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Author name code: pesnell
ADS astronomy entries on 2022-09-14
author:"Pesnell, William Dean"
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Title: Two New Methods for Counting and Tracking the Evolution of
Polar Faculae
Authors: Hovis-Afflerbach, B.; Pesnell, W. Dean
2022SoPh..297...48H Altcode: 2022arXiv220410863H
Polar faculae are the footpoints of magnetic-field lines near the Sun's
poles that are seen as bright regions along the edges of granules. The
time variation in the number of polar faculae has been shown to
correlate with the strength of the polar magnetic field and to be a
predictor of the subsequent solar cycle. Due to the small size and
transient nature of these features, combined with different techniques
and observational factors, previous counts of polar faculae differ
in magnitude. Further, there were no scalable techniques to measure
the statistical properties of the faculae, such as the variation
of the facular lifetime with time or solar activity. Using data
from the Helioseismic and Magnetic Imager (HMI) onboard the Solar
Dynamics Observatory (SDO), we present two new methods for tracking
faculae and measuring their properties. In the first, we calculate
the pixel-by-pixel standard deviation of the HMI continuum intensity
images over one day, visualizing the faculae as streaks. The lifetime
of the facula is found by dividing the angular length of the streaks
by the latitude-dependent rotation rate. We apply this method to the
more visible pole each day for a week every six months, from September
2010 to March 2021. Combining all of the measured facular lifetimes
provides a statistical distribution with a mean of 6.0 hours, a FWHM
of 5.4 hours, and a skew towards longer lifetimes, with some faculae
lasting up to 1 day. In the second method, we overlay images of the
progressive standard deviation with the HMI magnetogram to show the
close relationship between the facular candidates and the magnetic
field. The results of this method allow us to distinguish between
motion due to the Sun's rotation and "proper motion" due to faculae
moving across the Sun's surface, confirming that faculae participate
in convective motions at the poles. Counts of polar faculae using both
methods agree with previous counts in their variation with the solar
cycle and the polar magnetic field. These methods can be extended to
automate the identification and measurement of other properties of
polar faculae, which would allow for daily measurements of all faculae
since SDO began operation in 2010.
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Title: Comparing the Sun Watcher Using Active Pixel System Detector
and Image Processing Instrument to the Atmosphere Imaging Assembly
Instrument Through Measurements of Polar Coronal Holes
Authors: Kirk, Michael S. F.; Pesnell, W. Dean; Arge, C. Nickolos;
West, Matthew J.; Attié, Raphael
2022SoPh..297...42K Altcode:
The PRoject for OnBoard Autonomy 2/Sun Watcher using Active pixel
system detector and image Processing (PROBA2/SWAP) instrument images
the full-disk extreme ultraviolet (EUV) Sun using a complementary
metal-oxide semiconductor active-pixel sensor (CMOS-APS) detector
with a filter centered on a 174 Å passband at a cadence of one to two
minutes. In contrast, the Atmosphere Imaging Assembly (AIA) instrument
onboard the Solar Dynamics Observatory (SDO) has a passband filter
centered on 171 Å and uses a charge-coupled device (CCD) detector
to make full-disk observations of the EUV corona. The images that
these two telescope designs produce are visually quite similar in
active regions, coronal loops, and the quiet corona. This work takes a
deeper look at the stability of the most difficult coronal features to
capture in an image: polar coronal holes. Polar coronal holes are the
longest-lived features on the Sun and are critical to understand the
global state of the solar corona, but because of an oblique viewing
angle, obstruction due to the coronal plasma scale height and lack of
ground-truth magnetic-field measurements make reliable segmentation
of polar holes difficult. We use perimeter tracing to make consistent
measurements of a polar-hole's perimeter and area in both SWAP 174
Å and AIA 171 Å images. The generated time series of coronal-hole
parameters rarely agree with each other. Direct comparison of polar-hole
measurements generated by these two imagers allows us to simultaneously
analyze the physical properties of polar coronal holes and to identify
systematic differences between the two different instruments.
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Title: Properties of Polar Faculae
Authors: Pesnell, William; Hovis-Afflerbach, Beryl; Wampler, Paul
2021AGUFMSH34D..03P Altcode:
Polar Faculae (PFe) are bright points at the edges of granules that
illuminate where magnetic field lines intersect the solar surface
near the Suns poles. We previously reported the average PF lifetime
determined from the Helioseismic and Magnetic Imager (HMI) on Solar
Dynamics Observatory (SDO) is 6.0 2.7 hours. We also showed that
the number of PFe in Solar Cycle 24 is correlated with the strength
of the polar magnetic field and anti-correlated with the sunspot
number. Those correlations had been known before but, as with any
solar activity variable, the time dependence is more complicated than
a linear correlation. We report on our continuing analysis of HMI PF
data, extending the time coverage of the number of PFe and measuring
the magnetic field associated with a sample of those PFe. We will map
the proper motion of those PF that appear to move in latitude. This
proper motion confirms that faculae participate in convective motions
at the poles. By measuring the presence, trajectory, and magnetic field
strength of a large sample of faculae, we can better understand polar
faculae and therefore the polar magnetic field and its evolution,
as well as conditions and convective motions at the poles. These
observations will help design space missions to observe the solar
polar regions.
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Title: Solar Cycle 25 Spits and Sputters, but Fireworks are Predicted
Authors: Pesnell, William
2021AGUFMSH43B..01P Altcode:
Solar Cycle 25 has begun its rapid rise to solar maximum. The
increase in EUV spectral irradiances will cause thermospheric
densities to increase and create satellite drag. Ham radio operators
look forward to improved propagation conditions. We have learned much
about predicting solar activity in Solar Cycle 24, especially with the
data provided by SDO, STEREO, and other missions and observatories. At
least 54 predictions of the amplitude of activity in Solar Cycle 25
have been published. Some of these predictions were made long before
solar minimum while others are still appearing. As with Solar Cycle 24,
these predictions depend heavily on statistics and precursors. The next
step in our attempts to predict solar activity is to produce accurate
error bars that can be used in simulations of the thermosphere over
the years of a space mission. An updated prediction of Solar Cycle 25
using the SODA polar field precursor method will be presented. This
precursor has accurately predicted the last three cycles. I will also
comment on the data needed to understand the polar regions of the Sun
--- the seeds of the next cycle.
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Title: Using Hilbert curves to organize, sample, and sonify solar data
Authors: Pesnell, W. Dean; Ingram-Johnson, Kyle; Addison, Kevin
2021AmJPh..89..943P Altcode:
How many ways can we explore the Sun? We have images in many wavelengths
and squiggly lines of many parameters that we can use to characterize
the Sun. We know that while the Sun is blindingly bright to the naked
eye, it also has regions that are dark in some wavelengths of light. All
of those classifications are based on vision. Hearing is another sense
that can be used to explore solar data. Some data, such as the sunspot
number or the extreme ultraviolet spectral irradiance, can be readily
sonified by converting the data values to musical pitches. Images are
more difficult. Using a raster scan algorithm to convert a full-disk
image of the Sun to a stream of pixel values creates variations that
are dominated by the pattern of moving on and off the limb of the
Sun. A sonification of such a raster scan will contain discontinuities
at the limbs that mask the information contained in the image. As
an alternative, Hilbert curves are continuous space-filling curves
that map a linear variable onto the two-dimensional coordinates of an
image. We have investigated using Hilbert curves as a way to sample and
analyze solar images. Reading the image along a Hilbert curve keeps
most neighborhoods close together as the resolution (i.e., the order
of the Hilbert curve) increases. It also removes most of the detector
size periodicities and may reveal larger-scale features. We present
several examples of sonified solar data, including sunspot number,
extreme ultraviolet (EUV) spectral irradiances, an EUV image, and a
sequence of EUV images during a filament eruption.
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Title: Two new methods for counting and tracking the evolution of
polar faculae
Authors: Hovis-Afflerbach, B.; Pesnell, W.
2021AAS...23811302H Altcode:
Polar Faculae are the unipolar footpoints of field lines near the sun's
poles and are visible as bright points on the edges of granules. Their
number has been shown to correlate with the strength of the polar
magnetic field, and therefore better understanding polar faculae enables
better understanding of the polar magnetic field and its evolution,
as well as conditions and convective motions at the poles. We present
two methods of tracking faculae. In one the standard deviation of HMI
continuum intensity images is calculated over a day and the facular
candidates identified by their trails. The other overlays images of
the progressive standard deviation over the course of the day with
individual HMI magnetograms to show the close relationship between
the facular candidates and the magnetic field. We apply this method
to one pole each day for a week every 6 months, beginning September
2010. Our results confirm that faculae track regions of unipolar
magnetic field that match the polarity of the visible pole. We observe
the motion of the faculae and distinguish between motion due to the
sun's rotation and "proper motion" due to faculae moving on the sun's
surface, confirming that faculae participate in convective motions at
the poles. This method provides a larger daily count of faculae than
previous studies, allowing for a valid statistical determination of the
facular lifetime. We show that the lifetime has a mode of 1-3 hours,
with some faculae lasting up to 10 hours.
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Title: FISHA: the science case for a fast solar imager
Authors: Inglis, A.; Kirk, M.; Attie, R.; Pesnell, W.
2021AAS...23831305I Altcode:
The modern era of high-resolution solar EUV imaging at multiple
wavelengths has unlocked a wealth of scientific discovery. Despite
this, there are two fundamental issues that limit our ability to
understand bright, rapidly evolving events on the Sun. These are 1)
temporal cadence, and 2) image saturation. The combination of these
two issues means that the fast dynamics on the Sun, particularly during
eruptive events, are difficult to resolve in both time and space. This
is problematic because models predict and observations show that
during flares reconnection and particle acceleration processes can
occur on < 1s timescales. These processes lead to rapidly varying
thermal responses in chromospheric and coronal plasma. <P />We present
the science case for the FISHA concept, a fast imager for the solar
atmosphere. FISHA would image the Sun at high spatial resolution and
sub-second temporal cadence, providing targeted observations of bright,
transient features. This can be achieved while avoiding saturation
effects using a combination of short exposure times and rapid readout
detector capabilities. FISHA would also employ situational exposure
and cadence control to allow observations of a wide range of solar
phenomena. Here, we explore the potential science that FISHA could
achieve and discuss methods of implementation.
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Title: LORRI observations of waves in Pluto's atmosphere
Authors: Jacobs, Adam D.; Summers, Michael E.; Cheng, Andrew F.;
Gladstone, G. Randall; Lisse, Carey M.; Pesnell, W. Dean; Bertrand,
Tanguy; Strobel, Darrell F.; Young, Leslie A.; Weaver, Harold A.;
Kammer, Joshua; Gao, Peter
2021Icar..35613825J Altcode:
Observations during the New Horizons (NH) spacecraft flyby of Pluto
in July 2015 revealed that Pluto's atmosphere supports an extensive
circumplanetary haze with embedded layers, suggesting several possible
microphysical and/or dynamical excitation processes. The purpose
of this paper is to build upon existing observations and analyses of
Pluto's atmosphere-specifically of the complex haze layer structures-to
identify wave structure in Pluto's atmosphere. Here three NH/Long
Range Reconnaissance Imager (LORRI) image sequences from the flyby
at high phase angles (148°-169°) and three different resolutions
(0.093 km/pix, 0.96 km/pix, and 3.86 km/pix) are analyzed. Several
haze layer characteristics were extracted, namely-slope, amplitude,
waveform, and the associated power spectral densities (PSDs); and
their variations with local geography. These are then explored in the
context of possible wave types in Pluto's atmosphere, such as tidal
and orographically driven inertia-gravity (buoyancy) waves. PSD peaks
at 8-10 km and 18-22 km vertical wavelength are found in NH images,
which is consistent with the perturbations seen in Earth-based stellar
occultations of Pluto's atmosphere. The 8-10 km signals are localized
to low-latitudes and equatorial regions and the 18-22 km signals are
more globally distributed. Haze layer background relative amplitudes
were found to be around 0.01-0.04. Slopes of layers were found to
be correlated with the emergence and disappearance of a 25 km layer
around 30°N. An amplitude increase of oscillations below 30 km altitude
exists in the high-resolution image sequence. These findings indicate
the possibility of waves in Pluto's atmosphere and motivate further
studies of wave dynamics combining NH data with state-of-the-art models
of Pluto's atmosphere. These results are important because they can
provide strong constraints to models and to the type of waves that
can be present in Pluto's atmosphere.
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Title: A Study of Equatorial Coronal Holes and Active regions during
the Maximum Phase of four Solar Cycles
Authors: Karna, Nishu; DeLuca, Edward; Pesnell, William; Saar, Steven;
Karna, Mahendra
2021cosp...43E.920K Altcode:
The 11-year Solar Cycle (SC) is characterized by periodic changes
in solar activity indicators such as number of sunspots, coronal
holes, active regions (ARs), as well as the occurrence rate of solar
energetic events such as filament eruptions, flares and coronal mass
ejections (CMEs). In this work we performed a statistical study of the
equatorial coronal holes (ECHs) and ARs during the maximum phase of the
last four solar cycles: SC 21 (1979--1982), SC 22 (1989--1992), SC 23
(1999--2002) and SC 24 (2012--2015). We compared the number of ECHs and
ARs, separations between their centroids, solar wind speed, pressure
and the number of intense geomagnetic storms (IGS) data over these four
cycles. We note a strong anticorrelation between the number of ARs and
ECHs. We found that the number of close ARs and ECHs, solar wind speed,
and the number of IGS increases with average sunspot maximum number
for even cycles and decreases with average sunspot maximum for odd
cycles. These odd-even trends largely (though not entirely) disappear
in the relation between the wind properties and the numbers of close
AR and ECH. This suggests a possible link between ECH-AR interactions
and the solar wind phenomena, though residual odd-even trends point to
the importance of other effects (e.g., Sun-earth magnetic alignment)
as well.
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Title: SunCET: The Sun Coronal Ejection Tracker Concept
Authors: Mason, James Paul; Chamberlin, Phillip C.; Seaton, Daniel;
Burkepile, Joan; Colaninno, Robin; Dissauer, Karin; Eparvier, Francis
G.; Fan, Yuhong; Gibson, Sarah; Jones, Andrew R.; Kay, Christina; Kirk,
Michael; Kohnert, Richard; Pesnell, W. Dean; Thompson, Barbara J.;
Veronig, Astrid M.; West, Matthew J.; Windt, David; Woods, Thomas N.
2021JSWSC..11...20M Altcode: 2021arXiv210109215M
The Sun Coronal Ejection Tracker (SunCET) is an extreme ultraviolet
imager and spectrograph instrument concept for tracking coronal mass
ejections through the region where they experience the majority
of their acceleration: the difficult-to-observe middle corona. It
contains a wide field of view (0-4 R<SUB>⊙</SUB>) imager and a 1 Å
spectral-resolution-irradiance spectrograph spanning 170-340 Å. It
leverages new detector technology to read out different areas of the
detector with different integration times, resulting in what we call
"simultaneous high dynamic range", as opposed to the traditional high
dynamic range camera technique of subsequent full-frame images that
are then combined in post-processing. This allows us to image the
bright solar disk with short integration time, the middle corona
with a long integration time, and the spectra with their own,
independent integration time. Thus, SunCET does not require the use
of an opaque or filtered occulter. SunCET is also compact - ~15 × 15
× 10 cm in volume - making it an ideal instrument for a CubeSat or a
small, complementary addition to a larger mission. Indeed, SunCET is
presently in a NASA-funded, competitive Phase A as a CubeSat and has
also been proposed to NASA as an instrument onboard a 184 kg Mission
of Opportunity.
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Title: Predicting Solar Cycle 25 with an Ap/F10.7 Geomagnetic
Precursor Pair
Authors: Pesnell, W. D.
2020AGUFMSH053..08P Altcode:
Long-term predictions of solar activity indices are used in orbital
prediction and mission planning. We describe using an Ap/F10.7
geomagnetic precursor pair to predict the amplitude of the just-started
Solar Cycle 25. The method is an evolution of an earlier algorithm that
now removes the baseline solar activity cycle-by-cycle. A recurrence
index is used to determine the timing of the precursor peak used in
the prediction. Unlike previous times, when the recurrence index showed
well-defined peaks during the decline from solar maxima, the recurrence
index in the decline of Solar Cycle 24 increases rapidly after solar
maximum in 2014 and remains at a large value until 2020. The effect of
this on the timing of the precursor value will be examined. We conclude
that Solar Cycle 25 will be no stronger than average and could be much
weaker than average.
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Title: Lessons learned from predictions of Solar Cycle 24
Authors: Pesnell, W. Dean
2020JSWSC..10...60P Altcode:
Solar Cycle 24 has almost faded and the activity of Solar Cycle 25 is
appearing. We have learned much about predicting solar activity in Solar
Cycle 24, especially with the data provided by SDO and STEREO. Many
advances have come in the short-term predictions of solar flares and
coronal mass ejections, which have benefited from applying machine
learning techniques to the new data. The arrival times of coronal mass
ejections is a mid-range prediction whose accuracy has been improving,
mostly due to a steady flow of data from SoHO, STEREO, and SDO. Longer
term (greater than a year) predictions of solar activity have benefited
from helioseismic studies of the plasma flows in the Sun. While these
studies have complicated the dynamo models by introducing more complex
internal flow patterns, the models should become more robust with the
added information. But predictions made long before a sunspot cycle
begins still rely on precursors. The success of some categories of
the predictions of Solar Cycle 24 will be examined. The predictions
in successful categories should be emphasized in future work. The SODA
polar field precursor method, which has accurately predicted the last
three cycles, is shown for Solar Cycle 25. Shape functions for the
sunspot number and F10.7 are presented. What type of data is needed
to better understand the polar regions of the Sun, the source of the
most accurate precursor of long-term solar activity, will be discussed.
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Title: A Study of Equatorial Coronal Holes during the Maximum Phase
of Four Solar Cycles
Authors: Karna, Mahendra Lal; Karna, Nishu; Saar, Steven H.; Pesnell,
W. Dean; DeLuca, Edward E.
2020ApJ...901..124K Altcode:
The 11 yr solar cycle (SC) is characterized by periodic changes in
solar activity indicators such as the number of sunspots, coronal
holes, and active regions (ARs), as well as the occurrence rate of
solar energetic events such as filament eruptions, flares, and coronal
mass ejections. In this work we performed a statistical study of the
equatorial coronal holes (ECHs) and ARs during the maximum phase
of the last four SCs: SC 21 (1979-1982), SC 22 (1989-1992), SC 23
(1999-2002), and SC 24 (2012-2015). We compared the number of ECHs and
ARs, separations between their centroids, solar wind speed, pressure,
and the number of intense geomagnetic storm (IGS) data over these four
cycles. We note a strong anticorrelation between the number of ARs and
ECHs. We found that the number of close ARs and ECHs, solar wind speed,
and the number of IGS increases with average sunspot maximum number
for even cycles and decreases with average sunspot maximum for odd
cycles. Also, we find strong odd-even trends in the relation between
the wind properties and the numbers of close AR and ECH. These results
obtained from the annual average data suggest a possible link between
ECH and AR proximity and the solar wind phenomena, though odd-even
trends point to the importance of other effects (e.g., Sun-Earth
magnetic alignment) as well.
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Title: A Study of Equatorial Coronal Holes during the Maximum Phase
of four Solar Cycles
Authors: Karna, N.; Karna, M.; Saar, S.; Pesnell, W.; DeLuca, E.
2020SPD....5120903K Altcode:
The 11-year Solar Cycle (SC) is characterized by periodic changes
in solar activity indicators such as a number of sunspots, coronal
holes, active regions (ARs), as well as the occurrence rate of solar
energetic events such as filament eruptions, flares and coronal mass
ejections (CMEs). In this work we performed a statistical study of
the equatorial coronal holes (ECHs) and ARs during the maximum phase
of the last four solar cycles: SC 21 (1979-1982), SC 22 (1989-1992),
SC 23 (1999-2002) and SC 24 (2012-2015). We compared the number of
ECHs and ARs, separations between their centroids, solar wind speed,
pressure and the number of intense geomagnetic storms (IGS) data
over these four cycles. We note a strong anticorrelation between the
number of ARs and ECHs. We found that the number of close ARs and ECHs
(which are potentially interacting), solar wind speed, and the number
of IGS increases with average sunspot maximum number for even cycles
and decreases with average sunspot maximum for odd cycles. Also,
we find strong odd-even trends in the relation between the wind
properties and the numbers of close AR and ECH. These results suggest a
possible link between ECH-AR interactions and the solar wind phenomena,
though odd-even trends point to the importance of other effects (e.g.,
Sun-earth magnetic alignment) as well.
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Title: Using Ephemeral Coronal Holes to Validate the SPOCA Database
of Coronal Holes
Authors: Pesnell, W. D.; Pant, N.; Kirk, M. S.; Inglis, A. R.
2019AGUFMSH11D3385P Altcode:
Given the relatively few examples of ephemeral coronal holes found
by direct examination of data from the Solar Dynamics Observatory
(SDO), we looked to the Spatial Possibilistic Clustering Algorithm
(SPOCA) feature-finding algorithm to identify more examples. The
SPOCA results are stored at the Heliophysics Event Knowledgebase
(HEK), which was interrogated for this research. Unlike the direct
examination, SPOCA identifies many small candidates for ephemeral
coronal holes. We will report several causes for this difference,
such as many candidates near the limb. Several filaments are also
included as coronal holes. A dipole moment algorithm was developed
to automatically eliminate these candidates from consideration. The
magnetic configuration around a polarity inversion line underlying a
filament has a more organized appearance than does the random field
line placement within a coronal hole. The algorithm will be described,
test cases presented, and solar examples will be presented.
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Title: Probing the solar corona with Sun-grazing comets: comparing
MHDsimulations with EUV observations
Authors: Jia, Y. D.; Pesnell, W. D.; Liu, W.; Downs, C.; Bryans, P.
2019AGUFMSH13A..03J Altcode:
Sun -grazing comets can dive within one solar radii of the Sun
's surface. The cometary materials expand along the comet's orbit,
and undergo various stages of fierce thermal-chemical reactions on
the scales of seconds to minutes. These reactions ionize cometary
ions through successive charge states , which is revealed by certain
emission lines in the AIA images. Such plasma reaction processes are
significantly affected by the transient structures in the corona, and
thus these structures are revealed by the structures and shapes of the
comet tail. We combine three numerical models: a global corona model,
particle transportation model, and cometary plasma interaction model
into one framework to simulate the interaction of Sun -grazing comets
in the low corona. In our framework, cometary ejecta are vaporized
and then ionized via multiple channels, and then confined by the
coronal magnetic field. Constrained by imaging observations of the
and cometary interaction images, we apply our framework to trace back
to the local condition of the ambient corona, and its spatiotemporal
variation. Previously, our model confirmed the importance of the
ambient magnetic field vector in shaping the tail. In this study,
we use the C/2011 W3 (Lovejoy) perihelion to determine the local
plasma and field conditions in the corona. Our framework is capable of
resolving structures from thousands of meters to tens of million meters,
so we can identify the fine spatial variations in plasma density and
magnetic field intensity, which may be visible in future/on-going
close-up coronal observations.
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Title: Tracking supergranulation near the poles with SDO/HMI
Authors: Attié, R.; Kirk, M. S.; Tremblay, B.; Muglach, K.; Hess
Webber, S. A.; Pesnell, W. D.; Thompson, B. J.
2019AGUFMSH13B..01A Altcode:
Due to the spherical curvature of the Sun, solar observers suffer
from an increasing loss of resolution as we move away from the solar
equator. Thus knowledge of the photospheric flows near the poles
has eluded the scope of traditional flow tracking algorithms that
are using granules as tracers of the underlying flows. Using the new
"Balltracking" framework which we adapted to the observations from
SDO/HMI, we present an unprecedented analysis of the horizontal flow
fields at latitudes beyond +/- 60 degrees. The flow fields are derived
every 4 hours at a spatial resolution of 4 Mm. Using flow segmentation
techniques, we extract geometric and spectral information on the
supergranular cells and compare them with those of the supergranulation
at lower latitude. The correlation with the dynamics of moving magnetic
features is also investigated.
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Title: A Study of Equatorial Coronal Holes during the Maximum Phase
of Four Solar Cycles
Authors: Karna, N.; Karna, M. L.; Saar, S. H.; Pesnell, W. D.;
DeLuca, E.
2019AGUFMSH44A..03K Altcode:
The 11-year Solar Cycle (SC) is characterized by periodic changes
in the solar activity such as sunspot numbers, coronal holes, active
regions, eruptions such as prominence eruptions, flares and coronal
mass ejections. In this work we performed a statistical study of the
equatorial coronal holes and the active regions during the maximum
phases of four solar cycles (SC 21 (1979, 1980, 1981 and 1982), SC 22
(1989, 1990, 1991 and 1992), SC 23 (1999, 2000, 2001 and 2002) and SC 24
(2012, 2013, 2014 and 2015)). We compared equatorial coronal hole and
active region numbers, separations between equatorial coronal holes and
active regions centroids, solar wind speed and the number of intense
geomagnetic storms data over these four cycles. We found that the
distance between equatorial coronal holes and active regions, the solar
wind speed, and the the number of intense geomagnetic storms increases
with average sunspot maximum number for even cycles and decreases
with average sunspot maximum for odd cycles. We also noticed that the
solar wind speeds, pressures, and the number of intense geomagnetic
storms increase with the numbers of close equatorial coronal holes and
active regions, suggesting a possible link between equatorial coronal
holes--active regions interactions and the wind phenomena.
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Title: Comparing Polar Coronal Hole Size to Polar Magnetic Flux
Authors: Kirk, M. S.; Pesnell, W. D.; Arge, C. N.
2019AGUFMSH41B..02K Altcode:
Polar magnetic fields are a critical piece to understand the global
state of the solar corona. However, measuring the solar polar magnetic
fields are notoriously difficult because of the oblique viewing
angle. Polar coronal holes are the longest-lived features on the
sun and represent areas of open magnetic flux. We make comprehensive
measurements of polar hole's perimeter and area in three EUV wavelengths
between 1996 and 2018 using five different space-based imagers: SOHO
EIT, STEREO A and B EUVI, PROBA2 SWAP, and SDO AIA. The generated
time-series of coronal hole boundaries rarely agree with each other,
which presents a difficult data problem: multi-band, multi-instrument,
heteroscedastic measurements with periodic and systematic signals. We
combine these measurements using a parametric bootstrap method to
make an empirical estimation of the polar coronal hole's size and
boundary. This technique allows us to accurately characterize the
evolving area and boundary of the polar holes. From this timeseries
of polar hole area, we infer the evolving polar field flux over the
past 22 years.
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Title: A Time-Distance Helioseismology Method for Quasi-Linear
Geometries
Authors: Hess Webber, Shea A.; Pesnell, W. Dean
2019SoPh..294..151H Altcode:
Helioseismology is the study of the solar interior, through which
we extract flow and wave-speed information from Doppler velocity
observations at the surface. Local helioseismology involves the study
of small regions on the solar disk and is used to create a detailed
picture of the interior in that particular region. Perturbations
in the flow and wave-speed results indicate, e.g. magnetic-flux
or temperature variations. There are multiple methods used in
local-helioseismic research, but all current local-helioseismic
techniques assume a point-source perturbation. For this study, we
develop a new time-distance (TD) helioseismic methodology that can
exploit the quasi-linear geometry of an elongated feature, allowing
us to i) improve the signal-to-noise ratio of the TD results, and ii)
greatly decrease the number of calculations required and therefore the
computing time of the TD analysis. Ultimately, the new method will allow
us to investigate solar features with magnetic-field configurations
previously unexplored. We validate our new technique using a simple f
-mode wave simulation, comparing results of point-source and linear
perturbations. Results indicate that local-helioseismic analysis is
dependent on the geometry of the system and can be improved by taking
the magnetic-field configuration into account.
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Title: Characteristics of Ephemeral Coronal Holes
Authors: Inglis, A. R.; O'Connor, R. E.; Pesnell, W. D.; Kirk, M. S.;
Karna, N.
2019ApJ...880...98I Altcode: 2019arXiv190601757I
Small-scale ephemeral coronal holes may be a recurring feature on the
solar disk but have received comparatively little attention. These
events are characterized by compact structures and short total
lifetimes, which are substantially less than a solar disk crossing. We
present a systematic search for these events, using Atmospheric Imaging
Assembly extreme ultraviolet image data from the Solar Dynamics
Observatory, covering the time period of 2010-2015. Following
strict criteria, this search yielded four clear examples of the
ephemeral coronal hole phenomenon. The properties of each event are
characterized, including their total lifetime, growth and decay rates,
and areas. The magnetic properties of these events are also determined
using Helioseismic and Magnetic Imager data. Based on these four
events, ephemeral coronal holes experience rapid initial growth of
up to ∼3000 Mm<SUP>2</SUP> hr<SUP>-1</SUP>, while the decay phases
are typically more gradual. Like conventional coronal holes, the mean
magnetic field in each ephemeral coronal hole displays a consistent
polarity, with mean magnetic flux densities generally <10 G. No
evidence of a corresponding signature is seen in solar wind data at
1 au. Further study is needed to determine whether ephemeral coronal
holes are underreported events or are truly rare phenomena.
---------------------------------------------------------
Title: Orbits through polytropes
Authors: Gjerløv, Amalia; Pesnell, W. Dean
2019AmJPh..87..452G Altcode:
We describe how orbital tunnels could be used to transport payloads
through the Earth. If you use a brachistochrone for the tunnel, the
body forces in the tunnel become overwhelmingly large for small angular
distances traveled. Projectiles move along an orbital tunnel faster
than they would along a brachistochrone connecting the same points but
the body force components cancel. We describe how parabolic Keplerian
orbits outside the object merge onto quasi-Keplerian orbits inside
the object. We use models of the interior of the Earth with three
values of the polytropic index (n) to calculate interior orbits that
travel between surface points. The n = 3 results are also scaled to
the Sun. Numerical integrations of the equations describing polytropes
were used to generate the initial models. Numerical integration of the
equations of motion are then used to calculate the angular distance you
can travel along the surface and the traversal time as a function of
the parabolic periapsis distance for each model. Trajectories through
objects of low central condensation show a focussing effect that
decreases as the central condensation increases. Analytic solutions
for the trajectories in a homogeneous sphere are derived and compared
to the numeric results. The results can be scaled to other planets,
stars, or even globular clusters.
---------------------------------------------------------
Title: Characteristics of ephemeral coronal holes
Authors: Inglis, Andrew; O'Connor, Rachel; Pesnell, W. Dean; Kirk,
Michael S.; Karna, Nishu
2019AAS...23410605I Altcode:
Small-scale ephemeral coronal holes may be a recurring feature on the
solar disk, but have received comparatively little attention. These
events are characterized by compact structure and short total lifetimes,
substantially less than a solar disk crossing. Following a search of the
time period 2010 - 2015 using Atmospheric Imaging Assembly EUV image
data from the Solar Dynamics Observatory, we present analysis of four
of the clearest examples of the ephemeral coronal hole phenomenon. The
properties of each event are characterized, including their total
lifetime, growth and decay rates, and areas. The magnetic properties
of these events are also determined using Heliospheric Magnetic Imager
data. These ephemeral coronal holes possess common characteristics,
experiencing rapid initial growth of up to 3000 Mm<SUP>2</SUP> / hr,
while the decay phases are typically more gradual. Like conventional
coronal holes, the mean magnetic field in each ephemeral coronal
hole displays a consistent polarity, with mean fields generally <
10 G. No evidence of a corresponding signature is seen in solar wind
data at 1AU. Further study is needed to determine whether ephemeral
coronal holes are under-reported events or a truly rare phenomenon.
---------------------------------------------------------
Title: A Comprehensive Assessment of EUV Polar Coronal Holes: 1996
- 2018
Authors: Kirk, Michael S.; Pesnell, W. Dean; Arge, Charles
2019AAS...23412501K Altcode:
Polar Coronal Holes are the longest-lived features on the sun and
are a critical piece to understand the global state of the solar
corona. Because of the oblique viewing angle, obstruction due to
the coronal plasma scale height, and lack of ground truth make
segmentation of polar holes difficult. We make new measurements of
polar hole's perimeter and area in three EUV wavelengths between 1996
and 2018 using five different space-based imagers: SOHO EIT, STEREO
A and B EUVI, PROBA2 SWAP, and SDO AIA. The generated time-series of
coronal hole parameters rarely agree with each other, which presents a
difficult data problem: multi-band, multi-instrument, heteroscedastic
measurements with periodic and systematic signals. We combine these
measurements using a parametric bootstrap method to make an empirical
estimation of the polar coronal hole's size, boundary, and center of
mass. This technique allows us to simultaneously analyze the physical
properties of polar coronal holes and identify regular periodicities
in our data from other origins. We present a comprehensive view of
the EUV polar coronal hole over the past 22 years.
---------------------------------------------------------
Title: Listening to the Sun
Authors: Pesnell, W. Dean; Ingram-Johnson, Kyle
2019AAS...23410703P Altcode:
How many ways can we explore the Sun? We have images in many wavelengths
and squiggly lines of many parameters that we can use to characterize
the Sun. We learn that the Sun is bright with regions that are dark
in some wavelengths and bright in others. But those classifications
are both based on vision. Sound is another sense to use in exploring
solar data. Some data, such as the sunspot number or the extreme
ultraviolet spectral irradiance, can be easily sonified. Images are
more difficult. A simple raster scan is dominated by moving on and off
the limb of the Sun. Any sonification of the raster scan will contain
discontinuities at the limbs that mask the information contained in the
image. We propose to sample the curves with Hilbert curves to reduce
those discontinuities. Hilbert curves are continuous space-filling
curves that map the two-dimensional coordinates of an image onto a
linear variable. We have investigated using Hilbert curves as ways to
sample and analyze solar images. Reading the image along a Hilbert curve
keeps neighborhoods close together as the resolution (i.e., the length
of the Hilbert curve) increases. It also removes most of the detector
size periodicities and actually shows the presence of longer-scale
features. We shall provide several examples of sonified solar data,
including the sunspot number, a selection of EUV spectral irradiances,
an AIA 171 image, and a series of images during a solar flare.
---------------------------------------------------------
Title: Fractal Dimensions of Solar and Geomagnetic Indices
Authors: Pesnell, W. Dean
2019AAS...23411801P Altcode:
Correlations between solar and geomagnetic indices are often used
in space weather research. How sensitive are these correlations
to pre-whitening of the data and auto-correlation within the data
sets? Statistical and timeseries analyses of the sunspot number are
often used to predict solar activity. These methods have not been
completely successful as the solar dynamo changes over time and one
cycle's sunspots are not a faithful predictor of the next cycle's
activity. Can more accurate predictions be produced by partitioning
the data into periods when it obeys certain statistical properties? The
Hurst exponent and the related fractal dimension are two such ways to
partition the data. We can use these measures of complexity to compare
the sunspot number with other solar and geomagnetic indices. We use
five algorithms to calculate the Hurst exponent or fractal dimension
and examine what happens when the mean and a linear trend trends
are removed. We find that some algorithms are robust and return
similar or identical values for the original, mean-removed, and
linear-trend-subtracted data. The behavior of the Fourier transform
at low frequencies is the most sensitive to the type of pre-whitening
applied to the data. The rescaled-range algorithm is robust but needs
to be corrected for autocorrelation in the data.
