with an adaptive thresholding routine we are able to track the
boundaries of coronal holes across the entire solar surface at a cadence
of 12 hours. Notably, the combination of AIA and EUVI data allows
for the continuous tracking of coronal hole boundary evolution on the
far-side of the sun. Incorporating SOHO/EIT data allows access to these
boundaries spanning the previous solar cycle. We find that for solar
cycle 23 the unsigned magnetic flux enclosed by coronal hole boundaries
ranges from (2-5)x10^22 Mx, covering 5%-17% of the solar surface. For
solar cycle 24 this flux ranges from (2-4)x10^22 Mx, covering 5%-10%
of the solar surface. Notably, from both observational coronal hole
boundaries and modeled open magnetic field regions the low-latitude open
field contributes significantly to the total open magnetic flux. Using
a flux transport model in conjunction with a potential field model,
we compare observational coronal holes and computed open field for
solar cycles 23 and 24, paying particular attention to the latitudinal
distribution of open magnetic field. Carrington rotations 2099 and
2106 are additionally explored in more detail.
Title: A Comparison of EUV Coronal Hole Measurements and Modeled
Open Magnetic Field
Authors: Lowder, Chris; Qiu, Jiong; Leamon, Robert; Longcope, Dana;
Liu, Yang
Bibcode: 2014AAS...22432338L
Altcode:
Coronal holes are regions on the Sun's surface that map the footprints
of open magnetic field lines. We have developed an automated routine
to detect and track boundaries of long-lived coronal holes using
full-disk extreme-ultraviolet (EUV) images obtained by SOHO/EIT,
SDO/AIA, and STEREO/EUVI. Using these observations in conjunction
with the potential field source surface (PFSS) model, we find that
from 1996 through 2010, coronal holes extend between 5% and 17% of
the solar surface area, with total unsigned open flux varying between
(2-5)x1022 Mx. AIA/EUVI measurements spanning 2010 through
2013 mark coronal hole coverage areas of 5% to 10% of total solar
surface area, with total unsigned open magnetic flux ranging from
(2-4)x1022 Mx. A detailed comparison indicates that coronal
holes in low latitudes significantly contribute to the total open
magnetic flux. Previous studies using the He I 10830 line or EIT EUV
images do not always accurately measure these low latitude coronal
holes. Enhanced observations from AIA/EUVI in conjunction with an
observation-driven flux transport model allow a more accurate measure
of these low latitude coronal holes and their resulting contribution
to solar open magnetic flux.
Title: The Quasi-Annual Forcing of The Sun’s Eruptive, Radiative,
and Particulate Output
Authors: Leamon, Robert; McIntosh, Scott W.
Bibcode: 2014AAS...22442205L
Altcode:
The eruptive, radiative, and particulate output of the Sun are modulated
by our star’s enigmatic 11-year sunspot cycle. Over the past year
we have identified observational signatures which illustrate the ebb
and flow of the 11-year cycle - arising from the temporal overlap of
migrating activity bands which belong to the 22-year magnetic activity
cycle. (At the 2012 Fall AGU Meeting, Leamon & McIntosh presented
a prediction of minimum conditions developing in 2017 and Cycle 25
sunspots first appearing in late 2019.) As a consequence of this work we
have deduced that the latitudinal interaction of the oppositely signed
magnetic activity bands in each hemisphere (and across the equator near
solar minimum) dramatically impacts the production of Space Weather
events such as flares and Coronal Mass Ejections (CMEs). The same set
of observations also permits us to identify a quasi-annual variability
in the rotating convecting system which results in a significant local
modulation of solar surface magnetism. That modulation, in turn,
forces prolonged periods of significantly increased flare and CME
production, as well as significant changes in the Sun's ultraviolet
(UV), extreme ultraviolet (EUV), and X-Ray irradiance.
Title: Identifying Potential Markers of the Sun's Giant Convective
Scale
Authors: McIntosh, Scott W.; Wang, Xin; Leamon, Robert J.; Scherrer,
Philip H.
Bibcode: 2014ApJ...784L..32M
Altcode: 2014arXiv1403.0692M
Line-of-sight magnetograms from the Helioseismic and Magnetic Imager
(HMI) of the Solar Dynamics Observatory (SDO) are analyzed using a
diagnostic known as the magnetic range of influence (MRoI). The MRoI
is a measure of the length over which a photospheric magnetogram
is balanced and so its application gives the user a sense of the
connective length scales in the outer solar atmosphere. The MRoI maps
and histograms inferred from the SDO/HMI magnetograms primarily exhibit
four scales: a scale of a few megameters that can be associated with
granulation, a scale of a few tens of megameters that can be associated
with super-granulation, a scale of many hundreds to thousands of
megameters that can be associated with coronal holes and active regions,
and a hitherto unnoticed scale that ranges from 100 to 250 Mm. We
infer that this final scale is an imprint of the (rotationally driven)
giant convective scale on photospheric magnetism. This scale appears
in MRoI maps as well-defined, spatially distributed concentrations that
we have dubbed "g-nodes." Furthermore, using coronal observations from
the Atmospheric Imaging Assembly on SDO, we see that the vicinity of
these g-nodes appears to be a preferred location for the formation of
extreme-ultraviolet (and likely X-Ray) brightpoints. These observations
and straightforward diagnostics offer the potential of a near real-time
mapping of the Sun's largest convective scale, a scale that possibly
reaches to the very bottom of the convective zone.
Title: Measurements of EUV Coronal Holes and Open Magnetic Flux
Authors: Lowder, C.; Qiu, J.; Leamon, R.; Liu, Y.
Bibcode: 2014ApJ...783..142L
Altcode: 2015arXiv150206038L
Coronal holes are regions on the Sun's surface that map the footprints
of open magnetic field lines. We have developed an automated routine
to detect and track boundaries of long-lived coronal holes using
full-disk extreme-ultraviolet (EUV) images obtained by SOHO/EIT,
SDO/AIA, and STEREO/EUVI. We measure coronal hole areas and magnetic
flux in these holes, and compare the measurements with calculations
by the potential field source surface (PFSS) model. It is shown that,
from 1996 through 2010, the total area of coronal holes measured with
EIT images varies between 5% and 17% of the total solar surface area,
and the total unsigned open flux varies between (2-5)× 1022
Mx. The solar cycle dependence of these measurements is similar to the
PFSS results, but the model yields larger hole areas and greater open
flux than observed by EIT. The AIA/EUVI measurements from 2010-2013 show
coronal hole area coverage of 5%-10% of the total surface area, with
significant contribution from low latitudes, which is under-represented
by EIT. AIA/EUVI have measured much enhanced open magnetic flux in
the range of (2-4)× 1022 Mx, which is about twice the flux
measured by EIT, and matches with the PFSS calculated open flux, with
discrepancies in the location and strength of coronal holes. A detailed
comparison between the three measurements (by EIT, AIA-EUVI, and PFSS)
indicates that coronal holes in low latitudes contribute significantly
to the total open magnetic flux. These low-latitude coronal holes are
not well measured with either the He I 10830 line in previous studies,
or EIT EUV images; neither are they well captured by the static PFSS
model. The enhanced observations from AIA/EUVI allow a more accurate
measure of these low-latitude coronal holes and their contribution to
open magnetic flux.
Title: Coronal electron temperature in the protracted solar minimum,
the cycle 24 mini maximum, and over centuries
Authors: Schwadron, N. A.; Goelzer, M. L.; Smith, C. W.; Kasper,
J. C.; Korreck, K.; Leamon, R. J.; Lepri, S. T.; Maruca, B. A.;
McComas, D.; Steven, M. L.
Bibcode: 2014JGRA..119.1486S
Altcode:
Recent in situ observations of the solar wind show that
charge states (e.g., the O7+/O6+and
C6+/C5+abundance ratios) evolved through the
extended, deep solar minimum between solar cycles 23 and 24 (i.e.,
from 2006 to 2009) reflecting cooler electron temperatures in the
corona. We extend previous analyses to study the evolution of the
coronal electron temperature through the protracted solar minimum and
observe not only the reduction in coronal temperature in the cycles
23-24 solar minimum but also a small increase in coronal temperature
associated with increasing activity during the "mini maximum" in cycle
24. We use a new model of the interplanetary magnetic flux since 1749 to
estimate coronal electron temperatures over more than two centuries. The
reduction in coronal electron temperature in the cycles 23-24 protracted
solar minimum is similar to reductions observed at the beginning of
the Dalton Minimum (∼1805-1840). If these trends continue to reflect
the evolution of the Dalton Minimum, we will observe further reductions
in coronal temperature in the cycles 24-25 solar minimum. Preliminary
indications in 2013 do suggest a further post cycle 23 decline in
solar activity. Thus, we extend our understanding of coronal electron
temperature using the solar wind scaling law and compare recent
reductions in coronal electron temperature in the protracted solar
minimum to conditions that prevailed in the Dalton Minimum.
Title: The Evolving Magnetic Scales of the Outer Solar Atmosphere
and Their Potential Impact on Heliospheric Turbulence
Authors: McIntosh, Scott W.; Bethge, Christian; Threlfall, James;
De Moortel, Ineke; Leamon, Robert J.; Tian, Hui
Bibcode: 2013arXiv1311.2538M
Altcode:
The presence of turbulent phenomena in the outer solar atmosphere
is a given. However, because we are reduced to remotely sensing the
atmosphere of a star with instruments of limited spatial and/or spectral
resolution, we can only infer the physical progression from macroscopic
to microscopic phenomena. Even so, we know that many, if not all,
of the turbulent phenomena that pervade interplanetary space have
physical origins at the Sun and so in this brief article we consider
some recent measurements which point to sustained potential source(s)
of heliospheric turbulence in the magnetic and thermal domains. In
particular, we look at the scales of magnetism that are imprinted on
the outer solar atmosphere by the relentless magneto-convection of the
solar interior and combine state-of-the-art observations from the Solar
Dynamics Observatory (SDO) and the Coronal Multi-channel Polarimeter
(CoMP) which are beginning to hint at the origins of the wave/plasma
interplay prevalent closer to the Earth. While linking these disparate
scales of observation and understanding of their connection is near
to impossible, it is clear that the constant evolution of subsurface
magnetism on a host of scales guides and governs the flow of mass
and energy at the smallest scales. In the near future significant
progress in this area will be made by linking observations from high
resolution platforms like the Interface Region Imaging Spectrograph
(IRIS) and Advanced Technology Solar Telescope (ATST) with full-disk
synoptic observations such as those presented herein.
Title: Connecting Global EUV Coronal Hole Measurements and Open
Magnetic Field Boundaries
Authors: Lowder, Chris; Qiu, J.; Leamon, R.
Bibcode: 2013SPD....44..114L
Altcode:
This study seeks to further quantify the relationship between the
boundaries of coronal holes and open magnetic field regions. Utilizing
the combined observations of the SDO:AIA and STEREO:EUVI A/B
instruments, nearly full coverage of the solar surface in several
EUV filters is available. Using this data we have devised a
routine to define global observations of coronal hole boundaries
at high cadence. For comparison, several methods of global coronal
magnetic field extrapolation were considered, both potential and
non-potential. We considered both a direct spatio-temporal comparison
of boundaries as well as associated magnetic flux quantities.Abstract
(2,250 Maximum Characters): This study seeks to further quantify the
relationship between the boundaries of coronal holes and open magnetic
field regions. Utilizing the combined observations of the SDO:AIA and
STEREO:EUVI A/B instruments, nearly full coverage of the solar surface
in several EUV filters is available. Using this data we have devised
a routine to define global observations of coronal hole boundaries
at high cadence. For comparison, several methods of global coronal
magnetic field extrapolation were considered, both potential and
non-potential. We considered both a direct spatio-temporal comparison
of boundaries as well as associated magnetic flux quantities.
