explanation blue bibcodes open ADS page with paths to full text
Author name code: kariyappa
ADS astronomy entries on 2022-09-14
author:"Kariyappa, R."
---------------------------------------------------------
Title: Origin of the Solar Rotation Harmonics Seen in the EUV and
UV Irradiance
Authors: Giono, G.; Zender, J. J.; Kariyappa, R.; Damé, L.
2021SoPh..296..172G Altcode:
Long-term periodicities in the solar irradiance are often observed
with periods proportional to the solar rotational period of 27
days. These periods are linked either to some internal mechanism
in the Sun or said to be higher harmonics of the rotation without
further discussion of their origin. In this article, the origin of
the peaks in periodicities seen in the solar extreme ultraviolet (EUV)
and ultraviolet (UV) irradiance around the 7, 9, and 14 days periods is
discussed. Maps of the active regions and coronal holes are produced
from six images per day using the Spatial Possibilistic Clustering
Algorithm (SPoCA), a segmentation algorithm. Spectral irradiance at
coronal, transition-region/chromospheric, and photospheric levels are
extracted for each feature as well as for the full disk by applying
the maps to full-disk images (at 19.3, 30.4, and 170 nm sampling in
the corona/hot flare plasma, the chromosphere/transition region, and
the photosphere, respectively) from the Atmospheric Imaging Assembly
(AIA) on board the Solar Dynamics Observatory (SDO) from January 2011
to December 2018. The peaks in periodicities at 7, 9, and 14 days as
well as the solar rotation around 27 days can be seen in almost all
of the solar irradiance time series. The segmentation also provided
time series of the active regions and coronal holes visible area
(i.e. in the area observed in the AIA images, not corrected for the
line-of-sight effect with respect to the solar surface), which also show
similar peaks in periodicities, indicating that the periodicities are
due to the change in area of the features on the solar disk rather than
to their absolute irradiance. A simple model was created to reproduce
the power spectral density of the area covered by active regions also
showing the same peaks in periodicities. Segmentation of solar images
allows us to determine that the peaks in periodicities seen in solar
EUV/UV irradiance from a few days to a month are due to the change in
area of the solar features, in particular, active regions, as they are
the main contributors to the total full-disk irradiance variability. The
higher harmonics of the solar rotation are caused by the clipping of
the area signal as the regions rotate behind the solar limb.
---------------------------------------------------------
Title: Segmentation of Coronal Features to Understand the Solar
EUV and UV Irradiance Variability III. Inclusion and Analysis of
Bright Points
Authors: van der Zwaard, Rens; Bergmann, Matthias; Zender, Joe;
Kariyappa, Rangaiah; Giono, Gabriel; Damé, Luc
2021SoPh..296..138V Altcode:
The study of solar irradiance variability is of great importance in
heliophysics, Earth's climate, and space weather applications. These
studies require careful identifying, tracking and monitoring of features
in the solar photosphere, chromosphere, and corona. Do coronal bright
points contribute to the solar irradiance or its variability as input
to the Earth atmosphere? We studied the variability of solar irradiance
for a period of 10 years (May 2010 - June 2020) using the Large Yield
Radiometer (LYRA), the Sun Watcher using APS and image Processing
(SWAP) on board PROBA2, and the Atmospheric Imaging Assembly (AIA),
and applied a linear model between the segmented features identified
in the EUV images and the solar irradiance measured by LYRA. Based
on EUV images from AIA, a spatial possibilistic clustering algorithm
(SPoCA) is applied to identify coronal holes (CHs), and a morphological
feature detection algorithm is applied to identify active regions
(ARs), coronal bright points (BPs), and the quiet Sun (QS). The
resulting segmentation maps were then applied on SWAP images,
images of all AIA wavelengths, and parameters such as the intensity,
fractional area, and contribution of ARs/CHs/BPs/QS features were
computed and compared with LYRA irradiance measurements as a proxy for
ultraviolet irradiation incident to the Earth atmosphere. We modeled
the relation between the solar disk features (ARs, CHs, BPs, and QS)
applied to EUV images against the solar irradiance as measured by
LYRA and the F10.7 radio flux. A straightforward linear model was
used and corresponding coefficients computed using a Bayesian method,
indicating a strong influence of active regions to the EUV irradiance
as measured at Earth's atmosphere. It is concluded that the long- and
short-term fluctuations of the active regions drive the EUV signal as
measured at Earth's atmosphere. A significant contribution from the
bright points to the LYRA irradiance could not be found.
---------------------------------------------------------
Title: Solar Soft X-ray Irradiance Variability, I: Segmentation
of Hinode/XRT Full-Disk Images and Comparison with GOES (1 - 8 Å)
X-Ray Flux
Authors: Adithya, H. N.; Kariyappa, Rangaiah; Shinsuke, Imada; Kanya,
Kusano; Zender, Joe; Damé, Luc; Gabriel, Giono; DeLuca, Edward;
Weber, Mark
2021SoPh..296...71A Altcode:
It is of great interest and importance to study the variabilities of
solar EUV, UV and X-ray irradiance in heliophysics, in Earth's climate,
and space weather applications. A careful study is required to identify,
track, monitor and segment the different coronal features such as active
regions (ARs), coronal holes (CHs), the background regions (BGs) and
the X-ray bright points (XBPs) from spatially resolved full-disk images
of the Sun. Variability of solar soft X-ray irradiance is studied for a
period of 13 years (February 2007-March 2020, covers Solar Cycle 24),
using the X-Ray Telescope on board the Hinode (Hinode/XRT) and GOES
(1 - 8 Å). The full-disk X-ray images observed in Al_mesh filter
from XRT are used, for the first time, to understand the solar X-ray
irradiance variability measured, Sun as a star, by GOES instrument. An
algorithm in Python has been developed and applied to identify and
segment coronal X-ray features (ARs, CHs, BGs, and XBPs) from the
full-disk soft X-ray observations of Hinode/XRT. The segmentation
process has been carried out automatically based on the intensity
level, morphology and sizes of the X-ray features. The total intensity,
area, and contribution of ARs/CHs/BGs/XBPs features were estimated and
compared with the full-disk integrated intensity (FDI) and GOES (1 -
8 Å) X-ray irradiance measurements. The XBPs have been identified and
counted automatically over the full disk to investigate their relation
to solar magnetic cycle. The total intensity of ARs/CHs/BGs/XBPs/FD
regions are compared with the GOES (1 - 8 Å) X-ray irradiance
variations. We present the results obtained from Hinode/XRT full-disk
images (in Al_mesh filter) and compare the resulting integrated
full-disk intensity (FDI) with GOES X-ray irradiance. The X-ray
intensity measured over ARs/CHs/BGs/XBPs/FD is well correlated with
GOES X-ray flux. The contributions of the segmented X-ray features
to FDI and X-ray irradiance variations are determined. It is found
that the background and active regions have a greater impact on the
X-ray irradiance fluctuations. The mean contribution estimated for the
whole observed period of the background regions (BGs) will be around 65
±10.97 % , whereas the ARs, XBPs and CHs are 30 ±11.82 % , 4 ±1.18 %
and 1 ±0.52 % , respectively, to total solar X-ray flux. We observed
that the area and contribution of ARs and CHs varies with the phase of
the solar cycle, whereas the BGs and XBPs show an anti-correlation. We
find that the area of the coronal features is highly variable suggesting
that their area has to be taken into account in irradiance models,
in addition to their intensity variations. The time series results of
XBPs suggest for an existence of anti-correlation between the number
of XBPs and the sunspot numbers. It is also important to consider both
the number variation and the contribution of XBPs in the reconstruction
of total solar X-ray irradiance variability.