---------------------------------------------------------
Title: Characteristics of Ephemeral Coronal Holes
Authors: O'Connor, Rachel E.; Inglis, Andrew R.; Pesnell, W. Dean;
Kirk, Michael S.; Karna, Nishu
2019shin.confE.202O Altcode:
Small-scale ephemeral coronal holes may be a recurring feature on the
solar disk, but have received comparatively little attention. These
events are characterized by compact structure and short total lifetimes,
substantially less than a solar disk crossing. We present a systematic
search for these events, using Atmospheric Imaging Assembly EUV
image data from the Solar Dynamics Observatory, covering the time
period 2010 - 2015. Following strict criteria, this search yielded
four clear examples of the ephemeral coronal hole phenomenon. The
properties of each event are characterized, including their total
lifetime, growth and decay rates, and areas. The magnetic properties
of these events are also determined using Helioseismic and Magnetic
Imager data. Based on these four events, ephemeral coronal holes
experience rapid initial growth of up to 3000 Mm2/hr, while the decay
phases are typically more gradual. Like conventional coronal holes,
the mean magnetic field in each ephemeral coronal hole displays a
consistent polarity, with mean magnetic flux densities generally <
10 G. No evidence of a corresponding signature is seen in solar wind
data at 1 AU. Further study is needed to determine whether ephemeral
coronal holes are under-reported events or a truly rare phenomenon.
---------------------------------------------------------
Title: Quantifying the Variability of Coronal Hole Boundaries
Authors: Kirk, Michael S.; Pesnell, W. Dean; Arge, C. Nick
2019shin.confE..69K Altcode:
Polar Coronal Holes are the longest-lived features on the sun and
are a critical piece to understand the global state of the solar
corona. Because of the oblique viewing angle, obstruction due to the
coronal plasma scale height, and lack of ground truth make segmentation
of polar holes difficult. We make comprehensive measurements of polar
hole’s perimeter and area in three EUV wavelengths between 1996
and 2018 using five different space-based imagers: SOHO EIT, STEREO
A and B EUVI, PROBA2 SWAP, and SDO AIA. The generated time-series of
coronal hole boundaries rarely agree with each other, which presents a
difficult data problem: multi-band, multi-instrument, heteroscedastic
measurements with periodic and systematic signals. We combine these
measurements using a parametric bootstrap method to make an empirical
estimation of the polar coronal hole’s size, boundary, and center of
mass. This technique allows us to accurately characterize the evolving
boundary of the polar holes and identify the EUV band passes that best
capture these structures.
---------------------------------------------------------
Title: Simulations of Observed Haze Layer Structure in Pluto's
Atmosphere
Authors: Jacobs, A. D.; Summers, M. E.; Gladstone, R.; Cheng, A. F.;
Strobel, D. F.; Lisse, C. M.; Gao, P.; Young, L. A.; Pesnell, W. D.;
Kammer, J.; Weaver, H. A., Jr.
2018AGUFM.P51F2949J Altcode:
Observations during the New Horizons spacecraft flyby of Pluto in
July 2015 revealed that Pluto's atmosphere has an extensive haze with
embedded layers, suggesting several possible microphysical and/or
dynamical processes operating in the atmosphere. Orographically driven
gravity (buoyancy) waves are the main layering mechanism explored in
this study. A single scattering model was implemented to simulate three
LORRI image sequences at high phase angles (148˚-169<SUP>°</SUP>) and
three different resolutions (0.093 km/pix: HIPHASE_HIRES, 0.96 km/pix:
P_MULTI, and 3.5 km/pix: FULLFRAME). All scattering calculations were
done for the LORRI pivot wavelength of 607.6 nm. A 2D gravity wave
(GW) perturbation field created from an orographically-driven GW model
was used to generate north/south and east/west oriented 3D layered
structures. The two sets of GW perturbations were then applied to
two types of background haze densities. Haze layer I/F simulations
were further explored by applying LORRI's PSF to the simulated
images. Some discrepancies between model results and observations
still exist, including: (1) larger tilt/slope of modelled layers
for both GW orientations than observed in the P_MULTI sequence, (2)
smaller layer wavelength and larger layer distinctness/amplitude than
observed at altitudes below 40 km in the HIPHASE_HIRES sequence,
and (3) missing larger scale structure observed in the P_MULTI
and FULLFRAME sequences where haze layering is geographically most
distinct. These discrepancies may be accounted for by: (1) adjustments
to the GW model wind speed over terrain and/or changing the assumed
terrain/aspect ratio (i.e., by decreasing the assumed wind-aligned
wavenumber), (2) the inclusion of mixing processes or consideration of
faster layer dissipation processes for low altitude layers, and (3)
the superposition of different wave types (i.e., Rossby waves) with
orographically generated waves. Limitations on possible adjustments
to the GW model perturbations intrinsic tilt/slope that still allow
vertical propagation through Pluto's strong temperature inversion,
as well as power spectra extracted from LORRI images, are evidence
for the presence of other wave types that could cause haze layering
through generation mechanisms not considered by the orographic gravity
wave model.
---------------------------------------------------------
Title: Multi-wavelength Observations of Flare-Induced Acoustic Waves
Around Active Regions with SDO AIA
Authors: Monsue, Teresa; Pesnell, W. Dean; Hill, Frank; Kirk, Michael
2018csc..confE.111M Altcode:
Active regions on the Sun are abundant with a variety of waves that are
both acoustically helioseismic and magnetohydrodynamic in nature. The
occurrence of a solar flare can disrupt these waves, through MHD
mode-mixing or scattering by the excitation of these waves. We take
a multi-wavelength observational approach to understand the source
of these waves by studying active regions where flaring activity
occurs. Utilizing a Fast Fourier Transform (FFT) algorithm, our approach
is to search for signals within a time series of images by producing
multi-frequency power map movies and spatially sampling the time
series by radial sectors with constant area that minimizes the spatial
variation of the acoustic power. With this application we are able to
study the active region both spatially and temporally and correlate
data over multiple wavelengths, allowing us to observe the behavior
of the waves at different heights within the Solar atmosphere. We
apply multi-wavelength measurements utilizing NASA's SDO AIA 1700
(lower photosphere), 1600 (upper photosphere) and 304 (chromosphere)
passbands. When we run power map movies of the chromosphere we are able
to see a subtle propagating feature moving outward from the center of
the flare; this could be an MHD-wave propagating outward by the flaring
event. With our sector sampling method we observe power variation
around the flaring active region. This power variation corresponds to
the flare induced enhancement of the oscillations around the active
region. Furthermore, there seems to be absorptive properties observed
within the chromospheric line of the AIA 304 Å passband.
---------------------------------------------------------
Title: The Solar Dynamics Observatory, Eight Years of Science
Authors: Pesnell, W. Dean
2018csc..confE.110P Altcode:
The Solar Dynamics Observatory has been producing science and science
data since May 2010. I will describe some highlights of SDO results,
including filament eruptions, flares, and comets. The status of the
observatory hardware will also be discussed. The future of SDO will be
a series of extended missions, each lasting three years. Our second
extended mission started October 1, 2017. That gives us another year
to study the data before writing another proposal!
---------------------------------------------------------
Title: Roadmap for Reliable Ensemble Forecasting of the Sun-Earth
System
Authors: Nita, Gelu; Angryk, Rafal; Aydin, Berkay; Banda, Juan;
Bastian, Tim; Berger, Tom; Bindi, Veronica; Boucheron, Laura; Cao,
Wenda; Christian, Eric; de Nolfo, Georgia; DeLuca, Edward; DeRosa,
Marc; Downs, Cooper; Fleishman, Gregory; Fuentes, Olac; Gary, Dale;
Hill, Frank; Hoeksema, Todd; Hu, Qiang; Ilie, Raluca; Ireland,
Jack; Kamalabadi, Farzad; Korreck, Kelly; Kosovichev, Alexander;
Lin, Jessica; Lugaz, Noe; Mannucci, Anthony; Mansour, Nagi; Martens,
Petrus; Mays, Leila; McAteer, James; McIntosh, Scott W.; Oria, Vincent;
Pan, David; Panesi, Marco; Pesnell, W. Dean; Pevtsov, Alexei; Pillet,
Valentin; Rachmeler, Laurel; Ridley, Aaron; Scherliess, Ludger; Toth,
Gabor; Velli, Marco; White, Stephen; Zhang, Jie; Zou, Shasha
2018arXiv181008728N Altcode:
The authors of this report met on 28-30 March 2018 at the New Jersey
Institute of Technology, Newark, New Jersey, for a 3-day workshop
that brought together a group of data providers, expert modelers, and
computer and data scientists, in the solar discipline. Their objective
was to identify challenges in the path towards building an effective
framework to achieve transformative advances in the understanding
and forecasting of the Sun-Earth system from the upper convection
zone of the Sun to the Earth's magnetosphere. The workshop aimed to
develop a research roadmap that targets the scientific challenge
of coupling observations and modeling with emerging data-science
research to extract knowledge from the large volumes of data (observed
and simulated) while stimulating computer science with new research
applications. The desire among the attendees was to promote future
trans-disciplinary collaborations and identify areas of convergence
across disciplines. The workshop combined a set of plenary sessions
featuring invited introductory talks and workshop progress reports,
interleaved with a set of breakout sessions focused on specific topics
of interest. Each breakout group generated short documents, listing
the challenges identified during their discussions in addition to
possible ways of attacking them collectively. These documents were
combined into this report-wherein a list of prioritized activities
have been collated, shared and endorsed.
---------------------------------------------------------
Title: An Early Prediction of the Amplitude of Solar Cycle 25
Authors: Pesnell, W. Dean; Schatten, Kenneth H.
2018SoPh..293..112P Altcode:
A "Solar Dynamo" (SODA) Index prediction of the amplitude of Solar
Cycle 25 is described. The SODA Index combines values of the solar
polar magnetic field and the solar spectral irradiance at 10.7 cm
to create a precursor of future solar activity. The result is an
envelope of solar activity that minimizes the 11-year period of the
sunspot cycle. We show that the variation in time of the SODA Index is
similar to several wavelet transforms of the solar spectral irradiance
at 10.7 cm. Polar field predictions for Solar Cycles 21 - 24 are used
to show the success of the polar field precursor in previous sunspot
cycles. Using the present value of the SODA index, we estimate that the
next cycle's smoothed peak activity will be about 140 ±30 solar flux
units for the 10.7 cm radio flux and a Version 2 sunspot number of 135
±25 . This suggests that Solar Cycle 25 will be comparable to Solar
Cycle 24. The estimated peak is expected to occur near 2025.2 ±1.5
year. Because the current approach uses data prior to solar minimum,
these estimates may improve as the upcoming solar minimum draws closer.
---------------------------------------------------------
Title: Interaction between cool material from Sun-grazing comets
and the low corona
Authors: Jia, Yingdong; Pesnell, William; Liu, Wei; Downs, Cooper;
Bryans, Paul
2018cosp...42E1613J Altcode:
Sun-grazing comets dive into altitudes lower than 1 solar radius from
the chromosphere. Cool materials of temperature lower than 10 ^{3}K
explode from the comet into the 10 ^{6} K corona. These materials
undergone various stages of rapid chemical reactions in scales of
seconds to minutes. Such reactions Structures in such images of
various wavelengths indicate strong variation in ambient conditions
of the corona. We combine three numerical models: low corona model,
particle transportation model, and cometary plasma interaction model
into one framework to model the interaction of Sun-grazing comets in the
low corona. In our framework, cometary vapor are ionized via multiple
channels, and then detained by the coronal magnetic field. In seconds,
these ions are further ionized into their highest charge state, which
is revealed by certain emission lines. Constrained by coronal graphs
and cometary interaction images, we apply our framework to trace back
to the local condition of the ambient corona, and its spatial/time
variation. Our frame work is able to resolve structures of sub-million
meters to tens of million meters. Once trained by multiple stages of
the comet's journey in the low corona, this framework can identify the
fine spatial variations in plasma density and magnetic field intensity,
which may be visible to future close-up observations.
---------------------------------------------------------
Title: Predicting the Sun: Black Swans or Dragon Kings?
Authors: Pesnell, William Dean
2018tess.conf22405P Altcode:
Our goal of predicting the Sun spans timescales from seconds to
centuries and phenomena from flares to convective flows. We are
faced with questions of what extremes to expect when predicting
each phenomenon. Some extremes are obvious: What is the brightest
flare, largest active region or fastest coronal mass ejection we
can expect? Others are less so: What is the largest magnetic field
strength? Or how often should we expect a Grand Minimum, an era of low
to absent solar activity, and what happens to the irradiance of the
Sun during that era? Most phenomena have a robust set of observations
covering a wide range of possibilities that allows statistical methods
to be used. Every so often, an exceptional event is seen, such as
the X45 flare of November 2002 or the geomagnetic storm following
the Carrington Event in September 1859, that sits outside of those
statistics. Longer term examples include predicting sunspot cycles of
unusually large or small amplitude. I will describe Black Swans and
Dragon Kings and how they can be used to understand the predictions
of extreme events in solar physics.
---------------------------------------------------------
Title: The Recalibrated Sunspot Number: What It Is and How Will It
be Updated?
Authors: Clette, Frederic; Pesnell, William Dean; Lefevre, Laure
2018tess.conf30288C Altcode:
Recently, and for the first time since their creation, the definition
of the sunspot number and group number series were revisited. A fully
recalibrated version was officially released in July 2015 by the World
Data Center SILSO (Brussels). Those long-term reference series are
widely used as input data or as a calibration reference by many research
projects in solar physics and space weather. To clarify the nature of
the applied changes, we describe the different corrections applied to
the sunspot and group number series, which affect extended time periods
and can reach up to 40%. While some changes simply involve constant
scale factors, other corrections vary with time or are modulated by
the solar cycle. Depending on the research project and the selected
time interval, this can lead to different responses and biases. For
example, predictions of solar activity based on the sunspot number
should be redone using the new sunspot series, and methods already
used for predicting Solar Cycle 24 will require adaptations before
attempting predictions of the next cycles. In addition, the revised
sunspot series includes standard error estimates, which may help
in deriving more accurate uncertainties for predicted activity
indices. We conclude with the new round of recalibration that is
now undertaken in the framework of a broad multi-team collaboration
articulated around upcoming ISSI workshops. We outline the future
corrections that can still be expected in the future, as part of a
permanent upgrading process and quality control. From now on, future
sunspot-based predictive models should thus be made more adaptable,
and regular updates of such models should become common practice in
order to track periodic upgrades of the sunspot number series, just
like it is done when using other modern solar observational series.
---------------------------------------------------------
Title: Oscillations and Asymmetries in Polar Coronal Holes
Authors: Kirk, Michael S.; Pesnell, William Dean
2018tess.conf30921K Altcode:
Coronal holes are the origin of the fast solar wind and define the
quiescent heliosphere. Polar coronal holes are prevalent during
solar minimum, non-axisymmetric, and are stable. They also offer
an indirect measurement of the polar magnetic flux. Polar holes are
regularly observed capping the northern and southern solar poles in EUV
images of the corona and are understood as the primary source of the
fast solar wind. We make new measurements of polar hole's perimeter
and area in three EUV wavelengths between 1996 and 2017 using five
different space-based imagers: SOHO EIT, STEREO A and B EUVI, PROBA2
SWAP, and SDO AIA. The generated time-series of coronal hole parameters
have significant oscillatory power in them - however this produces a
difficult data problem: multi-band, multi-instrument, heteroscedastic
measurements with periodic signals. To separate the oscillations
associated with physical phenomena from systematic measurement errors,
we employ a generalized Lomb-Scargle periodic analysis. This technique
allows us to simultaneously analyze the physical properties of polar
coronal holes and identify regular periodicities in our data from
other origins.
---------------------------------------------------------
Title: Using the Solar Polar Magnetic Field for Longterm Predictions
of Solar Activity, Solar Cycles 21-25
Authors: Pesnell, W. D.; Schatten, K. H.
2017AGUFMSH13A2473P Altcode:
We briefly review the dynamo and geomagnetic precursor methods of
long-term solar activity forecasting. These methods depend upon the
most basic aspect of dynamo theory to predict future activity, future
magnetic field arises directly from the amplification of pre-existing
magnetic field. We then generalize the dynamo technique, allowing the
method to be used at any phase of the solar cycle, to the Solar Dynamo
Amplitude (SODA) index. This index is sensitive to the magnetic flux
trapped within the Sun's convection zone but insensitive to the phase
of the solar cycle. Since magnetic fields inside the Sun can become
buoyant, one may think of the acronym SODA as describing the amount of
buoyant flux. We will show how effective the SODA Index has been in
predicting Solar Cycles 23 and 24, and present a unified picture of
earlier estimates of the polar magnetic configuration in Solar Cycle
21 and 22. Using the present value of the SODA index, we estimate
that the next cycle's smoothed peak activity will be about 125 ± 30
solar flux units for the 10.7 cm radio flux and a sunspot number of 70
± 25. This suggests that Solar Cycle 25 will be comparable to Solar
Cycle 24. Since the current approach uses data prior to solar minimum,
these estimates may improve when the upcoming solar minimum is reached.
---------------------------------------------------------
Title: Digging into the corona: A modeling framework trained with
Sun-grazing comet observations
Authors: Jia, Y. D.; Pesnell, W. D.; Bryans, P.; Downs, C.; Liu, W.;
Schwartz, S. J.
2017AGUFMSH11B2437J Altcode:
Images of comets diving into the low corona have been captured a few
times in the past decade. Structures visible at various wavelengths
during these encounters indicate a strong variation of the ambient
conditions of the corona. We combine three numerical models: a global
coronal model, a particle transportation model, and a cometary plasma
interaction model into one framework to model the interaction of such
Sun-grazing comets with plasma in the low corona. In our framework,
cometary vapors are ionized via multiple channels and then captured
by the coronal magnetic field. In seconds, these ions are further
ionized into their highest charge state, which is revealed by certain
coronal emission lines. Constrained by observations, we apply our
framework to trace back to the local conditions of the ambient corona,
and their spatial/time variation over a broad range of scales. Once
trained by multiple stages of the comet's journey in the low corona,
we illustrate how this framework can leverage these unique observations
to probe the structure of the solar corona and solar wind.
---------------------------------------------------------
Title: Acoustic Oscillation Properties of Active Region 12193
Authors: Monsue, Teresa; Pesnell, William D.; Hill, Frank
2017SPD....4810904M Altcode:
Solar flares are dynamic objects occurring randomly and yet unannounced
in nature. In order to find an efficient detection method, we require
a greater breadth of knowledge of the system. One path to such a
method is to observe the solar atmosphere in a region around a flare
in different wavelengths of light and acoustic frequency bands. This
provides information from different altitudes in the solar atmosphere
and allows us to study the temporal evolution of each altitude through
the flaring event. A more complete understanding of the time evolution
may lead to yet undiscovered precursors of the flare. In this project,
we study Active Region 12192 using acoustic observations near an
X3 flare occurring on October 24, 2014 at 21:41UT. Our wavelet
analysis utilizes time series data to create Fourier power spectra
of individual pixels spatially resolved around the flare region, to
study the frequency bands. In order to study the power distribution
in regions around the flare and to search for any correlation we
apply several methods. One method we partition sub-regions in our
main flaring region and take a survey of the oscillations for each
frequency band within power maps. Another method we average the FFT
to take measurements within the p-modes (2-4 mHz) and chromospheric
(4-6 mHz) frequencies. The application of these methods should be able
to get us closer to tracking waveforms within power maps.
---------------------------------------------------------
Title: The Complexity of Solar and Geomagnetic Indices
Authors: Pesnell, W. Dean
2017SPD....48.0703P Altcode:
How far in advance can the sunspot number be predicted with any degree
of confidence? Solar cycle predictions are needed to plan long-term
space missions. Fleets of satellites circle the Earth collecting
science data, protecting astronauts, and relaying information. All
of these satellites are sensitive at some level to solar cycle
effects. Statistical and timeseries analyses of the sunspot number
are often used to predict solar activity. These methods have not
been completely successful as the solar dynamo changes over time
and one cycle's sunspots are not a faithful predictor of the next
cycle's activity. In some ways, using these techniques is similar to
asking whether the stock market can be predicted. It has been shown
that the Dow Jones Industrial Average (DJIA) can be more accurately
predicted during periods when it obeys certain statistical properties
than at other times. The Hurst exponent is one such way to partition
the data. Another measure of the complexity of a timeseries is the
fractal dimension. We can use these measures of complexity to compare
the sunspot number with other solar and geomagnetic indices. Our
concentration is on how trends are removed by the various techniques,
either internally or externally. Comparisons of the statistical
properties of the various solar indices may guide us in understanding
how the dynamo manifests in the various indices and the Sun.
---------------------------------------------------------
Title: The Formation and Maintenance of the Dominant Southern Polar
Crown Cavity of Cycle 24
Authors: Karna, N.; Zhang, J.; Pesnell, W. D.
2017ApJ...835..135K Altcode:
In this article, we report a study of the longest-lived polar crown
cavity of Solar Cycle 24, using an observation from 2013, and propose
a physical mechanism to explain its sustained existence. We used high
temporal and spatial resolution observations from the Atmospheric
Imaging Assembly (AIA) and the Helioseismic Magnetic Imager (HMI)
instruments on board the Solar Dynamics Observatory (SDO) to explore the
structure and evolution of the cavity. Although it existed for more than
a year, we examined the circumpolar cavity in great detail from 2013
March 21 to 2013 October 31. Our study reinforces the existing theory
of formation of polar crown filaments that involves two basic processes
to form any polar crown cavity as well as the long-lived cavity that
we studied here. First, the underlying polarity inversion line (PIL)
of the circumpolar cavity is formed between (1) the trailing part of
dozens of decayed active regions distributed in different longitudes and
(2) the unipolar magnetic field in the polar coronal hole. Second, the
long life of the cavity is sustained by the continuing flux cancellation
along the PIL. The flux is persistently transported toward the polar
region through surface meridional flow and diffusion. The continuing
flux cancellation leads to the shrinking of the polar coronal hole.
---------------------------------------------------------
Title: Identifying Long-term Oscillations in Polar Coronal Holes
Authors: Kirk, M. S.; Pesnell, W. D.; Young, C. A.
2016AGUFMSH11A2223K Altcode:
Polar coronal holes offer an indirect measurement of the polar
magnetic flux, which is a significant component to our understanding
of the solar cycle. Polar holes are prevalent during solar minimum,
non-axisymmetric, and are stable. They are regularly observed capping
the northern and southern solar poles in EUV images of the corona and
are understood as the primary source of the fast solar wind. We make
measurements of polar hole area with three EUV wavelengths from 1996
through 2016 using five different space-based imagers: SOHO EIT, STEREO
A and B EUVI, PROBA2 SWAP, and SDO AIA. Each time series of coronal
hole parameters have significant oscillatory power in them, however
this produces a difficult data problem: multi-band, multi-instrument,
heteroscedastic measurements with periodic signals. To separate the
oscillations associated with systematic measurement errors from physical
phenomena, we employ a Tikhonov regularization scheme to generalize the
conventional Lomb-Scargle method to a multi-band periodic analysis. This
technique allows us to simultaneously analyze the physical properties
of polar coronal holes and identify regular periodicities in our data
from other origins.
---------------------------------------------------------
Title: Comparing Time-Distance Results within a Coronal Hole to the
Quiet Sun
Authors: Hess Webber, Shea A.; Pesnell, W. Dean; Duvall, Thomas, Jr.;
Birch, Aaron; Cameron, Robert
2016usc..confE...1H Altcode:
Time-distance helioseismology studies perturbations in solar
wave modes. We use these techniques with SDO/HMI time-distance
velocity-tracked dopplergram data to investigate differences between f
-mode wave propagation within a coronal hole feature and without. We
use symmetry arguments to enhance the signal-to-noise ratio of the
cross-correlation results. We then look for phase and amplitude
discrepancies between the coronal hole and quiet sun by comparing
statistically significant differences between the regions.
---------------------------------------------------------
Title: Space Oddities: The Search For Ephemeral Coronal Holes
Authors: O'Connor, Rachel E.; Pesnell, W. Dean; Kirk, Michael S.;
Karna, Nishu
2016usc..confE...9O Altcode:
Ephemeral coronal holes are short-lived, volatile counterparts
to equatorial coronal holes. Very little is known about their
characteristics and behavior aside from their definition: open,
unipolar magnetic field lines resulting in darkened regions of the
corona. The first exemplar of this phenomenon was observed by NASA's
Solar Dynamics Observatory (SDO) on October 26, 2010, which spurred
our search for other occurrences in order to understand the frequency
and evolution of these phenomena. To accomplish this, we visually
evaluated SDO 211 Å images on a 12-hour cadence between June 2010
and June 2016. Each compact and isolated dim region we encountered was
flagged as a potential ephemeral coronal hole for further analysis. This
preliminary effort resulted in 149 candidate holes. For further analysis
of their characteristics, we applied a strict definition criterion of an
ephemeral coronal hole. This criterion was a set of four factors that
were created in order to ensure events being observed were isolated,
individual events- the candidates had to be dark relative to the
surrounding material, not influenced by a nearby eruption, not obviously
connected to other coronal hole structures, and their lifetime had to
occur completely within the disk crossing. This criterion was designed
so that events could be completely analyzed, from beginning to end, to
better understand the origins. Application of this criterion eliminated
all candidates but 5 of the original 149. True ephemeral coronal holes
are rare occurrences, appearing only five times in six years. Future
research in this area is needed to both locate additional events and
study the underlying driving forces behind these rare phenomena.
---------------------------------------------------------
Title: Estimating and Separating Noise from AIA Images
Authors: Kirk, Michael S.; Ireland, Jack; Young, C. Alex; Pesnell,
W. Dean
2016usc..confE..26K Altcode:
All digital images are corrupted by noise and SDO AIA is no
different. In most solar imaging, we have the luxury of high photon
counts and low background contamination, which when combined with
carful calibration, minimize much of the impact noise has on the
measurement. Outside high-intensity regions, such as in coronal holes,
the noise component can become significant and complicate feature
recognition and segmentation. We create a practical estimate of noise
in the high-resolution AIA images across the detector CCD in all seven
EUV wavelengths. A mixture of Poisson and Gaussian noise is well suited
in the digital imaging environment due to the statistical distributions
of photons and the characteristics of the CCD. Using state-of-the-art
noise estimation techniques, the publicly available solar images, and
coronal loop simulations; we construct a maximum-a-posteriori assessment
of the error in these images. The estimation and mitigation of noise
not only provides a clearer view of large-scale solar structure in
the solar corona, but also provides physical constraints on fleeting
EUV features observed with AIA.
---------------------------------------------------------
Title: On the Formation Mechanism of A Long-lived Polar Crown Cavity
Authors: Karna, Nishu; Pesnell, William D.; Zhang, Jie
2016usc..confE..22K Altcode:
We report the study of the longest-lived polar crown cavity of Solar
Cycle 24th observed in the year 2013 and propose a physical mechanism
to explain the sustained existence. We used high temporal and spatial
resolution observations from the Atmospheric Imaging Assembly (AIA)
and the Helioseismic Magnetic Imager (HMI) instruments on board
the Solar Dynamics Observatory (SDO) to explore the structure and
evolution. We examined the circumpolar cavity in great detail from
March 21, 2013, till October 31, 2013, while it existed for more
than one year. Our study suggests two necessary conditions to form a
long stable circumpolar cavity or any polar crown cavity. First, the
underlying polarity inversion line (PIL) of the circumpolar cavity is
formed between the trailing part of dozens of decayed active regions
distributed in different longitudes and the unipolar magnetic field
in the polar coronal hole. Second, the long life of the cavity is
sustained by the continuing flux cancellation along the polarity
inversion line. The flux is persistently transported toward the polar
region through surface meridional flow and diffusion, which also leads
to the shrinking of the polar coronal hole. Comparing with the existing
theory of the formation of polarity inversion lines, we introduce a
new category named as "Diffused trailing flux and polar coronal hole
interaction region" to explain the polar crown cavity. The existence
of such region also helps explain the process of polar reversal,
which provides insight into the solar cycle.
---------------------------------------------------------
Title: The Solar Dynamics Observatory, Six Years of Science
Authors: Pesnell, W. Dean
2016usc..confE..57P Altcode:
The Solar Dynamics Observatory has been producing science and science
data since May 2010. I will describe some highlights of SDO results,
including filament eruptions, flares, and comets. The status of the
observatory hardware will also be discussed. The future of SDO will
be a series of extended missions, each lasting two years. Our next
extended mission proposal will be due early next year and I will
discuss part of that process.
---------------------------------------------------------
Title: SDO 2016: Unraveling the Suns Complexity
Authors: Pesnell, W. Dean; Thompson, Barbara
2016usc..conf.....P Altcode:
Living With a Star Solar Dynamics Observatory research connects to many
areas of solar physics and many other solar missions. Tracing these
connections allows us to build a more accurate understanding of the Sun
and solar activity. The workshop will focus on our improved knowledge
and understanding of the Suns magnetic field that have come from the
SDO data, and what will come in the future. Scientific sessions will
feature a broad spectrum of science topics fundamental to SDO science
investigations: Atmospheric Imaging Assembly (AIA), EUV Variability
Experiment (EVE), and Helioseismic and Magnetic Imager (HMI), as
well as the overlap between SDO and other scientific missions and
activities. We invite you to celebrate the breadth of research topics
enabled by SDO during its Prime Mission and the First Extended Mission.
---------------------------------------------------------
Title: Solar Acoustic Oscillations Observations in SDO AIA and HMI
around AR 12192
Authors: Monsue, Teresa; Pesnell, W. Dean; Hill, Frank
2016usc..confE..89M Altcode:
Solar flares are dynamic objects occurring randomly and yet unannounced
in nature. In order to find an efficient detection method, we require a
greater breadth of knowledge of the system. One such mode is to observe
flares in different frequency bands at different depths and study
their temporal evolution through the flaring event. In this project we
obtain acoustic observations of an X3 flare occurring on October 24,
2014 at 21:41UT. We employ the study of active regions, near sunspots,
in which flaring activity is taking place. Our wavelet analysis utilizes
time series data to create Fourier power spectra of individual pixels
spatially resolved around the flare region, to study the frequency
bands. In order to study the power distribution in regions around the
flare and compare the measurements to magnetograms to search for any
correlation, we combine observations of oscillations in three SDO AIA
wavelengths: the 1600Å, 1700 Å and 304Å, and combine them with HMI
data. We then study how the frequency distribution evolves temporally
by constructing a Power Map Movie (PMM) of the regions. From these
PMMs we can partition sub-regions in our main flaring region and take
a survey of the oscillations for each frequency band.
---------------------------------------------------------
Title: Watching the Sun from space
Authors: Pesnell, W. Dean
2016AsJPh..25..233P Altcode:
Space-based solar observatories have made fundamental discoveries
about the lifecycle of the solar magnetic field and how that field
affects the solar system. Observing the Sun from space provides
access to all wavelengths of light and eliminates the smearing
of atmospheric seeing. Being in space means the emissions from
the highly-ionized material that are the natural emissions of the
corona can be measured. Continuous observations of the Sun can
be made from a single satellite in certain orbits. This leads to
unexpected discoveries, such as orbiting coronagraphs showing that
sun grazing comets are the most common class of observed comets. Or
when the coronal holes discovered with the solar X-ray telescopes on
Skylab explained long-noticed correlations in particle fluxes from the
Sun with solar longitudes. Space-based coronagraphs and heliospheric
imagers are able to track coronal mass ejections from when they leave
the Sun until they hit the Earth or another planet. In a more practical
point, as humans have become more entwined in the use of technology,
the magnetic field of the Sun has become more intrusive. Energetic
particles and high-energy photons from solar fares can compromise humans
and electronics in space. As a coronal mass ejection passes by and
interacts with the Earth's magnetosphere, it generates large currents
at the Earth's surface that can disrupt power distribution systems. The
measurements of Sun made possible by being in space will be described,
along with some highlights of the observatories that make them.
---------------------------------------------------------
Title: On the Formation Mechanism of A Long-lasting Polar Crown Cavity
Authors: Karna, Nishu; Pesnell, William Dean; Zhang, Jie
2016shin.confE.140K Altcode:
We report the observation of the longest-lived polar crown cavity
of Solar Cycle 24th observed in the year 2013 and propose a physical
mechanism to explain the sustained existence. We used high temporal and
spatial resolution observations from the Atmospheric Imaging Assembly
(AIA) and the Helioseismic Magnetic Imager (HMI) instruments on board
the Solar Dynamics Observatory (SDO) to explore the structure and
evolution. We examined the circumpolar cavity in great detail from
March 21, 2013, till October 31, 2013., while it existed for more
than one year. Our study suggests two necessary conditions to form a
long stable circumpolar cavity or any polar crown cavity. First, the
underlying polarity inversion line (PIL) of the circumpolar cavity is
formed between the trailing part of dozens of decayed active regions
distributed in different longitudes and the unipolar magnetic field
in the polar coronal hole. Second, the long lasting of the cavity
is sustained by the continuing flux cancellation along the polarity
inversion line. The flux is persistently transported toward the polar
region through surface meridional flow and diffusion, which also leads
to the shrinking of the polar coronal hole. Comparing with the existing
theory of the formation of polarity inversion lines, we introduce
a new category named as "Diffused bipole and polar coronal hole
interaction region" to explain the polar crown cavity. The existence
of such region also helps explain the process of polar reversal,
which provides insight into the solar cycle.
---------------------------------------------------------
Title: A Comprehensive study of Cavities on the Sun: Structure,
Formation, and Evolution
Authors: Karna, Nishu; Zhang, Jie; Pesnell, William D.
2016SPD....4710302K Altcode:
Coronal cavities are large-scale structures in the Sun's corona that
are closely related with the long-term evolution of the magnetic field
in the photosphere as well as associated with the energetic solar
activity such as prominence eruptions and coronal mass ejections. They
are observed as circular or elliptical-shaped relatively low-density
dark regions above the solar limb in EUV, X-ray, and white-light
coronal images. We used SDO/AIA limb synoptic maps, constructed from
annuli above the solar limb, to systematically identify cavities. We
observed 429 coronal prominence cavities between May 20, 2010 and Feb
1, 2015. We examined correlations between height, width, and length of
the cavities. Based on the fitting of the shape of the cross section,
we classified cavities in three types: prolate (38%), oblate (27%)
and circular (35%). We found that the cavities of all shapes are
common in shorter length while circular and oblate cavities are more
common in the longer length. In general, we found that the overall 3-D
topology of long stable cavities can be characterized as a long tube
with an elliptical cross-section. Next, we investigated the pattern of
cavity location and found that cavity systematically drifts towards
the pole. We found that cavities form a belt by making a plot using
SDO/HMI surface magnetogram similar to classical buttery diagram
of sunspots, we call that the cavity belt. Our analysis showed that
the cavity belts migrated towards higher latitude with time and the
cavity belts disappeared after the polar magnetic field reversal. This
result shows that cavity evolution provides new insight into the
solar cycle. Moreover, we studied the underlying magnetic field of
a circumpolar crown cavity (Mar 21, 2013- Oct 25, 2013) that was
observed for several Carrington Rotations. Our results showed that
the underlying polarity inversion line of cavities is formed between
the trailing part of decayed active regions and the unipolar magnetic
field in the pole. The long life of cavities was due to continuous
and sustained adding of trailing flux from multiple active regions as
their remnants diffused toward the pole.
