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. Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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.
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).
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.
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.
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.

The movie associated to Fig. 2 is available at http://www.aanda.org 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. Bibcode: 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. Bibcode: 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.
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.
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.
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. Bibcode: 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).
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).
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.
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.
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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 km2 s-2 to the variance of the observed velocities. The raw and corrected velocity measurements in both directions, i.e., (vx , vy ), have Gaussian distributions with standard deviations of (1.32, 1.22) and (1.00, 0.86) km s-1, 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 2011A&A...526A..78K Altcode:
Aims: We investigate the variability in temperature as a function of time among a sample of coronal X-ray bright points (XBPs).
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.
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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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.
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.
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. Bibcode: 2008A&A...485..289K Altcode: 2008arXiv0804.3480K Aims: Our aim is to investigate the intensity oscillations in coronal X-ray Bright Points (XBPs).
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.
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. Bibcode: 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. Bibcode: 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. Bibcode: 2008JApA...29..159K Altcode: No abstract at ADS Title: Contribution of Solar Chromospheric Fine Scale Features to UV Irradiance Variability Authors: Kariyappa, R. Bibcode: 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. Bibcode: 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 H2V(IH2V), 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 2005BASI...33..356H Altcode: No abstract at ADS Title: Period-brightness relationship in chromospheric bright points Authors: Kariyappa, R.; Narayanan, A. Satya; Dame, L. Bibcode: 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. Bibcode: 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. Bibcode: 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-1 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 Bibcode: 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. Bibcode: 2000JApA...21..293K Altcode: No abstract at ADS Title: Quiet-Sun Variability with the Solar Cycle Authors: Kariyappa, R. Bibcode: 1999ASPC..183..501K Altcode: 1999hrsp.conf..501K No abstract at ADS Title: Oscillations and Heating in Chromospheric Fine Scale Structures Authors: Kariyappa, R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1995JApAS..16..383K Altcode: No abstract at ADS Title: Intensity Oscillations in Nal d1 and d2 Lines Authors: Kariyappa, R.; Pap, J. M. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1994BASI...22..101K Altcode: No abstract at ADS Title: Study of Inhomogeneities in the Solar Atmosphere Authors: Kariyappa, R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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.