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Author name code: cadavid
ADS astronomy entries on 2022-09-14
author:"Cadavid, Ana Cristina"
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Title: Plasma Flows in the Atmospheric Layers of Coronal Hole and
Quiet-Sun Regions in the Context of Their Magnetic Field Environment
Authors: Shannon, Scott; Cadavid, Ana; Miralles, Mari Paz
2021AGUFMSH45B2363S Altcode:
Recent work (Kayshap et al. (2018), Tripathi et al. (2021)) have
identified similarities and differences in coronal hole and adjacent
quiet-Sun intensities and Doppler velocities depending on their
magnetic field distributions. In our present study, we improve on this
work by investigating the relation between plasma flows in different
atmospheric layers, chromosphere and transition region, in the context
of their magnetic field environment. We use UV spectroscopic data from
the Interface Region Imaging Spectrograph (IRIS) to calculate Doppler
and non-thermal velocities and spectral line profile asymmetries in
order to characterize the plasma flows. Contemporaneous line-of-sight
magnetic images obtained with the SDO/Helioseismic and Magnetic Imager
(HMI) are used to classify the plasma flow data according to their
associated magnetic field strengths. In addition, we also produce
potential field extrapolations to gain an insight on the topology
associated with the plasma flows in the different solar atmospheric
layers. This work is supported by NASA grant 80NSSC21K0725 to the
Smithsonian Astrophysical Observatory.
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Title: The Relation Between Plasma Properties And UV Intensity
Fluctuations In Equatorial Coronal Holes
Authors: Shannon, S. D.; Cadavid, A. C.; Miralles, M. P.; Wells, L.
2021AAS...23832812S Altcode:
While the origin of the solar wind is still an open problem,
observations indicate that fast, and sometimes slow, wind originates
from equatorial coronal holes. However, the exact locations
within them, and the mechanisms that cause the heating and outward
acceleration of solar plasmas, are not understood. In the present
study, we investigate the relation between the plasma properties in
the chromosphere, transition region, and corona and the properties of
UV intensity fluctuations in equatorial coronal holes. We analyzed
UV spectroscopic and imaging data from the Interface Region Imaging
Spectrograph (IRIS) in the lower atmosphere and EUV coronal images from
the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA)
spacecraft. Doppler and non-thermal velocities in the lower atmosphere
and contemporaneous UV emission time series are used to identify sites
of turbulent (or persistent) processes in the solar atmosphere. The
line-of-sight SDO/Helioseismic and Magnetic Imager (HMI) magnetic
field measurements provide a context for the physical environment.
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Title: A Machine Learning Approach to Identify Solar Stokes Profiles
in Flaring and Non-Flaring Active Regions
Authors: Venkatesan, V.; Cadavid, A. C.; Romich, K.; Choudhary, D. P.
2020AGUFMNG0040001V Altcode:
Solar flares are explosive events on the surface of the Sun that
release electromagnetic radiation, which can disrupt the earth's
atmosphere and cause havoc in our communication system. Models for
flare forecasting use properties of active region (AR) magnetic fields
as predictors of flare occurrence. The magnetic field properties are
obtained using inversion models that decode the information contained
in Stokes Profiles (SP) as the radiation passes through the solar
atmosphere. The inversion techniques ignore the rich information
contained in the SP since they tend to use line fitting methods
and derive average magnetic field properties. The line parameters
can give better information on the magnetic field complexity of
the AR atmosphere. We apply a modified K-means clustering method to
Hinode spectropolarimetric data to identify and classify the Stokes V
profiles in flaring and non-flaring ARs. The modified K-means method
leads to a stable result, in which random initializations converge to
comparable clustering. The profiles which characterize the centroids
of the clusters are used to calculate three-line parameters: the
amplitude asymmetry, the area asymmetry (associated with the degree
of non-linear polarization), and the percentage of atypical profiles
inside and outside the polarity inversion lines (PIL). We find that
the amplitude asymmetry is higher in non-flaring vs. flaring regions;
the area asymmetry is greater in flaring ARs vs. non-flaring ARs,
and inside the PIL vs. outside. Our results indicate that flaring ARs,
harbor a higher percentage of atypical profiles compared to non-flaring
ARs & outside the PIL. These results are compatible with those
found using the individual pixel profiles in the calculations. They
indicate that the three parameters can be used to distinguish flaring
from non-flaring ARs.
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Title: Four Solar Cycle Spectrum Variation of the Sun-as-a-Star
Authors: Choudhary, D. P.; Chapman, G. A.; Cadavid, A. C.; Cookson, A.
2020AGUFMA227.0008C Altcode:
The chromospheric activity of the Sun is governed by the magnetic
field anchored in the photosphere. The solar cycle 23 was a smaller
cycle compared to the recent cycles, in terms of sunspot number and
total disk integrated magnetic field. Comparison of the chromospheric
lines in past cycles may provide insight of the effect of magnetic
field on solar atmosphere. In this paper, we study the dependence
of chromospheric activity on magnetic field of the Sun-as-a-star
in four solar cycles during 1977-2018. The study is conducted by
merging the data obtained by Dr. W. Livingston and the observations by
Integrated Sunlight Spectrometer (ISS) and Vector Spectromagnetograph
(VSM) of Synoptic Optical Long-term Investigations of the Sun (SOLIS)
instrument. The chromospheric activity is measured as the line depth
and equivalent width (EW) of spectral lines in Hα, He I 10830 nm,
Ca II 854.2 nm, Ca II H and K, and Na D I 589.6 nm obtained with the
ISS. The full disk mean total magnetic flux (FDMTMF) observed with
the VSM is used as the measure of magnetic activity of the Sun. The
equivalent width of Ca II K and He I 10830 nm measured by Livingston
along with the Magnetic Plage Strength Index (MPSI) value and a Mount
Wilson Sunspot Index (MWSI) obtained with 150-Foot Solar Tower in
Mt. Wilson Observatory are used to further study the relationship
between the magnetic field and chromospheric activity.
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Title: Variability in Irradiance and Photometric Indices During the
Last Two Solar Cycles
Authors: Choudhary, Debi Prasad; Cadavid, Ana Cristina; Cookson,
Angela; Chapman, Gary A.
2020SoPh..295...15C Altcode:
The Total Solar Irradiance (TSI) primarily varies on an 11-year time
scale and is governed by features such as sunspots and associated
decay products such as plage and faculae. These short-lived physical
features can also modulate the solar irradiance at intermediate and
short temporal scales. Here we investigate the periodic variations,
at solar-surface-rotation time scales, of photometric indices
derived from images obtained at the San Fernando Observatory (SFO),
and we compare them to the properties of the contemporaneous TSI
as measured by the Total Irradiance Monitor (TIM) onboard the SOlar
Radiation and Climate Experiment (SORCE) spacecraft. Both the daily
ground- and space-based data, which span from early 2003 to late 2018,
present missing pixels. We use an autoregressive gap-filling method to
construct continuous time series to be analyzed via Fourier and wavelet
spectral techniques. Lomb-Scargle periodograms, which can handle time
series with missing data, are used for comparison. Both the Fourier
spectral power and the periodograms yield compatible results with
statistically significant periodicities in the range 25 - 35 days. All
of the time series have maximum power at 27 days. Significant secondary
periods are found at 29 - 30 days and 34 - 35 days. Wavelet analyses
of the full time series show that the photometric index resulting
from the red-continuum photometric sum [Σ<SUB>r</SUB>] and the
TSI exhibit common high power at surface-solar-rotation scales
during the active part of the solar cycle. The phase relation at
the surface-solar-rotation scales is not definite. During the solar
minimum interval between Solar Cycles (SCs) 23 and 24, variations in
the TSI are found to be related to variations both in the photometric
index Σ<SUB>K</SUB>, calculated from Ca II K-line photometric sums
and in the magnetic flux in the solar activity latitudinal band (as
found in previous work). This suggests that the TSI changes during the
minimum are caused by the reduced line-blanketing effect of diffused
magnetic field.
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Title: Comparison of the Scaling Properties of EUV Intensity
Fluctuations in Coronal Hole and Quiet-Sun Regions
Authors: Cadavid, Ana Cristina; Miralles, Mari Paz; Romich, Kristine
2019ApJ...886..143C Altcode: 2019arXiv191009541C
Using detrended fluctuation analysis and rescaled range analysis,
we investigate the scaling properties of extreme ultraviolet
(EUV) intensity fluctuations of low-latitude coronal holes (CHs)
and neighboring quiet-Sun (QS) regions in signals obtained with
the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly
instrument. Contemporaneous line-of-sight SDO/Helioseismic and
Magnetic Imager magnetic fields provide a context for the physical
environment. We find that the intensity fluctuations in the time series
of EUV images present at each spatial point a scaling symmetry over
the range ∼20 minute to ∼1 hr. Thus we are able to calculate a
generalized Hurst exponent and produce image maps, not of physical
quantities like intensity or temperature, but of a single dynamical
parameter that sums up the statistical nature of the intensity
fluctuations at each pixel. In QS regions and in CHs with magnetic
bipoles, the scaling exponent (1.0 < α ≤ 1.5) corresponds to
anticorrelated turbulent-like processes. In CHs, and in QS regions
primarily associated with (open) magnetic field of dominant polarity,
the generalized exponent (0.5 < α < 1) corresponds to positively
correlated (persistent) processes. We identify a tendency for α ∼
1 near CH boundaries and in other regions in which open and closed
magnetic fields are in proximity. This is a signature of an underlying
1/f type process that is characteristic for self-organized criticality
and shot-noise models.
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Title: Stokes Line Parameters as Possible Indicators of Flaring
Activity: A Comparison of Flaring and Non-Flaring Active Regions
Authors: Romich, K.; Cadavid, A. C.; Choudhary, D. P.; Beck, C.
2019AGUFMSH31D3338R Altcode:
While the association between solar active regions (ARs) and solar
flares is well-established, there is currently no reliable means
of determining when (or if) a given AR will flare. Much of flare
forecasting is based on the application of machine-learning statistical
techniques that use parameters derived from the local magnetic field
as predictors; these are commonly obtained through spectropolarimetric
inversions using Stokes profiles from the observed radiation. The
standard inversion codes, such as those based on the Milne-Eddington
approximation, yield the average magnetic field values at or near flare
locations. However, this fails to utilize the rich information contained
in the shape of Stokes profiles, such as the existence of line-of-sight
(LOS) magnetic and velocity gradients and multiple magnetic components
along the LOS or within the resolving element. The resulting loss
of information can potentially lead to inaccurate forecasts. We
propose a novel approach, in which line parameters derived from
spectrally-resolved Stokes profiles are considered as possible
precursors to flare events. Using data from the spectropolarimeter
onboard the Hinode satellite, we examine the amplitude asymmetry, net
circular polarization, and degree of complexity of Stokes V profiles
from several flaring and non-flaring ARs. Particular attention is given
to regions near the polarity inversion line (PIL) due to its documented
role in flare initiation. We define the PIL using the magnetic field
vector relative to the solar surface, which we calculate from the Stokes
Q, U, and V profiles; this corrects for projection effects arising
from LOS observations of magnetic flux from ARs off disc center. In
light of the shortcomings of existing methods, we hope to expand the
set of viable indicators of flaring activity with the long-term goal
of improving flare forecasting models.
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Title: Temporal relations between total solar irradiance and
photometric indices during the last two solar cycles.
Authors: Cadavid, A. C.; Choudhary, D. P.; Chapman, G. A.; Cookson, A.
2019AGUFMSH11D3391C Altcode:
Our present understanding, from both empirical and semi-empirical
models, indicates that the variations in the Total Solar Irradiance
(TSI) on time scales of days to the solar cycle are primarily
associated with solar surface magnetic activity, which encompasses
sunspots, faculae, and the network. In previous work, approximately
seven years of TSI measurements from the Total Irradiance Monitor
(TIM) on board the SOlar Radiation and Climate Experiment (SORCE)
spacecraft were compared with photometric indices derived from red and
K-line images obtained on a daily basis at the San Fernando Observatory
(SFO), California State University Northridge (CSUN). The best linear
regression model yielded a coefficient of multiple determination,
R<SUP>2</SUP>, of 0.9495. Expanding on this earlier work and employing
additional analysis techniques not previously used, we consider 16
years of SORCE and SFO data, from early 2003 to late 2018. We use
an autoregressive gap filling method to construct continuous series
which can be analyzed via Fourier and wavelet spectral techniques in
order to investigate the characteristics of the time signals on short
temporal scales. Lomb-Scargle periodograms, which can handle time
series with missing data, are used for comparison. Both the Fourier
spectral power and the periodograms yield compatible results with
significant periodicities on the solar rotation time scales. For both
active and quiet Sun periods, cross-wavelet transforms between the
TSI and the photometric indices signals are used to identify regions
of high common power in the time-frequency maps. The wavelet transform
coherence indicates local periods and times during which the photometric
indices signals and TSI have significant coherence and phase locking,
independent of the power.
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Title: Classification of Active-Region Stokes Profiles with Possible
Applications for Flare Forecasting
Authors: Romich, Kristine; Cadavid, Ana Cristina; Choudhary, Debi
Prasad
2019shin.confE.164R Altcode:
While the association between solar active regions (ARs) and
solar flares is well-established, there is currently no reliable
means of determining when (or if) a given AR will flare. Much of
flare forecasting is based on the application of machine-learning
statistical techniques that use quantities derived from the local
magnetic field as predictors. These properties, in turn, are derived
from dopplergrams obtained at different polarizations or through
spectropolarimetric inversions using Stokes profiles from the observed
radiation. The standard inversion techniques, such as those based on
the Milne-Eddington approximation, give the average magnetic field
values of flare locations. However, this fails to utilize the rich
information contained in the shape of Stokes profiles, such as the
existence of line-of-sight (LOS) magnetic and velocity gradients and
multiple magnetic components along the LOS or within the resolving
element. This results in loss of information and potentially inaccurate
forecasts. Here we outline a novel approach, in which parameters
derived from the raw Stokes profiles are examined as possible
precursors to flare events. Using data from the spectropolarimeter
onboard the Hinode satellite, we examine the amplitude asymmetry, net
circular polarization, and degree of complexity of Stokes profiles
from flaring and non-flaring ARs. Particular attention is given to
regions near the polarity inversion line due to its documented role in
flare initiation. In light of the shortcomings of existing methods,
we hope to expand the set of viable indicators of flaring activity
with the long-term goal of improving flare forecasting models.
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Title: EUV Intensity Fluctuations in Equatorial Coronal Holes,
Boundaries, and Adjacent Quiet-Sun Regions
Authors: Romich, Kristine; Cadavid, Ana Cristina; Miralles, Mari Paz
2018shin.confE..42R Altcode:
To quantify differences in the long-term dynamics of equatorial coronal
holes (CH) and neighboring quiet-Sun (QS) regions, we investigate the
scaling properties and long-term correlations of the fluctuations of
SDO/AIA EUV intensity signals. Contemporaneous SDO/HMI magnetic images
provide a physical context for these signals. We apply the methods
of rescaled range (R/S) analysis and detrended fluctuation analysis
(DFA) to generate image maps of Hurst exponents and generalized Hurst
exponents, respectively; these sum up the statistical nature of the
intensity fluctuations at each pixel. We also discuss similarities
and differences between CH interiors, adjacent QS regions, and the
boundaries between them.
