Author name code: tripathi ADS astronomy entries on 2022-09-14 author:"Tripathi, Durgesh" ------------------------------------------------------------------------ Title: On the formation solar wind, switchbacks and Quiet Sun heating Authors: Upendran, Vishal; Tripathi, Durgesh Bibcode: 2022cosp...44.1355U Altcode: Coronal holes (CHs) are regions with reduced intensity and enhanced blueshifts over Quiet Sun (QS) regions in the corona. These differences are seen in the transition region (TR) seen only for regions with similar photospheric magnetic flux density (|B|). This work studies the chromospheric Mg II h&k, the C II 1334 Å, and TR Si IV line in CHs and QS as a function of |B|. We find all lines to show an increase of intensities and velocities with |B|. The chromospheric lines show reduced intensity, excess blueshifts, and excess redshifts in CHs over QS for regions with similar |B|. In the TR line, CHs show excess blueshifts and reduced intensity and redshift. Cross-correlation of chromospheric and TR velocities shows that flows in the same direction are tightly correlated in both regions. In contrast, only the chromospheric downflows are correlated with TR upflows in the opposite sense of direction. The TR downflows (upflows) are preferentially larger in QS (CHs) for similar chromospheric flows. These results may be explained through impulsive heating in a stratified atmosphere causing larger downflow (upflow) deceleration (acceleration) in QS (CHs), which form due to bidirectional flows generated by impulsive events. The observed flows and intensities may be explained by invoking interchange (closed-loop) reconnection in CHs (QS). An interesting possibility of such a model is constraining the formation of switchbacks in the lower atmosphere through our observations. Thus, we provide evidence on solar wind formation in the chromosphere and further hint towards a unified heating scenario in QS and CHs. Title: Science from Aditya-L1 mission of the Indian Space Research Organization Authors: Tripathi, Durgesh Bibcode: 2022cosp...44.1354T Altcode: The Aditya-L1 is the first observatory of the Indian Space Research Organization (ISRO) in space dedicated to solar observations. The spacecraft will carry 7 payloads providing uninterrupted observations of the Sun using remote sensing as well as in-situ measurements from the first Lagrangian point. There are four remote sensing instruments namely a coronagraph, an NUV imager, full-sun integrated soft X-ray and hard X-ray spectrometers. In addition, there are three instruments for in-situ measurements including a magnetometer to study the magnetic field variations during energetic events. I will high-light some of the salient feature for the mission and the important roles it will play in enhancing our knowledge in the science of the solar atmosphere and inner solar corona. Title: Synchronization of Small-scale Magnetic Features, Blinkers, and Coronal Bright Points Authors: Shokri, Zahra; Alipour, Nasibe; Safari, Hossein; Kayshap, Pradeep; Podladchikova, Olena; Nigro, Giuseppina; Tripathi, Durgesh Bibcode: 2022ApJ...926...42S Altcode: 2022arXiv220104459S We investigate the relationship between different transients such as blinkers detected in images taken at 304 Å, extreme ultraviolet coronal bright points (ECBPs) at 193 Å, X-ray coronal bright points (XCBPs) at 94 Å on the Atmospheric Imaging Assembly, and magnetic features observed by the Helioseismic and Magnetic Imager during 10 yr of solar cycle 24. An automatic identification method is applied to detect transients, and the YAFTA algorithm is used to extract the magnetic features. Using 10 yr of data, we detect in total 7,483,827 blinkers, 2,082,162 ECBPs, and 1,188,839 XCBPs, respectively, with their birth rate of about 1.1 × 10-18 m-2 s-1, 3.8 × 10-19 m-2 s-1, and 1.5 × 10-19 m-2 s-1. We find that about 80% of blinkers are observed at the boundaries of supergranules, and 57% (34%) are associated with ECBPs (XCBPs). We further find that about 61%-80% of transients are associated with the isolated magnetic poles in the quiet Sun and that the normalized maximum intensities of the transients are correlated with the photospheric magnetic flux of poles via a power law. These results conspicuously show that these transients have a magnetic origin and their synchronized behavior provides further clues toward the understanding of the coupling among the different layers of the solar atmosphere. Our study further reveals that the appearance of these transients is strongly anticorrelated with the sunspots' cycle. This finding can be relevant for a better understanding of solar dynamo and magnetic structures at different scales during the solar cycle. Title: On the Formation of Solar Wind and Switchbacks, and Quiet Sun Heating Authors: Upendran, Vishal; Tripathi, Durgesh Bibcode: 2022ApJ...926..138U Altcode: 2021arXiv211111668U The solar coronal heating in quiet Sun (QS) and coronal holes (CHs), including solar wind formation, are intimately tied by magnetic field dynamics. Thus, a detailed comparative study of these regions is needed to understand the underlying physical processes. CHs are known to have subdued intensity and larger blueshifts in the corona. This work investigates the similarities and differences between CHs and QS in the chromosphere using the Mg II h and k, C II line, and transition region using Si IV line, for regions with identical absolute magnetic flux density (∣B∣). We find CHs to have subdued intensity in all of the lines, with the difference increasing with line formation height and ∣B∣. The chromospheric lines show excess upflows and downflows in CH, while Si IV shows excess upflows (downflows) in CHs (QS), where the flows increase with ∣B∣. We further demonstrate that the upflows (downflows) in Si IV are correlated with both upflows and downflows (only downflows) in the chromospheric lines. CHs (QS) show larger Si IV upflows (downflows) for similar flows in the chromosphere, suggesting a common origin to these flows. These observations may be explained due to impulsive heating via interchange (closed-loop) reconnection in CHs (QS), resulting in bidirectional flows at different heights, due to differences in magnetic field topologies. Finally, the kinked field lines from interchange reconnection may be carried away as magnetic field rotations and observed as switchbacks. Thus, our results suggest a unified picture of solar wind emergence, coronal heating, and near-Sun switchback formation. Title: Flows in Enthalpy-based Thermal Evolution of Loops Authors: Rajhans, Abhishek; Tripathi, Durgesh; Bradshaw, Stephen J.; Kashyap, Vinay L.; Klimchuk, James A. Bibcode: 2022ApJ...924...13R Altcode: 2021arXiv211003204R Plasma-filled loop structures are common in the solar corona. Because detailed modeling of the dynamical evolution of these structures is computationally costly, an efficient method for computing approximate but quick physics-based solutions is to rely on space-integrated 0D simulations. The enthalpy-based thermal evolution of loops (EBTEL) framework is a commonly used method to study the exchange of mass and energy between the corona and transition region. EBTEL solves for density, temperature, and pressure, averaged over the coronal part of the loop, velocity at coronal base, and the instantaneous differential emission measure distribution in the transition region. The current single-fluid version of the code, EBTEL2, assumes that at all stages the flows are subsonic. However, sometimes the solutions show the presence of supersonic flows during the impulsive phase of heat input. It is thus necessary to account for this effect. Here, we upgrade EBTEL2 to EBTEL3 by including the kinetic energy term in the Navier-Stokes equation. We compare the solutions from EBTEL3 with those obtained using EBTEL2, as well as the state-of-the-art field-aligned hydrodynamics code HYDRAD. We find that the match in pressure between EBTEL3 and HYDRAD is better than that between EBTEL2 and HYDRAD. Additionally, the velocities predicted by EBTEL3 are in close agreement with those obtained with HYDRAD when the flows are subsonic. However, EBTEL3 solutions deviate substantially from HYDRAD's when the latter predicts supersonic flows. Using the mismatches in the solution, we propose a criterion to determine the conditions under which EBTEL can be used to study flows in the system. Title: Machine learning inference of statistical signatures of heating events Authors: Upendran, Vishal; Tripathi, Durgesh Bibcode: 2021AGUFMSH15D2058U Altcode: The solar corona consists of a million degree Kelvin plasma. Quiet Sun regions (QS), which form a background over which large, dynamic events occur, must be studied well to understand the presence of this million degree plasma. In this work, we assume an impulsive heating forward model with the flaring frequency, flaring timescale and power-law slope as free parameters. We develop an inversion code using a Convolutional neural network to infer these free parameters and their associated uncertainties for coronal light curves. We apply this inversion scheme on light curves from each pixel in the 171, 193 and 211 A to infer the free parameters, and find impulsive events to be a viable source of generating intensity. We find the correlations between free parameters to be explained by the domination of conduction losses and the existence of an energy reservoir. We further apply this scheme on full disc integrated, and flux-calibrated light curves from X-ray Solar Monitor onboard Chandrayaan-2, and put lower bounds on the energy flux in QS. These findings give us a deeper understanding of the viability of impulsive events in heating up the solar corona, and the advantages offered by data-driven machine learning algorithms in accelerating science. Title: Properties of the C II 1334 Å Line in Coronal Hole and Quiet Sun as Observed by IRIS Authors: Upendran, Vishal; Tripathi, Durgesh Bibcode: 2021ApJ...922..112U Altcode: 2021arXiv210904287U Coronal holes (CHs) have subdued intensity and net blueshifts when compared to the quiet Sun (QS) at coronal temperatures. At transition region temperatures, such differences are obtained for regions with identical absolute photospheric magnetic flux density (∣B∣). In this work, we use spectroscopic measurements of the C II 1334 Å line from the Interface Region Imaging Spectrograph, formed at chromospheric temperatures, to investigate the intensity, Doppler shift, line width, skew, and excess kurtosis variations with ∣B∣. We find the intensity, Doppler shift, and linewidths to increase with ∣B∣ for CHs and QS. The CHs show deficit in intensity and excess total widths over QS for regions with identical ∣B∣. For pixels with only upflows, CHs show excess upflows over QS, while for pixels with only downflows, CHs show excess downflows over QS that cease to exist at ∣B∣ ≤ 40. Finally, the spectral profiles are found to be more skewed and flatter than a Gaussian, with no difference between CHs and QS. These results are important in understanding the heating of the atmosphere in CH and QS, including solar wind formation, and provide further constraints on the modeling of the solar atmosphere. Title: Multi-Stranded Simulations Mimicking FOXSI and AIA Observations : A Single Power-Law Distribution for Transients and Steady Background Authors: Rajhans, Abhishek; Tripathi, Durgesh; Kashyap, Vinay; Athiray, P. S.; Upendran, Vishal Bibcode: 2021AGUFMSH15E2063R Altcode: Solar Coronal Heating, which Maintains the Corona at 1 MK can be attributed to uniform steady background heating and transients like impulsive flaring events. Here we explore the possibility that the steady heating is attributable to a large swarm of small impulsive events with a single power law distribution of flare energies. We perform a realistic simulation of multi-stranded system of loops, mimicking data obtained from Atmospheric Imaging Assembly (AIA) and Focusing Optics X-ray Solar Imager (FOXSI) for an isolated loop complex. We use 0D description of coronal loops (Enthalpy Based Thermal Evolution of Loops) for performing simulations. The loop is modelled to have 100 strands, based on constraints provided by Hi-C on the cross sectional radii of strands. 10 30 ergs is deposited in the loop over 10,000 seconds of simulations in accordance with observed radiation flux. We simulate a large number of cases, uniquely determined by the slope of the power law distribution, along with the maximum and minimum energies that can be dissipated in an event. Preliminary results indicate that the observed light curve including the background and impulsive events can be best explained by a power law index of -1.8 and maximum and minimum energies differing by more than 7-8 orders of magnitudes. We discuss the implications of these results and possible extensions. Title: Solar wind signatures in the chromosphere Authors: Upendran, Vishal; Tripathi, Durgesh Bibcode: 2021AGUFMSH32B..05U Altcode: Coronal holes (CHs) are regions with reduced intensity and enhanced blueshifts when compared to Quiet Sun (QS) regions at coronal temperatures. However, such differences are seen in transition region temperatures only for regions with similar magnetic flux density (|B|). In this work, we study the chromospheric Mg II h&k, the C II doublet lines and transition region Si IV line in CHs and QS as a function of |B|. We find the intensities, velocities and the C II line widths to increase with increasing |B|. For both the chromospheric lines, we find reduced intensity, excess blueshifts as well as excess redshifts in CHs over QS for regions with similar |B|. Moreover, CHs show larger line width in CII than QS for regions with similar |B|. When synergy between the velocities of C II, Mg II and Si IV lines is investigated, we find: (a). Upflows, downflows in all the lines are tightly correlated. (b). Upflows in Mg II and C II have no correlation with downflows observed in Si IV. (c). Downflows of Mg II, C II are correlated with upflows of Si IV, with correlation values increasing from Mg II h2 to C II. These results may be explained if (a). Upflows in Mg II are accelerated till Si IV. (b), Downflows in Si IV are decelerated toward Mg II. (c). Bi-directional flows give rise to correlated transition region upflows and chromospheric downflows. Such bi-directional flows may occur due to impulsive events occurring between the formation height of Mg II/ C II and Si IV . The patterns of observed flows in CHs and QS may be explained by invoking impulsive heating in topologically different regions. These results provide evidence on the formation of solar wind in the chromosphere and further hints towards the unified heating scenario of the solar corona in the QS and CHs. Title: Characterizing the Spectral Profiles of Mg II, C II and Si IV in Solar Flares Authors: Roy, Soumya; Tripathi, Durgesh; Young, Peter Bibcode: 2021AGUFMSH25E2128R Altcode: Solar flares are the most energetic phenomena in the solar atmosphere with consequences for space weather through the generation of solar energetic particles and/or CMEs. Despite tremendous advances in understanding their characteristics, the complete physics of their origin and response to plasma in various layers of the solar atmosphere is not fully developed. Here, we study the characteristics of the spectral line profiles during different stages of flares as a function of photospheric magnetic flux density and compare those with the characteristics observed in quiescent active regions and quiet sun. For this purpose, we use archival observations from the Interface Region Imaging Spectrograph (IRIS). For context purposes, we used full-disk observations from the Atmospheric Imaging Assembly (AIA). We use the line-of-sight (LOS) magnetograms obtained by the Helioseismic and Magnetic Imager (HMI). We characterize the self-absorption observed and optical depth from the line intensities as a function of the magnetic flux density, which shows a signature of precipitation. We also see the Mg II triplets going into emission co-spatially in the regions where flare ribbons appear later. We use the 2791.6 A line to localize the regions where the triplet lines are observed. These results are important for the physics of flares and can be useful in predicting the location of a flare kernel. Title: Hydrodynamics of Small Transient Brightenings in the Solar Corona Authors: Rajhans, Abhishek; Tripathi, Durgesh; Kashyap, Vinay L. Bibcode: 2021ApJ...917...29R Altcode: 2021arXiv210508800R Small scale transients occur in the solar corona at much higher frequencies than flares and play a significant role in coronal dynamics. Here we study three well-identified transients discovered by Hi-C and also detected by the EUV channels of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. We use 0D enthalpy-based hydrodynamical simulations and produce synthetic light curves to compare with AIA observations. We have modeled these transients as loops of ~1.0 Mm length depositing energies ~1023 erg in ~50 s. The simulated synthetic light curves show reasonable agreement with the observed light curves. During the initial phase, conduction flux from the corona dominates over the radiation, like impulsive flaring events. Our results further show that the time-integrated net enthalpy flux is positive, hence into the corona. The fact that we can model the observed light curves of these transients reasonably well by using the same physics as those for nanoflares, microflares, and large flares, suggests that these transients may have a common origin. Title: On the Impulsive Heating of Quiet Solar Corona Authors: Upendran, Vishal; Tripathi, Durgesh Bibcode: 2021ApJ...916...59U Altcode: 2021arXiv210316824U The solar corona consists of a million degree Kelvin plasma. A complete understanding of this phenomenon demands the study of quiet Sun (QS) regions. In this work, we study QS regions in the 171 Å, 193 Å, and 211 Å passbands of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory, by combining the empirical impulsive heating forward model of Pauluhn & Solanki with a machine-learning inversion model that allows uncertainty quantification. We find that there are ≈2-3 impulsive events per minute, with a lifetime of about 10-20 minutes. Moreover, for all the three passbands, the distribution of power-law slope α peaks above 2. Our exploration of correlations among the frequency of impulsive events and their timescales and peak energy suggests that conduction losses dominate over radiative cooling losses. All these findings suggest that impulsive heating is a viable heating mechanism in QS corona. Title: Nonthermal Velocity in the Transition Region of Active Regions and Its Center-to-limb Variation Authors: Ghosh, Avyarthana; Tripathi, Durgesh; Klimchuk, James A. Bibcode: 2021ApJ...913..151G Altcode: 2021arXiv210315081G We derive the nonthermal velocities (NTVs) in the transition region of an active region using the Si IV 1393.78 Å line observed by the Interface Region Imaging Spectrograph and compare them with the line-of-sight photospheric magnetic fields obtained by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. The active region consists of two strong field regions with opposite polarity, separated by a weak field corridor that widened as the active region evolved. The means of the NTV distributions in strong field regions (weak field corridors) range between ∼18-20 (16-18) km s-1, albeit the NTV maps show a much larger range. In addition, we identify a narrow lane in the middle of the corridor with significantly reduced NTV. The NTVs do not show a strong center-to-limb variation, albeit they show somewhat larger values near the disk center. The NTVs are well correlated with redshifts as well as line intensities. The results obtained here and those presented in our companion paper on Doppler shifts suggest two populations of plasma in the active region emitting in Si IV. The first population exists in the strong field regions and extends partway into the weak field corridor between them. We attribute this plasma to spicules heated to ∼0.1 MK (often called type II spicules). They have a range of inclinations relative to vertical. The second population exists in the center of the corridor, is relatively faint, and has smaller velocities, likely horizontal. These results provide further insights into the heating of the transition region. Title: Thermodynamic evolution of a sigmoidal active region with associated flares Authors: Mulay, Sargam M.; Tripathi, Durgesh; Mason, Helen Bibcode: 2021MNRAS.504.1201M Altcode: 2021MNRAS.tmp..832M; 2021arXiv210309561M Active regions often show S-shaped structures in the corona called sigmoids. These are highly sheared and twisted loops formed along the polarity inversion line. They are considered to be one of the best pre-eruption signatures for CMEs. Here, we investigate the thermodynamic evolution of an on-disc sigmoid observed during 2015 December 24-28. For this purpose, we have employed Emission Measure (EM) and filter-ratio techniques on the observations recorded by the Atmospheric Imaging Assembly (AIA) on-board the Solar Dynamics Observatory (SDO) and X-ray Telescope (XRT) on-board Hinode. The EM analysis showed multithermal plasma along the sigmoid and provided a peak temperature of ~10-12.5 MK for all observed flares. The sigmoidal structure showed emission from Fe XVIII (93.93 Å) and Fe XXI (128.75 Å) lines in the AIA 94 and 131 Å channels, respectively. Our results show that the hot plasma is often confined to very hot strands. The temperature obtained from the EM analysis was found to be in good agreement with that obtained using the XRT, AIA, and GOES filter-ratio methods. These results provide important constraints for the thermodynamic modelling of sigmoidal structures in the core of active regions. Moreover, this study also benchmarks different techniques available for temperature estimation in solar coronal structures. Title: Transient Formation of Loops in the Core of an Active Region Authors: Tripathi, Durgesh Bibcode: 2021ApJ...909..105T Altcode: 2021arXiv210106622T We study the formation of transient loops in the core of the AR 11890. For this purpose, we have used the observations recorded by the Atmospheric Imaging Assembly (AIA) and the Interface Region Imaging Spectrograph (IRIS). For photospheric field configuration, we have used the line-of-sight (LOS) magnetograms obtained from the Helioseismic and Magnetic Imager. The transient is simultaneously observed in all the UV and EUV channels of AIA and the three slit-jaw images from IRIS. The coexistence of the transient in all AIA and IRIS SJI channels suggests the transient's multithermal nature. The transient consists of short loops located at the base of the transient, as well as long loops. A differential emission measure analysis shows that the transient has a clumpy structure. The highest emission observed at the base is within the temperature bin of $\mathrm{log}T=6.65\mbox{--}6.95$ . We observe the longer loops at a similar temperature, albeit very feeble. Using LOS magnetograms, we conclude that the magnetic reconnection may have caused the transient. Our observations further suggest that the physics of the formation of such transients may be similar to those of typical coronal jets, albeit in different topological configurations. Such multiwavelength observations shed light on the formation of hot plasma in the solar corona and provide further essential constraints on modeling the thermodynamics of such transients. Title: Coronal Heating and Solar Wind Formation in Quiet Sun and Coronal Holes: A Unified Scenario Authors: Tripathi, Durgesh; Nived, V. N.; Solanki, Sami K. Bibcode: 2021ApJ...908...28T Altcode: 2020arXiv201109803T Coronal holes (CHs) are darker than the quiet Sun (QS) when observed in coronal channels. This study aims to understand the similarities and differences between CHs and QS in the transition region using the Si IV 1394 Å line, recorded by the Interface Region Imaging Spectrograph, by considering the distribution of magnetic field measured by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. We find that Si IV intensities obtained in CHs are lower than those obtained in QS for regions with identical magnetic flux densities. Moreover, the difference in intensities between CHs and QS increases with increasing magnetic flux. For the regions with equal magnetic flux density, QS line profiles are more redshifted than those measured in CHs. Moreover, the blueshifts measured in CHs show an increase with increasing magnetic flux density unlike in the QS. The non-thermal velocities in QS, as well as in CHs, show an increase with increasing magnetic flux. However, no significant difference was observed in QS and CHs, albeit a small deviation at small flux densities. Using these results, we propose a unified model for the heating of the corona in the QS and in CHs and the formation of solar wind. Title: Space Climate Studies with the Solar Ultraviolet Imaging Telescope on board Aditya-L1 mission Authors: Tripathi, Durgesh Bibcode: 2021cosp...43E.917T Altcode: The Solar Ultraviolet Imaging Telescope (SUIT) is an instrument on-board Aditya-L1. It will measure and monitor the solar radiation in the wavelength range 200-400 nm, which is central to our understanding of Sun-climate relationship. SUIT will provide full disk images using 11 filters (3 broadband and eight narrowband) allowing us, for the first time, to measure and monitor spatially resolved solar spectral irradiance that governs the chemistry of oxygen and ozone in the stratosphere of the Earth's atmosphere. Title: Heliophysics Public Outreach in India Authors: Tripathi, Durgesh Bibcode: 2021cosp...43E2437T Altcode: In the era of growing technological dependence, space weather has a vital role to play in developing countries like India. Various funding agencies have recognized this in the country, including the Indian Space Research Organization. Several programmes have been running, both on core academic level as well as public outreach for the capacity building in Heliophysics. In this talk, I shall highlight some of the steps taken within the country with a focus on those taken by the SciPop centre of IUCAA. Title: Dynamics of Sunspot Shock Waves in the Chromosphere and Transition Region Authors: Kayshap, Pradeep; Tripathi, Durgesh; Jelínek, P. Bibcode: 2021ApJ...906..121K Altcode: 2020arXiv201110192K We study the dynamics of shock waves observed in the umbra of a sunspot using the spectroscopic observations from the Interface Region Imaging Spectrograph. The presence of a shock significantly deforms the shape of the spectral lines of Mg II, C II, and Si IV. We found that C II 1335.71 Å and Si IV 1393.75 Å show double-peaked profiles that change to a single peak later on. However, the Mg II h 2803.53 Å line first shows flat-top profiles that change into double peaks followed by the single peak. To study the shock dynamics, we isolate the shock component from the spectra by fitting two Gaussians. We find that the lifetime of the shock is largest in the Mg II h 2803.53 Å line. Moreover, the plasma motion shows both the acceleration and deceleration phases of the shock. Yet, in C II 1335.71 Å and Si IV 1393.75 Å, only the deceleration phase is observed. We observe a strong correlation between the largest blueshift of the shock and deceleration for all three spectral lines. We find a positive (negative) correlation between intensities contributed by the shocks in Mg II and C II (Si IV). This suggests that the shocks are first amplified in C II, followed by a decline in the height range corresponding to Si IV. These results may indicate the dissipation of shocks above the formation height of C II, and the shocks may have important roles in the dynamics of the upper chromosphere and transition region above sunspots. Title: ISRO's First Solar Observatory in Space: Aditya-L1 Mission Authors: Tripathi, D. Bibcode: 2020AGUFMSH056..01T Altcode: The dynamic and magnetically coupled atmosphere of the Sun presents several puzzling physical phenomena of great importance. For example, the existence of hotter chromosphere and corona above the photosphere. Due to these high-temperature layers, Sun radiates in UV and X-rays, which play a crucial role in the dynamics of the Earth's atmosphere. Similarly, the occurrence of highly energetic solar eruptions such as flares and coronal mass ejections, which has direct consequences on space weather and geo-space climate, has proven to be highly challenging to comprehend. The Aditya-L1 mission of the Indian Space Research Organization (ISRO) will help us study the dynamic coupling of the solar atmosphere as well as to measure and monitor the spatially resolved solar spectral irradiance in the near-ultraviolet band, which is central to the Earth's climate. The spacecraft will be located at the first Lagrangian Point and carry seven payloads -- four remote-sensing and three in-situ. Combining all the instruments, Aditya-L1 shall cover the wavelength range from Hard X-rays to infrared for remote sensing. Out of three in-situ payloads, two will provide measurements of the charged particles. The third is a magnetometer to assess the interplanetary magnetic field. I shall discuss the salient features of the experiments onboard Aditya-L1 mission. Title: Formation and dynamics of transequatorial loops Authors: Ghosh, Avyarthana; Tripathi, Durgesh Bibcode: 2020A&A...640A...3G Altcode: 2020arXiv200512839G
Aims: We aim to study the dynamical evolution of transequatorial loops (TELs) using imaging techniques and spectroscopy.