Title: EUV Coronal Holes as a Proxy for Open Magnetic Field Regions
Authors: Lowder, Chris; Qiu, Jiong; Leamon, Robert
Bibcode: 2013enss.confE.101L
Altcode:
Coronal holes are regions marked by a decreased intensity in the
extreme ultraviolet and x-ray wavelengths. Associated with regions of
open magnetic field, plasma is allowed to escape along open magnetic
field lines resulting in a rarefied plasma below. This study seeks
to quantify the relationship between boundaries of coronal holes and
open magnetic field. Using a combination of STEREO and SDO data in
EUV wavelengths, we can provide a full solar surface map of coronal
hole boundaries. These boundaries in conjunction with charts of radial
magnetic field can be used to calculate open magnetic fluxes. Direct
comparison is made with potential magnetic extrapolations as well as a
non-potential, magneto-frictional model. There is strong agreement both
in the geometry of regions as well as associated magnetic fluxes. These
data provide a unique opportunity to study the far side dynamics of
coronal holes and open magnetic field evolution.
Title: On the Modulation of the Solar Activity Cycles, and Hemispheric
Asymmetry of Solar Magnetism during the Cycle 23/24 Minimum
Authors: Leamon, Robert J.; McIntosh, Scott W.
Bibcode: 2013enss.confE.140L
Altcode:
We address the origin of the 11-year (quasi-)periodicity of the sunspot
cycle by tying it to the significant temporal overlap of activity bands
belonging to the 22-year magnetic activity cycle. Using a systematic
analysis of ubiquitous coronal brightpoints, and the prevalent
magnetic scale on which they form, we are able to observationally
demonstrate the entirety of the 22-year magnetic activity cycle. The
phases of the sunspot cycle occur as landmarks in the interaction and
evolution of the overlapping activity bands in each hemisphere. The
unusual conditions of the recent Cycle 23/24 minimum can be directly
attributed to the asymmetry (southern lag) between the two hemispheres
of the sun. The work presented establishes significant observational
constraints for models of the origins of solar magnetic activity and
will, as a result, improve our understanding of the structure of the
heliosphere and the modulation of our star's radiative and particulate
output. We demonstrate how the Sun can descend into, and recover from,
Grand Minima. Even if that is not where we're headed, we show why
Cycle 25 is likely to be even weaker than Cycle 24.
Title: Hemispheric Asymmetries of Solar Photospheric Magnetism:
Radiative, Particulate, and Heliospheric Impacts
Authors: McIntosh, Scott W.; Leamon, Robert J.; Gurman, Joseph B.;
Olive, Jean-Philippe; Cirtain, Jonathan W.; Hathaway, David H.;
Burkepile, Joan; Miesch, Mark; Markel, Robert S.; Sitongia, Leonard
Bibcode: 2013ApJ...765..146M
Altcode: 2013arXiv1302.1081M
Among many other measurable quantities, the summer of 2009 saw
a considerable low in the radiative output of the Sun that was
temporally coincident with the largest cosmic-ray flux ever measured
at 1 AU. Combining measurements and observations made by the Solar and
Heliospheric Observatory (SOHO) and Solar Dynamics Observatory (SDO)
spacecraft we begin to explore the complexities of the descending phase
of solar cycle 23, through the 2009 minimum into the ascending phase of
solar cycle 24. A hemispheric asymmetry in magnetic activity is clearly
observed and its evolution monitored and the resulting (prolonged)
magnetic imbalance must have had a considerable impact on the structure
and energetics of the heliosphere. While we cannot uniquely tie the
variance and scale of the surface magnetism to the dwindling radiative
and particulate output of the star, or the increased cosmic-ray flux
through the 2009 minimum, the timing of the decline and rapid recovery
in early 2010 would appear to inextricably link them. These observations
support a picture where the Sun's hemispheres are significantly out
of phase with each other. Studying historical sunspot records with
this picture in mind shows that the northern hemisphere has been
leading since the middle of the last century and that the hemispheric
"dominance" has changed twice in the past 130 years. The observations
presented give clear cause for concern, especially with respect to
our present understanding of the processes that produce the surface
magnetism in the (hidden) solar interior—hemispheric asymmetry is the
normal state—the strong symmetry shown in 1996 was abnormal. Further,
these observations show that the mechanism(s) which create and transport
the magnetic flux are slowly changing with time and, it appears, with
only loose coupling across the equator such that those asymmetries can
persist for a considerable time. As the current asymmetry persists and
the basal energetics of the system continue to dwindle we anticipate
new radiative and particulate lows coupled with increased cosmic-ray
fluxes heading into the next solar minimum.
Title: Full Surface Automated Coronal Hole Detection and
Characterization to Constrain Global Magnetic Field Models
Authors: Lowder, Chris; Qiu, J.; Leamon, R.; Liu, Y.
Bibcode: 2012AAS...22041106L
Altcode:
One of the primary mission goals of the Solar Terrestrial Relations
Observatory (STEREO) : Extreme Ultraviolet Imager (EUVI) is to
provide full extreme-ultraviolet (EUV) coverage of the solar surface
in conjunction with the Solar and Heliospheric Observatory (SOHO)
: Extreme Ultraviolet Imaging Telescope (EIT) or the Solar Dynamics
Observatory (SDO) : Atmospheric Imaging Assembly (AIA). Now, five years
after launch, sufficient orbital separation has occurred for this
to come to fruition. Using EUV images from STEREO:EUVI in 195Å and
SDO:AIA in 193Å, we can create full surface maps of coronal holes. Our
method employs an intensity thresholding technique in conjunction with
line-of-sight magnetic field measurements to automatically distinguish
coronal holes from filament channels. This full surface coverage
provides a unique opportunity to compare observed coronal holes with
the predicted open magnetic field regions from both potential field
models in addition to non-potential models. Our method is able to
detect and characterize both long-term coronal hole structures, as well
as shorter lived, transient coronal holes. Here, this method is
described in detail, with comparisons drawn between observed coronal
hole boundaries and open-field boundaries derived from models. In
addition, quantities that are crucially dependent on these boundaries
are considered, namely the open magnetic flux.
Title: Solar Cycle Variations in the Elemental Abundance of Helium
and Fractionation of Iron in the Fast Solar Wind - Indicators of an
Evolving Energetic Release of Mass from the Lower Solar Atmosphere
Authors: Kiefer, K. K.; Mcintosh, S. W.; Leamon, R. J.; Kasper, J. C.;
Stevens, M. L.
Bibcode: 2011AGUFMSH21B1915K
Altcode:
We present and discuss the strong correspondence between evolution of
the emission length scale in the lower transition region and in situ
measurements of the fast solar wind composition during this most recent
solar minimum. We combine recent analyses demonstrating the variance
in the (supergranular) network emission length scale measured by SOHO
(and STEREO) with that of the Helium abundance (from WIND) and the
degree of Iron fractionation in the solar wind (from the ACE and Ulysses
spacecrafts). The net picture developing is one where a decrease in the
Helium abundance and the degree of fractionation (approaching values
expected of the photosphere) in the fast wind indicate a significant
change in the process loading material into the fast solar wind during
the recent solar minimum. This result is compounded by a study of the
Helium abundance during the space age using the NASA OMNI database
which shows a slowly decaying amount of Helium being driven into the
heliosphere over the course of several solar cycles.
Title: The highest cosmic ray fluxes ever recorded: What happened
to the earth's deflector shield?
Authors: Leamon, R. J.; Mcintosh, S. W.; Burkepile, J.; Sitongia,
L.; Markel, R. S.; Gurman, J. B.; Olive, J.
Bibcode: 2011AGUFMSH23D..08L
Altcode:
The summer of 2009 saw the largest cosmic ray flux ever measured
at 1AU. Observed by neutron monitors this solar minimum flux was
6% larger than that of the last solar minimum in 1996, and 4%
larger than the previous high of the space age. Clearly, something
dramatically affected the cosmic ray "deflector shield" of the Earth
this time around, but what was it? Using a combination of serendipitous
observations made by the solid state recorder of the SOHO spacecraft,
an analysis of SOHO/MDI magnetograms combined with SOHO/EIT and SDO/AIA
coronal imaging, we deduce that a pronounced north-south asymmetry
in the meridional circulation flow resulted in the evolution of
the photospheric magnetic to a prolonged prevalence of the negative
magnetic polarity in the equatorial region that were the root cause
of the observed cosmic ray flux increase. The negative sign, weakness
and low rigidity of the interplanetary magnetic field, driven by the
excess of open magnetic flux resulting from the flow asymmetry in the
solar interior, enabled more cosmic rays of the energy range measured
at Earth to creep into our atmosphere than previously measured.
Title: A Snapshot of the Sun Near Solar Minimum: The Whole Heliosphere
Interval
Authors: Thompson, Barbara J.; Gibson, Sarah E.; Schroeder, Peter C.;
Webb, David F.; Arge, Charles N.; Bisi, Mario M.; de Toma, Giuliana;
Emery, Barbara A.; Galvin, Antoinette B.; Haber, Deborah A.; Jackson,
Bernard V.; Jensen, Elizabeth A.; Leamon, Robert J.; Lei, Jiuhou;
Manoharan, Periasamy K.; Mays, M. Leila; McIntosh, Patrick S.; Petrie,
Gordon J. D.; Plunkett, Simon P.; Qian, Liying; Riley, Peter; Suess,
Steven T.; Tokumaru, Munetoshi; Welsch, Brian T.; Woods, Thomas N.
Bibcode: 2011SoPh..274...29T
Altcode: 2011SoPh..tmp..413T
We present an overview of the data and models collected for the
Whole Heliosphere Interval, an international campaign to study the
three-dimensional solar-heliospheric-planetary connected system near
solar minimum. The data and models correspond to solar Carrington
Rotation 2068 (20 March - 16 April 2008) extending from below the
solar photosphere, through interplanetary space, and down to Earth's
mesosphere. Nearly 200 people participated in aspects of WHI studies,
analyzing and interpreting data from nearly 100 instruments and
models in order to elucidate the physics of fundamental heliophysical
processes. The solar and inner heliospheric data showed structure
consistent with the declining phase of the solar cycle. A closely
spaced cluster of low-latitude active regions was responsible for an
increased level of magnetic activity, while a highly warped current
sheet dominated heliospheric structure. The geospace data revealed an
unusually high level of activity, driven primarily by the periodic
impingement of high-speed streams. The WHI studies traced the solar
activity and structure into the heliosphere and geospace, and provided
new insight into the nature of the interconnected heliophysical system
near solar minimum.
Title: The Whole Heliosphere Interval in the Context of a Long and
Structured Solar Minimum: An Overview from Sun to Earth
Authors: Gibson, S. E.; de Toma, G.; Emery, B.; Riley, P.; Zhao, L.;
Elsworth, Y.; Leamon, R. J.; Lei, J.; McIntosh, S.; Mewaldt, R. A.;
Thompson, B. J.; Webb, D.