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Title: Comparison of the Scaling Properties of EUV Intensity
Fluctuations in Coronal Holes to those in Regions of Quiet Sun
Authors: Cadavid, Ana Cristina; Lawrence, John K.; Jennings, Peter John
2017SPD....4810613C Altcode:
We investigate the scaling properties of EUV intensity fluctuations
seen in low-latitude coronal holes (CH) and in regions of Quiet Sun
(QS), in signals obtained with the SDO/AIA instrument in the 193 Å
waveband. Contemporaneous time series in the 171 and 211 Å wavebands
are used for comparison among emissions at different heights in the
transition region and low corona. Potential-field extrapolations
of contemporaneous SDO/HMI line-of-sight magnetic fields provide a
context in the physical environment. Detrended fluctuation analysis
(DFA) shows that the variance of the fluctuations obeys a power-law
as a function of temporal scales with periods in the range ~15-60
min. This scaling is characterized by a generalized Hurst exponent
α. In QS regions, and in regions within CHs that include magnetic
bipoles, the scaling exponent lies in the range 1.0 < α < 1.5,
and it thus corresponds to anti-correlated, turbulent-like, dynamical
processes. Regions inside the coronal holes primarily associated
with magnetic field of a dominant single polarity, have a generalized
exponent (0.5 < α < 1) corresponding to positively correlated
(“persistent”) processes. The results indicate the influence of
the magnetic fields on the dynamics of the emission.
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Title: Multi-scaling Properties of EUV Intensity Fluctuations and
Models for Impulsive Heating
Authors: Cadavid, A. C.; Rivera, Y.; Lawrence, J. K.; Christian,
D. J.; Jennings, P.; Rappazzo, A. F.
2016AGUFMSH42B..05C Altcode:
There is wide agreement on the importance of impulsive processes
("nanoflares") to explain coronal heating. Diagnostics of observational
data are necessary to uncover signatures of the underlying mechanisms,
and, by comparing to those of simulated data, to determine whether a
model explains the observations. We have investigated the multi-scaling
properties that characterize the intermittency of AIA/SDO radiance
fluctuations. Lags between pairs of wavebands were used to distinguish
coronal from transition region (TR) signals. Noise degrades the signals,
so the 171Å emission, with the highest signal-to-noise ratio, provides
the best information. In an active region core, for both loops and
for diffuse emission, the probability distribution functions (PDFs) of
the increments of both TR and coronal signals are "quasi-Gaussian" for
large temporal scales and "leptokurtic" (peaked with heavy tails) for
small time increments, as expected for turbulent systems. Multifractal
Detrended Fluctuation Analysis (MF-DFA) shows that the variance of
the fluctuations obeys a power law as a function of temporal scales in
the range 15-45 min. The value of the scaling exponent indicates that,
on average, the time series are nonstationary and anti-persistent with
small fluctuations following large fluctuations and vice versa. Other
moments of the fluctuations obey corresponding power laws and the
multi-scaling exponents quantify the degree of the intermittency in
the context of multifractality. The variation in the scaling exponents
results from long term correlation in the time series. The multiscaling
of the EUV data agrees qualitatively with simulated intensity from a
simple model of impulsive bursts plus noise, and also with the ohmic
dissipation in a Reduced Magnetohydrodynamic (RMHD) model for coronal
loop heating. However, the observational data were found to disagree
with the modeled PDFs of increments. There is indication that the
multifractal properties in the observations could be related to a
modified multiplicative cascade model characterized by two parameters.
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Title: Multifractal Solar EUV Intensity Fluctuations and their
Implications for Coronal Heating Models
Authors: Cadavid, A. C.; Rivera, Y. J.; Lawrence, J. K.; Christian,
D. J.; Jennings, P. J.; Rappazzo, A. F.
2016ApJ...831..186C Altcode: 2016arXiv160902625C
We investigate the scaling properties of the long-range temporal
evolution and intermittency of Atmospheric Imaging Assembly/Solar
Dynamics Observatory intensity observations in four solar environments:
an active region core, a weak emission region, and two core loops. We
use two approaches: the probability distribution function (PDF) of
time series increments and multifractal detrended fluctuation analysis
(MF-DFA). Noise taints the results, so we focus on the 171 Å waveband,
which has the highest signal-to-noise ratio. The lags between pairs of
wavebands distinguish between coronal versus transition region (TR)
emission. In all physical regions studied, scaling in the range of
15-45 minutes is multifractal, and the time series are anti-persistent
on average. The degree of anti-correlation in the TR time series is
greater than that for coronal emission. The multifractality stems from
long-term correlations in the data rather than the wide distribution
of intensities. Observations in the 335 Å waveband can be described
in terms of a multifractal with added noise. The multiscaling of the
extreme-ultraviolet data agrees qualitatively with the radiance from
a phenomenological model of impulsive bursts plus noise, and also
from ohmic dissipation in a reduced magnetohydrodynamic model for
coronal loop heating. The parameter space must be further explored to
seek quantitative agreement. Thus, the observational “signatures”
obtained by the combined tests of the PDF of increments and the MF-DFA
offer strong constraints that can systematically discriminate among
models for coronal heating.
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Title: Photoelectric instability and debris disk rings: One theory
to rule them all
Authors: Lyra, Wladimir; Cadavid, Ana Cristina; Choudhary, Debi Prasad;
Christian, Damian; Kuchner, Marc Jason; Richert, Alexander John Wolf
2016hst..prop14572L Altcode:
HST images of circumstellar debris disks have helped advance
tremendously our understanding of these disks, thought to represent
planetary systems during the late stages of planet formation as the
gas clears and the system becomes optically thin. These systems are
analogs of the Kuiper belt in the solar system, and show a variety
of non-trivial structures attributed to planetary perturbations and
utilized to constrain the properties of the planets. However, analyses
of these systems have largely ignored the fact that, increasingly,
debris disks are found to contain small quantities of gas. We have
recently shown that dust-gas interactions with photoelectric heating
can produce some of the key patterns seen in debris disks that were
previously attributed to planets. We propose to code software and run
a suite of models to develop the theory of photoelectric instability in
gas-rich optically thin disks in light of the observational constrains
set by HST observations and its interaction with other dynamically
important processes such as hydromagnetic turbulence, radiation forces,
planetary perturbers, and stellar flares.
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Title: Scaling and Long Term Correlation Properties of EUV Intensity
Fluctuations and Implications for Impulsive Heating Mechanisms of
the Solar Corona
Authors: Rivera, Y.; Cadavid, A. C.; Lawrence, J. K.
2015AGUFMSH13B2445R Altcode:
Scaling properties of the stochastic component of EUV intensity
fluctuations from AIA/SDO observations show long-term correlations
and can carry information about the energetics of coronal loops. Power
spectra indicate that the stochastic time series are nonstationary. Thus
we apply the method of detrended fluctuation analysis (DFA), which
was designed to determine the true scaling properties of a signal. It
can identify the long-term correlations in noisy and nonstationary
time series after accounting for external influences. The scaling
exponents encountered in the solar fluctuation functions indicate
long-time correlations of the series. We study to what degree the
properties may correspond to those of fractional Brownian motion
(fBm) or fractional Gaussian noise (fGn) processes. Analysis of a
non-flaring active region (AR) indicates that the EUV emission in
the hot 131 Å (Fe XXI), hot 94 Å (Fe XVIII) and 335 Å intensity
bands has different properties from the warm emission in the 211, 193
and 171 Å bands. Further differences are found in the quiet vs AR
core regions. The intensity values satisfy probability distribution
functions (pdf)s corresponding to superposed lognormal and Gaussian
functions. The pdfs of the increments are Gaussian. The properties of
the data can be reproduced by a physically motivated phenomenological
model for impulsive heating with added noise. We propose that DFA,
complemented with the identification of the pdfs, can be a useful tool
to constrain more realistic models of coronal heating.
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Title: Correlation and scaling properties of non-stationary
intensity fluctuations in coronal EUVtime series in different
physical environments
Authors: Cadavid, Ana Cristina; Lawrence, John; Rivera, Yeimy
2015TESS....120307C Altcode:
Previously we have used EUV observations from AIA/SDO to examine
properties of energy deposition into coronal-loops in non-flaring
active region (AR) cores. The evolution of the loop apex intensity,
temperature, and electron density indicate that the loops are
impulsively heated in a mode compatible with high intensity nanoflare
storms characterized by a progressive cooling pattern in the EUV lines
with the hot channels leading the emission. Spectra of the hot 131
Å intensity (basically Fe XXI) and of the energy dissipation in a 2D
model of loop magneto-turbulence compatible with nanoflare statistics,
both exhibit three scaling regimes with low frequencies corresponding
to 1/f noise, the intermediate range indicating a persistent process,
and high frequencies corresponding to white noise. The varying power
law behavior in these spectra indicates that both the observational
and the simulated time series are not stationary. Therefore to
extend the analysis beyond the AR loops we apply the method of
detrended fluctuation analysis (DFA) that was developed to study
the long-range correlations in non-stationary signals. DFA provides
a scaling exponent that characterizes the correlation properties of
the signal and which can be related both to the spectral exponents
and to the Hurst exponent. In areas of diffuse emission and for all
the spectral channels the time series of intensity fluctuations are
characterized by scaling exponents that indicate a weak positive
correlation across all time scales. In regions with intermittent
intensity brightenings a cross-over occurs at timescales near 10 -
20 min with different exponents describing the degree of positive
correlation of the intensity fluctuations at short and long time
scales. Qualitative differences exist between the exponents of the
hotter and the cooler channels. We have further compared the scaling
properties of the time series associated with different physical
environments distinguished by the possibility of underlying nanoflare
storms, or by the strength of the magnetic field in contemporaneous
HMI images. Another comparison is made to the scaling properties of
simulations of energy dissipation in magnetoturbulence.
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Title: Heating Mechanisms for Intermittent Loops in Active Region
Cores from AIA/SDO EUV Observations
Authors: Cadavid, A. C.; Lawrence, J. K.; Christian, D. J.; Jess,
D. B.; Nigro, G.
2014ApJ...795...48C Altcode: 2014arXiv1404.7824C
We investigate intensity variations and energy deposition in five
coronal loops in active region cores. These were selected for their
strong variability in the AIA/SDO 94 Å intensity channel. We
isolate the hot Fe XVIII and Fe XXI components of the 94 Å and
131 Å by modeling and subtracting the "warm" contributions to the
emission. HMI/SDO data allow us to focus on "inter-moss" regions
in the loops. The detailed evolution of the inter-moss intensity
time series reveals loops that are impulsively heated in a mode
compatible with a nanoflare storm, with a spike in the hot 131 Å
signals leading and the other five EUV emission channels following in
progressive cooling order. A sharp increase in electron temperature
tends to follow closely after the hot 131 Å signal confirming the
impulsive nature of the process. A cooler process of growing emission
measure follows more slowly. The Fourier power spectra of the hot
131 Å signals, when averaged over the five loops, present three
scaling regimes with break frequencies near 0.1 min<SUP>-1</SUP>
and 0.7 min<SUP>-1</SUP>. The low frequency regime corresponds to
1/f noise; the intermediate indicates a persistent scaling process
and the high frequencies show white noise. Very similar results are
found for the energy dissipation in a 2D "hybrid" shell model of loop
magneto-turbulence, based on reduced magnetohydrodynamics, that is
compatible with nanoflare statistics. We suggest that such turbulent
dissipation is the energy source for our loops.
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Title: Different Periodicities in the Sunspot Area and the Occurrence
of Solar Flares and Coronal Mass Ejections in Solar Cycle 23 - 24
Authors: Choudhary, D. P.; Lawrence, J. K.; Norris, M.; Cadavid, A. C.
2014SoPh..289..649C Altcode:
In order to investigate the relationship between magnetic-flux
emergence, solar flares, and coronal mass ejections (CMEs), we study
the periodicity in the time series of these quantities. It has been
known that solar flares, sunspot area, and photospheric magnetic flux
have a dominant periodicity of about 155 days, which is confined to
a part of the phase of the solar cycle. These periodicities occur at
different phases of the solar cycle during successive phases. We present
a time-series analysis of sunspot area, flare and CME occurrence during
Cycle 23 and the rising phase of Cycle 24 from 1996 to 2011. We find
that the flux emergence, represented by sunspot area, has multiple
periodicities. Flares and CMEs, however, do not occur with the same
period as the flux emergence. Using the results of this study, we
discuss the possible activity sources producing emerging flux.
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Title: Non-steady, Intermittent, Hot Loops in an Active Region
Observed with the SDO/AIA
Authors: Cadavid, Ana C.; Lawrence, J. K.; Christian, D. J.
2013SPD....44...48C Altcode:
While there is accumulated evidence of high temperature coronal emission
in active region cores that corresponds to structures in equilibrium,
other studies have found of evolving loops. We investigate the EUV
intensity variations of two low and short coronal loops observed
in the core of NOAA AR 11250 on 13 July 2011 between UT 12:02
and 16:32. The loops (32 Mm loop 1, 23 Mm loop 2), run directly
between the AR opposite polarities, and are first detectable in
the 94Å band (effective temperature ~ 7 MK). Space-time slices
present intermittent brightenings evocative of turbulence. Spatial
averages over the intermoss loop region lead to light curves used to
analyze the temporal evolution of the loops. We find quantities with
scaling regimes that are characteristic of intermittent processes. In
particular intensity histograms display scaling ranges with slopes ~
-1.8, and spectra also show a scaling region for frequencies 1-8 mHz,
with slopes - 3.8 (loop 1) and -2.8 (loop 2). We further investigate
the time evolution of the loops in five other AIA EUV channels. The
results are separated into two classes. Group A (94Å, 335Å, 211Å)
characterized by hotter temperatures 2-6 MK), and group B (193Å, 171Å,
131Å) by cooler temperatures (0.4 - 1.6 MK). In loop 1 (group A) the
intensity peaks in the 94Å channel are followed by maxima in the 335
Å channel with a time lag of ~10 min, suggestive of a cooling pattern
with an exponential decay. The 211Å maxima follow those in the 335
Å channel, but there is no systematic relation which would indicate
a progressive cooling process. In group B the signals in the 171 and
131Å channels track each other closely, and tend to lag behind the
193Å. The three signals follow a general gradual increase reaching a
maximum at about the middle of the time series and then decrease. An
exponential cooling model can also be associated with the 193 and 171Å
pair. For loop 2 the observations in the group B light curves present
similar properties as in loop 1. In contrast the intensity curves
in group A only show one distinct case which could be a candidate
for exponential decay via a 94 Å to 335 Å cooling process.Abstract
(2,250 Maximum Characters): While there is accumulated evidence of high
temperature coronal emission in active region cores that corresponds
to structures in equilibrium, other studies have found of evolving
loops. We investigate the EUV intensity variations of two low and short
coronal loops observed in the core of NOAA AR 11250 on 13 July 2011
between UT 12:02 and 16:32. The loops (32 Mm loop 1, 23 Mm loop 2), run
directly between the AR opposite polarities, and are first detectable
in the 94Å band (effective temperature ~ 7 MK). Space-time slices
present intermittent brightenings evocative of turbulence. Spatial
averages over the intermoss loop region lead to light curves used to
analyze the temporal evolution of the loops. We find quantities with
scaling regimes that are characteristic of intermittent processes. In
particular intensity histograms display scaling ranges with slopes ~
-1.8, and spectra also show a scaling region for frequencies 1-8 mHz,
with slopes - 3.8 (loop 1) and -2.8 (loop 2). We further investigate
the time evolution of the loops in five other AIA EUV channels. The
results are separated into two classes. Group A (94Å, 335Å, 211Å)
characterized by hotter temperatures 2-6 MK), and group B (193Å, 171Å,
131Å) by cooler temperatures (0.4 - 1.6 MK). In loop 1 (group A) the
intensity peaks in the 94Å channel are followed by maxima in the 335
Å channel with a time lag of ~10 min, suggestive of a cooling pattern
with an exponential decay. The 211Å maxima follow those in the 335
Å channel, but there is no systematic relation which would indicate
a progressive cooling process. In group B the signals in the 171 and
131Å channels track each other closely, and tend to lag behind the
193Å. The three signals follow a general gradual increase reaching a
maximum at about the middle of the time series and then decrease. An
exponential cooling model can also be associated with the 193 and 171Å
pair. For loop 2 the observations in the group B light curves present
similar properties as in loop 1. In contrast the intensity curves in
group A only show one distinct case which could be a candidate for
exponential decay via a 94 Å to 335 Å cooling process.