---------------------------------------------------------
Title: Statistical Differences in Time-Distance Helioseismology
Results
Authors: Hess Webber, Shea A.; Pesnell, William D.; Duvall, Thomas;
Cameron, Robert; Birch, A. C.
2016SPD....4720301H Altcode:
Time-distance helioseismology studies phase correlations in solar wave
modes. We use these techniques to investigate the phase differences in
f-mode wave propagation within a coronal hole feature and without. We
isolate the coronal hole boundary location using edge detection
techniques on SDO AIA data. We then use this location information to
inform the analysis of the corresponding HMI time-distance velocity
tracked data product, provided by Stanford's JSOC archive. We look
at time-distance results inside the coronal hole, outside the coronal
hole, the coronal hole data as a whole, and an independent quiet sun
region. We use Student's t-Test to evaluate the significance of the
differences between the various regions.
---------------------------------------------------------
Title: On the Absence of EUV Emission from Comet C/2012 S1 (ISON)
Authors: Bryans, Paul; Pesnell, W. Dean
2016ApJ...822...77B Altcode:
When the sungrazing comet C/2012 S1 (ISON) made its perihelion passage
within two solar radii of the Sun’s surface, it was expected to be
a bright emitter at extreme ultraviolet (EUV) wavelengths. However,
despite solar EUV telescopes repointing to track the orbit of the comet,
no emission was detected. This “null result” is interesting in
its own right, offering the possibility of placing limits on the size
and composition of the nucleus. We explain the lack of detection by
considering the properties of the comet and the solar atmosphere that
determine the intensity of EUV emission from sungrazing comets. By
comparing these properties with those of sungrazing comet C/2011 W3
(Lovejoy), which did emit in the EUV, we conclude that the primary
factor resulting in non-detectable EUV emission from C/2012 S1 (ISON)
was an insufficiently large nucleus. We conclude that the radius
of C/2012 S1 (ISON) was at least a factor of four less than that of
C/2011 W3 (Lovejoy). This is consistent with white-light observations
in the days before perihelion that suggested the comet was dramatically
reducing in size on approach.
---------------------------------------------------------
Title: The Unusual Event of October 26, 2010: An "Almost" Coronal Hole
Authors: Pesnell, W. D.; O'Connor, R.
2015AGUFMSH52A..04P Altcode:
Coronal holes are dark regions in the solar corona that develop where
open magnetic field lines are found. They come in many different shapes,
sizes, and forms. Ephemeral coronal holes are a short-lived form of
the phenomena, sometimes lasting only a few rotations. On October 26,
2010, NASA's Solar Dynamics Observatory (SDO) observed what was first
thought to be an unusual ephemeral coronal hole, appearing for less
than 48 hours and surrounded by a filament. We present an analysis of
the area and magnetic signatures of the filament and suspected hole,
as well as solar wind data. Multiple EUV channels from SDO/AIA are
combined with magnetograms from SDO/HMI and the GONG network to quantify
the evolution of this event. Another ephemeral coronal hole from June
2015 is used a comparison. Results from this analysis show that the 2010
event was not an ephemeral coronal hole, but rather a solar 'hiccup' -
the attempted, and failed, formation of a small coronal hole. While the
reasons behind the failure remain speculative, these findings show that
a lot of potential lies in future research of this event - in observing
the interactions between the hole and the filament, and our continued
understanding of the formation and characteristics of coronal holes.
---------------------------------------------------------
Title: The Solar Non-activity Cycle of Polar Coronal Holes
Authors: Kirk, M. S.; Pesnell, W. D.; Young, C. A.
2015AGUFMSH33D..07K Altcode:
After the unusually extended minimum in 2008 and 2009, solar cycle 24
continues to be an exceptionally weak cycle both in sunspot number
and number of large magnetic storms. Coronal holes offer a direct
measurement of the non-activity solar cycle, a missing link in our
understanding of solar cycle progression. They are prevalent during
solar minimum, non-axisymmetric, and are stable. Polar coronal holes
are regularly observed capping the northern and southern solar poles
in EUV images of the corona and are understood as the primary source
of the fast solar wind. We make measurements of these features from
1996 through 2015 using four different NASA imagers: SOHO EIT, STEREO
A and B EUVI, and SDO AIA. A measurement of the axial symmetry of
the polar holes is seen to have clear solar cycle dependence. Polar
coronal holes are aligned with the solar rotation axis during minimum
and have a maximum asymmetry between holes of about 14 degrees in the
declining phase of the current solar cycle.
---------------------------------------------------------
Title: A comprehensive study of cavities on the Sun: Structures
and Evolution
Authors: Karna, N.; Pesnell, W. D.; Zhang, J.
2015AGUFMSH54B..03K Altcode:
Coronal cavities are often observed as circular or elliptical-shaped,
darkned regions above the solar limb in EUV coronal images. They are
believed to be regions of lower density relative to the surrounding
corona. The cavity surrounds the prominence: prior to the eruption and
as an aspect of CMEs. We used SDO/AIA limb synoptic maps, constructed
from annuli above the solar limb; best show cavities in the 211Å,
193Å and 171Å passbands. The prominence associated with each cavity
is best seen in the 304Å synoptic maps. We observed 429 cavities
between May 2010 - Feb 2015. We examined correlations between each
cavity's height, width and length. Our findings showed that around 38%
of cavities were prolate, 27% oblate and 35% circular in shape. The
lengths of the cavities ranged from 0.06-2.9 R¤. When a cavity is
longer than 1.5 R¤ it has a narrower height range (0.1-0.3 R¤),
whereas when the cavity was shorter than 1.5 R¤, it had a wider height
range (0.07-0.5 R¤). We find that the overall 3-D topology of the long
stable cavities can be characterized as a long tube with an elliptical
cross section. We also noticed that the circular and oblate cavities are
longer in length than prolate cavities. We also studied the physical
mechanisms behind the cavity drift towards the pole and found it to
be tied to the meridional flow. Finally, by observing the evolution
cavity regions using SDO/HMI surface magnetic field observations, we
found cavity belt formed near the polar coronal hole boundary. Results
showed that the cavity belt migrated towards higher latitude with
time and the cavity belt disappeared after the polar magnetic field
reversal. This result shows that cavity evolution provides new insight
into the solar cycle. Moreover, we selected 30 random cavities from
our catalog and studied their morphology, thermal properties, linear
polarization signatures, precursors of eruption, and underlying magnetic
field and tried to interpret the shapes and stability of the cavities.
---------------------------------------------------------
Title: Study of the 3D Geometric Structure and Temperature of a
Coronal Cavity Using the Limb Synoptic Map Method
Authors: Karna, N.; Zhang, J.; Pesnell, W. Dean; Hess Webber, S. A.
2015ApJ...810..124K Altcode:
We present the three-dimensional geometric structure and thermal
properties of a coronal cavity deduced from limb synoptic maps. The
observations are extreme ultraviolet images from the Atmospheric Imager
Assembly (AIA) and magnetic images from the Helioseismic Magnetic
Imager instruments on board the Solar Dynamics Observatory. We describe
a limb synoptic-map method used to effectively identify and measure
cavities from annuli of radiance above the solar limb. We find that
cavities are best seen in the 211, 193, and 171 Å passbands. The
prominence associated with each cavity is best seen in the 304 Å
synoptic maps. We also estimate the thermal properties of the cavity and
surrounding plasma by combining the AIA radiances with a differential
emission measure analysis. This paper focuses on one long cavity
from a catalog of coronal cavities that we are developing. Cavities
in this catalog are designated by a coded name using the Carrington
Rotation number and position. Cavity C211347177N was observed during
Carrington Rotation 2113 at the northwestern limb of the solar disk
with an average latitude of 47° N and a central longitude of 177°. We
showed the following. (1) The cavity is a long tube with an elliptical
cross-section with ratios of the length to width and the length to
height of 11:1 and 7:1, respectively. (2) The cavity is about 1360
Mm long, or 170° in longitude. (3) It is tilted in latitude. (4)
And it is slightly hotter than its surroundings.
---------------------------------------------------------
Title: Appearances and Statistics of Coronal Cavities During the
Ascending Phase of Solar Cycle 24
Authors: Karna, N.; Pesnell, W. D.; Zhang, J.
2015ApJ...810..123K Altcode:
We present a survey of 429 coronal prominence cavities found between
2010 May and 2015 February using the Solar Dynamics Observatory
(SDO)/Atmospheric Imaging Assembly limb synoptic maps. We examined
correlations between each cavity’s height, width, and length. Our
findings showed that around 38% of the cavities were prolate, 27%
oblate, and 35% circular in shape. The lengths of the cavities ranged
from 0.06 to 2.9 {R}<SUB>⊙ </SUB>. When a cavity is longer than
1.5 {R}<SUB>⊙ </SUB>, it has a narrower height range (0.1-0.3
{R}<SUB>⊙ </SUB>), whereas when the cavity was shorter than 1.5
{R}<SUB>⊙ </SUB>, it had a wider height range (0.07-0.5 {R}<SUB>⊙
</SUB>). We find that the overall three-dimensional topology of the
long, stable cavities can be characterized as a long tube with an
elliptical cross section. We also noted that the circular and oblate
cavities are longer in length than the prolate cavities. We also studied
the physical mechanisms behind the cavity drift toward the pole and
found it to be tied to the meridional flow. Finally, by observing the
evolution of the cavity regions using SDO/Helioseismic Magnetic Imager
(HMI) surface magnetic field observations, we found that the cavities
formed a belt near the polar coronal hole boundary; we call this the
cavity belt. Our results showed that the cavity belt migrated toward
higher latitude over time and the cavity belt disappeared after the
polar magnetic field reversal. This result shows that cavity evolution
provides new insight into the solar cycle.
---------------------------------------------------------
Title: Appearances and Statistics of Coronal Cavities During the
Ascending Phase of Solar Cycle 24
Authors: Karna, Nishu; Pesnell, William Dean; Zhang, Jie
2015shin.confE..72K Altcode:
We present a survey of 429 coronal prominence cavities found between May
2010-Feb 2015 using SDO/AIA limb synoptic maps. We examined correlations
between each cavity's height, width and length. Our findings showed
that around 38% of cavities were prolate, 27% oblate and 35% circular
in shape. The lengths of the cavities ranged from 0.06 - 2.9 R⊙
When a cavity is longer than 1.5 R⊙, it has a narrower height range
(0.1 - 0.3 R⊙), whereas when the cavity was shorter than 1.5 R⊙,
it had a wider height range (0.07 - 0.5 R). We find that the overall 3-D
topology of the long stable cavities can be characterized as a long tube
with an elliptical cross section. We also noticed that the circular
and oblate cavities are longer in length than prolate cavities. We
also studied the physical mechanisms behind the cavity drift towards
the pole and found it to be tied to the meridional flow. Finally, by
observing the evolution cavity regions using SDO/HMI surface magnetic
field observations, we found that cavities formed a belt near the
polar coronal hole boundary; we call this the cavity belt. Results
showed that the cavity belt migrated towards higher latitude with
time and the cavity belt disappeared after the polar magnetic field
reversal. This result shows that cavity evolution provides new insight
into the solar cycle.
---------------------------------------------------------
Title: Connecting the Evolution of Polar Coronal Holes to the
Heliosphere
Authors: Kirk, Michael S.; Pesnell, W. Dean; Hess-Webber, Shea
2015shin.confE.123K Altcode:
Polar coronal holes are regularly observed capping the northern and
southern solar poles in EUV images of the corona and are understood
as the primary source of the fast solar wind. Polar holes are also
the longest-lived solar magnetic features and observed to have strong
solar cycle dependence - becoming more stable and prominent in solar
minimum and disappearing at solar maximum. We make measurements of these
features from 1996 through 2015 using four different NASA imagers: SOHO
EIT, STEREO A and B EUVI, and SDO AIA. This dataset reveals several
long-term trends in the corona. A measurement of the axial symmetry
of the polar holes is seen to have clear solar cycle dependence. Polar
coronal holes are aligned with the solar rotation axis during minimum
and have a maximum off-axial perturbation of about 8 degrees in the
declining phase of the solar cycle. With nearly 20 years of coronal
hole measurements, we are able correlate the evolution of the polar
holes to complementary measurements of the solar wind.
---------------------------------------------------------
Title: Solar Cycle 24 up to Now: Flying Over Peaks and Through Streams
Authors: Pesnell, W. Dean
2015TESS....130804P Altcode:
Solar Cycle 24 has been a below-average sunspot cycle. There were
peaks in the daily and monthly-averaged sunspot number in the Northern
hemisphere in 2011 and in the Southern hemisphere in 2014. Now that
sunspot activity appears to be on the decline, another part of the
solar cycle becomes important. Energetic events from high-speed streams
flowing from the Sun can produce crippling radiation storms in the
magnetosphere. Predicting those events that will affect our assets in
space requires a different kind of solar prediction and some idea of how
the radiation will propagate through the solar system. With the rapid
increase in solar data and capability of numerical models of the solar
convection zone we are developing the ability to forecast the level of
the next solar cycle. But no prediction based only on sunspot number
will be usable for predicting the variation of the decline of a sunspot
cycle. I will describe the status of Solar Cycle 24, our need for solar
activity predictions at all phases of the solar cycle, and anticipate
how those predictions could be made more accurate in the future.
---------------------------------------------------------
Title: Trends Of The Void: Solar Cycles Observed Through Polar
Coronal Holes
Authors: Kirk, Michael S.; Hess Webber, Shea; Pesnell, W. Dean
2015TESS....130802K Altcode:
Coronal holes are defined by their open magnetic field configuration
and lack of emitting plasma. Holes that cap the northern and southern
solar poles are the longest-lived features observed on the Sun -
persisting for nearly an entire solar cycle. Polar holes disappear
briefly at solar maximum for about a year before returning. The size
and evolution of the polar holes are also strongly anti-correlated
with the solar activity cycle. Their longevity combined with this
solar activity relationship makes polar coronal holes an ideal proxy
for measuring the long-term evolution of the solar magnetic field. We
use a perimeter tracking technique to measure the size and location of
the polar coronal holes for 19 years starting in 1996. Utilizing the
SOHO EIT archive and current SDO AIA images, we present a comprehensive
look at how polar coronal holes evolve and what they can tell us about
our current and unusual solar cycle.
---------------------------------------------------------
Title: Statistical Studies of Coronal Cavities Since the Launch of SDO
Authors: Karna, Nishu; Zhang, Jie; Pesnell, W. Dean
2015TESS....140905K Altcode:
We present a survey of 409 coronal prominence cavities found between
May 2010- Sep 2014 using SDO/AIA limb synoptic maps. We examined
correlations between cavity’s height, width and length. Our finding
showed that around 50% of cavities were taller than wider, 40% wider and
10% circular in shape. The length of the cavity ranged from 0.09-2.9
R⊙. When the cavity length is greater than 1.5 R⊙, cavity had a
narrow height range (0.1-0.3 R⊙), whereas when the cavity length was
smaller than 1.5 R⊙, cavity had wider height range (0.07-0.5 R⊙). We
find that the overall 3-D topology of the long stable cavities can
be characterized as a long tube with an elliptical cross section. We
also studied the physical mechanisms behind the cavity drift towards
the pole and found it to be tied to the polar reversal. Finally, by
observing the evolution of the cavity region using SDO/HMI surface
magnetic field observations, we found that cavities formed a belt
between the polar coronal hole boundary and the active region belt; we
call this new belt the cavity belt. Results showed that the cavity belt
migrated towards higher and higher latitude with time and the cavity
belt disappeared after the polar magnetic field reversal. This result
shows that cavity evolution provides another dimension of knowledge
of studying the solar cycle.
---------------------------------------------------------
Title: Solar Dynamics Observatory (SDO)
Authors: Pesnell, W. Dean
2015hchp.book..179P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Pushing the Envelope of Extreme Space Weather
Authors: Pesnell, W. D.
2014AGUFMSH21C4129P Altcode:
Extreme Space Weather events are large solar flares or geomagnetic
storms, which can cost billions of dollars to recover from. We have few
examples of such events; the Carrington Event (the solar superstorm) is
one of the few that had superlatives in three categories: size of solar
flare, drop in Dst, and amplitude of aa. Kepler observations show that
stars similar to the Sun can have flares releasing millions of times
more energy than an X-class flare. These flares and the accompanying
coronal mass ejections could strongly affect the atmosphere surrounding
a planet. What level of solar activity would be necessary to strongly
affect the atmosphere of the Earth? Can we map out the envelope
of space weather along the evolution of the Sun? What would space
weather look like if the Sun stopped producing a magnetic field? To
what extreme should Space Weather go? These are the extremes of Space
Weather explored in this talk.
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Title: Areas of Polar Coronal Holes from 1996 Through 2010
Authors: Hess Webber, S. A.; Karna, N.; Pesnell, W. D.; Kirk, M. S.
2014SoPh..289.4047H Altcode: 2014SoPh..tmp..103H
Polar coronal holes (PCHs) trace the magnetic variability of the
Sun throughout the solar cycle. Their size and evolution have
been studied as proxies for the global magnetic field. We present
measurements of the PCH areas from 1996 through 2010, derived from an
updated perimeter-tracing method and two synoptic-map methods. The
perimeter-tracing method detects PCH boundaries along the solar
limb, using full-disk images from the SOlar and Heliospheric
Observatory/Extreme ultraviolet Imaging Telescope (SOHO/EIT). One
synoptic-map method uses the line-of-sight magnetic field from the
SOHO/Michelson Doppler Imager (MDI) to determine the unipolarity
boundaries near the poles. The other method applies thresholding
techniques to synoptic maps created from EUV image data from EIT. The
results from all three methods suggest that the solar maxima and
minima of the two hemispheres are out of phase. The maximum PCH area,
averaged over the methods in each hemisphere, is approximately 6 %
during both solar minima spanned by the data (between Solar Cycles
22/23 and 23/24). The northern PCH area began a declining trend in
2010, suggesting a downturn toward the maximum of Solar Cycle 24 in
that hemisphere, while the southern hole remained large throughout 2010.
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Title: Evolving Solar Activity and Its Influence on Space and Earth
Authors: Pesnell, W. Dean; Thompson, Barbara
2014esai.conf.....P Altcode:
The 2014 Living with a Star (LWS) Science Meeting will focus on
advancing the understanding of the integral system coupling the Sun
to the Earth. An important part of this meeting is the inclusion of
the Hinode-8 and IRIS-2 meetings with complementary objectives towards
improved understanding of the evolving solar activity.
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Title: Deciphering Solar Magnetic Activity. I. On the Relationship
between the Sunspot Cycle and the Evolution of Small Magnetic Features
Authors: McIntosh, Scott W.; Wang, Xin; Leamon, Robert J.; Davey,
Alisdair R.; Howe, Rachel; Krista, Larisza D.; Malanushenko, Anna V.;
Markel, Robert S.; Cirtain, Jonathan W.; Gurman, Joseph B.; Pesnell,
William D.; Thompson, Michael J.
2014ApJ...792...12M Altcode: 2014arXiv1403.3071M
Sunspots are a canonical marker of the Sun's internal magnetic
field which flips polarity every ~22 yr. The principal variation of
sunspots, an ~11 yr variation, modulates the amount of the magnetic
field that pierces the solar surface and drives significant variations
in our star's radiative, particulate, and eruptive output over that
period. This paper presents observations from the Solar and Heliospheric
Observatory and Solar Dynamics Observatory indicating that the 11
yr sunspot variation is intrinsically tied to the spatio-temporal
overlap of the activity bands belonging to the 22 yr magnetic activity
cycle. Using a systematic analysis of ubiquitous coronal brightpoints
and the magnetic scale on which they appear to form, we show that the
landmarks of sunspot cycle 23 can be explained by considering the
evolution and interaction of the overlapping activity bands of the
longer-scale variability.
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Title: Using Polar Coronal Hole Area Measurements to Determine the
Solar Polar Magnetic Field Reversal in Solar Cycle 24
Authors: Karna, N.; Hess Webber, S. A.; Pesnell, W. D.
2014SoPh..289.3381K Altcode: 2014SoPh..tmp...80K
An analysis of solar polar coronal hole (PCH) areas since the launch
of the Solar Dynamics Observatory (SDO) shows how the polar regions
have evolved during Solar Cycle 24. We present PCH areas from mid-2010
through 2013 using data from the Atmospheric Imager Assembly (AIA) and
Helioseismic and Magnetic Imager (HMI) instruments onboard SDO. Our
analysis shows that both the northern and southern PCH areas have
decreased significantly in size since 2010. Linear fits to the areas
derived from the magnetic-field properties indicate that, although
the northern hemisphere went through polar-field reversal and reached
solar-maximum conditions in mid-2012, the southern hemisphere had not
reached solar-maximum conditions in the polar regions by the end of
2013. Our results show that solar-maximum conditions in each hemisphere,
as measured by the area of the polar coronal holes and polar magnetic
field, will be offset in time.
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Title: Predicting Solar Cycle 24 Using a Geomagnetic Precursor Pair
Authors: Pesnell, W. Dean
2014SoPh..289.2317P Altcode: 2014SoPh..tmp...18P
We describe using Ap and F<SUB>10.7</SUB> as a geomagnetic-precursor
pair to predict the amplitude of Solar Cycle 24. The precursor is
created by using F<SUB>10.7</SUB> to remove the direct solar-activity
component of Ap. Four peaks are seen in the precursor function during
the decline of Solar Cycle 23. A recurrence index that is generated by
a local correlation of Ap is then used to determine which peak is the
correct precursor. The earliest peak is the most prominent but coincides
with high levels of non-recurrent solar activity associated with the
intense solar activity of October and November 2003. The second and
third peaks coincide with some recurrent activity on the Sun and show
that a weak cycle precursor closely following a period of strong solar
activity may be difficult to resolve. A fourth peak, which appears in
early 2008 and has recurrent activity similar to precursors of earlier
solar cycles, appears to be the "true" precursor peak for Solar Cycle
24 and predicts the smallest amplitude for Solar Cycle 24. To determine
the timing of peak activity it is noted that the average time between
the precursor peak and the following maximum is ≈ 6.4 years. Hence,
Solar Cycle 24 would peak during 2014. Several effects contribute to
the smaller prediction when compared with other geomagnetic-precursor
predictions. During Solar Cycle 23 the correlation between sunspot
number and F<SUB>10.7</SUB> shows that F<SUB>10.7</SUB> is higher than
the equivalent sunspot number over most of the cycle, implying that the
sunspot number underestimates the solar-activity component described by
F<SUB>10.7</SUB>. During 2003 the correlation between aa and Ap shows
that aa is 10 % higher than the value predicted from Ap, leading to
an overestimate of the aa precursor for that year. However, the most
important difference is the lack of recurrent activity in the first
three peaks and the presence of significant recurrent activity in the
fourth. While the prediction is for an amplitude of Solar Cycle 24 of
65±20 in smoothed sunspot number, a below-average amplitude for Solar
Cycle 24, with maximum at 2014.5±0.5, we conclude that Solar Cycle 24
will be no stronger than average and could be much weaker than average.
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Title: Coronal Cavity Catalog from SDO Observations
Authors: Karna, Nishu; Zhang, Jie; Pesnell, William D; Hess Webber,
Shea A.
2014AAS...22432355K Altcode:
We present a catalog of coronal cavities and prominences associated with
cavities since the launch of Solar Dynamics Observatory (SDO). Coronal
cavities are dark, circular regions observed above the solar limb in
white light and EUV coronal images. They are believed to be regions
of lower density relative to the surrounding corona. We use synoptic
maps made from EUV images from the Atmospheric Imager Assembly (AIA)
instrument on board SDO to study coronal cavities. The synoptic maps,
constructed from annuli above the solar limb, best show cavities in 211
A (Fe XIV, 2.0 MK) and 193 A (Fe XII, 1.6 MK) and 171 A (Fe IX, 0.6 MK)
passbands. Moreover, 304 A (He II, 0.05 MK) synoptic maps best show the
evolution of any prominences associated with a cavity. The catalog lists
the number of cavities seen in each Carrington rotation starting from
CR 2097, the cavity’s size, shape, and the heliographic longitudes
and latitudes of the appearance and disappearance of the cavity. Our
goal is to provide a consistent set of the cavity structures for broad
scientific use.
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Title: Coronal Diagnostics from Cometary Emission
Authors: Bryans, Paul; Pesnell, William D; Seaton, Daniel B; West,
Matthew J
2014AAS...22442203B Altcode:
The extreme ultraviolet (EUV) emission observed from sungrazing comets
as they pass through the solar atmosphere can be used to infer the
properties of the corona. In this paper we will discuss several of these
properties that can be estimated from the EUV observations of Comet
Lovejoy from AIA/SDO and SWAP/PROBA2. The longevity of the emission
allows us to constrain the coronal electron density through which
the comet passes. We will also discuss how dispersion of the emitting
cometary material we can be used to estimate the local Alfven speed in
the corona. Finally, measuring the deformation of the magnetic field
as it is impacted by the comet can be used to estimate the magnetic
field strength in this location. In the absence of the comet, none
of these parameters are directly measurable in the corona. Sungrazing
comets are thus unique probes of the solar atmosphere.
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Title: Asymmetries and the Off-Axial Wandering of Polar Coronal Holes
Authors: Kirk, Michael S.; Hess-Webber, Shea; Pesnell, W. Dean;
Karna, Nishu
2014shin.confE..23K Altcode:
Polar coronal holes are regularly observed capping the northern and
southern solar poles in EUV images of the corona and are understood
as the primary source of the fast solar wind. Polar holes are also
observed to have strong solar cycle dependence: becoming more stable and
prominent in solar minimum and disappearing at solar maximum. We extend
the perimeter tracking methods of Kirk et al. (2009) and Hess-Webber
et al. (2014, submitted) to examine the centroid of identified polar
coronal holes during solar cycle 24 by utilizing the entirety of the
EIT image archive on SOHO. We demonstrate that the centroids of the
polar holes have clear solar cycle dependence. Polar coronal holes are
symmetrically aligned during minimum and have a maximum asymmetry at
solar maximum of about 17 degrees.
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Title: Taking Extreme Space Weather to the Milky Way
Authors: Pesnell, W. Dean
2014AAS...22432359P Altcode:
Extreme Space Weather events are large solar flares or geomagnetic
storms, which can cause economic damage that cost billions of dollars to
recover from. We have few examples of such events; only the Carrington
Event (the solar superstorm) has superlatives in three categories: size
of solar flare, drop in Dst, and amplitude of aa. Kepler observations
show that stars similar to the Sun can have flares releasing thousands
of times more energy than an X-class flare. These flares would
strongly affect the atmosphere surrounding a planet orbiting such a
star. Particle and magnetic field outflows from these stars could
also be present. We are investigating the level of solar activity
that is necessary to strongly affect the atmosphere of terrestrial
planets. We assume that a habitable planet requires an atmosphere
with a temperature and composition that is stable in time. Can we
then extrapolate results from our solar system to determine a space
of stellar parameters in which habitable planets can exist?
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Title: Time-Series Analysis of Supergranule Characteristics at
Solar Minimum
Authors: Williams, Peter E.; Pesnell, W. Dean
2014SoPh..289.1101W Altcode:
Sixty days of Doppler images from the Solar and Heliospheric
Observatory (SOHO) / Michelson Doppler Imager (MDI) investigation
during the 1996 and 2008 solar minima have been analyzed to show
that certain supergranule characteristics (size, size range,
and horizontal velocity) exhibit fluctuations of three to five
days. Cross-correlating parameters showed a good, positive correlation
between supergranulation size and size range, and a moderate, negative
correlation between size range and velocity. The size and velocity
do exhibit a moderate, negative correlation, but with a small time
lag (less than 12 hours). Supergranule sizes during five days of
co-temporal data from MDI and the Solar Dynamics Observatory (SDO) /
Helioseismic Magnetic Imager (HMI) exhibit similar fluctuations with
a high level of correlation between them. This verifies the solar
origin of the fluctuations, which cannot be caused by instrumental
artifacts according to these observations. Similar fluctuations are
also observed in data simulations that model the evolution of the
MDI Doppler pattern over a 60-day period. Correlations between the
supergranule size and size range time-series derived from the simulated
data are similar to those seen in MDI data. A simple toy-model using
cumulative, uncorrelated exponential growth and decay patterns at
random emergence times produces a time-series similar to the data
simulations. The qualitative similarities between the simulated and
the observed time-series suggest that the fluctuations arise from
stochastic processes occurring within the solar convection zone. This
behavior, propagating to surface manifestations of supergranulation, may
assist our understanding of magnetic-field-line advection, evolution,
and interaction.
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Title: The Time-dependent Chemistry of Cometary Debris in the
Solar Corona
Authors: Pesnell, W. D.; Bryans, P.
2014ApJ...785...50P Altcode:
Recent improvements in solar observations have greatly progressed the
study of sungrazing comets. They can now be imaged along the entirety
of their perihelion passage through the solar atmosphere, revealing
details of their composition and structure not measurable through
previous observations in the less volatile region of the orbit further
from the solar surface. Such comets are also unique probes of the solar
atmosphere. The debris deposited by sungrazers is rapidly ionized and
subsequently influenced by the ambient magnetic field. Measuring the
spectral signature of the deposited material highlights the topology
of the magnetic field and can reveal plasma parameters such as the
electron temperature and density. Recovering these variables from the
observable data requires a model of the interaction of the cometary
species with the atmosphere through which they pass. The present paper
offers such a model by considering the time-dependent chemistry of
sublimated cometary species as they interact with the solar radiation
field and coronal plasma. We expand on a previous simplified model by
considering the fully time-dependent solutions of the emitting species'
densities. To compare with observations, we consider a spherically
symmetric expansion of the sublimated material into the corona and
convert the time-dependent ion densities to radial profiles. Using
emissivities from the CHIANTI database and plasma parameters derived
from a magnetohydrodynamic simulation leads to a spatially dependent
emission spectrum that can be directly compared with observations. We
find our simulated spectra to be consistent with observation.
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Title: Analysis of Supergranule Sizes and Velocities Using Solar
Dynamics Observatory (SDO)/ Helioseismic Magnetic Imager (HMI) and
Solar and Heliospheric Observatory (SOHO)/ Michelson Doppler Imager
(MDI) Dopplergrams
Authors: Williams, Peter E.; Pesnell, W. Dean; Beck, John G.; Lee,
Shannon
2014SoPh..289...11W Altcode:
Co-temporal Doppler images from Solar and Heliospheric Observatory
(SOHO)/Michelson Doppler Imager (MDI) and Solar Dynamics Observatory
(SDO)/Helioseismic Magnetic Imager (HMI) have been analyzed to extract
quantitative information about global properties of the spatial
and temporal characteristics of solar supergranulation. Preliminary
comparisons show that supergranules appear to be smaller and have
stronger horizontal velocity flows within HMI data than was measured
with MDI. There appears to be no difference in their evolutionary
timescales. Supergranule sizes and velocities were analyzed over a
ten-day time period at a 15-minute cadence. While the averages of
the time-series retain the aforementioned differences, fluctuations
of these parameters first observed in MDI data were seen in both
MDI and HMI time-series, exhibiting a strong cross-correlation. This
verifies that these fluctuations are not instrumental, but are solar
in origin. The observed discrepancies between the averaged values from
the two sets of data are a consequence of instrument resolution. The
lower spatial resolution of MDI results in larger observed structures
with lower velocities than is seen in HMI. While these results offer a
further constraint on the physical nature of supergranules, they also
provide a level of calibration between the two instruments.
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Title: The Perihelion Passage of Comet ISON as seen by SDO
Authors: Pesnell, W. D.; Schrijver, C. J.; Boerner, P.; DeRosa, M. L.;
Liu, W.; Thompson, B. J.
2013AGUFM.P24A..10P Altcode:
Comet ISON will fly through perihelion on November 28, 2013. It is one
of the largest sungrazing comets to be seen in the Space Age. The Solar
Dynamics Observatory (SDO) has seen two previous sungrazing comets in
the extreme ultraviolet channels of the Atmospheric Imaging Assembly
(AIA). Comet ISON will fly farther from the Sun (perihelion distance
of 2.7 Rsun compared to 1.15 for Comet Lovejoy), meaning it probes
a different part of the solar corona, but its larger size should
provide enough mass to illuminate the path of the nucleus. Based on
the latest ephemeris, SDO will be able to track Comet ISON through
the entire perihelion passage by a series of off-point maneuvers. We
will present the AIA data obtained from the Comet ISON perihelion,
discussing the differences between Comets ISON and Lovejoy. We will
then summarize what we have learned from the observations and offer
some thoughts on what sungrazing comets may reveal about comets,
the Sun, and their interaction.
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Title: What EUV Observations of Comet ISON Reveal About the Solar
Corona
Authors: Bryans, P.; Pesnell, W. D.
2013AGUFM.P31A1787B Altcode:
Recent advances in space-based solar observations have greatly
progressed the study of sungrazing comets. They can now be imaged along
the entirety of their perihelion passage, revealing details of their
composition, structure, and size. Such comets are also unique probes
of the solar corona. The debris deposited by sungrazers is rapidly
ionized and subsequently forced to follow the ambient magnetic field. In
this paper we present preliminary results from EUV observations of
Comet ISON. We estimate the size of the comet nucleus based on the
EUV radiance and compare with independent estimates. The variation
of the EUV emission with wavelength provides limits on the density of
the ambient corona, and the motion of ionized debris will be used to
infer the coronal magnetic field structure.
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Title: Inter-hemispheric coupling during northern polar summer
periods of 2002-2010 using TIMED/SABER measurements
Authors: Goldberg, R. A.; Feofilov, A. G.; Pesnell, W. D.; Kutepov,
A. A.
2013JASTP.104..277G Altcode:
It has been found that for more than one polar summer season between
2002 and 2010, the northern polar mesospheric region near and above
about 80 km was warmer than normal. The strongest warming effect of this
type was observed to occur during northern summer 2002. Observational
and theoretical studies imply that these “anomalies” were preceded
by unusual dynamical processes in the southern hemisphere. We have
analyzed temperature distributions measured by the SABER limb scanning
infrared radiometer aboard the NASA TIMED satellite between 2002 and
2010 at altitudes from 15 to 110 km and for latitudes between 83°S
and 83°N. We describe the approach to trace the spatial extent
of inter-hemispheric temperature correlations demonstrating the
global features that were unique for the “anomalous” northern
polar summers. From our analysis of SABER data from 2002 to 2010,
the anomalous heating for the northern mesopause region during
northern summer was accompanied by stratospheric heating in the
equatorial region. In the winter hemisphere it is accompanied by
heating in the lower stratosphere and mesopause region, and cooling
in the stratopause region. Also, all the elements of the temperature
anomaly structure appear to develop and fade away nearly simultaneously,
thereby suggesting either a global influence or a short lagging period
(less than 7 days).