Methods: We used the images recorded by the Atmospheric Imaging Assembly and the Helioseismic Magnetic Imager on board the Solar Dynamics Observatory together with spectroscopic observations taken from the Extreme-Ultraviolet Imaging Spectrometer on board Hinode.
Results: The data from the AIA 193 Å channel show that TELs are formed between AR 12230 and a newly emerging AR 12234, evolving between 10 and 14 December 2014. The xt-plots for 12 December 2014, obtained using AIA 193 Å data, reveal signatures of inflow and outflow towards an X-region. High-cadence AIA images also show recurrent intensity enhancements in close proximity to the X-region (P2), which is observed to have higher intensities for spectral lines that are formed at log T[K] = 6.20 and voids at other higher temperatures. The electron densities and temperatures in the X-region (and P2) are maintained steadily at log Ne= 8.5-8.7 cm-3 and log T[K] = 6.20, respectively. Doppler velocities in the X-region show predominant redshifts by about 5-8 km s-1 when they are closer to the disk center but blueshifts (along with some zero-velocity pixels) when away from the center. The full-width-half-maximum maps reveal non-thermal velocities of about 27-30 km s-1 for Fe XII, Fe XIII, and Fe XV lines. However, the brightest pixels have nonthermal velocities ∼62 km s-1 for Fe XII and Fe XIII lines. On the contrary, the dark X-region for Fe XV line have the highest non-thermal velocity (∼115 km s-1).
Conclusions: We conclude that the TELs are formed due to magnetic reconnection. We further note that the TELs themselves undergo magnetic reconnection, which leads to the re-formation of loops among individual ARs. Moreover, this study, for the first time, provides measurements of plasma parameters in X-regions, thereby providing essential constraints for theoretical studies.

The movie associated to Fig. 3 is available at https://www.aanda.org Title: Wave amplitude modulation in fan loops as observed by AIA/SDO Authors: Sharma, Aishawnnya; Tripathi, Durgesh; Erdélyi, Robertus; Gupta, Girjesh R.; Ahmed, Gazi A. Bibcode: 2020A&A...638A...6S Altcode: 2020arXiv200405797S
Aims: We perform a detailed analysis to understand the evolution and dynamics of propagating intensity disturbances observed in a fan loop system.
Methods: We performed multiwavelength time-distance analysis of a fan loop system anchored in an isolated sunspot region (AR 12553). The active region was observed by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. We measured the phase speeds of the propagating intensity disturbances by employing cross-correlation analysis, and by obtaining the slopes in xt-plots. We obtained original and detrended light curves at different heights of the time-distance maps and characterised them by performing Fourier and wavelet analysis, respectively.
Results: The time-distance maps reveal clear propagation of intensity oscillations in all the coronal extreme ultraviolet (EUV) channels except AIA 94 and 335 Å. We determine the nature of the intensity disturbances as slow magneto-acoustic waves by measuring their phase speeds. The time-distance maps, as well as the detrended light curves, show an increase and decrease in the amplitude of propagating 3 min oscillations over time. The amplitude variations appear most prominently in AIA 171 Å, though other EUV channels also show such signatures. The Fourier power spectrum yields the presence of significant powers with several nearby frequencies in the range of 2-3 min (5-8 mHz), along with many other smaller peaks between 2-4 min. Wavelet analysis shows an increase and decrease of oscillating power around 3 min simultaneous to the amplitude variations. We obtain the modulation period to be in the range of 20-30 min.
Conclusions: Our results provide the viability of occurrence of phenomenon like "Beat" among the nearby frequencies giving rise to the observed amplitude modulation. However, we cannot at this stage rule out the possibility that the modulation may be driven by variability in an underlying unknown source. Title: Signatures of Untwisting Magnetic Field in a Small Emerging Bipole in the Solar Photosphere Authors: Sangeetha, C. R.; Tripathi, Durgesh; Rajaguru, S. P. Bibcode: 2020ApJ...895...67S Altcode: 2020arXiv200405615S We perform a study of fluid motions and its temporal evolution in and around a small bipolar emerging flux region using observations made by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. We employ local correlation tracking of the Doppler observations to follow horizontal fluid motions and line-of-sight magnetograms to follow the flux emergence. Changes in vertical vorticity and horizontal divergence are used to derive signatures of evolving twists in the magnetic field. Our analysis reveals that the two polarities of the magnetic flux swirl in opposite directions in the early stages of flux emergence indicating an unwinding of the pre-emergence twists in the magnetic field. We further find that during the emergence, there is an increase in swirly motions in the neighboring nonmagnetic regions. We estimate the magnetic and kinetic energies and find that magnetic energy is about a factor of 10 larger than the kinetic energy. During the evolution, when the magnetic energy decreases, an increase in the kinetic energy is observed indicating transfer of energy from the unwinding of the magnetic flux tube to the surrounding fluid motions. Our results thus demonstrate the presence of pre-emergence twists in an emerging magnetic field that is important in the context of the hemispheric helicity rule warranting a detailed statistical study in this context. Further, our observations point to a possible widespread generation of torsional waves in emerging flux regions due to the untwisting magnetic field with implications for upward energy transport to the corona. Title: On the Ratios of Si IV Lines (λ1394/λ1403) in an Emerging Flux Region Authors: Tripathi, Durgesh; Nived, V. N.; Isobe, Hiroaki; Doyle, G. Gerard Bibcode: 2020ApJ...894..128T Altcode: 2020arXiv200404530T The resonance lines of Si IV formed at λ1394 and 1403 Å are the most critical for the diagnostics of the solar transition region in the observations of the Interface Region Imaging Spectrograph (IRIS). Studying the intensity ratios of these lines (1394 Å/1403 Å), which under optically thin conditions is predicted to be two, helps us to diagnose the optical thickness of the plasma being observed. Here we study the evolution of the distribution of intensity ratios in 31 IRIS rasters recorded for four days during the emergence of an active region. We found that during the early phase of the development, the majority of the pixels show intensity ratios smaller than two. However, as the active region evolves, more and more pixels show the ratios closer to two. Besides, there are a substantial number of pixels with ratio values larger than 2. At the evolved stage of the active region, the pixels with ratios smaller than two were located on the periphery, whereas those with values larger than 2 were in the core. However, for quiet Sun regions, the obtained intensity ratios were close to two irrespective of the location on the disk. Our findings suggest that the Si IV lines observed in active regions are affected by the opacity during the early phase of the flux emergence. The results obtained here could have important implications for the modeling of the solar atmosphere, including the initial stage of the emergence of an active region as well as the quiet Sun. Title: On Doppler Shift and Its Center-to-limb Variation in Active Regions in the Transition Region Authors: Ghosh, Avyarthana; Klimchuk, James A.; Tripathi, Durgesh Bibcode: 2019ApJ...886...46G Altcode: 2019arXiv191012033G A comprehensive understanding of the structure of Doppler motions in the transition region including the center-to-limb variation and its relationship with the magnetic field structure is vital for the understanding of mass and energy transfer in the solar atmosphere. In this paper, we have performed such a study in an active region using the Si IV 1394 Å emission line recorded by the Interface Region Imaging Spectrograph and the line-of-sight photospheric magnetic field obtained by the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory. The active region has two opposite polarity strong field regions separated by a weak field corridor, which widened as the active region evolved. On average, the strong field regions (corridor) show(s) redshifts of 5-10 (3-9) km s-1 (depending on the date of observation). There is, however, a narrow lane in the middle of the corridor with near-zero Doppler shifts at all disk positions, suggesting that any flows there are very slow. The Doppler velocity distributions in the corridor seem to have two components—a low velocity component centered near 0 km s-1 and a high-velocity component centered near 10 km s-1. The high-velocity component is similar to the velocity distributions in the strong field regions, which have just one component. Both exhibit a small center-to-limb variation and seem to come from the same population of flows. To explain these results, we suggest that the emission from the lower transition region comes primarily from warm type II spicules, and we introduce the idea of a “chromospheric wall”—associated with classical cold spicules—to account for a diminished center-to-limb variation. Title: ICSF: Intensity Conserving Spectral Fitting Authors: Klimchuk, James A.; Patsourakos, Spiros; Tripathi, Durgesh Bibcode: 2019ascl.soft03007K Altcode: ICSF (Intensity Conserving Spectral Fitting) "corrects" (x,y) data in which the ordinate represents the average of a quantity over a finite interval in the abscissa. A typical example is spectral data, where the average intensity over a wavelength bin (the measured quantity) is assigned to the center of the bin. If the profile is curved, the average will be different from the discrete value at the bin center location. ICSF, written in IDL and available separately and as part of SolarSoft (ascl:1208.013), corrects the intensity using an iterative procedure and cubic spline. The corrected intensity equals the "true" intensity at bin center, rather than the average over the bin. Unlike other methods that are restricted to a single fitting function, typically a spline, ICSF can be used with any function, such as a cubic spline or a Gaussian, with slight changes to the code. Title: Magnetic Fields and the Supply of Low-frequency Acoustic Wave Energy to the Solar Chromosphere Authors: Rajaguru, S. P.; Sangeetha, C. R.; Tripathi, Durgesh Bibcode: 2019ApJ...871..155R Altcode: The problem of solar chromospheric heating remains a challenging one with wider implications for stellar physics. Several studies in the recent past have shown that small-scale inclined magnetic field elements channel copious energetic low-frequency acoustic waves, which are normally trapped below the photosphere. These magnetoacoustic waves are expected to shock at chromospheric heights, contributing to chromospheric heating. In this work, exploiting simultaneous observations of photospheric vector magnetic field, Doppler, continuum, and line-core intensity (of Fe I 6173 Å) from the Helioseismic and Magnetic Imager and lower-atmospheric UV emission maps in the 1700 and 1600 Å channels of the Atmospheric Imaging Assembly, both on board the Solar Dynamics Observatory of NASA, we revisit the relationships between magnetic field properties (inclination and strength) and the propagation of acoustic waves (phase travel time). We find that the flux of acoustic energy, in the 2-5 mHz frequency range, between the upper photosphere and lower chromosphere is in the range of 2.25-2.6 kW m-2, which is about twice the previous estimates. We identify that the relatively less inclined magnetic field elements in the quiet Sun channel a significant amount of waves of frequency lower than the theoretical minimum acoustic cutoff frequency due to magnetic inclination. We also derive indications that these waves steepen and start to dissipate within the height ranges probed, while those let out due to inclined magnetic fields pass through. We explore connections with existing theoretical and numerical results that could explain the origin of these waves. Title: Magnetic fields and low-frequency acoustic wave-energy supply to the solar chromosphere Authors: Rajaguru, S. P.; Sangeetha, C. R.; Tripathi, Durgesh Bibcode: 2018arXiv181205322R Altcode: The problem of solar chromospheric heating remains a challenging one with wider implications for stellar physics. Several studies in the recent past have shown that small-scale inclined magnetic field elements channel copious amount of energetic low-frequency acoustic waves, that are normally trapped below the photosphere. These magneto-acoustic waves are expected to shock at chromospheric heights contributing to chromospheric heating. In this work, exploiting simultaneous photospheric vector magnetic field, Doppler, continuum and line-core intensity (of FeI 6173 Å) observations from the Helioseismic and Magnetic Imager (HMI) and lower-atmospheric UV emission maps in the 1700 Å and 1600 Å channels of the Atmospheric Imaging Assembly (AIA), both onboard the Solar Dynamics Observatory (SDO) of NASA, we revisit the relationships between magnetic field properties (inclination and strength) and the acoustic wave propagation (phase travel time). We find that the flux of acoustic energy, in the 2 - 5 mHz frequency range, between the upper photosphere and lower chromosphere is in the range of 2.25 - 2.6 kW m$^{-2}$, which is about twice the previous estimates. We identify that the relatively less-inclined magnetic field elements in the quiet-Sun channel a significant amount of waves of frequency lower than the theoretical minimum for acoustic cut-off frequency due to magnetic inclination. We also derive indications that these waves steepen and start to dissipate within the heights ranges probed, while those let out due to inclined magnetic fields pass through. We explore connections with existing theoretical and numerical results that could explain the origin of these waves. Title: Quiet-Sun and Coronal Hole in Mg II k Line as Observed by IRIS Authors: Kayshap, Pradeep; Tripathi, Durgesh; Solanki, Sami K.; Peter, Hardi Bibcode: 2018ApJ...864...21K Altcode: 2018arXiv180703494K Coronal hole (CH) regions are dark in comparison to the quiet Sun (QS) at coronal temperatures. However, at chromospheric and transition region temperatures, the QS and CHs are hardly distinguishable. In this study, we have used the Mg II 2796.35 Å spectral line recorded by the Interface Region Imaging Spectrometer (IRIS) to understand the similarities and differences in the QS and CH at chromospheric levels. Our analysis reveals that the emission from Mg II k3 and k2v that originates in the chromosphere is significantly lower in CH than in QS for the regions with similar magnetic field strength. The wing emissions of Mg II k that originates from the photospheric layer, however, do not show any difference between QS and CH. The difference in Mg II k3 intensities between QS and CH increases with increasing magnetic field strength. We further studied the effects of spectral resolution on these differences and found that the difference in the intensities decreases with decreasing spectral resolution. For a resolution of 11 Å, the difference completely disappears. These findings are not only important for mass and energy supply from the chromosphere to the corona but also provides essential ingredients for the modeling of the solar spectral irradiance for the understanding of the Sun-climate relationships. Title: Energetics of Hi-C EUV brightenings Authors: Subramanian, Srividya; Kashyap, Vinay L.; Tripathi, Durgesh; Madjarska, Maria S.; Doyle, John G. Bibcode: 2018A&A...615A..47S Altcode: 2018arXiv180309505S We study the thermal structure and energetics of the point-like extreme ultraviolet (EUV) brightenings within a system of fan loops observed in the active region AR 11520. These brightenings were simultaneously observed on 2012 July 11 by the High-resolution Coronal (Hi-C) imager and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). We identified 27 brightenings by automatically determining intensity enhancements in both Hi-C and AIA 193 Å light curves. The energetics of these brightenings were studied using the Differential Emission Measure (DEM) diagnostics. The DEM weighted temperatures of these transients are in the range log T(K) = 6.2-6.6 with radiative energies ≈1024-25 ergs and densities approximately equal to a few times 109 cm-3. To the best of our knowledge, these are the smallest brightenings in EUV ever detected. We used these results to determine the mechanism of energy loss in these brightenings. Our analysis reveals that the dominant mechanism of energy loss for all the identified brightenings is conduction rather than radiation. Title: Observation and Modeling of Chromospheric Evaporation in a Coronal Loop Related to Active Region Transient Brightening Authors: Gupta, G. R.; Sarkar, Aveek; Tripathi, Durgesh Bibcode: 2018ApJ...857..137G Altcode: 2018arXiv180311172G Using the observations recorded by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory and the Interface Region Imaging Spectrograph (IRIS) and the Extreme-ultraviolet Imaging Spectrometer and X-Ray Telescope both on board Hinode, we present evidence of chromospheric evaporation in a coronal loop after the occurrence of two active region transient brightenings (ARTBs) at the two footpoints. The chromospheric evaporation started nearly simultaneously in all of the three hot channels of AIA 131, 94, and 335 Å and was observed to be temperature dependent, being fastest in the highest temperature channel. The whole loop became fully brightened following the ARTBs after ≈25 s in 131 Å, ≈40 s in 94 Å, and ≈6.5 minutes in 335 Å. The differential emission measurements at the two footpoints (i.e., of two ARTBs) and at the loop top suggest that the plasma attained a maximum temperature of ∼10 MK at all these locations. The spectroscopic observations from IRIS revealed the presence of redshifted emission of ∼20 km s-1 in cooler lines like C II and Si IV during the ARTBs that was cotemporal with the evaporation flow at the footpoint of the loop. During the ARTBs, the line width of C II and Si IV increased nearly by a factor of two during the peak emission. Moreover, enhancement in the line width preceded that in the Doppler shift, which again preceded enhancement in the intensity. The observed results were qualitatively reproduced by 1D hydrodynamic simulations, where energy was deposited at both of the footpoints of a monolithic coronal loop that mimicked the ARTBs identified in the observations. Title: Direct Observations of Different Sunspot Waves Influenced by Umbral Flashes Authors: Sharma, Aishawnnya; Gupta, G. R.; Tripathi, Durgesh; Kashyap, V.; Pathak, Amit Bibcode: 2017ApJ...850..206S Altcode: 2017arXiv171008438S We report the simultaneous presence of chromospheric umbral flashes and associated umbral waves, and propagating coronal disturbances, in a sunspot and related active region. We have analyzed time-distance maps obtained using the observations from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. These maps show the simultaneous occurrence of different sunspot oscillations and waves such as umbral flashes, umbral waves, and coronal waves. Analysis of the original light curves, i.e., without implementing any Fourier filtering on them, shows that the amplitudes of different sunspot waves observed at different atmospheric layers change in synchronization with the light curves obtained from the umbral flash region, thus demonstrating that these oscillations are modulated by umbral flashes. This study provides the first observational evidence of the influence of sunspot oscillations within the umbra on other sunspot waves extending up to the corona. The properties of these waves and oscillations can be utilized to study the inherent magnetic coupling among different layers of the solar atmosphere above sunspots. Title: The Solar Ultraviolet Imaging Telescope on-board Aditya-L1 Authors: Tripathi, Durgesh; Ramaprakash, A. N.; Khan, Aafaque; Ghosh, Avyarthana; Chatterjee, Subhamoy; Banerjee, Dipankar; Chordia, Pravin; Gandorfer, Achim; Krivova, Natalie; Nandy, Dibyendu; Rajarshi, Chaitanya; Solanki, Sami K. Bibcode: 2017CSci..113..616T Altcode: 2022arXiv220407732T The Solar Ultraviolet Imaging Telescope (SUIT) is an instrument onboard the Aditya-L1 mission of ISRO that will measure and monitor the solar radiation emitted in the near-ultraviolet wavelength range (200-400 nm). SUIT will simultaneously map the photosphere and the chromosphere of the Sun using 11 filters sensitive to different wavelengths and covering different heights in the solar atmosphere and help us understand the processes involved in the transfer of mass and energy from one layer to the other. SUIT will also allow us to measure and monitor spatially resolved solar spectral irradiance that governs the chemistry of oxygen and ozone in the stratosphere of Earth's atmosphere. This is central to our understanding of the Sun climate relationship. Title: Fan Loops Observed by IRIS, EIS, and AIA Authors: Ghosh, Avyarthana; Tripathi, Durgesh; Gupta, G. R.; Polito, Vanessa; Mason, Helen E.; Solanki, Sami K. Bibcode: 2017ApJ...835..244G Altcode: 2017arXiv170101617G A comprehensive study of the physical parameters of active region fan loops is presented using the observations recorded with the Interface Region Imaging Spectrometer (IRIS), the EUV Imaging Spectrometer (EIS) on board Hinode, and the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). The fan loops emerging from non-flaring AR 11899 (near the disk center) on 2013 November 19 are clearly discernible in AIA 171 Å images and in those obtained in Fe viii and Si vii images using EIS. Our measurements of electron densities reveal that the footpoints of these loops are at an approximately constant pressure with electron densities of {log} {N}e=10.1 cm-3 at {log} [T/K]=5.15 (O IV), and {log} {N}e=8.9 cm-3 at {log} [T/K]=6.15 (Si x). The electron temperature diagnosed across the fan loops by means of EM-Loci suggest that two temperature components exist at {log} [T/K]=4.95 and 5.95 at the footpoints. These components are picked up by IRIS lines and EIS lines, respectively. At higher heights, the loops are nearly isothermal at {log} [T/K]=5.95, which remained constant along the loop. The measurement of the Doppler shift using IRIS lines suggests that the plasma at the footpoints of these loops is predominantly redshifted by 2-3 km s-1 in C II, 10-15 km s-1 in Si IV, and 15-20 km s-1 in O IV, reflecting the increase in the speed of downflows with increasing temperature from {log} [T/K]=4.40 to 5.15. These observations can be explained by low-frequency nanoflares or impulsive heating, and provide further important constraints on the modeling of the dynamics of fan loops. Title: MWA Observations of Solar Radio Bursts and the Quiet Sun Authors: Cairns, I.; Oberoi, D.; Morgan, J.; Bastian, T.; Bhatnagar, S.; Bisi, M.; Benkevitch, L.; Bowman, J.; Donea, A.; Giersch, O.; Jackson, B.; Chat, G. L.; Golub, L.; Hariharan, K.; Herne, D.; Kasper, J.; Kennewell, J.; Lonsdale, C.; Lobzin, V.; Matthews, L.; Mohan, A.; Padmanabhan, J.; Pankratius, V.; Pick, M.; Subramanian, P.; Ramesh, R.; Raymond, J.; Reeves, K.; Rogers, A.; Sharma, R.; Tingay, S.; Tremblay, S.; Tripathi, D.; Webb, D.; White, S.; Abidin, Z. B. Z. Bibcode: 2017mwa..prop..A06C Altcode: A hundred hours of observing time for solar observations is requested during the 2017-A observing semester. These data will be used to address science objectives for solar burst science (Goal A), studies of weak non-thermal radiation (Goal B) and quiet sun science (Goal C). Goal A will focus on detailed investigations of individual events seen in the MWA data, using the unsurpassed spectroscopic imaging ability of the MWA to address some key solar physics questions. Detailed observations of type II bursts, of which MWA has observed two, will be one focus, with MWA polarimetric imaging observations of type III bursts another focus. Goal B will address studies of the numerous short lived and narrow band emission features, significantly weaker than those seen by most other instruments revealed by the MWA. These emission features do not resemble any known types of solar bursts, but are possible signatures of "nanoflares" which have long been suspected to play a role in coronal heating. A large database of these events is needed to be able to reliably estimate their contribution to coronal heating. These observations will contribute to this database. Goal C will focus on characterizing the Sun's background thermal emission, their short and long term variability and looking for evidence of a scattering disc around the Sun. Title: The Aditya-L1 Mission of Indian Space Research Organization Authors: Tripathi, Durgesh Bibcode: 2016cosp...41E1937T Altcode: The Aditya-L1 is the first mission of the Indian Space Research Organization (ISRO) dedicated to solar observations. The spacecraft will be located at the first Lagrangian point and will provide continuous observations of the Sun using remote sensing as well as in-situ measurements. The spacecraft will carry 7 payloads including a coronagraph that will image the corona in visible and IR wavelength and will provide measurements of coronal magnetic field and will study the dynamics of coronal mass ejections; a NUV imaging telescope to study the coupling between solar photosphere and chromosphere and to measure spatially resolved solar spectral irradiance and its variation. There will be two payloads to study the soft X-ray and hard X-ray emission from the Sun, two payloads for in-situ measurements of the charged particles and a magnetometer to study the magnetic field variations during energetic events. Some of the salient features of the experiments on board Aditya-L1 mission will be discussed. Title: The Solar Ultraviolet Imaging Telescope onboard Aditya-L1 Authors: Ghosh, Avyarthana; Chatterjee, Subhamoy; Khan, Aafaque R.; Tripathi, Durgesh; Ramaprakash, A. N.; Banerjee, Dipankar; Chordia, Pravin; Gandorfer, Achim M.; Krivova, Natalie; Nandy, Dibyendu; Rajarshi, Chaitanya; Solanki, Sami K.; Sriram, S. Bibcode: 2016SPIE.9905E..03G Altcode: The Solar Ultraviolet Imaging Telescope (SUIT) is an instrument onboard the Aditya-L1 spacecraft, the first dedicated solar mission of the Indian Space Research Organization (ISRO), which will be put in a halo orbit at the Sun-Earth Langrage point (L1). SUIT has an off-axis Ritchey-Chrétien configuration with a combination of 11 narrow and broad bandpass filters which will be used for full-disk solar imaging in the Ultravoilet (UV) wavelength range 200-400 nm. It will provide near simultaneous observations of lower and middle layers of the solar atmosphere, namely the Photosphere and Chromosphere. These observations will help to improve our understanding of coupling and dynamics of various layers of the solar atmosphere, mechanisms responsible for stability, dynamics and eruption of solar prominences and Coronal Mass ejections, and possible causes of solar irradiance variability in the Near and Middle UV regions, which is of central interest for assessing the Sun's influence on climate. Title: Multiwavelength study of 20 jets that emanate from the periphery of active regions Authors: Mulay, Sargam M.; Tripathi, Durgesh; Del Zanna, Giulio; Mason, Helen Bibcode: 2016A&A...589A..79M Altcode: 2016arXiv160200151M
Aims: We present a multiwavelength analysis of 20 EUV jets which occurred at the periphery of active regions close to sunspots. We discuss the physical parameters of the jets and their relation with other phenomena such as Hα surges, nonthermal type-III radio bursts and hard X-ray (HXR) emission.