---------------------------------------------------------
Title: 2nd ATST-EAST Workshop in Solar Physics: Magnetic Fields from
the Photosphere to the Corona
Authors: Rimmele, T. R.; Tritschler, A.; Wöger, F.; Collados Vera,
M.; Socas-Navarro, H.; Schlichenmaier, R.; Carlsson, M.; Berger, T.;
Cadavid, A.; Gilbert, P. R.; Goode, P. R.; Knölker, M.
2012ASPC..463.....R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coupled Effects of a Perturbation in a Complex Structure
Observed with SDO/AIA, SDO/HMI and ROSA/HARDcam
Authors: Cadavid, A. C.; Lawrence, J. K.; Christian, D. J.; Jess,
D. B.; Mathioudakis, M.
2012AGUFMSH51A2197C Altcode:
We study properties of intensity fluctuations in NOAA Active Region
11250 observed on 13 July 2011 starting at UT 13:32. Included are
data obtained in the EUV bands of the Atmospheric Imaging Assembly
on board the Solar Dynamics Observatory (SDO/AIA) as well as nearly
simultaneous observations of the chromosphere made, at much higher
spatial and temporal resolution, with the Rapid Oscillations in the
Solar Atmosphere (ROSA) and Hydrogen-Alpha Rapid Dynamics camera
(HARDcam) systems at the Dunn Solar Telescope. A complex structure
seen in both the ROSA/HARDcam and SDO data sets comprises a system of
loops extending outward from near the boundary of the leading sunspot
umbra. It is visible in the ROSA Ca II K and HARDcam Hα images, as
well as the SDO 304 Å, 171 Å and 193 Å channels, and it thus couples
the chromosphere, transition region and corona. In the ground-based
images the loop structure is 4.1 Mm long. Some 17.5 Mm, can be traced
in the SDO/AIA data. The chromospheric emissions observed by ROSA and
HARDcam appear to occupy the inner, and apparently cooler and lower,
quarter of the loop. We compare the intensity fluctuations of two points
within the structure. From alignment with SDO/HMI images we identify a
point "A" near the loop structure, which sits directly above a bipolar
magnetic feature in the photosphere. Point "B" is characteristic of
locations within the loops that are visible in both the ROSA/HARDcam
and the SDO/AIA data. The intensity traces for point A are quiet
during the first part of the data string. At time ~ 19 min they
suddenly begin a series of impulsive brightenings. In the 171 Å and
193 Å coronal lines the brightenings are localized impulses in time,
but in the transition region line at 304 Å they are more extended
in time. The intensity traces in the 304 Å line for point B shows
a quasi-periodic signal that changes properties at about 19 min. The
wavelet power spectra are characterized by two periodicities. A 6.7 min
period extends from the beginning of the series until about 25 minutes,
and another signal with period ~3 min starts at about 20 min. The 193
Å power spectrum has a characteristic period of 5 min, before the
20 min transition and a 2.5 min periodicity afterward. In the case of
HARDcam Hα data a localized 4 min periodicity can be found until about
7 min, followed by a quiet regime. After ~20 min a 2.3 min periodicity
appears. Interestingly a coronal loop visible in the 94 Å line that
is centrally located in the AR, running from the leading umbra to the
following polarity, at about time 20 min undergoes a strong brightening
beginning at the same moment all along 15 Mm of its length. The fact
that these different signals all experience a clear-cut change at time
about 20 min suggests an underlying organizing mechanism. Given that
point A has a direct connection to the photospheric magnetic bipole,
we conjecture that the whole extended structure is connected in a
complex manner to the underlying magnetic field. The periodicities
in these features may favor the wave nature rather than upflows and
interpretations will be discussed.
---------------------------------------------------------
Title: Coupled Intensity Variations in Hot Coronal Loops Observed
with SDO/AIA
Authors: Lawrence, J. K.; Cadavid, A. C.; Christian, D. J.
2012AGUFMSH33D2265L Altcode:
Data from the AIA on board SDO allow us to study EUV intensity
variations of coronal loops. Here we study strong EUV brightenings
of coronal loops in NOAA Active Region 11250 on 13 July 2011 between
UT 13:32 and 14:32. The brightenings are seen only in the 94Å band
of Fe XVIII, implying an effective temperature ~ 8 MK. The relevant
loops run directly between the AR opposite polarities and are low
and short. One example is an apparently single loop north of the
AR midline. At UT 13:50 (18 min into the observational sequence -
see the image) it began a strong brightening in the 94 Å band. This
occurred at the same moment all along 15 Mm of its length to ~ 12 s
accuracy. This suggests the presence of stored free energy along the
loop that was released by an instability that must have propagated
along it at 1500 km/s or faster. The maximum rate of increase of the
94 Å intensity occurred at 20 min into the sequence, and the maximum
was reached at 23 min. It then decayed, reaching its former level
at time 40 min. Another example lay south of the AR midline (see the
image). On its trailing end this loop had two feet, suggesting that
it is a superposition of two loops seen in projection. This structure
showed two strong 94 Å brightenings peaking at 32 min and 37 min
into the data sequence. The first brightening was associated with an
intensity increase in the northern trailing foot, while the second was
associated with an intensity increase in the southern foot. Again,
this points to the presence of two superimposed loops. Brightenings
in the loop feet indicate upward motion of intensity features toward
the loop center at various speeds from 50 - 200 km/s. The intensity
in the central loop section shows a sequence of weaker increases at
4 min intervals preceding the strong brightenings and a still weaker
sequence at 5 min intervals afterward. These indicate releases of
stored energy along a 10 Mm loop segment by a periodically repeating
instability. The onset of the periodic energy releases in Example 2
and also the start of the loop brightening in Example 1 both occur
at time 18 min into the data sequence. This coincides with the time
of disturbances in other features of AR 11250 and suggests a complex
coupling among its various structures.; SDO/AIA images of AR11250 made
in the EUV 94 Å band at UT 13:53 and 14:03 on 13 July 2011. The images
are 94 Mm wide. The grayscale is reversed.
---------------------------------------------------------
Title: Turbulent Fluctuations in G-band and K-line Intensities
Observed with the Rapid Oscillations in the Solar Atmosphere (ROSA)
Instrument
Authors: Cadavid, A. C.; Lawrence, J. K.; Christian, D. J.; Jess,
D. B.; Mathioudakis, M.
2012ASPC..463...75C Altcode:
Using the Rapid Oscillation in the Solar Atmosphere (ROSA) instrument at
the Dunn Solar Telescope we have found that the spectra of fluctuations
of the G-band (cadence 1.05 s) and Ca II K-line (cadence 4.2 s)
intensities show correlated fluctuations above white noise out
to frequencies beyond 300 mHz and up to 70 mHz, respectively. The
noise-corrected G-band spectrum presents a scaling range (Ultra High
Frequency “UHF”) for f = 25-100 mHz, with an exponent consistent
with the presence of turbulent motions. The UHF power, is concentrated
at the locations of magnetic bright points in the intergranular lanes,
it is highly intermittent in time and characterized by a positive
kurtosis κ. Combining values of G-band and K-line intensities, the UHF
power, and κ, reveals two distinct “states” of the internetwork
solar atmosphere. State 1, with κ ≍ 6, which includes almost all
the data, is characterized by low intensities and low UHF power. State
2, with κ ≍ 3, including a very small fraction of the data, is
characterized by high intensities and high UHF power. Superposed epoch
analysis shows that for State 1, the K-line intensity presents 3.5
min chromospheric oscillations with maxima occurring 21 s after G-band
intensity maxima implying a 150-210 km effective height difference. For
State 2, the G-band and K-line intensity maxima are simultaneous,
suggesting that in the highly magnetized environment sites of G-band
and K-line emission may be spatially close together. Analysis of
observations obtained with Hinode/SOT confirm a scaling range in the
G-band spectrum up to 53 mHz also consistent with turbulent motions
as well as the identification of two distinct states in terms of the
H-line intensity and G-band power as functions of G-band intensity.
---------------------------------------------------------
Title: Observed Effect of Magnetic Fields on the Propagation of
Magnetoacoustic Waves in the Lower Solar Atmosphere
Authors: Lawrence, J. K.; Cadavid, A. C.
2012SoPh..280..125L Altcode: 2012SoPh..tmp..159L; 2012arXiv1206.4360L
We study Hinode/SOT-FG observations of intensity fluctuations in Ca II
H-line and G-band image sequences and their relation to simultaneous and
co-spatial magnetic field measurements. We explore the G-band and H-line
intensity oscillation spectra both separately and comparatively via
their relative phase differences, time delays and cross-coherences. In
the non-magnetic situations, both sets of fluctuations show strong
oscillatory power in the 3 - 7 mHz band centered at 4.5 mHz, but
this is suppressed as magnetic field increases. A relative phase
analysis gives a time delay of H-line after G-band of 20±1 s in
non-magnetic situations implying a mean effective height difference of
140 km. The maximum coherence is at 4 - 7 mHz. Under strong magnetic
influence the measured delay time shrinks to 11 s with the peak
coherence near 4 mHz. A second coherence maximum appears between 7.5
- 10 mHz. Investigation of the locations of this doubled-frequency
coherence locates it in diffuse rings outside photospheric magnetic
structures. Some possible interpretations of these results are offered.
---------------------------------------------------------
Title: Rapid Fluctuations in the Lower Solar Atmosphere
Authors: Lawrence, J. K.; Cadavid, A. C.; Christian, D. J.; Jess,
D. B.; Mathioudakis, M.
2011ApJ...743L..24L Altcode: 2011arXiv1111.4253L
The Rapid Oscillations in the Solar Atmosphere instrument reveals solar
atmospheric fluctuations at high frequencies. Spectra of variations
of the G-band intensity (I<SUB>G</SUB> ) and Ca II K-line intensity
(I<SUB>K</SUB> ) show correlated fluctuations above white noise to
frequencies beyond 300 mHz and 50 mHz, respectively. The noise-corrected
G-band spectrum for f = 28-326 mHz shows a power law with exponent -1.21
± 0.02, consistent with the presence of turbulent motions. G-band
spectral power in the 25-100 mHz ("UHF") range is concentrated at
the locations of magnetic bright points in the intergranular lanes
and is highly intermittent in time. The intermittence of the UHF
G-band fluctuations, shown by a positive kurtosis κ, also suggests
turbulence. Combining values of I<SUB>G</SUB> , I<SUB>K</SUB> , UHF
power, and κ reveals two distinct states of the solar atmosphere. State
1, including almost all the data, is characterized by low I<SUB>G</SUB>
, I<SUB>K</SUB> , and UHF power and κ ≈ 6. State 2, including only a
very small fraction of the data, is characterized by high I<SUB>G</SUB>
, I<SUB>K</SUB> , and UHF power and κ ≈ 3. Superposed epoch analysis
shows that the UHF power peaks simultaneously with spatio-temporal
I<SUB>G</SUB> maxima in either state. For State 1, I<SUB>K</SUB>
shows 3.5 minute chromospheric oscillations with maxima occurring 21
s after I<SUB>G</SUB> maxima implying a 150-210 km effective height
difference. However, for State 2 the I<SUB>K</SUB> and I<SUB>G</SUB>
maxima are simultaneous; in this highly magnetized environment sites
of G-band and K-line emission may be spatially close together.
---------------------------------------------------------
Title: Effect of Magnetic Fields on Wave Propagation in the Solar
Atmosphere
Authors: Lawrence, John K.; Cadavid, A. C.; Christian, D. J.
2011SPD....42.1729L Altcode: 2011BAAS..43S.1729L
We studied 1 - 24 mHz intensity fluctuations in 3-hour sequences of
high-cadence, high-resolution, broad-band filtergram images taken by the
SOT-FG on board the Hinode spacecraft. The observations consist of near
simultaneous, co-registered G-band (GB), Ca II H-line (HL) intensity
images, and line-of-sight magnetic images calibrated to Gauss with
MDI magnetograms. GB is typically used as a proxy for magnetic fields
while HL is a diagnostic of chromospheric heating. <P />We estimate the
height z1 of the "magnetic canopy,” where magnetic and gas pressures
balance, using potential field extrapolation and the Fontenla 2006
model atmosphere. When z1 is above the height of formation of both
signals, the coherence of the GB and HL oscillations is strong for
frequencies between 3 mHz and 6 mHz and maximal near 5 mHz, around the
acoustic cutoff frequency. Near 3 mHz there is no time delay between
the HL and GB signals indicating a pure standing wave. Above 7 mHz
the time delay settles near 20 sec indicating an upward propagating
acoustic wave. When z1 is below the GB and HL heights of formation the
coherence between the signals drops and has a maximum near 4 mHz. The
time delay remains zero at 3 mHz, but above 7 mHz it is less than 20
sec and decreases with frequency, suggesting that the original acoustic
fluctuations have undergone mode conversion. <P />A similar analysis
of ground-based data acquired with the Rapid Oscillations in the Solar
Atmosphere (ROSA) instrument at the Dunn Solar Telescope finds longer
time delays of 34 sec when z1 is high and 21 sec when z1 is low. This
is consistent with the greater effective formation height of the ROSA
narrowband (1 Å) Ca II K-line core compared to the more broadband
(3 Å) H-line in the Hinode data.
