Author name code: altrock
ADS astronomy entries on 2022-09-14
author:"Altrock, Richard C."
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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: Fe XIV Synoptic Observations as a Predictor for the Time of
Solar Maximum in Cycle 24
Authors: Altrock, Richard
Bibcode: 2015TESS....130805A
Altcode:
In 2012 (Am. Geophys. Union Fall Meeting, Abstract SH12A-05) and 2013
(Solar Phys. Online First, DOI 10.1007/s11207-012-0216-1) Altrock
discussed the status of Cycle 24 relative to synoptic observations
ofFe XIV from Sacramento Peak (http://nsosp.nso.edu/corona). He
found that using earlier cycles, in which solar maximum occurred
when Fe XIV emission features associated with the classic "Rush
to the Poles" reached latitudes 76 ± 2 degrees, the *northern
hemisphere* Fe XIV features predicted a maximum in the north at
2011.6 ± 0.3. This was confirmed by hemispheric sunspot numbers
from SIDC (http://www.sidc.be/silso/) and sunspot areas from NASA
MSFC http://solarscience.msfc.nasa.gov/greenwch.shtml). The earlier
papersalso noted that southern high-latitude Fe XIV emission indicated
the possibility of a southern maximum early in 2014. At low latitudes,
earlier cycles reached solar maximum when Fe XIV emission features
reached latitudes 20 ± 1.7 degrees. In 2013, these features were
at 21 and 15 degrees in the north, again indicating that northern
maximum had already occurred. In the south, the Fe XIV features
were at 24 degrees. Gopalswamy et al. (2012, Ap. J. Let. 750:L42)
come to similar conclusions from a study of microwave brightness and
prominence eruptions. This paper will extend the previous studies up
to 2014 to include the recent extraordinary surge of activity in the
southern hemisphere. In particular we will examine in more detail the
relationship between hemispheric Fe XIV emission features and both
global and hemispheric sunspot numbers to see (i) if the previous
studies correctly predicted the times of hemispheric solar maxima and
(ii) what we can learn from the inclusion of two more years of data. The
observations used herein are the result of a cooperative program of
the Air Force Research Laboratory and the National Solar Observatory.
Title: Solar Coronal Temperature During the Rise of Cycle 24
Authors: Altrock, Richard C.
Bibcode: 2014AAS...22432332A
Altcode:
Observations of the solar corona are obtained with the photoelectric
coronal photometer fed by the 40-cm coronagraph in the John W. Evans
Solar Facility at the National Solar Observatory at Sacramento Peak
in Sunspot, NM. The observations consist of daily scans every 3° in
latitude at 1.15 solar radii in Fe XIV 530.3 nm and Fe X 637.4 nm. The
scans were obtained from 1983 to 2013. The coronal temperature (Tc)
may be calculated as a function of the ratio of the intensities of
Fe XIV and Fe X, as shown by Guhathakurta, Fisher and Altrock (1993,
Astrophys. J. Lett., 414, L145). In this paper, I use this technique
to study the long-term, large-scale variation of Tc over the last 3
solar cycles. The observations are used to determine the variation
of Tc at latitudes above 30°. Latitudes below 30° are not studied,
because the technique used to determine Tc is not applicable to
active regions, where the assumption of a uniform temperature along
the line-of-sight is denied by the presence of many active-region
loops of varying temperatures. Suitable temporal averages are
taken to reduce noise.Prior to the last solar minimum we find that
(i) a well-defined solar-cycle variation of Tc at 1.15 Ro was seen,
varying by 0.4 MK near the poles, (ii) Tc near solar minimum decreased
strongly toward thepoles above 60° latitude, and (iii) a variation ~
0.1 MK was seen in the average Tc above 30° latitude.However, since
the last solar maximum, we show that the pattern established during
the previous two cycles was broken. The most important new conclusions
are Tc since minimum reached maximum earlier in the North than in
the South, and Tc at the maximum of Cycle 24 is significantly lower
than in previous cycles. We also found that (i) the polar Tc only
decreased by 0.3 MK from solar maximum to minimum instead of 0.4 MK,
(ii) Tc near solar minimum did not decrease strongly toward the poles
above 60° latitude, which it did in earlier cycles, (iii) the average
Tc above 30° latitude reached a record low value of 1.4 MK, but the
minimum polar Tc was 0.13 MK hotter than the previous cycle, and (iv)
the latitude-variation of Tc at solar minimum was less than 0.1 MK.
Title: Forecasting the Maxima of Solar Cycle 24 with Coronal Fe
XIV Emission
Authors: Altrock, Richard C.
Bibcode: 2014SoPh..289..623A
Altcode: 2012arXiv1209.2963A
The onset of the "Rush to the Poles" of polar-crown prominences
and their associated coronal emission is a harbinger of solar
maximum. Altrock (Solar Phys.216, 343, 2003) showed that the "Rush"
was well observed at 1.15 Ro in the Fe XIV corona at
the Sacramento Peak site of the National Solar Observatory prior
to the maxima of Cycles 21 to 23. The data show that solar maximum
in those cycles occurred when the center line of the Rush reached a
critical latitude of 76∘±2∘. Furthermore,
in the previous three cycles solar maximum occurred when the
highest number of Fe XIV emission features per day (averaged
over 365 days and both hemispheres) first reached latitudes
20∘±1.7∘. Applying the above conclusions to
Cycle 24 is difficult due to the unusual nature of this cycle. Cycle
24 displays an intermittent Rush that is only well-defined in the
northern hemisphere. In 2009 an initial slope of 4.6∘
year−1 was found in the north, compared to an average
of 9.4±1.7∘ year−1 in the previous
cycles. An early fit to the Rush would have reached 76∘
at 2014.6. However, in 2010 the slope increased to 7.5∘
year−1 (an increase did not occur in the previous three
cycles). Extending that rate to 76∘±2∘
indicates that the solar maximum in the northern hemisphere already
occurred at 2011.6±0.3. In the southern hemisphere the Rush to the
Poles, if it exists, is very poorly defined. A linear fit to several
maxima would reach 76∘ in the south at 2014.2. In 1999,
persistent Fe XIV coronal emission known as the "extended solar
cycle" appeared near 70∘ in the North and began migrating
towards the equator at a rate 40 % slower than the previous two solar
cycles. However, in 2009 and 2010 an acceleration occurred. Currently
the greatest number of emission features is at 21∘ in
the North and 24∘ in the South. This indicates that solar
maximum is occurring now in the North but not yet in the South.
Title: The 2011 Northern Hemisphere Solar Maximum
Authors: Altrock, Richard C.
Bibcode: 2013AAS...22141505A
Altcode:
Altrock (1997, Solar Phys. 170, 411) discusses a process in which Fe
XIV 530.3 nm emission features appear at high latitudes and gradually
migrate towards the equator, merging with the sunspot "butterfly
diagram". In cycles 21 - 23 solar maximum occurred when the number of
Fe XIV emission regions per day > 0.19 (averaged over 365 days and
both hemispheres) first reached latitudes 18°, 21° and 21°, for an
average of 20° ± 1.7°. Another high-latitude process is the "Rush
to the Poles" of polar crown prominences and their associated coronal
emission, including Fe XIV. The Rush is a harbinger of solar maximum
(cf. Altrock, 2003, Solar Phys. 216, 343). Solar maximum in cycles
21 - 23 occurred when the center line of the Rush reached a critical
latitude. These latitudes were 76°, 74° and 78°, respectively,
for an average of 76° ± 2°. Cycle 24 displays an intermittent
Rush that is only well-defined in the northern hemisphere. In 2009
an initial slope of 4.6°/yr was found in the north, compared to an
average of 9.4 ± 1.7 °/yr in the previous three cycles. However,
in 2010 the slope increased to 7.5°/yr. Extending that rate to 76°
± 2° indicates that the solar maximum smoothed sunspot number in
the northern hemisphere already occurred at 2011.6 ± 0.3. In the
southern hemisphere the Rush is very poorly defined. A linear fit
to several maxima would reach 76° in the south at 2014.2. In 1999,
persistent Fe XIV coronal emission connected with the ESC appeared near
70° in the north and began migrating towards the equator at a rate 40%
slower than the previous two solar cycles. A fit to the early ESC would
not reach 20° until 2019.8. However, in 2009 and 2010 an acceleration
occurred. Currently the greatest number of emission regions is at 21°
in the north and 24°in the south. This indicates that solar maximum
is occurring now in the north but not yet in the south. The latest
global smoothed sunspot numbers show an inflection point in late 2011,
which could represent solar maximum in the northern hemisphere. Sunspot
areas in the northern hemisphere reached a maximum in late 2011. The
southern areas are still increasing.
Title: The Extended Solar Cycle Tracked High into the Corona
Authors: Tappin, S. J.; Altrock, R. C.
Bibcode: 2013SoPh..282..249T
Altcode: 2012arXiv1209.2969T; 2012SoPh..tmp..241T
We present observations of the extended solar cycle activity in
white-light coronagraphs, and compare them with the more familiar
features seen in the Fe XIV green-line corona. We show that the
coronal activity zones seen in the emission corona can be tracked high
into the corona. The peak latitude of the activity, which occurs near
solar maximum, is found to be very similar at all heights. But we find
that the equatorward drift of the activity zones is faster at greater
heights, and that during the declining phase of the solar cycle, the
lower branch of activity (that associated with the current cycle)
disappears at about 3R⊙. This implies that during the
declining phase of the cycle, the solar wind detected near Earth is
likely to be dominated by the next cycle. The so-called "rush to the
poles" is also seen in the higher corona. In the higher corona it is
found to start at a similar time but at lower latitudes than in the
green-line corona. The structure is found to be similar to that of
the equatorward drift.
Title: Coronal Activity and Extended Solar Cycles
Authors: Altrock, R. C.
Bibcode: 2012AGUFMSH12A..05A
Altcode:
Wilson et al. (1988, Nature 333, 748) discussed a number of solar
parameters, which appear at high latitudes and gradually migrate
towards the equator, merging with the sunspot "butterfly diagram". They
found that this concept had been identified by earlier investigators
extending back to 1957. They named this process the "Extended Solar
Cycle" (ESC). Altrock (1997, Solar Phys. 170, 411) found that this
process continued in Fe XIV 530.3 nm emission features. In cycles 21 -
23 solar maximum occurred when the number of Fe XIV emission regions
per day > 0.19 (averaged over 365 days and both hemispheres)
first reached latitudes 18°, 21° and 21°, for an average of 20°
± 1.7°. Other recent studies have shown that Torsional Oscillation
(TO) negative-shear zones are co-located with the ESC from at least
50° down to the equator and also in the zones where the Rush to
the Poles occur. These phenomena indicate that coronal activity
occurring up to 50° and higher latitudes is related to TO shear zones,
another indicator that the ESC is an important solar process. Another
high-latitude process, which appears to be connected with the ESC,
is the "Rush to the Poles" ("Rush") of polar crown prominences and
their associated coronal emission, including Fe XIV. The Rush is is
a harbinger of solar maximum (cf. Altrock, 2003, Solar Phys. 216,
343). Solar maximum in cycles 21 - 23 occurred when the center line
of the Rush reached a critical latitude. These latitudes were 76°,
74° and 78°, respectively, for an average of 76° ± 2°. Applying
the above conclusions to Cycle 24 is difficult due to the unusual
nature of this cycle. Cycle 24 displays an intermittent "Rush" that
is only well-defined in the northern hemisphere. In 2009 an initial
slope of 4.6°/yr was found in the north, compared to an average of
9.4 ± 1.7 °/yr in the previous three cycles. This early fit to the
Rush would have reached 76° at 2014.6. However, in 2010 the slope
increased to 7.5°/yr (an increase did not occur in the previous three
cycles). Extending that rate to 76° ± 2° indicates that the solar
maximum smoothed sunspot number in the northern hemisphere already
occurred at 2011.6 ± 0.3. In the southern hemisphere the Rush to the
Poles, if it exists, is very poorly defined. A linear fit to several
maxima would reach 76° in the south at 2014.2. In 1999, persistent
Fe XIV coronal emission connected with the ESC appeared near 70° in
the north and began migrating towards the equator at a rate 40% slower
than the previous two solar cycles. A fit to the early ESC would not
reach 20° until 2019.8. However, in 2009 and 2010 an acceleration
occurred. Currently the greatest number of emission regions is at 21°
in the north and 24°in the south. This indicates that solar maximum
is occurring now in the north but not yet in the south. Gopalswamy et
al. (2012, Ap. J. Let. 752, L42 1919) come to similar conclusions from
a study of microwave brightness and prominence eruptions. The latest
global smoothed sunspot numbers show an inflection point in late 2011,
which could represent solar maximum in the northern hemisphere. The
observations used herein are the result of a cooperative program of
the Air Force Research Laboratory and the National Solar Observatory.
Title: Cycle 24 Northern-Hemisphere Solar Maximum Observed in Fe XIV
Authors: Altrock, Richard C.
Bibcode: 2012AAS...22012303A
Altcode:
The onset of the "Rush to the Poles" of polar crown prominences
and their associated coronal emission is a harbinger of solar
maximum. Altrock (2003, Solar Phys. 216, 343) showed that the "Rush"
was well-observed in the the Fe XIV corona at the Sacramento Peak site
of the National Solar Observatory prior to the maxima of Cycles 21
to 23. He found that solar maximum in those cycles occurred when the
center line of the Rush reached a critical latitude. These latitudes
were 76°, 74° and 78°, respectively, for an average of 76° ±
2°. Applying this method to Cycle 24 is difficult due to the
unusual nature of this cycle. Cycle 24 displays an intermittent "Rush"
that is only definable in the northern hemisphere. In 2009 an initial
slope of 4.6°/yr was found, compared to an average of 9.4 ± 1.7 °/yr
in the previous cycles. However, in 2010 the slope increased to 7.5°/yr
(an increase did not occur in the previous three cycles). Extending
that rate to 76° ± 2° indicates that the maximum smoothed sunspot
number in the northern hemisphere ALREADY OCCURRED at 2011.6 ±
0.3. Unfortunately, the smoothed sunspot number uses 12-month running
means, so the result may not be testable for several more months. Solar
maximum may not be detectable in the southern hemisphere.
Title: Coronal Fe XIV Emission During the Whole Heliosphere Interval
Campaign
Authors: Altrock, Richard C.
Bibcode: 2011SoPh..274..251A
Altcode: 2011arXiv1106.3998A
Solar Cycle 24 is having a historically long and weak
start. Observations of the Fe XIV corona from the Sacramento Peak
site of the National Solar Observatory show an abnormal pattern of
emission compared to observations of Cycles 21, 22, and 23 from the
same instrument. The previous three cycles have shown a strong, rapid
"Rush to the Poles" (previously observed in polar crown prominences
and earlier coronal observations) in the parameter N(t,l,dt) (average
number of Fe XIV emission features per day over dt days at time t and
latitude l). Cycle 24 displays a weak, intermittent, and slow "Rush"
that is apparent only in the northern hemisphere. If the northern Rush
persists at its current rate, evidence from the Rushes in previous
cycles indicates that solar maximum will occur in early 2013 or
late 2012, at least in the northern hemisphere. At lower latitudes,
solar maximum previously occurred when the time maximum of N(t,l,365)
reached approximately 20° latitude. Currently, this parameter is at or
below 30° and decreasing in latitude. Unfortunately, it is difficult at
this time to calculate the rate of decrease in N(t,l,365). However, the
southern hemisphere could reach 20° in 2011. Nonetheless, considering
the levels of activity so far, there is a possibility that the maximum
could be indiscernible.