Methods: These jets were observed between August 2010 and June 2013 by the Atmospheric Imaging Assembly (AIA) instrument that is onboard the Solar Dynamic Observatory (SDO). We selected events that were observed on the solar disk within +/-60° latitude. Using AIA wavelength channels that are sensitive to coronal temperatures, we studied the temperature distribution in the jets using the line of sight (LOS) differential emission measure (DEM) technique. We also investigated the role of the photospheric magnetic field using the LOS magnetogram data from the Helioseismic and Magnetic Imager (HMI) onboard SDO.
Results: It has been observed that most of the jets originated from the western periphery of active regions. Their lifetimes range from 5 to 39 min with an average of 18 min and their velocities range from 87 to 532 km s-1 with an average of 271 km s-1. All the jets are co-temporally associated with Hα surges. Most of the jets are co-temporal with nonthermal type-III radio bursts observed by the Wind/WAVES spacecraft in the frequency range from 20 kHz to 13 MHz. We confirm the source region of these bursts using the potential field source surface (PFSS) technique. Using Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observations, we found that half of the jets produced HXR emission and they often shared the same source region as the HXR emission (6-12 keV). Ten out of 20 events showed that the jets originated in a region of flux cancellation and six jets in a region of flux emergence. Four events showed flux emergence and then cancellation during the jet evolution. DEM analyses showed that for most of the spires of the jets, the DEM peaked at around log T [K] = 6.2/6.3 (~2 MK). In addition, we derived an emission measure and a lower limit of electron density at the location of the spire (jet 1: log EM = 28.6, Ne = 1.3 × 1010 cm-3; jet 2: log EM = 28.0, Ne = 8.6 × 109 cm-3) and the footpoint (jet 1 - log EM = 28.6, Ne = 1.1 × 1010 cm-3; jet 2: log EM = 28.1, Ne = 8.4 × 109 cm-3). These results are in agreement with those obtained earlier by studying individual active region jets.
Conclusions: The observation of flux cancellation, the association with HXR emission and emission of nonthermal type-III radio bursts, suggest that the initiation and therefore, heating is taking place at the base of the jet. This is also supported by the high temperature plasma revealed by the DEM analysis in the jet footpoint (peak in the DEM at log T [K] = 6.5). Our results provide substantial constraints for theoretical modeling of the jets and their thermodynamic nature.

Movies are available in electronic form at http://www.aanda.org Title: On the Bright Loop Top Emission in Post-eruption Arcades Authors: Sharma, Rohit; Tripathi, Durgesh; Isobe, Hiroaki; Ghosh, Avyarthana Bibcode: 2016ApJ...823...47S Altcode: 2016arXiv160304959S Observations of post-eruption arcades (PEAs) in X-rays and EUV reveal strong localized brightenings at the loop top regions. The origins of these brightenings and their dynamics are not well understood to date. Here, we study the dynamics of PEAs using one-dimensional hydrodynamic modeling, focusing on understanding the formation of localized brightening. Our findings suggest that these brightenings are the result of collisions between the counter-streaming chromospheric evaporation from both the footpoints. We perform forward modeling of the emission observed in simulated results in various spectral lines observed by the Extreme-Ultraviolet Imaging Telescope on board Hinode. The forward-modeled intensities in various spectral lines are in close agreement with a flare observed on 2006 December 17 by EIS. Title: A Hot Flux Rope Observed by SDO/AIA Authors: Aparna, V.; Tripathi, Durgesh Bibcode: 2016ApJ...819...71A Altcode: 2016arXiv160101620A A filament eruption was observed on 2010 October 31 in the images recorded by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO) in its Extreme Ultra-Violet (EUV) channels. The filament showed a slow-rise phase followed by a fast rise and was classified to be an asymmetric eruption. In addition, multiple localized brightenings which were spatially and temporally associated with the slow-rise phase were identified, leading us to believe that the tether-cutting mechanism initiated the eruption. An associated flux rope was detected in high-temperature channels of AIA, namely 94 and 131 Å, corresponding to 7 and 11 MK plasma respectively. In addition, these channels are also sensitive to cooler plasma corresponding to 1-2 MK. In this study, we have applied the algorithm devised by Warren et al. to remove cooler emission from the 94 Å channel to deduce only the high-temperature structure of the flux rope and to study its temporal evolution. We found that the flux rope was very clearly seen in the clean 94 Å channel image corresponding to Fe xviii emission, which corresponds to a plasma at a temperature of 7 MK. This temperature matched well with that obtained using Differential Emission Measure analysis. This study provides important constrains in the modeling of the thermodynamic structure of the flux ropes in coronal mass ejections. Title: Intensity Conserving Spectral Fitting Authors: Klimchuk, J. A.; Patsourakos, S.; Tripathi, D. Bibcode: 2016SoPh..291...55K Altcode: 2015SoPh..tmp..180K The detailed shapes of spectral-line profiles provide valuable information about the emitting plasma, especially when the plasma contains an unresolved mixture of velocities, temperatures, and densities. As a result of finite spectral resolution, the intensity measured by a spectrometer is the average intensity across a wavelength bin of non-zero size. It is assigned to the wavelength position at the center of the bin. However, the actual intensity at that discrete position will be different if the profile is curved, as it invariably is. Standard fitting routines (spline, Gaussian, etc.) do not account for this difference, and this can result in significant errors when making sensitive measurements. We have developed an iterative procedure that corrects for this effect. It converges rapidly and is very flexible in that it can be used with any fitting function. We present examples of cubic-spline and Gaussian fits and give special attention to measurements of blue-red asymmetries of coronal emission lines. Title: IRIS and SDO Observations of Recurrent Explosive Events Authors: Gupta, G. R.; Tripathi, Durgesh Bibcode: 2015ApJ...809...82G Altcode: 2015arXiv150605327G Observations of recurrent explosive events (EEs) with timescales of 3-5 minutes are reported. These EEs have been observed with the Interface Region Imaging Spectrograph (IRIS) and have a spatial dimension of ∼ 1\buildrel{\prime\prime}\over{.} 5 along the slit. The spectral line profiles of C ii 1335/1336 Å and Si iv 1394/1403 Å become highly broadened both in red as well as blue wings. Several absorption lines on top of the broadened profiles were identified. In addition, emission lines corresponding to neutral lines such as Cl i 1351.66 Å, C i 1354.29 Å, and C i 1355.84 Å were identified. The C i 1354.29 Å and C i 1355.84 Å lines were found only during the EEs, whereas Cl i 1351.66 Å broadens during the EEs. The estimated lower limit on electron number density obtained using the line ratios of Si iv and O iv is about {10}13.5 cm-3, suggesting that the observed events are most likely occurring at heights corresponding to a lower chromosphere. To the best of our knowledge, for the first time we have detected short-period variability (30 s and 60-90 s) within the EE bursts. Observations of the photospheric magnetic fields underneath EEs indicate that a negative polarity field emerges in the neighborhood of oppositely directed positive fields that undergo repetitive reconnection (magnetic flux cancellation) events. The dynamic changes observed in AIA 1700 Å, 1600 Å, C ii 1330 Å, and Si iv 1400 Å intensity images corresponded very well with the emergence and cancellation of photospheric magnetic field (negative polarity) on a timescale of 3-5 minutes. The observations reported here suggest that these EEs are formed due to magnetic reconnection and are occurring in the lower chromosphere. Title: Intensity Conserving Spline Interpolation (ICSI): A New Tool for Spectroscopic Analysis Authors: Klimchuk, James A.; Patsourakos, Spiros; Tripathi, Durgesh Bibcode: 2015TESS....120309K Altcode: 2015arXiv150608102K Spectroscopy is an extremely powerful tool for diagnosing astrophysical and other plasmas. For example, the shapes of line profiles provide valuable information on the distribution of velocities along an optically thin line-of-sight and across the finite area of a resolution element. A number of recent studies have measured the asymmetries of line profiles in order to detect faint high-speed upflows, perhaps associated with coronal nanoflares or perhaps associated with chromospheric nanoflares and type II spicules. Over most of the Sun, these asymmetries are very subtle, so great care must be taken. A common technique is to perform a spline fit of the points in the profile in order to extract information at a spectral resolution higher than that of the original data. However, a fundamental problem is that the fits do not conserve intensity. We have therefore developed an iterative procedure called Intensity Conserving Spline Interpolation that does preserve the observed intensity within each wavelength bin. It improves the measurement of line asymmetries and can also help with the determination of line blends. Title: Sunspot waves and triggering of homologous active region jets Authors: Chandra, R.; Gupta, G. R.; Mulay, Sargam; Tripathi, Durgesh Bibcode: 2015MNRAS.446.3741C Altcode: 2014arXiv1410.8315C We present and discuss multiwavelength observations of five homologous recurrent solar jets that occurred in active region NOAA 11133 on 2010 December 11. These jets were well observed by the Solar Dynamic observatory (SDO) with high spatial and temporal resolution. The speed of the jets ranged between 86 and 267 km s-1. A type III radio burst was observed in association with all the five jets. The investigation of the overall evolution of magnetic field in the source regions suggested that the flux was continuously emerging on longer term. However, all the jets but J5 were triggered during a local dip in the magnetic flux, suggesting the launch of the jets during localized submergence of magnetic flux. Additionally, using the PFSS modelling of the photospheric magnetic field, we found that all the jets were ejected in the direction of open field lines. We also traced sunspot oscillations from the sunspot interior to foot-point of jets and found presence of ∼3 min oscillations in all the SDO/AIA (Atmospheric Imaging Assembly) passbands. The wavelet analysis revealed an increase in amplitude of the oscillations just before the trigger of the jets, that decreased after the jets were triggered. The observations of increased amplitude of the oscillation and its subsequent decrease provides evidence of wave-induced reconnection triggering the jets. Title: Spectroscopic Observations of a Coronal Loop: Basic Physical Plasma Parameters Along the Full Loop Length Authors: Gupta, G. R.; Tripathi, Durgesh; Mason, Helen E. Bibcode: 2015ApJ...800..140G Altcode: 2014arXiv1412.7428G Coronal loops are the basic structures of the solar transition region and corona. Understanding of the physical mechanisms behind the loop heating, plasma flows, and filling are still considered a major challenge in solar physics. The mechanism(s) should be able to supply mass to the corona from the chromosphere and to heat the plasma over 1 MK within a small distance of a few hundred kilometers from the chromosphere to the corona. This problem makes coronal loops an interesting target for detailed study. In this study, we focus on spectroscopic observations of a coronal loop observed in its full length in various spectral lines as recorded by the Extreme-ultraviolet Imaging Spectrometer on board Hinode. We derive physical plasma parameters such as electron density, temperature, pressure, column depth, and filling factors along the loop length from one footpoint to the another. The obtained parameters are used to infer whether the observed coronal loop is overdense or underdense with respect to gravitational stratification of the solar atmosphere. These new measurements of physical plasma parameters, from one footpoint to another, provide important constraints on the modeling of the mass and energy balance in coronal loops. Title: Observations and Modeling of North-South Asymmetries Using a Flux Transport Dynamo Authors: Shetye, Juie; Tripathi, Durgesh; Dikpati, Mausumi Bibcode: 2015ApJ...799..220S Altcode: 2014arXiv1412.3245S The peculiar behavior of solar cycle 23 and its prolonged minima has been one of the most studied problems over the past few years. In the present paper, we study the asymmetries in active region magnetic flux in the northern and southern hemispheres during the complete solar cycle 23 and the rising phase of solar cycle 24. During the declining phase of solar cycle 23, we find that the magnetic flux in the southern hemisphere is about 10 times stronger than that in the northern hemisphere; however, during the rising phase of cycle 24, this trend is reversed. The magnetic flux becomes about a factor of four stronger in the northern hemisphere than in the southern hemisphere. Additionally, we find that there was a significant delay (about five months) in change of the polarity in the southern hemisphere in comparison with the northern hemisphere. These results provide us with hints of how the toroidal fluxes have contributed to the solar dynamo during the prolonged minima in solar cycle 23 and in the rising phase of solar cycle 24. Using a solar flux-transport dynamo model, we demonstrate that persistently stronger sunspot cycles in one hemisphere could be caused by the effect of greater inflows into active region belts in that hemisphere. Observations indicate that greater inflows are associated with stronger activity. Some other change or difference in meridional circulation between hemispheres could cause the weaker hemisphere to become the stronger one. Title: The evolution of the emission measure distribution in the core of an active region Authors: Del Zanna, Giulio; Tripathi, Durgesh; Mason, Helen; Subramanian, Srividya; O'Dwyer, Brendan Bibcode: 2015A&A...573A.104D Altcode: 2014arXiv1411.0128D We study the spatial distribution and evolution of the slope of the emission measure (EM) between 1 MK and 3 MK in the core of the active region (AR) NOAA 11193, first when it appeared near the central meridian and then again when it reappeared after a solar rotation. We use observations recorded by the Extreme-ultraviolet Imaging Spectrometer (EIS) aboard Hinode, with a new radiometric calibration. We also use observations from the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory (SDO). We present the first spatially resolved maps of the EM slope in the 1-3 MK range within the core of the AR using several methods, either from approximations or from the differential emission measure (DEM). A significant variation of the slope is found at different spatial locations within the active region. We selected two regions that were not greatly affected by lower temperature emission along the line of sight. We found that the EM had a power law of the form EM ∝ Tb, with b = 4.4 ± 0.4, and 4.6 ± 0.4, during the first and second appearance of the active region, respectively. During the second rotation, line-of-sight effects become more important, although difficult to estimate. We found that the use of the ground calibration for Hinode/EIS and the approximate method to derive the EM, used in previous publications, produce an underestimation of the slopes. The EM distribution in active region cores is generally found to be consistent with high frequency heating, and does not change much during the evolution of the active region. Title: Intensity Conserving Spline Interpolation (ICSI): A New Tool for Spectroscopic Analysis Authors: Klimchuk, J. A.; Patsourakos, S.; Tripathi, D. Bibcode: 2014AGUFMSH13B4109K Altcode: Spectroscopy is an extremely powerful tool for diagnosing astrophysical and other plasmas. For example, the shapes of line profiles provide valuable information on the distribution of velocities along an optically thin line-of-sight and across the finite area of a resolution element. A number of recent studies have measured the asymmetries of line profiles in order to detect faint high-speed upflows, perhaps associated with coronal nanoflares or perhaps associated with chromospheric nanoflares and type II spicules. Over most of the Sun, these asymmetries are very subtle, so great care must be taken. A common technique is to perform a spline fit of the points in the profile in order to extract information at a spectral resolution higher than that of the original data. However, a fundamental problem is that the fits do not conserve intensity. We have therefore developed an iterative procedure called Intensity Conserving Spline Interpolation that does preserve the observed intensity within each wavelength bin. It improves the measurement of line asymmetries and can also help with the determination of line blends. Title: Emission Measure Distribution for Diffuse Regions in Solar Active Regions Authors: Subramanian, Srividya; Tripathi, Durgesh; Klimchuk, James A.; Mason, Helen E. Bibcode: 2014ApJ...795...76S Altcode: 2014arXiv1409.1447S Our knowledge of the diffuse emission that encompasses active regions is very limited. In this paper we investigate two off-limb active regions, namely, AR 10939 and AR 10961, to probe the underlying heating mechanisms. For this purpose, we have used spectral observations from Hinode/EIS and employed the emission measure (EM) technique to obtain the thermal structure of these diffuse regions. Our results show that the characteristic EM distributions of the diffuse emission regions peak at log T = 6.25 and the coolward slopes are in the range 1.4-3.3. This suggests that both low- as well as high-frequency nanoflare heating events are at work. Our results provide additional constraints on the properties of these diffuse emission regions and their contribution to the background/foreground when active region cores are observed on-disk. Title: Initiation of Coronal Mass Ejection Event Observed on 2010 November 3: Multi-wavelength Perspective Authors: Mulay, Sargam; Subramanian, Srividya; Tripathi, Durgesh; Isobe, Hiroaki; Glesener, Lindsay Bibcode: 2014ApJ...794...78M Altcode: 2014arXiv1407.5837M One of the major unsolved problems in solar physics is that of coronal mass ejection (CME) initiation. In this paper, we have studied the initiation of a flare-associated CME that occurred on 2010 November 3 using multi-wavelength observations recorded by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory and the Reuven Ramaty High Energy Solar Spectroscopic Imager. We report an observation of an inflow structure initially in the 304 Å and the 1600 Å images a few seconds later. This inflow structure was detected as one of the legs of the CME. We also observed a non-thermal compact source concurrent and near co-spatial with the brightening and movement of the inflow structure. The appearance of this compact non-thermal source, brightening, and movement of the inflow structure and the subsequent outward movement of the CME structure in the corona led us to conclude that the CME initiation was caused by magnetic reconnection. Title: Determination of Prominence Plasma β from the Dynamics of Rising Plumes Authors: Hillier, Andrew; Hillier, Richard; Tripathi, Durgesh Bibcode: 2014IAUS..300...94H Altcode: Observations of quiescent prominences show rising plumes, dark in chromospheric lines, that propagate from large bubbles. In this paper we present a method that may be used to determine the plasma β (ratio of gas pressure to magnetic pressure) from the rising plumes. Using the classic fluid dynamic solution for flow around a circular cylinder, the compression of the prominence material can be estimated. Application to a prominence gave an estimate of the plasma β as β=0.47-1.13 for a ratio of specific heats of γ=1.4-1.7. Title: SDO/AIA Observations of a Partially Erupting Prominence Authors: Tripathi, Durgesh; Reeves, Katharine K.; Gibson, Sarah E.; Srivastava, Abhishek; Joshi, Navin C. Bibcode: 2013ApJ...778..142T Altcode: 2013arXiv1310.0162T We report an observation of a partially erupting prominence and its associated dynamical plasma processes based on observations recorded by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. The prominence first went through a slow rise (SR) phase followed by a fast rise (FR) phase. The SR phase began after a couple of small brightenings were seen toward the footpoints. When the prominence had transitioned from SR to FR, it had already become kinked. The prominence shows strong brightening at the central kink location during the start of FR. We interpret this as an internal magnetic reconnection occurring at a vertical current sheet forming between the two legs of the erupting prominence (flux rope). The brightening at the central kink location is seen in all EUV channels of AIA. The contributions of differential emission at higher temperatures are larger compared to that for typical coronal temperatures supporting a reconnection scenario at the central kink location. The plasma above the brightening location is ejected as a hot plasmoid-like structure embedded in a coronal mass ejection, and those below the brightening move down in the form of blobs moving toward the Sun's surface. The unique time resolution of the AIA has allowed these eruptive aspects, including SR-to-FR, kinking, central current sheet formation, plasmoid-like eruption, and filament "splitting," to be observed in a single event, providing strong and comprehensive evidence in favor of the model of partially erupting flux ropes. Title: Asymmetries in Coronal Spectral Lines and Emission Measure Distribution Authors: Tripathi, Durgesh; Klimchuk, James A. Bibcode: 2013ApJ...779....1T Altcode: 2013arXiv1310.0168T It has previously been argued that (1) spicules do not provide enough pre-heated plasma to fill the corona, and (2) even if they did, additional heating would be required to keep the plasma hot as it expands upward. Here we address whether spicules play an important role by injecting plasma at cooler temperatures (<2 MK), which then gets heated to coronal values at higher altitudes. We measure red-blue asymmetries in line profiles formed over a wide range of temperatures in the bright moss areas of two active regions. We derive emission measure distributions from the excess wing emission. We find that the asymmetries and emission measures are small and conclude that spicules do not inject an important (dominant) mass flux into the cores of active regions at temperatures >0.6 MK (log T > 5.8). These conclusions apply not only to spicules but also to any process that suddenly heats and accelerates chromospheric plasma (e.g., a chromospheric nanoflare). The traditional picture of coronal heating and chromospheric evaporation appears to remain the most likely explanation of the active region corona. Title: Where is Coronal Plasma Heated? Authors: Klimchuk, James A.; Bradshaw, S.; Patsourakos, S.; Tripathi, D. Bibcode: 2013SPD....4420006K Altcode: The coupling between the chromosphere and corona is a question of great current interest. It has long been understood that coronal mass originates in the chromosphere and that the energy which powers the corona flows up through the chromosphere. However, the details of how this happens are now being questioned. In the traditional view, “mechanical” energy flows into the corona in the form of waves or gradually increasing magnetic stresses. The waves and stresses dissipate and heat the plasma. The resulting downward thermal conduction flux causes material to evaporate from the chromosphere and fill the corona. If the heating is steady, an equilibrium is established whereby radiation and thermal conduction balance the energy input. If the heating is impulsive (a nanoflare), the evaporated plasma cools and drains, only to reappear during the next event. In either case, the heating occurs in the corona. A new idea is that the heating occurs instead in the chromosphere. Cold plasma is directly heated to coronal temperatures and then flows upward due to expansion and perhaps also an