---------------------------------------------------------
Title: Segmentation of coronal features to understand the solar EIV
and UV irradiance variability
Authors: Zender, Joe; van der Zwaart, Rens; Kariyappa, Rangaiah;
Damé, Luc; Giono, Gabriel
2020EGUGA..2219496Z Altcode:
The study of solar irradiance variability is of great importance in
heliophysics, the Earth's climate, and space weather applications. These
studies require careful identifying, tracking and monitoring of
features in the solar magnetosphere, chromosphere, and corona. We
studied the variability of solar irradiance for a period of 10 years
(May 2010-January 2020) using the Large Yield Radiometer (LYRA), the
Sun Watcher using APS and image Processing (SWAP) on board PROBA2, the
Atmospheric Imaging Assembly (AIA), and the Helioseismic and Magnetic
Imager (HMI) of on board the Solar Dynamics Observatory (SDO), and
applied a linear model between the identified features and the measured
solar irradiance by LYRA.We used the spatial possibilistic clustering
algorithm (SPoCA) to identify coronal holes, and a morphological feature
detection algorithm to identify active regions (AR), coronal bright
points (BPS), and the quite sun (QS) and segment coronal features from
the EUV observations of AIA. The AIA segmentation maps were then applied
on SWAP images, images of all AIA wavelengths, HMI line-of-sight (LOS)
magnetograms, and parameters such as the intensity, fractional area,
and contribution of ARs/CHs/BPs/QS features were computed and compared
with LYRA irradiance measurements as a proxy for ultraviolet irradiation
incident to the Earth atmosphere.We modelled the relation between the
solar disk features (ARs, CHs, BPs, and QS) applied to magnetrogram
and EUV images against the solar irradiance as measured by LYRA and the
F10.7 radio flux. To avoid correlation between different the segmented
features, a principal component analysis (PCM) was done. Using the
independent component, a straightforward linear model was used and
corresponding coefficients computed using the Bayesian framework. The
model selected is stable and coefficients converge well.The application
of the model to data from 2010 to 2020 indicates that both at solar
cycle timeframes as well as shorter timeframes, the active region
influence the EUV irradiance as measured at Earth. Our model replicates
the LYRA measured irradiance well.
---------------------------------------------------------
Title: Segmentation of photospheric magnetic elements corresponding to
coronal features to understand the EUV and UV irradiance variability
Authors: Zender, J. J.; Kariyappa, R.; Giono, G.; Bergmann, M.;
Delouille, V.; Damé, L.; Hochedez, J. -F.; Kumara, S. T.
2017A&A...605A..41Z Altcode:
Context. The magnetic field plays a dominant role in the solar
irradiance variability. Determining the contribution of various magnetic
features to this variability is important in the context of heliospheric
studies and Sun-Earth connection. <BR /> Aims: We studied the solar
irradiance variability and its association with the underlying magnetic
field for a period of five years (January 2011-January 2016). We used
observations from the Large Yield Radiometer (LYRA), the Sun Watcher
with Active Pixel System detector and Image Processing (SWAP) on board
PROBA2, the Atmospheric Imaging Assembly (AIA), and the Helioseismic
and Magnetic Imager (HMI) on board the Solar Dynamics Observatory
(SDO). <BR /> Methods: The Spatial Possibilistic Clustering Algorithm
(SPoCA) is applied to the extreme ultraviolet (EUV) observations
obtained from the AIA to segregate coronal features by creating
segmentation maps of active regions (ARs), coronal holes (CHs) and
the quiet sun (QS). Further, these maps are applied to the full-disk
SWAP intensity images and the full-disk (FD) HMI line-of-sight (LOS)
magnetograms to isolate the SWAP coronal features and photospheric
magnetic counterparts, respectively. We then computed full-disk
and feature-wise averages of EUV intensity and line of sight (LOS)
magnetic flux density over ARs/CHs/QS/FD. The variability in these
quantities is compared with that of LYRA irradiance values. <BR />
Results: Variations in the quantities resulting from the segmentation,
namely the integrated intensity and the total magnetic flux density
of ARs/CHs/QS/FD regions, are compared with the LYRA irradiance
variations. We find that the EUV intensity over ARs/CHs/QS/FD is well
correlated with the underlying magnetic field. In addition, variations
in the full-disk integrated intensity and magnetic flux density values
are correlated with the LYRA irradiance variations. <BR /> Conclusions:
Using the segmented coronal features observed in the EUV wavelengths as
proxies to isolate the underlying magnetic structures is demonstrated
in this study. Sophisticated feature identification and segmentation
tools are important in providing more insights into the role of various
magnetic features in both the short- and long-term changes in the solar
irradiance. <P />The movie associated to Fig. 2 is available at <A
href="http://www.aanda.org/10.1051/0004-6361/201629924/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Nonlinear Force-free Field Modeling of the Solar Magnetic
Carpet and Comparison with SDO/HMI and Sunrise/IMaX Observations
Authors: Chitta, L. P.; Kariyappa, R.; van Ballegooijen, A. A.;
DeLuca, E. E.; Solanki, S. K.
2014ApJ...793..112C Altcode: 2014arXiv1408.0497C
In the quiet solar photosphere, the mixed polarity fields form a
magnetic carpet that continuously evolves due to dynamical interaction
between the convective motions and magnetic field. This interplay is a
viable source to heat the solar atmosphere. In this work, we used the
line-of-sight (LOS) magnetograms obtained from the Helioseismic and
Magnetic Imager on the Solar Dynamics Observatory, and the Imaging
Magnetograph eXperiment instrument on the Sunrise balloon-borne
observatory, as time-dependent lower boundary conditions, to study the
evolution of the coronal magnetic field. We use a magneto-frictional
relaxation method, including hyperdiffusion, to produce a time series
of three-dimensional nonlinear force-free fields from a sequence
of photospheric LOS magnetograms. Vertical flows are added up to a
height of 0.7 Mm in the modeling to simulate the non-force-freeness
at the photosphere-chromosphere layers. Among the derived quantities,
we study the spatial and temporal variations of the energy dissipation
rate and energy flux. Our results show that the energy deposited in
the solar atmosphere is concentrated within 2 Mm of the photosphere and
there is not sufficient energy flux at the base of the corona to cover
radiative and conductive losses. Possible reasons and implications are
discussed. Better observational constraints of the magnetic field in
the chromosphere are crucial to understand the role of the magnetic
carpet in coronal heating.
---------------------------------------------------------
Title: Two-dimensional segmentation of small convective patterns in
radiation hydrodynamics simulations
Authors: Lemmerer, B.; Utz, D.; Hanslmeier, A.; Veronig, A.; Thonhofer,
S.; Grimm-Strele, H.; Kariyappa, R.
2014A&A...563A.107L Altcode: 2015arXiv150500325L
Context. Recent results from high-resolution solar granulation
observations indicate the existence of a population of small granular
cells that are smaller than 600 km in diameter. These small convective
cells strongly contribute to the total area of granules and are located
in the intergranular lanes, where they form clusters and chains. <BR />
Aims: We study high-resolution radiation hydrodynamics simulations of
the upper convection zone and photosphere to detect small granular
cells, define their spatial alignment, and analyze their physical
properties. <BR /> Methods: We developed an automated image-segmentation
algorithm specifically adapted to high-resolution simulations to
identify granules. The resulting segmentation masks were applied to
physical quantities, such as intensity and vertical velocity profiles,
provided by the simulation. A new clustering algorithm was developed
to study the alignment of small granular cells. <BR /> Results:
Small granules make a distinct contribution to the total area of
granules and form clusters of chain-like alignments. The simulation
profiles demonstrate a different nature for small granular cells
because they exhibit on average lower intensities, lower horizontal
velocities, and are located deeper inside of convective layers than
regular granules. Their intensity distribution deviates from a normal
distribution as known for larger granules, and follows a Weibull
distribution.
---------------------------------------------------------
Title: Segmentation of coronal features to understand the solar EUV
and UV irradiance variability
Authors: Kumara, S. T.; Kariyappa, R.; Zender, J. J.; Giono, G.;
Delouille, V.; Chitta, L. P.; Damé, L.; Hochedez, J. -F.; Verbeeck,
C.; Mampaey, B.; Doddamani, V. H.