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Title: Time-dependent chemisty of outgassed cometary detritus in
the solar corona
Authors: Bryans, Paul; Pesnell, W. D.
2013SPD....44...32B Altcode:
Recent observations of sungrazing comets have opened an exciting novel
methof of probing the solar atmosphere. As well as providing valuable
insight on the magnetic field of the lower corona, sungrazing comets
also promise the potential of measuring the solar wind as their detritus
follows the open field lines of the corona. In this work, we model the
chemisty of the material sublimated from comets as they skim across
the Sun. This material, largely water ice, is rapidly dissociated and
ionized by the solar radiation field and coronal electrons. We track
the evolution of the ionizing material as it expands into the corona
using a generalized Haser-like model. Based on these results, we have
predicted the emission resulting from these ions in different regions
of the corona and compared the results with SDO/AIA observations.
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Title: What Will Comet ISON Debris Teach Us About the Sun?
Authors: Pesnell, W. D.; Bryans, P.
2013SPD....44...34P Altcode:
Comet ISON is a large sun-grazing comet due to pass perihelion on
November 28, 2013. It will go through the corona 2.7 Rsun above
the surface, much higher than earlier EUV comets. We will use our
time-dependent models of cometary debris to discuss how the trail of
Comet ISON can be used to probe the solar corona. The debris trail left
behind as a sun-grazing comet passes by the Sun undergoes different
chemical processes at different distances from the Sun. Near the Sun
the material is rapidly converted to atomic ions and becomes part of
the solar corona. Far from the Sun the evaporated material can remain in
molecular form for a long time, while the grains of asteroidal material
can exist long enough to become meteors in planetary atmospheres. The
larger fragments may survive as independent comets, until the next
perihelion passage. In between those limits the material moves in the
solar wind acceleration region. The debris could become entrained in
the solar wind and be measured by satellites far from the Sun. This
material would be observed as abundance anomalies in the solar wind. We
will describe the fate of the cometary debris trail left by Comet ISON
and what the trail can tell us about the solar corona and solar wind.
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Title: The study of the cavity’s morphology, density, thermal and
magnetic properties from the SDO observations
Authors: Karna, Nishu; Zhang, J.; Pesnell, W. D.; Hess Webber, S. A.
2013SPD....44...47K Altcode:
Coronal cavities are circular darkened regions observed above the
solar limb in white light and EUV coronal images. It is a region
of low density relative to the surrounding corona. In this study,
we are using synoptic maps made from EUV images from the Atmospheric
Imager Assembly (AIA) instrument and vector magnetogram images from
Helioseismic and Magnetic Imager (HMI) on the SDO to determine the
structure and evolution of cavities. The EUV synoptic maps, constructed
from circular rings above the limb, are found to best show cavities in
211Å (Fe XIV, ~2.0 MK) and 193 Å (Fe XII, ~1.6 MK) and171 Å (Fe IX,
~0.6 MK) pass bands. Moreover, 304Å (He II, ~0.05 MK) synoptic map best
shows the evolution of prominence associated with cavity. Magnetogram
synoptic map constructed from the central meridian, shows the underlying
magnetic structure of the cavity and prominence. We have also used EUV
synoptic map to construct the polar view of the cavities. DEM analysis
was used to calculate the temperature and density of the cavities. The
high spatial and time resolution combined with the broad temperature
coverage provides a consistent picture of the cavity material and
the dynamics of the structure.Abstract (2,250 Maximum Characters):
Coronal cavities are circular darkened regions observed above the
solar limb in white light and EUV coronal images. It is a region
of low density relative to the surrounding corona. In this study,
we are using synoptic maps made from EUV images from the Atmospheric
Imager Assembly (AIA) instrument and vector magnetogram images from
Helioseismic and Magnetic Imager (HMI) on the SDO to determine the
structure and evolution of cavities. The EUV synoptic maps, constructed
from circular rings above the limb, are found to best show cavities in
211Å (Fe XIV, ~2.0 MK) and 193 Å (Fe XII, ~1.6 MK) and171 Å (Fe IX,
~0.6 MK) pass bands. Moreover, 304Å (He II, ~0.05 MK) synoptic map best
shows the evolution of prominence associated with cavity. Magnetogram
synoptic map constructed from the central meridian, shows the underlying
magnetic structure of the cavity and prominence. We have also used EUV
synoptic map to construct the polar view of the cavities. DEM analysis
was used to calculate the temperature and density of the cavities. The
high spatial and time resolution combined with the broad temperature
coverage provides a consistent picture of the cavity material and the
dynamics of the structure.
---------------------------------------------------------
Title: Coronal Cavities from SDO Observations
Authors: Karna, Nishu; Zhang, J.; Pesnell, W. D.; Hess Webber, S. A.
2013shin.confE.101K Altcode:
Coronal cavities are circular darkened regions observed above the
solar limb in white light and EUV coronal images. It is a region
of low density relative to the surrounding corona. In this study,
we are using synoptic maps made from EUV images from the Atmospheric
Imager Assembly (AIA) instrument and vector magnetogram images from
Helioseismic and Magnetic Imager (HMI) on the SDO to determine
the structure and evolution of cavities. The EUV synoptic maps,
constructed from circular rings above the limb, are found to best
show cavities in 211Å (Fe XIV, 2.0 MK) and 193Å (Fe XII, 1.6 MK)
and171Å (Fe IX, 0.6 MK) pass bands. Moreover, 304Å (He II, 0.05
MK) synoptic map best shows the evolution of prominence associated
with cavity. Magnetogram synoptic map constructed from the central
meridian, shows the underlying magnetic structure of the cavity and
prominence. We have also used EUV synoptic map to construct the polar
view of the cavities. The high spatial and time resolution combined
with the broad temperature coverage provides a consistent picture of
the cavity material and the dynamics of the structure.
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Title: Exploring the Network of SDO Science
Authors: Pesnell, W. Dean; Thompson, Barbara
2013enss.conf.....P Altcode:
Living With a Star's Solar Dynamics Observatory invites you to its
2013 Science Workshop to be held March 3-8, 2013 at the Hyatt Regency
Chesapeake Bay in Cambridge, MD (http://chesapeakebay.hyatt.com/). The
workshop is a follow-on to the "Many Spectra of Solar Activity" workshop
held May 1-5, 2011 in Squaw Valley, CA. <P />Scientific sessions will
feature a broad spectrum of science topics fundamental to SDO's science
investigations: Atmospheric Imaging Assembly (AIA), EUV Variability
Experiment (EVE), and Helioseismic and Magnetic Imager (HMI), as well
as the overlap between SDO and other scientific missions and activities.
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Title: Polar Coronal Hole Areas from 1996 through Present
Authors: Hess Webber, S. A.; Karna, N.; Pesnell, W. D.
2013enss.confE..20H Altcode:
The evolutionary analysis of the polar coronal hole (PCH) areas from
the beginning of solar cycle 23 through the cycle 24 minimum has
introduced several new scientific results regarding changes in the
magnetic field configuration during the past solar cycle. Observations
show that the PCH sizes peak at discrete times in the two hemispheres,
suggesting that the two poles reach solar minimum (magnetic maximum)
up to three years apart. The northern polar hole has also decreased
significantly in size since 2010, while the southern hole has remained
stable. This indicates that the northern hemisphere has already reached
solar maximum even though the southern hemisphere has yet to peak.
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Title: EUV Emission from Sungrazing Comets
Authors: Bryans, Paul; Pesnell, W. Dean
2013enss.confE..33B Altcode:
The EUV emission resulting from comets' passage through the solar
atmosphere has opened many exciting avenues of study. The observations
show the sublimated cometary material to interact with ambient magnetic
field and highlight magnetic features that are not normally visible with
EUV telescopes. The first step, however, is to explain why the comet
produces the EUV emission. In this talk, I will outline a model that
describes the interaction of the cometary atmosphere with the quiescent
solar background and results in such emission. In particular, the model
accurately predicts the temporal and wavelength response of the emission
detected by SDO/AIA. After describing the emission process, I will go on
to discuss what we can learn about the corona from these observations.
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Title: Coronal Cavities from SDO Observations
Authors: Karna, N.; Zhang, J.; Pesnell, W. D.; Hess Webber, S. A.
2013enss.confE.134K Altcode:
Coronal cavities are circular darkened regions observed above the solar
limb in white light and EUV coronal images. It is believed a region of
low density relative to the surrounding corona. In this study, we are
using synoptic maps made from EUV images from the Atmospheric Imager
Assembly (AIA) instrument on the SDO to determine the structure and
evolution of cavities. The synoptic maps, constructed from circular
rings above the limb, are found to best show cavities in 211Å (Fe
XIV, 2.0 MK) and 193 Å (Fe XII, 1.6 MK) and171 Å (Fe IX, 0.6 MK)
pass bands. Moreover, 304Å (He II, 0.05 MK) synoptic map best shows
the evolution of prominence associated with cavity. The high spatial
and time resolution combined with the broad temperature coverage
provides a consistent picture of the cavity material and the dynamics
of the structure. Our goal in this work is to study the cavity's sizes
(height, diameter and length), density and temperature properties.
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Title: The Solar Dynamics Observatory after three years in orbit
Authors: Poland, D.; Ekinci, F. M.; Fink, D.; Pesnell, W. D.
2013aero.confE.183P Altcode:
There are three instruments aboard the Solar Dynamics Observatory
(SDO): EVE, which measures the extreme ultraviolet irradiance of the
Sun; AIA, which images the Sun at high cadence in ten wavelengths; and
HMI, which measures the solar magnetic field and velocity of the solar
surface. These instruments have returned roughly 1.5 Tbytes of solar
data per day nearly continuously since the beginning of SDO's science
operations in May 2010, which has been facilitated by a continuous
downlink from geosynchronous orbit to SDO's dedicated pair of 18-m
antennas in White Sands, New Mexico. Science data returned from SDO
is continually advancing knowledge of and research in prominence and
filament eruptions, late phase flares, and the solar vector magnetic
field, amongst other areas. Additionally, observations made during orbit
maintenance, collision avoidance, and ground system operations have
yielded lessons learned about the need to account for extreme weather
in antenna design and the importance of clear, direct communication
channels with other satellite operators. These observations and lessons
are being used to improve the SDO ground system and operations approach
and may prove useful for future mission design.
---------------------------------------------------------
Title: Investigating Coronal Activity by Release Using Sublimation
Authors: Moore, T. E.; Bryans, P.; Pesnell, W. D.; Thompson, B. J.
2012AGUFMSH21D..05M Altcode:
Plasma tails left by sun-grazing comets are visible in EUV, expanding
their traditional role as "windsocks" into the low corona and serving
as natural "chemical release" experiments. SDO obtained spectrally
resolved video imagery of passages as close as 0.15 Rs to the solar
photosphere at 12 sec frame cadence. Vaporized cometary materials
form sublimation trails or "subtrails" that persist as long as 20
min. in 13.1 and 17.1 nm channels. Striation along local magnetic flux
tubes implies filamentation of the visible plasma, and the subtrails
exhibit substantial deviations from the comet orbital track. These
reveal coronal winds and shears with velocities that are comparable to
the comet velocity of up to 600 km/s. We analyze the likely origins
and directionality of these winds and their implications for coronal
heating in the altitude range where ion-neutral collision mean free
paths are longer than the gyro radius but shorter than the atmospheric
scale height, that is, the solar transition region. With active impact
or photo-ionization, and charge exchange, the inferred super-thermal,
sub-Alfvenic ion-neutral relative velocities will lead to ion pick-up
distributions that decay or relax into "kappa" distributions with
super-thermal power law tails that are relevant to the formation of
the corona.
---------------------------------------------------------
Title: Time-dependent Chemistry of Detritus from Sun-grazing Comets
Authors: Pesnell, W. D.; Bryans, P.
2012AGUFMSH13B2253P Altcode:
As a sun-grazing comet passes the Sun at perihelion it leaves behind
a trail of water vapor and detritus. The latter are grains of stony
material that rapidly heat and vaporize in the intense radiation field
of the solar photosphere. A large amount of O is produced from both the
water and the stony material. The atomic material does not continue
along the comet's orbital path but appears to move along the ambient
magnetic field. This requires an ionization mechanism that rapidly
converts the neutral atoms into ions. We propose two models of the
time-dependent chemistry that can be used to calculate the ionization
balance of O and Fe. One is an extension of the Haser model to include
many stages of ionization but without recombination. The advantage
is that an analytic solution can be derived for an arbitrary numbers
of ionization stages. Once the time dependence is known it can be
converted to the radial profile in either spherical or cylindrical
symmetry. The other model integrates in time the equations describing
ionization/recombination balance. Both types of solutions can be
numerically inverted to estimate the radiance profiles. The models give
the same sequence to the ionization stages, but the time dependence
and radial profiles are shown to differ. Although we concentrate on
the O and Fe chemistry because it is observed from SDO/AIA, any atom
can be considered.
---------------------------------------------------------
Title: Solar Cycle Predictions (Invited Review)
Authors: Pesnell, W. Dean
2012SoPh..281..507P Altcode: 2012SoPh..tmp..135P; 2012SoPh..tmp..105P
Solar cycle predictions are needed to plan long-term space missions,
just as weather predictions are needed to plan the launch. Fleets
of satellites circle the Earth collecting many types of science data,
protecting astronauts, and relaying information. All of these satellites
are sensitive at some level to solar cycle effects. Predictions of drag
on low-Earth orbit spacecraft are one of the most important. Launching
a satellite with less propellant can mean a higher orbit, but
unanticipated solar activity and increased drag can make that a
Pyrrhic victory as the reduced propellant load is consumed more
rapidly. Energetic events at the Sun can produce crippling radiation
storms that endanger all assets in space. Solar cycle predictions also
anticipate the shortwave emissions that cause degradation of solar
panels. Testing solar dynamo theories by quantitative predictions
of what will happen in 5 - 20 years is the next arena for solar
cycle predictions. A summary and analysis of 75 predictions of the
amplitude of the upcoming Solar Cycle 24 is presented. The current
state of solar cycle predictions and some anticipations of how those
predictions could be made more accurate in the future are discussed.
---------------------------------------------------------
Title: The Extreme-ultraviolet Emission from Sun-grazing Comets
Authors: Bryans, P.; Pesnell, W. D.
2012ApJ...760...18B Altcode: 2012arXiv1209.5708B
The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory
has observed two Sun-grazing comets as they passed through the solar
atmosphere. Both passages resulted in a measurable enhancement of
extreme-ultraviolet (EUV) radiance in several of the AIA bandpasses. We
explain this EUV emission by considering the evolution of the cometary
atmosphere as it interacts with the ambient solar atmosphere. Molecules
in the comet rapidly sublimate as it approaches the Sun. They are
then photodissociated by the solar radiation field to create atomic
species. Subsequent ionization of these atoms produces a higher
abundance of ions than normally present in the corona and results in
EUV emission in the wavelength ranges of the AIA telescope passbands.
---------------------------------------------------------
Title: Coronal Cavities from SDO Observations
Authors: Karna, Nishu; Hess Webber, Shea A.; Pesnell, W. Dean; Zhang,
Jie; Kirk, M. S.
2012shin.confE.207K Altcode:
Coronal cavities are circular darkened regions observed above the
solar limb in white light and EUV coronal images. It is a region of
low density relative to the surrounding corona. In this study, we are
using synoptic maps made from EUV images from the Atmospheric Imager
Assembly (AIA) instrument on the SDO to determine the structure and
evolution of cavities. The synoptic maps, constructed from circular
rings above the limb, are found to best show cavities in 211Å (Fe XIV,
2.0 MK) and 193 Å (Fe XII, 1.6 MK) pass bands. The high spatial and
time resolution combined with the broad temperature coverage provides
a consistent picture of the cavity material and the dynamics of the
structure. Our goal is to study the cavity"s sizes (height, diameter
and length), density and temperature properties. Moreover, we will
examine the correlation between cavity morphology and underlying
magnetic field distribution using Heliosesmic and Magnetic imager
(HMI) instrument on SDO. This study will shed light on the origin,
evolution and dynamics of coronal cavities.
---------------------------------------------------------
Title: Solar Cycle 23/24 Polar Coronal Hole Areas: Scientific Results
Authors: Hess Webber, Shea A.; Karna, Nishu; Pesnell, W. Dean
2012shin.confE.118H Altcode:
The evolutionary analysis of the polar coronal hole (PCH) areas from
the beginning of solar cycle 23 through the cycle 24 minimum has
introduced several new scientific results regarding changes in the
magnetic field configuration during the past solar cycle. Observations
show that the PCH sizes peak at discrete times in the two hemispheres,
suggesting that the two poles reach solar minimum (magnetic maximum)
up to three years apart. The northern polar hole has also decreased
significantly in size since 2010, while the southern hole has remained
stable. This indicates that the northern hemisphere has already reached
solar maximum even though the southern hemisphere has yet to peak. The
relationship between the temporal difference of the PCH area peaks at
solar minimum and that of the area drop-offs during solar maximum are
under investigation.
---------------------------------------------------------
Title: The Journey of Sungrazing Comet Lovejoy
Authors: Bryans, Paul; A'Hearn, M.; Battams, K.; Biesecker, D.;
Bodewits, D.; Boice, D.; Brown, J.; Caspi, A.; Chodas, P.; Hudson,
H.; Jia, Y.; Jones, G.; Keller, H. U.; Knight, M.; Linker, J.; Lisse,
C.; Liu, W.; McIntosh, S.; Pesnell, W. D.; Raymond, J.; Saar, S.;
Saint-Hilaire, P.; Schrijver, C.; Snow, M.; Tarbell, T.; Thompson,
W.; Weissman, P.; Comet Lovejoy Collaboration Team
2012AAS...22052507B Altcode:
Comet Lovejoy (C/2011 W3) was the first sungrazing comet, observed
by space-based instruments, to survive perihelion passage. First
observed by ground-based telescopes several weeks prior to perihelion,
its journey towards the Sun was subsequently recorded by several solar
observatories, before being observed in the weeks after perihelion by
a further array of space- and ground-based instruments. Such a surfeit
of wide-ranging observations provides an unprecedented insight into
both sungrazing comets themselves, and the solar atmosphere through
which they pass. This paper will summarize what we have learnt from the
observations thus far and offer some thoughts on what future sungrazing
comets may reveal about comets, the Sun, and their interaction.
---------------------------------------------------------
Title: The Solar Polar Coronal Holes in Solar Cycle 24
Authors: Hess Webber, Shea; Karna, N.; Pesnell, W. D.; Kirk, M. S.
2012AAS...22020201H Altcode:
We have measured the area of the solar polar coronal holes in both
hemispheres. One data series uses synoptic maps from two instruments
on SOHO and the AIA instrument on SDO. The other used the perimeter
tracking method on data from SoHO EIT. This allows us to calculate the
areas of the solar polar coronal holes from the beginning of Solar Cycle
23 up to late 2010. This method used synoptic maps constructed from
170 Carrington Rotations of the 171, 195, and 304 Å channels of the
Extreme-ultraviolet Imaging Telescope (EIT) on SoHO. Our second method
used synoptic maps constructed from the Michelson Doppler Imager (MDI)
for 187 Carrington Rotations from mid 1996 through 2010. In this method,
polar coronal holes are easily distinguished from the equatorial coronal
hole regions. The north and south polar hole areas were noticeably
smaller in the recent minimum than they were at the beginning of Solar
Cycle 23. We compared these polar hole areas with the polar coronal
hole area found using a perimeter tracking to analyze a series of 171,
195, and 304 Å full disk images from EIT to measure the perimeter of
polar coronal holes as they appear on the limbs. It is found that both
the Northern and Southern polar coronal hole areas obtained from the
perimeter tracking method similar to those from the synoptic maps. The
coronal hole areas will be compared with the polar magnetic fields to
estimate what phase of the solar cycle the hemispheres have reached.
---------------------------------------------------------
Title: The EUV Emission from Sun-Grazing Comets
Authors: Bryans, Paul; Pesnell, W. D.
2012AAS...22042305B Altcode:
The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory
(SDO) has, to date, viewed two Sun-grazing comets as they passed
through the solar corona. Both passages resulted in the significant
enhancement of Extreme Ultraviolet (EUV) emission in several of
the AIA bandpasses. We explain this EUV emission by considering the
evolution of the cometary atmosphere as it interacts with the ambient
solar atmosphere. Water ice in the comet rapidly sublimates as it
approaches the Sun. This water vapor is then photodissociated by
the solar radiation field to create atomic H and O. Other molecules
present in the comet also evaporate and dissociate to give atomic
Fe and other metals. Subsequent ionization of these atoms produces a
high abundance of ions not normally present at the temperature of the
corona and results in EUV emission in the wavelength ranges of the
AIA telescopes. Understanding the EUV emission places constraints on
the cometary composition and provides valuable insight to the nature
of the upper solar atmosphere.
---------------------------------------------------------
Title: Coronal Cavities from SDO Observations
Authors: Karna, Nishu; Hess Webber, S. A.; Pesnell, W. D.; Zhang,
J.; Kirk, M. S.
2012AAS...22020204K Altcode:
Coronal cavities are circular darkened regions observed above the
solar limb in white light and EUV coronal images. It is a region of
low density relative to the surrounding corona. In this study, we are
using synoptic maps made from EUV images from the Atmospheric Imager
Assembly (AIA) instrument on the SDO to determine the structure and
evolution of cavities. The synoptic maps, constructed from circular
rings above the limb, are found to best show cavities in 211Å (Fe XIV,
2.0 MK) and 193 Å (Fe XII, 1.6 MK) pass bands. The high spatial and
time resolution combined with the broad temperature coverage provides
a consistent picture of the cavity material and the dynamics of the
structure. Our goal is to study the cavity’s sizes (height, diameter
and length), density and temperature properties. Moreover, we will
examine the correlation between cavity morphology and underlying
magnetic field distribution using Heliosesmic and Magnetic imager
(HMI) instrument on SDO. This study will shed light on the origin,
evolution and dynamics of coronal cavities.
---------------------------------------------------------
Title: The Solar Dynamics Observatory (SDO) Education and Outreach
(E/PO) Program: Changing Perceptions One Program at a Time
Authors: Drobnes, E.; Littleton, A.; Pesnell, W. D.; Beck, K.; Buhr,
S.; Durscher, R.; Hill, S.; McCaffrey, M.; McKenzie, D. E.; Myers,
D.; Scherrer, D.; Wawro, M.; Wolt, A.
2012SoPh..275..391D Altcode: 2011SoPh..tmp..420D; 2011SoPh..tmp..424D; 2011SoPh..tmp..367P
We outline the context and overall philosophy for the combined Solar
Dynamics Observatory (SDO) Education and Public Outreach (E/PO)
program, present a brief overview of all SDO E/PO programs along with
more detailed highlights of a few key programs, followed by a review
of our results to date, conclude a summary of the successes, failures,
and lessons learned, which future missions can use as a guide, while
incorporating their own content to enhance the public's knowledge
and appreciation of science and technology as well as its benefit
to society.
---------------------------------------------------------
Title: Destruction of Sun-Grazing Comet C/2011 N3 (SOHO) Within the
Low Solar Corona
Authors: Schrijver, C. J.; Brown, J. C.; Battams, K.; Saint-Hilaire,
P.; Liu, W.; Hudson, H.; Pesnell, W. D.
2012Sci...335..324S Altcode:
Observations of comets in Sun-grazing orbits that survive solar
insolation long enough to penetrate into the Sun's inner corona provide
information on the solar atmosphere and magnetic field as well as on
the makeup of the comet. On 6 July 2011, the Solar Dynamics Observatory
(SDO) observed the demise of comet C/2011 N3 (SOHO) within the low solar
corona in five wavelength bands in the extreme ultraviolet (EUV). The
comet penetrated to within 0.146 solar radius (~100,000 kilometers)
of the solar surface before its EUV signal disappeared. Before that,
material released into the coma - at first seen in absorption - formed
a variable EUV-bright tail. During the final 10 minutes of observation
by SDO's Atmospheric Imaging Assembly, ~6 × 10^8 to 6 × 10^10 grams
of total mass was lost (corresponding to an effective nucleus diameter
of ~10 to 50 meters), as estimated from the tail's deceleration due to
interaction with the surrounding coronal material; the EUV absorption
by the comet and the brightness of the tail suggest that the mass was
at the high end of this range. These observations provide evidence
that the nucleus had broken up into a family of fragments, resulting
in accelerated sublimation in the Sun's intense radiation field.
---------------------------------------------------------
Title: The Solar Dynamics Observatory (SDO)
Authors: Pesnell, W. Dean; Thompson, B. J.; Chamberlin, P. C.
2012SoPh..275....3P Altcode:
The Solar Dynamics Observatory (SDO) was launched on 11 February 2010 at
15:23 UT from Kennedy Space Center aboard an Atlas V 401 (AV-021) launch
vehicle. A series of apogee-motor firings lifted SDO from an initial
geosynchronous transfer orbit into a circular geosynchronous orbit
inclined by 28° about the longitude of the SDO-dedicated ground station
in New Mexico. SDO began returning science data on 1 May 2010. SDO
is the first space-weather mission in NASA's Living With a Star (LWS)
Program. SDO's main goal is to understand, driving toward a predictive
capability, those solar variations that influence life on Earth and
humanity's technological systems. The SDO science investigations will
determine how the Sun's magnetic field is generated and structured,
how this stored magnetic energy is released into the heliosphere and
geospace as the solar wind, energetic particles, and variations in the
solar irradiance. Insights gained from SDO investigations will also
lead to an increased understanding of the role that solar variability
plays in changes in Earth's atmospheric chemistry and climate. The
SDO mission includes three scientific investigations (the Atmospheric
Imaging Assembly (AIA), Extreme Ultraviolet Variability Experiment
(EVE), and Helioseismic and Magnetic Imager (HMI)), a spacecraft bus,
and a dedicated ground station to handle the telemetry. The Goddard
Space Flight Center built and will operate the spacecraft during
its planned five-year mission life; this includes: commanding the
spacecraft, receiving the science data, and forwarding that data to the
science teams. The science investigations teams at Stanford University,
Lockheed Martin Solar Astrophysics Laboratory (LMSAL), and University
of Colorado Laboratory for Atmospheric and Space Physics (LASP) will
process, analyze, distribute, and archive the science data. We will
describe the building of SDO and the science that it will provide
to NASA.
---------------------------------------------------------
Title: The EUV Emission in Comet-Solar Corona Interactions
Authors: Bryans, P.; Pesnell, W. D.; Schrijver, C. J.; Brown, J. C.;
Battams, K.; Saint-Hilaire, P.; Liu, W.; Hudson, H. S.
2011AGUFMSH34B..05B Altcode:
The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory
(SDO) viewed a comet as it passed through the solar corona on 2011 July
5. This was the first sighting of a comet by a EUV telescope. For 20
minutes, enhanced emission in several of the AIA wavelength bands marked
the path of the comet. We explain this EUV emission by considering
the evolution of the cometary atmosphere as it interacts with the
ambient solar atmosphere. Water ice in the comet rapidly sublimates
as it approaches the Sun. This water vapor is then photodissociated,
primarily by Ly-α, by the solar radiation field to create atomic H and
O. Other molecules present in the comet also evaporate and dissociate
to give atomic Fe and other metals. Subsequent ionization of these
atoms can be achieved by a number of means, including photoionization,
electron impact, and charge exchange with coronal protons and other
highly-charged species. Finally, particles from the cometary atmosphere
are thermalized to the background temperature of the corona. Each step
could cause emission in the AIA bandpasses. We will report here on
their relative contribution to the emission seen in the AIA telescopes.
---------------------------------------------------------
Title: Time-Series Analyses of Supergranule Characteristics Compared
Between SDO/HMI, SOHO/MDI and Simulated Datasets
Authors: Williams, P. E.; Pesnell, W. D.
2011AGUFMSH23D..03W Altcode:
Supergranulation is a well-observed solar phenomenon despite its
underlying mechanisms remaining a mystery. Originally considered to
arise due to convective motions, alternative mechanisms have been
suggested such as the cumulative downdrafts of granules as well as
displaying wave-like properties. Supergranule characteristics are well
documented, however. Supergranule cells are approximately 35 Mm across,
have lifetimes on the order of a day and have divergent horizontal
velocities of around 300 m/s, a factor of 10 higher than their central
radial components. While they have been observed using Doppler methods
for more than half a century, their existence is also observed in
other datasets such as magnetograms and Ca II K images. These datasets
clearly show the influence of supergranulation on solar magnetism
and how the local field is organized by the flows of supergranule
cells. The Heliospheric and Magnetic Imager (HMI) aboard the Solar
Dynamics Observatory (SDO) continues to produce Doppler images enabling
the continuation of supergranulation studies made with SOHO/MDI, but
with superior temporal and spatial resolution. The size-distribution
of divergent cellular flows observed on the photosphere now reaches
down to granular scales, allowing contemporaneous comparisons between
the two flow components. SOHO/MDI Doppler observations made during the
minima of cycles 22/23 and 23/24 exhibit fluctuations of supergranule
characteristics (global averages of the supergranule size, size-range
and horizontal velocity) with periods of 3-5 days. Similar fluctuations
have been observed in SDO/HMI Dopplergrams and the high correlation
between co-temporal HMI & MDI suggest a solar origin. Their nature
has been probed by invoking data simulations that produce realistic
Dopplergrams based on MDI data.
---------------------------------------------------------
Title: Using the EUV to Weigh a Sun-grazing Comet as it Disappears
in the Solar Corona
Authors: Pesnell, W. D.; Schrijver, C. J.; Brown, J. C.; Battams,
K.; Saint-Hilaire, P.; Hudson, H. S.; Lui, W.
2011AGUFMSH33A2040P Altcode:
On July 6, 2011, the Atmospheric Imaging Assembly (AIA) on the
Solar Dynamics Observatory (SDO) observed a comet in most of its
EUV passbands. The comet disappeared while moving through the solar
corona. The comet penetrated to 0.146 solar radii ( ∼~100,000
km) above the photosphere before its EUV faded. Before then, the
comet's coma and a tail were observed in absorption and emission,
respectively. The material in the variable tail quickly fell behind
the nucleus. An estimate of the comet's mass based on this effect,
one derived from insolation, and one using the tail's EUV brightness,
all yield ∼ 50 giga-grams some 10 minutes prior to the end of
its visibility. These unique first observations herald a new era in
the study of Sun-grazing comets close to their perihelia and of the
conditions in the solar corona and solar wind. We will discuss the
observations and interpretation of the comet by SDO as well as the
coronagraph observations from SOHO and STEREO. A search of the SOHO
comet archive for other comets that could be observed in the SDO/AIA
EUV channels will be described.
---------------------------------------------------------
Title: A Comparison of Solar Polar Coronal Hole Areas Between Solar
Cycles 23 and 24
Authors: Hess Webber, Shea A.; Karna, Nishu; Pesnell, W. Dean; Kirk,
Michael S.
2011mfpc.confE...1H Altcode:
We have used the perimeter tracing algorithm and analysis of EUV
and magnetic field synoptic maps to extend our time series of polar
coronal hole areas through solar minimum between cycles 23 and 24
(through 2010). Both EUV algorithms use 171, 195, and 304 Å images
from the Extreme ultraviolet Imaging Telescope (EIT) on SOHO. The
perimeter tracing algorithm measures the polar coronal hole boundaries
as they appear on the limbs over each polar rotation and calculates
the enclosed area, while the synoptic method calculates the area of
the polar coronal holes from the meridional boundary through each
Carrington rotation. Line-of-sight magnetic field synoptic maps from
SOHO's Michelson Doppler Imager (MDI) instrument are used to estimate
the polar coronal hole areas via polarity signatures. We remain
convinced that the northern polar hole area is measurably smaller in
the recent minimum than it was at the beginning of cycle 23, while
the southern polar hole area is roughly the same.
---------------------------------------------------------
Title: Solar Dynamics and Magnetism from the Interior to the
Atmosphere
Authors: Pesnell, W. Dean; Thompson, Barbara
2011sdmi.conf.....P Altcode:
The goal of the workshop is to discuss recent advances and new problems
in the exploration of the Sun's interior structure, solar dynamics and
dynamo, mechanisms of sunspot and active regions formation, sources of
solar irradiance variations, and links between the subsurface dynamics,
flaring and CME activity. <P />NASA's Solar Dynamics Observatory (SDO)
mission is providing a large amount of new data on solar dynamics and
magnetic activities during the rising phase of the current and highly
unusual solar cycle. These data are complemented by the continuing
SOHO mission, and by ground-based observatories that include the GONG
helioseismology network and the New Solar Telescope. This unprecedented
amount of data provides a unique opportunity for multi-instrument
investigations that address fundamental problems of the origin of
solar magnetic activity at various spatial and temporal scales. <P
/>The data is being used to develop new methods for forecasting
solar cycles, emergence and evolution of active regions and their
flaring and CME activity. <P />The scientific program will begin
on Monday, October 31 at 9 AM, and conclude on Friday, November
4 at 1PM. Abstracts are solicited on the following topics: <P />-
"Local and Global Helioseismology" - "Large-Scale Dynamics, Magnetism
and Dynamo" - "Emerging Magnetic Flux and Subsurface Dynamics" -
"Formation, Structure and Evolution of Sunspots and Active Regions" -
"Numerical Simulations and Laboratory Experiments" - "Observations of
the Solar Dynamics and Magnetism" - "Links between the Solar Interior
and Atmosphere" - "Sources of Spectral and Total Irradiance Variations"
- "Dynamics and Magnetic Topology of Flares and CMEs" <P />The workshop
program will include invited and contributed talks, as well as poster
sessions. On the last day, 4 splinter working group meetings will be
organized: <P />1. Helioseismology (organizers R. Bogart, R. Komm,
A. Kosovichev) 2. Vector Magnetometry (organizer T. Hoeksema and
A. Pevtsov) 3. Feature Recognition, and Data Distribution and Access
(organizers P. Martens and N. Hurlburt) 4. Numerical Simulations and
Modeling (organizers N. Mansour and I. Kitiashvili)
---------------------------------------------------------
Title: An Error Analysis of Oscillations in Solar Polar Coronal
Hole Areas
Authors: Hess Webber, Shea A.; Pesnell, W. Dean; Karna, Nishu
2011shin.confE.169H Altcode:
The results obtained from our polar coronal hole (PCH) area analysis
of EUV images from the Extreme ultraviolet Imaging Telescope (EIT)
on SOHO show an annual periodicity propagating through the data
set. Investigations into the cause of this variability have been
inconclusive. However, the frequency of the oscillation suggests that
the uncertainty comes from orbital effects. We discuss the relevant
orbital variations of the SOHO spacecraft and analytically determine
the potential error due to those variations. These effects include the
variations in solar B0 and L0 angles within the working coordinate
system, and B0 projection effects of coronal material. Our goal in
conducting this error analysis is to gain a better understanding of how
SOHO's orbital variations affect the determination of solar coordinates,
particularly at the limb and poles. This work is supported by the
Solar Dynamics Observatory.