ejection process. The hot tips of type II spicules are one example, though spicules need not be involved. I will discuss these two fundamentally different scenarios and the observational predictions that they make. A comparison with actual observations leads to the conclusion that only a small fraction of the hot plasma in the corona comes from chromospheric heating. Most coronal plasma is a consequence of heating that occurs in the corona itself. Title: Origin of Macrospicule and Jet in Polar Corona by a Small-scale Kinked Flux Tube Authors: Kayshap, P.; Srivastava, Abhishek K.; Murawski, K.; Tripathi, Durgesh Bibcode: 2013ApJ...770L...3K Altcode: 2013arXiv1305.0338K We report an observation of a small-scale flux tube that undergoes kinking and triggers the macrospicule and a jet on 2010 November 11 in the north polar corona. The small-scale flux tube emerged well before the triggering of the macrospicule and as time progresses the two opposite halves of this omega-shaped flux tube bent transversely and approach each other. After ~2 minutes, the two approaching halves of the kinked flux tube touch each other and an internal reconnection as well as an energy release takes place at the adjoining location and a macrospicule was launched which goes up to a height of 12 Mm. Plasma begins to move horizontally as well as vertically upward along with the onset of the macrospicule and thereafter converts into a large-scale jet in which the core denser plasma reaches up to ~40 Mm in the solar atmosphere with a projected speed of ~95 km s-1. The fainter and decelerating plasma chunks of this jet were also seen up to ~60 Mm. We perform a two-dimensional numerical simulation by considering the VAL-C initial atmospheric conditions to understand the physical scenario of the observed macrospicule and associated jet. The simulation results show that reconnection-generated velocity pulse in the lower solar atmosphere steepens into slow shock and the cool plasma is driven behind it in the form of macrospicule. The horizontal surface waves also appeared with shock fronts at different heights, which most likely drove and spread the large-scale jet associated with the macrospicule. Title: Doppler Shifts in Active Region Moss Using SOHO/SUMER Authors: Winebarger, Amy; Tripathi, Durgesh; Mason, Helen E.; Del Zanna, Giulio Bibcode: 2013ApJ...767..107W Altcode: The velocity of the plasma at the footpoint of hot loops in active region cores can be used to discriminate between different heating frequencies. Velocities on the order of a few kilometers per second would indicate low-frequency heating on sub-resolution strands, while velocities close to zero would indicate high-frequency (steady) heating. To discriminate between these two values requires accurate velocity measurements; previous velocity measurements suffer from large uncertainties, mainly due to the lack of an absolute wavelength reference scale. In this paper, we determine the velocity in the loop footpoints using observations from Solar Ultraviolet Measurements of Emitted Radiation (SUMER) on Solar and Heliospheric Observatory. We use neutral spectral lines to determine the wavelength scale of the observations with an uncertainty in the absolute velocity of <3.5 km s-1 and co-aligned Transition Region and Coronal Explorer (TRACE) images to identify footpoint regions. We studied three different active regions and found average redshifts in the Ne VIII 770 Å emission line (formed at 6 × 105 K) of 5.17 ± 5.37 km s-1 and average redshifts in the C IV 1548 and 1550 Å emission lines (formed at 1 × 105 K) of 13.94 ± 4.93 km s-1 and 14.91 ± 6.09 km s-1, respectively. We find no correlation between the brightness in the spectral line and the measured velocity, nor do we find correlation between the Ne VIII and C IV velocities measured co-spatially and co-temporally. SUMER scanned two of the active regions twice; in those active regions we find positive correlation between the co-spatial velocities measured during the first and second scans. These results provide definitive and quantitative measurements for comparisons with simulations of different coronal heating mechanisms. Title: Observational Evidence of Sausage-pinch Instability in Solar Corona by SDO/AIA Authors: Srivastava, A. K.; Erdélyi, R.; Tripathi, Durgesh; Fedun, V.; Joshi, N. C.; Kayshap, P. Bibcode: 2013ApJ...765L..42S Altcode: 2013arXiv1302.1286S We present the first observational evidence of the evolution of sausage-pinch instability in active region 11295 during a prominence eruption using data recorded on 2011 September 12 by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). We have identified a magnetic flux tube visible in AIA 304 Å that shows curvatures on its surface with variable cross-sections as well as enhanced brightness. These curvatures evolved and thereafter smoothed out within a timescale of a minute. The curved locations on the flux tube exhibit a radial outward enhancement of the surface of about 1-2 Mm (a factor of two larger than the original thickness of the flux tube) from the equilibrium position. AIA 193 Å snapshots also show the formation of bright knots and narrow regions in-between at the four locations as that of 304 Å along the flux tube where plasma emission is larger compared to the background. The formation of bright knots over an entire flux tube as well as the narrow regions in <60 s may be the morphological signature of the sausage instability. We also find the flows of confined plasma (propagation of brightness) in these bright knots along the field lines, which indicates the dynamicity of the flux tube that probably causes the dominance of the longitudinal field component over short temporal scales. The observed longitudinal motion of the plasma frozen in the magnetic field lines further vanishes the formed curvatures and plasma confinements as well as growth of instability to stabilize the flux tube. Title: Heating of active region cores: Impulsive or steady? Authors: Tripathi, Durgesh Bibcode: 2013ASInC..10...73T Altcode: The question of active region heating has proven to be highly challenging since its discovery in 1940s. The recent observational facilities have shed new lights towards the understanding of this problem. In this paper we review some of the new measurements to study the heating mechanisms in the hot core loops of active regions using the observations recorded by Solar Ultraviolet Measurements of Emitted Radiation (SUMER) onboard SoHO and the Extreme-ultraviolet Imaging Spectrometer (EIS) aboard Hinode. These new measurements show that the properties of hot core loops are consistent with by impulsive heating -- low frequency nanoflare - scenario. However, the evidences are not strong enough to rule-out steady heating completely. Further measurement using better spectral resolution and temperature coverage is required, which will be provided by Interface Region Imaging Spectrometer (IRIS) and Solar-C in near future. Title: Determination of Prominence Plasma β from the Dynamics of Rising Plumes Authors: Hillier, Andrew; Hillier, Richard; Tripathi, Durgesh Bibcode: 2012ApJ...761..106H Altcode: 2012arXiv1211.0742H Observations by the Hinode satellite show in great detail the dynamics of rising plumes, dark in chromospheric lines, in quiescent prominences that propagate from large (~10 Mm) bubbles that form at the base of the prominences. These plumes present a very interesting opportunity to study magnetohydrodynamic (MHD) phenomena in quiescent prominences, but obstacles still remain. One of the biggest issues is that of the magnetic field strength, which is not easily measurable in prominences. In this paper we present a method that may be used to determine a prominence's plasma β when rising plumes are observed. Using the classic fluid dynamic solution for flow around a circular cylinder with an MHD correction, the compression of the prominence material can be estimated. This has been successfully confirmed through simulations; application to a prominence gave an estimate of the plasma β as β = 0.47 ± 0.079 to 1.13 ± 0.080 for the range γ = 1.4-1.7. Using this method it may be possible to estimate the plasma β of observed prominences, therefore helping our understanding of a prominence's dynamics in terms of MHD phenomena. Title: Doppler shift of hot coronal lines in a moss area of an active region Authors: Dadashi, N.; Teriaca, L.; Tripathi, D.; Solanki, S. K.; Wiegelmann, T. Bibcode: 2012A&A...548A.115D Altcode: 2012arXiv1211.5473D The moss is the area at the footpoint of the hot (3 to 5 MK) loops forming the core of the active region where emission is believed to result from the heat flux conducted down to the transition region from the hot loops. Studying the variation of Doppler shift as a function of line formation temperatures over the moss area can give clues on the heating mechanism in the hot loops in the core of the active regions. We investigate the absolute Doppler shift of lines formed at temperatures between 1 MK and 2 MK in a moss area within active region NOAA 11243 using a novel technique that allows determining the absolute Doppler shift of EUV lines by combining observations from the SUMER and EIS spectrometers. The inner (brighter and denser) part of the moss area shows roughly constant blue shift (upward motions) of 5 km s-1 in the temperature range of 1 MK to 1.6 MK. For hotter lines the blue shift decreases and reaches 1 km s-1 for Fe xv 284 Å (~2 MK). The measurements are discussed in relation to models of the heating of hot loops. The results for the hot coronal lines seem to support the quasi-steady heating models for nonsymmetric hot loops in the core of active regions. Title: Temperature and Extreme-ultraviolet Intensity in a Coronal Prominence Cavity and Streamer Authors: Kucera, T. A.; Gibson, S. E.; Schmit, D. J.; Landi, E.; Tripathi, D. Bibcode: 2012ApJ...757...73K Altcode: We analyze the temperature and EUV line emission of a coronal cavity and surrounding streamer in terms of a morphological forward model. We use a series of iron line ratios observed with the Hinode Extreme-ultraviolet Imaging Spectrograph (EIS) on 2007 August 9 to constrain temperature as a function of altitude in a morphological forward model of the streamer and cavity. We also compare model predictions to the EIS EUV line intensities and polarized brightness (pB) data from the Mauna Loa Solar Observatory (MLSO) Mark 4 K-coronameter. This work builds on earlier analysis using the same model to determine geometry of and density in the same cavity and streamer. The fit to the data with altitude-dependent temperature profiles indicates that both the streamer and cavity have temperatures in the range 1.4-1.7 MK. However, the cavity exhibits substantial substructure such that the altitude-dependent temperature profile is not sufficient to completely model conditions in the cavity. Coronal prominence cavities are structured by magnetism so clues to this structure are to be found in their plasma properties. These temperature substructures are likely related to structures in the cavity magnetic field. Furthermore, we find that the model overestimates the EUV line intensities by a factor of 4-10, without overestimating pB. We discuss this difference in terms of filling factors and uncertainties in density diagnostics and elemental abundances. Title: Active Region Moss: Doppler Shifts from Hinode/Extreme-ultraviolet Imaging Spectrometer Observations Authors: Tripathi, Durgesh; Mason, Helen E.; Klimchuk, James A. Bibcode: 2012ApJ...753...37T Altcode: 2012arXiv1204.6550T Studying the Doppler shifts and the temperature dependence of Doppler shifts in moss regions can help us understand the heating processes in the core of the active regions. In this paper, we have used an active region observation recorded by the Extreme-ultraviolet Imaging Spectrometer (EIS) on board Hinode on 2007 December 12 to measure the Doppler shifts in the moss regions. We have distinguished the moss regions from the rest of the active region by defining a low-density cutoff as derived by Tripathi et al. in 2010. We have carried out a very careful analysis of the EIS wavelength calibration based on the method described by Young et al. in 2012. For spectral lines having maximum sensitivity between log T = 5.85 and log T = 6.25 K, we find that the velocity distribution peaks at around 0 km s-1 with an estimated error of 4-5 km s-1. The width of the distribution decreases with temperature. The mean of the distribution shows a blueshift which increases with increasing temperature and the distribution also shows asymmetries toward blueshift. Comparing these results with observables predicted from different coronal heating models, we find that these results are consistent with both steady and impulsive heating scenarios. However, the fact that there are a significant number of pixels showing velocity amplitudes that exceed the uncertainty of 5 km s-1 is suggestive of impulsive heating. Clearly, further observational constraints are needed to distinguish between these two heating scenarios. Title: On the Multiple Energy Release and Filament Activation during M5.4 Class Flare from NOAA AR 11121 on 06 November 2010 Authors: Kayshap, Pradeep; Chandra, Ramesh; Tripathi, Durgesh; Srivastava, Abhishek K.; Joshi, N. C. Bibcode: 2012cosp...39..903K Altcode: 2012cosp.meet..903K No abstract at ADS Title: Observations of Flows and Waves in Active Regions: An observational Overview Authors: Tripathi, Durgesh Bibcode: 2012cosp...39.2002T Altcode: 2012cosp.meet.2002T In order to understand one of the most intensely studies problem in solar physics i.e. the problem of solar coronal heating, it is mandatory to understand the mass and energy transport in the outer solar atmosphere. Doppler shift measurements in the transition and corona reveal an abundance of plasma flow across a range of temperature having different patterns in different part of the active region, suggesting flow of material. The high resolution imaging observations have revealed that there is an abundance of quasi periodic propagating features which are often interpreted as manifestation of slow magneto-acoustic waves propagating into the atmosphere guided by loop structures. In this talk we will review some recent highlights of the studies of flows and waves and their role in understanding the mass and energy transport in the outer atmosphere. Title: Observations of Plasma Upflow in a Warm Loop with Hinode/EIS Authors: Tripathi, Durgesh; Mason, Helen E.; Del Zanna, Giulio; Bradshaw, Steven Bibcode: 2012ApJ...754L...4T Altcode: 2012arXiv1206.3367T A complete understanding of Doppler shift in active region loops can help probe the basic physical mechanism involved into the heating of those loops. Here, we present observations of upflows in coronal loops detected in a range of temperatures (log T = 5.8-6.2). The loop was not discernible above these temperatures. The speed of upflow was strongest at the footpoint and decreased with height. The upflow speed at the footpoint was about 20 km s-1 in Fe VIII, which decreased with temperature, being about 13 km s-1 in Fe X, about 8 km s-1 in Fe XII, and about 4 km s-1 in Fe XIII. To the best of our knowledge, this is the first observation providing evidence of upflow of plasma in coronal loop structures at these temperatures. We interpret these observations as evidence of chromospheric evaporation in quasi-static coronal loops. Title: Cross-Calibration of Hinode/EIS and SDO/AIA Authors: O'Dwyer, B.; Zanna, G. D.; Mason, H. E.; Weber, M. A.; Tripathi, D. Bibcode: 2012ASPC..455..369O Altcode: We examine the contribution of spectral lines and continuum emission to the EUV channels of the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) in different regions of the solar atmosphere (coronal hole, quiet Sun, active region, and flare plasma). We highlight the contribution of particular spectral lines which under certain conditions can affect the interpretation of SDO AIA data. In addition we use simultaneous observations from the Hinode Extreme-ultraviolet Imaging Spectrometer (EIS) and SDO/AIA to examine their relative intensity calibration. Good agreement is found between the two instruments for an active region observation. Title: Understanding Coronal Heating with Emission Measure Distributions Authors: Klimchuk, James A.; Tripathi, D.; Bradshaw, S. J.; Mason, H. E. Bibcode: 2012AAS...22042302K Altcode: It is widely believed that the cross-field spatial scale of coronal heating is small, so that the fundamental plasma structures (loop strands) are spatially unresolved. We therefore must appeal to diagnostic techniques that are not strongly affected by spatial averaging. One valuable observable is the emission measure distribution, EM(T), which indicates how much material is present at each temperature. Using data from the Extreme-ultraviolet Imaging Spectrograph on the Hinode mission, we have determined emission measure distributions in the cores of two active regions. The distributions have power law slopes of approximately 2.4 coolward of the peak. We compare these slopes, as well as the amount of emission measure at very high temperature, with the predictions of a series of models. The models assume impulsive heating (nanoflares) in unresolved strands and take full account of nonequilibrium ionization. Title: Temperature Structure of a Coronal Cavity and Streamer Authors: Kucera, Therese A.; Gibson, S. E.; Schmit, D. J.; Landi, E.; Tripathi, D. Bibcode: 2012AAS...22052113K Altcode: We analyze the temperature and EUV line emission of a coronal cavity and surrounding streamer in terms of a morphological forward model. We use a series of iron line ratios observed with the Hinode Extreme-ultraviolet Imaging Spectrograph (EIS) on 2007 Aug. 9 to constrain temperature as a function of altitude in a morphological forward model of the streamer and cavity. We also compare model prediction of the EIS EUV line intensities and polarized brightness (pB) data from the Mauna Loa Solar Observatory (MLSO) MK4. This work builds on earlier analysis using the same model to determine geometry of and density in the same cavity and streamer (Gibson et al. 2010 and Schmit and Gibson 2011). The fit to the data with altitude dependent temperature profiles indicates that both the streamer and cavity have temperatures in the range 1.4-1.7 MK. However, the cavity exhibits substantial substructure such that the altitude dependent temperature profile is not sufficient to completely model conditions in the cavity. This work is supported in part by the NASA SHP program Title: Spectroscopic Diagnostics and Heating of Active Region Cores Authors: Tripathi, D.; Mason, H. E.; Klimchuk, J. A. Bibcode: 2012decs.confE..92T Altcode: It is widely believed that we are still far from spatially resolving the fundamental plasma structures in solar corona. Therefore, we must use spectroscopic diagnostic techniques such as emission measure distribution (EM(T)) and Doppler shifts that are not affected by spatial averaging. Using observations recorded by the Extreme ultraviolet Imaging Spectrometer we have studies emission measure (EM) distribution and Doppler shift in the moss and inter-moss regions. The EM distributions obtained for moss regions cab be reproduced by considering strong coronal condensation scenario suggesting bulk downflow of the plasma. Doppler shift measurements for the moss regions show that almost all the moss regions are red-shifted with velocities up to 15km/s with mean velocity of 5 km/s. However, the uncertainty on the Doppler shift was large. The EM distributions obtained for inter-moss regions have power law slopes of approximately 2.4 coolward of the peak. We compare the EM for inter-moss region with that obtained from nanoflare model using EBTEL (Enthalpy-Based Thermal Evolution of Loops). Our results suggest that the EM distribution for both the moss as well as inter-moss regions and Doppler shift in the moss regions can be explained by nanoflare heating. IRIS will provide a better account of the Doppler shift in the moss regions, which will dramatically enhance our understanding of the heating of active region core. Title: Rotation of an erupting filament observed by STEREO EUVI and COR1 instruments (Corrigendum) Authors: Bemporad, A.; Mierla, M.; Tripathi, D. Bibcode: 2012A&A...537C...1B Altcode: Present Address: inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, 411007 Pune, India. Title: Understanding Coronal Heating with Emission Measure Distributions Authors: Klimchuk, J. A.; Tripathi, D.; Bradshaw, S. J.; Mason, H. E. Bibcode: 2011AGUFMSH43F..03K Altcode: It is widely believed that the cross-field spatial scale of coronal heating is small, so that the fundamental plasma structures (loop strands) are spatially unresolved. We therefore must appeal to diagnostic techniques that are not strongly affected by spatial averaging. One valuable observable is the emission measure distribution, EM(T), which indicates how much material is present at each temperature. Using data from the Extreme-ultraviolet Imaging Spectrograph on the Hinode mission, we have determined emission measure distributions in the cores of two active regions. The distributions have power law slopes of approximately 2.4 coolward of the peak. We compare these slopes, as well as the amount of emission measure at very high temperature, with the predictions of a series of models. The models assume impulsive heating (nanoflares) in unresolved strands and take full account of nonequilibrium ionization. A variety of nanoflare properties and initial conditions are considered. We also comment on the selection of spectral lines for upcoming missions like Solar Orbiter. Title: Emission Measure Distribution and Heating of Two Active Region Cores Authors: Tripathi, Durgesh; Klimchuk, James A.; Mason, Helen E. Bibcode: 2011ApJ...740..111T Altcode: 2011arXiv1107.4480T Using data from the Extreme-ultraviolet Imaging Spectrometer aboard Hinode, we have studied the coronal plasma in the core of two active regions. Concentrating on the area between opposite polarity moss, we found emission measure distributions having an approximate power-law form EMvpropT 2.4 from log T = 5.5 up to a peak at log T = 6.55. We show that the observations compare very favorably with a simple model of nanoflare-heated loop strands. They also appear to be consistent with more sophisticated nanoflare models. However, in the absence of additional constraints, steady heating is also a viable explanation. Title: Rotation of an erupting filament observed by the STEREO EUVI and COR1 instruments Authors: Bemporad, A.; Mierla, M.; Tripathi, D. Bibcode: 2011A&A...531A.147B Altcode: On August 31, 2007, a prominence eruption was observed by the Solar TErrestrial RElations Observatory (STEREO) in the Extreme-UltraViolet Imager (EUVI) 304 images and later on, as the core of a three-part coronal mass ejection (CME) in images acquired by the inner STEREO coronagraph (COR1). Because they were covered by both STEREO spacecraft from right vantage points, these observations provide an excellent opportunity to perform a three-dimensional (3D) prominence reconstruction and study its evolution. We employed the tie-pointing technique to reconstruct the 3D shape and trajectory of the prominence, which has been followed from an heliocentric distance of ~1.3 up to ~2.4 R during the first 1.3 h of eruption. Data show evidence for a progressive clockwise prominence rotation by ~90° occurring not only in the early phase of the eruption sampled by EUVI, but also at larger heliocentric distances as seen by COR1. Interestingly, a counter-clockwise rotation of the filament was observed in Hα images in the week before the eruption; the filament does not show a twisted shape. In the same period, the potential field extrapolated at different times shows a clockwise rotation of closed lines overlying the filament. This suggests that a magnetic helicity storage occurred not in the filament itself, but in the global magnetic field configuration of the surrounding corona. Moreover, close inspection to the high-resolution EUVI images revealed a small scale helical feature along the erupting prominence. The sense of rotation of this helix agrees with the observed prominence rotation, providing evidence for the conversion of twist into writhe. The observed rotation of an erupting prominence, if representative of the flux rope rotation, may have a strong impact on the definition of geo-effectiveness of CMEs for space weather forecasting purposes.