2014A&A...561A...9K Altcode:
Context. The study of solar irradiance variability is of great
importance in heliophysics, the Earth's climate, and space weather
applications. These studies require careful identifying, tracking
and monitoring of active regions (ARs), coronal holes (CHs), and the
quiet Sun (QS). <BR /> Aims: We studied the variability of solar
irradiance for a period of two years (January 2011-December 2012)
using the Large Yield Radiometer (LYRA), the Sun Watcher using APS and
image Processing (SWAP) on board PROBA2, and the Atmospheric Imaging
Assembly (AIA) on board the Solar Dynamics Observatory (SDO). <BR />
Methods: We used the spatial possibilistic clustering algorithm (SPoCA)
to identify and segment coronal features from the EUV observations of
AIA. The AIA segmentation maps were then applied on SWAP images, and
parameters such as the intensity, fractional area, and contribution
of ARs/CHs/QS features were computed and compared with the full-disk
integrated intensity and LYRA irradiance measurements. <BR /> Results:
We report the results obtained from SDO/AIA and PROBA2/SWAP images
taken from January 2011 to December 2012 and compare the resulting
integrated full-disk intensity with PROBA2/LYRA irradiance. We
determine the contributions of the segmented features to EUV and UV
irradiance variations. The variations of the parameters resulting
from the segmentation, namely the area, integrated intensity, and
relative contribution to the solar irradiance, are compared with LYRA
irradiance. We find that the active regions have a great impact on the
irradiance fluctuations. In the EUV passbands considered in this study,
the QS is the greatest contributor to the solar irradiance, with up
to 63% of total intensity values. Active regions, on the other hand,
contribute to about 10%, and off-limb structures to about 24%. We
also find that the area of the features is highly variable suggesting
that their area has to be taken into account in irradiance models,
in addition to their intensity variations. <BR /> Conclusions:
We successfully show that the feature extraction allows us to use
EUV telescopes to measure irradiance fluctuations and to quantify
the contribution of each part to the EUV spectral solar irradiance
observed with a calibrated radiometer. This study also shows that
SPoCA is viable, and that the segmentation of images can be a useful
tool. We also provide the measurement correlation between SWAP and
AIA during this analysis.
---------------------------------------------------------
Title: Observations and Modeling of the Emerging Extreme-ultraviolet
Loops in the Quiet Sun as Seen with the Solar Dynamics Observatory
Authors: Chitta, L. P.; Kariyappa, R.; van Ballegooijen, A. A.;
DeLuca, E. E.; Hasan, S. S.; Hanslmeier, A.
2013ApJ...768...32C Altcode: 2013arXiv1303.3426C
We used data from the Helioseismic and Magnetic Imager (HMI) and the
Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory
(SDO) to study coronal loops at small scales, emerging in the quiet
Sun. With HMI line-of-sight magnetograms, we derive the integrated
and unsigned photospheric magnetic flux at the loop footpoints in the
photosphere. These loops are bright in the EUV channels of AIA. Using
the six AIA EUV filters, we construct the differential emission measure
(DEM) in the temperature range 5.7-6.5 in log T (K) for several hours
of observations. The observed DEMs have a peak distribution around
log T ≈ 6.3, falling rapidly at higher temperatures. For log T <
6.3, DEMs are comparable to their peak values within an order of
magnitude. The emission-weighted temperature is calculated, and its
time variations are compared with those of magnetic flux. We present
two possibilities for explaining the observed DEMs and temperatures
variations. (1) Assuming that the observed loops are composed of
a hundred thin strands with certain radius and length, we tested
three time-dependent heating models and compared the resulting DEMs
and temperatures with the observed quantities. This modeling used
enthalpy-based thermal evolution of loops (EBTEL), a zero-dimensional
(0D) hydrodynamic code. The comparisons suggest that a medium-frequency
heating model with a population of different heating amplitudes can
roughly reproduce the observations. (2) We also consider a loop model
with steady heating and non-uniform cross-section of the loop along
its length, and find that this model can also reproduce the observed
DEMs, provided the loop expansion factor γ ~ 5-10. More observational
constraints are required to better understand the nature of coronal
heating in the short emerging loops on the quiet Sun.
---------------------------------------------------------
Title: Cooler and Hotter X-ray Bright Points from Hinode/XRT
Observations
Authors: Kariyappa, R.; DeLuca, E. E.; Saar, S. H.; Golub, L.; Damé,
L.; Varghese, B. A.
2012ASPC..454..149K Altcode:
We use a 7-hour (17:00 UT - 24:00 UT) time sequence of soft X-ray images
observed almost simultaneously in two filters (Ti_poly and Al_mesh) on
April 14, 2007 with X-Ray Telescope (XRT) on-board the Hinode mission
to determine the temperature of X-ray bright points (XBPs). A sample
of 14 XBPs and 2 background coronal regions have been identified and
selected on both the images for detailed analysis. The temperature of
XBPs is determined by filter ratio method. We find that the XBPs show
temperature fluctuations and that the average temperature ranges from
1.1 MK to 3.4 MK which may correspond to different X-ray fluxes. These
results suggest the existence of cooler and hotter XBPs and that the
heating rate of XBPs is highly variable on short time scales.
---------------------------------------------------------
Title: Solar Activity Monitoring of Flares and CMEs Precursors:
the Importance of Lyman-Alpha
Authors: Damé, Luc; Kretzschmar, Matthieu; Dammasch, Ingolf; Kumara,
S. T.; Kariyappa, R.; Dominique, Marie; Ueno, Satoru; Khaled, Safinaz
2012cosp...39..395D Altcode: 2012cosp.meet..395D
No abstract at ADS
---------------------------------------------------------
Title: Segmentation of Coronal Features to Understand the UV and
EUV Irradiance Variations
Authors: Kumara, S. T.; Hochedez, Jean-François; Damé, Luc;
Doddamani, Vijayakumar H.; Kariyappa, R.
2012cosp...39.1641K Altcode: 2012cosp.meet.1641K
No abstract at ADS
---------------------------------------------------------
Title: Dynamics of the Solar Magnetic Bright Points Derived from
Their Horizontal Motions
Authors: Chitta, L. P.; van Ballegooijen, A. A.; Rouppe van der Voort,
L.; DeLuca, E. E.; Kariyappa, R.
2012ApJ...752...48C Altcode: 2012arXiv1204.4362C
The subarcsecond bright points (BPs) associated with the small-scale
magnetic fields in the lower solar atmosphere are advected by
the evolution of the photospheric granules. We measure various
quantities related to the horizontal motions of the BPs observed in
two wavelengths, including the velocity autocorrelation function. A
1 hr time sequence of wideband Hα observations conducted at the
Swedish 1 m Solar Telescope (SST) and a 4 hr Hinode G-band time
sequence observed with the Solar Optical Telescope are used in this
work. We follow 97 SST and 212 Hinode BPs with 3800 and 1950 individual
velocity measurements, respectively. For its high cadence of 5 s as
compared to 30 s for Hinode data, we emphasize more the results from
SST data. The BP positional uncertainty achieved by SST is as low as 3
km. The position errors contribute 0.75 km<SUP>2</SUP> s<SUP>-2</SUP>
to the variance of the observed velocities. The raw and corrected
velocity measurements in both directions, i.e., (v<SUB>x</SUB> ,
v<SUB>y</SUB> ), have Gaussian distributions with standard deviations
of (1.32, 1.22) and (1.00, 0.86) km s<SUP>-1</SUP>, respectively. The
BP motions have correlation times of about 22-30 s. We construct the
power spectrum of the horizontal motions as a function of frequency,
a quantity that is useful and relevant to the studies of generation
of Alfvén waves. Photospheric turbulent diffusion at timescales less
than 200 s is found to satisfy a power law with an index of 1.59.
---------------------------------------------------------
Title: Coronal Rotation from XBPs Observed with Hinode/XRT
Authors: Kariyappa, R.; DeLuca, E.
2012ASPC..456..207K Altcode:
We have selected a large number of X-ray bright points (XBPs) over
synoptic soft X-ray full-disk images observed using Al-Mesh with X-Ray
Telescope (XRT) onboard the Hinode spacecraft during July-December,
2008. We have analyzed the full-disk images using SSW in IDL. We used
the tracer method to identify and trace the passage of XBPs over the
solar disc with the help of overlaying grids. We also obtained the
position (Latitude and Longitude), size & brightness information
for XBPs using tracer method as a function of time and thus calculated
sidereal angular rotation rate of corona at different latitudes. We
have compared the rotation rate with latitude, size and brightness of
XBPs. We found that the corona rotates differentially and it appears
that the larger XBPs show a lower sidereal angular rotation rate,
the smaller XBPs exhibit higher rotation rate, similar to sunspots.
---------------------------------------------------------
Title: Dynamics of the Photospheric Bright Points Observed With SST
and Hinode
Authors: Chitta, Lakshmi Pradeep; van Ballegooijen, A.; Rouppe van
der Voort, L.; DeLuca, E.; Kariyappa, R.