Title: Solar Coronal Temperature and Line Emission During the Long
Minimum and the Rise of Cycle 24
Authors: Altrock, R. C.
Bibcode: 2011AGUFMSH33A2029A
Altcode:
Solar Cycle 24 had a weak start following an extraordinarily long
minimum. Observations of the Fe XIV corona from the Sacramento Peak
site of the National Solar Observatory showed an abnormal pattern
of emission compared to observations of Cycles 21, 22, and 23 from
the same instrument. The previous three cycles had a strong, rapid
"Rush to the Poles" in Fe XIV. Cycle 24 displays a delayed, weak,
intermittent, and slow "Rush" that is mainly apparent in the northern
hemisphere. This paper discusses (i) the characteristics of emission
from Fe XIV and other coronal ions and (ii) the coronal temperature
calculated from the NSO observations in order to further characterize
coronal conditions during this epoch and their implications for Cycle
24 maximum.
Title: The slow rise of Cycle 24 as seen in Fe XIV
Authors: Altrock, Richard C.
Bibcode: 2011shin.confE.150A
Altcode:
Solar Cycle 24 had a historically prolonged and weak start. Observations
of the Fe XIV corona from the Sacramento Peak site of the National
Solar Observatory showed an abnormal pattern of emission compared to
observations of Cycles 21, 22, and 23 from the same instrument. The
previous three cycles had a strong, rapid Rush to the Poles" in
Fe XIV. Cycle 24 displays a delayed, weak, intermittent, and slow
"Rush" that is mainly apparent in the northern hemisphere. If
this Rush persists at its current rate, evidence from previous
cycles indicates that solar maximum will occur in approximately
early 2013. At lower latitudes, solar maximum previously occurred
when the greatest number of Fe XIV emission regions* first reached
approximately 20° latitude. Currently, the value of this parameter
at 20° is approximately 0.15. Previous behavior of this parameter
indicates that solar maximum should occur in approximately two years,
or 2013. Thus, both techniques yield an expected time of solar maximum
in early 2013. *annual average number of Fe XIV emission features
per day > 0.19
Title: Torsional Oscillations and Coronal Activity
Authors: Altrock, Richard C.
Bibcode: 2011shin.confE...8A
Altcode:
Howe et al. (2009) demonstrate that solar activity appears to move
towards the equator somewhat parallel to the latitude motion of
torsional oscillation flows. However, Snodgrass (1987) had previously
suggested that the regions between the fast and slow torsional
oscillation flows represent zones where magnetic field is concentrated,
which results in the formation of activity. In an attempt to test this
suggestion, Altrock et al. (2008) compared the location of bright Fe
XIV coronal regions to the latitude derivative of torsional oscillation
frequencies and found that the bright regions occurred over regions
where the latitude derivative was at its lowest (negative) value;
i.e., between the fast and slow streams, thus verifying Snodgrass'
suggestion. This paper extends and verifies the results of Altrock
et al., that solar activity occurs over the "shear" zone between fast
and slow torsional oscillation flows.
Title: Whither goes Cycle 24? A View from the Fe XIV Corona
Authors: Altrock, Richard C.
Bibcode: 2011SPD....42.1804A
Altcode: 2011BAAS..43S.1804A
Solar Cycle 24 had a historically prolonged and weak start. Observations
of the Fe XIV corona from the Sacramento Peak site of the National
Solar Observatory showed an abnormal pattern of emission compared to
observations of Cycles 21, 22, and 23 from the same instrument. The
previous three cycles had a strong, rapid "Rush to the Poles" in
Fe XIV. Cycle 24 displays a delayed, weak, intermittent, and slow
"Rush" that is mainly apparent in the northern hemisphere. If
this Rush persists at its current rate, evidence from previous
cycles indicates that solar maximum will occur in approximately
early 2013. At lower latitudes, solar maximum previously occurred
when the greatest number of Fe XIV emission regions* first reached
approximately 20° latitude. Currently, the value of this parameter
at 20° is approximately 0.15. Previous behavior of this parameter
indicates that solar maximum should occur in approximately two years,
or 2013. Thus, both techniques yield an expected time of solar maximum
in early 2013. *annual average number of Fe XIV emission features
per day greater than 0.19
Title: What is the relationship between solar torsional oscillations
and solar activity?
Authors: Altrock, R. C.
Bibcode: 2010AGUFMSH53B..04A
Altcode:
Howe et al. (2009) demonstrate that solar activity appears to move
towards the equator somewhat parallel to the latitude motion of
torsional oscillation flows. However, Snodgrass (1987) had previously
suggested that the regions between the fast and slow torsional
oscillation flows represent zones where magnetic field is concentrated,
which results in the formation of activity. In an attempt to test this
suggestion, Altrock et al. (2008) compared the location of bright Fe
XIV coronal regions to the latitude derivative of torsional oscillation
frequencies and found that the bright regions occurred over regions
where the latitude derivative was at its lowest (negative) value;
i.e., between the fast and slow streams, thus verifying Snodgrass'
suggestion. This paper extends and verifies the results of Altrock et
al., that SOLAR ACTIVITY OCCURS OVER THE ``SHEAR'' ZONE BETWEEN FAST
AND SLOW TORSIONAL OSCILLATION FLOWS. References: Howe, R., et al.,
ApJ Letters 701, L87, 2009; Snodgrass, H., ApJ 316, L91, 1987; Altrock,
R., et al., ASPCS 363, 335, 2008. Thanks to R. Howe and R. Ulrich
for providing their torsional oscillation data. Fe XIV coronal bright
regions (shading) and MWO torsional oscillation latitude derivative
(contours) from 1982 to 2007.
Title: What happened to Cycle 24? Evidence from the Fe XIV corona.
Authors: Altrock, Richard C.
Bibcode: 2010shin.confE.151A
Altcode:
Cycle 24 is having a historically long and weak start. Observations
of the Fe XIV corona from the Sacramento Peak site of the National
Solar Observatory show a peculiar pattern of emission, when compared
to observations of cycles 21, 22 and 23 from the same instrument. The
previous three cycles have shown a strong, rapid
Title: The Progress of Solar Cycle 24 at High Latitudes
Authors: Altrock, R. C.
Bibcode: 2010ASPC..428..147A
Altcode: 2010arXiv1002.2401A
The "extended" solar cycle 24 began in 1999 near 70° latitude,
similarly to cycle 23 in 1989 and cycle 22 in 1979. The extended cycle
is manifested by persistent Fe XIV coronal emission appearing near
70° latitude and slowly migrating towards the equator, merging with
the latitudes of sunspots and active regions (the "butterfly diagram")
after several years. Cycle 24 began its migration at a rate 40% slower
than the previous two solar cycles, thus indicating the possibility
of a peculiar cycle. However, the onset of the "Rush to the Poles" of
polar crown prominences and their associated coronal emission, which
has been a precursor to solar maximum in recent cycles (cf. Altrock
2003), has just been identified in the northern hemisphere. Peculiarly,
this "rush" is leisurely, at only 50% of the rate in the previous two
cycles. The properties of the current "Rush to the Poles" yields an
estimate of 2013 or 2014 for solar maximum.
Title: High-Latitude Coronal Fe XIV Emission During the Long Minimum
and its Implications for Cycle 24
Authors: Altrock, Richard C.
Bibcode: 2010AAS...21640102A
Altcode: 2010BAAS...41..857A
The "extended" solar cycle 24 began in 1999 near 70° latitude,
similarly to cycle 23 in 1989 and cycle 22 in 1979. The extended cycle
is manifested by persistent Fe XIV coronal emission appearing near
70° latitude and slowly migrating towards the equator, merging with
the latitudes of sunspots and active regions (the "butterfly diagram")
after several years. Cycle 24 began its migration at a rate 40% slower
than the previous two solar cycles, thus indicating the possibility
of a peculiar cycle. However, the onset of the "Rush to the Poles" of
polar crown prominences and their associated coronal emission, which
has been a precursor to solar maximum in recent cycles (cf. Altrock
2003), has been identified in the northern hemisphere. Peculiarly,
this "Rush" is leisurely, at only 50% of the rate in the previous two
cycles. The properties of the current "Rush to the Poles" yields an
estimate of 2013 or 2014 for solar maximum.
Title: "Extended-Solar-Cycle" Activity During the Current Solar
Minimum
Authors: Altrock, R. C.
Bibcode: 2009AGUFMSH14A..04A
Altcode:
Altrock (1997, Solar Phys. 170, 411) and earlier authors discussed the
high-latitude "extended" solar cycle seen in the Fe XIV corona prior to
the appearance of sunspots and active regions at lower latitudes. For
example, persistent coronal emission appeared near 70 degrees latitude
in 1979 and 1989 and slowly migrated towards the equator, merging
with the latitudes of sunspots and active regions after several
years. Altrock (2007AGUFMSH53A1052A) showed that the high-latitude
coronal emission was situated above the high-latitude neutral line
of the large-scale photospheric magnetic field seen in Wilcox Solar
Observatory synoptic maps, thus implying a connection with the solar
dynamo. In 1999, persistent Fe XIV coronal emission appeared near 70
degrees latitude and began migrating towards the equator, but at a rate
40% slower than the previous two solar cycles. However, the onset of
the "Rush to the Poles" of polar crown prominences and their associated
coronal emission, which has preceded solar maximum by approximately two
years in recent cycles (cf. Altrock, 2003, Solar Phys. 216, 343), has
just occurred. Implications of these two events for predictions of the
timing of the maximum of cycle 24 will be discussed. The observations
used herein are the result of a cooperative program of the Air Force
Research Laboratory and the National Solar Observatory.
Title: The Progress of Solar Cycle 24 at High Latitudes
Authors: Altrock, Richard C.
Bibcode: 2009SPD....40.2405A
Altcode:
Altrock (Solar Phys., 170, 411, 1997) and earlier authors discussed
the high-latitude "extended" solar cycle seen in the Fe XIV corona
prior to the appearance of sunspots and active regions at lower
latitudes. For example, persistent coronal activity appeared near 70
degrees latitude in 1979 and 1989 and slowly migrated towards the
equator, merging with the latitudes of sunspots and active regions
after several years. Altrock (2007AGUFMSH53A1052A) showed that the
high-latitude coronal activity was situated above the high-latitude
neutral line of the large-scale photospheric magnetic field seen in
Wilcox Solar Observatory synoptic maps, thus implying a connection with
the solar dynamo. In 1999, persistent Fe XIV coronal activity
appeared near 70 degrees latitude and began slowly migrating towards
the equator at a rate similar to the previous two solar cycles. Thus,
it appears that the solar dynamo that will produce the activity of
cycle 24 is progressing normally. The current state of the extended
solar cycle will be presented, with emphasis on determining whether
the "Rush to the Poles" that will herald the cycle 24 maximum has
begun (cf. Altrock, Solar Phys., 216, 343, 2003). Samples of current
solar-minimum coronal activity will be shown.
Title: Solar Torsional Oscillations and Their Relationship to
Coronal Activity
Authors: Altrock, R. C.; Howe, R.; Ulrich, R.
Bibcode: 2008AGUSMSP31D..03A
Altcode:
Torsional Oscillations (TO) were first observed on the surface of the
Sun as waves of small deviations from differential rotation, which
propagate from high latitudes to the equator over solar-cycle time
scales. More recently they have been inferred from observations of
solar global oscillations to occur in the convection zone. Long-lived
brightenings in the corona have also been observed to propagate from
near the poles to the equator over similar time scales. This paper will
discuss the relationship between TO as observed on the solar surface
and in the convection zone and brightenings in the corona. We find
that there is an apparent connection between these two phenomena that
extends from the equator to latitudes as high as 70 to 80 degrees. This
may imply control of both of these phenomena by the driver of the solar
cycle (the solar dynamo) and thus place observational constraints on
dynamo models. R. C. Altrock was supported by the Air Force Office of
Scientific Research.
Title: Solar Torsional Oscillations and Their Relationship to
Coronal Activity
Authors: Altrock, R.; Howe, R.; Ulrich, R.
Bibcode: 2008ASPC..383..335A
Altcode:
Torsional Oscillations (TO) were first observed on the surface of the
Sun as waves of small deviations from differential rotation, which
propagate from high latitudes to the equator over solar-cycle time
scales. More recently they have been inferred from observations of
solar global oscillations to occur in the convection zone. Long-lived
brightenings in the corona have also been observed to propagate from
near the poles to the equator over similar time scales. This paper will
discuss the relationship between TO as observed on the solar surface
and in the convection zone and brightenings in the corona. We find that
there is an apparent connection between these two phenomena that extends
from the equator to latitudes as high as 70° to 80°. This may imply
control of both of these phenomena by the driver of the solar cycle (the
solar dynamo) and thus place observational constraints on dynamo models.
Title: The Fe XIV Corona Approaching Solar Minimum
Authors: Altrock, R. C.
Bibcode: 2007AGUFMSH53A1052A
Altcode:
Although the solar disk is often devoid of sunspots around solar
minimum, the upper atmosphere never rests. The most prominent features
approaching the minimum of coronal activity are dense regions overlying
mid-latitude boundaries of the large scale magnetic field. Seen above
the limb, these features typically give the impression of "ears" (and
"jowls"). Samples of these features will be shown, and the relationship
to the "extended solar cycle" running from near the poles to the
equator over 18 years will be discussed.
Title: The Fe XIV and Fe X Corona at Solar Minimum
Authors: Altrock, Richard C.
Bibcode: 2007AAS...210.2506A
Altcode: 2007BAAS...39..132A
Although the solar disk is often devoid of sunspots around solar
minimum, the upper atmosphere never rests. The most prominent features
at the absolute minimum of coronal activity are dense regions overlying
high latitude boundaries of the large scale magnetic field. Seen above
the limb, these features typically give the impression of "ears" (and
"jowls"). Samples of these features will be shown and their cause (the
"extended solar cycle" running from near the poles to the equator over
18 years) explained. The author was supported by the Air Force Office
of Scientific Research.
Title: Using Solar-Minimum Polar Coronal Activity to Predict the
Magnitude of the Following- Cycle Maximum
Authors: Altrock, R. C.
Bibcode: 2006AGUFMSH21A0323A
Altcode:
Observations of the Fe XIV solar corona have been obtained for the
past three solar activity cycles at the Sacramento Peak site of
the National Solar Observatory with the 40-cm coronagraph and the
photoelectric coronal photometer. This study compares the properties of
these observations near the poles near solar minimum with the maximum
sunspot number of the following solar cycle. Preliminary results
indicate that the number of coronal bright regions near the poles near
solar minimum may be inversely correlated with the maximum amplitude
of the following solar cycle. Using these results from previous cycles,
a prediction will be made of the maximum sunspot number for cycle 24.
Title: Solar Torsional Oscillations and Their Relationship to
Coronal Activity
Authors: Altrock, Richard C.; Howe, R.; Ulrich, R.
Bibcode: 2006SPD....37.3203A
Altcode: 2006BAAS...38..258A
Torsional Oscillations were first observed on the surface of
the sun aswaves of small deviations from differential rotation,
which propagatefrom the pole to the equator over solar-cycle time
scales. Morerecently they have been inferred from observations of
solar globaloscillations to occur in the convection zone. Long-lived
brighteningsin the corona have also been observed to propagate from
near the polesto the equator over similar time scales. This paper will
discuss therelationship between torsional oscillations as observed
on the surfaceand in the convection zone and brightenings in the
corona. We findthat there is an apparent connection between these
two phenomena thatextends from the equator to latitudes as high as
70 to 80 degrees.R. C. Altrock was supported by the Air Force Office
of ScientificResearch.