Bibcode: 2011SoPh..274....5G
Altcode: 2011SoPh..tmp..427G
Throughout months of extremely low solar activity during the recent
extended solar-cycle minimum, structural evolution continued to be
observed from the Sun through the solar wind and to the Earth. In
2008, the presence of long-lived and large low-latitude coronal holes
meant that geospace was periodically impacted by high-speed streams,
even though solar irradiance, activity, and interplanetary magnetic
fields had reached levels as low as, or lower than, observed in past
minima. This time period, which includes the first Whole Heliosphere
Interval (WHI 1: Carrington Rotation (CR) 2068), illustrates the
effects of fast solar-wind streams on the Earth in an otherwise quiet
heliosphere. By the end of 2008, sunspots and solar irradiance had
reached their lowest levels for this minimum (e.g., WHI 2: CR 2078),
and continued solar magnetic-flux evolution had led to a flattening
of the heliospheric current sheet and the decay of the low-latitude
coronal holes and associated Earth-intersecting high-speed solar-wind
streams. As the new solar cycle slowly began, solar-wind and geospace
observables stayed low or continued to decline, reaching very low
levels by June - July 2009. At this point (e.g., WHI 3: CR 2085) the
Sun-Earth system, taken as a whole, was at its quietest. In this article
we present an overview of observations that span the period 2008 -
2009, with highlighted discussion of CRs 2068, 2078, and 2085. We show
side-by-side observables from the Sun's interior through its surface and
atmosphere, through the solar wind and heliosphere and to the Earth's
space environment and upper atmosphere, and reference detailed studies
of these various regimes within this topical issue and elsewhere.
Title: Solar Cycle Variations in the Elemental Abundance of Helium
and Fractionation of Iron in the Fast Solar Wind: Indicators of an
Evolving Energetic Release of Mass from the Lower Solar Atmosphere
Authors: McIntosh, Scott W.; Kiefer, Kandace K.; Leamon, Robert J.;
Kasper, Justin C.; Stevens, Michael L.
Bibcode: 2011ApJ...740L..23M
Altcode: 2011arXiv1109.1408M
We present and discuss the strong correspondence between evolution of
the emission length scale in the lower transition region and in situ
measurements of the fast solar wind composition during the most recent
solar minimum. We combine recent analyses demonstrating the variance
in the (supergranular) network emission length scale measured by the
Solar and Heliospheric Observatory (and STEREO) with that of the helium
abundance (from Wind) and the degree of iron fractionation in the solar
wind (from the Advanced Composition Explorer and Ulysses). The net
picture developing is one where a decrease in the helium abundance
and the degree of iron fractionation (approaching values expected
of the photosphere) in the fast wind indicate a significant change
in the process loading material into the fast solar wind during the
recent solar minimum. This result is compounded by a study of the
helium abundance during the space age using the NASA OMNI database,
which shows a slowly decaying amount of helium being driven into the
heliosphere over the course of several solar cycles.
Title: A Decade of Solar Wind Dissipation Range Dynamics
Authors: Smith, Charles William; Vasquez, Bernard J.; Stemkowski,
Matthew R.; Stawarz, Joshua E.; Leamon, Robert J.; Matthaeus, William
H.; Hamilton, Kathleen; Forman, Miriam A.; MacBride, Benjamin T.
Bibcode: 2011shin.confE..99S
Altcode:
In light of recent suggestions that the so-called ion dissipation range
for interplanetary magnetic fluctuations is, in fact, not representative
of dissipation processes, but arises only due to dispersion effects
associated with perpendicular Kinetic Alfven Waves (KAW), we review 13
years of study that points to a fundamentally different interpretation
of the observations. We present evidence that thermal protons are
heated from 0.3 to 100 AU by means that are in excellent agreement
with the computed rate at which the inertial range transports energy to
the ion dissipation scales. We discuss the role of the power spectrum
and variance anisotropy in determining changes in the wave modes as
energy passes from the inertial to the dissipation range. We review
the single-spacecraft technique for determining the distribution of
energy between parallel and perpendicular wave vectors and show how this
distribution changes between inertial and dissipation scales. Moreover,
we present direct evidence that the multi-dimensional autocorrelation
function supports these conclusions. Lastly, we will review the basic
energy budget analysis that arises when one attempts to balance cascade
with dissipation processes that are separately polarization-dependent,
such as cyclotron damping, and polarization-independent. We conclude
that energy dissipation and ion heating occurs via a wide range of
dynamical processes at scales comparable to the ion inertial scale. We
do not preclude there being a secondary inertial range at electron
scales, but we do argue that the bulk of the inertial range cascade
energy dissipates at ion scales.
Title: Observing Evolution in the Supergranular Network Length Scale
During Periods of Low Solar Activity
Authors: McIntosh, Scott W.; Leamon, Robert J.; Hock, Rachel A.;
Rast, Mark P.; Ulrich, Roger K.
Bibcode: 2011ApJ...730L...3M
Altcode: 2011arXiv1102.0303M
We present the initial results of an observational study into the
variation of the dominant length scale of quiet solar emission:
supergranulation. The distribution of magnetic elements in the lanes
that from the network affects, and reflects, the radiative energy in
the plasma of the upper solar chromosphere and transition region at
the magnetic network boundaries forming as a result of the relentless
interaction of magnetic fields and convective motions of the Suns'
interior. We demonstrate that a net difference of ~0.5 Mm in the
supergranular emission length scale occurs when comparing observation
cycle 22/23 and cycle 23/24 minima. This variation in scale is
reproduced in the data sets of multiple space- and ground-based
instruments and using different diagnostic measures. By means of
extension, we consider the variation of the supergranular length
scale over multiple solar minima by analyzing a subset of the Mount
Wilson Solar Observatory Ca II K image record. The observations and
analysis presented provide a tantalizing look at solar activity in
the absence of large-scale flux emergence, offering insight into
times of "extreme" solar minimum and general behavior such as the
phasing and cross-dependence of different components of the spectral
irradiance. Given that the modulation of the supergranular scale
imprints itself in variations of the Suns' spectral irradiance, as well
as in the mass and energy transport into the entire outer atmosphere,
this preliminary investigation is an important step in understanding
the impact of the quiet Sun on the heliospheric system.
Title: The Spectroscopic Footprint of the Fast Solar Wind
Authors: McIntosh, Scott W.; Leamon, Robert J.; De Pontieu, Bart
Bibcode: 2011ApJ...727....7M
Altcode: 2010arXiv1011.3066M
We analyze a large, complex equatorial coronal hole (ECH) and its
immediate surroundings with a focus on the roots of the fast solar
wind. We start by demonstrating that our ECH is indeed a source of the
fast solar wind at 1 AU by examining in situ plasma measurements in
conjunction with recently developed measures of magnetic conditions
of the photosphere, inner heliosphere, and the mapping of the solar
wind source region. We focus the bulk of our analysis on interpreting
the thermal and spatial dependence of the non-thermal line widths
in the ECH as measured by SOHO/SUMER by placing the measurements in
context with recent studies of ubiquitous Alfvén waves in the solar
atmosphere and line profile asymmetries (indicative of episodic heating
and mass loading of the coronal plasma) that originate in the strong,
unipolar magnetic flux concentrations that comprise the supergranular
network. The results presented in this paper are consistent with a
picture where a significant portion of the energy responsible for
the transport of heated mass into the fast solar wind is provided by
episodically occurring small-scale events (likely driven by magnetic
reconnection) in the upper chromosphere and transition region of the
strong magnetic flux regions that comprise the supergranular network.
Title: The Highest Cosmic Ray Fluxes Ever Recorded: What Happened
to the Earth's Deflector Shield?
Authors: Burkepile, J.; McIntosh, S. W.; Gurman, J. B.; Leamon, R. J.
Bibcode: 2010AGUFMSH51B1676B
Altcode:
The summer of 2009 saw the largest cosmic ray flux ever measured at
Earth. Cosmic ray intensities in the 270-450 MeV/nucleon range were
nearly 20% larger than anything previously recorded. Clearly, something
dramatically affected the cosmic ray 'deflector shield' of the Earth
during the most recent solar activity minimum. We explore the cause
of this marked increase by examining properties of the global solar
magnetic field and conditions in the solar wind during the previous
solar minimum and compare these to previous solar cycles using in-situ
and remote sensing observations.
Title: The Impact of New EUV Diagnostics on CME-Related Kinematics
Authors: McIntosh, Scott W.; De Pontieu, Bart; Leamon, Robert J.
Bibcode: 2010SoPh..265....5M
Altcode: 2010SoPh..tmp...74M; 2010arXiv1001.2022M
We present the application of novel diagnostics to the spectroscopic
observation of a Coronal Mass Ejection (CME) on disk by the Extreme
Ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft. We
apply a recently developed line profile asymmetry analysis to the
spectroscopic observation of NOAA AR 10930 on 14 - 15 December 2006
to three raster observations before and during the eruption of a 1000
km s−1 halo CME. We see the impact that the observer's
line-of-sight and magnetic field geometry have on the diagnostics
used. Further, and more importantly, we identify the on-disk signature
of a high-speed outflow behind the CME in the dimming region arising
as a result of the eruption. Supported by recent coronal observations
of the STEREO spacecraft, we speculate about the momentum flux
resulting from this outflow as a secondary momentum source to the
CME. The results presented highlight the importance of spectroscopic
measurements in relation to CME kinematics, and the need for full-disk
synoptic spectroscopic observations of the coronal and chromospheric
plasmas to capture the signature of such explosive energy release as
a way of providing better constraints of CME propagation times to L1,
or any other point of interest in the heliosphere.
Title: STEREO observations of quasi-periodically driven high velocity
outflows in polar plumes
Authors: McIntosh, S. W.; Innes, D. E.; de Pontieu, B.; Leamon, R. J.
Bibcode: 2010A&A...510L...2M
Altcode: 2010arXiv1001.3377M
Context. Plumes are one of the most ubiquitous features seen at the
limb in polar coronal holes and are considered to be a source of
high density plasma streams to the fast solar wind.
Aims: We
analyze STEREO observations of plumes and aim to reinterpret and place
observations with previous generations of EUV imagers within a new
context that was recently developed from Hinode observations.
Methods: We exploit the higher signal-to-noise, spatial and temporal
resolution of the EUVI telescopes over that of SOHO/EIT to study
the temporal variation of polar plumes in high detail. We employ
recently developed insight from imaging (and spectral) diagnostics of
active region, plage, and quiet Sun plasmas to identify the presence
of apparent motions as high-speed upflows in magnetic regions as
opposed to previous interpretations of propagating waves.
Results: In almost all polar plumes observed at the limb in these
STEREO sequences, in all coronal passbands, we observe high speed
jets of plasma traveling along the structures with a mean velocity of
135 km s-1 at a range of temperatures from 0.5-1.5 MK. The
jets have an apparent brightness enhancement of ~5% above that of the
plumes they travel on and repeat quasi-periodically, with repeat-times
ranging from five to twenty-five minutes. We also notice a very
weak, fine scale, rapidly evolving, but ubiquitous companion of the
plumes that covers the entire coronal hole limb.