2012AAS...22020614C Altcode: 2012AAS...22020614P
The horizontal motions of the solar magnetic bright points (BPs)
observed in two wavelengths (SST Halpha and Hinode/SOT G-band)
is studied in detail. With emphasis on SST results: the velocity
distribution of horizontal motions is found to be a Gaussian. The
auto-correlations of observed velocities is also obtained. An
empirical fit to the observed auto-correlation gives us a positional
uncertainty of 3 km and the error in the velocity measurements to be
0.87 km s$^{-1}$. Due to the non-Lorentzian, cusp-like nature of the
auto-correlation, the power spectrum of the BP motions shows enhanced
power at frequencies exceeding 0.02 Hz. The diffusion of magnetic field
due to granular evolution at short timescales is found to satisfy a
power law with a slope of 1.59.
---------------------------------------------------------
Title: Preliminary Results on Irradiance Measurements from Lyra
and Swap
Authors: Kumara, S. T.; Kariyappa, R.; Dominique, M.; Berghmans, D.;
Damé, L.; Hochedez, J. F.; Doddamani, V. H.; Chitta, Lakshmi Pradeep
2012AdAst2012E...5K Altcode: 2012AdAst2012E..10K
No abstract at ADS
---------------------------------------------------------
Title: Observations of the Interaction of Acoustic Waves and
Small-scale Magnetic Fields in a Quiet Sun
Authors: Chitta, Lakshmi Pradeep; Jain, Rekha; Kariyappa, R.;
Jefferies, Stuart M.
2012ApJ...744...98C Altcode: 2012ApJ...744...98P
The effect of the magnetic field on photospheric intensity and
velocity oscillations at the sites of small-scale magnetic fields
(SMFs) in a quiet Sun near the solar disk center is studied. We use
observations made by the G-band filter in the Solar Optical Telescope
on board Hinode for intensity oscillations; Doppler velocity, magnetic
field, and continuum intensity are derived from an Ni I photospheric
absorption line at 6767.8 Å using the Michelson Doppler Imager on
board the Solar and Heliospheric Observatory. Our analysis shows that
both the high-resolution intensity observed in the G band and velocity
oscillations are influenced by the presence of a magnetic field. While
intensity oscillations are suppressed at all frequencies in strong
magnetic field regions compared to weak magnetic field regions,
velocity oscillations show an enhancement of power in the frequency
band 5.5-7 mHz. We find that there is a drop of 20%-30% in the p-mode
power of velocity oscillations within the SMFs when compared to the
regions surrounding them. Our findings indicate that the nature of the
interaction of acoustic waves with the quiet Sun SMFs is similar to
that of large-scale magnetic fields in active regions. We also report
the first results of the center-to-limb variation of such effects
using the observations of the quiet Sun from the Helioseismic and
Magnetic Imager (HMI) aboard the Solar Dynamics Observatory (SDO). The
independent verification of these interactions using SDO/HMI suggests
that the velocity power drop of 20%-30% in p-modes is fairly constant
across the solar disk.
---------------------------------------------------------
Title: Temperature variability in X-ray bright points observed
with Hinode/XRT
Authors: Kariyappa, R.; Deluca, E. E.; Saar, S. H.; Golub, L.; Damé,
L.; Pevtsov, A. A.; Varghese, B. A.
2011A&A...526A..78K Altcode:
<BR /> Aims: We investigate the variability in temperature as
a function of time among a sample of coronal X-ray bright points
(XBPs). <BR /> Methods: We analysed a 7-h (17:00-24:00 UT) long time
sequence of soft X-ray images observed almost simultaneously in two
filters (Ti_poly and Al_mesh) on April 14, 2007 with X-ray telescope
(XRT) onboard the Hinode mission. We identified and selected 14 XBPs
for a detailed analysis. The light curves of XBPs were derived using
the SolarSoft library in IDL. The temperature of XBPs was determined
using the calibrated temperature response curves of the two filters
by means of the intensity ratio method. <BR /> Results: We find that
the XBPs show a high variability in their temperature and that the
average temperature ranges from 1.1 MK to 3.4 MK. The variations
in temperature are often correlated with changes in average X-ray
emission. It is evident from the results of time series that the XBP
heating rate can be highly variable on short timescales, suggesting
that it has a reconnection origin.
---------------------------------------------------------
Title: Long-period intensity oscillations of the quiet solar
atmosphere from TRACE 1600 Åcontinuum observations.
Authors: Kariyappa, R.; Damé, L.
2010MmSAI..81..786K Altcode:
We have analysed a 6-hour long time sequence of ultraviolet (uv) images
obtained on May 24, 2003 in 1600 Å continuum under high spatial
and temporal resolutions from the Transition Region and Coronal
Explorer (TRACE). We have selected 15 isolated bright points, 15
network elements and 15 quiet background regions from these images for
detailed analysis. We derived the cumulative intensity values and the
light curves of these features for the total duration of observations,
and performed also a power spectrum analysis using the complete time
series data. We found that the uv bright points, the uv network and
the uv background regions exhibit long-period intensity oscillations
namely, 5.5 hours, 4.6 hours and 3.4 hours respectively, in addition
to the more familiar small scale intensity fluctuations. We suggest
that these longer periods of oscillation might be related to solar
atmospheric g-modes.
---------------------------------------------------------
Title: Bright Points in G-Band and Ca IIH Images from Hinode
Authors: Pradeep, C. L.; Kariyappa, R.
2010ASSP...19..424P Altcode: 2010mcia.conf..424P
We analyze a time sequence simultaneous G-band and Ca IIH images
taken with Hinode/SOT on 14 April 2007 during 17:00-18:00UT. In
each sequence, we selected 20 bright points and derived their light
curves. Power-spectrum analysis was performed to determine periodicities
in these light curves, which are 2-5min for the Gband bright points
and 3-4 min for the Ca IIH bright points, respectively. Comparison of
the light curves indicates the presence of a phase difference, which
suggests the occurrence of propagating waves that may be responsible
for heating the chromosphere in Ca IIH bright points.
---------------------------------------------------------
Title: Dynamical Evolution of X-Ray Bright Points with Hinode/XRT
Authors: Kariyappa, R.; Varghese, B. A.; DeLuca, E. E.; van
Ballegooijen, A. A.
2010ASSP...19..440K Altcode: 2010mcia.conf..440K
We analyzed a 7-h long time sequence of soft X-ray images obtained
on 14 April 2007 from a quiet region using the X-Ray Telescope (XRT)
onboard Hinode. The aim was to observe intensity oscillations in
coronal XBPs of different brightness and to study differences, if
any, in the periodicity of the intensity variations and the heating
mechanism during their dynamical evolution. We have compared the XRT
images with GONG magnetograms using Coronal Modeling Software (CMS),
and found that some of the XBPs are located at magnetic bipoles. The
coronal XBPs are highly dynamic and oscillatory in nature, showing a
wide variety of time scales in their intensity variations.
---------------------------------------------------------
Title: Solar coronal rotation determined by X-ray bright points in
Hinode/XRT and Yohkoh/SXT full-disc images
Authors: Kariyappa, R.
2008A&A...488..297K Altcode: 2008arXiv0804.3508K
Aims: Our aim is to identify and trace the X-ray bright points
(XBPs) over the disc and use them as tracers to determine the coronal
rotation. This investigation will help to clarify and understand several
issues: (i) whether the corona rotates differentially; (ii) whether
the rotation depends on the sizes of the XBPs; and (iii) whether there
is a dependence on phases of the solar magnetic cycle. <BR />Methods:
We analysed the daily full-disc soft X-ray images observed with (i)
X-Ray Telescope (XRT) onboard the Hinode mission during January, March,
and April 2007; and (ii) Soft X-ray Telescope (SXT) onboard the Yohkoh
from 1992 to 2001 using SSW in IDL. We used the tracer method to trace
the passage of XBPs over the solar disc with the help of overlaying
grids and derived the sidereal angular rotation velocity and the
coordinates (latitude and longitude) of the XBPs. <BR />Results:
We have determined the position of a large number of XBPs, both in
Hinode/XRT and Yohkoh/SXT images, and followed them over the solar
disc as a function of time. We derived the coronal sidereal angular
rotation velocity and compared it with heliocentric latitude and as a
function of solar activity cycle. In addition, we measured the sizes of
all the XBPs and related them to the coronal rotation. The important
results derived from these investigations are: (i) the solar corona
rotates differentially like the photosphere and chromosphere; (ii) the
sidereal angular rotation velocity is independent of the sizes of the
XBPs; (iii) the sidereal angular rotation velocity does not depend on
phases of the solar magnetic cycle; and (iv) the differential rotation
of the corona is present throughout the solar magnetic cycle.