---------------------------------------------------------
Title: An Error Analysis of Oscillations in Solar Polar Coronal
Hole Areas
Authors: Hess Webber, Shea A.; Karna, Nishu; Pesnell, W. Dean
2011shin.confE...1H Altcode:
The results obtained from our polar coronal hole (PCH) area analysis
of EUV images from the Extreme ultraviolet Imaging Telescope (EIT)
on SOHO show an annual periodicity propagating through the data
set. Investigations into the cause of this variability have been
inconclusive. However, the frequency of the oscillation suggests that
the uncertainty comes from orbital effects. We discuss the relevant
orbital variations of the SOHO spacecraft and analytically determine
the potential error due to those variations. These effects include the
variations in solar B0 and L0 angles within the working coordinate
system, and B0 projection effects of coronal material. Our goal in
conducting this error analysis is to gain a better understanding of how
SOHO's orbital variations affect the determination of solar coordinates,
particularly at the limb and poles. This work is supported by the
Solar Dynamics Observatory.
---------------------------------------------------------
Title: The evolution of the Polar Coronal Hole During Solar Cycles
23 and 24
Authors: Karna, Nishu; Hess Webber, Shea A.; Pesnell, W. Dean; Kirk,
M. S.
2011shin.confE.168K Altcode:
Synoptic maps made from two instruments on SOHO are analyzed to track
the size of the solar polar coronal holes (PCH) over Solar Cycles
23 and 24. The first method uses 171 Å, 195 Å, and 304 Å synoptic
maps constructed from the Extreme-ultraviolet Imaging Telescope (EIT)
on SOHO for 145 Carrington Rotations from mid 1996 through mid 2007
from archive. After this time, we have created the synoptic maps for
42 Carrington Rotation to compare the fractional PCH area between two
solar minima and extending our time series up to 2010. Our second method
used line-of-sight magnetic field synoptic maps from SOHO's Michelson
Doppler Imager (MDI) instrument to estimate the polar coronal hole
area via polarity signatures for 187 Carrington Rotations from mid
1996 through 2010. There is a good correlation between the estimated
PCH extracted form EIT and MDI. This work was supported by the Solar
Dynamics Observatory.
---------------------------------------------------------
Title: Solar Polar Coronal Hole Areas Through the Past Solar Minimum
Authors: Hess Webber, Shea A.; Karna, Nishu; Pesnell, W. Dean; Kirk,
Michael S.
2011lws..workE...1H Altcode:
We have used the perimeter tracking algorithm and analysis of EIT
synoptic maps to extend our time series of polar coronal hole areas
through solar minimum (through 2010). Both algorithms use 171, 195,
and 304 Å images from the Extreme ultraviolet Imaging Telescope (EIT)
on SOHO, the first to measure the perimeter of polar coronal holes as
they appear on the limbs and the second the area of the polar coronal
hole during each Carrington rotation. Line-of-sight magnetic field
synoptic maps are also used to estimate the polar coronal hole area. We
have updated the time series and we are analyzing uncertainties in
EIT ephemeris data. We remain convinced that the northern polar hole
area is measurably smaller in the recent minimum than it was at the
beginning of cycle 23, while the southern polar hole area is roughly
the same. Polar hole areas found via perimeter tracking agree within
uncertainty with those determined using EIT synoptic map analysis.
---------------------------------------------------------
Title: Solar Polar Coronal Hole Areas Through the Past Solar Minimum
Authors: Hess Webber, Shea; Karna, N.; Pesnell, W. D.; Kirk, M.
2011SPD....42.1825H Altcode: 2011BAAS..43S.1825H
We have used the perimeter tracking algorithm and analysis of EIT
synoptic maps to extend our timeseries of polar coronal hole areas
through solar minimum (through 2010). Both algorithms use 171, 195,
and 304 Å images from the Extreme ultraviolet Imaging Telescope (EIT)
on SOHO, the first to measure the perimeter of polar coronal holes as
they appear on the limbs and the second the area of the polar coronal
hole during each Carrington rotation. Line-of-sight magnetic field
synoptic maps are also used to estimate the polar coronal hole area. We
have updated the time series and we are analyzing uncertainties in
EIT ephemeris data. We remain convinced that the northern polar hole
area is measurably smaller in the recent minimum than it was at the
beginning of cycle 23, while the southern polar hole area is roughly
the same. Polar hole areas found via perimeter tracking agree within
uncertainty with those determined using EIT synoptic map analysis. This
work was supported by the Solar Dynamics Observatory.
---------------------------------------------------------
Title: Time-Series Analysis of Supergranule Characteristics Derived
from SOHO/MDI Dopplergrams.
Authors: Williams, Peter E.; Pesnell, W. D.
2011SPD....42.1725W Altcode: 2011BAAS..43S.1725W
Supergranulation exhibits both radial and horizontal velocity
components within Doppler data. The weak, radial flows drag magnetic
field lines to the surface while their strong, divergent, horizontal
counterparts advect the field to the edges of the supergranulation
cells. Field congregation at supergranule boundaries is observed in
magnetic filed images and via Ca II K observations of the chromospheric
network. <P />Supergranulation characteristics, such as typical sizes
and velocities, have been studied using MDI Doppler data and tracked
over 60-days of observations made in 1996 and 2008, relating to periods
of solar minimum. Time-series of these characteristics exhibit regular
fluctuations on the order of 3-5 days. These time-series are analyzed
to extract frequency information and cross-correlated to investigate any
temporal link between the characteristics. <P />Whether the fluctuations
are an instrumental artifact is studied by comparing contemporaneous
time series produced from SOHO/MDI and SDO/HMI Dopplergrams. There
exists a high correlation between the two time-series showing that
the fluctuations are solar in origin.
---------------------------------------------------------
Title: Comparisons of Supergranule Characteristics During the Solar
Minima of Cycles 22/23 and 23/24
Authors: Williams, Peter E.; Pesnell, W. Dean
2011SoPh..270..125W Altcode: 2011SoPh..tmp...28W; 2011arXiv1103.1696W
Supergranulation is a component of solar convection that manifests
itself on the photosphere as a cellular network of around 35 Mm across,
with a turnover lifetime of 1 - 2 days. It is strongly linked to the
structure of the magnetic field. The horizontal, divergent flows within
supergranule cells carry local field lines to the cell boundaries, while
the rotational properties of supergranule upflows may contribute to the
restoration of the poloidal field as part of the dynamo mechanism, which
controls the solar cycle. The solar minimum at the transition from cycle
23 to 24 was notable for its low level of activity and its extended
length. It is of interest to study whether the convective phenomena
that influence the solar magnetic field during this time differed in
character from periods of previous minima. This study investigates
three characteristics (velocity components, sizes and lifetimes) of
solar supergranulation. Comparisons of these characteristics are made
between the minima of cycles 22/23 and 23/24 using MDI Doppler data from
1996 and 2008, respectively. It is found that whereas the lifetimes are
equal during both epochs (around 18 h), the sizes are larger in 1996
(35.9 ± 0.3 Mm) than in 2008 (35.0 ± 0.3 Mm), while the dominant
horizontal velocity flows are weaker (139 ± 1 m s<SUP>−1</SUP>
in 1996; 141 ± 1 m s<SUP>−1</SUP> in 2008). Although numerical
differences are seen, they are not conclusive proof of the most recent
minimum being inherently unusual.
---------------------------------------------------------
Title: Comparison of Vector Magnetograms from the Solenoidal and
Irrotational Components of the Magnetic Field
Authors: Bryans, Paul; Pesnell, W. D.
2011SPD....42.2108B Altcode: 2011BAAS..43S.2108B
According to the Helmholtz Theorem, the solar magnetic field can be
defined in terms of an irrotational and a solenoidal component. We will
discuss the partitioning of the field into these components as a means
of attributing elements of the magnetic field to its vorticity and
divergence. We will then discuss the advantages of this decomposition
as a metric for comparing vector magnetograms of varying spatial and
temporal resolution.
---------------------------------------------------------
Title: Properties of Supergranulation During the Solar Minima of
Cycles 22/23 and 23/24
Authors: Williams, Peter E.; Pesnell, W. Dean
2011JPhCS.271a2082W Altcode:
The solar minimum at the transition from cycle 23 to 24 was notable for
its low level of activity and its extended duration. Among the various
fields of study, the evolution of the solar convection zone may provide
insight into the causes and consequences of this recent minimum. This
study continues previous investigations of the characteristics of
solar supergranulation, a convection component strongly linked to the
structure of the magnetic field, namely the time-evolution of the global
mean of supergranule cell size, determined from spectral analysis of
MDI Dopplergrams from the two previous solar minima. Analyses of the
global mean of supergranule sizes show a quasi-oscillatory nature to the
evolution of this particular supergranule characteristic. Performing
similar analyses on realistic, synthetic Doppler images show similar
time-dependent characteristics. We conclude that the observed
fluctuations are not observational artifacts, and that an underlying
trend exists within the evolution of the supergranulation network.
---------------------------------------------------------
Title: Analysis of Photospheric Convection Cells with SDO/HMI
Authors: Williams, P. E.; Pesnell, W. D.
2010AGUFMSH14A..06W Altcode:
Supergranulation is a component of solar convection that assists in
the outward transportation of internal energy. Supergranule cells
are approximately 35 Mm across, have lifetimes on the order of a day
and have divergent horizontal velocities of around 300 m/s, a factor
of 10 higher than their central radial components. While they have
been observed using Doppler methods for around half a century, their
existence is also observed in other datasets such as magnetograms
and Ca II K images. These datasets clearly show the influence of
supergranulation on solar magnetism and how the local field is organized
by the flows of supergranule cells. The Heliospheric and Magnetic Imager
(HMI) aboard SDO is making fresh observations of convection phenomena
at a higher cadence and a higher resolution that should make granular
features visible. Granulation and supergranulation characteristics can
now be compared within the same datasets, which may lead to further
understanding of any mutual influences. The temporal and spatial
enhancements of HMI will also reduce the noise level within studies
of convection so that more detailed studies of their characteristics
may be made. We present analyses of SDO/HMI Dopplergrams that provide
new estimates of convection cell sizes, lifetimes, and velocity flows,
as well as the rotation rates of the convection patterns across the
solar disk. We make comparisons with previous data produced by MDI,
as well as from data simulations.
---------------------------------------------------------
Title: Comparisons of Supergranule Properties from SDO/HMI with
Other Datasets
Authors: Pesnell, W. D.; Williams, P. E.
2010AGUFMSH21C..02P Altcode:
While supergranules, a component of solar convection, have been well
studied through the use of Dopplergrams, other datasets also exhibit
these features. Quiet Sun magnetograms show local magnetic field
elements distributed around the boundaries of supergranule cells,
notably clustering at the common apex points of adjacent cells, while
more solid cellular features are seen near active regions. Ca II K
images are notable for exhibiting the chromospheric network representing
a cellular distribution of local magnetic field lines across the solar
disk that coincides with supergranulation boundaries. Measurements
at 304 Å further above the solar surface also show a similar pattern
to the chromospheric network, but the boundaries are more nebulous in
nature. While previous observations of these different solar features
were obtained with a variety of instruments, SDO provides a single
platform, from which the relevant data products at a high cadence and
high-definition image quality are delivered. The images may also be
cross-referenced due to their coincidental time of observation. We
present images of these different solar features from HMI & AIA
and use them to make composite images of supergranules at different
atmospheric layers in which they manifest. We also compare each data
product to equivalent data from previous observations, for example
HMI magnetograms with those from MDI.
---------------------------------------------------------
Title: “ALTITUDE Variation” of the CO2(V2)-O Quenching Rate
Coefficient in Mesosphere and Lower Thermosphere
Authors: Feofilov, A.; Kutepov, A.; She, C.; Smith, A. K.; Pesnell,
W. D.; Goldberg, R. A.
2010AGUFMSA52A..07F Altcode:
Among the processes governing the energy balance in the mesosphere and
lower thermosphere (MLT), the quenching of CO2(ν2) vibrational levels
by collisions with oxygen atoms plays an important role. However, the
k(CO2-O) values measured in the lab and retrieved from atmospheric
measurements vary from 1.5 x 10-12 cm3 s-1 through 9.0 x 10-12 cm3
s-1 that requires further studying. In this work we used synergistic
data from a ground based lidar and a satellite infrared radiometer
to estimate k(CO2-O). We used the night- and daytime temperatures
between 80 and 110 km measured by the Colorado State University
narrow-band sodium (Na) lidar located at Fort Collins, Colorado
(41N, 255E) as ground truth of the SABER/TIMED nearly simultaneous
(±10 minutes ) and common volume (within ±1 degree in latitude,
±2 degrees in longitude) observations. For each altitude in 80-110
km interval we estimate an “optimal” value of k(CO2-O) needed to
minimize the discrepancy between the simulated 15 μm CO2 radiance and
that measured by the SABER/TIMED instrument. The k(CO2-O) obtained in
this way varies in altitude from 3.5 x 10-12 cm3 s-1 at 80 km to 5.2
x 10-12 cm3 s-1 for altitudes above 95 km. We discuss this variation
of the rate constant and its impact on temperature retrievals from 15
μm radiance measurements and on the energy budget of MLT.
---------------------------------------------------------
Title: An Update of the Automatic Detection of Polar Coronal Holes
in the EUV
Authors: Hess Webber, Shea A.; Karna, Nishu; Pesnell, W. Dean; Kirk,
Michael S.
2010eddy.confE...1H Altcode:
An automated detection method of polar coronal holes was presented
by Kirk et al. in 2009. This method, called perimeter tracking, uses
a series of 171, 195, and 304 Å full disk images from the Extreme
ultraviolet Imaging Telescope (EIT) on SOHO to measure the perimeter
of polar coronal holes as they appear on the limbs. We have updated
the previous time series, which ranged from mid 1996 through 2007,
up to the most recently available EIT data in 2010, and refined the
detection parameters, adjusting them to fit the data more precisely
and accurately. Additionally, we increased our analysis to utilize
all available EIT images rather than one image per day in the previous
work. We find the wavelength average of the northern hole is about 5.5%
of the solar surface area while the southern hole average measures
about 4.5% during 1996 in the revised data set. These values are
somewhat larger then we previously reported due to the improvements in
the algorithm. We also find that in 2010, the northern and southern
hole areas are about 3.0% and 3.5% of the total solar surface,
respectively. The north and south polar hole areas are now noticeably
smaller in the recent minimum than they were at the beginning of cycle
23. This is especially true in the northern hemisphere. We will compare
these polar hole areas with the total coronal hole area found using
EIT synoptic maps over the same time series and wavelengths.
---------------------------------------------------------
Title: An Update of the Automatic Detection of Polar Coronal Holes
in the EUV
Authors: Hess Webber, Shea A.; Karna, Nishu; Pesnell, W. Dean; Kirk,
Michael S.
2010shin.confE...1H Altcode:
An automated detection method of polar coronal holes was presented
by Kirk et al. in 2009. This method, called perimeter tracking, uses
a series of 171, 195, and 304 Å full disk images from the Extreme
ultraviolet Imaging Telescope (EIT) on SOHO to measure the perimeter
of polar coronal holes as they appear on the limbs. We have updated
the previous time series, which ranged from mid 1996 through 2007,
up to the most recently available EIT data in 2010, and refined the
detection parameters, adjusting them to fit the data more precisely
and accurately. Additionally, we increased our analysis to utilize
all available EIT images rather than one image per day in the previous
work. We had observed the area of the northern polar hole in 1996, at
the beginning of solar cycle 23, to be about 4.2% of the total solar
surface area. The area of the southern polar hole was observed to be
about 4.0% in 1996. These numbers are slightly larger in the revised
data set, the northern hole at about 5.5% of the solar surface area in
1996 and the southern hole measuring about 4.5%. We further find that
in 2010, the northern and southern hole areas are about 2.8% and 3.0%
of the total solar surface, respectively. The north and south polar
hole areas are no more than 1/3 smaller now than they were at the
beginning of cycle 23. We will compare these polar hole areas with
the total coronal hole area found using EIT synoptic maps over the
same time series and wavelengths
---------------------------------------------------------
Title: Automated Detection of Polar Coronal Holes in EUV
Authors: Pesnell, W. Dean; Hess Webber, Shea A.; Karna, Nishu; Kirk,
Michael S.
2010shin.confE.158P Altcode:
Perimeter tracking is an automated detection method of polar coronal
holes that uses full-disk images to measure the perimeter of polar
coronal holes as they appear on the limbs. We applied this technique
to images at three wavelengths (171, 195, and 304 Å) from the
Extreme ultraviolet Imaging Telescope (EIT) on SOHO. We have updated
the previous time series to the most recently available EIT data in
2010, and refined the detection parameters, adjusting them to more
accurately fit the data. We also modified the analysis to use all
available EIT images rather than the one image per day used in the
previous work. With these changes, the northern polar hole area in the
304 channel is observed to be about 4.4% of the solar surface area in
the previous solar minimum (1996/1997) while the southern hole measures
about 4%. We also find that the northern polar hole reached a maximum
area of about 3.7% in 2007/2008 while the southern hole area reached
a maximum of about 4% in mid-2009. We will compare these polar hole
areas with the areas found using EIT synoptic maps over the same time
period and wavelengths.
---------------------------------------------------------
Title: Photospheric Manifestations of Supergranules during the Last
Two Solar Minima
Authors: Williams, P. E.; Pesnell, W. D.
2010ASPC..428..127W Altcode: 2010arXiv1004.0936W
Solar supergranulation plays an important role in generating
and structuring the solar magnetic field and as a mechanism
responsible for the 11-year solar cycle. It is clearly detected
within SOHO/MDI Dopplergrams, from which a variety of properties may
be derived. Techniques that extract spatial, temporal, and kinematic
characteristics and provide comparisons for the two most recent solar
minima are described. Although supergranule lifetimes are comparable
between these minima, their sizes may be slightly smaller during the
recent minimum.
---------------------------------------------------------
Title: Comparisons of Photospheric Convection Cell Characteristics
During the Solar Minima of Cycles 22-23 and 23-24
Authors: Williams, Peter E.; Pesnell, W. D.
2010AAS...21631702W Altcode: 2010BAAS...41..898W
With its elongated tail and extended periods of zero activity, the
period marking the transition from solar cycle 23 to 24 has seemed
peculiar when compared to other minima. Among the various phenomena
studied, the evolution of the solar convection zone may provide
insight into the causes and consequences of this recent minimum. <P
/>Convection in the Sun plays an important role in generating and
structuring the solar magnetic field and as a mechanism responsible
for the 11-year solar cycle. The observed phenomena are strongly
linked within both observational and physical regimes. <P />This study
uses SOHO/MDI Dopplergrams to highlight supergranulation within the
line-of-sight velocity data. Suites of analysis methods are applied to
time-series of Doppler images to quantitatively describe supergranule
flow velocities, spatial scales and temporal lifetimes. <P />The
results show similarities in supergranule evolution (1/e lifetimes
of 18 hours), while their sizes are smaller and their flows stronger
during the 23-24 minimum compared to 22-23. We also present provisional
results of statistical analyses performed both within and between
the various data sets, some of which tend to show a quasi-oscillatory
nature. <P />Future studies to place this work in the wider context of
the solar cycle are discussed, as a whole as well as investigations
of supergranule characteristics found in various other data such as
magnetograms and CaIIK images. Observed hemispheric asymmetries will be
presented and how our methods may be applied to further these enquiries.
---------------------------------------------------------
Title: The Solar Dynamics Observatory: Your eye on the Sun
Authors: Pesnell, William
2010cosp...38.4183P Altcode: 2010cosp.meet.4183P
The Solar Dynamics Observatory (SDO) was launched on February 11,
2010 into partly cloudy skies over Cape Canaveral, Florida. SDO has
since moved into a 28 degree inclined geosyn-chronous orbit over the
longitude of the ground station in New Mexico. SDO is the first Space
Weather Mission in NASA's Living With a Star Program. SDO's main goal
is to understand and predict those solar variations that influence life
on Earth and our technological systems. The SDO science investigations
will determine how the Sun's magnetic field is generated and structured,
how this stored magnetic energy is released into the heliosphere and
geospace as the solar wind, energetic particles, and variations in
the solar irradiance. The SDO mission consists of three scientific
investigations (AIA, EVE, and HMI), a spacecraft bus, and a ded-icated
Ka-band ground station to handle the 150 Mbps data flow. Science teams
at LMSAL, LASP, and Stanford are responsible for processing, analyzing,
distributing, and archiving the science data. We will talk about the
building of SDO, its launch, and the data and science it will provide
to NASA.
---------------------------------------------------------
Title: Conditions for PMC formation in 2002-2008 estimated from
TIMED/SABER measurements
Authors: Feofilov, Artem; Goldberg, Richard A.; Kutepov, Alexander;
Pesnell, William
2010cosp...38.1232F Altcode: 2010cosp.meet.1232F
In this work, mesospheric temperature, pressure, and water vapor
concentration measured by the Sounding of the Atmosphere using Broadband
Emission Radiometry (SABER) instrument on board the Thermosphere
Ionosphere Mesosphere Energetics and Dynamics (TIMED) satel-lite are
used to estimate the probability of the polar mesospheric ice clouds
(PMC) formation for the summer periods of 2002-2008. We show the
zonal averages of the PMC probability distri-butions and estimated
PMC heights for both hemispheres and compare them to ground-based and
satellite observations.
---------------------------------------------------------
Title: Recent STEREO Observations of Coronal Mass Ejections
Authors: St Cyr, O. C.; Xie, H.; Mays, M. L.; Davila, J. M.; Gilbert,
H. R.; Jones, S. I.; Pesnell, W. D.; Gopalswamy, N.; Gurman, J. B.;
Yashiro, S.; Wuelser, J.; Howard, R. A.; Thompson, B. J.; Thompson,
W. T.
2009AGUFMSH11A1491S Altcode:
Over 400 CMEs have been observed by STEREO SECCHI COR1 during
the mission's three year duration (2006-2009). Many of the solar
activity indicators have been at minimal values over this period,
and the Carrington rotation-averaged CME rate has been comparable to
that measured during the minima between Cycle 21-22 (SMM C/P) and
Cycle 22-23 (SOHO LASCO). That rate is about 0.5 CMEs/day. During
the current solar minimum (leading to Cycle 24), there have been
entire Carrington rotations where no sunspots were detected and the
daily values of the 2800 MHz solar flux remained below 70 sfu. CMEs
continued to be detected during these exceptionally quiet periods,
indicating that active regions are not necessary to the generation of
at least a portion of the CME population. In the past, researchers were
limited to a single view of the Sun and could conclude that activity
on the unseen portion of the disk might be associated with CMEs. But
as the STEREO mission has progressed we have been able to observe an
increasing fraction of the Sun's corona with STEREO SECCHI EUVI and
were able to eliminate this possibility. Here we report on the nature
of CMEs detected during these exceptionally-quiet periods, and we
speculate on how the corona remains dynamic during such conditions.
---------------------------------------------------------
Title: Comparisons of Photospheric Convection Cell Characteristics
Authors: Pesnell, W. D.; Wiliams, P. E.
2009AGUFMSH11A1500P Altcode:
Solar convection plays an important role in generating and structuring
the solar magnetic field as well as a mechanism responsible for
the 11-year solar cycle. The observed phenomena are strongly linked
within both observational and physical regimes. Our main focus is
the study of supergranulation from SOHO/MDI Dopplergrams. Suites
of analysis methods are applied to time-series of Doppler images to
quantitatively describe supergranule flow velocities, spatial scales
and temporal lifetimes. SOHO/MDI magnetograms also show cellular
structures, which trace the clustering of magnetic field lines around
supergranule boundaries. These boundaries are extrapolated into the
chromosphere where they are observed as a cellular network. We present
preliminary results of applying methods similar to those applied to the
Dopplergrams for estimating the spatial and temporal characteristics
of this network. We extend our study to above the photosphere to the
chromosphere where another cellular network is seen. Once again the
responsibility lies with supergranulation. Spatial analysis on CaIIK
data from the Precision Solar Photometric Telescope (PSPT) provides
typical size scales for the network that can be compared to both the
magnetogram network and supergranulation itself. Data comparisons
over time can be made, notably between Doppler data received
during the current (2008) and previous (1996) solar minima. Our
provisional findings show that horizontal and radial velocity
flows within supergranules are stronger during the current minimum,
while the supergranules themselves appear larger during the previous
minimum. However, comparable results are found for the 1/e lifetimes
derived from each data set. We extend these provisional results by
performing statistical analyses both within and between the various
data sets.
---------------------------------------------------------
Title: CO2(ν2)-O Quenching Rate Coefficient Derived From Coincidental
Fort Collins Lidar and SABER Measurements
Authors: Feofilov, A.; Kutepov, A.; She, C.; Smith, A. K.; Pesnell,
W. D.; Goldberg, R. A.
2009AGUFMSA53A1238F Altcode:
Among the processes governing the energy balance in the mesosphere and
lower thermosphere (MLT), the quenching of CO2(ν2) vibrational levels
in collisions with oxygen atoms plays an important role. However,
neither the rate coefficient of this process (k(CO2-O)) nor the
atomic oxygen concentrations ([O]) in the MLT are well known. The
discrepancy between k(CO2-O) measured in the lab and retrieved from
atmospheric measurements is of about factor of 2.5. At the same
time, the discrepancy between [O] in the MLT measured by different
instruments is of the same order of magnitude. In this work we combine
temperature data from a ground based lidar with limb radiances from
a satellite infrared radiometer to estimate k(CO2-O). We used the
night- and daytime temperatures between 80 and 110 km measured by the
Colorado State University narrow-band sodium (Na) lidar located at
Fort Collins, Colorado (41N, 255E) as ground truth of the SABER/TIMED
nearly simultaneous (±10 minutes ) and common volume (within ±1 degree
in latitude, ±2 degrees in longitude) observations. We used ALI-ARMS
non-LTE research code designed to calculate the non-equilibrium radiance
in planetary atmospheres to retrieve the product of k(CO2-O) x [O] from
15 μm CO2 limb radiance measured by SABER. The values retrieved for
all overlapping measurements were then used to estimate the k(CO2-O)
rate coefficient and its possible variation range by utilizing the
[O] values measured by the SABER and other instruments.
---------------------------------------------------------
Title: What is an Extreme Solar Minimum?
Authors: Pesnell, William Dean
2009shin.confE.143P Altcode:
The study of solar minimum has been a poor cousin to solar maximum
due to the large variations seen in the Sun during maximum. Solar
activity is low or absent during solar minimum and all of the phenomena
that follow the sunspot number are also smaller in frequency and
strength. Even the definition of solar minimum is difficult because
the main indicator of solar activity is zero for an extended period of
time. But the Sun presents a different face at minimum. The magnetic
field is weaker but far more symmetric, almost a dipole for the few
minimum that have been measured. A similar behavior is seen in the
corona measured by coronagraphs and magnetic fields measured in the
heliosphere. Particle fluxes in the solar wind are smaller. As a result
the scattering of galactic cosmic rays is reduced and a larger flux of
GCRs is be seen at Earth. The current solar minimum has been extreme in
having weaker surface fields than previous measurements, few spots for
longer than average, and an interesting signature in Earth's magnetic
field. We shall discuss these magnetic signatures and the implications
for Space Weather and climate of a time with weak solar activity.
---------------------------------------------------------
Title: Automated detection of EUV Polar Coronal Holes during Solar
Cycle 23
Authors: Kirk, M. S.; Pesnell, W. D.; Young, C. A.; Hess Webber, S. A.
2009SoPh..257...99K Altcode: 2009arXiv0901.1158K
A new method for automated detection of polar coronal holes is
presented. This method, called perimeter tracing, uses a series of
171, 195, and 304 Å full disk images from the Extreme ultraviolet
Imaging Telescope (EIT) on SOHO over solar cycle 23 to measure the
perimeter of polar coronal holes as they appear on the limbs. Perimeter
tracing minimizes line-of-sight obscurations caused by the emitting
plasma of the various wavelengths by taking measurements at the solar
limb. Perimeter tracing also allows for the polar rotation period to
emerge organically from the data as 33 days. We have called this the
Harvey rotation rate and count Harvey rotations starting 4 January
1900. From the measured perimeter, we are then able to fit a curve to
the data and derive an area within the line of best fit. We observe
the area of the northern polar hole area in 1996, at the beginning of
solar cycle 23, to be about 4.2% of the total solar surface area and
about 3.6% in 2007. The area of the southern polar hole is observed
to be about 4.0% in 1996 and about 3.4% in 2007. Thus, both the north
and south polar hole areas are no more than 15% smaller now than they
were at the beginning of cycle 23. This compares to the polar magnetic
field measured to be about 40% less now than it was a cycle ago.
---------------------------------------------------------
Title: Automated Detection of Polar Coronal Holes in the EUV
Authors: Kirk, Michael S.; Pesnell, W. D.
2009SPD....40.1407K Altcode:
A new method for automatically detecting and measuring Polar Coronal
Holes in the EUV is presented. We use a series of full solar disk
images over solar cycle 23 to measure the perimeter of polar coronal
holes as they appear on the limbs. This method utilizes 171, 195,
and 304 Å solar images from the Extreme ultraviolet Imaging Telescope
(EIT) on SOHO. We are able to more accurately define the size and shape
of the polar hole by taking measurements on the limb and making two
measurements per image rather than the one used to construct synoptic
maps. This method also minimizes line-of-sight obscurations caused
by the emitting plasma of the various wavelengths. Perimeter tracking
allows for the polar coronal rotation period to emerge organically from
the data as 33 days. We have called this the Harvey Rotation rate and
count Harvey Rotations starting January 4, 1900. From the measured
perimeter we are then able to fit a curve to the data and derive an
area within the line of best fit. This method can be adapted to work
with any extended data set of full disk solar images. Extending our
data set to past NSO full disk spectroheliograms creates a base line
of more than three solar cycles. In the future, SDO images will be
added to further expand polar hole measurements.
---------------------------------------------------------
Title: Predicting Solar Cycle 24 With Geomagnetic Precursors
Authors: Pesnell, W. Dean
2009SPD....40.1105P Altcode:
We describe using a geomagnetic precursor to predict the amplitude of
the upcoming solar cycle. The amplitude prediction for Solar Cycle 24
is 65 +/- 20 in smoothed sunspot number, indicating a below-average
amplitude for Solar Cycle 24. Four precursor peaks are seen in the
decline of Solar Cycle 23. The earliest is the most prominent but
coincides with large levels of non-recurrent geomagnetic activity
associated with the Halloween storms. The second and third peaks are
for smaller amplitudes and show that a weak cycle precursor closely
following a period of strong solar activity may be difficult to
resolve. A fourth peak, in early 2008, which has recurrent activity
similar to precursors of earlier solar cycles and appears to be the
“true" precursor peak for Solar Cycle 24, predicts the smallest
amplitude for Solar Cycle 24. Several effects contribute to the
smaller prediction when compared to other geomagnetic precursor
predictions. During Solar Cycle 23 the correlation between sunspot
number and F10.7 shows that F10.7 is greater than the equivalent
sunspot number over most of the cycle, implying the sunspot
number underestimates the solar activity component. During 2003 the
correlation between aa and Ap shows that aa is much greater than the
value predicted from Ap, leading to an overestimate of the aa precursor
for that year. But the most important effect is the lack of recurrent
geomagnetic activity until 2008. We conclude that Solar Cycle 24 will
be no stronger than average and could be much weaker than average.
---------------------------------------------------------
Title: Analysis of Photospheric Convection Flows Over a Solar Cycle
Authors: Williams, Peter E.; Pesnell, W. D.
2009SPD....40.0919W Altcode:
Convection in the Sun plays an important role as a mechanism
responsible for the 11-year solar cycle. Magnetic field phenomena
are thus inextricably linked to the convective process, an example
being the gathering of magnetic field lines around supergranule
boundaries observed as the chromospheric network. <P />Our research
asks to what extent variations in the global magnetic field affect
particular characteristics of photospheric convection features,
using Dopplergrams derived from SOHO/MDI data during the course of
Solar Cycle 23. <P />We look ahead to the higher resolution data that
SDO/HMI will provide and any further insight such data may provide.
---------------------------------------------------------
Title: Temperature Trends in the Polar Mesosphere between 2002--2007
using TIMED/SABER Data
Authors: Goldberg, R. A.; Feofilov, A. G.; Kutepov, A. A.; Pesnell,
W. D.; Latteck, R.; Russell, J. M.
2008AGUFMSA43A1574G Altcode:
The TIMED Satellite was launched on December 7, 2001 to study the
dynamics and energy of the mesosphere and lower thermosphere. The
TIMED/SABER instrument is a limb scanning infrared radiometer designed
to measure a large number of minor constituents as well as the
temperature of the region. In this study, we have concentrated on the
polar mesosphere, to investigate the temperature characteristics as a
function of spatial and temporal considerations. We used the recently
revised SABER dataset (1.07) that contains improved temperature
retrievals in the Earth polar summer regions. Weekly averages are
used to make comparisons between the winter and summer, as well as to
study the variability in different quadrants of each hemisphere. For
each year studied, the duration of polar summer based on temperature
measurements compares favorably with the PMSE (Polar Mesospheric Summer
Echoes) season measured by radar at the ALOMAR Observatory in Norway
(69°N). The PMSE period should also define the summer period suitable
for the occurrence of polar mesospheric clouds. The unusual short and
relatively warm polar summer in the northern hemisphere during 2002
is also clearly defined in this analysis and shown to be unique for
the period analyzed.
---------------------------------------------------------
Title: Temperature and water vapor measured by SABER/TIMED and
implications for mesospheric ice clouds
Authors: Feofilov, A. G.; Kutepov, A. A.; Marshall, B. T.; Pesnell,
W. D.; Goldberg, R. A.; Gordley, L. L.; Russell, J. M.
2008AGUFMSA43A1575F Altcode:
The SABER instrument on board the TIMED Satellite is a limb
scanning infrared radiometer designed to measure temperature and
minor constituent vertical profiles and energetics parameters in
the mesosphere and lower thermosphere. We applied an updated non-LTE
model for the interpretation of the 6.3 micron H2O radiance measured
by SABER. The obtained meridional and seasonal distributions of the
H2O density in the mesosphere are discussed. The conditions for the
mesospheric ice particle formation are estimated using the combination
of SABER H2O and temperature (V1.07) profiles.
---------------------------------------------------------
Title: Recent studies of the behavior of the Sun's white-light corona
over time
Authors: St. Cyr, O. C.; Young, D.; Pesnell, W. D.; Lecinski, A.;
Eddy, J.
2008AGUFMSH44A..06S Altcode:
Predictions of upcoming solar cycles are often related to the nature
and dynamics of the Sun's polar magnetic field and its influence on
the corona. For the past 30 years we have a more-or-less continuous
record of the Sun's white-light corona from groundbased and spacebased
coronagraphs. Over that interval, the large scale features of the corona
have varied in what we now consider a "predictable" fashion--complex,
showing multiple streamers at all latitudes during solar activity
maximum; and a simple dipolar shape aligned with the rotational pole
during solar minimum. Over the past three decades the white-light
corona appears to be a better indicator of "true" solar minimum than
sunspot number since sunspots disappear for months (even years) at
solar minimum. Since almost all predictions of the timing of the next
solar maximum depend on the timing of solar minimum, the white-light
corona is a potentially important observational discriminator for future
predictors. In this contribution we describe recent work quantifying
the large-scale appearance of the Sun's corona to correlate it with
the sunspot record, especially around solar minimum. These three
decades can be expanded with the HAO archive of eclipse photographs
which, although sparse compared to the coronagraphic coverage, extends
back to 1869. A more extensive understanding of this proxy would give
researchers confidence in using the white-light corona as an indicator
of solar minimum conditions.