Conclusions:
The observed jets are remarkably similar in intensity enhancement,
periodicity and velocity to those observed in other magnetic regions
of the solar atmosphere. They are multi-thermal in nature. We infer
that the jets observed on the plumes are a source of heated mass
to the fast solar wind. Further, based on the previous results that
motivated this study, we suggest that these jets originated in the
upper chromosphere. Five movies are only available in electronic
form at http://www.aanda.org
Title: More of the Inconvenient Truth About Coronal Dimmings
Authors: McIntosh, S. W.; Burkepile, J.; Leamon, R. J.
Bibcode: 2009ASPC..415..393M
Altcode: 2009arXiv0901.2817M
We continue the investigation of a CME-driven coronal dimming
from December 14 2006 using unique high resolution imaging of the
chromosphere and corona from the Hinode spacecraft. Over the course
of the dimming event we observe the dynamic increase of non-thermal
line broadening of multiple emission lines as the CME is released
and the corona opens; reaching levels seen in coronal holes. As
the corona begins to close, refill and brighten, we see a reduction
of the non-thermal broadening towards the pre-eruption level. The
dynamic evolution of non-thermal broadening is consistent with the
expected change of Alfvén wave amplitudes in the magnetically open
rarefied dimming region, compared to the dense closed corona prior to
the CME. The presented data reinforce the belief that coronal dimmings
must be temporary sources of the fast solar wind. It is unclear if such
a rapid transition in the thermodynamics of the corona to a solar wind
state has an effect on the CME itself.
Title: How the Solar Wind Ties to its Photospheric Origins
Authors: Leamon, Robert J.; McIntosh, Scott W.
Bibcode: 2009ApJ...697L..28L
Altcode: 2009arXiv0904.0614L
We present a new method of visualizing the solar photospheric
magnetic field based on the "Magnetic Range of Influence" (MRoI). The
MRoI is a simple realization of the magnetic environment in the
photosphere, reflecting the distance required to balance the integrated
magnetic field contained in any magnetogram pixel. It provides a new
perspective on where subterrestrial field lines in a Potential Field
Source Surface (PFSS) model connect to the photosphere, and thus
the source of Earth-directed solar wind (within the limitations of
PFSS models), something that is not usually obvious from a regular
synoptic magnetogram. In each of three sample solar rotations,
at different phases of the solar cycle, the PFSS footpoint either
jumps between isolated areas of high MRoI or moves slowly within one
such area. Footpoint motions are consistent with Fisk's interchange
reconnection model.
Title: How the Solar Wind Ties to Its Photospheric Origins
Authors: Leamon, Robert; McIntosh, S. W.
Bibcode: 2009SPD....40.3101L
Altcode:
We present a new method of visualizing the solar photospheric magnetic
field based on the "Magnetic Range of Influence" (MRoI). The MRoI is
a simple realization of the magnetic environment in the photosphere,
reflecting the distance required to balance the integrated magnetic
field contained in any magnetogram pixel. It provides a new perspective
on where sub-terrestrial field lines in a Potential Field Source
Surface (PFSS) model connect to the photosphere, and thus the
source of Earth-directed solar wind (within the limitations of
PFSS models), something that is not usually obvious from a regular
synoptic magnetogram. In each of three sample solar rotations,
at different phases of the solar cycle, the PFSS footpoint either
jumps between isolated areas of high MRoI or moves slowly within one
such area. Footpoint motions are consistent with Fisk's interchange
reconnection model. We explore the relationships between the MRoI and
flux at the footpoint and the in situ composition of the resulting wind.
Title: The Spectroscopic Footprint of the Fast Solar Wind
Authors: McIntosh, S. W.; Leamon, R. J.; de Pontieu, B.
Bibcode: 2008AGUFMSH41A1612M
Altcode:
We explore a large, complex equatorial coronal hole (ECH) and its
immediate surroundings through the temperature dependence of the
non-thermal line widths of three transition region emission lines
observed by SOHO/SUMER, placing them in context with recent studies of
the other spectroscopic measures taken. Using a recent semi-empirical
model of the solar wind as a basis, we explore the structure of the
solar wind during the observing period and seek to gain a better
understanding of the interaction of this region with the nascent
solar wind.
Title: The Center-to-Limb Variation of TRACE Travel-Times
Authors: Leamon, R. J.; McIntosh, S. W.
Bibcode: 2008AGUFMSH41A1610L
Altcode:
We explore the limb-to-limb behavior of multi-frequency Transition
Region and Coronal Explorer (TRACE) travel-time measurements of
magneto-atmospheric waves in the solar chromosphere. We establish that
while the higher frequency acoustic travel-times (~ 7~mHz) show little
or no limb-to-limb variation, the previously documented variations of
travel-time measurements on the magnetic environment through which the
waves propagate are evident: increased travel-times in coronal holes;
decreased travel-times in strong closed magnetic concentrations. For
frequencies approaching the classical acoustic cut-off frequency
(5.2~mHz) and below there is an increasing dependence of the measured
travel-time with viewing angle and decreasing frequency. In this
paper we demonstrate, using supporting observations from the Solar
Optical Telescope on Hinode, that the center-to-limb variation of
the low-frequency travel-times is the signature of propagating waves
on magnetic network structures at granular spatial scales [i.e.,
structures close the spatial Nyquist frequency of TRACE] whose signal
is a result of sub-resolution UV emission line 'contamination' in the
1600Å passband. Further, these structures must have a line-of-sight
extension normal to the solar surface that increases across the disk
as we approach the limb. We deduce that the low- frequency travel-time
signal is directly caused by spicule motions which are increasingly
inclined to the TRACE line-of-sight. Similarly, using SOT support,
we propose that the apparent TRACE travel-time enhancement in coronal
holes from TRACE, at same granular network locations, is the result
of a change in vertical stratification in the coronal hole compared
to quiet Sun counterpart emission. This effort is of particular
relevance to full-disk travel-time investigations from the Solar
Dynamics Observatory.
Title: Could We Have Forecast "The Day the Solar Wind Died"?
Authors: Leamon, Robert J.; McIntosh, Scott W.
Bibcode: 2008ApJ...679L.147L
Altcode:
In 1999 May an interval of unusually slow (<300 km s-1)
and rarefied (<1 cm-3) solar wind was observed upstream
of Earth by the ACE spacecraft. The event has been dubbed "The Day
the Solar Wind Died." We apply our solar wind forecast model to the
interval in question, to ask whether we could have predicted the
phenomenon. The model fails, but by the manner in which it fails, we
support the conclusion that the rarefaction was caused by a suppression
of coronal outflow from a region that earlier provided fast wind flow,
possibly caused by a rapid restructuring of solar magnetic fields.
Title: Anisotropies and helicities in the solar wind inertial and
dissipation ranges at 1 AU
Authors: Hamilton, Kathleen; Smith, Charles W.; Vasquez, Bernard J.;
Leamon, Robert J.
Bibcode: 2008JGRA..113.1106H
Altcode:
We have constructed a database of ACE observations at 1 AU based on 960
intervals spanning the broadest possible range of solar wind conditions
including magnetic clouds. Using spectral analysis of high-resolution
magnetic field data we compare inertial range characteristics with
properties in the measured dissipation range. We find that previous
conclusions by Leamon et al. (1998a, 1998b, 1998c) are upheld: average
wave vectors are more field-aligned in the dissipation range than
in the inertial range, magnetic fluctuations are less transverse
to the mean field in the dissipation range, and cyclotron damping
plays an important but not exclusive role in the formation of the
dissipation range. However, field-aligned wave vectors play a larger
role in the formation of the dissipation range than was previously
found. In the process we find significant contrast between these
inertial range results and the conclusions of Dasso et al. (2005) who
examine larger-scale fluctuations within the inertial range. Dasso et
al. found a dominance of field-aligned wave vectors in the high-speed
wind and a dominance of quasi-perpendicular (two-dimensional) wave
vectors in low-speed winds. We find that the orientation of the wave
vectors for the smallest scales within the inertial range are not
organized by wind speed and that on average all samples show the same
distribution of energy between perpendicular and field-aligned wave
vectors. We conclude that this is due to the time required to evolve
the spectrum toward a two-dimensional state where the smaller inertial
range scales examined here evolve more quickly than the larger scales
of earlier analysis. Likewise, we find no such organization within
the dissipation range.
Title: Anisotropies and Helicities in the Solar Wind Inertial and
Dissipation Ranges at 1 AU
Authors: Smith, C. W.; Vasquez, B. J.; Leamon, R. J.; Hamilton, K.
Bibcode: 2007AGUFMSH32B..01S
Altcode:
We have constructed a data base of ACE observations at 1 AU based
on 960 intervals spanning the broadest possible range of solar
wind conditions including magnetic clouds. Using spectral analysis
of high resolution magnetic field data we compare inertial range
characteristics with properties in the measured dissipation range. We
find that previous conclusions by Leamon et al. [1998a,b,c] are upheld:
average wave vectors are more field-aligned in the dissipation range
than in the inertial range, magnetic fluctuations are less transverse
to the mean field in the dissipation range, and cyclotron damping
plays an important, but not exclusive role in the formation of the
dissipation range. However, field-aligned wave vectors play a larger
role in the formation of the dissipation range than was previously
found. In the process we examine characteristics of the inertial
range that are relevant to the manner in which the dissipation range
is created. We find significant contrast between these inertial range
results and the conclusions of Dasso et al. [2005] who examine larger
scale fluctuations within the inertial range. Dasso et al. found a
dominance of field-aligned wave vectors in the high-speed wind and
a dominance of 2D wave vectors in low-speed winds. We find that the
orientation of the wave vectors for the smallest scales within the
inertial range are not organized by wind speed and that on average all
samples show the same distribution of energy between perpendicular and
field-aligned wave vectors. We conclude that this is due to the time
required to evolve the spectrum toward a 2D state where the smaller
inertial range scales examined here evolve more quickly than the larger
scales of earlier analysis. Likewise, we find no such organization by
to wind speed within the dissipation range.
Title: Turbulence spectrum of interplanetary magnetic fluctuations
and the rate of energy cascade
Authors: Smith, Charles W.; Vasquez, Bernard J.; Hamilton, Kathleen;
MacBride, Benjamin T.; Tessein, Jeffrey A.; Forman, Miriam A.; Leamon,
Robert J.
Bibcode: 2007AIPC..932...96S
Altcode:
There is growing evidence that a turbulent cascade of energy from large
to small scales accounts for the dissipation of fluid energy (magnetic
and velocity fluctuations) that heats the background plasma. However,
much remains to be done to understand the dynamics of that cascade. We
apply a structure function formalism originally derived for hydrodynamic
turbulence and recently extended to include magnetohydrodynamics (MHD)
to map the cascade of energy in the inertial range at 1 AU. We also
examine the anisotropies associated with inertial range magnetic
fluctuations in the hope of better understanding inertial- and
dissipation-range dynamics.
Title: Evaluation of the turbulent energy cascade rates from the
upper inertial range in the solar wind at 1 AU
Authors: Vasquez, Bernard J.; Smith, Charles W.; Hamilton, Kathleen;
MacBride, Benjamin T.; Leamon, Robert J.