---------------------------------------------------------
Title: Intensity oscillations and heating of the coronal X-ray bright
points from Hinode/XRT
Authors: Kariyappa, R.; Varghese, B. A.
2008A&A...485..289K Altcode: 2008arXiv0804.3480K
Aims: Our aim is to investigate the intensity oscillations in coronal
X-ray Bright Points (XBPs). <BR />Methods: We analysed a 7 h long
time sequence of the soft X-ray images obtained on April 14, 2007
with a 2 min cadence using the X-Ray Telescope (XRT) on-board the
Hinode mission. We use SSW in IDL to derive the time series of 14
XBPs and 2 background regions. For the first time, we have tried to
use power spectrum analysis on XBP data to determine the periods of
intensity oscillations. <BR />Results: The power spectra of XBPs show
several significant peaks at different frequencies corresponding to
time scales that range from a few minutes to hours. The light curves
of all the XBPs give the impression that the XBPs can be grouped into
three classes depending on emission levels: (i) weak XBPs; (ii) bright
XBPs; and (iii) very strong XBPs. The periods of intensity oscillation
are consistent in all the XBPs and are independent of their brightness
level, suggesting that the heating mechanisms in all the three groups
of XBPs are similar. The different classes of XBPs may be related to
the different strengths of the magnetic field with which they have
been associated.
---------------------------------------------------------
Title: Detection of mesogranulation at the upper chromosphere from
SOHO/SUMER observations
Authors: Kariyappa, R.; Varghese, B. A.; Curdt, W.
2008arXiv0804.3659K Altcode:
We have analyzed a time series of spectra in the hydrogen Lyman lines
and the Lyman continuum obtained by the Solar Ultraviolet Measurements
of Emitted Radiation (SUMER) spectrometer on the SOlar Heliospheric
Observatory (SOHO). The time series of about 2 hours and 22 minutes
was obtained on 1999 March 9 in a quiet region near the center of
the solar disk. For our analysis, we have selected a Lyman continuum
window around 907 A, and the five Lyman lines: Ly5 (937.8 A), Ly7
(926.2 A), Ly9 (920.9 A), Ly11 (918.1 A), and Ly15 (915.3 A). A Fast
Fourier analysis has been performed in the spatial domain, all along
the slit length used, for all the spectra and for the total duration
of the observations. We have detected a significant periodic spatial
variations with Fourier transform power peaks around 9-10 arcsec and at
4 arcsec. They correspond to the scale of the mesogranulation structure
and the width of the supergranular boundary, respectively. For the first
time, this provides evidence for the existence of a meso-scale in the
upper chromosphere, of the same size as observed in the photosphere and
lower chromosphere by earlier studies. We find from the analysis that
there seems to be no signature of any temporal evolution associated
with the mesogranules, at least not during our observing period. This
result suggests that the life time of mesogranules will be several
hours or more, which confirms the earlier findings. In addition,
we notice that the size (9-10 arcsec) of the mesocells appears to be
the same in all Lyman lines and in the continuum, which are formed at
different depths in the chromosphere.
---------------------------------------------------------
Title: Observational searches for g-mode oscillations in the quiet
solar atmosphere from TRACE 1600A Continuum Observations
Authors: Kariyappa, R.; Dame, L.
2008arXiv0804.3502K Altcode:
Our aim is to search for atmospheric g-mode oscillations in UV
network, UV bright points and Uv background regions. We have analysed
a 6-hours of time sequence of ultraviolet (uv) images obtained on
May 24, 2003 in 1600A continuum under high spatial and temporal
resolution from Transition Region and Coronal Explorer (TRACE). We
have selected an isolated 15 uv bright points, 15 uv network elements
and 15 uv background regions in a quiet region from the images for
the detailed analysis. We derived the cumulative intensity values of
these features. The light curves of all the features have been derived
for the total duration of observations and done the power spectrum
analysis using the time series data. We found that the uv bright points,
the uv network and uv background regions will exhibit a longer period
of intensity oscillations namely, 5.5 hours, 4.6 hours and 3.4 hours
respectively, in addition to the more familiar small scale intensity
fluctuations. We suggest that the longer periods of oscillation may
be related to solar atmospheric g-modes.
---------------------------------------------------------
Title: Spatially resolved images and solar irradiance variability
Authors: Kariyappa, R.
2008JApA...29..159K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Contribution of Solar Chromospheric Fine Scale Features to
UV Irradiance Variability
Authors: Kariyappa, R.
2006ihy..workE..31K Altcode:
The Sun is the primary source of energy responsible for governing
both the weather and climate of Earth. For that reason alone one would
expect that changes in the amount and type of energy Earth received from
the Sun could alter weather and climate on the Earth. The variations
in the UV irradiance are produced by surface manifestation of solar
magnetic activity. Considering the variations in the solar UV flux
may cause significant changes in the Earth’s climate, understanding
the physical origin of UV irradiance changes is an extremely important
issue in Solar and Space Physics. We have segregated the (i) plages,
(ii) magnetic network, and (iii) intranetwork + the background regions
from the Call K spectroheliograms of 1980 and 1992, observed at the
National Solar Observatory at Sacramento Peak, using their histograms
taken for the full-disk. The different parameters like the intensity and
area of the chromospheric features, the full-disk intensity (spatial
K index), and the full width at half maximum (FWHM) of the histograms
have been derived from the images. The spatial K index, FWHM, and the
intensity of various features have been compared to the UV irradiance
measured in the Mgll h and k lines by the Nimbus7 and NOAA9 satellites
and it has been found that they are correlated with the Mgll h and
k c/w ratio. We established, for the first time, from the results of
1992 images and of 1980 that the FWHM can be used as a good index for
measuring and describing the chromospheric activity in the K-line. The
results of both 1980 and 1992 images show an anticorrelation between the
intensity and area of the network elements, which confirm the earlier
findings derived entirely from different data set from Kodaikanal Call
K spectroheliograms analyzed for the center of the solar disc in a
quiet regions for a longer time interval of 1951 to 1983 (Kariyappa and
Sivaraman, 1994). During solar minimum the network is fainter but covers
a larger area than during solar maximum. These results suggest that the
variations in both the intensity and area of the various chromospheric
features have to be taken into account in irradiance models.
---------------------------------------------------------
Title: Observational Searches for Chromospheric g-Mode
Oscillationsfrom CaII H-Line Observations
Authors: Kariyappa, R.; Dame, L.; Hiremath, K. M.
2006JApA...27..327K Altcode:
We have used a high spatial and temporal resolution of long time
sequence of spectra in CaII H-line obtained at the Vacuum Tower
Telescope (VTT) of the Sacramento Peak Observatory on a quiet region
at the center of the solar disk over a large number of bright points
and network elements to search for atmospheric (chromospheric) g-mode
oscillations. An important parameter of the H-line profile, intensity at
H<SUB>2V</SUB>(IH<SUB>2V</SUB>), has been derived from a large number
of line profiles. We derived the light curves of all the bright points
and network elements. The light curves represent the main pulse with
large intensity amplitude and followed by several follower pulses with
lower intensity amplitudes. The light curves of these bright points
would give an impression that one can as well draw curves towards and
away from the highest peak (main pulse) showing an exponential growth
and decay of the amplitudes. An exponential decaying function has been
fitted for all the light curves of the bright points to determine the
damping time of the modes that are more or less the same, and one
value of the coefficient of exponent can represent reasonably well
the decay for all the cases. The FFT analysis of temporal variation of
both the bright points and the network elements indicates around 10-min
periodicity. We speculate that this longer period of oscillation may
be related to chromospheric g-mode oscillations.
---------------------------------------------------------
Title: The Extreme Solar Activity during October-November 2003
Authors: Hiremath, K. M.; Lovely, M. R.; Kariyappa, R.
2006JApA...27..333H Altcode:
The positional measurements of sunspots from the Kodaikanal Observatory
and Solar Geophysical data are used to study the association between
occurrence of the abnormal activities of big sunspot groups that were
observed during the period of October-November 2003 and occurrence
of the flares. During the evolution of the sunspot groups, we have
investigated the temporal variations in (i) areas; (ii) rotation rates;
(iii) longitudinal extents; and (iv) number of small spots produced
in a sunspot group. Among all these activity variations, we find that
the spot groups that experience abnormal rotation rates during their
evolutionary phases eventually trigger the flares.