Two movies are available in electronic form at http://www.aanda.org Title: Solar plasma spectroscopy: achievements and future challenges Authors: Del Zanna, Giulio; Tripathi, Durgesh; Young, Peter Bibcode: 2011A&G....52b..17D Altcode: MEETING REPORT Giulio Del Zanna, Durgesh Tripathi and Peter Young report on a meeting to celebrate the career of Helen Mason - and the development of an important field in solar physics. Title: Hinode extreme-ultraviolet imaging spectrometer observations of a limb active region Authors: O'Dwyer, B.; Del Zanna, G.; Mason, H. E.; Sterling, A. C.; Tripathi, D.; Young, P. R. Bibcode: 2011A&A...525A.137O Altcode:
Aims: We investigate the electron density and temperature structure of a limb active region.
Methods: We have carried out a study of an active region close to the solar limb using observations from the Extreme-ultraviolet Imaging Spectrometer (EIS) and the X-ray telescope (XRT) on board Hinode. The electron density and temperature distributions of the coronal emission have been determined using emission line intensity ratios. Differential emission measure (DEM) analysis and the emission measure (EM) loci technique were used to examine the thermal structure of the emitting plasma as a function of distance from the limb.
Results: The highest temperature and electron density values are found to be located in the core of the active region, with a peak electron number density value of 1.9 × 1010 cm-3 measured using the Fe XII 186.887 Å to 192.394 Å line intensity ratio. The plasma along the line of sight in the active region was found to be multi-thermal at different distances from the limb. The EIS and XRT DEM analyses appear to be in agreement in the temperature interval from log T = 6.5-6.7.
Conclusions: Our results provide new constraints for models of coronal heating in active regions. Title: Three-dimensional morphology of a coronal prominence cavity Authors: Gibson, S. E.; Kucera, T. A.; Rastawicki, D.; Dove, J.; de Toma, G.; Hao, J.; Hill, S. M.; Hudson, H. S.; Marque, C.; McIntosh, P. S.; Rachmeler, L.; Reeves, K. K.; Schmieder, B.; Schmit, D. J.; Sterling, A.; Tripathi, D.; Williams, D. R.; Zhang, M. Bibcode: 2010AGUFMSH51A1667G Altcode: We present a three-dimensional density model of coronal prominence cavities, and a morphological fit that has been tightly constrained by a uniquely well-observed cavity. Observations were obtained as part of an International Heliophysical Year campaign by instruments from a variety of space- and ground-based observatories, spanning wavelengths from radio to soft-X-ray to integrated white light. From these data it is clear that the prominence cavity is the limb manifestation of a longitudinally-extended polar-crown filament channel, and that the cavity is a region of low density relative to the surrounding corona. As a first step towards quantifying density and temperature from campaign spectroscopic data, we establish the three-dimensional morphology of the cavity. This is critical for taking line-of-sight projection effects into account, since cavities are not localized in the plane of the sky and the corona is optically thin. We have augmented a global coronal streamer model to include a tunnel-like cavity with elliptical cross-section and a Gaussian variation of height along the tunnel length. We have developed a semi-automated routine that fits ellipses to cross-sections of the cavity as it rotates past the solar limb, and have applied it to Extreme Ultraviolet Imager (EUVI) observations from the two Solar Terrestrial Relations Observatory (STEREO) spacecraft. This defines the morphological parameters of our model, from which we reproduce forward-modeled cavity observables. We find that cavity morphology and orientation, in combination with the viewpoints of the observing spacecraft, explains the observed variation in cavity visibility for the east vs. west limbs. Title: Three-dimensional Morphology of a Coronal Prominence Cavity Authors: Gibson, S. E.; Kucera, T. A.; Rastawicki, D.; Dove, J.; de Toma, G.; Hao, J.; Hill, S.; Hudson, H. S.; Marqué, C.; McIntosh, P. S.; Rachmeler, L.; Reeves, K. K.; Schmieder, B.; Schmit, D. J.; Seaton, D. B.; Sterling, A. C.; Tripathi, D.; Williams, D. R.; Zhang, M. Bibcode: 2010ApJ...724.1133G Altcode: We present a three-dimensional density model of coronal prominence cavities, and a morphological fit that has been tightly constrained by a uniquely well-observed cavity. Observations were obtained as part of an International Heliophysical Year campaign by instruments from a variety of space- and ground-based observatories, spanning wavelengths from radio to soft X-ray to integrated white light. From these data it is clear that the prominence cavity is the limb manifestation of a longitudinally extended polar-crown filament channel, and that the cavity is a region of low density relative to the surrounding corona. As a first step toward quantifying density and temperature from campaign spectroscopic data, we establish the three-dimensional morphology of the cavity. This is critical for taking line-of-sight projection effects into account, since cavities are not localized in the plane of the sky and the corona is optically thin. We have augmented a global coronal streamer model to include a tunnel-like cavity with elliptical cross-section and a Gaussian variation of height along the tunnel length. We have developed a semi-automated routine that fits ellipses to cross-sections of the cavity as it rotates past the solar limb, and have applied it to Extreme Ultraviolet Imager observations from the two Solar Terrestrial Relations Observatory spacecraft. This defines the morphological parameters of our model, from which we reproduce forward-modeled cavity observables. We find that cavity morphology and orientation, in combination with the viewpoints of the observing spacecraft, explain the observed variation in cavity visibility for the east versus west limbs. Title: Science Objectives for an X-Ray Microcalorimeter Observing the Sun Authors: Laming, J. Martin; Adams, J.; Alexander, D.; Aschwanden, M; Bailey, C.; Bandler, S.; Bookbinder, J.; Bradshaw, S.; Brickhouse, N.; Chervenak, J.; Christe, S.; Cirtain, J.; Cranmer, S.; Deiker, S.; DeLuca, E.; Del Zanna, G.; Dennis, B.; Doschek, G.; Eckart, M.; Fludra, A.; Finkbeiner, F.; Grigis, P.; Harrison, R.; Ji, L.; Kankelborg, C.; Kashyap, V.; Kelly, D.; Kelley, R.; Kilbourne, C.; Klimchuk, J.; Ko, Y. -K.; Landi, E.; Linton, M.; Longcope, D.; Lukin, V.; Mariska, J.; Martinez-Galarce, D.; Mason, H.; McKenzie, D.; Osten, R.; Peres, G.; Pevtsov, A.; Porter, K. Phillips F. S.; Rabin, D.; Rakowski, C.; Raymond, J.; Reale, F.; Reeves, K.; Sadleir, J.; Savin, D.; Schmelz, J.; Smith, R. K.; Smith, S.; Stern, R.; Sylwester, J.; Tripathi, D.; Ugarte-Urra, I.; Young, P.; Warren, H.; Wood, B. Bibcode: 2010arXiv1011.4052L Altcode: We present the science case for a broadband X-ray imager with high-resolution spectroscopy, including simulations of X-ray spectral diagnostics of both active regions and solar flares. This is part of a trilogy of white papers discussing science, instrument (Bandler et al. 2010), and missions (Bookbinder et al. 2010) to exploit major advances recently made in transition-edge sensor (TES) detector technology that enable resolution better than 2 eV in an array that can handle high count rates. Combined with a modest X-ray mirror, this instrument would combine arcsecondscale imaging with high-resolution spectra over a field of view sufficiently large for the study of active regions and flares, enabling a wide range of studies such as the detection of microheating in active regions, ion-resolved velocity flows, and the presence of non-thermal electrons in hot plasmas. It would also enable more direct comparisons between solar and stellar soft X-ray spectra, a waveband in which (unusually) we currently have much better stellar data than we do of the Sun. Title: Evidence of Impulsive Heating in Active Region Core Loops Authors: Tripathi, Durgesh; Mason, Helen E.; Klimchuk, James A. Bibcode: 2010ApJ...723..713T Altcode: 2010arXiv1009.0663T Using a full spectral scan of an active region from the Extreme-Ultraviolet Imaging Spectrometer (EIS) we have obtained emission measure EM(T) distributions in two different moss regions within the same active region. We have compared these with theoretical transition region EMs derived for three limiting cases, namely, static equilibrium, strong condensation, and strong evaporation from Klimchuk et al. The EM distributions in both the moss regions are strikingly similar and show a monotonically increasing trend from log T[K] = 5.15-6.3. Using photospheric abundances, we obtain a consistent EM distribution for all ions. Comparing the observed and theoretical EM distributions, we find that the observed EM distribution is best explained by the strong condensation case (EMcon), suggesting that a downward enthalpy flux plays an important and possibly dominant role in powering the transition region moss emission. The downflows could be due to unresolved coronal plasma that is cooling and draining after having been impulsively heated. This supports the idea that the hot loops (with temperatures of 3-5 MK) seen in the core of active regions are heated by nanoflares. Title: SDO/AIA response to coronal hole, quiet Sun, active region, and flare plasma Authors: O'Dwyer, B.; Del Zanna, G.; Mason, H. E.; Weber, M. A.; Tripathi, D. Bibcode: 2010A&A...521A..21O Altcode:
Aims: We examine the contribution of spectral lines and continuum emission to the EUV channels of the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) in different regions of the solar atmosphere.
Methods: Synthetic spectra were obtained using the CHIANTI atomic database and sample differential emission measures for coronal hole, quiet Sun, active region and flare plasma. These synthetic spectra were convolved with the effective area of each channel, in order to determine the dominant contribution in different regions of the solar atmosphere.
Results: We highlight the contribution of particular spectral lines which under certain conditions can affect the interpretation of SDO/AIA data. Title: Active region moss. Basic physical parameters and their temporal variation Authors: Tripathi, D.; Mason, H. E.; Del Zanna, G.; Young, P. R. Bibcode: 2010A&A...518A..42T Altcode: 2010arXiv1005.2220T Context. Active region moss are transition region phenomena, first noted in the images recorded by the Transition Region and Coronal Explorer (TRACE) in λ171. Moss regions are thought to be the footpoints of hot loops (3-5 MK) seen in the core of active regions. These hot loops appear “fuzzy” (unresolved). Therefore, it is difficult to study the physical plasma parameters in individual hot core loops and hence their heating mechanisms. Moss regions provide an excellent opportunity to study the physics of hot loops. In addition, they allow us to study the transition region dynamics in the footpoint regions.
Aims: To derive the physical plasma parameters such as temperature, electron density, and filling factors in moss regions and to study their variation over a short (an hour) and a long time period (5 consecutive days).
Methods: Primarily, we have analyzed spectroscopic observations recorded by the Extreme-ultraviolet Imaging Spectrometer (EIS) aboard Hinode. In addition we have used supplementary observations taken from TRACE and the X-Ray Telescope (XRT) aboard Hinode.
Results: The moss emission is strongest in the Fe XII and Fe XIII lines. Based on analyses using line ratios and emission measure we found that moss regions have a characteristic temperature of log T[K] = 6.2. The temperature structure in moss region remains almost identical from one region to another and it does not change with time. The electron densities measured at different locations in the moss regions using Fe XII ratios are about 1-3 × 1010 cm-3 and about 2-4 × 109 cm-3 using Fe XIII and Fe XIV. The densities in the moss regions are similar in different places and show very little variation over short and long time scales. The derived electron density substantially increased (by a factor of about 3-4 or even more in some cases) when a background subtraction was performed. The filling factor of the moss plasma can vary between 0.1-1 and the path length along which the emission originates is from a few 100 to a few 1000 kms long. By combining the observations recorded by TRACE, EIS and XRT, we find that the moss regions correspond to the footpoints of both hot and warm loops. Title: Thermal Properties of Coronal Cavities as Observed by the X-Ray Telescope on Hinode Authors: Reeves, Kathy; Gibson, S. E.; Kucera, T. A.; Hudson, H. S.; Tripathi, D. Bibcode: 2010AAS...21640511R Altcode: 2010BAAS...41..891R Coronal cavities are voids in coronal emission often observed above high latitude filament channels. Sometimes, these cavities have areas of bright X-ray emission in their centers (i.e. Hudson et al

1999). In this study, we use data from the X-ray Telescope (XRT) on Hinode to examine the thermal emission properties of two kinds of coronal cavities, those with and without enhanced emission at their centers. For cavities with bright X-ray emission in their centers, we find evidence for elevated temperatures in the cavity center. We find no obvious correlation between the presence of

bright cavity cores and filament presence or eruption.