---------------------------------------------------------
Title: Predictions of Solar Cycle 24
Authors: Pesnell, William Dean
2008SoPh..252..209P Altcode: 2008SoPh..tmp..152P
A summary and analysis of more than 50 predictions of the amplitude
of the upcoming Solar Cycle 24 is presented. All of the predictions
were published before solar minimum and represent our efforts to
anticipate solar maximum at ever-earlier epochs. The consistency of the
predictions within their assigned categories is discussed. Estimates
of the significance of the predictions, compared to the climatological
average, are presented.
---------------------------------------------------------
Title: SABER/TIMED Mesospheric Water Vapor and Temperature
Authors: Feofilov, A. G.; Kutepov, A. A.; GarciA-Comas, M.;
Lopez-Puertas, M.; Marshall, B. T.; Gordley, L. L.; Manuilova, R. O.;
Yankovsky, V. A.; Pesnell, W. D.; Goldberg, R. A.; Petelina, S.;
Russell, J. M.
2008AGUSMSA41D..09F Altcode:
Low temperatures and abundant water vapor are the necessary components
for the mesospheric water ice forming. The SABER instrument on board
the TIMED Satellite is a limb scanning infrared radiometer designed
to measure temperature and minor constituent vertical profiles and
energetics parameters in the mesosphere and lower thermosphere. This
paper describes the methodology of the water vapor retrieval from the
broadband 6.3μm non-LTE emissions and discusses some aspects of the
temperature retrieval from the 15μm non-LTE CO2 emissions measured
by SABER. The non-LTE models of H2O and CO2 are validated using
the comparisons with the ACE-FTS occultation measurement and lidar
temperature measurements, respectively. The seasonal and latitudinal
distributions of water vapor and temperatures retrieved from the
SABER measurements are shown and the conditions for ice clouds forming
are discussed.
---------------------------------------------------------
Title: Seasonal variations of magnesium atoms in the
mesosphere-thermosphere
Authors: Correira, J.; Aikin, A. C.; Grebowsky, J. M.; Pesnell, W. D.;
Burrows, J. P.
2008GeoRL..35.6103C Altcode:
UV radiances from the Global Ozone Monitoring Experiment (GOME)
spectrometer on the ERS-2 satellite are used to determine long-term
dayside temporal variations of the total vertical column density below
795 km of the meteoric metal species Mg and Mg<SUP>+</SUP> in the upper
atmosphere. The GOME instrument has the ability to observe the ground
state transition lines of Mg I at 285.2 nm and resolve the Mg II at
280 nm. A retrieval algorithm has been developed to determine column
densities and applied to the years 1996-1997. Results show the middle
latitude dayside Mg<SUP>+</SUP> peaks in total vertical content during
the summer, while neutral Mg demonstrates a much more subtle maximum
in summer. Dayside trends are opposite previous midlatitude nighttime
lidar observations, with the exception of calcium. The Mg<SUP>+</SUP>/Mg
ratio has a seasonal variation, reaching a maximum in the summer. The
total content of Mg<SUP>+</SUP> is twice that of neutral Mg.
---------------------------------------------------------
Title: The Solar Dynamics Observatory: Your eye on the Sun
Authors: Pesnell, William
2008cosp...37.2412P Altcode: 2008cosp.meet.2412P
The Sun hiccups and satellites die. That is what NASA's Living With a
Star Program is all about. The Solar Dynamics Observatory (SDO) is the
first Space Weather Mission in LWS. SDO's main goal is to understand,
driving towards a predictive capability, those solar variations that
influence life on Earth and humanity's technological systems. The past
decade has seen an increasing emphasis on understanding the entire Sun,
from the nuclear reactions at the core to the development and loss of
magnetic loops in the corona. SDO's three science investigations (HMI,
AIA, and EVE) will determine how the Sun's magnetic field is generated
and structured, how this stored magnetic energy is released into the
heliosphere and geospace as the solar wind, energetic particles,
and variations in the solar irradiance. SDO will return fulldisk
Dopplergrams, full-disk vector magnetograms, full-disk images at seven
EUV wavelengths, and EUV spectral irradiances, all taken at a rapid
cadence. This means you can "observe the database" to study events,
but we can also move forward in producing quantitative models of what
the Sun is doing today. SDO is scheduled to launch in 2008 on an Atlas
V rocket from the Kennedy Space Center, Cape Canaveral, Florida. The
satellite will fly in a 28 degree inclined geosynchronous orbit about
the longitude of New Mexico, where a dedicated Ka-band ground station
will receive the 150 Mbps data flow. How SDO data will transform
the study of the Sun and its affect on Space Weather studies will
be discussed.
---------------------------------------------------------
Title: Chromospheric Lines as Diagnostics of Stellar Oscillations
Authors: Paulson, Diane B.; Pesnell, W. Dean; Deming, L. Drake; Snow,
Martin; Metcalfe, Travis S.; Woods, Tom; Hesman, Brigette
2008psa..conf..311P Altcode:
Gravitational waves in the chromosphere, theorized as early as
1963 [10], are thoroughly explored in the more recent papers by
[7, 8]. Theory predicts that the convective overshoot in the upper
photosphere and low chromosphere will readily excite gravity waves. [9]
note that these waves are not easily detected because of the long
periods, short wavelengths required and slanted propagation angles of
the waves themselves (causing small velocity shifts and short duration
on individual detector pixels). Recently, [9] find evidence for gravity
waves manifested in the f 700Å chromospheric line with frequencies
<1 mHz.
---------------------------------------------------------
Title: SDO in Virtual Reality: A New Spacecraft Interactive
Authors: Drobnes, Emilie; Pesnell, W. D.
2007AAS...211.9408D Altcode: 2007BAAS...39..893D
Have you ever dreamed of rocketing into space as an astronaut? Or
wished you could just float out among the stars and satellites? Well,
now you can! With the new Solar Dynamics Observatory (SDO) Spacecraft
Interactive you can spin, rotate, and explore the various parts of a
spacecraft as if you were in space, without leaving the comforts and
gravity of our home planet. This new and innovative interactive is a
great cross-cutting tool with applications from project management to
Education and Public Outreach (EPO). The current model allows users
to explore the spacecraft and all of its various components creating
a user-unique experience. When adapted to an immersive technology
environment, users will be able to experience this exploration as if
actually floating in space with the star field projected all around
you. In either form, this interactive could also be used by program
managers to navigate a photograph and video archive.
---------------------------------------------------------
Title: Variability of Solar Irradiances Using Wavelet Analysis
Authors: Pesnell, W. D.
2007AGUFMSH13A1100P Altcode:
We have used wavelets to analyze the sunspot number, F10.7 (the solar
irradiance at a wavelength of 10.7~cm), and Ap (a geomagnetic activity
index). Three different wavelets are compared, showing how each selects
either temporal or scale resolution. Our goal is an envelope of solar
activity that better bounds the large amplitude fluctuations form solar
minimum to maximum. We show how the 11-year cycle does not disappear
at solar minimum, that minimum is only the other part of the solar
cycle. Power in the fluctuations of solar-activity-related indices
may peak during solar maximum but the solar cycle itself is always
present. The Ap index has a peak after solar maximum that appears
to be better correlated with the current solar cycle than with the
following cycle.
---------------------------------------------------------
Title: Self-consistent Non-LTE Model of Infrared Molecular Emissions
and Oxygen Dayglows in the Mesosphere and Lower Thermosphere
Authors: Kutepov, A. A.; Feofilov, A. G.; Yankovsky, V. A.; Manuilova,
R. O.; Pesnell, W. D.; Goldberg, R. A.
2007AGUFMSA41A0293K Altcode:
We describe the new version of the ALI-ARMS (for Accelerated
Lambda Iterations for Atmospheric Radiation and Molecular Spectra)
model. The model allows simultaneous, self-consistent calculations
of the non-LTE populations of the electronic- vibrational levels of
ozone and O2 photolysis products and the vibrational level populations
of CO2, N2, O2, O3, H2O, CO, and other molecules with a detailed
accounting of electronic-vibrational, vibrational-vibrational and
vibrational-translational energy exchange processes. The model
is used as the reference for modeling O2 dayglow experiments and
for the infrared molecular emissions measured by the multi-channel
observations of MLT in the SABER experiment on TIMED. It also permits
the re-evaluation of the thermalization efficiency of absorbed solar
ultraviolet energy and infrared radiative cooling/heating of MLT
through a detailed accounting of the electronic-vibrational relaxation
of excited photolysis products via a complex chain of collisional energy
conversion processes down to the vibrational energy of optically active
trace gas molecules.
---------------------------------------------------------
Title: Mesospheric Water Vapor Retrieved From SABER/TIMED Measurements
Authors: Feofilov, A. G.; Marshall, B. T.; Garci-A-Comas, M.; Kutepov,
A. A.; Lopez-Puertas, M.; Manuilova, R. O.; Yankovsky, V. A.; Pesnell,
W. D.; Goldberg, R. A.; Gordley, L. L.; Petelina, S.; Russell, J. M.
2007AGUFMSA41A0291F Altcode:
The SABER instrument on board the TIMED Satellite is a limb
scanning infrared radiometer designed to measure temperature and
minor constituent vertical profiles and energetics parameters in
the mesosphere and lower thermosphere (MLT). The H2O concentrations
are retrieved from 6.3 micron band radiances. The interpretation of
this radiance requires developing a non-LTE H2O model that includes
energy exchange processes with the system of O3 and O2 vibrational
levels populated at the daytime through a number of photoabsorption
and photodissociation processes. We developed a research model based
on an extended H2O non-LTE model of Manuilova et al, 2001 coupled
with the novel model of the electronic-vibrational kinetics of the
O2 and O3 photolysis products suggested by Yankovsky and Manuilova,
2006. The performed study of this model helped us to develop and test
an optimized operational model for interpretation of SABER 6.3 micron
band radiances. The sensitivity of retrievals to the parameters of
the model is discussed. The H2O retrievals are compared to other
measurements for different seasons and locations.
---------------------------------------------------------
Title: Methods of Detecting Polar Coronal Holes in the EUV
Authors: Kirk, M. S.; Pesnell, W. D.
2007AGUFMSH13A1099K Altcode:
One method of forecasting the peak amplitude of future solar cycles uses
the polar magnetic field strength at solar minimum to predict the value
of the upcoming maximum. Because the polar field is closely related to
the polar coronal hole, we would like to consider the size and shape
of the polar hole on the prediction. We measure the perimeter of polar
coronal holes over solar cycle 23 as they appear on the limb of the
sun in 171, 195, and 304 Å\ solar images from the Extreme ultraviolet
Imaging Telescope (EIT) on SOHO. The area within the perimeter can
easily be determined. Taking measurements on the limb minimizes the
effects of differences in scale height between the material emitting
the various wavelengths. Perimeter tracking also allows for the coronal
rotation rate to emerge organically from the data rather than forcing
a period on the data. This method should help to improve our estimates
of the size and shape of the polar coronal holes.
---------------------------------------------------------
Title: Getting Something from Nothing: Polar Coronal Holes in Cycles
22 and 23
Authors: Hess Webber, Shea A.; Kirk, Michael S.; Pesnell, W. Dean
2007fste.conf...38H Altcode:
Methods of predicting the peak amplitude of solar cycles currently
disagree as to whether Solar Cycle 24 will have a high or low level
activity. One method uses the polar magnetic field lines at minimum
to predict the value of the upcoming maximum. Because it uses the
polar field, we would like to assess the impact of the size and
shape of the polar coronal hole on the prediction. We will measure
the area of the polar coronal holes during solar cycles 22 and 23
by measuring the opening angle of the hole as it appears on the limb
of the sun. A correlation of coronal hole parameters from Kitt Peak
10,830Å solar images with 171, 195, and 304Å solar images from the
Extreme ultraviolet Imaging Telescope (EIT) on the SoHO satellite taken
during the ascending phase of Solar Cycle 23 will be used to produce
a continuous set of coronal holes during Cycles 22 and 23. This will
also provide a smooth transition between the current EIT images and the
Kitt Peak data. Using multiple wavelengths will allow a more consistent
definition of the boundaries of the polar coronal holes. To accomplish
these tasks, an automatic detection method is employed. This method
should help to refine our understanding of the polar field precursor
of solar activity.
---------------------------------------------------------
Title: SDO Asks: What's The Sun Doing Now?
Authors: Pesnell, W. D.
2007AAS...21010101P Altcode: 2007BAAS...39..228P
Solar observations have tended to emphasize events like flares and
CMEs, and what leads to these events. The past decade has seen an
increasing emphasis on understanding the entire Sun, from the nuclear
reactions at the core to the development and loss of magnetic loops
in the corona. The Solar Dynamics Observatory (SDO) will return
synoptic data, taken at a regular cadence and covering the entire
Sun. This means you can still study events, but can also move forward
to producing a quantitative model of what the Sun is doing today. The
science investigations of SDO will determine how the Sun's magnetic
field is generated and structured, how this stored magnetic energy is
released into the heliosphere and geospace as the solar wind, energetic
particles, and variations in the solar irradiance. How SDO data will
transform the study of the Sun and the affect on stellar astrophysics
will be discussed.
---------------------------------------------------------
Title: Solar Cycle 24 and the Solar Dynamo
Authors: Pesnell, W. D.; Schatten, K.
2007AAS...210.9204P Altcode: 2007BAAS...39..209P
We will discuss the polar field precursor method for solar activity
prediction, which predicts cycle 24 will be significantly lower than
recent activity cycles, and some new ideas rejuvenating Babcock's
shallow surface dynamo. The polar field precursor method is based on
Babcock and Leighton's dynamo models wherein the polar field at solar
minimum plays a major role in generating the next cycle's toroidal field
and sunspots. Thus, by examining the polar fields of the Sun near solar
minimum, a forecast for the next cycle's activity is obtained. With
the current low value for the Sun's polar fields, this method predicts
solar cycle 24 will be one of the lowest in recent times, with smoothed
F10.7 radio flux values peaking near 135 ± 35 (2 σ), in the 2012-2013
timeframe (equivalent to smoothed Rz near 80 ± 35 [2 σ]). One may
have to consider solar activity as far back as the early 20th century
to find a cycle of comparable magnitude. We discuss unusual behavior
in the Sun's polar fields that support this prediction. Normally, the
solar precursor method is consistent with the geomagnetic precursor
method, wherein geomagnetic variations are thought to be a good measure
of the Sun's polar field strength. Because of the unusual polar field,
the Earth does not appear to be currently bathed in the Sun's extended
polar field (the interplanetary field), hence negating the primal
cause behind the geomagnetic precursor technique. We also discuss how
percolation may support Babcock's original shallow solar dynamo. In
this process ephemeral regions from the solar magnetic carpet, guided
by shallow surface fields, may collect to form pores and sunspots.
---------------------------------------------------------
Title: Family Science Night: Changing Perceptions One Family at a Time
Authors: Pesnell, W. D.; Drobnes, E.; Mitchell, S.; Colina-Trujillo, M.
2007AAS...210.0503P Altcode: 2007BAAS...39Q.100P
If students are not encouraged to succeed in science, mathematics,
and technology classes at school, efforts to improve the quality of
content and teaching in these subjects may be futile. Parents and
families are in a unique position to encourage children to enroll and
achieve in these classes. The NASA Goddard Space Flight Center Family
Science Night program invites middle school students and their families
to explore the importance of science and technology in our daily lives
by providing a venue for families to comfortably engage in learning
activities that change their perception and understanding of science
- making it more practical and approachable for participants of all
ages. Family Science Night strives to change the way that students and
their families participate in science, within the program and beyond.
---------------------------------------------------------
Title: The Polar Summer MLT Plasma Environment as Seen by the DROPPS
Sounding Rockets
Authors: Assis, M. P.; Goldberg, R. A.; Webb, P. A.; Pesnell, W. D.;
Voss, H. D.
2006AGUFMSA21A0240A Altcode:
During early July, 1999, the DROPPS (Distribution and Role of Particles
in the Polar Summer Mesosphere) campaign launched two rocket payloads
whose purpose was to study the polar summer MLT (mesosphere and lower
thermosphere), particularly PMSEs (polar mesospheric summer echoes)
and PMCs (polar mesospheric clouds). The rockets were launched from
the Andøya Rocket Range in Norway the nights of the 5th and 14th
of July. Both payloads included a front-mounted PID (Particle Impact
Detector) consisting of charge and mass telescopes to measure aerosol
and dust mass distributions. Ice particles of nanometer size are
believed to be responsible for PMSEs through the process of electron
scavenging. Evidence for this process is suggested, for example,
by the presence of an electron "biteout" simultaneously measured by
several instruments at an altitude of ~82-87 km during the first
DROPPS launch. This presentation will characterize similarities
and differences between both flights as seen by the charge and mass
telescopes, starting at launch until the loss of data on the downleg
of each flight. Various stages of the flights will be considered in
detail, such as the PMSE layer and the apogee at 117 km, as well as
the calibration of the data before launch.
---------------------------------------------------------
Title: Revised correlation between Odin/OSIRIS PMC properties and
coincident TIMED/SABER mesospheric temperatures
Authors: Feofilov, A.; Petelina, S. V.; Kutepov, A. A.; Pesnell,
W. D.; Goldberg, R. A.; Llewellyn, E. J.; Russell, J. M.
2006AGUFMSA21A0243F Altcode:
The Optical Spectrograph and Infrared Imaging System (OSIRIS) instrument
on board the Odin satellite detects Polar Mesospheric Clouds (PMCs)
through the enhancement in the limb-scattered solar radiance. The
Sounding of the Atmosphere using the Broadband Emission Radiometry
(SABER) instrument on board the TIMED satellite is a limb scanning
infrared radiometer that measures temperature and vertical profiles
and energetic parameters for minor constituents in the mesosphere
and lower thermosphere. The combination of OSIRIS and SABER data
has been previously used to statistically derive thermal conditions
for PMC existence [Petelina et al., 2005]. In this work, we employ
the simultaneous common volume measurements of PMCs by OSIRIS and
temperature profiles measured by SABER for the Northern Hemisphere
summers of 2002--2005 and corrected in the polar region by accounting
for the vibrational-vibrational energy exchange among the CO2 isotopes
[Kutepov et al., 2006]. For each coincidence identified within ±1
degree latitude, ±2 degrees longitude and ≤1 hour time the frost
point temperatures were calculated using the corresponding SABER
temperature profile and water vapor densities of 1, 3, and 10 ppmv. We
found that the PMC presence and brightness correlated only with
the temperature threshold that corresponds to the frost point. The
absolute value of the temperature below the frost point, however,
didn't play a significant role in the intensity of PMC signal for the
majority of selected coincidences. The presence of several bright
clouds at temperatures above the frost point is obviously related
to the limitation of the limb geometry when some near- or far-field
PMCs, actually located at higher (and colder) altitudes are detected
at lower altitudes. S.V. Petelina, D.A. Degenstein, E.J. Llewellyn,
N.D. Lloyd, C.J. Mertens, M.G. Mlynczak, and J.M. Russell III, "Thermal
conditions for PMC existence derived from Odin/OSIRIS and TIMED/SABER
data", Geophys. Res. Lett., 32, L17813, doi: 10.1029/2005GL023099,
(2005) A.A. Kutepov, A.G. Feofilov, B.T. Marshall, L.L. Gordley,
W. D. Pesnell, R.A. Goldberg, and J.M. Russell III, "SABER temperature
observations in the summer polar mesosphere and lower thermosphere:
importance of accounting for the CO2 ν_2 quanta V -V exchange",
accepted for publication in Geophys. Res. Lett., (2006)
---------------------------------------------------------
Title: Sources, Propagators, and Sinks of Space Weather
Authors: Pesnell, W. D.
2006AGUFMSA53A1371P Altcode:
Space Weather is a complex web of sources, propagators, and sinks of
energy, mass, and momentum. A complete understanding of Space Weather
requires specifying, and an ability to predict, each link in this
web. One important problem in Space Weather is ranking the importance of
a particular measurement or model in a research program. One way to do
this ranking is to examine the simplest linked diagram of the sources,
propagators, and sinks and produce. By analyzing only those components
that contribute to a particular area the individual contributions can
be better appreciated. Several such diagrams will be shown and used
to discuss how long-term effects of Space Weather can be separated
from the impulsive effects.
---------------------------------------------------------
Title: SABER temperature observations in the summer polar
mesosphere and lower thermosphere: Importance of accounting for the
CO<SUB>2</SUB> ν<SUB>2</SUB> quanta V-V exchange
Authors: Kutepov, Alexander A.; Feofilov, Artem G.; Marshall, Benjamin
T.; Gordley, Larry L.; Pesnell, W. Dean; Goldberg, Richard A.; Russell,
James M.
2006GeoRL..3321809K Altcode:
The polar summer thermal structure, with its cold mesopause and steep
temperature gradients, both below and above the mesopause, produces
the largest non-LTE effects in the CO<SUB>2</SUB> ν<SUB>2</SUB> mode
manifold states. In this paper we focus on validating the non-LTE
model applied for operational temperature retrievals from the SABER
15 μm limb radiance observations for these extreme conditions. We
demonstrate that accounting for the redistribution of ν<SUB>2</SUB>
quanta among various CO<SUB>2</SUB> isotopes shifts the retrieved
summer 2002 polar mesopause altitude upwards by 2 to 4 km. It brings
the SABER temperature measurements into a better agreement with those
of falling sphere experiments, lidar observations, as well as with
climatological data.
---------------------------------------------------------
Title: Sensitivity of IR Temperature Retrievals in the Polar Summer
MLT to NLTE considerations
Authors: Kutepov, A.; Feofilov, A.; Marshall, B. T.; Gordley, L. L.;
Pesnell, W. D.; Goldberg, R. A.; Russell, J. M.
2006AGUSMSA53A..07K Altcode:
Adequate retrieval of kinetic temperature and other parameters in the
summer polar mesosphere and lower thermosphere (MLT) from limb infrared
radiances requires detailed accounting for the breakdown of local
thermodynamic equilibrium (NLTE). A large fraction of the limb radiance
is formed by resonant scattering of the upwelling radiation from the
stratosphere and therefore, does not have links to the local thermal
radiation sources. Moreover, in case of CO2, this scattering depends
strongly on the V-V rate of the ν2 quanta exchange between isotopes. As
a result, both the temperature values and the position of the retrieved
mesopause depend on the rate coefficient of this process. On the other
hand, the lower boundary of a noctilucent cloud (NLC) lies near the
lower crossing point of the temperature profile and the frost point
curve. This suggests that NLC observations may provide an important
tool for validating temperature and water vapor density retrievals as
well as the NLTE model describing the formation of infrared radiance
in the MLT. This paper will describe these considerations including
examples using the TIMED-SABER data for the polar summer mesosphere.
---------------------------------------------------------
Title: Particulate and plasma variations in NLC and PMSE during
DROPPS 1 and 2 flights
Authors: Voss, H. D.; Webb, P. A.; Pesnell, W. D.; Gumbel, J.; Assiss,
M. P.; Goldberg, R. A.
2006cosp...36.3336V Altcode: 2006cosp.meet.3336V
High-time resolution rocket measurements have been made of charged
particulates under polar summer mesospheric conditions on 5 and 14 July
1999 during the DROPPS campaign at And o ya Rocket Range Norway Each
rocket carried a Particle Impact Detector PID composed of two telescopes
with three biased grids and which were pointed into the rocket ram
during both up- and downleg On the first night the rocket DROPPS 1 was
flown into a strong PMSE polar mesospheric summer echo condition with a
weak NLC noctilucent cloud located at the base of the PMSE The second
flight DROPPS 2 was launched into a bright NLC with no PMSE present
For DROPPS 1 large amounts of negatively charged particulates were
observed in the PMSE region with relatively small size distributions
1 nm radius Net positive charge particulates were measured in the
NLC regions for both flights Ions and charged particulates have been
simulated using a finite difference code SIMION 3D to trace particle
paths and resulting grid currents For the simulations the thermal
effects through the shock and within the sensor cause the ice rocky
particulates to sublimate and lose mass In addition the particulates
are observed to decelerate due to the ram pressure and electric fields
for subsequent charge collection on the grids The background current
on grid 2 -4 volt is consistent with the altitude variation and flux
expected for UV photoionization Consistent effects were observed on
another instrument PAT particle trap during the same flights
---------------------------------------------------------
Title: Non-LTE effects in the polar summer mesosphere and lower
thermosphere and TIMED SABER temperature retrievals
Authors: Feofilov, A. G.; Kutepov, A. A.; Marshall, B. T.; Gordley,
L. L.; Pesnell, W. D.; Goldberg, R. A.; Russell, J. M., III
2006cosp...36.2516F Altcode: 2006cosp.meet.2516F
The mesosphere lower thermosphere MLT is one of the most intriguing
regions of Earth s atmosphere In past decades a large number of rocket
and lidar experiments have been performed to explore catalogue and
explain the thermal structure of MLT However the description of this
region is sophisticated due to the large number of processes which
govern the vibrational molecular levels populations The frequency of
inelastic molecular collisions in MLT becomes low and one has to take
into account various other processes which populate and de-populate
the levels absorption and emission of radiation in molecular bands
redistribution of excitation between colliding molecules chemical
excitation The populations must be found by solving the system
of rate equations expressing the balance of all these processes
non-LTE Therefore the interpretation of radiance measurements in MLT
depends on accuracy of non-LTE model Non-LTE effects for the CO 2 nu
2 manifold levels responsible for the 15 mu m CO 2 emission are more
pronounced in the polar summer MLT than in other regions due to the
cold mesopause and high vertical temperature gradients both below and
above the mesopause region This case provides an example of a very
strong infrared radiative coupling between warm stratosphere and cold
mesosphere The SABER a instrument on board the TIMED b satellite is
a limb scanning infrared radiometer designed to measure temperature
and minor constituent vertical profiles and energetics parameters in
the MLT Temperatures in the MLT are retrieved from the
---------------------------------------------------------
Title: Refinement of the DROPPS Polar Summer Mesosphere Particle Data
Authors: Webb, P.; Goldberg, R.; Pesnell, W.; Voss, H.; Assis, M.
2006cosp...36.3413W Altcode: 2006cosp.meet.3413W
The two Black Brant payloads flown during the DROPPS Distribution and
Role of Particles in the Polar Summer Mesosphere rocket program were
launched during early July 1999 from And o ya Rocket Range ARR Norway
The purpose was to investigate the polar summer mesosphere particularly
polar mesospheric summer echoes PMSE Both DROPPS payloads included
front mounted side by side Particle Impact Detector PID charge and mass
telescopes Computer simulations have shown that the PID telescopes
have the potential to detect atmospheric ice particles within the
mesosphere having dimensions of a few nanometers Ice particles of
nanometer size are believed to be responsible for PMSEs through the
process of scavenging Evidence for this process is suggested by the
presence of an electron biteout observed in the same region as the
observation of nanometer size particles at an altitude of sim 82-87 km
over And o ya during the first DROPPS launch sequence Evidence for this
dusty plasma was observed independently by several instruments aboard
the DROPPS payload By comparing PID observations with the computer
simulations we can obtain information concerning the properties of the
PMSE particles including their rocky core size ice mantle thickness and
distribution We have previously presented results from an analysis of
the two detectors that suggested on the first flight particles with
radius of approximately 2 nm were present in the PMSE layer We have
recently realised that our interpretation of the PID data required
further refinement For example we have now
---------------------------------------------------------
Title: Sources, Propagators, and Sinks of Space Weather
Authors: Pesnell, W. D.
2006cosp...36.2994P Altcode: 2006cosp.meet.2994P
Space Weather is a complex web of sources propagators and sinks of
energy mass and momentum A complete understanding of Space Weather
would require specifying and an ability to predict each link in this
web One important problem in Space Weather is ranking the importance
of a particular measurement or model in a research program One way to
do this ranking is to identify the sources propagators and sinks and
produce the simplest linked diagram of the components Such a diagram
will be shown and used to discuss how longterm effects of Space Weather
can be separated from the impulsive effects
---------------------------------------------------------
Title: Using the Far-Infrared to Understand the Thermosphere
Authors: Pesnell, W. D.; Arnett, K.
2005AGUFMSA51B1140P Altcode:
Atomic oxygen is the dominant constituent of the thermospheres of the
Earth, Venus, and Mars. It is formed by photodissociation of a major
molecular species from the lower atmosphere of each planet. Remote
sensing of O greatly increases the amount of data available from each
atmosphere. Several parts of the electromagnetic spectrum can be used
to sense O, but the far-infrared line at 63~μm has several advantages,
which we will discuss. The greatest advantage to using this line is
the ability to resolve the tidal structure of the thermosphere. Using
broadband radiometry to measure the limb radiance of this spectral
feature will be discussed in the context of the OPIE (Oxygen Profiling
Infrared Experiment) instrument. Some thoughts on the optimal orbit
for these instruments with be presented.
---------------------------------------------------------
Title: The Temperature Climatology of the Polar Mesosphere in
2002-2004 Using SABER/TIMED Data
Authors: Feofilov, A.; Kutepov, A.; Goldberg, R. A.; Pesnell, W. D.;
Russell, J. M.; Mlynczak, M. G.
2005AGUFMSA43A1086F Altcode:
The TIMED Satellite was launched on December 7, 2001 to study the
dynamics and energy of the mesosphere and lower thermosphere. The
SABER instrument is a limb scanning infrared telescope designed
to measure minor atmospheric constituents as well as temperature
and pressure of the region. In this study we have concentrated on
data retrieved for the polar mesosphere, to investigate spatial
and temporal temperature characteristics of this region. We made the
comparisons between the winter and summer, and studied both short- and
long-term variability in different quadrants of each hemisphere. The
sharp transition between summer and winter, first demonstrated using
falling-sphere meteorological rocket data, will be described for each
hemisphere with a data base including variations in many geophysical
parameters. Differences in this climatological base between 2002-2004
will also be discussed.
---------------------------------------------------------
Title: The Nature of Icy Dust Particles in the Polar Summer Mesosphere
From Rocket Measurements During DROPPS
Authors: Goldberg, R. A.; Webb, P. A.; Pesnell, W. D.; Voss, H. D.
2005AGUFMSA22A..08G Altcode:
The two Black Brant payloads flown during the DROPPS (Distribution
and Role of Particles in the Polar Summer Mesosphere) rocket program
were launched during early July, 1999 from Andoya Rocket Range (ARR),
Norway. Both payloads included front mounted side by side Particle
Impact Detector (PID) charge and mass telescopes. Computer simulations
have shown that the PID telescopes have the potential to detect
atmospheric ice particles within the mesosphere, having dimensions of
a few nanometers. Ice particles of nanometer size are believed to be
responsible for polar mesospheric summer echoes (PMSEs), such as those
observed at an altitude of ~82-87 km over Andoya during the first DROPPS
launch sequence. We have previously presented results from the longer
PID charge telescope that indicated two possible particle distributions
differing by mean particle size. Due to the different geometries of
the PID telescopes (primarily, that the charge telescope is longer than
the mass telescope) each PID telescope collects a different portion of
the nanometer sized PMSE particles distribution. When compared to the
previous PID charge telescope results, the PID mass telescope results
allow the true PMSE particle size distribution to be estimated. This
talk will introduce the new observations from the shorter PID mass
telescope and the comparison to the previous PID charge telescope. By
then comparing PID observations with the computer simulations provides
information concerning the properties of the PMSE particles, including
their "rocky" core size, ice mantle thickness and distribution.
---------------------------------------------------------
Title: Venus Metal ion and Metal Neutral Species Distributions and
Meteor Magnitudes
Authors: Webb, P. A.; Grebowsky, J. M.; Pesnell, W. D.
2005AGUFM.P33A0237W Altcode:
The lower ionospheres of all planetary atmospheres and any of those
satellites that hold substantial atmospheres have a high likelihood
of containing complex layers of metallic ions and their neutral
species. These metal species arise from the ablation and subsequent
ionization of small particles from the solar system cloud of meteoroids
impacting their atmospheres. Venus is no exception and is unique in that
it has the highest upper limit for incoming meteoroid velocities in
the solar system and its extremely slow atmosphere revolution makes a
one-dimensional modeling a better approximation than for other faster
rotating bodies in the solar system. Previous modeling of one of the
major meteoroid species, Mg, showed that indeed a prominent metallic
layer expected with ion concentrations comparable to those seen
at Earth. However the modeled Mg+ peak altitude was lower than any
total electron density peak observed by spacecraft radio occultation
measurements at Venus. A further analysis adding the contributions of
other metal species and their chemistry has now shown that each metal
ion species layers at a different altitude. Indeed the metal species
Fe has its counterpart ion layer above 120 km in a region where there
are sometimes traces of occultation electron density structures. Also,
the new analysis includes estimates of the visual magnitudes of typical
meteors as they would be observed from a satellite above the atmosphere.
---------------------------------------------------------
Title: Temporal evolution of the vertical content of metallic ion
and neutral species
Authors: Aikin, A. C.; Grebowsky, J. M.; Burrows, J. P.; Correira,
J.; Pesnell, W. D.
2005JASTP..67.1238A Altcode: 2005JATP...67.1238A
Temporal changes in the vertical column contents of the meteoric
metals Mg<SUP>+</SUP>, Mg, Fe<SUP>+</SUP>, and Fe have been measured
at ∼1030 LT for all longitudes in the latitude zone of 10°N 30°N
during November 1996, encompassing the period of the Leonid meteor
shower. The column contents were obtained using UV radiances measured
by the GOME instrument on the ERS-2 satellite. Throughout the month
there are several interesting prominent content enhancements of all
species. After the Leonid shower peak on 17 November the ion species
contents increase before the contents of the neutrals. However, it
is difficult to confirm that this is a shower effect given the other
similar variations seen earlier in the contents and in the sporadic
meteor flux enhancements. The peaks in visual meteors on 17 November
are not observed in the total metal column amounts. The GOME instrument
has been in continuous operation since April 1995 and is an excellent
resource for studying the temporal behavior of meteoric metals on a
global scale.
---------------------------------------------------------
Title: The Physical Properties of PMSE Ice Particles as Determined
During DROPPS by Measurements With the Particle Impact Detector
Authors: Webb, P. A.; Goldberg, R. A.; Pesnell, W. D.; Voss, H. D.