---------------------------------------------------------
Title: Search For Atmospheric G-mode Oscillations from TRACE
Observations
Authors: Kariyappa, R.; Dame, L.; Varghese, B. A.
2006IAUJD...3E...1K Altcode:
An identification and clarification of different modes of oscillations
may eventually illuminate the solar neutrino problem. The internal
g-modes of the Sun are the most powerful tool for investigation of
solar core and the neutrino problem. The detection of atmospheric
g-mode oscillations are also equally important in order to know
the role of different kinds of oscillations in the heating of the
chromosphere and corona. We have analysed a 6-hours of time sequence of
ultraviolet images obtained on May 24, 2003 in 1600 Å continuum under
high spatial and temporal resolution with TRACE Space Mission. We have
chosen 15 uv bright points, 15 uv network elements and 15 uv background
regions from the time sequence images for the detailed analysis. We
derived the cumulative intensity values of all these features using
SolarSoftware (SSW) in IDL. The light curves of all the features have
been generated for the total duration of observations. We have done
the power spectrum analysis using their time series data. We find that
the uv bright points, the uv network and uv background regions will
exhibit longer period of intensity oscillations namely, 5.5 hours,
4.6 hours and 3.4 hours respectively, in addition to small scale
intensity fluctuations. We suggest that these periods may be related
to a very high order atmospheric g-modes showing a large periods at
the transition region.
---------------------------------------------------------
Title: Contribution of Chromospheric Features to UV Irradiance
Variability
Authors: Kariyappa, R.; Dame, L.
2006IAUJD...8E...1K Altcode:
We have determined the time series data of the different parameters
like the intensity, area, the full-disk intensity (spatial K index),
and the Full Width at Half Maximum (FWHM) for the segregated features
of the chromosphere from the CaII K spectroheliograms of 1992 and 1980,
observed at the NSO at Sac Peak, using their histograms taken for the
full-disk. We established, for the first time, from the results of 1992
and 1980 images that the FWHM can be used as a good index for measuring
and describing the chromospheric activity in the K-line. Our study
shows that besides the plages, a significant portion of the variation
observed in UV irradiance is related to the changing emission of the
network and intranetwork + background regions. This indicates that in
addition to plages and network, the intranetwork + background regions
may also play a significant role in their contribution to the variation
in UV irradiance. We estimated the contribution of various chromospheric
features to the total CaII K flux from the intensity time series data
and found that about 50% of the CaII K solar cycle variability results
from plages, about 32% from network, and about 18% from intranetwork +
background features.
---------------------------------------------------------
Title: An Observational Evidence for Solar Atmospheric G-Mode
Oscillations From 1600A UV Continuum Observations
Authors: Kariyappa, R.; Dame, L.
2006cosp...36....6K Altcode: 2006cosp.meet....6K
An identification and clarification of different modes of oscillations
may eventually illuminate the solar neutrino problem Particularly the
internal g-modes of the Sun are the most powerful tool for investigation
of solar core and a way to solve for instance the neutrino problem We
have used a high spatial and temporal resolution of long time sequence
of images obtained under high spatial and temporal resolution with
TRACE Space Mission in 1600A UV continuum We derived the cumulative
intensity values of the UV bright points The light curves of the UV
bright points have been generated The FFT analysis of temporal variation
of the UV bright points of the transition region indicates an evidence
of longer periods of oscillations of the order of 45-min and 10-min This
confirms the results obtained from CaII H -line observations Kariyappa
et al 2005 and suggest that the longer period of oscillations may be
related to solar atmospheric g-mode oscillations The detailed results
of this analysis will be discussed in this paper
---------------------------------------------------------
Title: Observational Evidence for Chromospheric g-mode Oscillations
Authors: Kariyappa, R.
2006cosp...36....5K Altcode: 2006cosp.meet....5K
An identification and clarification of different modes of oscillations
may eventually illuminate the solar neutrino problem Particularly the
internal g-modes of the Sun are the most powerful tool for investigation
of solar core and a way to solve for instance the neutrino problem We
have used a high spatial and temporal resolution of long time sequence
of spectra in CaII H-line obtained at the Vacuum Tower Telescope VTT
of the Sacramento Peak Observatory on a quiet region at the center
of the solar disk over a large number of bright points and network
elements to search for atmospheric chromospheric g-mode oscillations An
important parameter of the H-line profile intensity atH 2VI H 2V has
been derived from a large number of line profiles at the locations of
29 bright points and 3 network elements We derived the light curves of
all the bright points and network elements for the total duration of
our observations The light curves represent the main pulse with large
intensity amplitude and followed by several follower pulses with lower
intensity amplitudes The light curves of these bright points would
give an impression that one can as well draw curves towards and away
to the highest peak main pulse showing an exponential growth and decay
of the amplitudes The exponential functions have been fitted for all
the light curves of the bright points and found that the slopes are
more or less the same and one value of the exponent can represent
reasonably well the decay for all the cases We find an
---------------------------------------------------------
Title: Variability of CaII K Emission Flux Over the Solar Cycle
Authors: Kariyappa, R.; Sivaraman, K. R.
2005BASI...33..365K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Contribution of Solar Chromospheric Features to UV Irradiance
Variability
Authors: Kariyappa, R.; Hiremath, K. M.; Dame, L.
2005BASI...33..364K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar Abnormal Activity During Oct.-Nov. 2003
Authors: Hiremath, K. M.; Lovely, M. R.; Kariyappa, R.
2005BASI...33..356H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Period-brightness relationship in chromospheric bright points
Authors: Kariyappa, R.; Narayanan, A. Satya; Dame, L.
2005BASI...33...19K Altcode:
Chromospheric bright points are sites where intense heating takes
place by 3-min period waves. A 35-min-long time series of photographic
spectra obtained in CaII H-line on a quiet region at the center of the
solar disk under high spatial, spectral, and temporal resolution at
the Vacuum Tower Telescope (VTT) of the Sacramento Peak Observatory
has been analyzed to show that the period of intensity oscillations
associated with bright points in the interior of the supergranular
cells is independent of their intensity enhancements. We find evidence
for a constant period of oscillations in bright points, independent
of their peak brightness, and different from the period of network
oscillations. This suggests that the heating mechanism may be identical
(by 3-min period waves) in any class of bright points while in the
case of network elements it may be an entirely different mechanism (by
5-7 min period waves). In addition, it is shown that the amplitudes of
the main and the follower pulses of bright points decay exponentially
with time and the decay rate is constant with their brightness in any
class of bright points.
---------------------------------------------------------
Title: Change of level population density with time in the solar
quiet chromospheric atmosphere
Authors: Barman, S. K.; Kariyappa, R.
2001BASI...29..245B Altcode:
Employing a law of weak acoustic wave, the ratio of population density
N2/N1 with time for the Ca II H and K lines appropriate for the solar
quiet chromosphere have been calculated. This has been done by solving
the equations of radiative transfer and statistical equilibrium for
two level plus continuum atom simultaneously. From the calculation it
has been shown that even a small deposit of weak acoustic wave energy
can enhance the emission peak of resonance lines.
---------------------------------------------------------
Title: Temporal and spatial variations of the quiet upper chromosphere
from SOHO/SUMER observations of hydrogen Lyman lines
Authors: Kariyappa, R.; Varghese, B. A.; Curdt, W.
2001A&A...374..691K Altcode:
We have analyzed a time series of spectra in the hydrogen Lyman lines
and the Lyman continuum obtained by the Solar Ultraviolet Measurements
of Emitted Radiation (SUMER) spectrometer on the SOlar Heliospheric
Observatory (SOHO). The time series of about 2 hours and 22 min was
obtained on 1999 March 9 in a quiet region near the center of the
solar disk. For our analysis, we have selected a Lyman continuum
window around 907 Å, and the five Lyman lines: Ly5 (937.8 Å),
Ly7 (926.2 Å), Ly9 (920.9 Å), Ly11 (918.1 Å), and Ly15 (915.3
Å). We derived the central intensity of these lines for a large
number of locations over the network and inter-network regions. We
found from their line-center intensity time series and from the power
spectrum analysis that the network and inter-network regions at the
upper chromosphere are associated with 5-7 min and 3-min period of
intensity oscillations, respectively. Phase difference analysis shows
that there is a preponderance of upward-propagating waves in the
upper chromosphere. The phase velocity was estimated to be roughly
4-5 km s<SUP>-1</SUP> in the network regions. In addition, a Fast
Fourier analysis has been performed in the spatial domain, all along
the slit length used, for all the spectra and for the total duration
of the observations. We have detected significant periodic spatial
variations with Fourier transform power peaks around 9-10 arcsec and at
4 arcsec. They correspond to the scale of mesogranulation structure and
the width of the supergranular boundary, respectively. This provides
evidence for the existence of a meso-scale in the upper chromosphere,
of the same size as observed in the photosphere and lower chromosphere
by earlier studies. We notice that the size (9-10 arcsec) of the
meso-scale structures appears to be the same in all Lyman lines and in
the continuum, which are formed at different depths in the chromosphere.