Title: A Search for Torsional Oscillations in the Fe XIV Solar Corona
Authors: Altrock, R. C.
Bibcode: 2005AGUFMSH41B1132A
Altcode:
Previous studies of the rotation of the solar corona have found
evidence for variations with time in the differential rotation rate
similar to what has been referred to as torsional oscillations in the
photosphere and the convection zone. However, the consistent data set
of Fe XIV intensities obtained at Sacramento Peak since 1973 has not
been exhaustively studied to determine if such oscillations exist. This
data set has the advantage that a single photoelectric technique has
been used to obtain the data over its entire length, whereas other
studies have used data sets compiled from data obtained in a variety
of methods from several observatories. The use of the Sacramento Peak
database also has the advantage that the data have been corrected for
sky-background variations in real time and thus are very precise over
the time required to take a single scan. The results of this analysis
will be presented and compared with those using other data sets.
Title: Comparison of the Sacramento Peak Fe XIV Index with a Model
Index Computed from Differential Emission Measure Maps
Authors: Cook, J. W.; Newmark, J. S.; Altrock, R. C.
Bibcode: 2005ApJ...633..518C
Altcode:
We compare the Sacramento Peak Fe XIV 5303 Å green line index with a
model index time series for the period of operations of the EUV Imaging
Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO),
covering the years 1996-2002, from cycle minimum past the peak of the
current activity cycle 23. We compute a differential emission measure
(DEM) map for each day using images from the four channels of EIT at
171, 195, 284, and 304 Å. From the daily DEM map we then calculate
a daily synthetic Fe XIV 5303 Å intensity image. The Sacramento Peak
index is an average intensity, measured using a circular aperture 1.1
arcmin in diameter, sampling the off-limb corona in 3° steps around
disk center. It is taken at several different heights beyond the daily
white light limb. We modeled the daily index values, for the aperture
center at 1.15 and 1.25 Rsolar from disk center, as the
weighted average intensity within an annulus covering 1.11-1.19 and
1.21-1.29 Rsolar superposed on the daily synthetic intensity
image. We compare the observed index with our model results and find a
high correlation of the short-term values but a long-term systematic
difference in the absolute values. We examine the accuracy of the
respective calibrations and argue that the model results, based on
the calibration of the EIT images used to produce the daily DEM maps,
are more plausible in absolute value.
Title: Solar Torsional Oscillations and the Extended Solar Cycle
Authors: Altrock, R. C.; Howe, R.
Bibcode: 2005AGUSMSP32A..04A
Altcode:
Torsional Oscillations were first observed on the surface of the sun as
waves of small deviations from differential rotation, which propagate
from the pole to the equator over solar-cycle time scales. More
recently they have been inferred from observations of solar global
oscillations to occur in the convection zone. Other solar phenomena,
such as ephemeral regions and brightenings in the corona, have also
been observed to propagate from near the poles to the equator over
similar time scales. These other phenomena have been collectively
referred to as the "Extended Solar Cycle". This paper will discuss
the relationship between torsional oscillations as observed on the
surface and in the convection zone and the "Extended Solar Cycle" as
observed in the corona. R. C. Altrock was supported by the Air Force
Office of Scientific Research.
Title: Solar Torsional Oscillations and the Extended Solar Cycle
Authors: Altrock, R.; Howe, R.
Bibcode: 2004AGUFMSH53B0312A
Altcode:
Torsional Oscillations were first observed on the surface of the sun as
waves of small deviations from differential rotation, which propagate
from the pole to the equator over solar-cycle time scales. More
recently they have been inferred from observations of solar global
oscillations to occur in the convection zone. Other solar phenomena,
such as ephemeral regions and brightenings in the corona, have also been
observed to propagate from near the poles to the equator over similar
time scales. These other phenomena have been collectively referred to
as the "Extended Solar Cycle". This paper will discuss the relationship
between torsional oscillations as observed in the convection zone and
the "Extended Solar Cycle" as observed in the corona.
Title: Solar Torsional Oscillations and the Extended Solar Cycle
Authors: Altrock, R. C.; Howe, R.
Bibcode: 2004AAS...205.4301A
Altcode: 2004BAAS...36.1411A
Torsional Oscillations were first observed on the surface of the sun as
waves of small deviations from differential rotation, which propagate
from the pole to the equator over solar-cycle time scales. More
recently they have been inferred from observations of solar global
oscillations to occur in the convection zone. Other solar phenomena,
such as ephemeral regions and brightenings in the corona, have also been
observed to propagate from near the poles to the equator over similar
time scales. These other phenomena have been collectively referred to
as the "Extended Solar Cycle". This paper will discuss the relationship
between torsional oscillations as observed in the convection zone and
the "Extended Solar Cycle" as observed in the corona. R. C. Altrock
was supported by the Air Force Office of Scientific Research.
Title: The Solar Mass-Ejection Imager (SMEI) Mission
Authors: Jackson, B. V.; Buffington, A.; Hick, P. P.; Altrock, R. C.;
Figueroa, S.; Holladay, P. E.; Johnston, J. C.; Kahler, S. W.; Mozer,
J. B.; Price, S.; Radick, R. R.; Sagalyn, R.; Sinclair, D.; Simnett,
G. M.; Eyles, C. J.; Cooke, M. P.; Tappin, S. J.; Kuchar, T.; Mizuno,
D.; Webb, D. F.; Anderson, P. A.; Keil, S. L.; Gold, R. E.; Waltham,
N. R.
Bibcode: 2004SoPh..225..177J
Altcode:
We have launched into near-Earth orbit a solar mass-ejection imager
(SMEI) that is capable of measuring sunlight Thomson-scattered from
heliospheric electrons from elongations to as close as 18∘
to greater than 90∘ from the Sun. SMEI is designed to
observe time-varying heliospheric brightness of objects such as coronal
mass ejections, co-rotating structures and shock waves. The instrument
evolved from the heliospheric imaging capability demonstrated by the
zodiacal light photometers of the Helios spacecraft. A near-Earth
imager can provide up to three days warning of the arrival of a mass
ejection from the Sun. In combination with other imaging instruments
in deep space, or alone by making some simple assumptions about the
outward flow of the solar wind, SMEI can provide a three-dimensional
reconstruction of the surrounding heliospheric density structures.
Title: The Temperature of the Low Corona During Solar Cycles 21 23
Authors: Altrock, Richard C.
Bibcode: 2004SoPh..224..255A
Altcode: 2005SoPh..224..255A
Observations of the forbidden coronal lines Fe XIV 530.3 nm and Fe
X 637.4 nm obtained at the National Solar Observatory at Sacramento
Peak are used to determine the variation of coronal temperature
at latitudes above 30∘ during solar activity cycles
21-23. Features of the long-term variation of emission in the two lines
are also discussed. Temperatures at latitudes below 30∘
are not studied because the technique used to determine the coronal
temperature is not applicable in active regions. The polar temperature
varies cyclically from approximately 1.3 to 1.7 MK. The temperatures
are similar in both hemispheres. The temperature near solar minimum
decreases strongly from mid-latitudes to the poles. The temperature
of the corona above 80∘ latitude generally follows the
sunspot cycle, with minima in 1985 and 1995-1996 (cf. 1986 and 1996 for
the smoothed sunspot number, Rz) and maxima in 1989 and 2000 (cf. 1989
and 2000 for Rz). The temperature of the corona above 30∘
latitude at solar maximum is nearly uniform, i.e., there is little
latitude dependence. If the maximum temperatures of cycles 22 and
23 are aligned in time (superposed epochs), the average annual N +
S temperature (average of the northern and southern hemisphere)
in cycle 23 is hotter than that in cycle 22 at all times both above
80∘ latitude and above 30∘ latitude. The
difference in the average annual N + S maximum temperature between
cycles 23 and 22 was 56 kK near the poles and 64 kK for all latitudes
above 30∘. Cycle 23 was also hotter at mid-latitudes
than cycle 22 by 60 kK. The last 3 years of cycle 21 were hotter than
the last 3 years of cycle 22. The difference in average annual N +
S temperatures at the end of cycles 21 and 22 was 32 kK near the poles
and 23 kK for all latitudes above 30∘. Cycle 21 was also
hotter at mid-latitudes than cycle 22 by at least 90 kK. Thus, there
does not seem to be a solar-cycle trend in the low-coronal temperature
outside of active regions.
Title: Observations of the "Extended Solar Cycle" During Solar
Cycle 23
Authors: Altrock, R. C.
Bibcode: 2004AAS...204.2007A
Altcode: 2004BAAS...36..687A
Altrock (1997, Solar Phys. 170, 411-423) previously observed
high-latitude Fe XIV 530.3 nm emission features during solar cycles 21
and 22 at the National Solar Observatory at Sacramento Peak. He found
that the observations supported the concept of "Extended" Solar Cycles,
which begin every 11 years but last for approximately 19-20 years. This
concept is based on observations by several earlier investigators
extending back to 1957 (see Wilson et al., 1988, Nature 333, 748-750,
for references). More recent investigations of high-latitude coronal
activity have used satellite observations (cf. Benevolenskaya,
Kosovichev and Scherrer, 2001, Astrophys. J. 554, L107-L110). This
paper will compare the results of Altrock (1997) with newer data to
determine if the earlier inferences of Extended Solar Cycles find added
support during solar cycle 23. In addition, I will compare the results
of these ground-based studies with those obtained using satellite data.
Title: Sky Brightness and Transparency at the National Solar
Observatory at Sacramento Peak
Authors: Altrock, R. C.
Bibcode: 2003AGUFMSH21B0141A
Altcode:
Records of sky brightness and transparency have been kept at the
National Solar Observatory at Sacramento Peak in Sunspot, NM, for the
past 20 years. Annual variations and long-term trends will be analyzed
and presented.
Title: Use of ground-based coronal data to predict the date of
solar-cycle maximum
Authors: Altrock, Richard C.
Bibcode: 2003SoPh..216..343A
Altcode:
Prediction of the exact date of the maximum of the 11-year solar
activity cycle is a matter of disagreement among solar scientists and
of some importance to satellite operators, space-system designers,
etc. Most predictions are based on physical conditions occurring
at or before the solar-cycle minimum preceding the maximum in
question. However, another indicator of the timing of the maximum occurs
early in the rise phase of the solar cycle. A study of the variation
over two previous solar cycles of coronal emission features in Fe xiv
from the National Solar Observatory at Sacramento Peak has shown that,
prior to solar maximum, emission features appear above 50° latitude in
both hemispheres and begin to move towards the poles at a rate of 8°
to 11° of latitude per year. This motion is maintained for a period
of 3 or 4 years, at which time the emission features disappear near
the poles. This phenomenon has been referred to as the `Rush to the
Poles'. These observations show that the maximum of solar activity,
as seen in the sunspot number, occurs approximately 19 ± 2 months
before the features reach the poles. In 1997, Fe xiv emission features
appeared near 55° latitude, and began to move towards the poles. Using
the above historical data from cycles 21 and 22, we will see how the
use of progressively more data from cycle 23 affects the prediction of
the date of solar maximum. The principal conclusion is that the date
of solar maximum for cycle 23 could be predicted to within 6 months as
early as 1997. For solar cycle 24, when this phenomenon first becomes
apparent later this decade, the average parameters for cycles 21-23
can be used to predict the date of solar maximum.
Title: Is the Solar Corona getting hotter?
Authors: Altrock, R. C.
Bibcode: 2003SPD....34.1912A
Altcode: 2003BAAS...35..844A
Observations of the forbidden coronal lines Fe XIV 530.3 nm and Fe
X 637.4 nm obtained at the National Solar Observatory at Sacramento
Peak are used to determine the variation of coronal temperature at
latitudes above 30 degrees during solar activity cycles 21, 22 and
23. Latitudes below 30 degrees are not studied, because the technique
used to determine the coronal temperature is not applicable in active
regions. The variation of temperature as a function of latitude
and time is seen to be nearly symmetric about solar maximum and
consistent between the northern and southern hemisphere during all three
cycles. The variation with time at various latitudes will be studied in
order to determine any long-term trends in coronal temperature. The
author was supported by the Air Force Office of Scientific Research.
Title: A Study of the Rotation of the Solar Corona
Authors: Altrock, Richard C.
Bibcode: 2003SoPh..213...23A
Altcode:
Synoptic photoelectric observations of the coronal Fe xiv and Fe x
emission lines at 530.3 nm and 637.4 nm, respectively, are analyzed
to study the rotational behavior of the solar corona as a function
of latitude, height, time and temperature between 1976 (1983 for Fe
x) and 2001. An earlier similar analysis of the Fe xiv data at 1.15
R⊙ over only one 11-year solar activity cycle (Sime,
Fisher, and Altrock, 1989, Astrophys. J.336, 454) found suggestions
of solar-cycle variations in the differential (latitude-dependent)
rotation. These results are tested over the longer epoch now
available. In addition, the new Fe xiv 1.15 R⊙ results
are compared with those at 1.25 R⊙ and with results from
the Fe x line. I find that for long-term averages, both ions show a
weakly-differential rotation period that may peak near 80° latitude
and then decrease to the poles. However, this high-latitude peak may
be due to sensing low-latitude streamers at higher latitudes. There
is an indication that the Fe xiv rotation period may increase with
height between 40° and 70° latitude. There is also some indication
that Fe x may be rotating slower than Fe xiv in the mid-latitude
range. This could indicate that structures with lower temperatures
rotate at a slower rate. As found in the earlier study, there is very
good evidence for solar-cycle-related variation in the rotation of Fe
xiv. At latitudes up to about 60°, the rotation varies from essentially
rigid (latitude-independent) near solar minimum to differential
in the rising phase of the cycle at both 1.15 R⊙ and
1.25 R⊙. At latitudes above 60°, the rotation at 1.15
R⊙ appears to be nearly rigid in the rising phase and
strongly differential near solar minimum, almost exactly out of phase
with the low-latitude variation.
Title: Use of Ground-Based Coronal Data to Predict the Time of
Solar-Cycle Maximum
Authors: Altrock, R. C.
Bibcode: 2002AAS...20113001A
Altcode: 2002BAAS...34.1314A
Prediction of the exact time of solar-cycle maximum is a matter
of disagreement among solar scientists and of some importance to
satellite operators, space-system designers, etc. Most predictions
are based on physical conditions occurring at or before the long-term
minimum of activity preceding the maximum in question. However, another
indicator of the timing of the maximum occurs early in the rise phase
of the solar activity cycle. A study of the variation over two previous
solar cycles of coronal emission features in Fe XIV from the National
Solar Observatory at Sacramento Peak has shown that, prior to solar
maximum, emission features appear near 55 degrees latitude in both
hemispheres and begin to move towards the poles at a rate of 9 to 13
degrees of latitude per year. This motion is maintained for a period
of 3 or 4 years, at which time the emission features disappear near
the poles. This phenomenon has been referred to as the "Rush to the
Poles". These observations show that the maximum of solar activity, as
seen in the sunspot number, occurs approximately 15 +/- 1 months before
the features reach the poles. In 1997, Fe XIV emission features appeared
near 55 degrees latitude, and began to move towards the poles. Using
the above historical data from cycles 21 and 22, we will see how the
use of progressively more data from cycle 23 affects the prediction
of the time of solar maximum. For example, based on observations up
through April 1999, the extrapolated Rush to the Poles is predicted
to reach the poles in approximately June 2001, which results in a
prediction for solar maximum of between January and April 2000. The
actual smoothed sunspot number maximized in April 2000. This work was
supported by the Air Force Office of Scientific Research.