---------------------------------------------------------
Title: Rapid Oscillations in the Solar Atmosphere: Spectra and
Physical Effects
Authors: Lawrence, John K.; Christian, D. J.; Cadavid, A. C.; Jess,
D. B.; Mathioudakis, M.
2011SPD....42.1727L Altcode: 2011BAAS..43S.1727L
High-frequency fluctuations are observed with the Rapid Oscillations in
the Solar Atmosphere (ROSA) instrument (Jess et al. 2010, Solar Phys,
261, 363) at the Dunn Solar Telescope. This can produce simultaneous
observations in up to six channels, at different heights in the
photosphere and chromosphere, at an unprecedentedly high cadence of 0.5
seconds, and at a spatial resolution of 100 km after photometrically
correct speckle reconstruction. <P />Here we concentrate on observations
at two levels. The first is in the G-band of the CH radical at 4305.5Å,
bandpass 9.2Å, with height of formation z < 250 km at a cadence
of 0.525 sec corresponding to Nyquist frequency 950 mHz. The second
is in the Ca II K-line core at 3933.7Å, bandpass 1.0Å, with height
of formation z < 1300 km, and cadence 4.2 sec giving Nyquist
frequency 120 mHz. The data span 53 min, and the maximum field of
view is 45 Mm. The data were taken on 28 May 2009 in internetwork
and network near disk center. <P />Using both Fourier and Morlet
wavelet methods we find evidence in the G-band spectra for intensity
fluctuations above noise out to frequencies f >> 100 mHz. The
K-line signal is noisier and is seen only for f < 50 mHz. With
wavelet techniques we find that G-band spectral power with 20 <
f < 100 mHz is clearly concentrated in the intergranular lanes and
especially at the locations of magnetic elements indicated by G-band
bright points. This wavelet power is highly intermittent in time. By
cross-correlating the data we find that pulses of high-frequency G-band
power in the photosphere tend to be followed by increases in K-line
emission in the chromosphere with a time lag of about 2 min.
---------------------------------------------------------
Title: Space - Time Distribution of G-band and Ca II H-line Intensity
Oscillations in Hinode/SOT - FG Observations
Authors: Lawrence, J. K.; Cadavid, A. C.
2010SoPh..261...35L Altcode: 2009arXiv0907.5001L
We study the space - time distributions of intensity fluctuations in 2
- 3 hour sequences of multi-spectral, high-resolution, high-cadence,
broad-band filtergram images of the Sun made by the SOT - FG system
aboard the Hinode spacecraft. In the frequency range 5.5<f<8.0
mHz both G-band and Ca II H-line oscillations are suppressed in
the presence of magnetic fields, but the suppression disappears for
f>10 mHz. By looking at G-band frequencies above 10 mHz we find
that the oscillatory power, both at these frequencies and at lower
frequencies, lies in a mesh pattern with cell scale 2 - 3 Mm, clearly
larger than normal granulation, and with correlation times on the order
of hours. The mesh pattern lies in the dark lanes between stable cells
found in time-integrated G-band intensity images. It also underlies
part of the bright pattern in time-integrated H-line emission. This
discovery may reflect dynamical constraints on the sizes of rising
granular convection cells together with the turbulence created in
strong intercellular downflows.
---------------------------------------------------------
Title: Magnetic and Dynamical Properties of Intensity Oscillations
in the Lower Solar Atmosphere
Authors: Cadavid, A. C.; Lawrence, J. K.
2009AGUFMSH51A1259C Altcode:
We study 1 - 24 mHz intensity fluctuations in 2-3 hour sequences of
high-cadence, high-resolution images taken by the SOT-FG on board
Hinode. The observations consist of near simultaneous, co-registered
G-Band (GB), Ca II H-Line (HL), and line-of-sight polarization density
(V/I) images. MDI full-disk and high-resolution magnetograms are used
to calibrate the V/I to magnetic field in Gauss. This equips us to
compare fluctuations in magnetic and non-magnetic regions, as well as to
study recently discovered patterns of enhanced oscillatory power in the
photosphere and chromosphere. Oscillatory power in non-magnetic regions
of HL images peaks at ~5 mHz, characteristic of an acoustic signal. As
magnetic field increases up to ~ 200 G the spectrum is significantly
diminished in strength, with a shift toward lower frequencies ~ 4 mHz
starting between 100 - 200 G. In GB images the magnetic spectrum is
dominant below ~3 mHz, perhaps due to contributions from GB bright
points, while in non-magnetic regions the acoustic contribution
peaks at ~ 4 mHz. To further investigate these effects we estimate
the height of the “magnetic canopy,” where plasma β≈1, via
potential field extrapolation from calibrated magnetic images and
the VAL 3C or more recent model atmospheres. We then segregate the
various contributions to the power according to whether the signal
originates above or below the canopy. We have found previously that
GB oscillatory power at frequencies above 10 mHz lies in a mesh-like
pattern with characteristic cell scale 2 - 3 Mm, larger than normal
granulation, and with correlation times on the order of hours. By
appropriate segregation of image pixels we find that at the sites
of enhanced > 10 mHz GB spectral power, there is in fact excess
spectral power at all frequencies, both in GB and HL.
---------------------------------------------------------
Title: G-Band Bright Point Oscillations Underlying Chromospheric Ca
II H-Line Emission
Authors: Lawrence, John K.; Cadavid, A. C.
2009SPD....40.1004L Altcode:
We study the spatial distributions of oscillatory power and of
emission in two sequences of high-cadence, high-resolution images
taken by the Solar Optical Telescope on board Hinode. The sequences
consist of simultaneous, co-registered G-Band (GB) and Ca II H-Line
(HL) images with pixel scale 80 km and fields of view 40 x 40 Mm
and 80 x 40 Mm. The first sequence has cadence 21 s over 3 hours on
2007 April 14; the other has cadence 24 s over 2 hours on 2007 March
30. Both sequences include network and internetwork at heliocentric
angle 35 degrees. <P />The G-Band images were filtered to emphasize
the smallest features and thus to isolate phenomena connected to the
G-Band bright points (GBPs). These appear in intergranular lanes and
are associated with magnetic elements. The filtered G-Band images
serve to segment areas in H-Line and magnetic images and therefore
to explore their connections to the GBPs. <P />Time averaged Morlet
wavelet transforms give smoothed Fourier spectra for each spatial
location in the data. Averaging over four different frequency bands
highlights different physical regimes: "evolutionary” timescales (f
< 1.2 mHz); evanescent frequencies just below the acoustic cutoff
(2.6 mHz < f < 4.2 mHz); high frequencies just above the cutoff
(5.5 mHz <f 10mHz). These last frequencies require data cadences
< 50 s. Spectral images for the filtered GBP data show that the
associated spectral power is greatest in the evanescent frequency
band. The apparent absence of magnetic shadowing suggests non-acoustic
waves. An image of time-integrated H-Line emission shows strong and
detailed correlation with the spatial distribution of spectral power
in the GBP data, thus suggesting a possible energy source.
---------------------------------------------------------
Title: Sources and Propagation of High Frequency Waves in the Solar
Photosphere and Chromosphere
Authors: Lawrence, John K.; Cadavid, A. C.
2009SPD....40.1002L Altcode:
We study the spatial distribution of oscillatory power in two sequences
of high-cadence, high-resolution images taken by the Solar Optical
Telescope on board Hinode. The sequences consist of simultaneous,
co-registered G-Band (GB) and Ca II H-Line (HL) images with pixel
scale 80 km and fields of view 40 x 40 Mm and 80 x 40 Mm. The first
sequence has cadence 21 s over 3 hours on 2007 April 14; the other
has cadence 24 s over 2 hours on 2007 March 30. Both sequences include
network and internetwork at heliocentric angle 35 degrees. <P />Time
averaging of Morlet wavelet transforms gives smoothed Fourier spectra
for each spatial location in the GB and HL data. We averaged over four
different frequency bands to highlight different physical regimes:
"evolutionary” timescales (f < 1.2 mHz); evanescent frequencies
just below the acoustic cutoff ( 2.6 mHz < f < 4.2 mHz); high
frequencies just above the cutoff (5.5 mHz <f 10mHz) These last
frequencies require data cadences < 50 s. <P />The evanescent and
high frequency spectral images display clear magnetic shadowing in both
GB and HL channels, though more strongly in the HL. Thus the heights at
which the GB and HL are formed must both straddle the magnetic canopy,
with the HL higher up. Interestingly, in the VHF band the magnetic
shadowing is markedly weakened. The VHF case shows GB power in the
internetwork that is arranged in the boundary web of a cellular pattern
with scales 2 - 3 Mm. These are found to coincide with the boundaries
of stable clusters of granules. These dark boundaries may correspond
to downflows that control the cell structuring and that could be the
source of acoustic power.
---------------------------------------------------------
Title: Phase And Time Lags Between G-band, H-line And Magnetic
Fluctuations In The Photosphere And Chromosphere
Authors: Cadavid, Ana Cristina; Lawrence, J.
2009SPD....40.1003C Altcode:
We study the oscillatory power in two sequences of high-cadence,
high-resolution images taken by the SOT on board Hinode. The sequences
consist of simultaneous, co-registered G-Band (GB), Ca II H-Line (HL),
and the absolute value of line-of-sight magnetic field (|B|) images,
with pixel scale 80 km and fields of view 40 x 40 Mm and 80 x 40 Mm. The
first sequence has cadence 21 s over 3 hours on 2007 April 14; the
other has cadence 24 s over 2 hours on 2007 March 30. Both sequences
include network and internetwork at heliocentric angle 35 degrees. <P
/>We investigate phase relations between fluctuations of pairs of the
three data sets as functions of their common frequencies. The height Z1
of the "magnetic canopy,” where plasma beta equal 1, is estimated via
a potential field extrapolation and the VAL 3C model atmosphere. The
phase shifts at each frequency are taken as the maxima of normalized
histograms made by binning the phase shifts for all space-time pixels
segregated by high or low Z1. We interpret the phase shifts as a
constant phase shift plus a constant time shift. For Z1 > 1.3 Mm G
leads H with a constant time lag of 10 sec for frequencies above the
acoustic cut-off, suggesting propagating acoustic waves. For Z1 <
1.15 Mm the time lag between the G and H signals is smaller. Both G and
H lead the |B| fluctuations by a constant phase shift of 100 degrees for
all Z1. For Z1 < 1.15 G also leads |B| by 3±1 sec and H trails |B|
by 6±1 sec. For Z1 > 1.3 Mm these time lags disappear. Thus we can
locate an effective "height” of |B| about 20 km above GB and of HL
about 40 km above |B|.
---------------------------------------------------------
Title: Fine Scale, Rapid Dynamics of the Solar Atmosphere from
Space-Based Versus Ground- Based Observations
Authors: Lawrence, J. K.; Cadavid, A. C.
2008AGUFMSH41A1609L Altcode:
We compare analyses of multi-wavelength, high-cadence sequences of
high-resolution solar images that are derived from ground-based
observations and from space-based observations. The original
analyses aim to show the effects of magnetism on the propagation of
wave energy from the photosphere into the solar atmosphere. Here we
focus on differences that arise from the differing circumstances of
the data acquisition. The ground-based data are a 9 hour sequence of
Swedish Vacuum Solar Telescope filtergram images made on 1998 May 30
in the photospheric G-band and in the chromospheric CaII K-line with
21 s cadence. Atmospheric distortion was removed by phase diversity
reconstruction, and the images were 4 x 4 square averaged to a spatial
resolution of 0.24 Mm/px. A sequence of line-of-sight magnetograms had
lesser resolution and longer cadence. The primary space-based data are
a 6 hour sequence at 1 min cadence of Hinode SOT-FG images in G-band
and CaII H-line and line-of-sight magnetic field, made on 2007 May
2. For space-based data phase reconstruction is irrelevant. The spatial
scale is 0.08 Mm/px but can be averaged to lower resolutions. The
relative phases of oscillations in the different data channels and the
correlations between oscillation periods and spectral intensities show
significant differences between the space- and ground-based cases. These
differences may come partly from terrestrial atmospheric fluctuations
that, in spite of phase reconstruction, act to artificially strengthen
correlations among the ground-based data channels. For example, the
photospheric and the chromospheric intensity fluctuations are more
strongly correlated in the ground data than in the space data. The
relative phases of oscillations in the three data channels show some
different dependences on magnetic field strength between the two
cases. This may be attributable to the higher quality of the available
space magnetic data.
---------------------------------------------------------
Title: Quasi-periodic patterns coupling the Sun, solar wind and
the Earth
Authors: Ruzmaikin, Alexander; Cadavid, Ana Cristina; Lawrence, John
2008JASTP..70.2112R Altcode:
The spectrum of velocity and magnetic fields in the solar wind is
self-similar (power-law type) in the frequency range greater than
>1/day indicating well-mixed turbulence. But it loses self-similarity
for lower frequencies indicating the presence of large-scale patterns,
which are intermittently generated inside the Sun and propagate from the
Sun to the Earth. Here we discuss the spatia-temporal characteristics
and origin of the 1.3-year quasi-periodic pattern found inside the Sun
by helioseismic methods and detected in the solar wind. To identify
and characterize this pattern on the Sun we use time series of solar
magnetic Carrington maps generated at the Wilcox Solar Observatory
and independent component data analysis. This analysis shows the
latitudinal distribution of the pattern, its variable frequency and
intermittent appearance.
---------------------------------------------------------
Title: Rotational Quasi-Periodicities and the Sun - Heliosphere
Connection
Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A.
2008SoPh..252..179L Altcode: 2008arXiv0803.3260L; 2008SoPh..tmp..138L
Mutual quasi-periodicities near the solar-rotation period appear in
time series based on the Earth's magnetic field, the interplanetary
magnetic field, and signed solar-magnetic fields. Dominant among these
is one at 27.03±0.02 days that has been highlighted by Neugebauer et
al. (J. Geophys. Res.105, 2315, 2000). Extension of their study in
time and to different data reveals decadal epochs during which the
≈ 27.0 days, or a ≈ 28.3 days, or other quasi-periods dominate
the signal. Space-time eigenvalue analyses of time series in 30 solar
latitude bands, based on synoptic maps of unsigned photospheric fields,
lead to two maximally independent modes that account for almost 30%
of the data variance. One mode spans 45° of latitude in the northern
hemisphere and the other one in the southern. The modes rotate
around the Sun rigidly, not differentially, suggesting connection
with the subsurface dynamo. Spectral analyses yield familiar dominant
quasi-periods 27.04±0.03 days in the North and at 28.24±0.03 days
in the South. These are replaced during cycle 23 by one at 26.45±0.03
days in the North. The modes show no tendency for preferred longitudes
separated by ≈ 180°.
---------------------------------------------------------
Title: Principal Components and Independent Component Analysis of
Solar and Space Data
Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A.
2008SoPh..248..247C Altcode: 2007arXiv0709.3263C
Principal components analysis (PCA) and independent component analysis
(ICA) are used to identify global patterns in solar and space data. PCA
seeks orthogonal modes of the two-point correlation matrix constructed
from a data set. It permits the identification of structures that remain
coherent and correlated or that recur throughout a time series. ICA
seeks for maximally independent modes and takes into account all
order correlations of the data. We apply PCA to the interplanetary
magnetic field polarity near 1 AU and to the 3.25R<SUB>⊙</SUB>
source-surface fields in the solar corona. The rotations of the
two-sector structures of these systems vary together to high accuracy
during the active interval of solar cycle 23. We then use PCA and ICA
to hunt for preferred longitudes in northern hemisphere Carrington
maps of magnetic fields.
---------------------------------------------------------
Title: Search for Persistent Quasi-Periodicities in the Solar and
Interplanetary Magnetic Fields
Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A.