---------------------------------------------------------
Title: Application of Non-linear Analysis to Intensity Oscillations
of the Chromospheric Bright Points
Authors: Bhattacharya, Joydeep; Pereda, Ernesto; Kariyappa, Rangaiah;
Pratim Kanjilal, Partha
2001SoPh..199..267B Altcode:
We have applied several nonlinear techniques to the intensity
oscillations of the chromospheric bright points observed at the Vacuum
Tower Telescope (VTT) of the Sacramento Peak Observatory. A 35-min time
sequence obtained in the Ca ii H line over a quiet region at the center
of the solar disk under high spatial, spectral, and temporal resolution
has been used. A relatively new approach is used to detect the hidden
periodicity and to extract the associated periodic component(s) from an
apparently irregular time series. The unique feature of this approach is
that the constituent component(s) can be non-sinusoidal in nature. The
periodicity analysis shows that time series of intensity oscillations
of most of the bright points can be composed of two non-sinusoidal
periodic components with periodicity varying between 2.4 min and 5.8
min. With the help of a multivariate embedding technique, globally
significant spatial nonlinear correlation is found. The identification
of the nonlinear interaction between bright points is performed by
using the methods of dynamical phase synchronization and the similarity
index. The analysis indicates that bright points are interconnected
in the sense that some bright points are more active and can influence
the other relatively passive bright points.
---------------------------------------------------------
Title: CaII K Imaging to Understand UV Irradiance Variability
Authors: Kariyappa, R.
2000JApA...21..293K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Quiet-Sun Variability with the Solar Cycle
Authors: Kariyappa, R.
1999ASPC..183..501K Altcode: 1999hrsp.conf..501K
No abstract at ADS
---------------------------------------------------------
Title: Oscillations and Heating in Chromospheric Fine Scale Structures
Authors: Kariyappa, R.
1999ASPC..183..420K Altcode: 1999hrsp.conf..420K
No abstract at ADS
---------------------------------------------------------
Title: Erratum: Solar Oscillations in Strong and Weak Fraunhofer
Lines over a Quiet Region
Authors: Kariyappa, R.
1996SoPh..168..225K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Contribution of Chromospheric Features to UV Irradiance
Variability from Spatially-Resolved CA II K Spectroheliograms,
Authors: Kariyappa, R.; Pap, J. M.
1996SoPh..167..115K Altcode:
We have digitized the Ca II K spectroheliograms, observed at the
National Solar Observatory at Sacramento Peak, for the period 1980
(maximum of solar cycle 21), 1985 (minimum of solar cycle 21),
1987 (beginning of the ascending phase of solar cycle 22), 1988
and 1989 (ascending phase and maximum of solar cycle 22), and 1992
(declining phase of solar cycle 22). A new method for analyzing the
K spectroheliograms has been developed and applied to the K images
for the time interval of 1992. Using histograms of intensity, we
have segregated and measured the cumulative intensity and area of
various chromospheric features like the plages, magnetic network and
intranetwork elements. Also, the full width at half maximum (FWHM)
derived from the histograms has been introduced as a new index for
describing the chromospheric activity in the K-line. The full-disk
intensity (spatial K index) has been derived from spatially-resolved
K images and compared to the spectral K index derived from the line
profiles for the full disk. Both the spatial K index and FWHM have
been compared to the UV irradiance measured in the Mg II h and k lines
by the NOAA9 satellite and found that they are highly correlated with
the Mg II h and k c/w ratio.
---------------------------------------------------------
Title: Solar Oscillations in Strong and Weak Fraunhofer Lines over
a Quiet Region
Authors: Kariyappa, R.
1996SoPh..165..211K Altcode:
We have analysed a 35-min-long time sequence of spectra in the CaII H
line, NaI D1 and D2 lines, and in a large number of strong and weak FeI
lines taken over a quiet region at the center of the solar disk. The
time series of these spectra have been observed simultaneously in these
lines under high spatial, spectral, and temporal resolution at the
Vacuum Tower Telescope (VTT) of the Sacramento Peak Observatory. We
have derived the line profiles and their central intensity values
at the sites of the chromospheric bright points, which are visible
in the H line for easy identification. We have done a power spectrum
analysis for all the lines, using their central intensity values to
determine the period of oscillations. It is shown that the 3 FeI lines,
present ∼ 23 Å away from the core of the H line representing the pure
photospheric lines, NaI D1 and D2 lines, 6 FeI lines at the wings of
H line, and Can H line exhibit 5-min, 4.05-min, 3.96-min, and 3.2-min
periodicity in their intensity oscillations, respectively. Since all
these lines form at different heights in the solar atmosphere from low
photosphere to middle chromosphere and show different periodicities in
their intensity oscillations, these studies may give an idea about the
spatial and temporal relation between the photospheric and chromospheric
intensities. Therefore these studies will help to better understand
the physical mechanisms of solar oscillations. It is clearly seen that
the period of intensity oscillations decreases outward from the low
photosphere to the middle chromosphere. Since we have studied a single
feature at a time on the Sun (i.e., bright points seen in the H line)
in all these spectral lines simultaneously, this may explain about
the footpoints of the bright points, the origin of 3-min oscillations,
and the relation to other oscillations pertaining to these locations on
the Sun. We have concluded that 80% of the bright points are associated
with dark elements in the true continuum, and they may seem to have
a relationship with the dark intergranular lanes of the photosphere,
after carefully examining the brightness (bright threads) extending
from the core to the far wings of the H line at the locations of a
large number of bright points, using their time sequence of spectra.
---------------------------------------------------------
Title: CA II K Line Profile of the Truly Quiet Sun
Authors: Sivaraman, K. R.; Gupta, S. S.; Kariyappa, R.
1996SoPh..163...93S Altcode:
While evaluating the chromospheric variability (solar cycle related or
any other) using the Ca II K line (λ3933.684 Å) as an indicator, an
essential prerequisite is the knowledge of the profile of a truly quiet
Sun in the integrated light. Such a profile can serve as a bench mark
over which enhancements can be measured, particularly when modelling
variability. This paper describes how such a K-line profile has been
derived for the quiet Sun using disc-integrated light.
---------------------------------------------------------
Title: Direct Observational Evidence for the Heating of the Solar
Chromosphere
Authors: Kariyappa, R.; Sivaraman, K. R.; Anandaram, M. N.
1995JApAS..16..383K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Intensity Oscillations in Nal d1 and d2 Lines
Authors: Kariyappa, R.; Pap, J. M.
1995ESASP.376b.521K Altcode: 1995soho....2..521K; 1995help.confP.521K
No abstract at ADS
---------------------------------------------------------
Title: Preliminary Results of the Analysis of CAII K Spectroheliograms
Authors: Kariyappa, R.; Pap, J. M.; Balasubramaniam, K. S.; Kuhn, J. R.
1995ESASP.376b.429K Altcode: 1995help.confP.429K; 1995soho....2..429K
No abstract at ADS
---------------------------------------------------------
Title: The Relation Between the Period of Oscillations and Brightness
in Chromospheric Bright Points
Authors: Kariyappa, R.
1995ESASP.376b.525K Altcode: 1995help.confP.525K; 1995soho....2..525K
No abstract at ADS
---------------------------------------------------------
Title: Pole-Equator Difference and the Variability of the Brightness
of the Chromospheric Call-K-NETWORK Elements in Quiet Regions Over
the Solar Cycle
Authors: Kariyappa, R.
1995ESASP.376b.437K Altcode: 1995help.confP.437K; 1995soho....2..437K
No abstract at ADS
---------------------------------------------------------
Title: Intensity Oscillations in Chromospheric Bright Points and
Network Elements
Authors: Kariyappa, R.