Bibcode: 2007JGRA..112.7101V
Altcode: 2007JGRA..11207101V
We construct a database from ACE spacecraft measurements of solar
wind magnetic field fluctuations at 1 AU which resolves ∼2 decades
in frequency at the high end of the inertial range. Using magnetic
field measurements outside of magnetic clouds in combination with
plasma measurements, we evaluate expressions for the Kolmogorov
and Kraichnan cascade rates at 0.01 Hz from magnetic field power
spectra and consider both isotropic and cross-field rates. We examine
these rates as functions of proton temperature and solar wind speed,
comparing them to the expected rate based on the heating of protons at
1 AU. The average Kolmogorov rate is consistently more than a factor
of 10 greater than expected. We conclude that the cascade rate cannot
be estimated using the Kolmogorov prescription and power spectra. The
Kraichnan rate is close to the expected rate and is potentially a good
way to estimate the cascade rate. No distinction is found between
the isotropic and cross-field rates at 1 AU. However, consideration
of the likely dependence of cascade rates with distance from the Sun
shows that a distinction should exist at distances closer than 1 AU but
not outside 1 AU. Moreover, we find that inside 1 AU, the cross-field
Kraichnan prediction can maintain agreement with the expected heating
rate whereas the isotropic prediction cannot.
Title: The Posteruptive Evolution of a Coronal Dimming
Authors: McIntosh, Scott W.; Leamon, Robert J.; Davey, Alisdair R.;
Wills-Davey, Meredith J.
Bibcode: 2007ApJ...660.1653M
Altcode: 2007astro.ph..1347M
We discuss the posteruptive evolution of a ``coronal dimming'' based
on observations of the EUV corona from the Solar and Heliospheric
Observatory and the Transition Region and Coronal Explorer (TRACE). This
discussion highlights the roles played by magnetoconvection-driven
magnetic reconnection and the global magnetic environment of the
plasma in the ``filling'' and apparent motion of the region following
the eruption of a coronal mass ejection (CME). A crucial element in
our understanding of the dimming region's evolution is developed by
monitoring the disappearance and reappearance of bright TRACE ``moss''
around the active region that gives rise to the CME. We interpret the
change in the TRACE moss as a proxy of the changing coronal magnetic
field topology behind the CME front. We infer that the change in the
global magnetic topology also results in a shift of the energy balance
in the process responsible for the production of the moss emission while
the coronal magnetic topology evolves from closed to open and back to
closed again because, following the eruption, the moss reforms around
the active region in almost exactly its pre-event configuration. As a
result of the moss's evolution, combining our discussion with recent
spectroscopic results of an equatorial coronal hole, we suggest that
the interchangeable use of the term ``transient coronal hole'' to
describe a coronal dimming is more than just a simple coincidence.
Title: Empirical Solar Wind Forecasting from the Chromosphere
Authors: Leamon, R. J.; McIntosh, S. W.
Bibcode: 2007ApJ...659..738L
Altcode: 2007astro.ph..1348L
Recently, we correlated the inferred structure of the solar
chromospheric plasma topography with solar wind velocity and composition
data measured at 1 AU. We now offer a physical justification of these
relationships and present initial results of an empirical prediction
model based on them. While still limited by the fundamentally complex
physics behind the origins of the solar wind and how its structure
develops in the magnetic photosphere and expands into the heliosphere,
our model provides a near-continuous range of solar wind speeds and
composition quantities that are simply estimated from the inferred
structure of the chromosphere. We suggest that the derived quantities
may provide input to other, more sophisticated, prediction tools or
models such as those that study coronal mass ejection (CME) propagation
and solar energetic particle (SEP) generation.
Title: An Empirical Solar Wind Forecast Model From The Chromosphere
Authors: Leamon, R. J.; McIntosh, S. W.
Bibcode: 2006AGUFMSH44A..08L
Altcode:
Recently, we [McIntosh and Leamon, ApJL, 624, 117, 2005] correlated
the inferred topography of the solar chromospheric plasma with in situ
solar wind velocity and composition data measured at 1~AU. Specifically,
the measured separation in height of the TRACE 1600Å\ and 1700Å\
UV band pass filters correlate very strongly with solar wind
velocity and inversely with the ratio of ionic oxygen (O^{7+/O^{6+}})
densities. Here, we build on our previous results by presenting initial
results of a model developed to so predict interplanetary solar wind
conditions, using SOHO/MDI magnetograms with 96 minute cadence as
proxies of chromospheric topography as input. Specifically, we use the
observed correlation between the measured chromospheric travel-time
and the magnetic field strength to allow us to convert the into a
(reasonable) full-disk travel-time diagnostic (in place of limited
field of view TRACE observations). Maps of full-disk travel-time are
scaled to wind diagnostic maps which are then "forward" mapped into
the heliosphere using a PFSS model. The resulting wind forecast matches
the observed state of the solar wind remarkably well for a simple model.
Title: The Role of Magnetoconvection in the Evolution of Active
Regions Before, During and After the Eruption of Coronal Mass
Ejections
Authors: McIntosh, S. W.; Leamon, R. J.
Bibcode: 2006AGUFMSH43B1529M
Altcode:
We discuss the pre-eruptive evolution of an active region filament
and the evolution of the ensuing post-eruptive "coronal dimming"
based on observations of the EUV corona from the Solar and Heliospheric
Observatory and the Transition Region and Coronal Explorer. We speculate
that the erosion of coronal loop footpoints anchored in the weakest
magnetic portions of an active region by magneto-convective flux
emergence driven reconnection acts as a stochastic "tether cutting"
mechanism. We discuss how this erosion of tethering magnetic flux is
capable of creating a topological instability and eventual coronal
mass ejection (CME) eruption. The magnetoconvection-driven magnetic
reconnection and the global magnetic enviroment of the plasma are
equally important in the "filling" and apparent motion of the region
following the eruption of the CME. Further, we speculate that coronal
dimmings could pose a potential secondary source of driving momentum
to the CMEs that cause their initial appearance.
Title: Two New Results in Solar Wind Turbulence
Authors: Smith, C. W.; Vasquez, B. J.; Hamilton, K.; Leamon, R. J.
Bibcode: 2006AGUFMSH12A..02S
Altcode:
We have created a data base of interplanetary magnetic field spectra
from over 900 separate solar wind intervals at 1 AU using data from
the Advanced Composition Explorer (ACE) spacecraft. These intervals
embrace a broad range of solar wind conditions including fast-
and slow-wind conditions, rarefaction regions, shocked plasma, and
magenetic clouds. Every attempt was made to identify samples from the
broadest possible range of solar wind conditions without regard for
occurrence frequency. We have examined the ratio of magnetic power
in the component perpendicular to the mean field to that parallel
to the mean field (the so-called variance anisotropy) as measured
in the high-frequency regime of the inertial range and find it to be
strongly correlated to the proton beta. The variance anisotropy may
be a proxy for the spectrum of density fluctuations in this region of
the spectrum that is unresolved by ACE instruments and that is often
unresolved by current flight hardware. The observed correlation with
proton beta appears to be in keeping with predictions derived from
magnetohydrodynamic turbulence concepts where the compressive component
is driven by the incompressible turbulence in the low turbulent Mach
number regime. This apparent agreement strongly suggests that the
compressive component arises from in situ dynamics and has little if
anything to do with solar origins. We have also investigated the nature
of turbulent magnetic dissipation range. Focussing on the spectral
properties at spacecraft frequencies ≥ 0.5 Hz, we show that while
the inertial range at lower frequencies displays a tightly constrained
range of spectral indexes, the dissipation range exhibits a broad
range of power law indexes. We show that the explanation for this
variation lies with the dependence of the dissipation range spectrum
on the rate of energy cascade through the inertial range such that
steeper spectral forms result from greater cascade rates.
Title: Turbulent Cascade Rates in the Upper Inertial Range
Authors: Hamilton, K.; Vasquez, B. J.; Smith, C. W.; MacBride, B. T.;
Leamon, R. J.
Bibcode: 2006AGUFMSH11B..05H
Altcode:
We have constructed a data base from ACE spacecraft measurements of
solar wind magnetic field fluctuations at the high end of the inertial
range near 1 AU. Using magnetic field measurements outside of magnetic
clouds in combination with plasma measurements, we have evaluated
expressions for the Kolmogorov and Kraichnan cascade rates at 0.01
Hz from magnetic field power spectra. We have examined these rates
as a function of proton temperature and solar wind speed and have
compared them to the expected rate based on the heating of protons
at 1 AU. We find that the average Kolmogorov rate is consistently
more than a factor of 10 greater than expected. We conclude that the
cascade rate cannot be estimated using a Kolmogorov prescription and
power spectra. The Kraichnan rate is close to the expected rate and
is potentially a valid way to estimate the cascade rate.
Title: Empirical Solar Wind Forecasting from the Chromosphere
Authors: Leamon, R.; McIntosh, S. W.
Bibcode: 2006ESASP.617E..13L
Altcode: 2006soho...17E..13L
No abstract at ADS
Title: Dependence of the Dissipation Range Spectrum of Interplanetary
Magnetic Fluctuationson the Rate of Energy Cascade
Authors: Smith, Charles W.; Hamilton, Kathleen; Vasquez, Bernard J.;
Leamon, Robert J.
Bibcode: 2006ApJ...645L..85S
Altcode:
We investigate the nature of turbulent magnetic dissipation in the solar
wind. We employ a database describing the spectra of over 800 intervals
of interplanetary magnetic field and solar wind measurements recorded
by the ACE spacecraft at 1 AU. We focus on the spectral properties of
the dissipation range that forms at spacecraft frequencies >=0.3 Hz
and show that while the inertial range at lower frequencies displays
a tightly constrained range of spectral indexes, the dissipation
range exhibits a broad range of power-law indexes. We show that
the explanation for this variation lies with the dependence of the
dissipation range spectrum on the rate of energy cascade through the
inertial range such that steeper spectral forms result from greater
cascade rates.
Title: Two New Results in Solar Wind Turbulence
Authors: Smith, Charles W.; Hamilton, K.; Vasquez, B. J.; Leamon, R. J.
Bibcode: 2006SPD....37.1105S
Altcode: 2006BAAS...38..239S
We have created a data base of interplanetary magnetic field spectra
from over 900 separate solar wind intervals at 1 AU using data from
the Advanced Composition Explorer (ACE) spacecraft. These intervals
embrace a broad range of solar wind conditions including fast- and
slow-wind conditions, rarefaction regions, shocked plasma, and magenetic
clouds. Every attempt was made to develop a data base that samples the
broadest possible range of solar wind conditions without regard for
occurrence frequency. We have examined the ratio of magnetic power
in the component perpendicular to the mean field to that parallel
to the mean field (the so-called variance anisotropy) as measured
in the high-frequency regime of the inertial range and find it to be
strongly correlated to the proton beta. The variance anisotropy may
be a proxy for the spectrum of density fluctuations in this region of
the spectrum that is unresolved by ACE instruments and that is often
unresolved by current flight hardware. The observed correlation with
proton beta appears to be in keeping with predictions derived from
magnetohydrodynamic turbulence concepts where the compressive component
is driven by the incompressible turbulence in the low turbulent Mach
number regime. This apparent agreement strongly suggests that the
compressive component arises from in situ dynamics and has little
if anything to do with solar origins. We have also investigated the
nature of turbulent magnetic dissipation range. We show that while the
inertial range at lower frequencies displays a tightly constrained
range of spectral indexes, the dissipation range exhibits a broad
range of power law indexes. We show that the explanation for this
variation lies with the dependence of the dissipation range spectrum
on the rate of energy cascade through the inertial range such that
steeper spectral forms result from greater cascade rates.
Title: Dissipation Range Spectral Characteristics at 1 AU
Authors: Hamilton, K.; Smith, C. W.; Leamon, R. J.