2005AGUSMSA43A..07W Altcode:
The two Black Brant payloads flown during the DROPPS (Distribution
and Role of Particles in the Polar Summer Mesosphere) rocket program
were launched during early July, 1999 from Andoya Rocket Range (ARR),
Norway. Both payloads included a Particle Impact Detector (PID)
charge telescope onboard. Computer simulations have shown that the PID
instrument had the potential to detect atmospheric ice particles within
the mesosphere, having dimensions of a few nanometers. Ice particles
of nanometer size are believed to be responsible for polar mesospheric
summer echoes (PMSEs), such as those observed at an altitude of ~82-87
km over Andoya during the first DROPPS launch sequence. This talk will
discuss the analysis of the PID data obtained from the DROPPS campaign
and comparison of these data to the results obtained from the nanometer
scale ice particle computer simulations. Intercomparison of the PID
observations with the computer simulations provides information
concerning the properties of the PMSE particles, including their
"rocky" core size, ice mantle thickness and distribution.
---------------------------------------------------------
Title: Non-LTE Analysis of SABER 15 μm Limb Observations of the
Summer 2002 Polar Mesopause Region
Authors: Kutepov, A. A.; Feofilov, A. G.; Pesnell, W. D.; Goldberg,
R. A.; Gusev, O. A.; Marshall, T.
2005AGUSMSA43A..13K Altcode:
The SABER instrument on TIMED measures the limb radiance in ten
broadband infrared channels for an altitude range that includes the
mesosphere and lower thermosphere. In this altitude range the effects of
non-local thermal equilibrium (non-LTE) must be included to understand
the measurements. The non-LTE algorithms and computer code package
developed to analyze CRISTA infrared spectral limb radiances were
adapted for this purpose. We retrieved temperature profiles from the
15 μm limb radiances measured in the summer 2002 polar mesopause. The
retrieved temperature profiles will be compared with other retrievals,
the coincident falling sphere experiments of the MaCWAVE campaign,
and climatological data. Sources of the discrepancies between the
various results are discussed.
---------------------------------------------------------
Title: From the Sun to You at the Speed of Light: The SDO Data System
Authors: Pesnell, W. D.
2005AGUSMSH42A..06P Altcode:
The Solar Dynamics Observatory (SDO) is on track to launch in April
2008. Solar images in the extreme ultraviolet, the EUV spectral
irradiance, magnetic field maps, and Dopplergrams are the primary data
products of this mission. Each primary data product is produced on a
rapid cadence. For example, some space weather products, suitable for
use in ionosphere-thermosphere models, should be produced every 10--20
seconds with a 5--10 minute delay between observation and appearance
in the data system. Derived data products, including helioseismic
properties and active region tracked in various wavelengths, will also
be available from the data system. As part of NASA's Living With a
Star Program, SDO will release data to the public as soon as possible
after receipt from the satellite. The science teams will make the data
available through Web-oriented interfaces, such as the Virtual Solar
Observatory, allowing external people to make inquiries and have data
delivered to their site. We will present an overview of the SDO data
system and philosophy.
---------------------------------------------------------
Title: Meteoric Ions in Venus' Atmosphere
Authors: Pesnell, W. D.; Grebowsky, J.; Webb, P. A.
2004AGUFM.P23A0238P Altcode:
From a thorough modeling of the altitude profile of meteoric ionization
in the cytherean atmosphere we have deduced that layers of magnesium,
iron, and sodium ions should exist between altitudes between 115
and 120~km. Based on the estimated meteoroid mass flux density, a
peak ion density of several 10<SUP>3</SUP> ions cm{}<SUP>-3</SUP>
is predicted. Allowing for the uncertainties in all of the model
parameters, this value is probably within an order of magnitude
of the correct density. The peak density is most sensitive to the
meteoroid mass flux density, which determines the source function for
Mg from the ablating meteoroids, the eddy viscosity coefficient, which
determines the effectiveness of mixing the meteoric input downwards,
and the presence of sulfuric acid droplets, which is an efficient sink
of metallic compunds. We examine the effect of the aerosol layers in
the upper mesosphere of Venus' atmosphere on the metallic layers.
---------------------------------------------------------
Title: Comparisons of PMSE Ice Particle Simulations With Observations
From the DROPPS Rocket Campaign
Authors: Goldberg, R. A.; Webb, P. A.; Pesnell, W. D.
2004AGUFMSA24A..01G Altcode:
The origin of polar mesospheric summer echoes (PMSEs) and their proposed
relationship to dust and aerosol particles and to noctilucent clouds
(NLCs) are among the most pressing questions governing the physics of
the polar summer mesosphere. Recent studies show increasing evidence
for the presence of these particles, and their importance particularly
in a charged state. One theory for the formation of the PMSE particles
is that they are composed of a rocky core of meteoritic origin, which
acts as a seed about which an ice mantle forms. Computer simulations
have been conducted to model the flight trajectory and sublimation of
spherical ice/rock particles with radius of 0.5 - 6.0 nm through the
Particle Impact Detector (PID) charge telescope onboard two rockets
that were part of the DROPPS (Distribution and Role of Particles in the
Polar Summer Mesosphere) campaign. DROPPS involved two rocket sequences
in July, 1999 launched from Andoya, Norway. The first launch sequence
was nighttime (July 5-6) during the presence of a strong PMSE and a
weak NLC. The second sequence (July 13-14) occurred during a bright
NLC, but with no PMSE present. By comparing the PID observations from
these two flights with the computer simulations, information about
the properties of the PMSE particles, including their core size,
ice mantle thickness and distribution, can be deduced.
---------------------------------------------------------
Title: Watching meteors on Triton
Authors: Pesnell, W. Dean; Grebowsky, J. M.; Weisman, Andrew L.
2004Icar..169..482P Altcode: 2004Icar..169..482D
The thin atmosphere of Neptune's moon Triton is dense enough to
ablate micrometeoroids as they pass through. A combination of Triton's
orbital velocity around Neptune and its orbital velocity around the
Sun gives a maximum meteoroid impact velocity of approximately 19 km
s <SUP>-1</SUP>, sufficient to heat the micrometeoroids to visibility
as they enter. The ablation profiles of icy and stony micrometeoroids
were calculated, along with the estimated brightness of the meteors. In
contrast to the terrestrial case, visible meteors would extend very
close to the surface of Triton. In addition, the variation in the
meteoroid impact velocity as Triton orbits Neptune produces a large
variation in the brightness of meteors with orbital phase, a unique
Solar System phenomenon.
---------------------------------------------------------
Title: SABER observations of mesospheric temperatures and comparisons
with falling sphere measurements taken during the 2002 summer
MaCWAVE campaign
Authors: Mertens, Christopher J.; Schmidlin, Francis J.; Goldberg,
Richard A.; Remsberg, Ellis E.; Pesnell, W. Dean; Russell, James M.;
Mlynczak, Martin G.; López-Puertas, Manuel; Wintersteiner, Peter P.;
Picard, Richard H.; Winick, Jeremy R.; Gordley, Larry L.
2004GeoRL..31.3105M Altcode: 2004GeoRL..3103105M
The SABER instrument was launched onboard the TIMED satellite in
December 2001. Vertical profiles of kinetic temperature (Tk) are
derived from broadband measurements of CO<SUB>2</SUB> 15 μm limb
emission, in combination with measurements of CO<SUB>2</SUB> 4.3
μm limb emission used to derive CO<SUB>2</SUB> volume mixing ratio
(vmr). Infrared emission from the CO<SUB>2</SUB> ro-vibrational bands
are in non-local thermodynamic equilibrium (non-LTE) in the mesosphere
and lower thermosphere (MLT), requiring new radiation transfer and
retrieval methods. In this paper we focus on Tk and show some of the
first SABER observations of MLT Tk and compare SABER Tk profiles with
rocket falling sphere (FS) measurements taken during the 2002 summer
MaCWAVE campaign at Andøya, Norway (69°N, 16°E). The comparisons are
very encouraging and demonstrate a significant advance in satellite
remote sensing of MLT limb emission and the ability to retrieve Tk
under extreme non-LTE conditions.
---------------------------------------------------------
Title: Global measurements of atmospheric content of metallic ion
and neutral species
Authors: Aikin, A. C.; Grebowsky, J. M.; Pesnell, W. D.; Burrows, J. P.
2004cosp...35..371A Altcode: 2004cosp.meet..371A
Changes in the ion and neutral composition of the persistent atmospheric
metal layers associated with the Leonid showers are determined using
solar-induced resonant radiation measurements from the European Remote
Sensing Satellite (ERS-2) platform. The nadir-viewing Global Ozone
Measuring Experiment (GOME) UV/VIS spectrometer on ERS-2 is utilized
to measure vertical column densities of meteoric metals including,
Mg, Mg^+, Fe, Fe^+, and Si. The satellite orbits the Earth 14 times
per day at 795 km with an equatorial crossing time of 10:30 AM. The
spectral range of GOME is 237 to 793 nm with a wavelength resolution
of 0.2 nm between 237 to 316 nm - the region in which the metal species
lines we analyze are observed. The instrument measures all wavelengths
simultaneously during a scan through the satellite nadir every 1.5
seconds. The spectral range is divided into 5 channels. The 2 channels
comprising the 237 to 316 nm range are integrated for 12 seconds giving
a spatial resolution of 100 by 960 km. Metal data are examined for
periods bracketing several Leonid meteor showers to isolate changes
in the mesospheric and thermospheric abundances of meteoric material
due to the showers. Since the Leonids occur annually in mid-November,
global data from the entire month of November are analyzed for the
years 1996 through 2002.
---------------------------------------------------------
Title: Experimental evidence for dusty plasmas in the polar summer
mesosphere using rocket, lidar, and radar measurements
Authors: Goldberg, R. A.; Pesnell, W. D.
2004cosp...35..321G Altcode: 2004cosp.meet..321G
The origin of PMSEs (polar mesospheric summer echoes)and their proposed
relationship to dust and aerosol particles and to NLCs (noctilucent
clouds) are among the most important questions governing the physics
of the polar summer mesosphere. Recent studies show increasing
evidence for the presence of these particles, and their importance
particularly in a charged state. Several recent experimental programs
have concentrated on detection of these particles in the MLT (mesosphere
and lower thermosphere) region, with an attempt to determine their
role in the structure, dynamics and chemistry of the MLT. Here, we
concentrate on results of the DROPPS program (Andøya, Norway,1999)
and the MaCWAVE program (Andoya, 2002), both of which were designed
to study problems relating to this issue. DROPPS involved two rocket
sequences in July, 1999. The first launch sequence was nighttime (July
5-6) during the presence of a strong PMSE and a weak NLC. The second
sequence (July 13-14) occurred during a bright NLC, but with no PMSE
present. MaCWAVE also involved two summertime launch sequences, with
emphasis on the influence of gravity waves on the MLT region, but with
adequate instrumentation to search for charged dust or aerosols. In
this case, launch sequences occurred on the nights of July 1-2, and
4-5, each during the presence of PMSE events. By combining results
from the rocket instruments with radar and lidar soundings from ALOMAR
Observatory (also at Andøya), it has been possible to analyze each
event in sufficient detail to gain an improved understanding of the
polar summer MLT and it's response to a dusty plasma environment.
---------------------------------------------------------
Title: SABER Observations of Polar Summer/Winter Mesospheric and
Lower Thermospheric Temperatures and Comparisons With Correlative
Measurements Taken During the MaCWAVE Campaign
Authors: Remsberg, E. E.; Mertens, C. J.; Schmidlin, F. J.; Goldberg,
R. A.; She, C.; Williams, B. P.; Pesnell, W. D.; Russell, J. M.;
Mlynczak, M. G.; Gordley, L. L.; Lopez-Puertas, M.; Picard, R. H.;
Winick, J. R.; Wintersteiner, P. P.
2003AGUFMSA41B0439R Altcode:
The Sounding of the Atmosphere using Broadband Emission Radiometry
(SABER) experiment was launched onboard the TIMED satellite in December
2001. SABER derives kinetic temperature (Tk) in the mesosphere and
lower thermosphere (MLT) from broadband measurements of CO<SUB>2</SUB>
15 um limb emission, in combination with measurements of CO<SUB>2</SUB>
4.3 um limb emission used to derive CO<SUB>2</SUB> volume mixing
ratio. Infrared emissions from the CO<SUB>2</SUB> ro-vibrational
bands are in non-local thermodynamic equilibrium (non-LTE) in the MLT,
requiring non-LTE processes to be accurately modeled in the retrieval
algorithm. In this paper we focus on Tk and show results derived
from the non-LTE retrieval algorithm. We demonstrate the ability
to retrieve Tk in an extreme non-LTE environment by comparing SABER
MLT Tk with rocket falling sphere (FS) and sodium lidar measurements
taken during the 2002 summer MaCWAVE campaign. The summer Tk profiles
show that the SABER non-LTE retrieval algorithm improves upper
mesospheric Tk retrievals by 35 K to 45 K, as compared to SABER LTE
Tk retrievals. Combined measurements from SABER and MaCWAVE show a
mesopause region that is highly variable in space and time. SABER data
also show a mesopause altitude that changes with latitude and season,
consistent with the bimodal character of the mesopause height. We also
show preliminary comparisons with the recently available FS and sodium
lidar measurements taken during the 2003 winter MaCWAVE campaign.
---------------------------------------------------------
Title: Occultation of π Arietis by asteroid (828) Lindemannia on
November 10 2002
Authors: Sada, Pedro V.; Nugent, Richard; Maley, Paul; Frankenberger,
Rick; Preston, Steve; Dunham, David; Pesnell, W. Dean
2003OccN....9d...9S Altcode:
The occultation of the bright star π Arietis (HIP 13165) by the
asteroid (828) Lindemannia was recorded by 10 observers in Texas on
November 10, 2002. Clouds hampered many more potential observers. Nine
disappearances, ten reappearances, and 2 near misses are reported. A
least-squares fit to the data results in a 52.6 km × 50.8 km ellipse
with the major axis oriented at a PA of 90.0o. However, deviations
from a perfect ellipse were observed.
---------------------------------------------------------
Title: Evolution of relativistic electrons during a magnetic storm
as seen in low-earth orbit
Authors: Pesnell, W. Dean; Goldberg, Richard A.; Chenette, D. L.;
Schulz, M.; Gaines, E. E.
2003AdSpR..31.1059P Altcode:
Highly relativistic electron events (HREs) are periods of intense,
long-lived, energetic electron fluxes in the outer radiation zone. We
are using measurements from the High Energy Particle Spectrometer (HEPS)
on the Upper Atmosphere Research Satellite (UARS) to develop a database
of the pitch-angle and energy-resolved electron fluxes with energies
between 30 keV and 5 MeV. The data acquired by HEPS have overlapped
with the declining phase of solar cycle 22 making these data very
important, since HREs are thought to peak in frequency and intensity
during this phase of the solar cycle. We find a consistent scenario
of electrons being injected into the radiation belts by a magnetic
storm (deduced from Dst) and being slowly accelerated to ever higher
energies over days to weeks. The energy dependence of the flux is an
essential part of the analysis. Electrons with energies greater than
300 keV are the last to appear following an injection and also linger
longer than electrons with lower energies.
---------------------------------------------------------
Title: Meteoric Material-An Important Component of Planetary
Atmospheres
Authors: Grebowsky, Joseph M.; Moses, Julianne I.; Pesnell, W. Dean
2002GMS...130..235G Altcode: 2002assc.book..235G
Interplanetary dust particles (IDPs) interact with all planetary
atmospheres and leave their imprint as perturbations of the background
atmospheric chemistry and structure. They lead to layers of metal
ions that can become the dominant positively charged species in
lower ionospheric regions. Theoretical models and radio occultation
measurements provide compelling evidence that such layers exist in all
planetary atmospheres. In addition IDP ablation products can affect
neutral atmospheric chemistry, particularly at the outer planets where
the IDPs supply oxygen compounds like water and carbon dioxide to the
upper atmospheres. Aerosol or smoke particles from incomplete ablation
or recondensation of ablated IDP vapors may also have a significant
impact on atmospheric properties.
---------------------------------------------------------
Title: Growth and decay of relativistic electrons during a magnetic
storm as seen in low-Earth orbit
Authors: Pesnell, W. Dean; Goldberg, Richard A.; Chenette, D. L.;
Gaines, E. E.; Schulz, M.
2001JGR...10630039P Altcode:
Highly relativistic electron events (HREs) are periods of intense,
long-lived, energetic electron fluxes in the outer radiation zone. We
are using measurements from the High Energy Particle Spectrometer (HEPS)
on the Upper Atmosphere Research Satellite (UARS) to develop a database
of the pitch-angle-resolved and energy-resolved electron fluxes with
energies between 30 keV and 5 MeV. The data acquired by HEPS have
overlapped with the declining phase of solar cycle 22, making these
data very important, since HREs are thought to peak in frequency and
intensity during this phase of the solar cycle. We find a consistent
scenario of electrons being injected into the radiation belts by a
magnetic storm (deduced from Dst) and being slowly accelerated to ever
higher energies over days to weeks. The energy dependence of the flux
is an essential part of the analysis. Above 700 keV the most energetic
electrons are the last to appear and the slowest to fade following an
injection event.
---------------------------------------------------------
Title: Meteoric Material - One of the Least Explored Components of
Planetary Atmospheres
Authors: Moses, J. I.; Grebowsky, J. M.; Pesnell, W. D.; Weisman, A. L.
2001AGUFMSA42A..09M Altcode:
Interplanetary dust particles (IDPs) continuously impact all the planets
and their satellites in the solar system. In all planetary atmospheres
IDPs leave their imprint as aerosols or smoke particles that are left
behind when the IDPs do not ablate completely or when the ablated vapors
recondense. In addition, in all atmospheres they produce ionization
layers comprised of metallic ions, predominantly Mg<SUP>+</SUP> and
Fe<SUP>+</SUP>. On Earth the metal ions are frequently measured to be
the dominant positively charged species in low-latitude ionospheric
layers. Theoretical models provide evidence that such layers exist at
Venus, Mars, Jupiter, Saturn, Neptune and Saturn's moon Titan. Even
the sparse atmosphere of Triton may be lit up by meteors. Spacecraft
radio occultation measurements reveal low altitude, narrow ionosphere
layers at each of the giant planets. These narrow features appear
to be consistent with the presence of metallic ions that have been
compressed by electrodynamic processes as on Earth. Observations at
Mars and Venus do not show clear evidence of such layers. The IDPs
also deposit nonmetal neutral species in the ablation process. For
the inner planets these species blend unnoticed into the atmosphere,
but for the outer planets they can lead to persistent amounts of water
vapor and carbon dioxide. Although many measurements are available for
the Earth, measurements of the IDP distributions and their atmospheric
signatures at other planets are in their initial stages at the present
time. Modeling efforts are still qualitative as the chemical reaction
rates for many of the ablated gases are not established. Most of our
knowledge of long lasting IDP atmospheric effects is derived from
what we know about Earth, for which our understanding is still far
from complete. This component of all atmospheres must be treated as
a key factor in all planetary atmospheric aeronomy systems.
---------------------------------------------------------
Title: Ionospheric Dynamics Effects on the Ionospheric Magnesium-Iron
Ion Concentration Ratios
Authors: Grebowsky, J. M.; Pesnell, W. D.; Aikin, A. C.
2001AGUSM..SA31A04G Altcode:
Sounding rocket and satellite ion composition measurements show that
the meteoric Fe<SUP>+</SUP> concentration typically exceeds that of
Mg <SUP>+</SUP> in the main meteor ionization layer and above. This
is a puzzle because the assumed source of the metal ions is the
sporadic background of infalling meteoroids, which are on average
chondritic in nature and hence should deposit a higher portion
of Mg in the atmosphere than Fe. A more detailed investigation
the ionosphere measurements revealed that the ratio varies from
measurement to measurement with Mg <SUP>+</SUP> and Fe <SUP>+</SUP>
often switching dominance roles, although on average Fe <SUP>+</SUP>
dominates. Possible sources for the relative variations between the two
species include differential ablation, species-dependent ion-neutral
chemical processes, non-isotropic interplanetary particle populations
and neutral wind and electrodynamic influences. We will discuss the
observations and show that ionospheric dynamics and electrodynamic
processes can play an important role.
---------------------------------------------------------
Title: Meteoric Ions in the Ionosphere of Jupiter
Authors: Kim, Y. H.; Pesnell, W. Dean; Grebowsky, J. M.; Fox, J. L.
2001Icar..150..261K Altcode:
A reanalysis of the Voyager 2 radio occultation data has recently
revealed a low-altitude layer in the jovian ionosphere (Hinson et
al. 1998, J. Geophys. Res. 103, 9505-9520). The peak electron density
of the layer measured on egress, which was at 93° solar zenith angle
near the morning terminator, was inferred to be of the order of 10
<SUP>4</SUP> cm <SUP>-3</SUP>. A substantial low-altitude layer of
hydrocarbon ions in the jovian ionosphere was predicted by Kim and
Fox (1994), but the peak total ion density at predawn was about 10
<SUP>2</SUP> cm <SUP>-3</SUP>, two orders of magnitude smaller than
the noon values, due to the efficient recombination of molecular ions
during the night. The existence of large electron densities in the
jovian ionospheric E region at predawn suggests the presence of ions
with long lifetimes and/or those produced by a source that exhibits
little local time dependence, such as ions originating from meteoroid
ablation in Jupiter's atmosphere. We have modeled the production
rates and subsequent chemistry of seven meteoric ions, including O
<SUP>+</SUP>, C <SUP>+</SUP>, Si <SUP>+</SUP>, Fe <SUP>+</SUP>, Mg
<SUP>+</SUP>, Na <SUP>+</SUP>, and S <SUP>+</SUP>, their compounds
with H, H <SUP>2</SUP>, and hydrocarbons, and the corresponding
neutral species. The models predict a layer of meteoric ions in the
altitude region of 350-450 km above the 1-bar level, with peak total ion
densities of several times 10 <SUP>4</SUP> cm <SUP>-3</SUP>, which are
comparable to the observed values. The peak of the meteoric atomic ion
layer is most apparent at predawn and is located higher than that of the
hydrocarbon ion layer during the daytime and higher than the altitude
of peak production of ions by meteor ablation. At the altitude of peak
ablation, about 350 km, meteoric ions are mainly removed by reactions
with hydrocarbons in either two-body or three-body reactions, and the
molecular ions produced are neutralized efficiently by dissociative
recombination. Meteoric ions may also form adduct ions by termolecular
reactions with hydrogen molecules, but metallic ions, such as Na
<SUP>+</SUP>, Mg <SUP>+</SUP>, and Fe <SUP>+</SUP>, may be reformed
from the adduct ions by a series of reactions with H atoms. Thus the
net ion loss process at the metal ion peak may be dominated by rediative
recombination, and the meteoric ion density profiles show little diurnal
variation. The predicted peak electron density and altitude and the
relative densities of the ions are dependent on the rate coefficients
assumed for many of the reactions involved, and measurements of key
rate coefficients are needed to further constrain the models.
---------------------------------------------------------
Title: Meteoric ions in planetary ionospheres
Authors: Pesnell, W. Dean; Grebowsky, J. M.
2001AdSpR..27.1807P Altcode: 2001AdSpR..27.1807D
Solar system debris, in the form of meteoroids, impacts every
planet. The flux, relative composition and speed of the debris at
each planet depends on the planet's size and location in the solar
system. Ablation of this debris by the atmosphere leaves behind metal
atoms. During the ablation process metallic ions are formed by impact
ionization. For small inner solar system planets, including Earth,
this source of ionization is typically small compared to either
photoionization or charge exchange with ambient molecular ions. For
Earth, the atmosphere above the main deposition region absorbs the
spectral lines capable of ionizing the major metallic atoms (Fe
and Mg) so that charge exchange with ambient ions is the dominant
cause of ionization. Within the carbon dioxide atmosphere of Mars
(and possibly Venus), photoionization is important in determining the
ion density. For a heavy planet like Jupiter, far from the sun, impact
ionization of ablated neutral atoms by impacts with molecules becomes a
prominent source of ionization due to the gravitational acceleration to
high incident speeds. We will describe the processes and location and
extent of metal ion layers for Mars, Earth and Jupiter, concentrating
on flagging the uncertainties in the models at the present time. This
is an important problem, because low altitude ionosphere layers for
the planets, particularly at night, probably consist predominantly of
metallic ions. Comparisons with Earth will be used to illustrate the
differing processes in the three planetary atmospheres.
---------------------------------------------------------
Title: Variation of mesospheric ozone during the highly relativistic
electron event in May 1992 as measured by the High Resolution Doppler
Imager instrument on UARS
Authors: Pesnell, W. Dean; Goldberg, Richard A.; Jackman, Charles H.;
Chenette, D. L.; Gaines, E. E.
2000JGR...10522943P Altcode:
Highly relativistic electron precipitation events (HREs) include
long-lived enhancements of the flux of electrons with E>1MeV
into the Earth's atmosphere. HREs also contain increased fluxes of
electrons with energies above 100 keV that have been predicted to
cause large depletions of mesospheric ozone. For some of the measured
instantaneous values of the electron fluxes during the HRE of May
1992, relative depletions greater than 22% were predicted to occur
between altitudes of 55 and 80 km, where HO<SUB>x</SUB> reactions
cause local minima in both the ozone number density and mixing ratio
altitude profiles. These ozone depletions should follow the horizontal
distribution of the electron precipitation, having a distinct boundary
equatorward of the L=3 magnetic shell. To search for these effects,
we have analyzed ozone data from the High Resolution Doppler Imager
(HRDI) instrument on UARS. Owing to the multiple, off-track viewing
angles of HRDI, observations in the region affected by the electrons
are taken at similar local solar times before, during, and after the
electron flux increase. Our analysis limits the relative ozone depletion
to values <10% during the very intense May 1992 HRE. We do observe
decreases in the ozone mixing ratio at several points in the diurnal
cycle that may be associated with the transport of water vapor into the
mesosphere during May 1992. This masking of the precipitating electron
effects by the seasonal variations in water vapor can complicate the
detection of those effects.
---------------------------------------------------------
Title: Meteoric magnesium ions in the Martian atmosphere
Authors: Pesnell, William Dean; Grebowsky, Joseph
2000JGR...105.1695P Altcode:
From a thorough modeling of the altitude profile of meteoric
ionization in the Martian atmosphere we deduce that a persistent
layer of magnesium ions should exist around an altitude of 70 km. On
the basis of the estimated meteoroid mass flux density, a peak ion
density of ~10<SUP>4</SUP>ionscm<SUP>-3</SUP> is predicted. Allowing
for the uncertainties in all of the model parameters, this value is
probably within an order of magnitude of the correct density. Of these
parameters, the peak density is most sensitive to the meteoroid mass
flux density which determines the source function for Mg from the
ablating meteoroids. Unlike the terrestrial case, where the metallic
ion production is dominated by charge-exchange of the deposited neutral
Mg with the ambient ions, Mg<SUP>+</SUP> in the Martian atmosphere
is produced predominantly by photoionization. The low ultraviolet
absorption of the Martian atmosphere makes Mars an excellent laboratory
in which to study meteoric ablation. Resonance lines in the ultraviolet
that cannot be seen in the spectra of terrestrial meteors may be
visible to a surface observatory in the Martian highlands.
---------------------------------------------------------
Title: Theoretical Stellar Evolution
Authors: Cox, Arthur N.; Becker, Stephen A.; Pesnell, W. Dean
2000asqu.book..499C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A search of UARS data for ozone depletions caused by the
highly relativistic electron precipitation events of May 1992
Authors: Pesnell, W. Dean; Goldberg, Richard A.; Jackman, Charles H.;
Chenette, D. L.; Gaines, E. E.
1999JGR...104..165P Altcode:
Highly relativistic electron precipitation (HRE) events containing
significant fluxes of electrons with E>1MeV have been predicted
by models to deplete mesospheric ozone. For the electron fluxes
measured during the great HRE of May 1992, depletions were predicted
to occur between altitudes of 55 and 80 km, where HO<SUB>x</SUB>
reactions cause a local minimum in the ozone number density and mixing
ratio. Measurements of the precipitating electron fluxes by the particle
environment monitor (PEM) tend to underestimate their intensity; thus
the predictions of ozone depletion should be considered an estimate
of a lower limit. Since the horizontal distribution of the electron
precipitation follows the terrestrial magnetic field, it would show
a distinct boundary equatorward of the L=3 magnetic shell and be
readily distinguished from material that was not affected by the HRE
precipitation. To search for possible ozone depletion effects, we
have analyzed data from the cryogenic limb array etalon spectrometer
and microwave limb sounder instruments on UARS for the above HRE. A
simplified diurnal model is proposed to understand the ozone data from
UARS, also illustrating the limitations of the UARS instruments for
seeing the ozone depletions caused by the HRE events. This diurnal
analysis limits the relative ozone depletion at around 60 km altitude to
values of <10% during the very intense May 1992 event, consistent
with our prediction using an improved Goddard Space Flight Center
two-dimensional model.
---------------------------------------------------------
Title: Uptake coefficient of charged aerosols—implications for
atmospheric chemistry
Authors: Aikin, Arthur C.; Pesnell, W. Dean
1998GeoRL..25.1309A Altcode:
Gas uptake onto liquid particles is influenced by the electrical charge
on the particle. This charge rearranges the spatial distribution of
the dissolved reactant ions, modifying the solute-solvent reaction
at the surface and for some distance into the liquid. This results
in a modification of the uptake coefficient. A general expression,
applicable to laboratory and atmospheric conditions, is presented. The
change in the uptake coefficient is proportional to particle charge
and the square of the Debye length within the liquid. It is inversely
proportional to the square of the particle radius.
---------------------------------------------------------
Title: Do meteor showers significantly perturb the ionosphere?
Authors: Grebowsky, J. M.; Goldberg, R. A.; Pesnell, W. D.
1998JASTP..60..607G Altcode: 1998JATP...60..607G
More than 40 rocket flights through the main meteoric ionization
layer, which peaks near 95 km, have sampled the meteoric metallic ion
concentrations. Five of these flights were conducted during or near
the peak times of a meteor shower. In each of the latter studies the
observed meteoric ion concentrations were assumed to be a consequence
of the shower. These measurements were not complemented by baseline
observations made for similar ionospheric conditions immediately before
the shower and no rigorous quantitative comparisons were made using
average non-shower distributions. In order to further investigate the
impact of the shower on the ionosphere, all published ion concentration
altitude profiles obtained from sounding rockets in the meteoric
ionization regime have been scanned to develop a digital data base
of meteoric ion concentrations. These data are used to provide the
first empirical altitude profile of the metallic ions. The average
observed Mg<SUP>+</SUP> concentrations are lower than those yielded by
the most comprehensive model to date. This compiled ensemble of data
provides supporting evidence that meteor showers do have a significant
impact on the average ionosphere composition. Although there is much
variability in the observed meteoric layers, the peaks in the total
metallic ion concentrations at mid-latitudes, on the dayside, observed
during meteor showers had concentrations comparable to, or exceeding,
the highest concentrations measured in the same altitude regions during
non-shower periods.
---------------------------------------------------------
Title: Pioneer Venus Orbiter Measurements of Solar EUV Flux During
Solar Cycles 21 and 22
Authors: Mahajan, K. K.; Upadhyay, Hari Om; Sethi, N. K.; Hoegy,
W. R.; Pesnell, W. D.; Brace, L. H.
1998SoPh..177..203M Altcode:
The Pioneer Venus Orbiter (PVO) had on board the electron temperature
probe experiment which measured temperature and concentration of
electrons in the ionosphere of Venus. When the probe was outside the
Venus ionosphere and was in the solar wind, the probe current was
entirely due to solar photons striking the probe surface. This probe
thus measured integrated solar EUV flux (Ipe) over a 13-year period from
January 1979 to December 1991, thereby covering the declining phase of
solar cycle 21 and the rising phase of solar cycle 22. In this paper, we
examine the behavior of Ipe translated to the solar longitude of Earth
(to be called EIpe) during the two solar cycles. We find that total
EUV flux changed by about 60% during solar cycle 21 and by about 100%
in solar cycle 22. We also compare this flux with other solar activity
indicators such as F_10.7 , Lα, and the solar magnetic field. We find
that while the daily values of EIpe are highly correlated with F_10.7
(correlation coefficient 0.87), there is a large scatter in EIpe for
any value of this Earth-based index. A comparison of EIpe with SME
and UARS SOLSTICE Lα measurements taken during the same period shows
that EIpe tracks Lα quite faithfully with a correlation coefficient
of 0.94. Similar comparison with the solar magnetic field (Bs) shows
that EIpe correlates better with Bs than with F_10.7 . We also compare
EIpe with total solar irradiance measured during the same period.
---------------------------------------------------------
Title: A New Graphical Interface for the Paczynski Stellar Evolution
Code
Authors: Odell, A. P.; Pesnell, W. D.
1998ASPC..135...69O Altcode: 1998hcsp.conf...69O
The output of stellar structure and evolution codes has traditionally
been in enormous tabular form. We have extensively modified the
public-domain Paczynski Code to provide real-time screen-graphical
output for use in undergraduate and graduate courses at the college
level. Thus anyone studying the structure and evolution of stars
can compute such models of varying mass and composition, and see the
results (run of composition, energy generation, and gas properties
with mass) presented visually as the evolution through core carbon
burning proceeds.It is possible to determine the structure of the gray
atmosphere of a star assuming the mixing length theory of convection,
including the effects of different mixing length. One can watch as
the main- sequence homogeneous model converges. A summary program is
included which, at the end of an evolution sequence, will show the
various model characteristics as a function of time, and also an H-
R Diagram for comparison to real stars. We are currently working on
a pulsation code which will allow the user to generate and display
eigenfunctions for various modes.
---------------------------------------------------------
Title: Pioneer Venus Orbiter Measurements of Solar EUV Flux during
Solar Cycles 21 and 22
Authors: Mahajan, K. K.; Upadhyay, Hari Om; Sethi, N. K.; Hoegy,
W. R.; Pesnell, W. D.; Brace, L. H.
1998sers.conf..203M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Evolutionary and Pulsational Characteristics of Alpha
Virginis Including Turbulent Diffusive Mixing
Authors: Pesnell, W. D.; Odell, A. P.
1998ASPC..135...22P Altcode: 1998hcsp.conf...22P
The best-observed star (besides the sun) for comparison to stellar
evolution and pulsation theory is Alpha Virginis, a double-line
spectroscopic and "visual" binary which shows apsidal motion and
Beta Cephei-type pulsation. Unfortunately, it is impossible to fit
simultaneously all of the observed properties of this star with
one model that also exhibits an unstable pulsation mode of the
correct period (see Odell and Pesnell, 32nd Liege Colloquium 1995
procedings), even with new opacities computed by the OPAL group
of Rogers and Iglesias (Ap. J. Suppl. 79, 507, 1992).Lyubimkov et
al. (Astronomicheskii Zhurnal 72, 212, 1995) have observed that the
composition of Alpha Vir A differs from Alpha Vir B in that the helium
abundance in the atmosphere of the primary star is significantly higher
than the secondary, by approximately a factor of two. Denissenkov
(A&A 287, 113, 1994) has suggested that this and other abundance
anomolies (CN-cycle processed material) can be explained by Turbulent
Diffusive Mixing in early B-stars near the main sequence. Thus it is
of interest to determine the effects of this helium abundance change
on the properties and stability of models of Alpha Virginis.
---------------------------------------------------------
Title: Meteoric Ionization Layers in the Martian Atmosphere
Authors: Pesnell, W. D.; Grebowsky, J. M.