This work is part of the effort of the International Space Science Institute International Team on Prominence Cavities Title: Relationship Between Earth-Directed Solar Eruptions and Magnetic Clouds at 1 AU: A Brief Review Authors: Yurchyshyn, Vasyl; Tripathi, Durgesh Bibcode: 2010aogs...21...51Y Altcode: 2009arXiv0904.2366Y We review relationships between coronal mass ejections (CMEs), EIT post eruption arcades, and the coronal neutral line associated with global magnetic field and magnetic clouds near the Earth. Our previous findings indicate that the orientation of a halo CME elongation may correspond to the orientation of the underlying flux rope. Here we revisit these preliminary reports by comparing orientation angles of elongated LASCO CMEs, both full and partial halos, to the post eruption arcades. Based on 100 analysed events, it was found that the overwhelming majority of halo CMEs are elongated in the direction of the axial field of the post eruption arcades. Moreover, this conclusion also holds for partial halo CMEs as well as for events that originate further from the disk center. This suggests that the projection effect does not drastically change the appearance of full and partial halos and their images still bear reliable information about the underlying magnetic fields. We also compared orientations of the erupted fields near the Sun and in the interplanetary space and found that the local tilt of the coronal neutral line at 2.5 solar radii is well correlated with the magnetic cloud axis measured near the Earth. We suggest that the heliospheric magnetic fields significantly affect the propagating ejecta. Sometimes, the ejecta may even rotate so that its axis locally aligns itself with the heliospheric current sheet. Title: Geometric Model of a Coronal Cavity Authors: Kucera, Therese A.; Gibson, S. E.; Rastawicki, D.; Dove, J.; de Toma, G.; Hao, J.; Hudson, H. S.; Marque, C.; McIntosh, P. S.; Reeves, K. K.; Schmidt, D. J.; Sterling, A. C.; Tripathi, D. K.; Williams, D. R.; Zhang, M. Bibcode: 2010AAS...21640510K Altcode: 2010BAAS...41..890K We observed a coronal cavity from August 8-18 2007 during a multi-instrument observing campaign organized under the auspices of the International Heliophysical Year (IHY). Here we present initial efforts to model the cavity with a geometrical streamer-cavity model. The model is based the white-light streamer model of Gibson et al. (2003), which has been enhanced by the addition of a cavity and the capability to model EUV and X-ray emission. The cavity is modeled with an elliptical cross-section and Gaussian fall-off in length and width inside the streamer. Density and temperature can be varied in the streamer and cavity and constrained via comparison with data. Although this model is purely morphological, it allows for three-dimensional, multi-temperature analysis and characterization of the data, which can then provide constraints for future physical modeling. Initial comparisons to STEREO/EUVI images of the cavity and streamer show that the model can provide a good fit to the data. This work is part of the effort of the International Space Science Institute International Team on Prominence Cavities. Title: Diagnostics of Active Region Loops Observed with Hinode/EIS Authors: Tripathi, D.; Mason, H. E.; Dwivedi, B. N.; Del Zanna, G. Bibcode: 2009ASPC..415..260T Altcode: The Extreme Ultraviolet Imaging Spectrometer (EIS) on board Hinode provides us with an excellent opportunity to study the physical parameters in spatially resolved coronal structures. In this paper we have carried out a study of active region loops using observations from the EIS. The active region was observed on 2007 Ma 19 using the 1 arcsec slit of EIS. At coronal temperatures, we find that electron densities measured from Fe XII and Si X line ratios decrease along the loop length, being ≈10100 cm-3 at foot point and ≈108.5 cm-3 at a height of about 75 Mm. However, the electron densities measured from the Mg VII line ratios (at a transition region temperature) show significantly lower values at the foot point. The electron temperature along the loop increases with height from ≈0.8 MK (at foot point) to ≈1.5 MK (at a height of 75 Mm). The temperature diagnostics using EM-loci at different locations along the loop show that the loop is ``nearly isothermal'' or ``mildly multi-thermal'' along the LOS. These measurements provide important constraints on the theoretical modelling of coronal loops. Title: Large Amplitude Oscillations in Prominences Authors: Tripathi, D.; Isobe, H.; Jain, R. Bibcode: 2009SSRv..149..283T Altcode: 2009arXiv0910.4059T Since the first reports of oscillations in prominences in the 1930s, there have been major theoretical and observational developments to understand the nature of these oscillatory phenomena, leading to the whole new field of the so-called “prominence seismology”. There are two types of oscillatory phenomena observed in prominences; “small-amplitude oscillations” (2-3 km s-1), which are quite common, and “large-amplitude oscillations” (>20 km s-1) for which observations are scarce. Large-amplitude oscillations have been found as “winking filament” in H α as well as motion in the plane-of-sky in H α, EUV, micro-wave and He 10830 observations. Historically, it has been suggested that the large-amplitude oscillations in prominences were triggered by disturbances such as fast-mode MHD waves (Moreton wave) produced by remote flares. Recent observations show, in addition, that near-by flares or jets can also create such large-amplitude oscillations in prominences. Large-amplitude oscillations, which are observed both in transverse as well as longitudinal direction, have a range of periods varying from tens of minutes to a few hours. Using the observed period of oscillation and simple theoretical models, the obtained magnetic field in prominences has shown quite a good agreement with directly measured one and, therefore, justifies prominence seismology as a powerful diagnostic tool. On rare occasions, when the large-amplitude oscillations have been observed before or during the eruption, the oscillations may be applied to diagnose the stability and the eruption mechanism. Here we review the recent developments and understanding in the observational properties of large-amplitude oscillations and their trigger mechanisms and stability in the context of prominence seismology. Title: Rotation of White-light Coronal Mass Ejection Structures as Inferred from LASCO Coronagraph Authors: Yurchyshyn, Vasyl; Abramenko, Valentyna; Tripathi, Durgesh Bibcode: 2009ApJ...705..426Y Altcode: Understanding the connection between the magnetic configurations of a coronal mass ejection (CME) and their counterpart in the interplanetary medium is very important in terms of space weather predictions. Our previous findings indicate that the orientation of a halo CME elongation may correspond to the orientation of the underlying flux rope. Here we further explore these preliminary results by comparing orientation angles of elongated LASCO CMEs, both full and partial halos, to the EUV Imaging Telescope post-eruption arcades (PEAs). By analyzing a sample of 100 events, we found that the overwhelming majority of CMEs are elongated in the direction of the axial field of PEAs. During their evolution, CMEs appear to rotate by about 10° for most of the events (70%) with about 30°-50° for some events, and the corresponding time profiles display regular and gradual changes. It seems that there is a slight preference for the CMEs to rotate toward the solar equator and heliospheric current sheet (59% of the cases). We suggest that the rotation of the ejecta may be due to the presence of a heliospheric magnetic field, and it could shed light on the problems related to connecting solar surface phenomena to their interplanetary counterparts. Title: Large-Scale Flows in Prominence Cavities Authors: Schmit, D. J.; Gibson, S. E.; Tomczyk, S.; Reeves, K. K.; Sterling, Alphonse C.; Brooks, D. H.; Williams, D. R.; Tripathi, D. Bibcode: 2009ApJ...700L..96S Altcode: Regions of rarefied density often form cavities above quiescent prominences. We observed two different cavities with the Coronal Multichannel Polarimeter on 2005 April 21 and with Hinode/EIS on 2008 November 8. Inside both of these cavities, we find coherent velocity structures based on spectral Doppler shifts. These flows have speeds of 5-10 km s-1, occur over length scales of tens of megameters, and persist for at least 1 hr. Flows in cavities are an example of the nonstatic nature of quiescent structures in the solar atmosphere. Title: Temperature Tomography of a Coronal Sigmoid Supporting the Gradual Formation of a Flux Rope Authors: Tripathi, Durgesh; Kliem, Bernhard; Mason, Helen E.; Young, Peter R.; Green, Lucie M. Bibcode: 2009ApJ...698L..27T Altcode: 2009arXiv0904.4782T Multiwavelength observations of a sigmoidal (S-shaped) solar coronal source by the EUV Imaging Spectrometer and the X-Ray Telescope aboard the Hinode spacecraft and by the EUV Imager aboard STEREO are reported. The data reveal the coexistence of a pair of J-shaped hot arcs at temperatures T>2 MK with an S-shaped structure at somewhat lower temperatures (T ≈ 1-1.3 MK). The middle section of the S-shaped structure runs along the polarity inversion line of the photospheric field, bridging the gap between the arcs. Flux cancellation occurs at the same location in the photosphere. The sigmoid forms in the gradual decay phase of the active region, which does not experience an eruption. These findings correspond to the expected signatures of a flux rope forming, or being augmented, gradually by a topology transformation inside a magnetic arcade. In such a transformation, the plasma on newly formed helical field lines in the outer flux shell of the rope (S-shaped in projection) is expected to enter a cooling phase once the reconnection of their parent field line pairs (double-J shaped in projection) is complete. Thus, the data support the conjecture that flux ropes can exist in the corona prior to eruptive activity. Title: Active Region Loops: Hinode/Extreme-Ultraviolet Imaging Spectrometer Observations Authors: Tripathi, Durgesh; Mason, Helen E.; Dwivedi, Bhola N.; del Zanna, Giulio; Young, Peter R. Bibcode: 2009ApJ...694.1256T Altcode: 2009arXiv0901.0095T We have carried out a study of active region loops using observations from the Extreme-ultraviolet Imaging Spectrometer (EIS) on board Hinode using 1'' raster data for an active region observed on 2007 May 19. We find that active region structures which are clearly discernible in cooler lines (≈1 MK) become "fuzzy" at higher temperatures (≈2 MK). The active region was comprised of redshifted emissions (downflows) in the core and blueshifted emissions (upflows) at the boundary. The flow velocities estimated in the two regions located near the footpoints of coronal loop showed redshifted emission at transition region temperature and blueshifted emission at coronal temperature. The upflow speed in these regions increased with temperature. For more detailed study we selected one particular well-defined loop. Downward flows are detected along the coronal loop, being stronger in lower-temperature lines (rising up to 60 km s-1 near the footpoint). The downflow was localized toward the footpoint in transition region lines (Si VII) and toward the loop top in high-temperature line (Fe XV). By carefully accounting for the background emission we found that the loop structure was close to isothermal for each position along the loop, with the temperature rising from around 0.8 MK to 1.5 MK from the close to the base to higher up toward the apex (≈75 Mm). We derived electron density using well-established line ratio diagnostic techniques. Electron densities along the active region loop were found to vary from 1010 cm-3 close to the footpoint to 108.5 cm-3 higher up. A lower electron density, varying from 109 cm-3 close to the footpoint to 108.5 cm-3 higher up, was found for the lower temperature density diagnostic. Using these densities we derived filling factors in along the coronal loop which can be as low as 0.02 near the base of the loop. The filling factor increased with projected height of the loop. These results provide important constraints on coronal loop modeling. Title: Partially-erupting prominences: a comparison between observations and model-predicted observables Authors: Tripathi, D.; Gibson, S. E.; Qiu, J.; Fletcher, L.; Liu, R.; Gilbert, H.; Mason, H. E. Bibcode: 2009A&A...498..295T Altcode: 2009arXiv0902.1228T Aims: We investigate several partially-erupting prominences to study their relationship with other CME-associated phenomena and compare these observations with observables predicted by a model of partially-expelled-flux-ropes (Gibson & Fan 2006a, ApJ, 637, L65; 2006b, J. Geophys. Res., 111, 12103).
Methods: We studied 6 selected events with partially-erupting prominences using multi-wavelength observations recorded by the Extreme-ultraviolet Imaging Telescope (EIT), Transition Region and Coronal Explorer (TRACE), Mauna Loa Solar Observatory (MLSO), Big Bear Solar Observatory (BBSO), and Soft X-ray Telescope (SXT). The observational features associated with partially-erupting prominences were then compared with the predicted observables from the model.
Results: The partially-expelled-flux-rope (PEFR) model can explain the partial eruption of these prominences, and in addition predicts a variety of other CME-related observables that provide evidence of internal reconnection during eruption. We find that all of the partially-erupting prominences studied in this paper exhibit indirect evidence of internal reconnection. Moreover, all cases showed evidence of at least one observable unique to the PEFR model, e.g., dimmings external to the source region and/or a soft X-ray cusp overlying a reformed sigmoid.
Conclusions: The PEFR model provides a plausible mechanism to explain the observed evolution of partially-erupting-prominence-associated CMEs in our study. Title: Chapter 7: Active Region Diagnostics Authors: Mason, H. E.; Tripathi, D. Bibcode: 2008psa..book..127M Altcode: Active regions present us with complex and dynamic structures, which look relatively simple, but are in fact very difficult to model and explain. An active region is a region on the Sun where the magnetic field breaks through the surface (photosphere and chromosphere) to form giant arches of hot plasma. The magnetic field is stronger than in surrounding regions and the plasma is hotter, so emits strongly in UV and X-ray radiation. Figures 7.1 and 7.2 show UV images of the Sun taken with the Transition Region and Coronal Explorer (TRACE) spacecraft and the Extreme Ultraviolet Imaging Telescope (EIT) aboard the Solar and Heliospheric Observatory (SOHO) spacecraft. The hot plasma (around a million degree) traces out the magnetic field structures... Title: Active Region Microflares From Hinode and RHESSI Authors: Chifor, C.; Hannah, I. G.; Mason, H. E.; Isobe, H.; Yokoyama, T.; Young, P. R.; Tripathi, D. Bibcode: 2008ASPC..397..164C Altcode: We are studying microflares (A, B-C class flares) in active regions using coordinated observations from Hinode and RHESSI. Hinode/EIS has unprecedented diagnostic power for small, transient activity in the solar corona, providing temperature, density, and velocity information. For this purpose, we designed and ran an EIS observing sequence to provide high-cadence data at both transition region and coronal temperatures. A preliminary analysis of these observations is reported, with one data set given as an example. Title: Source Region Evolution of the Solar Wind Disappearance Event of 11 May 1999 Authors: Janardhan, P.; Tripathi, D.; Mason, H. E. Bibcode: 2008ESPM...122.118J Altcode: A recent, detailed study of the well known "solar wind disappearance event" of 11 May 1999 traced its origin to a coronal hole lying adjacent to a large active region, AR8525

in Carrington rotation 1949. The active region was located at central meridian on 05 May 1999 when the flows responsible for this event began. In this paper we examine the evolution of the active region-coronal hole complex during 5-6 May 1999 to study the changes that apparently played a key role in causing this disappearance event. To study the evolution of the solar source region of the disappearance event of 11 May 1999 we have used images from the Soft X-ray Telescope (SXT), the Extreme-ultraviolet Imaging Telescope (EIT) and the Michelson Doppler Imager (MDI) to examine the evolution of the coronal hole and active region complex at the source region of the disappearance event. We find a dynamic evolution taking place in the coronal hole-active region boundary at the source region of the disappearance event of 11 May 1999. Based on the combined observations it appears that the rapid evolution seen in the coronal hole is due to reconnection's taking place between the newly emerging flux and the open field regions from the coronal hole and the active region-coronal hole boundary regions. This evolution, which is found to reduce the area of the coronal hole, is accompanied by the formation of new loops in EUV images which are spatially and temporally correlated with emerging flux regions as seen in MDI data.

As opposed to the well known drivers of space weather phenomena like CME's or large flares, disappearance events are not associated with explosive solar phenomena. However, they do produce other observable effects that are not fully understood. In the period leading up to the disappearance event of 11 May 1999, our observations, during quiet solar conditions and in the absence of CMEs, provide the first clear evidence for Sun-Earth connection originating from an evolving active region-coronal hole region located at central meridian. With the exception of corotating interacting regions, these observations provide the first link between the Sun and space weather effects at 1 AU, arising from non-explosive solar events. Title: Density Structure in Active Regions from Hinode/EIS Authors: Tripathi, D.; Mason, H. E.; Young, P. R.; Chifor, C.; Del Zanna, G. Bibcode: 2008ASPC..397...45T Altcode: The Extreme-ultraviolet Imaging Spectrometer (EIS) on board Hinode provides an excellent opportunity to study the physical plasma parameters in spatially resolved coronal features. In this paper we present the density structure in an active region at many different temperatures. The active region was rastered on May 01, 2007 with the 2^{''} slit. We find that the electron density is highest in the core of the active region where it exceeds log_{10} N_e = 10.5. Title: The Filament-Moreton Wave Interaction of 2006 December 6 Authors: Gilbert, Holly R.; Daou, Antoun G.; Young, Daniel; Tripathi, Durgesh; Alexander, David Bibcode: 2008ApJ...685..629G Altcode: We utilize chromospheric observations obtained at MLSO of the 2006 December 6 Moreton wave, which exhibits two distinct fronts, and subsequent filament activation to conduct a comprehensive analysis of the wave-filament interaction. By determining the period, amplitude, and evolution of the oscillations in the activated filament, we make certain inferences regarding the physical properties of both the wave and the filament. The large-amplitude oscillations induced in the filament by the wave passage last on the order of 180 minutes and demonstrate a complicated mixture of transverse and perpendicular motion with respect to the filament spine. These oscillations are predominantly along the filament axis, with a period of ~29 minutes and maximum line-of-sight velocity amplitude of ~41 km s-1. A careful examination of the complex oscillatory response of the filament elucidates some of the fundamental characteristics of the related Moreton wave. Specifically, we infer the maximum total kinetic energy involved in the interaction, the structure and topology of the passing wave, and discuss implications for the topology of the responding magnetic structure supporting the filament. The results of this observational study equip us with a better understanding of how filaments become activated and the nature of their responses to large propagating disturbances. Title: The solar wind disappearance event of 11 May 1999: source region evolution Authors: Janardhan, P.; Tripathi, D.; Mason, H. E. Bibcode: 2008A&A...488L...1J Altcode: 2008arXiv0807.2697J Context: A recent, detailed study of the well-known “solar wind disappearance event” of 11 May 1999 traced its origin to a coronal hole (CH) lying adjacent to a large active region (AR), AR8525 in Carrington rotation 1949. The AR was located at central meridian on 05 May 1999 when the flows responsible for this event began. We examine the evolution of the AR-CH complex during 5-6 May 1999 to study the changes that apparently played a key role in causing this disappearance event.
Aims: To study the evolution of the solar source region of the disappearance event of 11 May 1999.
Methods: Using images from the Soft X-ray Telescope (SXT), the Extreme-ultraviolet Imaging Telescope (EIT) and the Michelson Doppler Imager (MDI) to examine the evolution of the CH and AR complex at the source region of the disappearance event.
Results: We find a dynamic evolution taking place in the CH-AR boundary at the source region of the disappearance event of 11 May 1999. This evolution, which is found to reduce the area of the CH, is accompanied by the formation of new loops in EUV images that are spatially-and-temporally correlated with emerging flux regions as seen in MDI data.
Conclusions: In the period leading up to the disappearance event of 11 May 1999, our observations, during quiet solar conditions and in the absence of CMEs, provide the first clear evidence for Sun-Earth connection originating from an evolving AR-CH region located at central meridian. With the exception of corotating interacting regions (CIR), these observations provide the first link between the Sun and space weather effects at 1 AU, arising from non-explosive solar events.

2 movies are only available in electronic form at http://www.aanda.org Title: Prominence Seismology: Wavelet Analysis of Filament Oscillations Authors: Pintér, Balázs; Jain, Rekha; Tripathi, Durgesh; Isobe, Hiroaki Bibcode: 2008ApJ...680.1560P Altcode: The temporal and spatial behavior of a large-amplitude filament oscillation is investigated using wavelet analysis. The extreme-ultraviolet (EUV) images of the phenomenon, which occurred on 2002 October 15, were taken from the EUV Imaging Telescope on board the Solar and Heliospheric Observatory (SOHO). The wavelet spectra, extracted from the intensity data, show that the filament oscillates as a rigid body, with a period of about 2.5-2.6 hr which is almost constant along the filament. The period slowly decreases with time until the filament erupts. No clear sign of the eruption is found in the wavelet spectrum prior to the eruption, that followed the filament oscillation. The axial component of the magnetic field is estimated between 1 and 5 G, which is believed to be reasonable for a polar crown filament of this kind. Title: Statistical Study of Orientations of Coronal Mass Ejections and EIT Flare Arcades Authors: Yurchyshyn, V.; Tripathi, D. Bibcode: 2008AGUSMSH43A..01Y Altcode: Coronal mass ejections (CMEs) and their interplanetary counterparts, interplanetary CMEs (ICMEs) usually exhibit a complex structure that very often includes a magnetic cloud (MC), which is thought to be a magnetic fluxrope. Our recent study indicates the orientation of a halo CME elongation may correspond to the orientation of the underlying flux rope. This is a continuation of the research and here we compare orientation angles of elongated LASCO CMEs, both halo and partial to the EIT post eruption arcades (PEA). Data for 100 events had been analyzed and er report the following: i) it is further supported that majority of halo CMEs are elongated in the direction of the aixial field of PEA arcades. This relationship is found to be weeker for partial CME and those events that originate further from the disk center. There also is an indication that events in the northern hemisphere generally exhibit better correlation that those in the southern hemisphere. Title: Multi-wavelength Comparison of Prominence Cavities Authors: Schmit, D. J.; Gibson, S.; de Toma, G.; Reeves, K.; Tripathi, D.; Kucera, T.; Marque, C.; Tomczyk, S. Bibcode: 2008AGUSMSP43B..04S Altcode: Recent observational campaigns have brought together a wealth of data specifically designed to explore the physical properties and dynamics of prominence cavities. In particular, STEREO and Hinode data have provided new perspectives on these structures. In order to effectively analyze the data in a cohesive manner, we produce overlays of several distinct and complimentary datasets including SOHO UVCS, CDS, and EIT, Hinode SOT and EIS, STEREO SECCHI, TRACE, and Nancay Radioheliograph data as well as new observations of coronal magnetic fields in cavities from the Coronal Multichannel Polarimeter. We are thus able to investigate how sensitive morphology is to the wavelength observed which details the nature of the plasma in the cavity. Title: Density structure of an active region and associated moss using Hinode/EIS Authors: Tripathi, D.; Mason, H. E.; Young, P. R.; Del Zanna, G. Bibcode: 2008A&A...481L..53T Altcode: 2008arXiv0802.3311T Context: Studying the problem of active region heating requires precise measurements of physical plasma parameters such as electron density, temperature, etc. It is also important to understand the relationship of coronal structures with the magnetic field. The Extreme-ultraviolet Imaging Spectrometer (EIS) aboard Hinode provides a rare opportunity to derive electron density simultaneously at different temperatures.
Aims: We study the density structure and characterise plasma in active regions and associated moss regions. In addition, we study its relationship to the photospheric magnetic field.
Methods: We used data recorded by the EIS, together with magnetic field measurements from the Michelson Doppler Imager (MDI) aboard SoHO and images recorded with the Transition Region And Coronal Explorer (TRACE) and X-Ray Telescope (XRT/Hinode).
Results: We find that the hot core of the active region is densest with values as high as 1010.5 cm-3. The electron density estimated in specific regions in the active region moss decreases with increasing temperature. The moss areas were located primarily on one side of the active region, and they map the positive polarity regions almost exactly. The density within the moss region was highest at log T=5.8{-}6.1, with a value around 1010.0{-10.5} cm-3. The moss densities were highest in the strong positive magnetic field region. However, there was no such correlation for the negative polarity areas, where there was a large sunspot. Title: An active region jet observed with Hinode Authors: Chifor, C.; Young, P. R.; Isobe, H.; Mason, H. E.; Tripathi, D.; Hara, H.; Yokoyama, T. Bibcode: 2008A&A...481L..57C Altcode: Aims:We study the physical properties of an active region (AR) jet in order to probe the mechanisms responsible for it.
Methods: We report 2007 January 15/16 observations of a recurring jet situated on the west side of NOAA AR 10938. Multi-wavelength data from all three instruments onboard Hinode were analysed. This paper focuses on one instance of a jet observed with the Hinode/EUV Imaging Spectrometer (EIS). Using EIS raster data we measured the temperatures, Doppler shifts, density, and filling factor.
Results: A strong blue-shifted component and an indication of a weak red-shifted component at the base of the jet was observed around Log Te = 6.2. The up-flow velocities exceeded 150 km s-1. The jet component was seen over a range of temperatures between 5.4 and 6.4 in Log T_e. Using Fe XII λ186 and λ195 line ratios, we measured densities above Log Ne = 11 for the high-velocity up-flow component. We found that the density of the high-velocity up-flow increases with velocity. We estimate the filling factor in the jet up-flow to be <0.03. With the Hinode/Solar Optical Telescope (SOT), we observed recurrent (quasi periodic) magnetic flux cancelations just before the recurrent jet emission was seen in images taken with the X-ray Telescope (XRT).
Conclusions: The high-velocity up-flows, together with the density dependence on velocity, support an evaporation scenario for the acceleration of this jet. The high density and small filling factor, coupled with the high Doppler velocities are strongly suggestive of multiple small-scale magnetic reconnection events being responsible for the production of both EUV and X-ray jets. Title: Relationship Between CME-Associated Waves Observed on 5 March 2000 Authors: Raouafi, N. -E.; Tripathi, D. Bibcode: 2008ASPC..383..421R Altcode: 2008arXiv0801.0766R We study the relationship between different wave phenomena associated with a coronal mass ejection (CME) observed on 05 Mar. 2000. EIT waves were observed in the images recorded by EIT at 195 Å. The white-light LASCO/C2 images show clear deflection and propagation of a kink along with the CME. Spectroscopic observations recorded by the UVCS reveals excessive line broadening in the two O VI lines (1032 and 1037 Å). Moreover very hot lines such as Si XII and Mg X were observed. Interestingly, the EIT wave, the streamer deflection and the intensity modulation along the slit were all propagating northeast. Spatial and temporal correlations show that the streamer deflection and spectral line broadening are highly likely to be due to a CME-driven shock wave and that the EIT wave is the signature of a CME-driven shock wave in the lower corona. Title: Entropy Maximization, Cutoff Distribution, and Finite Stellar Masses Authors: Dubey, Ritesh Kumar; Menon, V. J.; Pandey, M. K.; Tripathi, D. N. Bibcode: 2008AdAst2008E...3D Altcode: No abstract at ADS Title: Large-Amplitude Oscillation of an Erupting Filament as Seen in EUV, Hα, and Microwave Observations Authors: Isobe, H.; Tripathi, D.; Asai, A.; Jain, R. Bibcode: 2007SoPh..246...89I Altcode: 2007arXiv0711.3952I We present multiwavelength observations of a large-amplitude oscillation of a polar-crown filament on 15 October 2002, which has been reported by Isobe and Tripathi (Astron. Astrophys.449, L17, 2006). The oscillation occurred during the slow rise (≈1 km s−1) of the filament. It completed three cycles before sudden acceleration and eruption. The oscillation and following eruption were clearly seen in observations recorded by the Extreme-Ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO). The oscillation was seen only in a part of the filament, and it appears to be a standing oscillation rather than a propagating wave. The amplitudes of velocity and spatial displacement of the oscillation in the plane of the sky were about 5 km s−1 and 15 000 km, respectively. The period of oscillation was about two hours and did not change significantly during the oscillation. The oscillation was also observed in Hα by the Flare Monitoring Telescope at the Hida Observatory. We determine the three-dimensional motion of the oscillation from the Hα wing images. The maximum line-of-sight velocity was estimated to be a few tens of kilometers per second, although the uncertainty is large owing to the lack of line-profile information. Furthermore, we also identified the spatial displacement of the oscillation in 17-GHz microwave images from Nobeyama Radio Heliograph (NoRH). The filament oscillation seems to be triggered by magnetic reconnection between a filament barb and nearby emerging magnetic flux as was evident from the MDI magnetogram observations. No flare was observed to be associated with the onset of the oscillation. We also discuss possible implications of the oscillation as a diagnostic tool for the eruption mechanisms. We suggest that in the early phase of eruption a part of the filament lost its equilibrium first, while the remaining part was still in an equilibrium and oscillated. Title: On the relationship between coronal waves associated with a CME on 5 March 2000 Authors: Tripathi, D.; Raouafi, N. -E. Bibcode: 2007A&A...473..951T Altcode: Aims:To study the relationship between coronal mass ejection (CME) associated waves.