Bibcode: 2005ESASP.592..547H
Altcode: 2005soho...16E.103H; 2005ESASP.592E.103H
No abstract at ADS
Title: Chromospheric Origins of the Solar Wind: Composition and
Correlations
Authors: Leamon, R. J.; McIntosh, S. W.
Bibcode: 2005AGUSMSH11C..04L
Altcode:
Diagnostics of atmospheric "depth" in the chromosphere are made
for several observing periods in active, coronal hole and quiet Sun
regions. We track the coronal outflows from these regions to 1 AU using
a ballistic travel time approximation and correlate the chromospheric
quantities with counterpart in situ quantities from the same packets
of plasma Recently, we1 have shown that derived diagnostic quantities
correlate very strongly with solar wind velocity and inversely with the
ratio of ionic oxygen composition (O7+/O6+). We extend this work to show
that strong correlations exist between the state of the chromosphere
and other in situ observables, including proton temperatures, alpha
particle temperatures and alpha/proton ratios. (1) McIntosh and Leamon,
ApJL, submitted 2005
Title: The TRACE Inter-Network Oscillations (INO) Program II:
Observations of Limb and Coronal Hole Regions
Authors: McIntosh, S. W.; Crotser, D.; Leamon, R. J.; Fleck, B.;
Tarbell, T. D.
Bibcode: 2005AGUSMSH13C..06M
Altcode:
We will present results of the TRACE Inter-Network Oscillations (INO)
observing program from 2003 to the present. The INO program uses
near-simultaneous observations in the 1600Å and 1700Å UV continuum
pass bands as an acoustic probe of chromospheric structure. In
this poster we will discuss the INO observations of limb, polar and
coronal hole regions and show the key results found, thus far. These
observations offer us a remote means to study the structure and behavior
of the chromopsheric plasma topography at a potential driving base
for the heliospheric plasma system.
Title: Is There a Chromospheric Footprint of the Solar Wind?
Authors: McIntosh, S. W.; Leamon, R. J.
Bibcode: 2005ApJ...624L.117M
Altcode:
We correlate the inferred structure of the solar chromospheric
plasma topography with in situ solar wind velocity and composition
data measured at 1 AU. Diagnostics of atmospheric ``depth'' in the
chromosphere are made for several observing periods in active,
coronal hole, and quiet-Sun regions. We demonstrate that the
inferred chromospheric diagnostics correlate very strongly with
solar wind velocity and inversely with the ratio of ionic oxygen
(O+7/O+6) densities. These correlations suggest
that the structure of the solar wind is rooted deeper in the outer
solar atmosphere than has been previously considered.
Title: Statistical Relationships in Characteristics of a Sample of
Interplanetary Coronal Mass Ejections Detected Near Earth
Authors: McKenzie, D. E.; Wilson, K. G.; Leamon, R. J.
Bibcode: 2005AGUSMSH32A..02M
Altcode:
Using in situ measurements of solar wind conditions near Earth, we
compared the signatures of a sample of transients, which we tentatively
identify as magnetic clouds. Images from several solar observatories
were utilized to identify the source eruptions which launched each
ICME from the Sun. The plasma conditions within these structures were
compared, and trends were sought that would correlate with the type of
solar progenitor structure that spawned the eruptions. Additionally,
a magnetic model was fitted to the measurements of each ICME detected
near Earth. We present findings that suggest a systematic difference
in cloud structure, depending on progenitor type; also, we present
results indicating a relationship between the speed of transit from
Sun to Earth and the magnetic field strength in the ICME.
Title: The Importance of Topology and Reconnection in Active
Region CMEs
Authors: Leamon, Robert J.
Bibcode: 2005IAUS..226..302L
Altcode:
A distinctive characteristic of interplanetary magnetic clouds is
their rope-like magnetic structure, <e1>i.e.</e1>, their
smoothly-varying helical field lines whose pitch increases from their
core to their boundary. Because this regular structure helps to make
MCs particularly geo-effective, it is important to understand how it
arises.</p>We discuss recent work which relates the magnetic and
topological parameters of MCs to associated solar active regions. This
work strongly supports the notion that MCs associated with active region
eruptions are formed by magnetic reconnection between these regions
and their larger-scale surroundings, rather than simple eruption or
entrainment of pre-existing structures in the corona or chromosphere. We
discuss our findings in the context of other recent works on both the
solar and interplanetary sides, including ion composition and various
MHD models of magnetic cloud formation.
Title: Helicity of Magnetic Clouds and Their Associated Active Regions
Authors: Leamon, Robert J.; Canfield, Richard C.; Jones, Sarah L.;
Lambkin, Keith; Lundberg, Brian J.; Pevtsov, Alexei A.
Bibcode: 2005HiA....13..132L
Altcode:
Magnetic clouds are closely associated with Coronal Mass Ejections
(CMEs). Most CMEs are associated with active regions. What is the
relationship between the topology of these clouds and the associated
active region? For our purposes magnetic clouds can be modeled
adequately by a cylindrical force-free magnetic configuration (Lepping
1990). We have modeled the magnetic field topology of 14 magnetic
clouds and their associated active regions to determine values of
the force-free field parameter for both as well as total currents and
fluxes. We find that the number of turns of the magnetic field in the
full length of the cloud is typically an order of magnitude greater
than the same quantity in the associated active region. This finding
compels us to reject models of flux rope formation that do not invoke
magnetic reconnection and helicity conservation.
Title: Dissipation Range Observations in Interplanetary Magnetic
Clouds
Authors: Hamilton, K.; Smith, C. W.; Leamon, R. J.
Bibcode: 2004AGUFMSH51C0289H
Altcode:
In two earlier papers Leamon et al. [1998a,b] examined the properties
of the dissipation range for interplanetary magnetic fluctuations at
1 AU. In the first paper they focused on 33 1-hour samples of open
field line measurements chosen without any regard for context other
than being sufficiently well-behaved for sufficient time to yield
good spectra. All 33 intervals were chosen from WIND/MFI measurements
in the solar wind near 1 AU. They found that the dissipation range
typically set in at frequencies slightly greater than the proton
cyclotron frequency, had consistently steeper forms than the associated
inertial range spectra with power law indexes generally between -3 and
-5, were consistently more compressive than the inertial range, and
possessed wave vectors more nearly field aligned than in the inertial
range. In the second paper they chose to examine intervals from within
a single magnetic cloud. They found that the cloud spectra showed
generally less steepening in the dissipation range than did the open
field line examples. Inertial range fluctuations were significantly
less compressive in the cloud examples. Very little energy was seen
to reside with wave vectors parallel to the mean magnetic field
in either the inertial or dissipation ranges. We have examined 30
additional magnetic clouds observed by ACE in order to develop a
more statistically significant characterization of magnetic cloud
dissipation range spectra near 1 AU. We find that the Leamon results
characterize frequently observed aspects of cloud spectra, but that
they constitute a common example within a range of possible results. In
an effort to better understand the in situ heating of magnetic clouds,
we present the statistics we have gathered and compare these results
with typical open field line observations. Leamon et al., JGR, A103,
4775--4787, 1998a Leamon et al., GRL, 25, 2505--2509, 1998b
Title: Geoeffective CMEs, Filaments, and Sigmoids
Authors: McKenzie, D. E.; Leamon, R. J.
Bibcode: 2004AAS...204.3801M
Altcode: 2004BAAS...36..712M
Coronal mass ejections--particularly those with flux rope
structures--have the potential to trigger geomagnetic storms, depending
on the properties of the flux ropes. Eruptions of both filaments and
coronal sigmoids have been indicated as important drivers of space
weather, and both filaments and sigmoids have been modeled with flux
rope structure. However, the analysis reported by Leamon et al. (2002)
suggested that magnetic clouds associated with filament eruptions are
different from magnetic clouds associated with erupting sigmoids. In
this investigation, we are exploring the possibility of predicting
the geoeffectiveness of CMEs through analysis of the pre-eruption
magnetic structures.
Title: Helicity of magnetic clouds and their associated active regions
Authors: Leamon, Robert J.; Canfield, Richard C.; Jones, Sarah L.;
Lambkin, Keith; Lundberg, Brian J.; Pevtsov, Alexei A.
Bibcode: 2004JGRA..109.5106L
Altcode:
In this work we relate the magnetic and topological parameters of twelve
interplanetary magnetic clouds to associated solar active regions. We
use a cylindrically symmetric constant-α force-free model to derive
field line twist, total current, and total magnetic flux from in situ
observations of magnetic clouds. We compare these properties with those
of the associated solar active regions, which we infer from solar
vector magnetograms. Our comparison of fluxes and currents reveals:
(1) the total flux ratios ΦMC/ΦAR tend to be of
order unity, (2) the total current ratios IMC/IAR
are orders of magnitude smaller, and (3) there is a statistically
significant proportionality between them. Our key findings in comparing
total twists αL are that (1) the values of (αL)MC are
typically an order of magnitude greater than those of (αL)AR
and (2) there is no statistically significant sign or amplitude
relationship between them. These findings compel us to believe that
magnetic clouds associated with active region eruptions are formed by
magnetic reconnection between these regions and their larger-scale
surroundings, rather than simple eruption of preexisting structures
in the corona or chromosphere.
Title: Physics of superfast coronal mass ejections observed during
cycle 23
Authors: Lawrence, G.; Gallagher, P.; Leamon, R.; Stenborg, G.
Bibcode: 2004cosp...35.2882L
Altcode: 2004cosp.meet.2882L
Between January 1996 and the present time the Large Angle Spectrometric
Coronagraphs (LASCO) onboard the Solar and Heliospheric Observatory
(SOHO) have observed over 6000 coronal mass ejections (CMEs). The
typical speed of these CMEs has been found to vary between 400-500 km/s
during the present solar cycle, and the vast majority of all CMEs are
found to have speeds below 1,000 km/s. However, a high-speed tail to
the distribution is clearly present, and a small fraction of all CMEs,
20 events in total, are found to have speeds in the range 2,000 - 2,500
km/s. This category of 'superfast CMEs' is doubly significant because
they appear to correspond the extreme limits of physics involved in the
initiation and acceleration processes, and because such events when
directed earthwards have characteristically short transit times and
hence leave little reaction/assessment time for potentially sensitive
systems. The superfast CMEs are all associated with significant solar
flares, and the large flare/very fast CME paradigm is studied. Of
particular interest is the acceleration of such very fast CMEs and
the nature, magnitude and timing of the acceleration process is
characterised within the limits of the observations.
Title: What Is the Role of the Kink Instability in Solar Coronal
Eruptions?
Authors: Leamon, Robert J.; Canfield, Richard C.; Blehm, Zachary;
Pevtsov, Alexei A.
Bibcode: 2003ApJ...596L.255L
Altcode:
We report the results of two simple studies that seek observational
evidence that solar coronal loops are unstable to the MHD kink
instability above a certain critical value of the total twist. First,
we have used Yohkoh soft X-ray telescope image sequences to measure the
shapes of 191 X-ray sigmoids and to determine the histories of eruption
(evidenced by cusp and arcade signatures) of their associated active
regions. We find that the distribution of sigmoid shapes is quite
narrow and the frequency of eruption does not depend significantly on
shape. Second, we have used Mees Solar Observatory vector magnetograms
to estimate the large-scale total twist of active regions in which
flare-related signatures of eruption are observed. We find no evidence
of eruption for values of large-scale total twist remotely approaching
the threshold for the kink instability.