1994SoPh..154...19K Altcode:
From a 35-min time series of photographic spectra in the CaII H-line
obtained at the Vacuum Tower Telescope (VTT) of the Sacramento Peak
Observatory under high spatial, spectral, and temporal resolution,
we have derived a large number of H-line profiles at the sites of
the bright points in the interior of the supergranulation cells,
and at the network elements, on a quiet region at the centre of the
solar disc. It is shown that the bright points are associated with
3-min periodicity in their intensity oscillations whereas the network
elements exhibit ∼7-min periodicity. It is surmised that the large
difference in periods of the intensity oscillations, the strength of
the magnetic fields, and the intensity enhancements at the sites of
the bright points and the network elements themselves may probably be
taken as evidence to argue that the mechanisms of heating in the two
cases are dissimilar, irrespective of the sizes of these structures.
---------------------------------------------------------
Title: Variability of the Solar Chromospheric Network Over the
Solar Cycle
Authors: Kariyappa, R.; Sivaraman, K. R.
1994SoPh..152..139K Altcode: 1994svs..coll..139K; 1994IAUCo.143..139K
From a large sample of the Kodaikanal spectroheliograms in the Call
K line we have studied the variations in the intensity of the network
elements over two solar cycles and have estimated their contribution to
the overall variability seen in the disc-averaged K line profiles. The
relative contribution of the network elements and the bright points to
the K-emission are of the order of 25% and 15% respectively. We have
shown that the area of the network elements is anti-correlated with
the solar activity, and it increases by about 24% during the solar
minimum compared to the maximum period.
---------------------------------------------------------
Title: Heating of the Quiet Solar Chromosphere - Part One
Authors: Kariyappa, R.; Sivaraman, K. R.; Anadaram, M. N.
1994SoPh..151..243K Altcode:
We have analyzed a large number of CaII H line profiles at the sites of
the bright points in the interior of the network using a 35-min-long
time sequence of spectra obtained at the Vacuum Tower Telescope
(VTT) of the Sacramento Peak Observatory on a quiet regon of the
solar disc and studied the dynamical processes associated with these
structures. Our analysis shows that the profiles can be grouped into
three classes in terms of their evolutionary behaviour. It is surmized
that the differences in their behaviour are directly linked with the
inner network photospheric magnetic points to which they have been
observed to bear a spatial correspondence. The light curves of these
bright points give the impression that the `main pulse', which is
the upward propagating disturbance carrying energy, throws the medium
within the bright point into a resonant mode of oscillation that is
seen as the follower pulses. The main pulse as well as the follower
pulses have identical periods of intensity oscillations, with a mean
value around 190 ± 20 s. We show that the energy transported by these
main pulses at the sites of the bright points over the entire visible
solar surface can account for a substantial fraction of the radiative
loss from the quiet chromosphere, according to current models.
---------------------------------------------------------
Title: Notes and News
Authors: Kariyappa, R.
1994BASI...22..101K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Study of Inhomogeneities in the Solar Atmosphere
Authors: Kariyappa, R.
1993PASP..105.1366K Altcode:
We have analysed a large number of Ca II line profiles at the site of
the bright points in the interior of the network using a 35-minute
long time sequence spectra obtained at hte Vacuum Tower Telesope
(VTT) of hte Sacramento Peak Observatory on a quiet region of the
solar disc and studied the dynamical processes associated with these
structures. Our analysis shows that the profiles can be grouped into
three classes in terms of their evolutionary behavior. It is surmised
that the differences in their behavior is directly linked with the
inner network photospheric magnetic points to which they have been
observed to bear a spatial correspondence. The light curves of these
bright points give the impression that the"main pulse" which is the
upward propagating disturbance carrying energy throws the medium within
the bright point into a resonant mode of oscillation that are seen as
the follower pulses. The main pulse as well as the follower pulses
have identical periods of intensity oscillations, with a mean value
around 190 +/- 20 secs. We show that the energy transported by these
main pulses at the sits of the bright points over the entire visible
solar surface can account for a substantial freedom of the radiative
loss from the quiet chromosphere according to current models. (SECTION:
Dissertation Summaries)
---------------------------------------------------------
Title: What is a quiet sun CaII K line profile?
Authors: Sivaraman, K. R.; Gupta, S. S.; Kariyappa, R.
1993BASI...21..659S Altcode:
We have derived a mean disc averaged K line profile from observations
at the Kodaikanal Solar Tower Telescope on days when sun was relatively
very quiet during the years 1985-86. This mean profile would represent
the K-line profile of a truly quiet sun.
---------------------------------------------------------
Title: Study of inhomogeneities in the solar atmosphere.
Authors: Kariyappa, R.
1993BASI...21..365K Altcode:
The thesis deals with the study of the dynamical processes leading
to the heating of the quiet solar chromosphere at the site of
inhomogeneities.
---------------------------------------------------------
Title: Solar variability in the Ca II K line during solar cycles 21
and 22.
Authors: Sivaraman, K. R.; Gupta, S. S.; Kariyappa, R.; Aleem,
P. S. M.; Sundararaman, K.
1993BASI...21..655S Altcode:
The authors have monitored the Sun in the light of the Ca II K line and
obtained the disc integrated profiles for the year 1974 - 91. From these
profiles they have estimated the variability of the Sun as a star as
seen in the various K line parameters. The 1 Å index shows an increase
of about 35% in 1990 from its minimum value attained in 1986 - 87.
---------------------------------------------------------
Title: A double-pass spectrograph for solar research.
Authors: Kariyappa, R.; Jayarajan, A. P.; Raheem, K. C. A.; Sivaraman,
K. R.
1993BASI...21..139K Altcode:
The authors describe the double-pass spectrograph built at the Indian
Institute of Astrophysics. Measurements of the scattered light within
the spectrograph using the photoelectric scans of the Na I D-lines
show that this is a good near-scatter-free system. The instrument is
used to monitor the disk integrated Ca II K line profile of the sun
on a regular basis.
---------------------------------------------------------
Title: Role of small scale dynamical processes in the heating of
the solar chromosphere.
Authors: Sivaraman, K. R.; Kariyappa, R.; Gupta, S. S.
1991BASI...19..207S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Calibration on the Sun for Stellar Magnetic Fields
Authors: Sivaraman, K. R.; Bagare, S. P.; Gupta, S. S.; Kariyappa, R.
1987LNP...291...47S Altcode: 1987csss....5...47S; 1987LNP87.291...47S
The intimate association between the surface magnetic fields and the
Ca II K line emission known to exist on the sun, holds a promise for
using this property to detect the presence of global magnetic fields on
sun - like stars. We have obtained a large number of K line profiles
over a variety of plages on the sun and related the 1A emission flux
centred at the K3 minimum for these profiles with the corresponding
values of the longitudinal component of the photospheric magnetic
field. This provides a calibration for detecting and estimating the
surface magnetic fields on stars that show K emission.
---------------------------------------------------------
Title: K-Line Emission and the Integrated Surface Magnetic Field on
the Sun
Authors: Sivaraman, K. R.; Kariyappa, R.
1986LNP...254..496S Altcode: 1986csss....4..496S
We have made plots of the Ca II K line emission vs the global surface
magnetic field for the sun for the years 1975-1982 representing both
solar minimum as well as solar maximum epochs. These plots show that
the K-line emission is not related to the global magnetic fields. An
explanation for the absence of a correlation is offered. A direct
measurement of the global magnetic field of the sun or similar stars
will give an algebraic sum of the magnetic fields present on the
surface, whereas the K-line emission will be additive Irrespective of
the polarity of the fields. K-line emission being a sign insensitive
indicator of magnetic field, is advantageous and with a proper
calibration, the surface fields and the partition of fields according
to signs can be evaluated through a calibration. This possibility is
extended to sun-like stars where the presence of surface fields can
be established reliably.
---------------------------------------------------------
Title: Broad band photometry of the solar corona of 1983, June 11.
Authors: Sivaraman, K. R.; Singh, J.; Kapoor, R. C.; Kariyappa, R.
1985KodOB...5...31S Altcode:
The solar corona was photographed at an effective wavelength of
6300 Å during the total eclipse of 1983, June 11 at Indonesia. From
the isophotes of the corona, the intensity distributions along the
equator, poles, streamers and gaps have been derived. The brightness
distribution and the Ludendorff parameters of this corona are typical
of the intermediate phase of the solar cycle.