Methods: Analysis of CME eruption observations on 5 Mar. 2000 recorded by the Large Angle Spectrometric Coronagraph (LASCO), the Ultraviolet Coronagraph Spectrometer (UVCS), and the Extreme-ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO).
Results: Images recorded by the LASCO/C2 show a clear deflection and kink in a streamer located eastward of the CME. The kink in the streamer propagated outwards along with the associated CME. No CME material was seen between the bright front of the CME and the streamer. UVCS spectra show large spectral line broadening, Doppler shifts and intensity changes in the O VI (λ1032 & 1037) lines. Moreover, intensity enhancements in lines such as Si XII λ 520 and Mg X λ 625 forming at very high temperatures (>2 MK; not often observed in the corona) were also observed. EIT images show the propagation of a wave from the CME source region. The speed of the wave was about 55 km s-1 and it propagated predominantly in the North-East direction from the source region. Furthermore, it does not propagate through active regions and coronal holes. The deflection in the streamer recorded in the LASCO/C2 was in the same direction as that of the EIT wave.
Conclusions: Spatial and temporal correlations show that the deflection and the propagation of the kink in the streamer (based on the LASCO data), and plasma heating and spectral line broadening (based on the UVCS data), are basically due to a CME-driven shock wave. The spatial and temporal correlations between the EIT wave and the shock wave provide strong evidence in favor of the interpretation that the EIT waves are indeed the counterpart of CME-driven shock waves in the lower corona. Although, we cannot rule out the possibility that the EIT waves are just a manifestation of the stretching of the field lines due to the outward propagation of the CMEs.

The movie is only available in electronic form at http://www.aanda.org Title: A bright coronal downflow seen in multi-wavelength observations: evidence of a bifurcating flux-rope? Authors: Tripathi, D.; Solanki, S. K.; Mason, H. E.; Webb, D. F. Bibcode: 2007A&A...472..633T Altcode: 2008arXiv0802.3616T Aims:We study the origin and characteristics of a bright coronal downflow seen after a coronal mass ejection associated with erupting prominences on 5 March 2000.
Methods: This study extends that of Tripathi et al. (2006b, A&A, 449, 369) based on the Extreme-ultraviolet Imaging Telescope (EIT), the Soft X-ray Telescope (SXT) and the Large Angle Spectrometric Coronagraph (LASCO) observations. We combined those results with an analysis of the observations taken by the Hα and the Mk4 coronagraphs at the Mauna Loa Solar Observatory (MLSO). The combined data-set spans a broad range of temperature as well as continuous observations from the solar surface out to 30 R.
Results: The downflow started at around 1.6 R and contained both hot and cold gas. The downflow was observed in the Hα and the Mk4 coronagraphs as well as the EIT and the SXT and was approximately co-spatial and co-temporal providing evidence of multi-thermal plasma. The Hα and Mk4 images show cusp-shaped structures close to the location where the downflow started. Mk4 observations reveal that the speed of the downflow in the early phase was substantially higher than the free-fall speed, implying a strong downward acceleration near the height at which the downflow started.
Conclusions: The origin of the downflow was likely to have been magnetic reconnection taking place inside the erupting flux rope that led to its bifurcation.

Movies are available in electronic form at http://www.aanda.org Title: X-ray precursors to flares and filament eruptions Authors: Chifor, C.; Tripathi, D.; Mason, H. E.; Dennis, B. R. Bibcode: 2007A&A...472..967C Altcode: Aims:To study preflare X-ray brightenings as diagnostics of the destabilisation of flare-associated erupting filaments/prominences.
Methods: We combine new observations from the Transition Region and Coronal Explorer (TRACE) and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), as well as revisit events reported in the literature to date, in order to scrutinise the preflare activity during eight flare-associated filament eruptions.
Results: The preflare activity occurs in the form of discrete, localised X-ray brightenings observed between 2 and 50 min before the impulsive phase of the flare and filament acceleration. These transient preflare brightenings are situated on or near (within 10{ arcsec} of) the polarity inversion line (PIL), coincident with emerging and/or canceling magnetic flux. The filaments begin to rise from the location of the preflare brightenings. In five out of eight events, the preflare brightenings were observed beneath the filament channel, close to the filament footpoint first observed to rise. Both thermal and nonthermal hard X-ray emissions during the preflare enhancement were detected with RHESSI, suggesting that both plasma heating and electron acceleration occurred at this time. The main energy release during the impulsive phase of the flare is observed close to (within 50{ arcsec} of) the preflare brightenings. The fast-rise phase of the filament eruption starts at the same time as the onset of the main flare or up to 5 min later.
Conclusions: The preflare brightenings are precursors to the flare and filament eruption. These precursors represent distinct, localised instances of energy release, rather than a gradual energy release prior to the main flare. The X-ray precursors represent clearly observable signatures in the early stages of the eruption. Together with the timing of the filament fast-rise at or after the main flare onset, the X-ray precursors provide evidence for a tether-cutting mechanism initially manifested as localised magnetic reconnection being a common trigger for both flare emission and filament eruption.

Movies and Appendix A are only available in electronic form at http://www.aanda.org Title: Filament Activation Due To A Moreton Wave Observed On Dec. 6, 2006 Authors: Gilbert, Holly; deToma, G.; Tripathi, D. Bibcode: 2007AAS...210.2505G Altcode: 2007BAAS...39..131G Flare generated Moreton waves have been historically observed to activate filaments located at regions far from the flare site, causing them to oscillate (sometimes referred to as “winking”). A recent example of such an activation occurred on December 6, 2006 in which a large flare occurring near the east limb created a dramatic response in a filament located far to the south. We present an analysis of this filament activation using He I (1083 nm) intensity and velocity data taken at the Mauna Loa Solar Observatory (MLSO). The He I (1083 nm) line-of-sight velocity data provide a close examination of the motions and velocities involved in this dynamic filament response. Title: Ellerman Bombs and Jets Associated with Resistive Flux Emergence Authors: Isobe, H.; Tripathi, D.; Archontis, V. Bibcode: 2007ApJ...657L..53I Altcode: Using two-dimensional (2D) magnetohydrodynamic simulations we study the effects of resistive processes in the dynamics of magnetic flux emergence and its relation to Ellerman bombs and other dynamic phenomena in the Sun. The widely accepted scenario of flux emergence is the formation and expansion of Ω-shaped loops due to the Parker instability. Since the Parker instability has the largest growth rate at finite wavelength λp~10H-20H, where H is the scale height (~200 km in the solar photosphere), a number of magnetic loops may rise from the initial flux sheet if it is sufficiently long. This process is shown in our numerical simulations. The multiple emerging loops expand in the atmosphere and interact with each other, leading to magnetic reconnection. At first reconnection occurs in the lower atmosphere, which allows the sinking part of the flux sheet to emerge above the photosphere. This reconnection also causes local heating that may account for Ellerman bombs. In the later stage, reconnection between the expanding loops occurs at higher levels of the atmosphere and creates high-temperature reconnection jets, and eventually a large (>>λp) coronal loop is formed. Cool and dense plasma structures, which are similar to Hα surges, are also formed. This is not because of magnetic reconnection but due to the compression of the plasma in between the expanding loops. Title: Evolution of the photospheric magnetic field in the source regions of coronal mass ejections Authors: Bothmer, V.; Tripathi, D. Bibcode: 2007msfa.conf..257B Altcode: Six coronal mass ejections associated with erupting quiescent filaments on the visible solar disk were identified in data from SoHO (Solar and Heliospheric Observatory) LASCO (Large Angle and Spectrometric Coronagraph), EIT (Extreme ultraviolet Imaging Telescope) and MDI (Michelson Doppler Imager) data and ground-based Hα observations from Big Bear and Meudon observatories. These events were analysed to investigate whether their initiations could be related to changes of the underlying photospheric field. The results show that in five out of the six events, substantial changes in the photospheric magnetic field occurred in the source regions prior and around the CME's lift-off times as identified from emerging/diminishing flux detected by MDI. In one event large magnetic flux changes could be identified not in the source region itself, but in a neighbouring active region. The results demonstrate that new missions, such as STEREO and Hinode (Solar-B) in conjunction with SoHO and ground-based measurements, will provide joint data sets that have the potential to provide new insight into the physical causes of CMEs. Title: EIT and TRACE responses to flare plasma Authors: Tripathi, D.; Del Zanna, G.; Mason, H. E.; Chifor, C. Bibcode: 2006A&A...460L..53T Altcode: 2008arXiv0802.3852T Aims.To understand the contribution of active region and flare plasmas to the λ195 channels of SOHO/EIT (Extreme-ultraviolet Imaging Telescope) and TRACE (Transition Region and Coronal Explorer).
Methods: .We have analysed an M8 flare simultaneously observed by the Coronal Diagnostic Spectrometer (CDS), EIT, TRACE and RHESSI. We obtained synthetic spectra for the flaring region and an outer region using the differential emission measures (DEM) of emitting plasma based on CDS and RHESSI observations and the CHIANTI atomic database. We then predicted the EIT and TRACE count rates.
Results: .For the flaring region, both EIT and TRACE images taken through the λ195 filter are dominated by Fe XXIV (formed at about 20 MK). However, in the outer region, the emission was primarily due to the Fe XII, with substantial contributions from other lines. The average count rate for the outer region was within 25% the observed value for EIT, while for TRACE it was a factor of two higher. For the flare region, the predicted count rate was a factor of two (in case of EIT) and a factor of three (in case of TRACE) higher than the actual count rate.
Conclusions: .During a solar flare, both TRACE and EIT λ195 channels are found to be dominated by Fe XXIV emission. Reasonable agreement between predictions and observations is found, however some discrepancies need to be further investigated. Title: The early phases of a solar prominence eruption and associated flare: a multi-wavelength analysis Authors: Chifor, C.; Mason, H. E.; Tripathi, D.; Isobe, H.; Asai, A. Bibcode: 2006A&A...458..965C Altcode: Aims.We aim to examine the precursor phases and early evolution of a prominence eruption associated with a M4-class flare and a partial halo coronal mass ejection (CME) observed on 2005 July 27. Our main goal is to investigate the precursor eruption signatures observed in EUV, X-ray and microwave emission and their relation to the prominence destabilisation.
Methods: .We perform a multi-wavelength study of the prominence morphology and motion using high-cadence and spatial resolution EUV 171 Å images from the TRACE satellite. The high-temperature flare radiative emission in soft and hard X-rays are analysed through imaging and spectral modeling with RHESSI. Complementary microwave images (17 GHz and 34 GHz) from NoRH are also investigated.
Results: .The activation of the filament proceeds from one anchored footpoint. We observe "pre-eruption" brightenings in X-ray and EUV images, close to the erupting footpoint of the prominence, being temporally correlated to the point when the prominence first enters a slow-rise phase, and then an accelerated fast-rise phase. The brightness temperature (T_b) of the prominence at 34 GHz is increasing during the eruption. We also find very good correlation between the prominence height-time profile and the spatially integrated soft X-ray (SXR) emission.
Conclusions: .We discuss the observed precursor brightenings with respect to possible mechanisms that might be responsible for the prominence destabilisation and acceleration. Our observations suggest that reconnection events localised beneath the erupting footpoint may eventually destabilise the entire prominence, causing the eruption. Title: EUV and Coronagraphic Observations of Coronal Mass Ejections Authors: Tripathi, Durgesh Bibcode: 2006JApA...27..193T Altcode: The Large Angle Spectrometric Coronagraph (LASCO) and Extreme-ultraviolet Imaging Telescope (EIT) onboard Solar and Heliospheric Observatory (SOHO) provide us with unprecedented multiwavelength observations helping us to understand different dynamic phenomena on the Sun and in the corona. In this paper we discuss the association between post-eruptive arcades (PEAs) detected by EIT and white-light coronal mass ejections (CMEs) detected by LASCO/C2 telescope. Title: Multi-Wavelength Investigation of a Sigmoidal Active Region Authors: Tripathi, D.; Mason, H. E.; Young, P. R. Bibcode: 2006ESASP.617E.148T Altcode: 2006soho...17E.148T No abstract at ADS Title: Asymmetric Prominence Eruption: A "Domino Effect"? Authors: Chifor, C.; Mason, H. E.; Tripathi, D.; Isobe, H.; Asai, A. Bibcode: 2006ESASP.617E.121C Altcode: 2006soho...17E.121C No abstract at ADS Title: SOHO Observations of CME-Driven Shock and EIT Waves Authors: Tripathi, D.; Raouafi, N. -E. Bibcode: 2006ESASP.617E.149T Altcode: 2006soho...17E.149T No abstract at ADS Title: On the propagation of brightening after filament/prominence eruptions, as seen by SoHO-EIT Authors: Tripathi, D.; Isobe, H.; Mason, H. E. Bibcode: 2006A&A...453.1111T Altcode: Aims.To study the relationship between the propagation of brightening and erupting filaments/prominences in order to get some insight into the three-dimensional picture of magnetic reconnection.
Methods: .Analysis of the observations taken with the EIT (Extreme-ultraviolet Imaging Telescope) aboard SoHO (Solar and Heliospheric Observatory).
Results: .When the prominences/filaments erupted having one point fixed - asymmetric eruption - the brightening propagated along the neutral line together with the expansion/separation from the polarity inversion line (PIL) as expected from the standard models. However in case of symmetric eruptions, the brightening propagated towards both end points starting at the middle. When the prominence/filament erupted faster then the speed of the propagating brightening was faster and vice-versa.
Conclusions: .Based on these observations we conclude that the eruption and magnetic reconnection - propagation (along the PIL) and separation (away from PIL) of the brightening - are dynamically coupled phenomena. These observations can be explained by a simple extension of the 2D models illustrating eruption and magnetic reconnection to a 3D model. Title: Photospheric Field Evolution in the Source Regions of Coronal Mass Ejections Authors: Bothmer, V.; Tripathi, D. Bibcode: 2006ESASP.617E..20B Altcode: 2006soho...17E..20B No abstract at ADS Title: Stable galaxies of finite masses in the most probable distribution Authors: Menon, V. J.; Dubey, Ritesh Kumar; Tripathi, D. N. Bibcode: 2006PhyA..367..269M Altcode: Conventional equilibrium statistical mechanics of bound gravitational systems is known to suffer from the serious difficulties that galaxies acquire unbounded radii, become infinitely massive, and evaporate away continuously. We point out that these troubles disappear automatically if we use the exact, most probable, distribution having an inherent upper energy cutoff. Title: Observation of a bright coronal downflow by SOHO/EIT Authors: Tripathi, D.; Solanki, S. K.; Schwenn, R.; Bothmer, V.; Mierla, M.; Stenborg, G. Bibcode: 2006A&A...449..369T Altcode: A distinct coronal downflow has been discovered in the course of a prominence eruption associated coronal mass ejection (CME) imaged by EIT (Extreme ultraviolet Imaging Telescope) and LASCO (Large Angle Spectrometric Coronagraph) on board SOHO (Solar and Heliospheric Observatory) on 5-Mar.-2000. Evolution of the prominences seen by EIT was tracked into the LASCO/C2 and C3 field-of-view where they developed as the core of a typical three-part CME. In contrast to the inflow structures reported earlier in the literatures, which were dark and were interpreted as plasma voids moving down, the downflow reported here was bright. The downflow, which was only seen in EIT FOV had an onset time that coincided with the deceleration phase of the core of the CME. The downflow showed a rapid acceleration followed by a strong deceleration. The downflow followed a curved path which may be explained by material following the apex of a contracting magnetic loop sliding down along other field lines, although other explanations are also possible. Irrespective of the detailed geometry, this observation provides support for the pinching off of the field lines drawn-out by the erupting prominences and the contraction of the arcade formed by the reconnection. Title: Large amplitude oscillation of a polar crown filament in the pre-eruption phase Authors: Isobe, H.; Tripathi, D. Bibcode: 2006A&A...449L..17I Altcode: 2006astro.ph..2432I Aims.We report observation of a large-amplitude filament oscillation followed by an eruption. This is used to probe the pre-eruption condition and the trigger mechanism of solar eruptions.Methods.We used the EUV images from the Extreme-Ultraviolet Imaging Telescope on board SOHO satellite and the Hα images from the Flare Monitoring Telescope at Hida Observatory. The observed event is a polar crown filament that erupted on 15 Oct. 2002.Results.The filament clearly exhibited oscillatory motion in the slow-rising, pre-eruption phase. The amplitude of the oscillation was larger than 20 km s-1, and the motion was predominantly horizontal. The period was about 2 h and seemed to increase during the oscillation, indicating weakening of restoring force.Conclusions.Even in the slow-rise phase before the eruption, the filament retained equilibrium and behaved as an oscillator, and the equilibrium is stable to nonlinear perturbation. The transition from such nonlinear stability to either instabilities or a loss of equilibrium that leads to the eruption occurred in the Alfvén time scale (~1 h). This suggests that the onset of the eruption was triggered by a fast magnetic reconnection that destabilized the pre-eruption magnetic configuration, rather than by the slow shearing motion at the photosphere. Title: The Pre-CME Sun Authors: Gopalswamy, N.; Mikić, Z.; Maia, D.; Alexander, D.; Cremades, H.; Kaufmann, P.; Tripathi, D.; Wang, Y. -M. Bibcode: 2006SSRv..123..303G Altcode: 2006SSRv..tmp...77G The coronal mass ejection (CME) phenomenon occurs in closed magnetic field regions on the Sun such as active regions, filament regions, transequatorial interconnection regions, and complexes involving a combination of these. This chapter describes the current knowledge on these closed field structures and how they lead to CMEs. After describing the specific magnetic structures observed in the CME source region, we compare the substructures of CMEs to what is observed before eruption. Evolution of the closed magnetic structures in response to various photospheric motions over different time scales (convection, differential rotation, meridional circulation) somehow leads to the eruption. We describe this pre-eruption evolution and attempt to link them to the observed features of CMEs. Small-scale energetic signatures in the form of electron acceleration (signified by nonthermal radio bursts at metric wavelengths) and plasma heating (observed as compact soft X-ray brightening) may be indicative of impending CMEs. We survey these pre-eruptive energy releases using observations taken before and during the eruption of several CMEs. Finally, we discuss how the observations can be converted into useful inputs to numerical models that can describe the CME initiation. Title: Coronal Observations of CMEs. Report of Working Group A Authors: Schwenn, R.; Raymond, J. C.; Alexander, D.; Ciaravella, A.; Gopalswamy, N.; Howard, R.; Hudson, H.; Kaufmann, P.; Klassen, A.; Maia, D.; Munoz-Martinez, G.; Pick, M.; Reiner, M.; Srivastava, N.; Tripathi, D.; Vourlidas, A.; Wang, Y. -M.; Zhang, J. Bibcode: 2006SSRv..123..127S Altcode: 2006SSRv..tmp...58S CMEs have been observed for over 30 years with a wide variety of instruments. It is now possible to derive detailed and quantitative information on CME morphology, velocity, acceleration and mass. Flares associated with CMEs are observed in X-rays, and several different radio signatures are also seen. Optical and UV spectra of CMEs both on the disk and at the limb provide velocities along the line of sight and diagnostics for temperature, density and composition. From the vast quantity of data we attempt to synthesize the current state of knowledge of the properties of CMEs, along with some specific observed characteristics that illuminate the physical processes occurring during CME eruption. These include the common three-part structures of CMEs, which is generally attributed to compressed material at the leading edge, a low-density magnetic bubble and dense prominence gas. Signatures of shock waves are seen, but the location of these shocks relative to the other structures and the occurrence rate at the heights where Solar Energetic Particles are produced remains controversial. The relationships among CMEs, Moreton waves, EIT waves, and EUV dimming are also cloudy. The close connection between CMEs and flares suggests that magnetic reconnection plays an important role in CME eruption and evolution. We discuss the evidence for reconnection in current sheets from white-light, X-ray, radio and UV observations. Finally, we summarize the requirements for future instrumentation that might answer the outstanding questions and the opportunities that new space-based and ground-based observatories will provide in the future. Title: Multi-Wavelength Observations of CMEs and Associated Phenomena. Report of Working Group F Authors: Pick, M.; Forbes, T. G.; Mann, G.; Cane, H. V.; Chen, J.; Ciaravella, A.; Cremades, H.; Howard, R. A.; Hudson, H. S.; Klassen, A.; Klein, K. L.; Lee, M. A.; Linker, J. A.; Maia, D.; Mikic, Z.; Raymond, J. C.; Reiner, M. J.; Simnett, G. M.; Srivastava, N.; Tripathi, D.; Vainio, R.; Vourlidas, A.; Zhang, J.; Zurbuchen, T. H.; Sheeley, N. R.; Marqué, C. Bibcode: 2006SSRv..123..341P Altcode: 2006SSRv..tmp...60P This chapter reviews how our knowledge of CMEs and CME-associated phenomena has been improved, since the launch of the SOHO mission, thanks to multi-wavelength analysis. The combination of data obtained from space-based experiments and ground based instruments allows us to follow the space-time development of an event from the bottom of the corona to large distances in the interplanetary medium. Since CMEs originate in the low solar corona, understanding the physical processes that generate them is strongly dependant on coordinated multi-wavelength observations. CMEs display a large diversity in morphology and kinematic properties, but there is presently no statistical evidence that those properties may serve to group them into different classes. When a CME takes place, the coronal magnetic field undergoes restructuring. Much of the current research is focused on understanding how the corona sustains the stresses that allow the magnetic energy to build up and how, later on, this magnetic energy is released during eruptive flares and CMEs. Multi-wavelength observations have confirmed that reconnection plays a key role during the development of CMEs. Frequently, CMEs display a rather simple shape, exhibiting a well known three-part structure (bright leading edge, dark