Title: Magnetic Cloud and Active Region Topology Compared
Authors: Canfield, R. C.; Leamon, R. J.; Jones, S. L.; Lambkin, K.;
Lundberg, B.
Bibcode: 2003SPD....34.0518C
Altcode: 2003BAAS...35..817C
Magnetic clouds are closely associated with Coronal Mass Ejections
(CMEs). Most CMEs are associated with active regions. What is
the relationship between the topology of these clouds and the
associated active region? For our purposes magnetic clouds can be
modeled adequately by a cylindrical force-free magnetic configuration
(Lepping, 1990). We have modeled the magnetic field topology of 14
magnetic clouds and their associated active regions to determine
values of the force-free field parameter for both, as well as total
currents and fluxes. We find that the number of turns of the twisted
magnetic field in the full length of the cloud is typically an order of
magnitude greater than the same quantity across the associated active
region. This finding compels us to reject models of flux rope formation
that do not invoke magnetic reconnection and helicity conservation.
Title: Magnetic Cloud and Active Region Topology Compared
Authors: Leamon, Robert J.; Canfield, Richard C.; Jones, Sarah L.;
Lundberg, Brian
Bibcode: 2003IAUJD...3E..24L
Altcode:
Magnetic clouds are closely associated with Coronal Mass Ejections
(CMEs). Most CMEs are associated with active regions. What is the
relationship between the topology of these clouds and the associated
active region? For our purposes magnetic clouds can be modeled
adequately by a cylindrical force-free magnetic configuration (Lepping
1990). We have modeled the magnetic field topology of 14 magnetic
clouds and their associated active regions to determine values of
the force-free field parameter for both as well as total currents and
fluxes. We find that the number of turns of the magnetic field in the
full length of the cloud is typically an order of magnitude greater
than the same quantity in the associated active region. This finding
compels us to reject models of flux rope formation that do not invoke
magnetic reconnection and helicity conservation.
Title: Properties of magnetic clouds and geomagnetic storms associated
with eruption of coronal sigmoids
Authors: Leamon, Robert J.; Canfield, Richard C.; Pevtsov, Alexei A.
Bibcode: 2002JGRA..107.1234L
Altcode:
We study 46 solar coronal eruptions associated with sigmoids seen
in images from the Yohkoh Soft X-ray Telescope (SXT). We relate
the properties of the sigmoids to in situ measurements at 1 AU and
geomagnetic storms. Our primary result is that erupting sigmoids tend
to produce geoeffective magnetic clouds (MCs): 85% of the erupting
sigmoidal structures studied spawned at least a "moderate" (|Dst| ≥
50 nT) geomagnetic storm. A collateral result is that MCs associated
with sigmoids do not show the same solar-terrestrial correlations
as those associated with filaments and, as such, form a distinct
class of events. First, rather than reversing with the global solar
dipole (at solar maximum), the leading field in MCs weakly (2:1)
shows a solar cycle (Hale polarity) based correlation (reversing at
solar minimum). Second, whereas the handedness of MCs associated with
filament eruptions is strongly (95%) related to their launch hemisphere,
that of MCs associated with sigmoid eruptions is only weakly (∼70%)
so related. Finally, we are unaware of any model of the magnetic fields
of sigmoids and their eruption that gives a useful prediction of the
leading field orientation of their associated MC.
Title: What is the role of the kink instability in eruption of
X-ray sigmoids?
Authors: Leamon, R.; Canfield, R.; Blehm, Z.; Pevtsov, A.
Bibcode: 2002AGUSMSH32D..03L
Altcode:
Observers see ample evidence of helical structures in erupting solar
filaments, X-ray sigmoids and CMEs. It has been argued that the total
amount of twist in a given loop is a factor in its MHD stability
[Priest, 1984]. A simple model illustrates this point. Consider a
cylindrical force-free magnetic field with constant α = T /L, where
L is the length of the tube and T is the total twist contained within
it. The tube is stable to the MHD kink instability for total twist
below a critical value Tc ~ 2 π . Rust and Kumar [1996]
compared the shape of 49 transient, bright sigmoid structures to the
signature of a helically kinked flux rope. From a study of the aspect
ratios of these transient sigmoid brightenings, they inferred that the
cause of CMEs is the eruption of an unstable, kinked magnetic field. We
have analyzed 155 X-ray sigmoids in the the Yohkoh SXT data, measuring
the angle γ at which the sigmoid crosses its central axis and the
length of the sigmoid along that axis (which is not identical to L,
but is closely related to it). In a simple 2D force-free analysis,
Pevtsov et al. [1997] showed that α = ( π / L ) sin γ , implying
that sin γ is a measure of the total twist T. By simple visual
inspection of the Yohkoh SXT movies, we have identified well-known
signatures of eruption, i.e., X-ray cusps and arcades. We find no
relationship between the frequency of occurrence of such signatures
of eruption and sin γ . {Pevtsov, A. A.}, {Canfield, R. C.}, and
{McClymont, A. N.}, Astrophys J., 481, 973, 1997. {Priest, E. R.},
{Solar Magneto-Hydrodynamics}, {Reidel: Dordrecht}, {1984}. {Rust,
D. M.}, and {Kumar, A.}, Astrophys J., 464, L199, 1996.
Title: What is the role of the kink instability in eruption of
X-ray sigmoids?
Authors: Canfield, R. C.; Leamon, R. J.; Blehm, Z.; Pevtsov, A. A.
Bibcode: 2002AAS...200.2001C
Altcode: 2002BAAS...34..672C
Observers see ample evidence of helical structures in erupting solar
filaments, X-ray sigmoids and CMEs. It has been argued that the total
amount of twist in a given loop is a factor in its MHD stability
[Priest, 1984]. A simple model illustrates this point. Consider
a cylindrical force-free magnetic field with constant α = T /L,
where L is the length of the tube and T is the total twist contained
within it. The tube is stable to the MHD kink instability for total
twist below a critical value Tc ~ 2 π . Rust and Kumar
[1996] compared the shape of 49 transient, bright sigmoid structures
to the signature of a helically kinked flux rope. From a study of the
aspect ratios of these transient sigmoid brightenings, they inferred
that the cause of CMEs is the eruption of an unstable, kinked magnetic
field. We have analyzed 191 X-ray sigmoids in the the Yohkoh SXT data,
measuring the angle γ at which the sigmoid crosses its central axis
and the length of the sigmoid along that axis (which is not identical
to L, but is closely related to it). In a simple 2D force-free analysis,
Pevtsov et al. [1997] showed that α = ( π / L ) sin γ , implying that
sin γ is a measure of the total twist T. By simple visual inspection
of the Yohkoh SXT movies, we have identified well-known signatures of
eruption, i.e., X-ray cusps and arcades. We find no relationship between
the frequency of occurrence of such signatures of eruption and sin γ .
Title: Properties of Magnetic Clouds Resulting from Eruption of
Coronal Sigmoids
Authors: Leamon, R. J.; Canfield, R. C.; Pevtsov, A. A.
Bibcode: 2001AGUSM..SH31C08L
Altcode:
We study over 40 eruptions which originated with coronal sigmoids seen
in Yohkoh SXT images, with subsequently observed in situ magnetic
clouds (MCs) and geomagnetic storms at 1~AU. We correlate solar and
interplanetary features so as to infer terrestrial event properties
from their solar sources. A collateral result from studying this
database is that CMEs and MCs resulting from erupting sigmoids seem
not to adhere to rules such as leading Bz versus solar
dipole orientation and, as such, form a distinct class of events. %
Instead of a large-scale dipole rule, we find there is a weak (3:2)
solar cycle (Hale polarity)-based rule for leading interplanetary
field in MCs. We find that the helicity of magnetic clouds is much more
strongly correlated (>90%) with launch hemisphere than the 60--70%\
rule of photospheric active region helicity. This rule appears to hold
for all CMEs, taking the 28 years of events of Bothmer &\ Rust
[``Coronal Mass Ejections,'' AGU Monograph Series 99, 139, 1997]. %
At least half of Bothmer &\ Rust's events are associated with
disparitions brusques, outside active regions. We therefore suggest
that active region sigmoids and disappearing filaments are the origins
of two different classes of CMEs.
Title: MHD-driven Kinetic Dissipation in the Solar Wind and Corona
Authors: Leamon, R. J.; Matthaeus, W. H.; Smith, C. W.; Zank, G. P.;
Mullan, D. J.; Oughton, S.
Bibcode: 2000ApJ...537.1054L
Altcode:
Mechanisms for the deposition of heat in the lower coronal plasma
are discussed, emphasizing recent attempts to reconcile the fluid and
kinetic perspectives. Structures at magnetohydrodynamic (MHD) scales may
drive a nonlinear cascade, preferentially exciting high perpendicular
wavenumber fluctuations. Relevant dissipative kinetic processes must be
identified that can absorb the associated energy flux. The relationship
between the MHD cascade and direct cyclotron absorption, including
cyclotron sweep, is discussed. We conclude that for coronal and solar
wind parameters the perpendicular cascade cannot be neglected and may
be more rapid than cyclotron sweep. Solar wind observational evidence
suggests the relevance of the ion inertial scale, which is associated
with current sheet thickness during reconnection. We conclude that a
significant fraction of dissipation in the corona and solar wind likely
proceeds through a perpendicular cascade and small-scale reconnection,
coupled to kinetic processes that act at oblique wavevectors.
Title: Dissipation of magnetic fluctuations in the solar wind
Authors: Leamon, Robert James
Bibcode: 2000PhDT........10L
Altcode:
The dissipation range for interplanetary magnetic field fluctuations
is formed by those fluctuations with spatial scales comparable to
the gyroradius of a thermal ion. The dissipation range represents
the final fate of magnetic energy that is transferred from the
largest spatial scales via nonlinear processes until resonance with
the thermal ions removes the energy from the spectrum and heats
the background distribution. Typically, the dissipation range at
1 AU sets in at spacecraft frame frequencies of a few tenths of a
Hertz. It is characterized by a steepening of the power spectrum
and often demonstrates a bias of the polarization or magnetic
helicity spectrum. We examine WIND observations of inertial and
dissipation range spectra in an attempt to better understand the
processes that form the dissipation range and how these processes
depend on the ambient solar wind parameters (e.g., IMF intensity,
ambient proton density and temperature, etc.). Despite the commonly
held belief that parallel-propagating waves such as Alfvén waves
form the bulk of inertial range fluctuations, we argue that such
waves are inconsistent with spectral break location data. Instead,
we show that kinetic Alfvén waves propagating at large angles to
the background magnetic field are consistent with the observations,
and we describe some possible motivations for this solution. We also
show that MHD turbulence consisting of a slab/2-D composite geometry is
consistent with the observations and may form the dissipation range,
thereby being responsible for heating the background ions. Lastly,
we demonstrate that heating of the background electrons is a likely,
or possibly, necessary, byproduct of magnetic dissipation.
Title: Dissipation range dynamics: Kinetic Alfvén waves and the
importance of βe
Authors: Leamon, Robert J.; Smith, Charles W.; Ness, Norman F.; Wong,
Hung K.