2007AGUFMSH23A1165L Altcode:
Previous analysis of the radial component of the interplanetary magnetic
field from 1962 - 1998 has revealed a dominant frequency of 27.03 days
to 0.02 day accuracy (Neugebauer, et al., 2000). We have repeated and
extended this analysis with OMNI data from 1963 - 2007 obtained from the
Coordinated Heliospheric Observations (COHO) database. Over this longer
data string we find that the 27.03 day Lomb-Scargle periodogram peak
is reduced while two side peaks near 26.8 days and 27.6 days become
almost as strong. In the interval 1999-2007 there are two dominant
periods near 26.5 days and 27.2 days. As a solar counterpart to the
above analysis we have searched for persistent rotation periods near
27 days of global patterns of photospheric magnetic fields derived from
Wilcox Solar Observatory synoptic Carrington rotation maps. Techniques
applied include, principal components analysis, independent component
analysis, singular spectrum analysis, wavelet spectral analysis,
and complex demodulation. We find a variety of quasi- periodicities
between 26 and 29 days that remain coherent for 1 - 2 years. In the
southern solar hemisphere the strongest periodicity is at 28.2 days,
while in the northern hemisphere it is around 26.5 days. Neugebauer,
M., Smith, Smith, E.J., Ruzmaikin, A., Feynman, J., Vaughan, A.H. 2000,
J. Geophys. Res., 106, A5, 8363.
---------------------------------------------------------
Title: Quasi-Periodicities, Magnetic Clusters and Solar Activity
Authors: Cadavid, A. C.; Lawrence, J. K.; Sandor, C.; Ruzmaikin, A.
2006AGUFMSH21A0325C Altcode:
To investigate quasi-periodicities, 12 hour averages of the radial
component of the interplanetary magnetic field and the solar wind speed,
covering ~ 42 (1963-2005) years were analyzed. A Lomb periodogram for
data up to 1998 showed a dominant period of 27.03 days as fpund in
earlier results. Including cycle 23, a dominant period of 27.06 days
was identified. Analysis of the solar cycles independently showed a
dominant period of 27.03 days in solar cycle 20, but not in the other
cycles. To investigate the degree of persistency of a particular signal,
the technique of complex demodulation was applied since it permits
the determination of continuous changes in time of the amplitude and
frequency of the signal relative to the test signal. It was found that
a period of ~27.6 days gave an overall flat phase function in time,
while other periods < ~0.5 day shorter and longer, with comparable
but lesser amplitude, come and go. To investigate the solar sources
of these periods, the method of principal component analysis (PCA) was
applied to ~ 27 years (1976-2003) of synoptic maps obtained with the NSO
Kitt Peak Vaccum Telescope. Before the analysis, the original synoptic
maps were shifted relative to the previous maps using the period under
investigation. Using PCA the Empirical Orthogonal Functions (EOFs)
and Pricipal Components (PCs) were found for the set of synoptic maps
rescaled to the rotation rate 27.03 days in 1999-2003. The patterns
characterized by EOFs 1 and 2 are mostly axisymmetric and PCs 1 and
2 show solar cycle variability. EOF3 shows only one well-localized
pattern in the Southern Hemisphere which is markedly non-axisymmetric
and PC3 has peaks at times when fast CMEs occur.
---------------------------------------------------------
Title: Solar Cycle Dependence of Solar Wind Geoeffectiveness
Authors: Lawrence, J. K.; Cadavid, A. C.
2006AGUFMSH24A..04L Altcode:
We find clear solar cycle dependence of the specific ways in which
different physical properties of the solar wind (SW) couple to
different aspects of geomagnetic activity. Geomagnetic activity is
described by orthogonalized versions Kp, PC/Kp, and Dst/Kp/PC of
the familiar indices. These represent, respectively, geomagnetic
activity measured at mid-latitudes, geomagnetic activity measured
in the (North) polar region and forced to be linearly independent
of Kp, and finally geomagnetic activity measured at low latitudes
and forced to be independent of both Kp and PC. Solar wind inputs
are hourly averages of the SW plasma beta, dynamical pressure, the
imposed duskward electric field, and a derived parameter related to
nonthermally fast SW structures. These were measured by the Wind and
ACE spacecraft from 1995 through December 2005. They were obtained from
the OMNI2 data set. We connect these quantities using multivatiate
factor analysis. During the active phase of Cycle 23 (1998- 2003)
we find that Kp is primarily governed by SW dynamical pressure, PC/Kp
almost entirely by the imposed electric field, and Dst/Kp/PC by the SW
plasma beta and by nonthermal structures. This result holds separately
for the rising and falling phases of the active Sun. However, during
the preceding quiet Sun period (1995-1997) the nonthermal structures
were unimportant. Then Dst/Kp/PC was governed by the SW plasma beta
and dynamical pressure. At the same time, Kp was coupled directly to
SW pressure and electric field, and negatively to plasma beta.
---------------------------------------------------------
Title: Persistent Peridicities in the Solar Wind and Photospheric
Magnetic Field Coherent Structures
Authors: Cadavid, Ana C.; Lawrence, J. K.; Ruzmaikin, A.
2006SPD....37.1106C Altcode: 2006BAAS...38..239C
To investigate persistent periodicities, 12-hour averages of the
radial component of the interplanetary magnetic field and the solar
wind speed, covering 42 years (1963-2005), were analyzed. A Lomb
periodogram for the data up to 1998 showed maximum spectral power at
a period of 27.03 days, as encountered previously by Neugebauer et
al. (2000). Including cycle 23 shifted the peak to 27.06 days. Analysis
of solar cycles 20 - 23 separately showed a dominant period of 27.03
days in solar cycle 20, but not in the other cycles.To investigate
the degree of persistency and phase coherence of a particular signal,
the technique of complex demodulation was applied since it permits
the determination of continuous changes in time of the amplitude and
frequency of the signal relative to a test signal. It was found that
for a reference signal of 27.03 days, the phase was a flat function of
time during the intervals 1965-1972 and 1995-1997. The phase decreased
in time from 1972-1995 and increased after 1997. This implies that
for the intervals 1972-1995 and 1997-2005 other periodicities better
characterize the data. A period of 27.6 days gave an overall flat phase
function in time, while other periods < 0.5 day shorter and longer,
with comparable but lesser amplitude, come and go.To investigate the
solar sources of these periods, the methods of principal component
analysis (PCA) and independent component analysis (ICA) were applied
to 27 years (1976-2003) of synoptic maps obtained with the NSO Kitt
Peak Vacuum Telescope. Before the analysis, the original synoptic
maps were shifted relative to the previous maps using the particular
period under investigation. PCA and ICA identified 3 modes for the
27.03 reference period and 2 modes for the 27.6 period that showed
clusters of magnetic activity at preferred longitudes.
---------------------------------------------------------
Title: Stellar Objects with Infrared Excess in the \textit{Spitzer
Space Telescope} Wide-Area Infrared Extragalactic Survey (SWIRE)
Authors: Morales, F. Y.; Werner, M. W.; Padgett, D.; Fajardo-Acosta,
S.; Stevens Stern, D.; Chary, R. -R.; Dawson, S.; Dickinson, M.;
Stauffer, J. R.; Smith, B.; Walton, S.; Cadavid, A. C.; SWIRE Team;
Ana Christina Cadavid Collaboration
2005AAS...207.6344M Altcode: 2005BAAS...37Q1254M
We have identified two new debris disk candidates in the \textit{Spitzer
Space Telescope} Legacy Project Wide-Area InfraRed Extragalactic Survey
(SWIRE). We searched two of the six SWIRE photometric survey fields,
and present 3.6-160 μ m photometry obtained with the Infrared
Array Camera (IRAC) and the Multiband Imaging Photometer (MIPS)
instruments. We followed up the candidates with spectro-photometry
from 4-36 μ m using the Infrared Spectrometer (IRS) low resolution
modules. The candidates spectral energy distributions (SEDs) were
constructed from Keck's LRIS optical spectroscopy, \textit{2MASS} J,
H, Ks, \textit{Spitzer's} IRAC 3.6, 4.5, 5.8, 8.0 μ m bands, and MIPS
24 m photometry (70 and 160 μ m when detected). The two candidates,
Lockman_tile32_1228 and EN1_tile22_11767, were selected by their 24
μ m emission above photospheric expected levels, an indicator of
the Vega phenomenon, or the presence of circumstellar dust at ∼120
K. Object Lockman_tile32_1228 has 70 and 160 μ m surplus in flux,
suggesting the presence of cold dust represented by blackbody curves
of ∼65 and ∼23 Kelvin. The infrared spectra reveal both sources to
have infrared excess at wavelengths shorter than 24 μ m as well. The
shape of Lockman_tile32_1228's SED exhibits interesting features
from 8 to 20 μ m, possibly due to the composition of the emitting
material. To confirm these sources are stellar objects, 0.32-0.95 μ
m optical spectra was obtained via W.M. Keck Observatory's LRIS dual
spectrometer. LRIS blue and red arm spectroscopy confirms the candidates
are K-type main sequence stars about 195 and 160 pc away from the
Sun. At high-galactic latitudes, where interstellar material is scarce,
the SEDs of these sources illustrate there can exist a diversity of
debris disk evolutionary states in foreground stars of the Galaxy. <P
/>This work is based on observations made with \textit{Spitzer Space
Telescope}, which is operated by the Jet Propulsion Laboratory,
California Institute of Technology, under NASA contract 1407.
---------------------------------------------------------
Title: Solar Wind Interaction and Orthogonal Magnetospheric Indices
Authors: Lawrence, J. K.; Cadavid, A. C.
2005AGUFMSM43A1214L Altcode:
Multivariate methods can help to untangle connections between indices
of magnetospheric activity and solar wind (SW) parameters. The data are
3-hour resolution time series spanning the period 1996 JAN 25 to 2004
SEP 17. The time series include Kp, the Dst and PC (polar cap) indices
and an auroral POES index derived from NOAA satellite observations,
plus OMNI SW data. The Kp index correlates with many other indices
of magnetospheric activity due to its association with the convection
electric field (see the survey in Thomsen 2004). We find correlation
coefficients C(Kp,PC)=0.57, C(Dst,Kp)=-0.44 and C(Dst,PC)=-0.37. POES
correlations are small. We replace PC with a variable PC/Kp containing
that part of PC orthogonal to Kp. Likewise we replace Dst with Dst/KpPC,
orthogonal to both Kp and to PC/Kp. The independent indices behave
very differently from the original ones. Factor analysis gives five
latent factor modes relating the terrestrial and SW sets. (1) The only
factor containing the solar cycle connects sunspot number fluctuations
to POES and PC/Kp only. This is the only factor containing POES or
PC/Kp, so these vary mainly together. (2) Only one factor contains
the south IMF, and this connects its fluctuations to Kp only. (3)
A third factor relates strong responses in Dst/KpPC to increases
in SW ram pressure, temperature and to alpha/proton ratio, an
indicator of solar ejecta in the SW. (4) A fourth factor relates
strong responses in Dst/KpPC to increases in excess SW coolness,
another indicator of solar ejecta, along with drops in mean IMF, SW
ram pressure and plasma beta. (5) The fifth factor relates increases
in Kp to increased mean IMF, SW speed, coolness and plasma beta. We
present a path analysis calculation quantifying the web of causal
relations between the SW and the independent terrestrial indices via
the intermediate latent factors. Thomsen, M.F. 2004, Space Weather,
2, S11004, doi:10.1029/2004SW000089
---------------------------------------------------------
Title: Coherent Structures vs Independent Modes of the Axisymmetric
Magnetic Field Fluctuations
Authors: Cadavid, A. C.; Lawrence, J. K.; McDonald, D. P.; Ruzmaikin,
A.
2005ASPC..346...91C Altcode:
Quasi periodicities on scales of 1 to 2.5 years have been observed in
solar, interplanetary and geomagnetic time series. The relation of
these signals to 1 and 1.3 yr fluctuations in the solar interior,
suggest the presence of structures or characteristic modes in
the magnetic field, generated by the dynamo, that extend into the
heliosphere. We have applied the methods of principal component
analysis (PCA) and independent component analysis (ICA) to search
for the coherent structures (PCA) and independent global modes (ICA)
of the axisymmetric solar magnetic field. While PCA is effective in
identifying the coherent modes that describe the 22 yr solar cycle,
ICA uncovers the independent global modes the with characteristic 1 to
2.5 yr quasi periods observed in heliospheric and helioseismic time
series. Five modes capture the salient properties of the data. Two
modes describe the polar and high latitude fields, and present 1-1.5
yr quasi periodicities. The other three modes correspond to low and
mid-latitude phenomena and show both 1.3 yr and 1.7 yr variations.
---------------------------------------------------------
Title: Quasi periodicities in the Fluctuations of the Axisymmetric
Solar Magnetic Field from Independent Component Analysis
Authors: McDonald, D. P.; Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin,
A.
2005AGUSMSP43B..05M Altcode:
Observed solar, interplanetary and geomagnetic time series contain quasi
periodicities on the order of 1 to 2.5 years. The further discovery
of 1.3 year fluctuations in helioseismic observations suggests that
a variety of signals may be related to the underlying dynamo in the
Sun. We have applied the methods of principal component analysis (PCA)
and independent component analysis (ICA) to search for the coherent
structures (PCA) and independent global modes (ICA) of the axisymmetric
solar magnetic field. While PCA was shown to be effective in identifying
the coherent modes that describe the 22 yr solar cycle, ICA uncovers the
independent global modes with characteristic 1 to 2.5 yr quasi periods
observed in heliospheric and helioseismic time series. We found that
five modes effectively describe the data in both spatial and temporal
domains. Two modes describe the polar and high latitude fields,
and present 1-1.5 year quasi periodicities. The other three modes
correspond to low and mid-latitude phenomena and show both 1.3 year
and 1.7 year variations. By comparing the characteristic timescales,
dates of occurrence and heliocentric latitudes of these modes, we
connect them to their manifestations in heliospheric time series.
---------------------------------------------------------
Title: Coherent Structures and Rotation Rates in Coronal Activity,
from Principal Component Analysis
Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A.
2005AGUSMSP21B..07C Altcode:
Principal component analysis (PCA) offers a way to extract those
structures that remain spatially coherent throughout a time series. We
apply this method to a ~ 28 year time series of Wilcox Solar Observatory
Carrington rotation maps (CR) of the 3.25 R coronal source surface field
obtained via a potential field extrapolation. We find that over 99%
of the variance is contained in the first eight modes. Mode 1, carrying
81.5% of the variance, and modes 2 and 3 containing 13% of the variance,
have "dipole" structures. Modes 4-8, with a "quadruple" structure,
contain 4.5% of the variance. The principal components (PCs) give the
time dependence of the modes. We combine the PCs of modes 2 and 3 to
get the amplitude and phase of a structure that behaves essentially as
a dipole in the equatorial plane. During activity minima the structure
is relatively weak and rotates at the 27.275 day Carrington rate. During
the active periods of cycles 21 and 22 the amplitude is large and highly
intermittent, and the dipole rotates more rapidly than the Carrington
rate with a synodic period of 26.6 days. During cycle 23, however, the
dipole moves backward in Carrington longitude with a synodic period
of 27.8 days. The average of these is ~ 27.0 days, though this is
actually realized only sporadically. The phase changes that occur at
shorter time scales and that coincide with intermittent changes in the
dipole amplitude seem to represent essentially random effects of the
passage of the magnetic field through the convection zone. While the
lower modes tend to lock the hemispheres together the higher modes
present separate Northern and Southern hemisphere quadrupole-type
patterns that drift in Carrington longitude similarly to the equatorial
dipole. Over some periods the drift in each hemisphere closely tracks
the other over a wide range of timescales. However, there are large,
decadal-scale excursions in which first one hemisphere leads in phase
by 3 or 4 rotations and then the other leads by a similar amount.