1997AAS...191.2703P Altcode: 1997BAAS...29.1254P
Mars, like the other planets, is bombarded by meteorites. At least two
families of particles impact the planets: sporadic and shower. In the
terrestrial atmosphere both families cause sporadic-E layers when the
introduced material is ionized by charge-exchange, photoionization, or
impact ionization. Narrow layers of ionized material are produced when
the long-lived metallic ions are compressed by tidal or gravity wave
motions in the atmosphere. We will examine how the ion-neutral chemistry
and dynamics of the Martian atmosphere affect the deposited meteoric
material. Our emphasis is on magnesium, an easily ionized species that
is a major component of the meteoric debris. The parameters that affect
the meteoric ionization differ between Earth and Mars. In particular,
the atmospheric compositions and ionospheric densities differ. Further,
the lower atmospheric pressure on Mars means lower altitudes for the
bulk of the atmospheric ablation of the meteorites. However, the range
of atmospheric density variation at high altitudes is greater at Mars
than at Earth, so that sputtering of high speed shower streams which
occurs at high altitudes may be relatively more important at Mars
than Earth.
---------------------------------------------------------
Title: A Student-Oriented Graphical Interface for the Paczynski
Stellar Evolution Code
Authors: Odell, A. P.; Pesnell, W. D.
1997AAS...191.1202O Altcode: 1997BAAS...29.1227O
The output of stellar structure and evolution codes has traditionally
been in enormous tabular form. We have extensively modified the
public-domain Paczynski Code to provide real-time screen-graphical
output for use in undergraduate and graduate college courses. Thus
anyone studying the structure and evolution of stars can compute models
of chosen mass and composition, and see the results (run of composition,
energy generation, and gas properties with mass) presented visually
as the evolution through core carbon burning proceeds. Programs
are included to generate gray stellar envelopes with mixing-length
convection, converge homogeneous main-sequence models, integrate
evolution sequences, and create summaries of model characteristics as
a function of time, such as a theoretical H-R diagram.
---------------------------------------------------------
Title: A comparison of solar EUV flux from langmuir probe
photoelectron measurements on the pioneer venus orbiter with other
solar activity indicators
Authors: Mahajan, K. K.; Hoegy, W. R.; Pesnell, W. D.; Brace, L. H.;
Sethi, N. K.
1997AdSpR..20..187M Altcode:
The electron temperature probe acted as a photo-diode on the Pioneer
Venus Orbiter (PVO) and measured the integrated solar EUV flux
(I_pe) over a 13 year period from January 1979 to December 1991, thus
covering the declining phase of solar cycle 21 and the rising phase
of solar cycle 22. Gross features in the solar activity variations
of this flux during the 13 year period have earlier been studied
by Brace et al. (1988) and Hoegy et al. (1993). In this paper,
we study the fine features by translating the observed I_pe to the
solar longitude of Earth (to be called as EI_pe) and comparing it with
other solar activity indicators like F_10.7, Lyman alpha and the solar
magnetic field. We find that while the daily values of EI_pe are highly
correlated with F10.7 (correlation coefficient 0.87), there is a large
scatter in EI_pe for any value of this earth based index. Comparison
of EI_pe with SME and UARS-SOLSTICE Lyman-alpha measurements taken
during the same period indicates that EI_pe tracks Lyman-alpha quite
faithfully. Similar comparison with the solar magnetic field (B_s)
shows that EI_pe correlates better with B_s than with F10.7.
---------------------------------------------------------
Title: High-speed correction factor to the O(+)-O resonance charge
exchange collision frequency
Authors: Omidvar, K.; Pesnell, W. D.
1995AnGeo..13..253O Altcode:
The high-speed correction factor to the O+-O collision frequency,
resulting from drift velocities between ions and neutrals, is calculated
by solving the integral expression in this factor both numerically and
analytically. Although the analytic solution is valid for either small
or large drift velocities between ions and neutrals, for temperatures of
interest and all drift velocities considered, agreement is found between
analytic and detailed numerical integration results within less than 1%
error. Let Tr designate the average of the ion and neutral temperatures
in K, and u=vd/<alpha>, where vd is the relative drift velocity
in cm s-1, and <alpha>=4.56×10<SUP>3</SUP>sqrtT<SUB>r</SUB>
cm s<SUP>-1</SUP> is the thermal velocity of the O<SUP>+</SUP>-O
system. Then, as u ranges from 0 to 2, the correction factor multiplying
the collision frequency increases monotonically from 1 to about
1.5. An interesting result emerging from this calculation is that the
correction factor for temperatures of aeronomical interest is to a
good approximation independent of the temperature, depending only on
the scaled velocity u.
---------------------------------------------------------
Title: Alpha Virginis : A Test of Upper Main Sequence Stellar
Structure and Evolution
Authors: Odell, A. P.; Pesnell, W. D.
1995LIACo..32..417O Altcode: 1995sews.book..417O
No abstract at ADS
---------------------------------------------------------
Title: O<SUP>+</SUP>-O collision frequency in high-speed flows
Authors: Pesnell, William Dean; Omidvar, Kazem; Hoegy, Walter R.;
Wharton, Larry E.
1994JGR....9921375P Altcode:
Throughout much of the terrestrial thermosphere and ionosphere,
the motions of the neutral and ionized constituents are
closely coupled and relative velocities are small, of the
order of 100 ms<SUP>-</SUP><SUP>1</SUP> or less. This is
particularly true at midlatitudes to low latitudes where typical
velocities in the neutral gas due to tidal forcing are only 20-50
ms<SUP>-</SUP><SUP>1</SUP>. However, the solar wind-magnetosphere
interaction drives a large-scale convection pattern in the polar
ionosphere. When the rapid adjustment of the plasma to changes in
the solar wind is combined with the slower response of the more
massive neutral gas, large relative velocities on the order of 1
kms<SUP>-</SUP><SUP>1</SUP> can exist for substantial lengths of
time. This will be more common during periods of high geomagnetic
activity, as a result of the greater number of magnetic substorms
and other particle precipitation events. When a significant relative
velociy is present, the calculation of interaction parameters of the
two gases passing through each other, such as collision frequency,
must include that velocity. These effects are usually neglected when
interpreting wind and ion drift observations. We show how the collision
frequency is affected by a directed relative velocity between any two
gases interacting with a power law or exponential potential energy
curves. The directed velocity increases the collision frequency at all
temperatures for most ion-neutral interactions. For certain power law
potentials, such as the charge quadrupole, the collision frequency is
decreased. We present an analytic solution for the high-speed collision
integral using the resonance charge exchange cross section.
---------------------------------------------------------
Title: Accuracy of O<SUP>+</SUP>-O collision cross-section deduced
from ionosphere-thermosphere observations
Authors: Reddy, C. A.; Hoegy, W. R.; Pesnell, W. D.; Mayr, H. G.;
Hines, C. O.
1994GeoRL..21.2429R Altcode:
Aeronomic observations applied to the empirical derivation of the
ion-neutral collision cross-section—a basic parameter governing
the mutual interactions between the neutral and plasma components in
the Earth's upper atmosphere—have given values considerably larger
than those derived from theory. The empirical scheme uses the plasma
velocities obtained with the Incoherent Scatter Radar and the neutral
winds obtained with the Fabry-Perot Interferometer. It is shown here
that such an analysis overestimates the collision cross-section due to
the effects of errors in the observables. The effect may be sufficiently
large to bring about agreement with theory, and calls for a re-analysis
of the aeronomic data using methods which minimize the bias caused by
measurement errors.
---------------------------------------------------------
Title: A Solar Dynamo Pediction: Cycle 23-Cycle 22
Authors: Schatten, K. H.; Pesnell, W. D.
1993AAS...183.2507S Altcode: 1993BAAS...25.1332S
No abstract at ADS
---------------------------------------------------------
Title: The Solar Cycle in the Extreme Ultraviolet
Authors: Pesnell, W. D.; Hoegy, W. R.
1993AAS...183.2506P Altcode: 1993BAAS...25.1331P
We present Pioneer Venus Orbiter observations of the solar EUV flux. The
13 years of measurements cover the last part of Solar Cycle 21 and
the majority of Solar Cycle 22. The Ipe flux is a direct measure of
the solar EUV flux that correlated extremely well with earth based
measurements until the onset of Solar Cycle 22. We demonstrate this
correlation with the 10.7 cm. radio flux and ionospheric conditions. Our
measurements show that Solar Cycle 22 was one of the most active ever
recorded. The Ipe flux is a yield-weighted integration over wavelengths
from 100 Angstroms to 1300 Angstroms. It is dominated by emission
in L_alpha lambda 1216, with roughly 50% of the flux coming from the
remaining wavelengths. Other EUV proxy measurements are compared to
the Ipe flux.
---------------------------------------------------------
Title: An Early Solar Dynamo Prediction: Cycle 23 ∼ Cycle 22
Authors: Schatten, Kenneth H.; Pesnell, W. Dean
1993GeoRL..20.2275S Altcode:
In this paper, we briefly review the “dynamo” and “geomagnetic
precursor” methods of long-term solar activity forecasting. These
methods depend upon the most basic aspect of dynamo theory to predict
future activity, future magnetic field arises directly from the
magnification of pre-existing magnetic field. We then generalize the
dynamo technique, allowing the method to be used at any phase of the
solar cycle, through the development of the “Solar Dynamo Amplitude”
(SODA) index. This index is sensitive to the magnetic flux trapped
within the Sun's convection zone but insensitive to the phase of the
solar cycle. Since magnetic fields inside the Sun can become buoyant,
one may think of the acronym SODA as describing the amount of buoyant
flux. Using the present value of the SODA index, we estimate that
the next cycle's smoothed peak activity will be about 210 ± 30 solar
flux units for the 10.7 cm radio flux and a sunspot number of 170 ±
25. This suggests that solar cycle #23 will be large, comparable to
cycle #22. The estimated peak is expected to occur near 1999.7 ± 1
year. Since the current approach is novel (using data prior to solar
minimum), these estimates may improve when the upcoming solar minimum
is reached.
---------------------------------------------------------
Title: Momentum transfer collision frequency of O<SUP>+</SUP>-O
Authors: Pesnell, W. D.; Omidvar, Kazem; Hoegy, Walter R.
1993GeoRL..20.1343P Altcode:
The interaction of the thermosphere and ionosphere is largely
governed by collisions between ions and neutral particles. On
Venus and the Earth, O<SUP>+</SUP> is a dominant ion, and atomic O
dominates throughout much of the thermosphere; therefore an accurate
O<SUP>+</SUP>-O cross section is an important prerequisite for
understanding the dynamics of planetary upper atmospheres. The cross
section and momentum, transfer collision frequency are calculated with
a quantum mechanical code which includes resonance charge exchange,
polarization, and charge-quadrupole effects. Our results agree well
with earlier calculations of Stubbe [1968] and Stallcop et al [1991].
---------------------------------------------------------
Title: How active was solar cycle 22?
Authors: Hoegy, W. R.; Pesnell, W. D.; Woods, T. N.; Rottman, G. J.
1993GeoRL..20.1335H Altcode:
Solar EUV observations from the Langmuir probe on Pioneer Venus Orbiter
suggest that at EUV wavelengths solar cycle 22 was more active than
solar cycle 21. The Langmuir probe, acting as a photodiode, measured the
integrated solar EUV flux over a 13 1/2 year period from January 1979
to June 1992, the longest continuous solar EUV measurement. The Ipe EUV
flux correlated very well with the SME measurement of L<SUB>α</SUB>
during the lifetime of SME and with the UARS SOLSTICE L<SUB>α</SUB>
from October 1991 to June 1992 when the Ipe measurement ceased. Starting
with the peak of solar cycle 21, there was good general agreement
of Ipe EUV with the 10.7 cm, Ca K, and He 10830 solar indices, until
the onset of solar cycle 22. From 1989 to the start of 1992, the 10.7
cm flux exhibited a broad maximum consisting of two peaks of nearly
equal magnitude, whereas Ipe EUV exhibited a strong increase during
this time period making the second peak significantly higher than the
first. The only solar index that exhibits the same increase in solar
activity as Ipe EUV and L<SUB>α</SUB> during the cycle 22 peak is
the total magnetic flux. The case for high activity during this peak
is also supported by the presence of very high solar flare intensity.
---------------------------------------------------------
Title: Dynamical interactions between the middle atmosphere and
thermosphere
Authors: Mayr, H. G.; Harris, I.; Pesnell, W. D.
1992AdSpR..12j.335M Altcode: 1992AdSpR..12..335M
Based on modeling, we discuss some interactions between the middle
atmosphere and thermosphere: (1) Upward propagating tides affect
the wind field and the temperature (and density) variations of the
thermosphere at higher altitudes. (2) The thermospheric circulations
driven by radiative and auroral heating affect the O concentration and
temperature of the upper mesosphere through the exchange of chemical
energy. (3) Gravity waves excited by auroral processes are ducted
through the lower atmosphere and leak back into the thermosphere,
permitting them to propagate large distances away from the source.
---------------------------------------------------------
Title: Properties of thermospheric gravity waves on Earth, Venus
and Mars.
Authors: Mayr, H. G.; Harris, I.; Pesnell, W. D.
1992GMS....66...91M Altcode:
The authors review a spectral model with sherical harmonics and
Fourier components that can simulate atmospheric perturbations in the
global geometry of a multiconstituent atmosphere. The boundaries are
the planetary surface where the transport velocities vanish and the
exobase where molecular heat conduction and viscosity dominate. The
time consuming integration of the conservation equations is reduced
to computing the transfer function (TF) which describes the dynamic
properties of the medium divorced from the complexities in the temporal
and horizontal variations of the excitation source. Given the TF, the
atmospheric response to a chosen source distribution is then obtained
in short order. Theoretical studies are presented to illuminate some
properties of gravity waves on Earth, Venus and Mars.
---------------------------------------------------------
Title: Thermospheric Gravity Waves - Observations and Interpretation
Using the Transfer Function Model / Ftm
Authors: Mayr, H. G.; Harris, I.; Herrero, F. A.; Spencer, N. W.;
Varosi, F.; Pesnell, W. D.
1990SSRv...54..297M Altcode:
Gravity waves are prominent in the polar region of the terrestiral
thermosphere, and can be excited by perturbations in Joule heating and
Lorents force due to magnetospheric processes. We show observations
from the Dynamics Explorer-2 satellite to illustrate the complexity
of the phenomenon and review the transfer function model (TFM) which
has guided our interpretation. On a statistical basis, the observed
atmospheric perturbations decrease from the poles toward the equator
and tend to correlate with the magnetic activity index, Ap, although
individual measurements indicate that the magnetic index is often a poor
measure of gravity wave excitation. The theoretical models devised
to describe gravity waves are multifaceted. On one end are fully
analytical, linear models which are based on the work of Hines. On
the other end are fully numerical, thermospheric general circulation
models (TGCMs) which incorporate non-linear processes and wave mean
flow interactions. The transfer function model (TFM) discussed in this
paper is between these two approaches. It is less restrictive than the
analytical approach and relates the global propagation of gravity waves
to their excitation. Compared with TGCMs, the TFM is simplified by its
linear approximation; but it is not limited in spatial and temporal
resolution, and the TFM describes the wave propagation through the
lower atmosphere. Moreover, the TFM is semianalytical which helps in
delineating the wave components. Using expansions in terms of spherical
harmonics and Fourier components, the transfer function is obtained from
numerical height integration. This is time consuming computationally but
needs to be done only once. Once such a transfer function is computed,
the wave response to arbitrary source distributions on the globe can
then be constructed in very short order. In this review, we discuss some
numerical experiments performed with the TFM, to study the various wave
components excited in the auroral regions which propagate through the
thermosphere and lower atmosphere, and to elucidate the properties of
realistic source geometries. The model is applied to the interpretation
of satellite measurements. Gravity waves observed in the thermosphere
of Venus are also discussed.
---------------------------------------------------------
Title: Nonradial, Nonadiabatic Stellar Pulsations
Authors: Pesnell, W. Dean
1990ApJ...363..227P Altcode:
This paper describes how nonradial stellar pulsations can be modeled
using a Lagrangian formulation. The adiabatic eigenvalues of this
operator are compared to previously published results, using simple
stellar models to show the equivalence of this method and other
techniques. Nonadiabatic effects are included by appending the thermal
equation to the adiabatic operator. At this point, it becomes necessary
to include variations in the convective energy transport. Several ways
of doing this by 'freezing' the convection are examined.
---------------------------------------------------------
Title: Line Profile Variations in BW Vulpeculae
Authors: Pesnell, W. D.; Odell, A. P.
1990BAAS...22.1209P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Transfer Function Model for Thermospheric Gravity Waves
Authors: Mayr, Hans G.; Harris, Isadore; Pesnell, W. Dean
1990rete.conf...49M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Properties of Eoetvoes Spheres
Authors: Pesnell, W. Dean
1989ApJ...344..851P Altcode:
Derivations of the equations governing Eotvos spheres and degenerate
Eotvos objects are presented. These simplified stellar models
incorporate a short-range component in their gravitational potential. A
Yukawa formulation to agree with other workers in this field is used,
although any form that multiplies the normal inverse square law would
be acceptable. Both polytropic and completely degenerate equations of
state are used and separate equations governing the density distribution
derived. Various global relationships are obeyed by these objects,
much like the polytropes to which they are similar. A discussion of
whether the simplified potential is accurate enough for astrophysics
is included, along with a more accurate integral equation for the
potential.
---------------------------------------------------------
Title: Some Thoughts on the Rapidly Oscillating AP Stars
Authors: Pesnell, W. Dean
1989ApJ...339.1038P Altcode:
The effects of combining a weak, axisymmetric magnetic field and
slow rotation on the adiabatic pulsation frequencies of Ap stars are
discussed. It is shown that standing wave patterns on the surface of the
star are produced when the magnetic field dominates the rotation. When
rotation is more important than the magnetic field, the standing
waves are split into the usual running waves. It is shown how the
standing waves affect the line profiles of the star during a pulsation
cycle. When compared to the line profile variations of a running wave,
distinct differences are seen. The standing waves resemble a radial
pulsation at some rotation phases and almost disappear one-quarter of
a rotation cycle later.
---------------------------------------------------------
Title: On the Possibility of Detecting Weak Magnetic Fields in
Variable White Dwarfs
Authors: Jones, Philip W.; Pesnell, W. Dean; Hansen, Carl J.; Kawaler,
Steven D.
1989ApJ...336..403J Altcode:
It is suggested that 'weak' magnetic fields of strengths less than
10 to the 6th G may be detectable in some variable white dwarfs. Weak
fields can cause subtle changes in the Fourier power spectra of these
stars in the form of 'splitting' in frequency of otherwise degenerate
signals. Present-day observational and analysis techniques are capable
of detecting these changes. It is suggested suggested, by listing some
well-studied candidate stars, that perhaps the magnetic signature of
splitting has already been observed in at least one object and that
the difficult task of intensive measurements of weak fields should
now be undertaken of those candidates.
---------------------------------------------------------
Title: Pulsation Induced HeI Line Profile Variations
Authors: Pesnell, W. Dean
1989BAAS...21..714P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Pulsations of EÖTVÖS Spheres
Authors: Pesnell, W. Dean
1989upsf.conf..282P Altcode: 1989IAUCo.111..282P
No abstract at ADS
---------------------------------------------------------
Title: A Catalogue of Line Profile Variations Due to Nonradial
Pulsations
Authors: Jones, P. W.; Pesnell, W. D.; Hansen, C. J.; Smith, M. A.
1988BAAS...20..673J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Pulsations of White Dwarf Stars with Thick Hydrogen or Helium
Surface Layers
Authors: Cox, A. N.; Starrfield, S. G.; Kidman, R. B.; Pesnell, W. D.
1988IAUS..123..333C Altcode:
In order to see if there could be agreement between results of stellar
evolution theory and those of nonradial pulsation theory, calculations
of white dwarf models have been made for hydrogen surface masses of
10<SUP>-4</SUP>M_sun;. Earlier results by Winget et al. (1982) indicated
that surface masses greater than 10<SUP>-8</SUP>M_sun; would not allow
nonradial pulsations, even though all the driving and damping is in
surface layers only 10<SUP>-12</SUP> of the mass thick. The authors
show that the surface mass of hydrogen in the pulsating white dwarfs
(ZZ Ceti variables) can be any value as long as it is thick enough to
contain the surface convection zone.
---------------------------------------------------------
Title: Weight functions in adiabatic stellar pulsations. I - Radially
symmetric motion
Authors: Pesnell, W. Dean
1987PASP...99..975P Altcode:
Through the use of two classes of simple stellar models, the author
illustrates a weight function for radial pulsations that can be
interpreted in terms of two types of potential energy. The traditional
weight function is related to the present one via an integration by
parts, and it is argued that both formulations should be examined to
minimize possible errors that can arise from neglecting several surface
terms. The present form provides a different interpretation of radial
oscillations of stars with small central condensations. The author
also follows the radial fundamental of a highly centrally condensed
polytrope through the dynamic instability at γ = 4/3 and demonstrates
that the envelope is not involved in the instability.
---------------------------------------------------------
Title: Angular Standing Waves in Stellar Pulsations
Authors: Pesnell, W. D.
1987BAAS...19.1052P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Pulsations of White Dwarf Stars with Thick Hydrogen or Helium
Surface Layers
Authors: Cox, Arthur N.; Starrfield, Sumner G.; Kidman, Russell B.;
Pesnell, W. Dean
1987ApJ...317..303C Altcode:
Models for DA white dwarf stars with effective temperatures between 9000
and 12,000 K and models for DB white dwarfs with effective temperatures
of 25,000 K and 27,000 K have been tested for stability against both
radial and nonradial pulsations. The construction of the models
is discussed, and linear nonadiabatic nonradial pulsation results
for these models are given assuming frozen-in convection. The time
variation of convection is simulated in a crude way, and it is shown
that many unstable modes can be completely stabilized. The results
show that thick hydrogen shells can produce nonradial pulsations
and that the existence of convection blocking exists for both radial
and nonradial modes in DA and DB white dwarf stars. It is found that
convection at the surface of white dwarfs must be very efficient in
order for the theoretical nonradial instability strip to have a blue
edge hot enough to agree with observations.
---------------------------------------------------------
Title: A New Driving Mechanism for Stellar Pulsations
Authors: Pesnell, W. Dean
1987ApJ...314..598P Altcode:
A new driving mechanism termed "convective blocking", a variation
of the normal κ- and γ-mechanisms in Cepheids, is demonstrated
using two models of hydrogen white dwarf stars. This mechanism is
shown to be physically reasonable in the limit of frozen convection
(implying the time scale for convective readjustment is long compared
to a pulsation period). Some qualitative effects are given for when
the two time scales are not as disparate.
---------------------------------------------------------
Title: Ensampling White Dwarf g-Modes
Authors: Pesnell, W. Dean
1987LNP...274..363P Altcode: 1987stpu.conf..363P
We examine the pulsation spectrum of zero temperature models as a
first approximation to white dwarf stars. The g-mode spectrum of such
objects is found by using a constant adiabatic exponent and we have
found that the core is an important region for the determination of
the eigenvalue. A comparison to an evolutionary model is given.
---------------------------------------------------------
Title: Pulsations in Completely Degenerate Objects
Authors: Pesnell, W. D.
1986BAAS...18..951P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Pulsations of white dwarf stars with thick hydrogen or helium
surface layers
Authors: Cox, A. N.; Starrfield, S. G.; Kidman, R. B.; Pesnell, W. D.
1986STIN...8721774C Altcode:
In order to see if there could be agreement between results of
stellar evolution theory and those of nonradial pulsation theory,
calculations of white dwarf models have been made for hydrogen surface
masses of 10 to the -4 solar masses. Earlier results indicated that
surface masses greater than 10 to the -8 solar masses would not allow
nonradial pulsations, even though all the driving and damping is in
surface layers only 10 to the -12 of the mass thick. It is shown that
the surface mass of hydrogen in the pulsating white dwarfs (ZZ Ceti
variables) can be any value as long as it is thick enough to contain
the surface convection zone.
---------------------------------------------------------
Title: The Structure of the Thermal Modes in Pulsating Stars
Authors: Pesnell, W. D.; Buchler, J. R.
1986ApJ...303..740P Altcode:
The eigenvectors and eigenvalues of the linearized thermal diffusion
operator are studied and their effect on the thermal structure of
radial stellar pulsations is examined. It is shown on the basis of
two specific cases that the difference between these eigenvectors
may explain the lack of pulsational instability of radial modes in
the Beta Cephei stars. A rigorous definition of the thermal response
time of a model is attempted and the location of the transition from
adiabatic to highly nonadiabatic motion is discussed.
---------------------------------------------------------
Title: Brunt-Vaeisaelae Frequency and Semiconvection
Authors: Pesnell, W. D.
1986ApJ...301..204P Altcode:
A derivation of the Brunt-Väisälä frequency, valid in regions of a
star where both partial ionization and a varying nuclear composition
are present, is given. The final result shows that even in regions
where the total ionization approximation is valid, a reduction
of the Brunt-Väisälä when compared to the Ledoux criterion is
necessary. Areas where this function is important are discussed,
and examples are presented using different forms of equations of state.
---------------------------------------------------------
Title: The Connection Between Nonradial Pulsations and Stellar Winds
in Massive Stars
Authors: Abbott, D. C.; Garmany, C. D.; Hansen, C. J.; Henrichs,
H. F.; Pesnell, W. D.
1986PASP...98...29A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On one-zone models of stellar pulsation
Authors: Pesnell, W. D.
1985ApJ...299..161P Altcode:
A version of the one-zone model, the weakly coupled monomode model,
is derived, showing that the small parameter in stellar pulsation is
the coupling term in the momentum equation. A crude model of similar
derivation is found that describes a portion of the convection-pulsation
interaction. The latter model shows that the time dependence of the
perturbation in the convection variables can be an important part
of the convection-pulsation interaction. With the assumptions made,
the pulsation is stabilized when the convection field is unstable and
vice versa.
---------------------------------------------------------
Title: Ionization Driving Mechanisms in Pulsating Stars
Authors: Pesnell, W. D.
1985BAAS...17..894P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observable quantities of nonradial pulsations in the presence
of slowrotation.
Authors: Pesnell, W. D.
1985ApJ...292..238P Altcode:
Theoretical power spectra of both light and radial velocity variations
of a nonradially pulsating star that include the effects of rotation
are presented. Three classes of motion are defined, depending on the
symmetry of the mode of interest and its orientation with respect to
the rotating axis. The use of tabulated model atmospheres to predict
color variations is compared to the blackbody approximation for two
cases, a hydrogen white dwarf (DA) and a main-sequence B Star.
---------------------------------------------------------
Title: Rotational mode splitting about an inclined axis
Authors: Aizenman, M. L.; Hansen, C. J.; Pesnell, W. D.; Cox, J. P.
1984ApJ...286L..43A Altcode:
The authors have derived the "m-splitting" formula for the frequencies
of nonradial oscillations of stars due to slow rotation about an axis
which is inclined with respect to the pulsation axis. They obtain
the simple result that the usual formula applies, except that only
the component of the angular rotation velocity along the pulsation
axis, rather than the full angular rotation velocity, is to be used
in this formula.
---------------------------------------------------------
Title: Thermal response of stellar envelopes during nonradial
pulsations
Authors: Pesnell, W. D.
1984ApJ...285..778P Altcode:
The response of spherical stellar envelopes in hydrostatic and thermal
balance to nonradial thermal distributions is outlined. Because of the
nature of the initial model, the governing equations yield an operator
that is almost identical to the radial case. The use of propagation
velocities to estimate the nonadiabatic effects in a pulsation is
demonstrated.
---------------------------------------------------------
Title: An Analysis of the Nonradial Oscillations of the Central Star
of the Planetary Nebula K1-16
Authors: Starrfield, S.; Cox, A. N.; Kidman, R. B.; Pesnell, W. D.
1984BAAS...16R.975S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Simple Model of the Convection-Pulsation Interaction
Authors: Pesnell, W. D.
1984BAAS...16.1012P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Critique of the iterative theory of stellar pulsations
Authors: Buchler, J. R.; Pesnell, W. D.
1984ApJ...283..316B Altcode:
An attempt to define a mathematical formalism for computing the periodic
or multiperiodic oscillations of a weakly nonlinear oscillator is
presented. Attention is focused on iterative theory (IT), i.e., the
method of harmonic balances, applied to radial pulsators. The IT is
shown capable of predicting adiabatic oscillations correctly, provided
modifications are introduced to avoid divergences due to internal
resonance. Chaotic solutions are, however, not amenable to IT asymptotic
perturbation models. The IT is also extended to the nonadiabatic case
through the addition of a work integral. The technique is demonstrated
to be effective in the case of two incommensurate resonance modes in
a stellar evolutionary scenario.
---------------------------------------------------------
Title: Nonradial instability strips based on carbon and oxygen
partial ionization in hot, evolved stars.
Authors: Starrfield, S.; Cox, A. N.; Kidman, R. B.; Pesnell, W. D.
1984ApJ...281..800S Altcode:
The authors have calculated periods and growth rates for a new class
of nonradially pulsating variable stars in the linear, nonradial,
nonadiabatic theory. The best observed member of this class is PG
1159-035 which is observed to be pulsating in a number of periods
around 500 s and may well have an effective temperature exceeding
10<SUP>5</SUP>K. Stellar envelopes constructed for a 0.6 M_sun; star are
in the effective temperature range 7×10<SUP>4</SUP>K ≤ T<SUB>e</SUB>
≤ 1.5×10<SUP>5</SUP>K following the white dwarf cooling track at
radii 0.016 - 0.030 R_sun;. These envelopes have compositions of half
carbon and half oxygen by mass. The authors present their nonradial
results and discuss the newly discovered instability strip in some
detail. All unstable nonradial modes in the period range from ≡25
s to ≡1200 s and their growth rates are described. The implications
of these results for stellar evolution studies are examined.
---------------------------------------------------------
Title: Qualitative Aspects of the Convection-Pulsation Interaction
Authors: Pesnell, W. D.
1984LIACo..25..294P Altcode: 1984tpss.conf..294P; 1984trss.conf..294P
No abstract at ADS
---------------------------------------------------------
Title: Lagrangian, Non-Radial Stellar Pulsations
Authors: Pesnell, W. Dean
1984BAAS...16..409P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The discovery of nonradial instability strips for hot,evolved
stars.
Authors: Starrfield, S. G.; Cox, A. N.; Hodson, S. W.; Pesnell, W. D.
1983ApJ...268L..27S Altcode:
Three different interior compositions are used in the present radial
and nonradial, linear, nonadiabatic pulsation analyses of model stellar
envelopes in the effective temperature range of 80,000-150,000 K,
with total masses of 0.6 solar masses and radii chosen so that they
line up along a prewhite dwarf cooling curve: (1) 100 percent C; (2)
50 percent C-12 and 50 percent O-16 by mass; and (3) 10 percent C-12
and 90 percent O-16 by mass. Radial and nonradial instability strips
are found for each composition, caused the partial ionization of C,
or O, or both. Attention is given to the cause of the pulsations of
the hot, evolved star PG 1159-035, which, although perhaps too hot
to lie within the proposed instability strips, is in some measure
of agreement with models having significant amounts of O-16 near the
stellar surface. This implies a greater production of O-16 through He
burning than previously supposed.
---------------------------------------------------------
Title: Thermal Effects in Stellar Pulsations.
Authors: Pesnell, W. D.
1983PhDT........14P Altcode: 1984DiAbI..45.1218P
A Sturm-Liouville operator, embedded in the linearized radial
pulsation equations, is used to analyze the thermal effects of stellar
pulsations. Asymptotic expansions are utilized to demonstrate the
nature of these eigenfunctions and to define the thermal response time
of a stellar model. The eigenvalues and eigenvectors for models of a
Cepheid and Beta Cephei variable are given showing the differences
in the two classes of variables. The time scales introduced agree
with earlier ones in their common use of predicting the location of
possible driving zones. In addition, a way of displaying the temperature
variations in the hydrogen ionization zone without the customary "spike"
is demonstrated, and a new class of pulsations, called "sudden" modes,
is introduced.
---------------------------------------------------------
Title: Thermal effects in stellar pulsations
Authors: Pesnell, William Dean
1983PhDT.......114P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Non-Radial Pulsation Properties of Hot Hydrogen-Poor,
Evolved Stars
Authors: Starrfield, S.; Cox, A. N.; Hodson, S. N.; Pesnell, W. D.
1982BAAS...14..901S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Linear theory radial and nonradial pulsations of DA dwarf stars
Authors: Starrfield, S.; Cox, A. N.; Hodson, S.; Pesnell, W. D.
1982pccv.conf...78S Altcode:
The stellar envelope and radial linear nonadiabatic computer code, along
with a nonradial code are used to investigate the total hydrogen mass
necessary to produce the nonradial instability of DA dwarfs. Opacities
and equations of state are obtained for pure mixtures of hydrogen,
helium, and carbon. In some cases, a small amount of metals are included
in the composition in order to have a variety of mixtures available
to make gradual changes in composition from hydrogen to helium. The
presence of metals in these mixtures has no effect on the results.
---------------------------------------------------------
Title: Application of Two-Time Methods in Stellar Pulsations
Authors: Pesnell, W. D.; Regev, O.; Buchler, J. R.
1982pccv.conf..216P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stability analysis of slow spherical motion for a gravitating
fluid
Authors: Livio, M.; Buchler, J. R.; Pesnell, W. D.
1981ApJ...243..617L Altcode:
The stability of equations governing the spherical motion of a
gravitating compressible fluid against adiabatic perturbations
is analyzed. Assuming that the perturbation of the gravitational
potential can be neglected and that motion is slow, a perturbative
approach is used to obtain first-order corrections to the hydrostatic
eigenvalues. The expression for this correction may be used to study the
effect of velocity and acceleration fields on both stable and unstable
hydrostatic modes. When applied to the homogeneous compressible case
the correction gives the expected results, and stability criteria can
be obtained for specific modes. Possible implications for the study
of stellar collapse are noted.
---------------------------------------------------------
Title: The Light and Velocity Curve Bumps for Bw-Vulpeculae
Authors: Pesnell, W. D.; Cox, A. N.
1980SSRv...27..337P Altcode: 1980IAUCo..58..337P
BW Vulpeculae (HD 199140) is a well known Beta Cephei star, with
several unusual characteristics. It possesses the largest amplitude
in both light and radial velocity variations of any star in this
classification. The most outstanding feature of the observations is a
standstill, or bump, on the light curve, accompanied by doubled lines
in the radial velocity observations. In this paper, an attempt has been
made to explain these phenomena with two different models: firstly,
the resonance mechanism, from Simon and Schmidt (1976), and secondly,
a nonlinear calculation.
---------------------------------------------------------
Title: Spherical oscillation patterns
Authors: Pesnell, W. Dean; Coggins, James M.
1980SSRv...27..473P Altcode: 1980IAUCo..58..473P
Spherical harmonics are an integral part of the study of stellar
pulsations. To gain an understanding of how the star is affected by
non-radial pulsations, the radial part of the oscillation is plotted,
with an assumed sinusoidal time variation. The amplitude of the motion
is arbitrarily set at 20% of the radius.