Title: Long-Term Variation of Solar Coronal Fe XIV and Fe X Fluxes
Authors: Altrock, R. C.
Bibcode: 2002AAS...200.8809A
Altcode: 2002BAAS...34..790A
Synoptic photoelectric observations of the coronal Fe XIV and Fe X
emission lines at 530.3 nm and 637.4 nm, respectively, are analyzed
to study the output of the solar corona in these lines as a function
of time. The data used are measurements made with the NSO/Sacramento
Peak 40-cm coronagraph and Emission-Line Coronal Photometer of the
intensity of these lines observed at 1.15 solar radii between 1973
(1984 for Fe X) and 2002. A new calibration determination is used to
convert relative intensities to absolute intensities. The solar-cycle
variation of these fluxes will be compared to each other and to other
solar-cycle parameters. One interesting result is that a constant
minimum or basal corona may exist at solar minimum. This paper was
supported by the Air Force Office of Scientific Research.
Title: Long-term variation of solar coronal Fe XIV and Fe X fluxes
Authors: Altrock, R.
Bibcode: 2002cosp...34E1003A
Altcode: 2002cosp.meetE1003A
Synoptic photoelectric observations of the coronal Fe XIV and Fe X
emission lines at 530.3 nm and 637.4 nm, respectively, are analyzed
to study the output of the solar corona in these lines as a function
of time. The data used are measurements made with the NSO/Sacramento
Peak 40-cm coronagraph and Emission-Line Coronal Photometer of the
intensity of these lines observed at 1.15 solar radii between 1973
(1984 for Fe X) and 2002. A new calibration determination is used to
convert relative intensities to absolute intensities. The solar-cycle
variation of these fluxes will be compared to each other and to other
solar-cycle parameters. One interesting result is that a constant
minimum or basal corona may exist at solar minimum. This paper was
supported by the Air Force Office of Scientific Research.
Title: Long-Term Variation of the Rotation of the Solar Corona
Authors: Altrock, R. C.
Bibcode: 2002mwoc.conf..337A
Altcode:
Synoptic photoelectric observations of the coronal Fe XIV and Fe X
emission lines at 530.3 nm and 637.4 nm, respectively, are analyzed
to study the rotational behavior of the solar corona as a function of
latitude, height and time. The data used are measurements made with
the Sacramento Peak 40-cm coronagraph and Emission-Line Coronal
Photometer of the intensity of these lines observed at 1.15 to
1.45 solar radii (Ro) between 1973 (1984 for Fe X) and 2000. An
earlier similar temporal-correlation analysis of the Fe XIV data at
1.15 Ro over only one 11-year solar activity cycle (Sime, Fisher and
Altrock 1989, Astrophys. J. 336, 454) found suggestions of solar-cycle
variations in the differential-rotation and latitude-averaged-rotation
patterns that combined the effects of large-scale patterns seen in the
white-light corona and smaller-scale patterns seen in chromospheric
and photospheric rotation. These results will be tested over the longer
epoch now available. In addition, the new 1.15 Ro Fe XIV results will
be compared with those at greater heights and with results from the
Fe X line and radio frequencies (Vats et al. 2001, Astrophys. J., 548,
L87) to form a global picture of solar rotation throughout the corona
and over more than two solar cycles.
Title: Further Results on the Rotation of the Solar Corona
Authors: Altrock, R. C.
Bibcode: 2001AGUFMSH11A0700A
Altcode:
Synoptic photoelectric observations of the coronal Fe XIV and Fe X
emission lines at 530.3 nm and 637.4 nm, respectively, are analyzed
to study the rotational behavior of the solar corona as a function of
latitude, height and time. The data used are measurements made with
the Sacramento Peak 40-cm coronagraph and Emission-Line Coronal
Photometer of the intensity of these lines observed at 1.15 to
1.45 solar radii (Ro) between 1973 (1984 for Fe X) and 2000. An
earlier similar temporal-correlation analysis of the Fe XIV data at
1.15 Ro over only one 11-year solar activity cycle (Sime, Fisher and
Altrock 1989, Astrophys. J. 336, 454) found suggestions of solar-cycle
variations in the differential-rotation and latitude-averaged-rotation
patterns that combined the effects of large-scale patterns seen in the
white-light corona and smaller-scale patterns seen in chromospheric
and photospheric rotation. These results will be tested over the longer
epoch now available. In addition, the new 1.15 Ro Fe XIV results will
be compared with those at greater heights and with results from the
Fe X line and radio frequencies (Vats et al. 2001, Astrophys. J., 548,
L87) to form a global picture of solar rotation throughout the corona
and over more than two solar cycles.
Title: Long-Term Variation of the Rotation of the Solar Corona
Authors: Altrock, R. C.
Bibcode: 2001AGUSM..SP61A04A
Altcode:
Synoptic photoelectric observations of the coronal Fe XIV and Fe X
emission lines at 530.3 nm and 637.4 nm, respectively, are analyzed
to study the rotational behavior of the solar corona as a function of
latitude, height and time. The data used are measurements made with
the Sacramento Peak 40-cm coronagraph and Emission-Line Coronal
Photometer of the intensity of these lines observed at 1.15 to
1.45 solar radii (Ro) between 1973 (1984 for Fe X) and 2000. An
earlier similar temporal-correlation analysis of the Fe XIV data at
1.15 Ro over only one 11-year solar activity cycle (Sime, Fisher and
Altrock 1989, Astrophys. J. 336, 454) found suggestions of solar-cycle
variations in the differential-rotation and latitude-averaged-rotation
patterns that combined the effects of large-scale patterns seen in the
white-light corona and smaller-scale patterns seen in chromospheric
and photospheric rotation. These results will be tested over the longer
epoch now available. In addition, the new 1.15 Ro Fe XIV results will
be compared with those at greater heights and with results from the
Fe X line and radio frequencies (Vats et al. 2001, Astrophys. J., 548,
L87) to form a global picture of solar rotation throughout the corona
and over more than two solar cycles.
Title: Comparison of Sac Peak Fe XIV Index with Model Index Computed
from EIT Differential Emission Measure Maps
Authors: Cook, J. W.; Newmark, J. S.; Altrock, R. C.
Bibcode: 2001AGUSM..SP32B05C
Altcode:
We compare the Sac Peak Fe XIV green line index with a model index time
series for the period of operations of the Extreme-ultraviolet Imaging
Telescope (EIT) aboard the Solar and Heliospheric Observatory (SOHO),
covering the years 1996-2000, from cycle minimum to the peak of the
current activity cycle 23. We compute a differential emission measure
(DEM) map for each day using images from the four channels of EIT at
171 Å, 195 Å, 284 Å, and 304 Å. From the daily DEM map we then
calculate a daily Fe XIV 5304 Å intensity image (see Cook et al. 1999,
Proceedings of the 8th SOHO Workshop, ESA SP-446, pp. 241-246). The
Sac Peak index is an average intensity, measured using a circular
aperture 1 arcmin in diameter sampling the corona in 1 degree steps
around disk center. It is taken at several different heights beyond
the daily limb. We modeled the index values, for the aperture center
at 1.15 Rodot from disk center, as the average intensity
within a daily annulus covering 1.12 - 1.18 Rodot imposed on
the model intensity image. We compare the observed index with our model
results, and discuss in terms of the accuracy of the model intensities
which can be determined from our EIT-based DEM curves. We actually
produce a daily Fe XIV image for the entire EIT field-of-view. The
Sac Peak index provides one well calibrated, long term check on the
reliability of the DEM model calculation. This work has been supported
by NASA under W-19,348, and by the Office of Naval Research.
Title: Variation of the Large-Scale Coronal Temperature at Mid-to-High
Latitudes over 1.5 Solar Cycles
Authors: Altrock, R. C.
Bibcode: 2000SPD....31.0225A
Altcode: 2000BAAS...32..815A
Observations of the forbidden coronal lines Fe XIV 530.3 nm and Fe
X 637.4 nm obtained at the National Solar Observatory at Sacramento
Peak are used to determine the variation of coronal temperature at
latitudes above 30 degrees outside of active regions during cycles
22 and 23. A pattern, which is symmetric about solar maximum during
cycle 22 and consistent between the northern and southern hemisphere,
is seen. Beginning near solar minimum in 1985, the temperature above
60 degrees latitude is at a minimum value, varying from about 1.3 MK
near the poles to about 1.5 MK near 60 degrees. Near the time that
the "Rush-to-the-Poles" begins in 1987, the high-latitude temperature
increases abruptly, reaching values of 1.7 MK at the North pole and
1.6 MK at the South pole in 1989. After 1990, the process reverses,
and temperatures at the poles are below 1.3 MK by 1995. The rise to
the maximum of cycle 23 will be compared with that of cycle 22.
Title: Coronal index of solar activity for 1998
Authors: Altrock, R. C.; Rybansky, M.; Minarovjech, M.; Rusin, V.
Bibcode: 1999CoSka..29..105A
Altcode:
We present the Fe XIV 530.3 nm (green line) coronal index (CI) of
solar activity for 1998. A systematic increase of CI was observed
from January to October 1998. Toward the end of the year the rate of
increase slowed remarkably. A comparison of CI with similar indices
of solar activity (2800 MHz radio flux, the Wolf sunspot number and
the SUSIM Mg II index) shows a good correlation.
Title: Verification of a Method for Predicting the Time of Solar
Maximum
Authors: Altrock, R. C.
Bibcode: 1999AAS...194.9209A
Altcode: 1999BAAS...31..987A
Prediction of the exact time of solar maximum is a matter of
disagreement among solar scientists and of some importance to
satellite operators, space-system designers, etc. Most predictions
are based on physical conditions occurring at or before the long-term
minimum of activity preceding the maximum in question. However, a
perhaps-more-reliable indicator of the timing of the maximum occurs
early in the rise phase of the solar cycle. A study of the long-term
variation of coronal emission features in Fe XIV from the National
Solar Observatory at Sacramento Peak has shown that, prior to solar
maximum, emission features appear near 55 degrees latitude in both
hemispheres and begin to move towards the poles at a rate of 9 to 13
degrees of latitude per year. This motion is maintained for a period
of 3 or 4 years, at which time the emission features disappear near
the poles. This phenomenon has been referred to as the "Rush to the
Poles". The maximum of solar activity historically occurs approximately
16 +/- 1 months before the features reach the poles. In 1997, Fe XIV
emission features appeared near 55 degrees latitude, and subsequent
observations have shown that these features are moving towards the
poles. This then is the Rush to the Poles observed in previous solar
cycles. Based on observations up through October 1998 over three
cycles, these features will reach the poles in approximately October
2000, which results in a prediction for solar maximum of between June
and August 1999, substantially earlier than many other predictions. A
maximum smoothed sunspot number of approximately 160 is inferred from
the similarity of the rate of progression towards the poles in this
cycle compared to the two previous cycles. The current status of Rush
to the Poles and of the solar cycle will be reviewed and conclusions
drawn about the reliability of this method. This work was supported
by the Air Force Office of Scientific Research.
Title: Determination of the solar minimum period between cycles 22
and 23 from the coronal index of solar activity
Authors: Altrock, R. C.; Rybanský, M.; Rušin, V.; Minarovjech, M.
Bibcode: 1999SoPh..184..317A
Altcode:
We present the coronal index of solar activity (CI) for 1997 and use
the 1996 and 1997 data to examine the properties of the solar minimum
between cycles 22 and 23. To compute CI, we used only the intensities
of the green corona from Lomnický Štít and Sacramento Peak coronal
stations. Values of CI were low in the first half of 1997 with an
increase from September toward the end of 1997. We determined the
minimum in the green corona to be May 1996, which is in coincidence
with the results from 2800 MHz radio flux, the Mg II index and the
Wolf number.
Title: Synoptic Coronal Temperature; Magnetic Field and He 11083
NM Observations
Authors: Penn, M.; Altrock, R. C.; Henry, T.; Guhathakurta, M.
Bibcode: 1998ASPC..140..325P
Altcode: 1998ssp..conf..325P
No abstract at ADS
Title: Variation of Solar Coronal Intensity and Temperature in
Cycle 22
Authors: Altrock, Richard C.
Bibcode: 1998ASPC..140..339A
Altcode: 1998ssp..conf..339A
No abstract at ADS
Title: Electron Temperature Distribution in Coronal Holes
Authors: Halas, C. D.; Habbal, S. R.; Penn, M.; Uitenbroek, H.; Esser,
R.; Altrock, R.; Guhathakurta, M.
Bibcode: 1997AAS...191.7413H
Altcode: 1997BAAS...29Q1326H
Knowledge of the electron temperature within coronal holes is extremely
important for constructing solar wind models and for understanding
the coronal heating process. We report on the two-dimensional CCD
observations of the Fe IX 4585, Fe X 6374, Fe XI 7892 and Fe XIV 5303
{ Angstroms} emission lines made using a coronagraph at the National
Solar Observatory at Sacramento Peak. These iron lines, which have
a peak formation temperature of 5 10(5) , 10(6) , 1.2 10(6) , and 2
10(6) K, respectively, allow the examination of different temperature
plasmas within the same large scale magnetic structure. To account for
possible line of sight ambiguities from hot material in the foreground
or background of the coronal hole, Yohkoh data were used to determine
the extent of the coronal hole along the line of sight. Intensities and
widths of these spectral lines as a function of heliocentric distance
out to 1.15 R_s will be presented. A comparison will be made between
coronal hole and streamer observations.
Title: Design for the Solar Mass Ejection Imager (SMEI)
Authors: Keil, S. L.; Altrock, R. C.; Kahler, S. W.; Jackson, B. V.;
Buffington, A.; Hick, P. L.; Simnett, G.; Eyles, C.; Webb, D. F.;
Anderson, P.
Bibcode: 1997SPD....28.0227K
Altcode: 1997BAAS...29..897K
The Solar Mass Ejection Imager (SMEI) experiment is designed to detect
and measure transient plasma features in the heliosphere, including
coronal mass ejections (CMEs), shock waves, and structures such as
streamers which corotate with the Sun. SMEI will provide measurements
of the propagation of solar plasma clouds and high-speed streams
which can be used to forecast their arrival at Earth from one to
three days in advance. Data from SMEI will be used to develop models
and techniques that will, for the first time, allow us to predict the
onset and magnitude of geomagnetic storms that disrupt space operations
and affect communications and surveillance activities. We will present
the current design and observational plans for SMEI. SMEI is currently
under construction with instrument completion expected in 1999. We
plan to launch SMEI near the next solar maximum and will make the data
available to the scientific and space weather forecast communities.
Title: The High-Latitude Variation of Solar Coronal Temperature in
Cycle 22
Authors: Altrock, Richard C.
Bibcode: 1997SPD....28.0705A
Altcode: 1997BAAS...29..911A
Observations at 1.15 R_⊙ of the forebidden coronal lines Fe XIV
530.3 nm and Fe X 637.4 nm obtained at the National Solar Observatory
at Sacramento Peak are used to determine the variation of coronal
temperature at high latitudes during Cycle 22. An unexpected pattern,
symmetric about solar maximum and consistent between the northern and
southern hemisphere, is seen. Beginning near solar minimum in 1985,
the temperature above 60deg latitude is seen to be at a minimum value,
varying from about 1.3 MK near the poles to about 1.5 MK near 60deg
. Near the time that the "Rush-to-the-Poles" begins in 1987, the
high-latitude temperature increases abruptly, reaching values of 1.7
MK at the North pole and 1.6 MK at the South pole in 1989. After 1990,
the process reverses, and temperatures at the poles are below 1.3 MK
by 1995. This pattern may be consistent with the latitude variations
of polar-crown prominences. The author was supported by the Air Force
Office of Scientific Research.