---------------------------------------------------------
Title: Magnetic Topology and Wave Propagation in the Solar Atmosphere
Authors: Lawrence, J. K.; Cadavid, A. C.; McIntosh, S. W.; Berger,
T. E.
2005AGUSMSH13C..01L Altcode:
We analyze a 9 hr sequence of simultaneous, high resolution, 21 s
cadence SVST G-band and K-line solar filtergrams plus magnetograms
of lower cadence and resolution. The data include both network and
internetwork areas (Berger and Title 2001, Cadavid, et al. 2003,
Lawrence, et al. 2003). Time series of the G-band and K-line data are
compared after filtering by a Morlet wavelet transform of period 2.5
min. On the average, the K-line signal is delayed by several seconds
after the G-band signal Δ T = 8.6 ± 0.1 s for weak (|BZ| < 50 G)
magnetic field in internetwork but Δ T = 7.2 ± 0.1 s for weak field
in an area including network. The internetwork has no strong fields,
but in network (|BZ| > 80 G) the mean delay time drops to Δ T =
3.4 ± 0.3 s. This is consistent with results by McIntosh, Fleck and
Tarbell (2004) using TRACE 1600Å and 1700Å UV image series. Our
principal result is that the time delay is greater in the internetwork
than in the network by 1.4 ± 0.1 s, even for the same local magnetic
field strength. This suggests that the difference must be an effect
of the field topology. Spatial maps of time delays, in comparison
to maps of such topological quantities as the height in the solar
atmosphere at which the plasma β = 1, offer additional details of the
relationship between wave propagation and the magnetic fields in the
solar atmosphere. This work was supported in part by grants NSF-ATM
9987305 and NASA-NAG5-10880. The SVST is operated by the Swedish
Royal Academy of Sciences at the Spanish Observatorio del Roque de
los Muchachos of the Instituto de Astrofisica de Canarias. Berger,
T.E. and Title, A.M. 2001, ApJ, 553, 449. Cadavid, A.C., et al. 2003,
ApJ, 586, 1409. Lawrence, J.K., et al. 2003, ApJ, 597, 1178. McIntosh,
S.W., Fleck, B. and Tarbell, T.D. 2004, ApJ, 609, L95.
---------------------------------------------------------
Title: Independent Global Modes of Solar Magnetic Field Fluctuations
Authors: Cadavid, A. C.; Lawrence, J. K.; McDonald, D. P.; Ruzmaikin,
A.
2005SoPh..226..359C Altcode:
Observed solar, interplanetary and geomagnetic time series contain
quasi periodicities on scales of 1-2.5 years. The further discovery
of 1.3 year fluctuations in helioseismic observations suggests that
a variety of signals may be related to the underlying dynamo in the
Sun. We use independent component analysis to study the temporal and
spatial variations of a few statistically independent global modes of
the axisymmetric solar magnetic field over a period of 25 years. Five
modes capture the salient properties of the data. Two modes describe
the polar and high latitude fields, and present 1-1.5 year quasi
periodicities. The other three modes correspond to low and mid-latitude
phenomena and show both 1.3 and 1.7-year variations. By comparing
the characteristic time scales, dates of occurrence and heliocentric
latitudes of these modes, we connect them to their manifestations in
heliospheric time series.
---------------------------------------------------------
Title: Principal Component Analysis of the Latitudinal and
Longitudinal Structure of the Photospheric Magnetic Cycle
Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A.
2004AAS...204.3708L Altcode: 2004BAAS...36Q.710L
We average magnetic fields in NSO synoptic maps over longitude and bin
the result by sin(latitude). Also, we average over a band of latitudes
and bin by longitude. A time stack of one-dimensional latitude "images"
resembles the Maunder butterfly diagram. Time stacks of longitude
"images" can be re-mapped to arbitrary rotation periods. <P />Principal
component analysis recombines images in a stack into mutually orthogonal
"empirical orthogonal functions" (EOFs). The EOFs are ordered by
how well each correlates with the full set of images. The principal
components (PCs) give the evolution of each EOF as a function of any
ordering parameter, such as time. The original data can be wholly or
partially reconstructed from subsets of the EOFs and their PCs. <P />Our
latitudinal EOFs have a few leaders whose PCs show both the 11/22-year
cycle and repeating substructure. Following are EOFs whose PCs show
the cycle but no repeated substructure. Next are EOFs with small scale
structure independent of the cycle. The least correlated EOFs contain
high latitude, mostly unipolar fields. We suggest associating these four
subsets of the EOFs with, respectively, global dynamo toroidal fields,
turbulently disordered structures fed by the toroidal fields, a possible
local surface dynamo process, and a global poloidal component. <P
/>We also studied a stack of longitudinal images of fields that were
averaged over latitude between N25 and N35 degrees. Two especially
active longitudes 180 degrees apart rotate with a period of 27.8
days. Structure at these longitudes dominates the leading EOFs. The
corresponding PCs are active over the whole span of the data. <P />This
work was supported by NASA Grant NAG5-10880. NSO/Kitt Peak data used
here are produced cooperatively by NSF/NOAO, NASA/GSFC, and NOAA/SEL.
---------------------------------------------------------
Title: Two-dimensional Empirical Orthogonal Functions of the
Photospheric Magnetic Cycle
Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A.
2004AAS...204.3707C Altcode: 2004BAAS...36Q.710C
We carried out a principal component analysis (PCA) on sequences
of NSO magnetic flux synoptic maps by Carrington rotation. Two
data sets were investigated: (i) a sequence of 364 images from
Carrington rotation 1625 to 2007, with image size 360 x 180 pixels
(1 degree/pixel in longitude and sin(latitude)*90 in latitude for
both hemispheres); (ii) a sequence of 79 higher resolution maps of
size 1800 x 900 pixels starting at Carrington rotation 1913. The PCA
of a time series yields an eigenvalue spectrum, the corresponding
eigenfunctions (modes or "empirical orthogonal functions" (EOFs)),
and the principal components which describe the time evolution of the
modes. The dominant EOFs are associated with those structures that
remain spatially coherent throughout intervals of the time series,
and correspond to the functions with the highest eigenvalues. If the
eigenvalue spectrum is dominated by only a few large members, then
the corresponding few EOFs will mainly characterize the data. The rest
will contain transient fluctuations. We apply the technique to the two
dimensional maps and determine which EOFs dominate during different
times of the solar cycle. We find that the dominant modes are associated
with the active part of the cycle as expected, while the weaker modes
characterize the quiet periods. The increasing and declining phases
are associated with modes of intermediate eigenvalues. We reconstruct
the time series by projecting onto the three classes of modes and
investigate the probability distribution function (PDF) of "projected"
magnetic flux. We compare these results to the PDFs obtained from
artificial data generated by dynamo models. This work was supported
in part by Grant NASA-NAG5-10880. NSO/Kitt Peak data used here are
produced cooperatively by NSF/NOAO, NASA/GSFC, and NOAA/SEL.
---------------------------------------------------------
Title: A simple model of solar variability influence on climate
Authors: Ruzmaikin, Alexander; Lawrence, John K.; Cadavid, Ana Cristina
2004AdSpR..34..349R Altcode:
We present a simple dynamic model of solar variability influence on
climate, which is truncated from the stratospheric wave-zonal flow
interaction dynamics over a β-plane. The model consists of three
ordinary differential equations controlled by two parameters: the
initial amplitude of planetary waves and the vertical gradient of the
zonal wind. The changes associated with the solar UV variability, as
well as with seasonal variations, are introduced as periodic modulations
of the zonal wind gradient. Influence of the Quasi-Biennial Oscillation
is included as a periodic change of the width of the latitudinal extent
of the β-plane. The major climate response to these changes is seen
through modulation of the number of cold and warm winters.
---------------------------------------------------------
Title: Influence of Photospheric Magnetic Fields and Dynamics on
Chromospheric K-Line Emission
Authors: Lawrence, J. K.; Cadavid, A. C.; Miccolis, D.; Berger, T. E.;
Ruzmaikin, A.
2003ApJ...597.1178L Altcode:
We analyze a 9 hr sequence of simultaneous, high-resolution,
high-cadence G-band and K-line solar filtergrams plus magnetograms
of lower cadence and resolution. Images include both network
and internetwork. The magnetic and filtergram intensities, their
fluctuations, and relative phases change with progressive strengthening
of local magnetic field. At increased flux levels, sudden photospheric
downflows create long-lived magnetic elements. For weak magnetic fields
the K-line and G-band intensities include an oscillatory component
with period 4 minutes. For stronger fields, the K-line period shifts
to 5 minutes, while the G-band fluctuations fade due to dissociation
of their source, the CH radical. These K-line and G-band fluctuations,
whose periods are longer than the acoustic cutoff, are coherent and
in phase. They also are coherent with fluctuations of the magnetic
field. Weak-field magnetic fluctuations lead the intensity fluctuations
by a phase shift of 90°. Strong-field magnetic fluctuations trail the
intensities by 100°. These are interpreted as standing waves in the
photosphere and low chromosphere. Another class of G-band fluctuations,
with periods shorter than the acoustic cutoff, is associated both
with stronger magnetic fields and with enhanced K-line emission with
fluctuations longer than the cutoff period. This suggests waves excited
by rapid photospheric perturbations and propagating up along magnetic
flux tubes.
---------------------------------------------------------
Title: Influence of Photospheric Magnetism and Dynamics on
Chromospheric K-line Emission
Authors: Lawrence, J. K.; Cadavid, A. C.; Miccolis, D.; Berger, T. E.;
Ruzmaikin, A.
2003SPD....34.0704L Altcode: 2003BAAS...35..820L
We analyze a unique 9 hr sequence of near simultaneous, high resolution
and high cadence G-band and K-line SVST solar filtergrams together
with magnetograms of lower cadence and resolution. We focus on a
region of the solar surface that includes both internetwork and
network. We examine how the (temperature minimum/chromospheric)
CaII K-line and (photospheric) G-band intensities, their temporal
fluctuations and their coherence and phase relations, with each other
and with magnetic fluctuations, change as we progress from weak magnetic
fields (internetwork) to intermediate and strong fields (network). <P
/>As the background level of flux is increased, sudden photospheric
downflow events can create long-lived, compact (i.e. network) magnetic
elements. For weak magnetic fields the K-line and G-band intensity
signals show an oscillatory component with period centered on 4 min. As
we pass to strong fields, the K-line signal shifts to a 5 min period
while the G-band signal fades, presumably due to dissociation of the
CH radical. The K-line and G-band signals are coherent and nearly
in-phase. They are both coherent with fluctuations of the magnetic
field. For weak field the magnetic signal leads the intensity signals by
90<SUP>o</SUP> in phase. For intermediate and strong fields the magnetic
signal trails the intensities by 110<SUP>o</SUP>. We interpret this as
a transition from acoustic standing waves with weak, passive magnetic
field to a slow mode trapped magnetoacoustic wave. For intermediate
magnetic field we find, in addition to the coherent waves, that G-band
fluctuations at frequencies above the acoustic cutoff (period <
3.5 min) are associated with magnetic fields and with K-line emission
at periods > 3.5 min. This suggests the presence of flux tube
waves excited by rapid photospheric perturbations. <P />This work
was supported by grants NSF-ATM 9987305 and NASA-NAG5-10880. The SVST
is operated by the Swedish Royal Academy of Sciences at the Spanish
Observatorio del Roque de los Muchachos of the Instituto de Astrofisica
de Canarias.
---------------------------------------------------------
Title: Photospheric Sources of Chromospheric Dynamics in the
Internetwork
Authors: Cadavid, A. C.; Lawrence, J. K.; Berger, T. E.; Ruzmaikin, A.
2003SPD....34.0703C Altcode: 2003BAAS...35..820C
We analyze a unique 9 hr sequence of near simultaneous, high
resolution and high cadence G-band and K-line solar filtergrams
together with magnetograms of lower cadence and resolution, taken
with the SVST. We investigate an internetwork region characterized
by magnetic fields with strength < 150 Gauss and focus on the
phenomena surrounding discrete photospheric darkening “events”
in G-band intensities. 72 % of the darkenings are followed after 2
min by K-line brightenings. In the remaining cases the darkenings are
instead preceded by K-line brightenings 2 min earlier. In both cases
the preceding and following G-band minima are each associated with
transient magnetic enhancements, and thus, presumably, photospheric
inflows followed by outflows. The magnetic field appears to have no
role in coupling the photospheric phenomena to the chromosphere, and
acts as a passive tracer of horizontal photospheric flows that converge
on the photospheric darkening events and then rebound. The timing and
coupling of the photospheric darkenings and chromospheric brightenings
appear to be regulated by a pre-existing 4 min oscillation of the
solar atmosphere. Other oscillations with periods in the range 1-8
min also are present, and in general the wave power is doubled at the
time of an event. At short periods temporal structure is resolved. Our
results favor an acoustic source for enhanced amplitudes of K-line
intensity oscillations.
---------------------------------------------------------
Title: Photospheric Sources and Brightening of the Internetwork
Chromosphere
Authors: Cadavid, A. C.; Lawrence, J. K.; Berger, T. E.; Ruzmaikin, A.
2003ApJ...586.1409C Altcode:
We analyze a unique 9 hr sequence of near-simultaneous, high-resolution
and high-cadence G-band and K-line solar filtergrams, together with
magnetograms of lower cadence and resolution. Our focus is on the
phenomena surrounding discrete photospheric darkening “events” in
internetwork G-band intensities. 72% of the darkenings are followed
after 2 minutes by K-line brightenings. In the remaining cases,
the darkenings are instead preceded by K-line brightenings 2 minutes
earlier. Equivalent results are found when reference is shifted to
K-line brightening events, although these two sets overlap by no more
than 15%. The timing and coupling of the photospheric darkenings and
chromospheric brightenings appear to be regulated by a preexisting 4
minute oscillation of the solar atmosphere. Other oscillations with
periods in the range 1-8 minutes also are present, and in general
the wave power is doubled at the time of an event. Our results
favor an acoustic source for enhanced amplitudes of K-line intensity
oscillations. The magnetic field acts as a passive tracer of horizontal
photospheric flows that converge on the photospheric darkening events
and then rebound.
---------------------------------------------------------
Title: Mesogranulation from Principal Component Analysis of SVST
Photospheric Continuum Images
Authors: Bell, E.; Cadavid, A. C.; Lawrence, J. K.; Berger, T. E.