Bibcode: 1999JGR...10422331L
Altcode:
In a previous paper we argued that the damping of obliquely
propagating kinetic Alfvén waves, chiefly by resonant mechanisms,
was a likely explanation for the formation of the dissipation range for
interplanetary magnetic field fluctuations. This suggestion was based
largely on observations of the dissipation range at 1 AU as recorded
by the Wind spacecraft. We pursue this suggestion here with both a
general examination of the damping of obliquely propagating kinetic
Alfvén waves and an additional examination of the observations. We
explore the damping rates of kinetic Alfvén waves under a wide range of
interplanetary conditions using numerical solutions of the linearized
Maxwell-Vlasov equations and demonstrate that these waves display the
nearly isotropic dissipation properties inferred from the previous
paper. Using these solutions, we present a simple model to predict
the onset of the dissipation range and compare these predictions to
the observations. In the process we demonstrate that electron Landau
damping plays a significant role in the damping of interplanetary
magnetic field fluctuations which leads to significant heating of the
thermal electrons.
Title: Considerations limiting cyclotron-resonant damping of cascading
interplanetary turbulence and why the `slab' approximation fails
Authors: Leamon, Robert J.; Matthaeus, William H.; Smith, Charles W.;
Wong, Hung K.
Bibcode: 1999AIPC..471..465L
Altcode: 1999sowi.conf..465L
In attempting to understand the dissipation of MHD scale fluctuation
energy in the solar wind, the challenge is to harness kinetic
theory (1, 2) effects in a way that is consistent with the presence
of an active spectral cascade in a collisionless plasma. Recent
observational studies (3, 4) have begun the task of sorting out the
constraints that spacecraft observations place on dissipation range
dynamical processes. Here we examine some implications of inertial-
and dissipation-range correlation and spectral analyses extracted from
33 intervals of WIND magnetic field data (4). When field polarity and
signatures of cross helicity and magnetic helicity are examined most
of the data sets suggest some role of resonant dissipative processes
involving thermal protons. Here we seek an explanation for this effect
by postulating that an active spectral cascade into the dissipation
range is balanced by a combination of resonant and nonresonant kinetic
dissipation mechanisms. By solving a pair of rate equations, and
employing constraints from the data, this theory suggests that the ratio
of the two methods of dissipation is of order unity. With an additional
assumption that mixed cross helicity corresponds to random directional
sweeping, the theory approximates the relationship between magnetic and
cross helicities seen in the WIND datasets. Although highly simplified,
this approach appears to account for several observed features, and
explains why complete absorption, and the corresponding pure signature
in the magnetic helicity spectrum, is usually not observed. The results
of the theory are consistent with magnetic fluctuations having oblique
wave vectors, which is strongly supported by the inability of models
based on parallel-propagating waves to adequately predict the onset
of the dissipation range.
Title: Dynamics of the dissipation range for solar wind magnetic
fluctuations
Authors: Leamon, Robert J.; Ness, Norman F.; Smith, Charles W.; Wong,
Hung K.
Bibcode: 1999AIPC..471..469L
Altcode: 1999sowi.conf..469L
The dissipation range of interplanetary magnetic field (IMF)
fluctuations is perhaps the least-studied aspect of the IMF. This is
undoubtedly due, at least in part, to the large volume of data required
to perform thorough studies of the high-frequency spectrum. We examine
the properties of the dissipation range at 1 AU as observed by the
WIND spacecraft, which include: (1) a general steepening of the power
spectrum at spacecraft-frame frequencies comparable to, but greater
than, the proton cyclotron frequency; (2) magnetic fluctuations that
are largely transverse to the mean magnetic field, but less transverse
than is seen in the high-frequency extent of the inertial range; (3)
significant, but not maximal helicity and polarization signatures that
indicate that ion-resonant dissipation is contributing to the magnetic
spectrum; (4) a dominant fraction of the total magnetic energy is
associated with wavevectors at large angles to the mean magnetic field;
and (5) strong plasma β effects in the above results. In addition,
we present a comparison of the observed onset of dissipation with a
theory based on Kinetic Alfvén waves.
Title: The Dynamics of Dissipation Range Fluctuations with Application
to Cosmic Ray Propagation Theory
Authors: Leamon, Robert
Bibcode: 1999ICRC....6..366L
Altcode: 1999ICRC...26f.366L
Unlike larger spatial scales of the interplanetary magnetic field
fluctuation spectrum, study of the smallest scale fluctuations
(comparable to the gyroradius of a thermal proton) which form
the so-called dissipation range has been somewhat neglected. This
spectral range is characterized by a steeply falling power spectrum
and frequently nonzero magnetic helicity, features thought to result
from the dissipation of magnetic fluctuations by thermal particle
populations. Although this range contains relatively little energy,
it is relevant to energetic particle scattering because low-rigidity
particles and all particles at large pitch angles become resonant with
these fluctuations. Analyzing power and helicity spectra of WIND data,
we deduce the orientation of the wavevectors and find that most of
the wave energy is associated with wavevectors at large angles to the
mean magnetic field. We place these observations within an existing
framework for turbulent scattering of cosmic rays.
Title: Fluctuations, Dissipation and Heating in the Corona
Authors: Matthaeus, W. H.; Zank, G. P.; Leamon, R. J.; Smith, C. W.;
Mullan, D. J.; Oughton, S.
Bibcode: 1999SSRv...87..269M
Altcode:
Mechanisms for the deposition of heat in the lower coronal plasma
are discussed, emphasizing recent attempts to reconcile the fluid
and kinetic perspectives. Structures at the MHD scales are believed
to act as reservoirs for fluctuation energy, which in turn drive a
nonlinear cascade process. Kinetic processes act at smaller spatial
scales and more rapid time scales. Cascade-driven processes are
contrasted with direct cyclotron absorption, and this distinction is
echoed in the contrast between frequency and wavenumber spectra of the
fluctuations. Observational constraints are also discussed, along with
estimates of the relative efficiency of cascade and cyclotron processes.
Title: Contribution of Cyclotron-resonant Damping to Kinetic
Dissipation of Interplanetary Turbulence
Authors: Leamon, Robert J.; Matthaeus, William H.; Smith, Charles W.;
Wong, Hung K.
Bibcode: 1998ApJ...507L.181L
Altcode: 1998astro.ph..9017L
We examine some implications of inertial range and dissipation range
correlation and spectral analyses extracted from 33 intervals of Wind
magnetic field data. When field polarity and signatures of cross
helicity and magnetic helicity are examined, most of the data sets
suggest some role of cyclotron-resonant dissipative processes involving
thermal protons. We postulate that an active spectral cascade into the
dissipation range is balanced by a combination of cyclotron-resonant
and noncyclotron-resonant kinetic dissipation mechanisms, of which
only the former induces a magnetic helicity signature. A rate balance
theory, constrained by the data, suggests that the ratio of the two
mechanisms is of order unity. While highly simplified, this approach
appears to account for several observed features and explains why
complete cyclotron absorption, and the corresponding pure magnetic
helicity signature, is usually not observed.
Title: Characteristics of magnetic fluctuations within coronal mass
ejections: The January 1997 event
Authors: Leamon, Robert J.; Smith, Charles W.; Ness, Norman F.
Bibcode: 1998GeoRL..25.2505L
Altcode:
We determine the geometry of the fluctuations of the magnetic field at
frequencies just above the proton gyrofrequency for the January 10, 1997
CME and the magnetic cloud within. The transverse magnetic fluctuations
represent a greater fraction of the magnetic energy than is the case in
the typical undisturbed solar wind. The break in the power spectrum that
is associated with the the onset of magnetic dissipation falls within
the frequency range of interest. The fluctuation geometry is markedly
different above and below the spectral break frequency. The inertial
range geometry remains unchanged in the cloud with only ∼30% of the
energy associated with field-aligned wave vectors. The dissipation
range wave vectors are highly oblique to the mean magnetic field B
with up to 96% of the energy associated with oblique wave vectors.
Title: Observational constraints on the dynamics of the interplanetary
magnetic field dissipation range
Authors: Leamon, Robert J.; Smith, Charles W.; Ness, Norman F.;
Matthaeus, William H.; Wong, Hung K.
Bibcode: 1998JGR...103.4775L
Altcode:
The dissipation range for interplanetary magnetic field fluctuations
is formed by those fluctuations with spatial scales comparable
to the gyroradius or ion inertial length of a thermal ion. It is
reasonable to assume that the dissipation range represents the
final fate of magnetic energy that is transferred from the largest
spatial scales via nonlinear processes until kinetic coupling with
the background plasma removes the energy from the spectrum and heats
the background distribution. Typically, the dissipation range at
1 AU sets in at spacecraft frame frequencies of a few tenths of a
hertz. It is characterized by a steepening of the power spectrum and
often demonstrates a bias of the polarization or magnetic helicity
spectrum. We examine Wind observations of inertial and dissipation
range spectra in an attempt to better understand the processes that
form the dissipation range and how these processes depend on the
ambient solar wind parameters (interplanetary magnetic field intensity,
ambient proton density and temperature, etc.). We focus on stationary
intervals with well-defined inertial and dissipation range spectra. Our
analysis shows that parallel-propagating waves, such as Alfvén waves,
are inconsistent with the data. MHD turbulence consisting of a partly
slab and partly two-dimensional (2-D) composite geometry is consistent
with the observations, while thermal particle interactions with the
2-D component may be responsible for the formation of the dissipation
range. Kinetic Alfvén waves propagating at large angles to the
background magnetic field are also consistent with the observations
and may form some portion of the 2-D turbulence component.
Title: Origin and dynamics of field nulls detected in the jovian
magnetospheres
Authors: Southwood, D. J.; Dougherty, M. K.; Leamon, R. J.; Haynes,
P. L.
Bibcode: 1995AdSpR..16d.177S
Altcode: 1995AdSpR..16..177S
A surprise discovery during the Ulysses flyby of Jupiter was the
presence of what have been called null field events in the outer
magnetosphere. The signatures are quite distinct from those of the
multiple magnetodisk encounters seen closer to the planet. Subsequently,
similar events have been identified in both Pioneer and Voyager
spacecraft magnetometer data. We propose that these events are formed
by the breaking off of material from the outer edge of the magnetodisk
current sheet. We discuss their likely origin, evolution, dynamics
and internal structure.
Title: Magnetic nulls in the outer magnetosphere of Jupiter:
Detections by Pioneer and Voyager spacecraft
Authors: Leamon, R. J.; Dougherty, M. K.; Southwood, D. J.; Haynes,
P. L.
Bibcode: 1995JGR...100.1829L
Altcode:
First reported during the Ulysses flyby of Jupiter in February 1992,
null events are sporadic dropouts in the magnetic field strength
detected in the outer Jovian magnetospehre, with the magnitude of the
field strength decreasing to values that can be less than 0.2 nT. The
events occur in regions where the ambient field is primarily southward,
that is, aligned with the local planetary dipole field direction and
are distinct from the field depressions encountered in the center of
the magnetodisk in the middle magnetosphere. They also appear distinct
from the field structures encountered at the magnetopause. Here we
report a survey of the occurrence of such events in the magnetic field
data recorded by the earlier Pioneer and Voyager spacecraft passages
through the Jovian system. All of the previous spacecraft to fly through
the Jovian magnetosphere recorded field null events on their inbound
passes where the field magnitude dropped below 2 nT. There is little
or no evidence of any field reversal in the center of events. Only
Pioneer 11, which was the only spacecraft to exit on the dayside of
the magnetosphere, recorded events on its outbound pass.