Title: Coronal index of solar activity for 1996
Authors: Altrock, R. C.; Rybansky, M.; Rusin, V.; Minarovjech, M.
Bibcode: 1997CoSka..27...25A
Altcode:
We present the coronal index of solar activity (CI) for 1996. To compute
CI, we used only the intensities of the green corona from Lomnicky Stit
and Sacramento Peak coronal stations. Values of CI were low with an
increase toward the end of 1996. It appears that the minimum of solar
activity in the green corona occurred in March 1996. The rotational
rate of CI, as measured during the last half of 1996, is 26 days. The
results are compared to the Wolf number and 2800 MHz flux over the
entire cycle 22 (1986-1996).
Title: An `EXTENDED Solar Cycle' as Observed in fe XIV
Authors: Altrock, Richard C.
Bibcode: 1997SoPh..170..411A
Altcode:
Investigation of the behavior of coronal intensity above the limb in
Fexiv emission (530.3 nm) obtained at the National Solar Observatory at
Sacramento Peak over the last 23 years has resulted in the confirmation
of a second set of zones of solar activity at high latitudes,
separate from the Main Activity Zones (MAZ). Localized high-latitude
intensity maxima, which I will call High-latitude Emission Features
(HEF), are observed at 0.15 solar radii above the limb throughout
the solar cycle. They persist long enough at a given latitude to be
visible in long-term (e.g., annual) averages. I identify two types
of HEF. Poleward-moving HEF, which may be identified with the `Rush
to the Poles' phenomenon seen in polar-crown prominences, were first
seen to appear in this investigation near latitude 60° in 1978. In
1979 equatorward-moving HEF branched off from the poleward-moving HEF
(which continued on to reach the pole in 1980) at a latitude of 70°
to 80°. They evolved approximately parallel to the MAZ. Near solar
minimum, these HEF evolved into the MAZ of cycle 22, and the emission
continues its path towards the equator, where it should disappear soon.
Title: The Solar Mass Ejection Imager (SMEI)
Authors: Jackson, B.; Buffington, A.; Hick, P.; Keil, S.; Altrock,
R.; Kahler, S.; Simnett, G.; Eyles, C.; Webb, D.; Anderson, P.
Bibcode: 1997IAUJD..19E..27J
Altcode:
The Solar Mass Ejection Imager (SMEI) experiment is designed to
detect and measure transient plasma features in the heliosphere,
including coronal mass ejections (CMEs), shock waves, and structures
such as streamers which co-rotate with the Sun. SMEI will provide
measurements of the propagation of solar plasma clouds and high-speed
streams which can be used to forecast their arrival at Earth from
one to three days in advance. SMEI consists of three cameras, each
imaging a 60o times 3o field of view for a total
image size of 180o times 3o. As the satellite
orbits the earth, repeated images are used to build up a view of the
entire heliosphere at resolutions of better than one degree. Here,
we will show the most recent progress on this instrument, now under
prototype construction.
Title: Solar Mass Ejection Imager (SMEI)
Authors: Keil, Stephen L.; Altrock, Richard C.; Kahler, Stephen;
Jackson, Bernard V.; Buffington, Andrew; Hick, Paul; Simnett, George
M.; Eyles, Christopher J.; Webb, David; Anderson, Peter
Bibcode: 1996SPIE.2804...78K
Altcode:
The Solar Mass Ejection Imager (SMEI) experiment is designed to
detect and measure transient plasma features in the heliosphere,
including coronal mass ejections, shock waves, and structures such as
streamers which corotate with the Sun. SMEI will provide measurements
of the propagation of solar plasma clouds and high-speed streams
which can be used to forecast their arrival at Earth from one to
three days in advance. The white light photometers on the HELIOS
spacecraft demonstrated that visible sunlight scattered from the free
electrons of solar ejecta can be sensed in interplanetary space with
an electronic camera baffled to remove stray background light. SMEI
promises a hundred-fold improvement over the HELIOS data, making
possible quantitative studies of mass ejections. SMEI measurements
will help predict the rate of energy transfer into the Earth's
magnetospheric system. By combining SMEI data with solar, interplanetary
and terrestrial data from other space and ground-based instruments, it
will be possible to establish quantitative relationships between solar
drivers and terrestrial effects. SMEI consists of three cameras, each
imaging a 60 degree(s) X 3 degree(s) field of view for a total image
size of 180 degree(s) X 3 degree(s). As the satellite orbits the earth,
repeated images are used to build up a view of the entire heliosphere.
Title: Coronal synoptic temperature maps derived from the Fe XIV/Fe
X intensity ratio
Authors: Hick, P.; Jackson, B. V.; Altrock, R. C.
Bibcode: 1996AIPC..382..169H
Altcode:
The large-scale temperature structure of the low corona is investigated
using synoptic temperature maps, derived from the intensity ratio of
the green (Fe XIV) and red (Fe X) coronal lines as observed at the
National Solar Observatory/Sacramento Peak. This intensity ratio is
sensitive to coronal plasma with temperatures of 1-2 MK, a range of
temperatures usually associated with the quiet corona. The synoptic
maps indicate an association between high coronal temperature and the
large-scale magnetic field. A comparison with Stanford `source surface'
synoptic maps shows that, especially when the heliospheric current
sheet is stable over several rotations, the large-scale high-temperature
features follow the current sheet remarkably well. For recent Carrington
rotations, temperature maps are available for four heights between
1.15 and 1.45 Rsolar. For these maps the correspondence
with the current sheet (calculated at 2.5 Rsolar) improves
with height. Discrepancies between temperature structure and magnetic
structure appear to be largest when the magnetic structure changes
rapidly from rotation to rotation.
Title: The solar mass ejection imager
Authors: Jackson, B. V.; Buffington, A.; Hick, P. L.; Kahler, S. W.;
Altrock, R. C.; Gold, R. E.; Webb, D. F.
Bibcode: 1996AIPC..382..536J
Altcode:
We are designing a Solar Mass Ejection Imager (SMEI) capable of
observing Thomson-scattered signals from transient density features
in the heliosphere from a spacecraft situated near 1 AU. The imager is
designed to trace these features, which include coronal mass ejections,
corotating structures and shock waves, to elongations greater than
90° from the Sun. The instrument may be regarded as a progeny of the
heliospheric imaging capability shown possible by the zodiacal light
photometers of the HELIOS spacecraft. The instrument we are designing
would make more effective use of in situ solar wind data from spacecraft
in the vicinity of the imager by extending their observations to the
surrounding environment. An imager in Earth orbit could allow up to
three days warning of the arrival of a mass ejection from the Sun.
Title: The Solar Coronal Temperature Structure and the Heliospheric
Current Sheet
Authors: Altrock, R. C.; Hick, P.; Jackson, B. V.; Slater, G.; Henry,
T. W.
Bibcode: 1996AAS...188.8004A
Altcode: 1996BAAS...28..956A
We explore the large-scale temperature structure of the low corona
using synoptic temperature maps, derived from the intensity ratio
of the green (Fe XIV) and red (Fe X) coronal lines as observed at
the National Solar Observatory/Sacramento Peak, and temperature maps
derived from the Al0.1 and AlMgMn filter intensity ratio measured by
the Yohkoh/SXT instrument. The red/green intensity ratio is sensitive
to coronal plasma with temperatures in the range of 1--2 MK and is
therefore useful for studying the `quiet' corona. The Yohkoh/SXT filter
ratio covers a much wider range of coronal temperature (>= 1 MK)
and, in particular, is sensitive to the high temperatures (>= 3 MK)
commonly observed above active regions. We use the temperature maps to
study the evolution of the large-scale coronal temperature distribution,
in particular in relation to the large-scale magnetic field, as given
by the `source surface' maps derived from the Stanford potential field
model. We find that the large-scale high-temperature features follow
the heliospheric current sheet remarkably well, especially when the
current sheet is stable over several rotations.
Title: Solar coronal structure: a comparison of NSO/SP ground-based
coronal emission line intensities and temperatures with YOHKOH SXT
and WSO magnetic data
Authors: Altrock, R. C.; Hick, P.; Jackson, B. V.; Hoeksema, J. T.;
Zhao, X. P.; Slater, G.; Henry, T. W.
Bibcode: 1996AdSpR..17d.235A
Altcode: 1996AdSpR..17..235A
The large-scale structure of the solar corona is investigated using
synoptic maps produced from Fe XIV (530.3 nm), Fe X (637.4 nm) and
Ca XV (569.4 nm) data obtained at NSO/SP, Yohkoh/SXT X-ray data and
Wilcox Solar Observatory (WSO) `source surface' maps. We find that the
Fe XIV data are an excellent proxy for spatially-averaged Yohkoh/SXT
data. Isolated emission features and large-scale structures are nearly
identical in SXT and Fe XIV maps. In addition, coronal holes and other
low-emission regions are very similar. Synoptic temperature maps,
calculated from the Fe X/Fe XIV ratio, show a tendency for the highest
temperatures to occur where the large-scale magnetic fields change
polarity at high latitudes (cf. /1/), while lower-latitude features,
including active regions, have lower apparent temperatures. Regions
of enhanced temperature generally follow the heliospheric current
sheet (HCS) as defined by the WSO maps. Further, emission in Ca XV
(formed at T ~ 3 MK), generally occurs only over low-latitude regions
that are bright in both Fe X (T ~ 1 MK) and Fe XIV (T ~ 2 MK). Thus,
there is evidence for low (~1 MK), moderate (~2 MK) and high (~3 MK)
temperatures in close proximity in the low corona.
Title: IPS observations of heliospheric density structures associated
with active regions
Authors: Hick, P.; Jackson, B. V.; Altrock, R.; Woan, G.; Slater, G.
Bibcode: 1996AdSpR..17d.311H
Altcode: 1996AdSpR..17..311H
Interplanetary scintillation (IPS) measurements of the `disturbance
factor' g, obtained with the Cambridge (UK) array can be used to explore
the heliospheric density structure. We have used these data to construct
synoptic (Carrington) maps, representing the large-scale enhancements
of the g-factor in the inner heliosphere. These maps emphasize the
stable corotating, rather than the transient heliospheric density
enhancements. We have compared these maps with Carrington maps of Fe XIV
observations (NSO, Sacramento Peak) and maps based on Yohkoh/SXT X-ray
observations. Our results indicate that the regions of enhanced g tend
to map to active regions rather than the current sheet. The implication
is that active regions are the dominant source of the small-scale
(≈ 200 km) density variations present in the quiet solar wind.
Title: The Coronal Temperature Structure and the Current Sheet
Authors: Hick, Paul; Jackson, B. V.; Altrock, R. C.; Slater, G.;
Henry, T.
Bibcode: 1996ASPC...95..358H
Altcode: 1996sdit.conf..358H
No abstract at ADS
Title: The Solar Mass Ejection Imager (SMEI): Development and Use
in Space Weather Forecasting
Authors: Keil, S. L.; Altrock, R. C.; Kahler, S. W.; Jackson, B. V.;
Buffington, A.; Hick, P. L.; Simnett, G.; Eyles, C.; Webb, D. F.;
Anderson, P.
Bibcode: 1996ASPC...95..158K
Altcode: 1996sdit.conf..158K
No abstract at ADS
Title: Prediction of Coronal-Hole Solar Wind Velocities at ULYSSES
from NSO/SP Coronal Data
Authors: Altrock, Richard C.; Henry, Timothy W.
Bibcode: 1996ASPC...95..324A
Altcode: 1996sdit.conf..324A
No abstract at ADS
Title: Using Fe X 6374 Å and Fe XIV 5303 Å spectral line
intensities to study the effect of line of sight integration on
coronal temperature inferences
Authors: Esser, R.; Brickhouse, N. S.; Habbal, S. R.; Altrock, R. C.;
Hudson, H. S.
Bibcode: 1995JGR...10019829E
Altcode:
Polar coronal holes are relatively stable structures persisting
over many solar rotations. The appearance of coronal holes in
remote observations, however, can change on a daily basis due to
variations of the denser and hotter plasma surrounding them. We
explore the effect of these denser and hotter surrounding regions on
coronal hole observations, using daily intensity measurements at 1.15
RS of the green Fe XIV 5303 Å and red Fe X 6374 Å spectral
lines. The observations, which were carried out at the National Solar
Observatory a Sacramento Peak, New Mexico, cover at time period of
about four solar rotations. We show that the ``coronal hole''
temperatures derived using the line ratio technique, vary by more than
0.8×106 K over the time interval considered here. We also
provide a short discussion of the expected accuracy of the atomic data
for these two iron spectral lines. Using intensity measurements as a
function of distance from the Sun, we briefly discuss how the regions
surrounding the coronal holes might influence the inference of the
temperature gradient in the coronal holes. The line of sight effect
on the temperature gradient should be explored in more detail in the
future using daily observations of the line intensities as a function
of distance. These observations could be provided by ground-based
coronagraphs and by instruments on board SOHO.
Title: The Solar Mass Ejection Imager
Authors: Jackson, B. V.; Buffington, A.; Hick, P. L.; Kahler, S. W.;
Altrock, R. C.; Gold, R. E.; Webb, D. F.
Bibcode: 1995sowi.confR..97J
Altcode:
We are designing a Solar Mass Ejection Imager (SMEI) capable
of observing the Thomson-scattered signal from transient density
features in the heliosphere from a spacecraft situated near AU. The
imager is designed to trace these features, which include coronal
mass ejections. corotating structures and shock waves, to elongations
greater than 90 deg from the Sun. The instrument may be regarded as a
progeny of the heliospheric imaging capability shown possible by the
zodiacal-light photometers of the HELIOS spacecraft. The instrument
we are designing would make more effective use of in-situ solar wind
data from spacecraft in the vicinity of the imager by extending these
observations to the surrounding environment. The observations from
the instrument should allow deconvolution of these structures from the
perspective views obtained as they pass the spacecraft. An imager at
Earth could allow up to three days warning of the arrival of a mass
ejection from the Sun .
Title: Coronal synoptic temperature maps derived from the Fe XIV/Fe
X intensity ratio
Authors: Hick, P.; Jackson, B. V.; Altrock, R.
Bibcode: 1995sowi.confQ..69H
Altcode:
The large-scale temperature structure of the low corona is investigated
using synoptic temperature maps, derived from the intensity ratio of the
green (Fe XIV) and red (Fe X) coronal lines as observed at the National
Solar Observatory/Sacramento Peak. This intensity ratio is sensitive to
coronal plasma with temperatures in the range of 1-2 MK. The synoptic
maps indicate an association between high coronal temperature and the
large-scale magnetic field. A comparison with WSO 'source surface'
synoptic maps shows that especially when the heliospheric current sheet
is stable over several rotations, the large-scale high-temperature
features follow the current sheet remarkably well. For recent Carrington
rotations temperature maps have been constructed for various heights
between 1.15 and 1.45 solar radii. For these maps the correspondence
with the current sheet (calculated at 2.5 solar radii) improves with
height. Deviations between temperature structure and magnetic structure
appears to be largest when the magnetic structure changes rapidly from
rotation to rotation.