2002AAS...200.3805B Altcode: 2002BAAS...34Q.699B
We analyze a sequence of 279 images of the photosphere made with the
Swedish Vacuum Solar Telescope on 1997 June 11. The sequence spans 3
hr with cadence 38 s. The images were taken in continuum near 4364
Å, and underwent phase diversity reconstruction. Resolution is ~
0.2 Mm and field of view 32 X 32 Mm. We carried out a principal
component analysis on sequences of 15 images spaced 6 min apart and
covering 1.5 hr. The 15 X 15 correlation matrix of each such set
of images was diagonalized, giving 15 eigenimages which are linear
combinations of the original 15. The eigenimage corresponding to the
largest eigenvalue is the linear combination that best resembles the
original set as a whole; those with smaller and smaller eigenvalues
resemble the overall set less and less well. Fourier spectra of the
eigenimages were calculated separately for several sequences and
then averaged together to reduce uncertainties. Fourier analysis
of the leading eigenimage reveals structure at two scales: one for
λ =1/ν ~ 1.5 Mm corresponding to granulation and another for λ ~
4.5 Mm. Because of their scale and because the time span of the sets
lies between the lifetimes of granules and mesogranules, we interpret
the latter as mesogranules. The subsequent eigenimages do not show the
larger structure, but show the granular peak at successively smaller
scales. This indicates a spatio-temporal scaling of the granulation
with shorter lifetimes for smaller features. For comparison purposes,
simulated granulation images (Cattaneo, Lenz and Weiss 2001) were
similarly analyzed and give similar results. Work supported in part
by grants NSF-ATM-9987305, NASA-NAG5-10880 and the NASA CSUN/JPL PAIR
Program. F. Cattaneo, D. Lenz and N. Weiss 2001, ApJ, 563, L91.
---------------------------------------------------------
Title: High Resolution Spatio-Temporal Study of Photospheric and
Chromospheric Energetics
Authors: Cadavid, A. C.; Lawrence, J. K.; Berger, T. E.
2002AAS...200.3809C Altcode: 2002BAAS...34..700C
We study the photosphere/chromosphere energetic connection using a
nine hour sequence of SVST images obtained May 30, 1998. The data
consist of co-spatial, nearly simultaneous filtergrams of G-band
(4305 Å ), Ca II K (3934 Å ), two (6563 Å) Hα channels offset by
0.35 Å and 0.7 Å , and Fe I (6302 Å) magnetograms. The cadence of
the G-band and Ca K observations is ~ 30 s; that of the other images
is ~ 2 min. The pixel scale is 0.06 Mm and field of view 48 X 48 Mm
on the Sun. The filtergram resolution is > 0.2 Mm; that of the
magnetograms > 0.3 Mm with single magnetogram sensitivity <
150 G. We have co-registered the images to 1 or 2 pixel accuracy. The
number distribution of Ca brightenings and of localized changes in
magnetic field strength, measured in standard deviations (σ ) from
the image means, present three different characteristic regimes;
that of the magnetic “free energy” (a derived measure based on
the local variance of magnetic field) presents two. Ca brightenings
below 3σ show a weak but significant correlation with local magnetic
field and free energy. At 3σ the strength of the correlation abruptly
increases. Above 5σ no correlation is apparent, but large magnetic
field values appear. Using a mask to remove the network areas, the
weakest brightenings (<1.5 σ ) show anti-correlation with the
magnetic field. For 1.5 σ to 4.5 σ there is no correlation. For
selected network examples we follow the time evolution in all observed
lines. We find cases in which an increase and then relaxation in the
magnetic free energy just precedes a local rise in Ca emission followed
by a drop to a lower background level than initially. Work supported
in part by NSF-ATM-9987305 and NASA-NAG5-10880.
---------------------------------------------------------
Title: Observations of the Structure of small scale photospheric
fields
Authors: Lawrence, J.; Cadavid, A.; Ruzmaikin, A.; Berger, T.
2002ocnd.confE..26L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A simple model of solar variability influence on climate.
Authors: Ruzmaikin, A.; Lawrence, J.; Cadavid, A.
2002cosp...34E.336R Altcode: 2002cosp.meetE.336R
We introduce and study a simple dynamic model of solar influence on
climate. The model is truncated from the stratospheric wave-zonal
flow interaction model suggested by Holton and Mass (1976). Our model
consists of three ordinary differential equations controlled by two
parameters: the initial amplitude of planetary waves and the vertical
gradient of the zonal wind. The changes associated with seasonal
variations and with the solar variability are introduced as periodic
modulations of the zonal wind gradient. The major atmospheric response
to these changes is seen through modulation of the number of cold and
warm winters.
---------------------------------------------------------
Title: Mesogranulation and Turbulence in Photospheric Flows
Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A.
2001SoPh..202...27L Altcode: 2001astro.ph..4354L
Below the scale of supergranules we find that cellular flows are present
in the solar photosphere at two distinct size scales, approximately 2 Mm
and 4 Mm, with distinct characteristic times. Simultaneously present in
the flow is a non-cellular component, with turbulent scaling properties
and containing 30% of the flow energy. These results are obtained by
means of wavelet spectral analysis and modeling of vertical photospheric
motions in a 2-hour sequence of 120 SOHO/MDI, high-resolution, Doppler
images near disk center. The wavelets permit detection of specific
local flow patterns corresponding to convection cells.
---------------------------------------------------------
Title: Spatiotemporal Scaling of Solar Surface Flows
Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A.; Berger, T. E.
2001PhRvL..86.5894L Altcode: 2001astro.ph..1224L
The sun provides an excellent natural laboratory for nonlinear
phenomena. We use motions of magnetic bright points on the solar
surface, at the smallest scales yet observed, to study the small scale
dynamics of the photospheric plasma. The paths of the bright points
are analyzed within a continuous time random walk framework. Their
spatial and temporal scaling suggests that the observed motions are
the walks of imperfectly correlated tracers on a turbulent fluid flow
in the lanes between granular convection cells.
---------------------------------------------------------
Title: Mesogranulation and Turbulence in Photospheric Flows
Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A.
2001AGUSM..SP41C02L Altcode:
Cellular flows are present in the solar photosphere at two
distinct size scales, 2 Mm and 4 Mm, with distinct characteristic
times. Simultaneously present in the flow is a non-cellular component,
with turbulent scaling properties between 1 Mm and 64 Mm, and containing
30 % of the flow energy. These results are obtained by means of wavelet
spectral analysis and modeling of vertical photospheric motions in
a 2-hour sequence of 120 SOHO/MDI, high resolution, Doppler images
near disk center. The wavelets permit detection of specific local flow
patterns corresponding to convection cells. Standard spectral techniques
have difficulty resolving mesogranules for three basic reasons: (1) the
mesogranules are near in scale to granules and weaker in velocity and
(2) they are hidden by overlying turbulence because (3) global basis
functions, such as Fourier waves or spherical harmonics, do not allow
attention to be paid to the local topologies that label cellular flows.
---------------------------------------------------------
Title: Response to weak solar forcing in a general circulation model
of the atmosphere.
Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. A.
2000BAAS...32R.832C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Random Walks of Magnetic Bright Points and Coronal Loop Heating
Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. A.
2000AAS...196.4903L Altcode: 2000BAAS...32..750L
The random walks of small-scale ( ~ 0.2 arcsec) magnetic bright points
(MBPs) in the lanes between photospheric granules are anomalous. The
temporal growth of the q-th moment of the displacement r(t) is a
power law with exponent q γ (q)/2. For normal, Gaussian walks γ
(q)= 1 for all q. However, for the MBP walks on time scales <
45 minutes we find that γ (2)<1 and that γ (q) is a decreasing
function of q. Many viable models for the heating of coronal loops are
based on the additon of energy via twisting and braiding of magnetic
flux lines by the random motions of their footpoints. If the MBPs are
associated with such footpoints, then the statistics of their motions
are directly relevant to coronal heating. For example, a number of
models derive heating rates based on moments of the displacements and
include the standard assumption that γ = 1. However, this assumption
is wrong for MBPs, and the actual value of γ depends on exactly which
moment enters the expression. All such models are therefore subject to
modification. The result γ (2)<1 is a result of pauses in the MBP
walks on all time scales (”fractal time”) up to ~ 45 min. This implies
that the motions of an individual footpoint are not statistically
stationary. This in turn means that the injection of energy into a
given loop will be strongly variable and intermittent. This can be
related to observations of the details of variability in coronal loop
emissions, giving information on the locations of energy deposition and
on time scales of energy release. We thus hope to further constrain
acceptable heating models. This work was supported in part by NSF
Grant ATM-9628882.
---------------------------------------------------------
Title: Response to Weak Solar Forcing in a General Circulation Model
of the Atmosphere
Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. A.
2000SPD....3102117C Altcode: 2000BAAS...32..832C
We study the effect of variable external forcing on a dynamical
system proposed by Lorenz as a simple general circulation model of
the atmosphere. When a strong annual cycle is included, numerical
exploration reveals the existence of a variety of multi-year climate
states, which fall into two basic types. In the space of external
forcing parameters, the different kinds of climate state are interleaved
in an intricate pattern at scales < 0.01. This is below the ~ 0.1
level of observed solar cycle irradiance variability which can thus
modulate the model climate state. If the solar cycle is accompanied
by a steady drift in forcing, it can produce periodic modulation
which appears, disappears and even reverses its phase. A parametric
drift by itself produces intervals of steady, but sometimes differing,
climates punctuated by intermittent bursts of variability. Different
forcing parameters for the Northern and Southern Hemispheres produce
different responses to variable forcing.
---------------------------------------------------------
Title: Anomalous Diffusion of Solar Magnetic Elements
Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. A.
1999ApJ...521..844C Altcode:
The diffusion properties of photospheric bright points associated
with magnetic elements (magnetic bright points) in the granulation
network are analyzed. We find that the transport is subdiffusive
for times less than 20 minutes but normal for times larger than 25
minutes. The subdiffusive transport is caused by the walkers being
trapped at stagnation points in the intercellular pattern. We find
that the distribution of waiting times at the trap sites obeys a
truncated Lévy type (power-law) distribution. The fractal dimension
of the pattern of sites available to the random walk is less than 2
for the subdiffusive range and tends to 2 in the normal diffusion
range. We show how the continuous time random walk formalism can
give an analytical explanation of the observations. We simulate this
random walk by using a version of a phenomenological model of renewing
cells introduced originally for supergranules by Simon, Title, &
Weiss. We find that the traps that cause the subdiffusive transport
arise when the renewed convection cell pattern is neither fixed nor
totally uncorrelated from the old pattern, as required in Leighton's
model, but in some intermediate state between these extremes.
---------------------------------------------------------
Title: General relativistic solitons. II
Authors: Cadavid, A. C.; Finkelstein, R. J.
1999PhRvD..59l4019C Altcode: 1998gr.qc.....7014C
We investigate the possible existence of nontopological solitons in
stringlike theories, or in other completions of Einstein theory,
by examining a simple extension of standard theory that describes
a nonlinear scalar field interacting with the Einstein, Maxwell,
and Weyl (dilaton) fields. The Einstein and Maxwell couplings are
standard while the dilatonic coupling is taken to agree with string
models. The nonlinear scalar potential is quite general. It is found to
be impossible to satisfy the dilatonic boundary conditions. Excluding
the dilaton field we find a variety of solitonic structures differing in
ways that depend on the nonlinear potential. In general the excited
states exhibit a discrete mass spectrum. At large distances the
gravitational field approaches the Reissner-Nordström solution.
---------------------------------------------------------
Title: Anomalous Diffusion of Solar Magnetic Elements
Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. A.
1999AAS...194.5506C Altcode: 1999BAAS...31..911C
The diffusion properties of photospheric bright points associated with
magnetic elements (MBP's) in the granulation network are analyzed. We
find that the transport is subdiffusive for times less than 20 minutes
but normal for times larger than 25 minutes. The subdiffusive transport
is caused by the walkers being trapped at stagnation points in the
intercellular pattern. We find that the distribution of waiting times at
the trap sites obeys a truncated Levy type (power law) distribution. The
fractal dimension of the pattern of sites available to the random
walk is less than 2 for the subdiffusive range and tends to 2 in the
normal diffusion range. We show how the continuous time random walk
formalism can give an analytical explanation of the observations. We
simulate this random walk by using a version of a phenomenological
model of renewing cells introduced originally for supergranules by
Simon, Title and Weiss (1995). We find that the traps which cause the
subdiffusive transport arise when the renewed convection cell pattern
is neither fixed nor is it totally uncorrelated from the old pattern
as required in Leighton's model, but in some intermediate state between
these extremes. (Work supported in part by NSF grant ATM-9628882).
---------------------------------------------------------
Title: Scaling Universality Classes and Analysis of Solar Data
Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. A.
1999AAS...194.9301L Altcode: 1999BAAS...31..988L
Many solar phenomena display a scaling symmetry associated with random
multiplicative cascades. Here a physical measure, initially uniform
on a spatial, temporal, or space-time set, is divided among subsets
according to randomly determined fractions. This division is repeated
on smaller and smaller sub-subsets, so that the resulting measure at
the smallest scale is given at any point by the product of a string of
random fractions comprising its fragmentation history. Such measures
are highly intermittent. They characterize such solar phenomena as the
spatial distribution of magnetic flux in an active region and the time
distribution of global X-ray emission. The probability distribution
functions (PDFs) governing the random fractions fall into universality
classes with robust properties (Hentschel 1994). For example, all
PDFs which allow for zero fractions lead to measures with local peaks
of unlimited strengths which are progressively less and less space
filling. The GOES-2 X-ray data belong to this class, which indicates
the presence of critical behavior associated with flares (Lu &
Hamilton 1991). We investigate a number of time series for the presence
or absence of this property. Multifractals in nature may fall into a
narrow universality class described by just 3 parameters (Schertzer, et
al. 1997). We find that at least some examples of active region magnetic
fields do indeed have the conjectured form. Further, we apply a causal
space-time version of this class of multiplicative cascade processes
to forecasting the evolution of solar velocity fields. This work was
supported in part by NSF grant ATM-9628882. Hentschel, H.G.E. 1994,
Phys. Rev. E, 50, 243. Lu, E.T. & Hamilton, R.J. 1991, ApJ, 380,
L89. Schertzer, D., Lovejoy, S., Schmitt, F., Chigirinskaya, Y. &
Marsan, D. 1997, Fractals, 5, 427.
---------------------------------------------------------
Title: Characteristic Scales of Photospheric Flows and Their Magnetic
and Temperature Markers
Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. A.
1999ApJ...513..506L Altcode:
We study the characteristic scales of quiet-Sun photospheric velocity
fields along with their temperature and magnetic markers in Doppler
images from the Michelson Doppler Imager aboard the SOHO satellite
(SOHO/MDI) in simultaneous, Doppler, magnetic, and intensity images
from the San Fernando Observatory and in full-disk magnetograms
and an intensity image from National Solar Observatory (Kitt
Peak). Wavelet flatness spectra show that velocity fluctuations are
normally distributed (Gaussian). This is often assumed in stochastic
models of turbulence but had not yet been verified observationally
for the Sun. Temperature fluctuations also are Gaussian distributed,
but magnetic fields are intermittent and are gathered into patterns
related to flow structures. Wavelet basis functions designed to detect
characteristic convection cell-flow topologies in acoustically filtered
SOHO/MDI Doppler images reveal granulation scales of 0.7-2.2 Mm and
supergranulation scales of 28-40 Mm. Mesogranular flows are weakly but
significantly detected in the range 4-8 Mm. The systematic flows account
for only 30% of the image variances at granular and supergranular
scales and much less in between. The main flows for the intermediate
range of 2-15 Mm are self-similar, i.e., chaotic or turbulent.