Title: Short-Term Periodicities in Soft X-ray Solar Flares
Authors: Airapetian, V. A.; Balasubramanian, K. S.; Altrock, R. C.;
Radick, R. R.
Bibcode: 1995SPD....26.1213A
Altcode: 1995BAAS...27..985A
No abstract at ADS
Title: The Track of Ulysses Across the Solar Southern Polar Coronal
Hole as Defined by NSO/SP Fe XIV Data, and Comparisons of the Two
Data Sets
Authors: Altrock, R. C.; Gosling, J. T.; Henry, T. W.
Bibcode: 1995SPD....26..902A
Altcode: 1995BAAS...27..973A
No abstract at ADS
Title: Association of Solar Coronal Temperature and Structure from
Ground-Based Emission-Line Data with Global Magnetic Field Models
and Yohkoh SXT Data (Abstract only)
Authors: Altrock, R. C.; Hick, P.; Jackson, B. V.; Hoeksema, J. T.;
Zhao, X. P.; Slater, G.; Henry, T. W.
Bibcode: 1995itsa.conf...45A
Altcode:
No abstract at ADS
Title: Photometric imaging observations of the emission corona
Authors: Altrock, R. C.; Smartt, R. N.
Bibcode: 1994ESASP.373..425A
Altcode: 1994soho....3..425A
No abstract at ADS
Title: Coronal Index of Solar Activity - Part Seven - Years 1988-1991
Authors: Rybansky, M.; Rusin, V.; Gaspar, P.; Altrock, Richard C.
Bibcode: 1994SoPh..152..487R
Altcode:
A brief description is given of the coronal index of solar activity (CI)
derived from ground-based observations of the green coronal line 530.3
nm (FeXIV) and its computation. The final data of CI are presented in
graphical form over the period 1988-1991. The maximum of CI coincided
with the Wolf number in cycle 22, and no second maximum, sometimes
seen two years after the first one, was observed in this cycle.
Title: The solar cycle variation of coronal temperature and density
during cycle 21-22
Authors: Guhathakurta, M.; Fisher, R. R.; Altrock, R. C.
Bibcode: 1994AdSpR..14d..49G
Altcode: 1994AdSpR..14...49G
In this paper we characterize the temperature and the density structure
of the corona utilizing co-spatial spectrophotometric observations
during the descending phase of cycle 21 through the ascending phase of
cycle 22. The data include ground-based intensity observations of the
green (5303Å Fe XIV) and red (6374Å Fe X) coronal forbidden lines from
Sacramento Peak and synoptic maps of white-light K-coronal polarized
brightness, pB from the High Altitude Observatory, and photospheric
magnetographs from the National Solar Observatory, Sacramento Peak. A
determination of plasma temperature T can be derived unambiguously
from the intensity ratio Fe X/Fe XIV, since both emission lines come
from ionized states of Fe, and the ratios are only weakly dependent on
density. The latitudinal variation of the temperature and the density
within the descending and the ascending phases of solar cycle 21 and
22 are presented. There is a large-scale organization of the inferred
coronal temperature distribution; these structures tend to persist
through most of the magnetic activity cycle. This distribution differs
in spatial and temporal characterization from the traditional picture
of sunspot and active region evolution over the range of sunspot cycle.
Title: Groundbased observations of the Sun's corona following the
perihelia of sungrazing comets.
Authors: St. Cyr, O. C.; Altrock, R. C.
Bibcode: 1993BAAS...25.1303S
Altcode:
No abstract at ADS
Title: Groundbased Observations of the Sun's Corona Following the
Perihelia of Sungrazing Comets
Authors: Cyr, O. C. St.; Altrock, R. C.
Bibcode: 1993AAS...183.0904C
Altcode: 1993BAAS...25Q1303C
During the period 1979-1989, two spaceborne coronagraphs discovered 16
sungrazing comets in observations of the white-light corona. All of the
comets discovered by NRL's Solwind telescope on the USAF satellite P78-1
and HAO's C/P telescope on NASA's SMM were members of the Kreutz family
of sungrazers. All of these comets were observed in the hours prior to
their individual perihelia, but none were detected post-perihelion by
the spaceborne coronagraphs. Further, none of these comets were directly
detected by groundbased observers. There was, however, a single report
by Czech observers of a coronal enhancement in Fe X following the first
Solwind comet. To investigate the possibility of a cometary signature
in the solar atmosphere we examined groundbased coronal observations
made at the National Solar Observatory site at Sacramento Peak with the
Fisher-Smartt Emission Line Coronal Photometer. For 13 of the 16 comets
described above, there were synoptic observations made at 5303A (Fe XIV)
at Sacramento Peak both the day before and the day after the comets'
perihelia. For a few cases, there were also scans at 5694A (Ca XV) and
6374A (Fe X). We report here on this work in progress. *Operated by
AURA Inc., under cooperative agreement with the NSF. Partial support
for NSO is provided by USAF under a Memorandum of Understanding with
the NSF. RCA gratefully acknowledges support from the US Air Force
Office of Scientific Research, Task PL011.
Title: Large-Scale Coronal Temperature and Density Distributions,
1984--1992
Authors: Guhathakurta, M.; Fisher, R. R.; Altrock, R. C.
Bibcode: 1993ApJ...414L.145G
Altcode:
We characterize the temperature and the density structure of the corona
utilizing spectrophotometric observations at different heights but at
the same latitude during the descending phase of cycle 21 through the
ascending phase of cycle 22. The data include ground-based intensity
observations of the green (Fe XIV 5303) and red (Fe X 6374) coronal
forbidden lines, photospheric magnetographs from the National Solar
Observatory, Kitt Peak, and synoptic maps of white-light K-coronal
polarized brightness from the High Altitude Observatory. A determination
of plasma temperature, T, can be estimated from the intensity ratio
Fe X/Fe XIV (where T is inversely proportional to the ratio), since
both emission lines come from ionized states of Fe, and the ratio
is only weakly dependent on density. Distributions of the electron
temperature from the line ratio and the polarized brightness which
yields electron density of the corona during the descending and the
ascending phases of solar cycles 21 and 22 are presented. These data
refer to structures of the corona which are relatively large scale,
having a temporal coherence of at least two or more synoptic rotation
periods, such as the streamer belts, the individual helmet streamers,
and the larger coronal holes.
Title: The Coronal Index of Solar Activity, 1988-1991
Authors: Altrock, R. C.; Rybansky, M.; Rusin, V.; Gaspar, P.
Bibcode: 1993BAAS...25.1200A
Altcode:
No abstract at ADS
Title: The Solar Mass Ejection Imager
Authors: Jackson, B. V.; Buffington, A.; Kahler, S. W.; Webb, D. F.;
Altrock, R.; Gold, R.
Bibcode: 1993BAAS...25.1191J
Altcode:
No abstract at ADS
Title: Coronal photometry and analysis of the eclipse corona of July
22, 1990
Authors: Koutchmy, S.; Altrock, R. C.; Darvann, T. A.; Dzubenko,
N. I.; Henry, T. W.; Kim, I.; Koutchmy, O.; Martinez, P.; Nitschelm,
C.; Rubo, G. A.
Bibcode: 1992A&AS...96..169K
Altcode:
Results are presented of aircraft-based observations and ground
observations from multiple stations, made during the July 1990
eclipse. The main results of the analysis of the large-scale features of
the inner corona concern the measurement of the flattening index of the
near-maximum-activity corona; the occurrence of a large coronal hole;
and the importance of the line emissions recorded on the broadband
white-light pictures, due to the presence of numerous large or faint
prominences all around the limb.
Title: Ground-based coronagraphic observations of solar streamers.
Authors: Altrock, Richard C.
Bibcode: 1992ESASP.348...83A
Altcode: 1992cscl.work...83A
The purpose of this paper is two-fold: first, to demonstrate that
ground-based coronagraphs can observe coronal streamers and, secondly,
to give examples of the type of streamer properties that can be deduced
from such observations. Emission-line and white-light (K-coronagraph)
observations relating to streamer electron density, magnetic field
and polarization, population, intensity, large-scale organization,
rotation, temperature and periodicities are included. This paper will
demonstrate the types of work that can be done.
Title: The Current Status of the ``Extended Solar Cycle'' as Observed
in Fe XIV
Authors: Altrock, Richard C.
Bibcode: 1992AAS...180.1104A
Altcode: 1992BAAS...24..746A
Investigation of the behavior of coronal intensity above the limb
in Fe XIV emission (5303 Angstroms) obtained at the National Solar
Observatory at Sacramento Peak over the last nineteen years has
resulted in the confirmation of a second zone of solar activity at
high latitudes separate from the Main Activity Zones (MAZ). Localized
high-latitude intensity maxima are observed at 0.15 Rsun
above the limb throughout the solar cycle. They persist long enough at
a given latitude to be visible in long-term (e.g., annual) averages and
thus form High-latitude Activity Zones (HAZ). We identify two types
of HAZ. Poleward-moving PHAZ, which we identify with the ``Rush to
the Poles'' phenomenon seen in polar-crown prominences, appeared near
latitude 60(deg) in 1978 (possibly earlier at lower latitudes). In 1979
equatorward-moving EHAZ branched off from the PHAZ (which continued
on to reach the poles in 1980) near 70 to 80(deg) . They evolved
approximately parallel to the MAZ. Near solar minimum, the EHAZ evolved
into the MAZ of Cycle 22, and the emission continues its monotonous
path towards the equator, where it should disappear around 1998. As of
early 1992, it is clear that the pattern seen earlier is repeating. The
PHAZ became apparent near the beginning of 1988 near 60(deg) in the
North and South hemispheres. The northern PHAZ reached the pole during
late 1989 to 1990, and polar emission effectively ceased at the end
of 1990. The southern PHAZ moved more slowly, and the southern-most
emission regions reached the pole in mid-1991. South-polar emission
was still occurring as of the latest observations. The EHAZ that are
the precursors of sunspot Cycle 23 became clearly established in the
Northern hemisphere near the beginning of 1990 at approximately 70(deg)
. Currently the zone is at about 55(deg) . The appearance of the EHAZ
in the South was less dramatic but probably began in mid-1990 near
70(deg) . Its current position is also near 55(deg) . These recent
observations increase the evidence for parallel overlapping solar
cycles that begin every 11 years but last for approximately 19-20 years.
Title: Coronal Density and Temperature Structure from Coordinated
Observations Associated with the Total Solar Eclipse of 1988 March 18
Authors: Guhathakurta, M.; Rottman, G. J.; Fisher, R. R.; Orrall,
F. Q.; Altrock, R. C.
Bibcode: 1992ApJ...388..633G
Altcode:
This paper explores and compares diagnostics for temperature and
density within large-scale structures of the inner corona based on
cospatial and cotemporal spectrophotometric observations made at the
time of the total solar eclipse of 1988 March 17/18. In the analysis
a determination of plasma temperature T can be derived unambiguously
from the intensity ratios Fe XIV/XUV or Fe XIV/Fe X since all the
emission lines come from the ionized state of Fe and the ratios
are only weakly dependent on density. These temperatures and the
densities found in well-defined large-scale coronal structures are
discussed. The emission-line temperature is found to be high (local
maxima) in the coronal structures with enhanced white-light emission
and associated with new cycle high-latitude magnetic fields separated
from the old cycle polar field of opposite polarity. Also the average
of the ratio of scale-height temperature/temperature over the entire
range of position angle is roughly unity although the ratio is higher
than unity (1.3-1.6) in the three most prominent streamers.
Title: Considerations of a Solar Mass Ejection Imager in a Low
Earth Orbit
Authors: Jackson, B. V.; Webb, D. F.; Altrock, R. C.; Gold, R.
Bibcode: 1992LNP...399..322J
Altcode: 1992esf..coll..322J; 1992IAUCo.133..322J
We are designing an imager capable of observing the Thomson scattering
signal from transient, diffuse features in the heliosphere[1]. The
imager is expected to trace these features, which include coronal mass
ejections, co-rotating structures and shock waves, to elongations
greater than 90° from the Sun from a spacecraft in an 800 km Earth
orbit. The predecessor of this instrument was the zodiacal-light
photometer experiment on the HELIOS spacecraft which demonstrated
the capability of remotely imaging transient heliospheric structures
[2]. The HELIOS photometers have shown it possible to image mass
ejections, co-rotating structures and the density enhancements behind
shock waves. The second-generation imager we are designing, would have
far higher spatial resolution enabling us to make a more complete
description of these features from the Sun to 1 AU. In addition, an
imager at Earth could allow up to three days warning of the arrival
of a solar mass ejection.
Title: The Solar Cycle Variation of Coronal Temperature during
Cycle 22
Authors: Guhathakurta, M.; Altrock, R. C.
Bibcode: 1992ASPC...27..395G
Altcode: 1992socy.work..395G
No abstract at ADS
Title: Fe XIV and Fe X Limb Flux as Proxies for Space and Ground-Based
Global Solar Parameters
Authors: Altrock, R. C.; Henry, T. W.
Bibcode: 1991BAAS...23.1068A
Altcode:
No abstract at ADS
Title: The solar mass ejection imager
Authors: Jackson, B.; Gold, R.; Altrock, R.
Bibcode: 1991AdSpR..11a.377J
Altcode: 1991AdSpR..11..377J
We have designed an imager capable of observing the Thomson scattering
signal from transient, diffuse features in the heliosphere from a
spacecraft situated near 1 AU. The imager is expected to trace these
features, which include coronal mass ejections, co-rotating structures
and shock waves, to elongations greater than 90° from the Sun. The
instrumentation ultimately may be regarded as a successor to the
heliospheric imaging cabability shown possible by the zodiacal-light
photometers of the HELIOS spacecraft. The second-generation instrument
we have designed, would make far more effective use of in-situ solar
wind data from spacecraft in the vicinity of the imager by extending
these observations to the structures surrounding it. In addition, an
imager at Earth could allow up to three days warning of the arrival
of a mass ejection from the Sun. Operated by the Association
of Universities for Research in Astronomy, Inc., under cooperative
agreement with the National Science Foundation. Partial support for
NSO is provided by the USAF under a Memorandum of Understanding with
the NSF.
Title: The variation of solar Fe XIV and Fe X flux over 1.5 solar
activity cycles.
Authors: Altrock, Richard C.
Bibcode: 1990NASCP3086..287A
Altcode: 1990cisv.nasa..287A
This paper presents a new source of data on the solar output, namely
"limb flux" from the one- and two-million degree corona. This parameter
is derived from data obtained at the National Solar Observatory at
Sacramento Peak with the 40 cm coronagraph of the John W. Evans Solar
Facility and the Emission Line Coronal Photometer. The limb flux is
defined to be the latitude-averaged intensity in millionths of the
brightness of disk center from an annulus of width 1.1' centered at a
height of 0.15 Rsun above the limb of emission
from lines at 6374 Å (Fe X) or 5303 Å (Fe XIV). Fe XIV data have
been obtained since 1973 and Fe X since 1984. Examination of the
Fe XIV data shows that there is ambiguity in the definition of the
last two solar activity minima, which can affect the determination of
cylce rise times and lengths. There is an indication that a constant
minimum or basal corona may exist at solar minimum. Cycle 22 has had
a much faster onset than Cycle 21 and has now overtaken Cycle 21. The
rise characteristics of the two cycles were very similar up until
Jul-Aug 1989, at which time a long-term maximum occurred in Fe X and
Fe XIV, which could possibly be the "solar maximum". Another maximum
is developing at the current time. Cycle 21 was characterized in Fe
XIV by at least 4 major thrusts or bursts of activity, each lasting
on the order of a year and all having similar maximum limb fluxes,
which indicates that coronal energy output is sustained over periods
in which the sunspot number declines significantly. Dramatic increases
in the limb fluxes occur from minimum to maximum, ranging from factors
of 14 to 21 in the two lines. Two different techniques to predict the
epoch of solar maximum have been applied to the Fe XIV data, resulting
in estimates of Apr 1989 (±1 mo) and May 1990 (±2 mo).
Title: A Search for Non-Rotational Periodicities in Solar Fe XIV
and Fe X Flux During Solar Cycles 21 and 22
Authors: Altrock, R. C.; Radick, R. R.; Henry, T. W.
Bibcode: 1990BAAS...22..873A
Altcode:
No abstract at ADS
Title: The Onset of Solar Cycle 22 in Coronal Emission Lines
Authors: Altrock, R. C.
Bibcode: 1989BAAS...21..829A
Altcode:
No abstract at ADS
Title: Rotation Characteristics of the Fe XIV (5303 Angstrom )
Solar Corona
Authors: Sime, D. G.; Fisher, R. R.; Altrock, R. C.
Bibcode: 1989ApJ...336..454S
Altcode:
The rotational characteristics of the solar corona as revealed by
the coronal Fe XIV line at 5303 A are examined. Measurements of the
intensity at 5303 A observed at a radius of 1.15 solar radii between
1973 and 1985 are presented. It is found that, on average, the Fe
XIV corona rotates more rigidly than do features in the photosphere
or chromosphere. The observations support the theory that the Fe
XIV coronal signal arises from the effects of local heating on the
large-scale density structure of the corona.
Title: SYSTEMATIC OBSERVATIONS OF THE SUN (In honour of Helen Dodson
Prince): Observations
Authors: McIntosh, P.; Snodgrass, H.; Mouradian, Z.; Harvey, K.;
Altrock, R.; Simon, P.; Legrand, J. -P.; Alissandrakis, G.; Neckel,
H.; Petropoulos, P.; Poulakis, X.; Gokhale, M. H.; Sivaraman, K. R.;
Pap, J.
Bibcode: 1989HiA.....8..672M
Altcode:
No abstract at ADS
Title: Further Evidence for an Extended Solar Cycle
Authors: Altrock, R. C.
Bibcode: 1988BAAS...20..723A
Altcode:
No abstract at ADS
Title: Observations of the Sun and Corona for the 1988 March 18
Total Solar Eclipse
Authors: Orrall, F. Q.; Lindsey, C. A.; Mickey, D. L.; Dulk, G.;
Rottman, G.; Altrock, R. C.; Fisher, R. R.; Sime, D. G.
Bibcode: 1988BAAS...20..703O
Altcode:
No abstract at ADS
Title: Solar and stellar coronal structure and dynamics. A Festschrift
in honor of Dr. John W. Evans. Proceedings.
Authors: Altrock, Richard C.
Bibcode: 1988sscd.conf.....A
Altcode:
Contents: 1. Stellar coronae. 2. Winds, holes, and bright
points. 3. Waves, oscillations, and heating. 4. Prominence
interface. 5. Structures and miscellaneous. 6. Solar-cycle
variations. 7. Observations and models of magnetic fields. 8. Mass
ejections, transients, and flares. Appendices.
Title: The solar emission-line corona: current and future ground-based
observational research.
Authors: Altrock, R. C.
Bibcode: 1988sscd.conf..288A
Altcode:
This is a review of discussions on the status of ground-based solar
coronal research, which took place during the Workshop on Solar and
Stellar Coronal Structure and Dynamics. Topics of discussion included
current observational capabilities, research problems suitable for
attack now and in the future, and possible future instrumentation,
including the Advanced Reflecting Coronagraph.
Title: Variation of solar coronal Fe XIV 5303 Å emission during
solar Cycle 21.
Authors: Altrock, Richard C.
Bibcode: 1988sscd.conf..414A
Altcode:
Investigation of the behavior of coronal intensity above the limb in Fe
XIV emission (5303 Å) obtained at Sacramento Peak Observatory over the
last fourteen years has resulted in the corfirmation of a second set
of zones of solar activity at high latitudes separate from the Main
Activity Zones (MAZ). Localized emission peaks in Fe XIV 5303 Å are
observed through most of the cycle at high latitudes in individual daily
scans, annual averages, and solar-cycle summary plots of the location
of all local maximum intensities at 0.15 Rsun above the
limb. Near solar minimum, the high-latitude coronal activity zones
that appeared after the beginning of Cycle 21 monotonically evolved
into the MAZ of Cycle 22. It thus appears that we have evidence for
parallel overlapping solar cycles that begin every 11 years but last
for approximately 19 - 20 years
Title: The Fe 15 solar corona at 5303 angstroms: an atlas of
synoptic charts from the Sacramento Peak coronal photometer, May
1973-December 1985
Authors: Altrock, R. C.; Gilliam, L. B.; Sime, D. G.; Fisher, R. R.
Bibcode: 1987scasc....Q....A
Altcode:
Synoptic photoelectric observations of the solar corona in the emission
from the green line (5303A) of Fe 15 were begun at the Sacramento Peak
Observatory in June 1973 and continue to the present. The observations
made during this program provide a record of the distribution and
brightness of the hotter regions of the corona (1,800,000 K) over an
entire solar cycle. As such, the green line data may provide a link
between the active regions of the chromosphere and the large scale
structure of the corona. In order to allow comparison of these data
with other observations of the Sun and corona, we present here an
atlas of the green line measurements in the same format as that used
to display the white light coronal structure recorded by the High
Altitude Observatory's K-coronameters on Mauna Loa, in previously
published atlases. It is our intent that this atlas be brought up to
date periodically as the observations permit.
Title: Long Term Variations in the Integrated Fe XIV Green Line Flux
(5303 Å) from the Solar Corona
Authors: Yasukawa, E. A.; Altrock, R. C.; Sime, D. G.; Fisher, R. R.
Bibcode: 1987BAAS...19..926Y
Altcode:
No abstract at ADS
Title: Fe XIV solar corona at 5303 angstroms: an atlas of synoptic
charts from the Sacramento Peak coronal photometer, May 1973-December
1985
Authors: Altrock, R. C.; Gilliam, L. B.; Sime, D. G.; Fisher, R. R.
Bibcode: 1987scasc....R....A
Altcode:
Presented is an atlas of synoptic charts from the Sacramento Peak
Coronal Photometer, of the Fe XIV solar corona at 5303 Angstroms. The
data covers the period from May 1973 until December 1985.
Title: The SOLAR-CYCLE-21 Variation of High-Latitude Coronal Fexiv
Emission
Authors: Altrock, R. C.
Bibcode: 1986PASP...98.1100A
Altcode:
No abstract at ADS
Title: Overlapping Solar Cycles as Discovered in Coronal Fe XIV
Emission
Authors: Altrock, R. C.
Bibcode: 1986BAAS...18.1010A
Altcode:
No abstract at ADS
Title: The Solar-Cycle 21 Variation of High-Latitude Coronal Fe
XIV Emission
Authors: Altrock, R. C.
Bibcode: 1986BAAS...18R.709A
Altcode:
No abstract at ADS
Title: Coronal Emission-Line Data and Solar-Terrestrial Predictions
Authors: Altrock, R.
Bibcode: 1986stp..conf..131A
Altcode: 1986STP.....2..131A
No abstract at ADS
Title: The Relationship of Emission-Line Transients in the Low Solar
Corona to Hα Activity
Authors: Altrock, R. C.; Smith, R. C.
Bibcode: 1985BAAS...17Q.842A
Altcode:
No abstract at ADS
Title: Coronal-Hole Detectability on Solar-type Stars
Authors: Altrock, R. C.
Bibcode: 1985ASSL..116..243A
Altcode: 1985rst..conf..243A
It is shown that light from the solar corona, which is integrated
over the visible disk (coronal flux or irradiance), can be used to
infer the disk passage of large coronal holes. Observations above the
limb of Fe XIV 5303 A are used to produce a synoptic intensity map of
the solar disk as it would appear in coronal light. The intensity at
each point on the map is summed to produce a daily value of coronal
irradiance. The time variation of this quantity shows a decrease of
28 percent, followed by recovery, as a large coronal hole transits
the disk from March 21 through April 7, 1984. The occurrence of
a coincident geomagnetic disturbance implies that the associated
high-speed solar-wind stream strikes the earth. Other solar data
sets, specifically sunspot number and 10.7 cm radio flux, do not have
unambiguous coronal hole signatures during this period. This technique
suggests that coronal holes might be observed on stars, if a suitable
method for isolating coronal radiation is used; e.g., radio or EUV.
Title: Results from the Coronal Photometry Program at NSO, I:
Three-Line Observations of the Corona in 1984
Authors: Altrock, R. C.; Fisher, R. R.; Sime, D. G.
Bibcode: 1985BAAS...17..637A
Altcode:
No abstract at ADS
Title: Results from the Coronal Photometry Program at NSO, III:
The Green Line and White Light Corona Compared
Authors: Fisher, R. R.; Altrock, R. C.; Sime, D. G.
Bibcode: 1985BAAS...17..638F
Altcode:
No abstract at ADS
Title: Results from the Coronal Photometry Program at NSO, II:
Rotation of the Green Corona over the Solar Cycle
Authors: Sime, D. G.; Fisher, R. R.; Altrock, R. C.
Bibcode: 1985BAAS...17..638S
Altcode:
No abstract at ADS
Title: Solar coronal white light, Fe 10, Fe 14 and CA 15 observations
during 1984: an atlas of synoptic charts
Authors: Sime, D. G.; Fisher, R. R.; Altrock, R. C.
Bibcode: 1985STIN...8616179S
Altcode:
Synoptic observations of the solar corona in white light and in three
emission lines (CaXV at 5964 A, FeXIV at 5303 A, and Fe X at 6374 A)
were carried out during most of 1984 at the High Altitude Observatory's
Mauna Loa Solar Observatory and at Sacramento Peak Observatory. These
observations were partly in support of the scientific program of
the repaired SMM spacecraft. The observations provide a record of
the distribution and brightness of the hotter regions of the corona
over the year. The authors present these data in the form of synoptic
maps for each rotation during the year for the purpose of providing
a context for the investigations which are to take place during the
Joint Study of Coronal and Prominence Plasmas organized by Goddard
Space Flight Center/NASA. In this way, they propose both to describe
the data coverage achieved and summarize the large scale properties
of the corona in this late descending phase of the solar cycle.
Title: Coronal-Hole Detectability on Solar-Type Stars
Authors: Altrock, R. C.
Bibcode: 1984BAAS...16..939A
Altcode:
No abstract at ADS
Title: Sacramento Peak Observatory Observing Weather and the El
Nino Phenomenon
Authors: Altrock, R. C.
Bibcode: 1984BAAS...16..478A
Altcode:
No abstract at ADS
Title: The Evolution of an Average Solar Granule
Authors: Altrock, R. C.
Bibcode: 1984ssdp.conf..130A
Altcode:
High-resolution photographic spectra of the center of the solar disk
have been obtained with the Vacuum Tower Telescope at Sacramento
Peak Observatory. A weak iron line and the neighboring continuum were
recorded with 40 sec time resolution and better than 1arcsec spatial
resolution over a period of 37 min. Intensity and velocity fluctuations
were obtained in the line and continuum as a function of time and space,
and 300 sec oscillations were filtered out. The resulting fluctuations,
due solely to granulation, were assembled into an ensemble average of
the center of a granule and the center of an intergranular lane, as a
function of time. It is found that the line parameters are distinctly
out of phase with continuum brightness.
Title: Coronal transients in Fe XIV 5303 Å: first two-dimensional
photoelectric ground-based observations.
Authors: Altrock, R. C.; Demastus, H. L.
Bibcode: 1983NASCP.2280..63A
Altcode: 1983sowi.conf...63A
An observational program was undertaken at Sacramento Peak Observatory
to photoelectrically detect coronal transients. Continuous observations
are made in the Fe XIV 5303A green line, utilizing the 40 cm coronagraph
and the Photoelectric Coronal Photometer. Scans at three heights
above the limb are combined to form a low resolution picture of the
greenline corona every 20 to 30 minutes. Difference pictures, relative
to an initial scan, are generated to search for sudden changes in the
corona. The first few days of operation of this program have yielded
three low-lying events ( 1.55 solar radii) following minor chromospheric
activity (a surge and eruptive prominences), which propagated up
through the corona with velocities on the order of 100 km/s.
Title: Solar Continuum-Intensity Oscillations in the Five-Minute Band
Authors: Altrock, R. C.
Bibcode: 1983BAAS...15..952A
Altcode:
No abstract at ADS
Title: Coronal Transients as Observed in Fe XIV 5303 A at Sacramento
Peak Observatory
Authors: Altrock, R. C.; Demastus, H. L.
Bibcode: 1983BAAS...15R.706A
Altcode:
No abstract at ADS
Title: The Evolution of an Average Solar Granule
Authors: Altrock, R. C.; Musman, S.
Bibcode: 1981BAAS...13..879A
Altcode:
No abstract at ADS
Title: Is Granulation a Periodic Phenomenon?
Authors: Altrock, R. C.; Musman, S.
Bibcode: 1980BAAS...12..894A
Altcode:
No abstract at ADS
Title: Solar Photospheric Evolution During the Lifetime of a Granule
Authors: Altrock, R. C.
Bibcode: 1980BAAS...12..474A
Altcode:
No abstract at ADS
Title: Anomalous Satellite Drag and the Green Line Corona (refereed)
Authors: Altrock, R. C.
Bibcode: 1980STP.....4....1A
Altcode:
No abstract at ADS
Title: The Evolution of an Average Solar Granule
Authors: Altrock, R. C.
Bibcode: 1980LNP...114...51A
Altcode: 1980sttu.coll...51A; 1980IAUCo..51...51A
No abstract at ADS
Title: Physical Development of an Average Solar Granule
Authors: Altrock, R. C.; Musman, S.
Bibcode: 1979BAAS...11..641A
Altcode:
No abstract at ADS
Title: Recurrent geomagnetic disturbances and coronal holes as
observed in Fe XIV λ5303 Å
Authors: Musman, S.; Altrock, R. C.
Bibcode: 1978JGR....83.4817M
Altcode:
We present data obtained with the Fe XIV λ5303-Å coronal photometer of
the Sacramento Peak Observatory for the period October 3 to December 22,
1976. During this period there was a pattern of three coronal holes and
three emission regions near the solar equator. Recurrent geomagnetic
disturbances were associated with two of these three holes. We propose
a simple method for predicting recurrent geomagnetic disturbances
were associated with two of these three holes. We propose a simple
method for predicting recurrent geomagnetic disturbances at times
of low solar activity based on coronal brightness and test it on our
data. We show that the method gives correct results 72% of the time,
compared with 64% for 27 day recurrence.
Title: Time Development of Solar Granulation
Authors: Altrock, R. C.; Musman, S.
Bibcode: 1978BAAS...10..623A
Altcode:
No abstract at ADS
Title: Intensity, velocity and temperature fluctuations in the upper
solar atmosphere.
Authors: Altrock, R. C.; Keil, S. L.