---------------------------------------------------------
Title: Kerr-Schild Description of a Rotating Dyon
Authors: Cadavid, A. C.; Finkelstein, R. J.
1999GReGr..31...31C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Spatiotemporal Correlations and Turbulent Photospheric Flows
from SOHO/MDI Velocity Data
Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. A.; Walton,
S. R.; Tarbell, T.
1998ApJ...509..918C Altcode:
Time series of high-resolution and full-disk velocity images obtained
with the Michelson Doppler Imager (MDI) instrument on board SOHO
have been used to calculate the spacetime spectrum of photospheric
velocity flow. The effects of different methods for filtering acoustic
oscillations have been carefully studied. It is found that the spectra
show contributions both from organized structures that have their origin
in the convection zone and from the turbulent flow. By considering
time series of different duration and cadence in solar regions with
different line-of-sight projections, it is possible to distinguish the
contributions of the spectra from the two different kinds of flows. The
spectra associated with the turbulent velocity fields obey power laws
characterized by two scaling parameters whose values can be used to
describe the type of diffusion. The first parameter is the spectral
exponent of the spatial correlation function and the second is a
scaling parameter of the time correlation function. Inclusion of the
time parameter is an essential difference between the present work
and other solar studies. Within the confidence limits of the data,
the values of the two parameters indicate that the turbulent part of
the flow in the scale range 16-120 Mm produces superdiffusive transport.
---------------------------------------------------------
Title: General relativistic solitons
Authors: Cadavid, A. C.; Finkelstein, R. J.
1998PhRvD..57.7318C Altcode:
A general relativistic and nontopological soliton is constructed
by coupling a nonlinear scalar field to the standard gravitational
field. Our results replicate the basic features of the special
relativistic case: namely, a singularity-free lump with a discrete
spectrum of eigensolutions. The central singularities and horizon that
appear in the black hole solitons of string theory are not present.
---------------------------------------------------------
Title: Dyonic Black Holes and Related Solitons
Authors: Cadavid, A. C.; Finkelstein, R. J.
1997gr.qc.....7031C Altcode:
There is a growing literature on dyonic black holes as they appear in
string theory. Here we examine the correspondence limit of a dyonic
black hole which is not supersymmetric. Assuming the existence of
a dyon with non-supersymmetric Kerr-Schild structure, we calculate
its gravitational and electromagnetic fields and compute its mass and
angular momentum to obtain a modified B.P.S. relation. The contributionn
of the angular momentum to the mass appears in the condition for the
appearance of a horizon.
---------------------------------------------------------
Title: Scale Dependence of Photospheric Magnetic, Velocity and
Temperature Structure
Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. A.
1997SPD....28.0247L Altcode: 1997BAAS...29..901L
Time series fluctuations may show different structure when observed
at different time scale resolutions. Thus, wavelet analysis reveals
that fluctuations in the International Sunspot Number are intermittent
(that is, distributed with kurtosis K>0) on scales less than 2 yr,
but truncated (K<0) on time scales between 2-8 yr. Terrestrial
temperature fluctuations are normally distributed (K=0) over discrete
timescale bands (<1 yr, 4-6 yr, 13 yr) interspersed by regimes of
intermittence (1-4 yr) and truncation (6-13 yr). Similar effects occur
for spatial phenomena. We employ various continuous, two-dimensional
wavelets to analyze digital solar images in Cartesian projection
(simultaneous, co-registered San Fernando Observatory magnetic,
Doppler and continuum images; SOHO/MDI high resolution Doppler images)
and full-disk images in hemispheric projection (KPNO magnetograms,
SOHO/MDI Doppler images). The temperature and velocity data are normally
distributed at all scales up to 64 arc sec, though the temperature
gradients are slightly intermittent (K~1). The magnetic data are mostly
intermittent. Wavelet power spectra for KPNO full-disk magnetograms
are quite featureless and indicate scale invariance of the magnetic
structures. Structural spectra of both active and quiet sun images,
however, show a strong peak in intermittence at a scale near 8 arc
sec. Wavelet analysis permits localization of structures in space as
well as in spatial scale. The highly intermittent structures can be
mapped and are found to be located not in active regions but in some,
though not all, areas of low magnetic activity. We discuss possible
physical relationships among the magnetic, velocity and temperature
distributions studied.
---------------------------------------------------------
Title: Decorrelation Time of Fourier modes in the Spectrum of Solar
Background Velocity Fields
Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. A.
1997SPD....28.0261C Altcode: 1997BAAS...29..904C
We calculate the power-energy spectrum of time series of SOHO/MDI
line-of sight high resolution Doppler images near disk center. While the
spatial spectrum presents velocity features at characteristic scales and
not a cascade in wavenumber space, we investigate the extent to which
it is still possible to describe in terms of a scaling exponent the
properties of the decorrelation time for each Fourier mode as a function
of wavelength. We explore the sensitivity of the result to different
methods for removing the contribution of the p-modes to the spectrum.
---------------------------------------------------------
Title: Wavelet and Multifractal Analyses of Spatial and Temporal
Solar Activity Variations
Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. A.
1997scma.conf..421L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Spectral Properties of Solar Convection and Diffusion
Authors: Ruzmaikin, A. A.; Cadavid, A. C.; Chapman, G. A.; Lawrence,
J. K.; Walton, S. R.
1996ApJ...471.1022R Altcode:
We present the results of a study of the scaling properties of
solar photo spheric motions. We use time series of Doppler images
obtained in good seeing conditions with the San Fernando Observatory
28 cm vacuum telescope and vacuum spectroheliograph in video
spectra-spectroheliograph mode. Sixty line-of- sight Doppler images of
an area of the quiet Sun near disk center are investigated. They were
taken at 60 s intervals over a 1 hr time span at ∼2" resolution. <P
/>After filtering to remove 5 minute acoustic oscillations, the
time-spatial spectrum of the velocity is calculated. To study the
turbulence of photospheric flows in the mesogranulation scale range,
we estimate two scaling parameters in the spectrum: the exponent of
the spatial part of the power spectrum and the exponent governing the
scaling of time correlations of each spatial mode. These parameters
characterize the type of diffusion involved and the fractal dimension of
the diffusion front. Our results indicate that the turbulent diffusion
produced by motions in this scale range is not normal diffusion but
superdiffusion.
---------------------------------------------------------
Title: On the Multifractal Distribution of Solar Magnetic Fields:
Erratum
Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. A.
1996ApJ...467..473L Altcode:
Many studies have pointed out fractal and multifractal properties of
photospheric magnetic fields, but placing the various approaches into
context has proved difficult. Although fractal quantities are defined
mathematically in the asymptotic limit of infinite resolution, real
data cannot approach this limit. Instead, one must compute fractal
dimensions or multifractal spectra within a limited range at finite
scales. The consequent effects of this are explored by calculation
of fractal quantities in finite images generated from analytically
known measures and also from solar data. We find that theorems relating
asymptotic quantities need not hold for their finite counterparts, that
different definitions of fractal dimension that merge asymptotically
give different values at finite scales, and that apparently elementary
calculations of dimensions of simple fractals can lead to incorrect
results. We examine the limits of accuracy of multifractal spectra from
finite data and point out that a recent criticism of one approach to
such problems is incorrect.
---------------------------------------------------------
Title: On the Multifractal Distribution of Solar Magnetic Fields
Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. A.
1996ApJ...465..425L Altcode:
Many studies have pointed out fractal and multifractal properties of
photospheric magnetic fields, but placing the various approaches into
context has proved difficult. Although fractal quantities are defined
mathematically in the asymptotic limit of infinite resolution, real
data cannot approach this limit. Instead, one must compute fractal
dimensions or multifractal spectra within a limited range at finite
scales. The consequent effects of this are explored by calculation
of fractal quantities in finite images generated from analytically
known measures and also from solar data. We find that theorems relating
asymptotic quantities need not hold for their finite counterparts, that
different definitions of fractal dimension that merge asymptotically
give different values at finite scales, and that apparently elementary
calculations of dimensions of simple fractals can lead to incorrect
results. We examine the limits of accuracy of multifractal spectra from
finite data and point out that a recent criticism of one approach to
such problems is incorrect.
---------------------------------------------------------
Title: Spectral Properties of the Solar Background Velocity Field
Authors: Cadavid, A. C.; Chapman, G. A.; Lawrence, J. K.; Ruzmaikin,
A. A.; Walton, S. R.
1996AAS...188.3506C Altcode: 1996BAAS...28Q.872C
We study the scaling properties of time series of Doppler images
obtained in good seeing conditions with the San Fernando Observatory
28 cm vacuum telescope and vacuum spectroheliograph in video
spectra-spectroheliograph mode. The images correspond to two areas
of quiet Sun near disk center taken at 60 second intervals from one
hour to six hour spans at ~ 2 arcsec resolution. After removal of 5
min acoustic oscillations the time-spatial spectrum of the velocity is
calculated. To study the turbulence of photospheric flows we estimate
two scaling parameters: the exponent of the spatial part of the power
spectrum and the exponent governing the scaling of time correlations
of each spatial mode. The implied diffusive behavior produced by the
solar convection in the mesogranulation scale range is discussed. This
includes characterization of the type of diffusion involved and the
fractal dimension of the diffusion front.
---------------------------------------------------------
Title: Turbulent and Chaotic Dynamics Underlying Solar Magnetic
Variability
Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. A.
1995ApJ...455..366L Altcode:
We examine the temporal scaling properties of solar magnetic activity
on timescales from days to decades. Because of more than 63,000
usable data points, we concentrate on the daily International Sunspot
Number. Some results have been checked with other data sets, primarily
the 10.7 cm microwave flux with about 16,000 data points. Such time
series provide a measure whose scaling and intermittency properties
are analyzed. <P />By means of correlation analysis and both Fourier
and wavelet spectral analysis, we distinguish two regimes of temporal
behavior of the magnetic variability. The scaling of the time series is
analyzed in terms of multiplicative cascade processes which prove to
be invariant over more than two decades of scale from about 2 yr down
to about 2 days or less. We interpret this result to indicate generic
turbulent structuring of the magnetic fields as they rise through the
convection zone. We find that a low-dimensional, chaotic behavior in the
sunspot number operates entirely at timescales longer than a transition
threshold scale of about 8 yr. Magnetic variability on timescales
between 2 yr and 8 yr apparently requires handling by direct simulation.
---------------------------------------------------------
Title: Turbulence and Chaos in Solar Variability
Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. A.
1995SPD....26..514C Altcode: 1995BAAS...27..960C
No abstract at ADS
---------------------------------------------------------
Title: Multiplicative cascade models of multifractal solar magnetic
fields
Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. A.
1995PhRvE..51..316L Altcode:
We present a multifractal analysis of digital, photoelectric images
of line-of-sight magnetic fields in solar active regions and quiet
photosphere. We study a positive definite measure related to the Ohmic
dissipation of magnetic energy. After calculation of the multifractal
spectrum directly and by scaling of the moments of the measure, we
focus on a multiplicative cascade approach. We infer a scale-invariant
rule by which the Ohmic dissipation measure is allocated among subsets
of its support through a hierarchy of scales. Knowledge of this rule,
which is hampered to some extent by image noise, permits the calculation
of the multifractal spectrum to great accuracy. The scaling of the
solar dissipation field resembles that of fully developed turbulence
in an atmospheric boundary layer. The cascade multiplier probability
distribution is itself a very useful quantity. It allows a convenient
display of image properties, such as self-similarity. Further, it is
more closely related than the multifractal spectrum to the physics
of the turbulent field evolution, and it thus can be used to impose
stronger constraints on turbulent dynamo models of magnetic field
generation.
---------------------------------------------------------
Title: Spectra of Solar Magnetic Fields and Diffusion
Authors: Ruzmaikin, A. A.; Cadavid, A. C.; Chapman, G. A.; Lawrence,
J. K.; Walton, S. R.
1995ASPC...76..292R Altcode: 1995gong.conf..292R
No abstract at ADS
---------------------------------------------------------
Title: Multifractal Models of Small-Scale Solar Magnetic Fields
Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. A.;
Kayleng-Knight, A.
1994ApJ...429..391C Altcode:
We generate, both analytically and numerically, artifical,
two-dimensional images composed of a known self-similar, and thus
multifractal measured with added Gaussian white noise. These are
used to interpret observed, line-of-sight, solar magnetic field
distributions noisy multifractals. The range of self-similar scaling of
observed, distributions is extended beyond that of previous work. Our
interpretation of the data is then used to confront theoretical models
for the generation of small-scale solar magnetic fields. We investigate
the multifractial structure of the field generated by two-dimensional,
random cell dynamos and find that self-similarity is relatively enhanced
for more intermittent distributions and strong correlations between
cells. An optimum value of the intercellular diffusion coefficient
maximizes the degree of intermittency. The simulated field from
a linear, kinematic, fast dynamo with two-dimensional, chaotic,
'ABC' flow displays scaling properties resembling those of observed
solar fields. We suggest that the chaotic element of this model is
the crucial ingredient for the long-range correlations that lead to
multifractal scaling.
---------------------------------------------------------
Title: Scaling properties of photospheric magnetic fields
Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. A.
1994ASIC..433..279L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Multifractal Measure of the Solar Magnetic Field
Authors: Lawrence, J. K.; Ruzmaikin, A. A.; Cadavid, A. C.
1993ApJ...417..805L Altcode:
We analyze high-resolution, digital, photoelectric images of solar
photospheric magnetic fields. The line-of-sight fields are found to
scale in a self-similar way with resolution and thus can be expressed
in the form of a signed multifractal measure. The scaling properties of
the measure are used to extrapolate field integrals, such as moments of
the magnetic field, below resolvable limits. The scaling of the field
moments is characteristic of highly intermittent fields. We suggest
that the quiet-Sun photospheric fields are generated by local dynamo
action based on random convective motions at high magnetic Reynolds
number. The properties of active region images are determined by the
presence of fields generated by the global, mean field dynamo.
---------------------------------------------------------
Title: Self-Similarity in Solar Magnetic Images
Authors: Lawrence, J. K.; Ruzmaikin, A. A.; Cadavid, A. C.
1993BAAS...25.1219L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Multiscale Measure of the Solar Magnetic Field
Authors: Ruzmaikin, A. A.; Lawrence, J. K.; Cadavid, A. C.
1993BAAS...25.1219R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar Magnetic Fields, Multifractals and Dynamos
Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. A.;
Kayleng-Knight, A.
1993BAAS...25R1206C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: (2,2) vacuum configurations for type IIA superstrings: N=2
supergravity Lagrangians and algebraic geometry
Authors: Bodner, M.; Cadavid, A. C.; Ferrara, S.
1991CQGra...8..789B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Dimensional reduction of type IIB supergravity and exceptional
quaternionic manifolds
Authors: Bodner, M.; Cadavid, A. C.
1990CQGra...7..829B Altcode:
No abstract at ADS