Bibcode: 1977A&A....57..159A
Altcode:
High-spatial-resolution photographic spectra of the Mg I 4571-A line
at 10 solar disk positions from center to limb are reduced to yield
intensity and velocity (line-shift) fluctuations along the spectrograph
slit for a height of about 300 km above the continuum level. The data
obtained are used to compute rms intensity and velocity fluctuations
corrected for instrument smearing. Comparison of the results with
those of Cannon and Wilson (1971) reveals a flatter distribution of
the rms intensity fluctuation as a function of heliocentric angle
and a 60% larger fluctuation at the disk center. It is inferred that
the correlation between velocity and intensity fluctuations exhibits
a large-scale random structure. The intensity-fluctuation data are
analyzed by calculating the emergent intensity from a three-dimensional
atmosphere having a sinusoidal checkerboard pattern of temperature
with a height-dependent amplitude, taking into account fluctuations in
electron pressure. The range of solutions for temperature fluctuations
is found to indicate that there are causes other than oscillations
for the temperature fluctuations in the upper photosphere.
Title: Coronal holes as observed in Fe XIV 5303 Å.
Authors: Altrock, R. C.; Musman, S. A.
Bibcode: 1977BAAS....9R.432A
Altcode:
No abstract at ADS
Title: The horizontal variation of temperature in the low solar
photosphere.
Authors: Altrock, R. C.
Bibcode: 1976SoPh...47..517A
Altcode:
Observations of the rms intensity fluctuations in the continuum
obtained by Pravdjuk et al. (Solnechnye Dannye, No. 2, p. 70, 1974)
from white-light photographs made with the Soviet Stratospheric Solar
Observatory are analyzed to obtain a horizontal temperature-fluctuation
amplitude as a function of depth. The results indicate that temperature
fluctuations increase with depth monotonically from a small value at
τ5000≅0.5 (cf. Figure 2). The initial rise of ΔT appears
quite steep, having a slope of approximately 20 K km−1. The
model of Wilson (Solar Phys.9, 303, 1969) is incompatible with the
data. Convective flux in the present model is approximately 6% of the
total flux at τ5000 = 1.
Title: Convective Flux in the Visible Photosphere
Authors: Altrock, R. C.
Bibcode: 1976BAAS....8..324A
Altcode:
No abstract at ADS
Title: Physical conditions in granulation.
Authors: Altrock, R. C.; Musman, S.
Bibcode: 1976ApJ...203..533A
Altcode:
High-resolution spectroheliograms made in the Ti I and Fe I 5016-A lines
with the diode array of a tower telescope are analyzed. Temperature
perturbations (delta T) were introduced into the Harvard-Smithsonian
Reference Atmosphere and varied empirically until the calculated line
profiles matched the observed profiles. It is found that the absolute
value of delta T increases going downward in the low photosphere. In the
middle photosphere, the absolute value does not exceed 70 K. It is also
found that the large buoyant forces implied by the solutions for delta T
are inconsistent with the small observed accelerations in the granular
flow. It is concluded that this incompatibility provides additional
evidence besides line broadening for the existence of microturbulence in
the low photosphere. The convective flux at an optical thickness of 3
(5000 A) is small compared with the total flux. Also, the temperature
fluctuations are much larger than those that would be produced by
the observed convective velocities alone. Thus, the observable low
photosphere appears to be near radiative equilibrium.
Title: Research at Sacramento Peak Observatory
Authors: Altrock, Richard
Bibcode: 1976srca.conf...89A
Altcode:
No abstract at ADS
Title: Physical condition in granulation
Authors: Altrock, R. C.; Musman, S.
Bibcode: 1976pmas.conf..285A
Altcode:
No abstract at ADS
Title: Heights of Formation of Non-Magnetic Solar Lines Suitable
for Velocity Studies
Authors: Altrock, R. C.; November, L. J.; Simon, G. W.; Milkey, R. W.;
Worden, S. P.
Bibcode: 1975SoPh...43...33A
Altcode:
Heights of formation of lines that do not exhibit Zeeman splitting
are calculated using an LTE, partial non-LTE, and full non-LTE
approach. Non-magnetic (g=0) lines are valuable for velocity
investigations in quiet-Sun magnetic field regions, and a knowledge
of their formation heights is useful for obtaining three dimensional
velocity profiles in these regions.
Title: Horizontal Temprature Fluctuations in the Low Solar
Photosphere.
Authors: Altrock, R. C.
Bibcode: 1975BAAS....7..406A
Altcode:
No abstract at ADS
Title: The Formation of Mg I 4571 Å in the Solar Atmosphere. V: The
Multi-Dimensional Structure of the Photosphere and Low Chromosphere
Authors: Altrock, R. C.; Cannon, C. J.
Bibcode: 1975SoPh...42..289A
Altcode:
The two-dimensional equation of transfer is solved for the case of
locally-controlled source function (LTE) and radiationally-controlled
ionization. Horizontal fluctuations in electron temperature and
macroscopic velocity fields are superposed on the basic one-dimensional
model (cf. Altrock and Cannon, 1972). Output intensities are compared
with observed rms intensity fluctuations and spatially-averaged
intensities in Mg I 4571 Å. We find that at least one model (with a
height-independent temperature fluctuation ΔT/T=±0.02 in the range
0⩽h⩽450 km) can predict the magnitude of the intensity fluctuations
in both the continuum and λ4571 Å. The asymmetry of the line can
be explained by adding a height-independent, temperature-correlated
flow of amplitude 1 to 2 km s−1. The relationship between
these results and other multi-dimensional analyses is discussed.
Title: Physical Conditions in Granulation
Authors: Altrock, R. C.; Musman, S.
Bibcode: 1975BAAS....7..362A
Altcode:
No abstract at ADS
Title: Analysis of the solar magnesium I spectrum.
Authors: Altrock, R. C.; Canfield, R. C.
Bibcode: 1974ApJ...194..733A
Altcode:
Without assuming local thermodynamic equilibrium (LTE), we
simultaneously solve the equations of statistical equilibrium and
radiative transfer for a model Mg I atom that includes the lines 4571,
5172 (b2), and 2852 A, which we then compare with observations. From
this comparison we determine by trial and error an optimum model of
run with height of electron temperature, electron density, and total
hydrogen density, and microturbulent velocity in the solar atmosphere up
to approximately h = 1000 km. In addition, we show that the assumption
of LTE for the 4571 A source function is valid to a high degree of
precision.
Title: The multi-dimensional structure of the photosphere and low
chromosphere of the sun.
Authors: Altrock, R. C.; Cannon, C. J.
Bibcode: 1974BAAS....6..428A
Altcode:
No abstract at ADS
Title: A Two-Dimensional Analysis of Intensity Fluctuations in MgI
4571 A on the Solar Disk
Authors: Altrock, Richard C.; Cannon, C. J.
Bibcode: 1974BAAS....6Q.284A
Altcode:
No abstract at ADS
Title: The Formation of Mg I 4571 Å in the Solar Atmosphere. IV:
Empirical vs Synthetic Analyses
Authors: Altrock, Richard C.
Bibcode: 1974SoPh...34...37A
Altcode:
A comparison is made of synthetic and empirical analyses for the 4571 Å
line of Mg I. First, several different inversion techniques are applied
to synthetic line profiles. The results show that at least some of
these techniques are able to correctly reproduce the input atmosphere
to a reasonable degree. Secondly, these same techniques are applied to
equivalent observational data. In this case some of the techniques yield
results that can be shown to be of comparable quality to the synthetic
analysis. I conclude that although the synthetic method is the best
method to use in analyzing observations, some of the simpler empirical
methods produce acceptable results in specified restricted cases.
Title: A Non-L.T.E. Analysis of the Solar Mg I Spectrum.
Authors: Altrock, R. C.; Canfield, R. C.
Bibcode: 1974BAAS....6..220A
Altcode:
No abstract at ADS
Title: A non-L.T.E. analysis of the solar Mg I spectrum.
Authors: Altrock, R. C.; Canfield, R. C.
Bibcode: 1974BAAS....6..219A
Altcode:
No abstract at ADS
Title: Erratum: "The formation of Mg I 4571 Å in the solar
atmosphere. II: The effect of one-dimensional macroscopic velocity
fields [Sol. Phys., Vol. 29, p. 275 - 286 (1973)].
Authors: Altrock, R. C.; Cannon, C. J.
Bibcode: 1973SoPh...31..524A
Altcode:
No abstract at ADS
Title: The Formation of Mg I 4571 Å in the Solar Atmosphere. II:
The Holweger Solar Model
Authors: Altrock, Richard C.; Cannon, C. J.
Bibcode: 1973SoPh...30...31A
Altcode:
No abstract at ADS
Title: The Formation of Mg I 4571 Å in the Solar Atmosphere. II:
The Effect of One-Dimensional Macroscopic Velocity Fields
Authors: Altrock, Richard C.; Cannon, C. J.
Bibcode: 1973SoPh...29..275A
Altcode:
An analysis of the 4571 Å line of neutral magnesium is presented in
which one-dimensional macroscopic velocity fields are included. It
is shown that gradients over restricted heights in the vertical
and horizontal components of the velocity field of order -0.005
s−1 and -0.004 s−1 (such that velocity towards
the observer decreases as height increases), respectively, result in
asymmetries in the computed line profile similar to those observed. The
heights in the solar atmosphere at which these velocity gradients exist
are shown to be very critical in reproducing the observations. It was
found that the best results were obtained when the gradients existed in
the height range from ∼ 200 km to ∼ 300 km below the temperature
minimum. The results indicate that for the Mg I 4571 Å line model
calculations that do not include one-dimensional flow velocities may
safely be compared with frequency-averaged observations.
Title: A One-Dimensional Approximation to the Macroturbulent Velocity
Field in the Solar Atmosphere
Authors: Altrock, R. C.; Cannon, C. J.
Bibcode: 1973BAAS....5R.268A
Altcode:
No abstract at ADS
Title: Empirical analysis of solar absorption line profiles.
Authors: Altrock, R. C.
Bibcode: 1973PASP...85R.529A
Altcode:
No abstract at ADS
Title: Erratum: The Minimum Temperature in the Solar Atmosphere.
Authors: Altrock, R. C.; Cannon, C. J.
Bibcode: 1972BAAS....4..426A
Altcode:
No abstract at ADS
Title: The Formation of Mg I 4571 Å in the Solar Atmosphere. I:
A Model Analysis of a One-Dimensional Static Atmosphere
Authors: Altrock, Richard C.; Cannon, C. J.
Bibcode: 1972SoPh...26...21A
Altcode:
A one-dimensional analysis of the 4571 Å line of neutral magnesium is
presented. The Harvard-Smithsonian Reference Atmosphere (HSRA) and the
Bilderberg Continuum Atmosphere (BCA) are used to compute the emergent
line profiles at various positions on the solar disc. The resultant
profiles, when compared to the observations, indicate that the HSRA
electron temperature distribution is a more satisfactory representation
of the solar atmosphere in the region of the temperature minimum than is
the BCA. A slight modification to the HSRA is suggested which reduces
the minimum temperature to 4140K and enables an even more satisfactory
`fit' to the available data.
Title: The Minimum Temperature in the Solar Atmosphere.
Authors: Altrock, R. C.; Cannon, C. J.
Bibcode: 1972BAAS....4..310A
Altcode:
No abstract at ADS
Title: Observations of Photospheric Pole-Equator Temperature
Differences
Authors: Altrock, Richard C.; Canfield, Richard C.
Bibcode: 1972SoPh...23..257A
Altcode:
Using photoelectric methods we have repeated Plaskett's (1970)
measurements of poleequator temperature differences. We average many
limb-darkening scans to reduce statistical errors. We then analyze the
differences between the average polar and equatorial scans. Plaskett's
large poleequator temperature differences are not confirmed. Our data
yield a pole-equator temperature difference of 1.5K±0.6K, although
we cannot rule out systematic errors of 3-4 K.
Title: Observations of the variation of temperature with latitude
in the upper solar photosphere.
Authors: Altrock, R. C.; Canfield, R. C.
Bibcode: 1972BAAS....4..268A
Altcode:
No abstract at ADS
Title: Measurements of the limb darkening in the forbidden Mg i line
at 4571.1 Å
Authors: White, O. R.; Altrock, R. C.; Brault, J. W.; Slaughter, C. D.
Bibcode: 1972SoPh...23...18W
Altcode:
We report high resolution measurements of the center-to-limb variation
of the MgI line at 4571.1 Å. This forbidden line is of interest because
it should be formed in LTE. Comparison of our measurements with the
Harvard-Smithsonian Reference Atmosphere show that the line center
radiation originates in the temperature minimum region from 330 to 550
km above the point where τcontinuum = 1. Observations near
the limb confirm that the temperature minimum is ∼4200K.
Title: Observations of the Variation of Temperature with Lattitude
in the Upper Solar Photosphere
Authors: Altrock, Richard C.; Canfield, Richard C.
Bibcode: 1972ApJ...171L..71A
Altcode:
We made photoelectric meridional and equatorial limb-darkening scans
during the period 15-22 June 1971, using a spectral region of 30 mA
width centered 0.77 A to the red of Ca II K3. The radiation observed
originates at r5000 10 . At the time of our observations the temperature
relative to the equatorial temperature was enhanced by 8 K + 2.5 K at
active-region latitudes and 5 K + 2 K at latitude 50 N.
Title: An empirical analysis of the infrared triplet of O I.
Authors: Altrock, R. C.
Bibcode: 1971BAAS....3..259A
Altcode:
No abstract at ADS
Title: The Empirical Analysis of Triplet Line Profiles
Authors: Altrock, Richard C.
Bibcode: 1970BAAS....2S.290A
Altcode:
No abstract at ADS
Title: Source Functions of Infrared Fraunhofer Lines from Equivalent
Widths
Authors: Altrock, Richard C.
Bibcode: 1969BAAS....1T.270A
Altcode:
No abstract at ADS
Title: Interpretation of Infrared Oxygen Spectroheliograms
Authors: Altrock, Richard C.
Bibcode: 1969SoPh....7..343A
Altcode:
Spectroheliograms have been obtained in the line cores of two infrared
multiplets of neutral oxygen. Those made in the lines of the 7770 Å
multiplet show a very smooth intensity distribution, with faculae and
sunspot penumbrae at a very low contrast with respect to the undisturbed
photosphere. Spectroheliograms made in the core of λ 8446.37 Å show
evidence of coupling with chromospheric features and of blending with
a line of neutral iron.
Title: Source Functions of Infrared Fraunhofer Lines from Equivalent
Widths
Authors: Altrock, Richard C.
Bibcode: 1969SoPh....7....3A
Altcode:
A method for obtaining the source function and value of r0
□ kc/kL,0 from the variation of equivalent width
across the solar disk has been applied to several infrared Fraunhofer
lines. The results indicate that most of the lines investigated
have non-L.T.E. source functions which are less than or equal to the
mean continuum intensity. DE JAGER and NEVEN (1968) appear to have
underestimated the departures from L.T.E. in a number of cases.
Title: A New Method for the Analysis of Equivalent Widths and its
Application to Solar Photospheric Oxygen
Authors: Altrock, Richard C.
Bibcode: 1968SoPh....5..260A
Altcode:
Six neutral atomic oxygen Fraunhofer multiplets were observed at nine
disk positions at Sacramento Peak Observatory. I filtered the data,
corrected them for the instrumental profile and obtained equivalent
widths.
Title: A Study of Neutral Atomic Oxygen in the Solar Atmosphere.
Authors: Altrock, Richard Charles
Bibcode: 1968PhDT.........1A
Altcode:
No abstract at ADS