cavity and bright knot). These types of events have led to the proposal of the ‘`standard model’' of the development of a CME, a model which predicts the formation of current sheets. A few recent coronal observations provide some evidence for such sheets. Other more complex events correspond to multiple eruptions taking place on a time scale much shorter than the cadence of coronagraph instruments. They are often associated with large-scale dimming and coronal waves. The exact nature of these waves and the physical link between these different manifestations are not yet elucidated. We also discuss what kind of shocks are produced during a flare or a CME. Several questions remain unanswered. What is the nature of the shocks in the corona (blast-wave or piston-driven?) How they are related to Moreton waves seen in Hα? How they are related to interplanetary shocks? The last section discusses the origin of energetic electrons detected in the corona and in the interplanetary medium. “Complex type III-like events,”which are detected at hectometric wavelengths, high in the corona, and are associated with CMEs, appear to originate from electrons that have been accelerated lower in the corona and not at the bow shock of CMEs. Similarly, impulsive energetic electrons observed in the interplanetary medium are not the exclusive result of electron acceleration at the bow shocks of CMEs; rather they have a coronal origin. Title: Multi-Wavelength Observations of CMEs and Associated Phenomena Authors: Pick, M.; Forbes, T. G.; Mann, G.; Cane, H. V.; Chen, J.; Ciaravella, A.; Cremades, H.; Howard, R. A.; Hudson, H. S.; Klassen, A.; Klein, K. L.; Lee, M. A.; Linker, J. A.; Maia, D.; Mikic, Z.; Raymond, J. C.; Reiner, M. J.; Simnett, G. M.; Srivastava, N.; Tripathi, D.; Vainio, R.; Vourlidas, A.; Zhang, J.; Zurbuchen, T. H.; Sheeley, N. R.; Marqué, C. Bibcode: 2006cme..book..341P Altcode: This chapter reviews how our knowledge of CMEs and CME-associated phenomena has been improved, since the launch of the SOHO mission, thanks to multi-wavelength analysis. The combination of data obtained from space-based experiments and ground based instruments allows us to follow the space-time development of an event from the bottom of the corona to large distances in the interplanetary medium. Since CMEs originate in the low solar corona, understanding the physical processes that generate them is strongly dependant on coordinated multi-wavelength observations. CMEs display a large diversity in morphology and kinematic properties, but there is presently no statistical evidence that those properties may serve to group them into different classes. When a CME takes place, the coronal magnetic field undergoes restructuring. Much of the current research is focused on understanding how the corona sustains the stresses that allow the magnetic energy to build up and how, later on, this magnetic energy is released during eruptive flares and CMEs. Multiwavelength observations have confirmed that reconnection plays a key role during the development of CMEs. Frequently, CMEs display a rather simple shape, exhibiting a well known three-part structure (bright leading edge, dark cavity and bright knot). These types of events have led to the proposal of the "standard model" of the development of a CME, a model which predicts the formation current sheets. A few recent coronal observations provide some evidence for such sheets. Other more complex events correspond to multiple eruptions taking place on a time scale much shorter than the cadence of coronagraph instruments. They are often associated with large-scale dimming and coronal waves. The exact nature of these waves and the physical link between these different manifestations are not yet elucidated. We also discuss what kind of shocks are produced during a flare or a CME. Several questions remain unanswered. What is the nature of the shocks in the corona (blast-wave or piston-driven?) How they are related to Moreton waves seen in Hα? How they are related to interplanetary shocks? The last section discusses the origin of energetic electrons detected in the corona and in the interplanetary medium. "Complex type III-like events," which are detected at hectometric wavelengths, high in the corona, and are associated with CMEs, appear to originate from electrons that have been accelerated lower in the corona and not at the bow shock of CMEs. Similarly, impulsive energetic electrons observed in the interplanetary medium are not the exclusive result of electron acceleration at the bow shocks of CMEs; rather they have a coronal origin. Title: Coronal Observations of CMEs Authors: Schwenn, R.; Raymond, J. C.; Alexander, D.; Ciaravella, A.; Gopalswamy, N.; Howard, R.; Hudson, H.; Kaufmann, P.; Klassen, A.; Maia, D.; Munoz-Martinez, G.; Pick, M.; Reiner, M.; Srivastava, N.; Tripathi, D.; Vourlidas, A.; Wang, Y. -M.; Zhang, J. Bibcode: 2006cme..book..127S Altcode: CMEs have been observed for over 30 years with a wide variety of instruments. It is now possible to derive detailed and quantitative information on CME morphology, velocity, acceleration and mass. Flares associated with CMEs are observed in X-rays, and several different radio signatures are also seen. Optical and UV spectra of CMEs both on the disk and at the limb provide velocities along the line of sight and diagnostics for temperature, density and composition. From the vast quantity of data we attempt to synthesize the current state of knowledge of the properties of CMEs, along with some specific observed characteristics that illuminate the physical processes occurring during CME eruption. These include the common three-part structures of CMEs, which is generally attributed to compressed material at the leading edge, a low-density magnetic bubble and dense prominence gas. Signatures of shock waves are seen, but the location of these shocks relative to the other structures and the occurrence rate at the heights where Solar Energetic Particles are produced remains controversial. The relationships among CMEs, Moreton waves, EIT waves, and EUV dimming are also cloudy. The close connection between CMEs and flares suggests that magnetic reconnection plays an important role in CME eruption and evolution. We discuss the evidence for reconnection in current sheets from white-light, X-ray, radio and UV observations. Finally, we summarize the requirements for future instrumentation that might answer the outstanding questions and the opportunities that new space-based and ground-based observatories will provide in the future. Title: Properties of structured coronal mass ejections in solar cycle 23 Authors: Cremades, H.; Bothmer, V.; Tripathi, D. Bibcode: 2006AdSpR..38..461C Altcode: The Solar and Heliospheric Observatory has provided to date doubtlessly the best dataset of coronal observations ever taken over the course of a solar cycle. Structured coronal mass ejections, i.e. events with clear white-light fine structures, have been selected from the dataset of the large angle spectroscopic coronagraph during the period 1996 2002. Their source regions in the low corona and photosphere have been deduced by analyzing data from the Extreme-ultraviolet Imaging Telescope and Michelson Doppler Imager onboard the Solar and Heliospheric Observatory and from ground-based Hα measurements. Based on this subset of coronal mass ejections, originally compiled to study their three-dimensional configuration, we have analyzed the variation of their properties during the present solar cycle. These properties include latitude and tilt angle of source regions of coronal mass ejections, position angle of coronal mass ejections, and deviation of coronal mass ejections with respect to their corresponding source regions. The results show a pronounced and systematic confinement of position angles at equatorial latitudes and equatorward deviations during low solar activity. In contrast, fluctuating position angles and deviations in all directions were found at times of high solar activity. A method to explain the observed deflections is presented. Title: The Pre-CME Sun Authors: Gopalswamy, N.; Mikić, Z.; Maia, D.; Alexander, D.; Cremades, H.; Kaufmann, P.; Tripathi, D.; Wang, Y. -M. Bibcode: 2006cme..book..303G Altcode: The coronal mass ejection (CME) phenomenon occurs in closed magnetic field regions on the Sun such as active regions, filament regions, transequatorial interconnection regions, and complexes involving a combination of these. This chapter describes the current knowledge on these closed field structures and how they lead to CMEs. After describing the specific magnetic structures observed in the CME source region, we compare the substructures of CMEs to what is observed before eruption. Evolution of the closed magnetic structures in response to various photospheric motions over different time scales (convection, differential rotation, meridional circulation) somehow leads to the eruption. We describe this pre-eruption evolution and attempt to link them to the observed features of CMEs. Small-scale energetic signatures in the form of electron acceleration (signified by nonthermal radio bursts at metric wavelengths) and plasma heating (observed as compact soft X-ray brightening) may be indicative of impending CMEs. We survey these pre-eruptive energy releases using observations taken before and during the eruption of several CMEs. Finally, we discuss how the observations can be converted into useful inputs to numerical models that can describe the CME initiation. Title: On the Internal Structures of Coronal Mass Ejections Authors: Tripathi, D.; Stenborg, G. Bibcode: 2005ESASP.600E.167T Altcode: 2005dysu.confE.167T; 2005ESPM...11..167T No abstract at ADS Title: EUV and coronagraphic observations of coronal mass ejections Authors: Tripathi, Durgesh Bibcode: 2005PhDT.........1T Altcode: To identify the exact source regions of coronal mass ejections (CMEs) and to understand the basic physical mechanisms involved in their initiation are amongst the major challenges of modern day solar physics. The Extreme-ultraviolet Imgaing Telescope (EIT) and Large Angle Spectrometric COronagraph (LASCO) aboard Solar and Heliospheric Observatory (SoHO) provides unique opportunity to study CMEs from 1.1 to 30 R since launch in December 1995. This thesis provides basic physical properties of EUV post-eruptive arcades (PEAs) observed by EIT at 195 Å and their role as tracers of source regions of CMEs. A detailed study of a specific EUV PEA event led to the discovery of a bright coronal inflow above the PEA. For specific PEA events line-of-sight magnetograms are analyzed to study the basic mechanism involved in CME initiation. Different varieties of evolutions in the photospheric magnetic field was detected during the time of CME eruption. We expect that the upcoming missions like STEREO and SOLAR-B will work in conjunction, helping us to understand the coupling between the photosphere and the corona. Title: SoHO/EIT Observation of a Coronal Inflow Authors: Tripathi, D.; Bothmer, V.; Solanki, S. K.; Schwenn, R.; Mierla, M.; Stenborg, G. Bibcode: 2005IAUS..226..133T Altcode: A distinct coronal inflow has been discovered after ∼90 min of prominence eruption associated coronal mass ejection (CME) on 05-Mar-2000 by EIT (Extreme ultraviolet Imaging Telescope) aboard SoHO (Solar and Heliospheric Observatory). Evolution of the prominence seen by EIT was tracked into the LASCO/C2 and C3 field-of-view (FOV; 4-10 R) where it developed as the core of a typical three-part CME. The speed of the inflow, which was only seen in EIT FOV, was 70-80 km/s at a height between 1.5-1.2 R coinciding with the deceleration phase of the core of the CME in LASCO/C2. In contrast to dark inflow structures observed earlier and interpreted as plasma void moving down, the inflow reported here was bright. The inflow showed a constant deceleration and followed a curved path suggesting the apex of a contracting magnetic loop sliding down along other field lines. Title: EUV and coronagraphic observations of coronal mass ejections Authors: Tripathi, Durgesh Kumar Bibcode: 2005PhDT.......163T Altcode: No abstract at ADS Title: The basic characteristics of EUV post-eruptive arcades and their role as tracers of coronal mass ejection source regions Authors: Tripathi, D.; Bothmer, V.; Cremades, H. Bibcode: 2004A&A...422..337T Altcode: The Extreme ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO) spacecraft provides unique observations of dynamic processes in the low corona. The EIT 195 Å data taken from 1997 to the end of 2002 were investigated to study the basic physical properties of post-eruptive arcades (PEAs) and their relationship with coronal mass ejections (CMEs) as detected by SOHO/LASCO (Large Angle Spectrometric Coronagraph). Over the investigated time period, 236 PEA events have been identified in total. For each PEA, its EUV lifetime as derived from the emission time at 195 Å, its heliographic position and length, and its corresponding photospheric source region inferred from SOHO/MDI (Michelson Doppler Imager) data has been studied, as well as the variation of these parameters over the investigated phase of solar cycle 23. An almost one to one correspondence is found between EUV PEAs and white-light CMEs. Based on this finding, PEAs can be considered as reliable tracers of CME events even without simultaneous coronagraph observations. A detailed comparison of the white-light, soft X-ray and EUV observation for some of the events shows, that PEAs form in the aftermath of CMEs likely in the course of the magnetic restructurings taking place at the coronal source sites. The average EUV emission life-time for the selected events ranged from 2 to 20 h, with an average of 7 h. The heliographic length of the PEAs was in the range of 2 to 40 degrees, with an average of 15 degrees. The length increased by a factor of 3 to 4 in the latitude range of 20 to 40 degrees in the northern and southern hemispheres, with longer PEAs being observed preferentially at higher latitudes. The PEAs were located mainly in the activity belts in both hemispheres, with the southern hemispheric ones being shifted by about 15 degree in latitude further away from the solar equator during 1997-2002. The decrease in latitude of the PEA positions was 10 to 15 degrees in the northern and southern hemispheres over this period. The axes of the PEAs were overlying magnetic polarity inversion lines when traced back to the MDI synoptic charts of the photospheric field. The magnetic polarities on both sides of the inversion lines agreed with the dominant magnetic pattern expected in cycle 23, i.e. being preferentially positive to the West of the PEA axes in the North and negative in the South. One third (31%) of the PEA events showed reversed polarities. The origin of PEAs is found not just in single bipolar regions (BPRs), but also in between pairs of neighboring BPRs.

Table 1 is available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/337 Title: VizieR Online Data Catalog: Solar EUV Post-Eruptive Arcades (Tripathi+, 2004) Authors: Tripathi, D.; Bothmer, V.; Cremades, H. Bibcode: 2004yCat..34220337T Altcode: The Extreme ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO) spacecraft provides unique observations of dynamic processes in the low corona. The EIT 195{AA} data taken from 1997 to the end of 2002 were investigated to study the basic physical properties of post-eruptive arcades (PEAs) and their relationship with coronal mass ejections (CMEs) as detected by SOHO/LASCO (Large Angle Spectrometric Coronagraph). Over the investigated time period, 236 PEA events have been identified in total. For each PEA, its EUV lifetime as derived from the emission time at 195{AA}, its heliographic position and length, and its corresponding photospheric source region inferred from SOHO/MDI (Michelson Doppler Imager) data has been studied, as well as the variation of these parameters over the investigated phase of solar cycle 23.

(1 data file). Title: Plasma dynamics of a prominence associated coronal mass ejection Authors: Tripathi, D.; Bothmer, V.; Solanki, S. K.; Schwenn, R.; Mierla, M.; Stenborg, G. Bibcode: 2004IAUS..223..401T Altcode: 2005IAUS..223..401T An erupting prominence seen by SOHO/EIT was tracked into the field of view of the LASCO C2 and C3 coronagraphs where it developed into the core of a structured CME. The erupting prominence was deflected by an angle of sim 20^{circ} towards the north pole whereas the consequent core of the CME and it's leading edge propagated in the outer corona at constant position angle. The prominence material underwent a constant acceleration phase until a height of sim1.5 solar radii before it started to decelerate up to a distance of 5.0 solar radii. An inflow of plasma with a speed of about 70-80 km/s was discovered in the EIT observations at a height of 1.5-1.2 solar radii in the course of the prominence eruption, matching in time the prominence deceleration phase. The downflowing material followed a curved path, suggestive of the apex of a contracting magnetic loop sliding down along other field lines. Title: Properties of Structured Coronal Mass Ejections in Solar Cycle 23 Authors: Cremades, H.; Bothmer, V.; Tripathi, D. Bibcode: 2004cosp...35.1939C Altcode: 2004cosp.meet.1939C The Solar and Heliospheric Observatory (SOHO) has provided to date the best dataset of coronal observations ever taken over the course of a solar cycle. Structured CMEs, i. e. events with clear white-light fine structures, have been selected from the LASCO (Large Angle Spectroscopic Coronagraph) dataset during the period 1996-2002. Their source regions (SRs) in the low corona and photosphere have been deduced by analyzing data from the EIT (Extreme-Ultraviolet Imaging Telescope) and MDI (Michelson Doppler Imager) instruments on board SOHO, and from ground-based Hα measurements. Based on this subset of CMEs, originally compiled to study the three-dimensional configuration of CMEs, we have analyzed the variation of their properties along the present solar cycle. These properties include SR latitude, tilt angle of CME SRs, CME position angle, and deviation of CMEs with respect to their corresponding SRs. Title: Evolution of the photospheric magnetic field in the source regions of coronal mass ejections Authors: Tripathi, D.; Bothmer, V.; Cremades, H. Bibcode: 2004cosp...35.1966T Altcode: 2004cosp.meet.1966T EIT (Extreme ultraviolet Imaging Telescope) and MDI (Michelson Doppler Imager) instruments on board SoHO (Solar and Heliospheric Observatory) provide an unprecedented opportunity to study the source regions of coronal mass ejections (CMEs) in the low corona and photosphere. Eight CMEs associated with filament eruptions observed by EIT near disk center were studied in detail. In five events new emerging magnetic flux occurred in spatial and temporal relationship with the instability sites of the filaments. In two cases field changes in nearby active regions seem to have triggered the filament eruptions. In one case, evidence for flux cancellation was found. The different possible causes of the eruptions are discussed in context with the related changes of the photospheric field. Title: Determination of the source regions, 3-D structures and magnetic field configurations of CMEs at the Sun and in the interplanetary medium Authors: Bothmer, V.; Cremades, H.; Tripathi, D. Bibcode: 2004cosp...35.1976B Altcode: 2004cosp.meet.1976B There are numerous unanswered questions concerning the origin, nature, evolution and consequences of coronal mass ejections at the Sun and in the interplanetary medium. STEREO will provide the first 3-D view of the Sun-Earth system and Solar-B will provide unprecedented measurements of the magnetic field structure of their photospheric source regions. The two NASA missions, scheduled for launch in 2006, will hence provide us with a new view of CMEs. In order to establish the scientific goals of these missions, this talk will provide: - A brief summary of our current understanding of the origin and evolution of CMEs based on the latest results obtained from SOHO, Yohkoh, TRACE, ACE and Wind observations. - A basic scheme explaining the 3-D structure and near-Sun evolution of CMEs that can be directly proven with STEREO and Solar-B. - An outline for joint science operations required to test existing models for the onset and evolution of CMEs up to Earth's orbit. Title: Stability Of Triangular Equilibrium Points In The Photo Gravitational Restricted Three Body Problem With Poynting-Robertson Drag Authors: Ishwar, B.; Tripathi, D. K. Bibcode: 2004cosp...35...66I Altcode: 2004cosp.meet...66I We have examined the stability of triangular equilibrium points in the photogravitational restricted three body problem with Poynting-Robertson drag. We consider both primaries as radiating. We have located the triangular equilibrium points of the problem, The position of triangular equilibrium points are affected by mass reduction factor and P-R drag. We have found the characteristic equation of the problem. We conclude that triangular equilibrium points remain unstable. All photogravitational and classical results of RTBP may be verified from this result. Title: 3D Magnetic Field Configuration and Evolution of Coronal Mass Ejections Authors: Cremades, H.; Bothmer, V.; Tripathi, D. Bibcode: 2003EAEJA......852C Altcode: Coronal Mass Ejections (CMEs) are the most energetic transient phenomena in the solar atmosphere. The origins of CMEs, their 3D structure and internal magnetic field configuration, as well as their evolution into interplanetary space are not well understood. Thanks to the high resolution telescopes of the SOHO Mission, for the first time magnetic fine structures can be resolved within CMEs observed close to the Sun. A set of CME events has been identified from a detailed investigation of LASCO (Large Angle Spectroscopic Coronagraph) observations taken since launch in 1995. This data set comprises those cases exhibiting white-light fine structures, from which their magnetic field configuration could be deduced. Since the observed white-light features are the result of an inherent line-of-sight integration projected on the plane of the sky, inferring the three-dimensional topology of CMEs is a challenging and complicated task. In order to reveal the actual 3D profile of a CME, an approach based on the characterization of their respective source region magnetic field configuration is addressed. The study indicates that many CMEs are comprised either of arcades of magnetic field lines or magnetic flux tubes which are trailed by prominence material. The analysis of additional coronal and magnetic field observations (EIT, MDI) shows that these magnetic structures seem to arise from already existing loop systems of much smaller scale that originate in bipolar field regions. Title: A Composite Stellar Model of Geostrophic Flows - Part Two Authors: Singh, H. P.; Tripathi, D. D.; Singh, S. C.; Mishra, R. B. Bibcode: 1988Ap&SS.143...63S Altcode: This paper contains a geometric study and solutions of the electromagneto-geostrophic flows, and spatially the geometrical treatments of magnetic field lines are discussed. Title: A Composite Stellar Model of Magnetofluid Continuum via Anholonomic Descriptions Authors: Singh, H. P.; Tripathi, D. D.; Mishra, R. B. Bibcode: 1988Ap&SS.141..415S Altcode: A theoretical analysis based on the equations of magnetofluid-dynamics is undertaken, in order to completely classify the geometry of the motion admitted by this pattern. Title: A Composite Stellar Model of Geostrophic Flows - Part One Authors: Singh, H. P.; Tripathi, D. D.; Singh, S. C.; Mishra, R. B. Bibcode: 1987Ap&SS.139..413S Altcode: This paper has been presented the geometric study and solutions of the electromagnetogeostrophic flows, and spatially the geometry of magnetic and current lines are discussed. Title: Rotational circulation-preserving magnetogeostrophic flows. Authors: Singh, H. P.; Tripathi, D. D.; Mishra, R. B. Bibcode: 1987Ap&SS.138..315S Altcode: It has been shown that the only steady, inviscid, magnetogeostrophic rotational circulation-preverving motion whose magnetic field line pattern is that of the irrotational motion is a complex-lamellar motion whose magnetic field magnitude bears a constant value on a magnetic field line. Title: The geometry of magnetic fieldlines in magnetogeostrophic flows. Authors: Singh, S. N.; Singh, B. P.; Tripathi, D. D. Bibcode: 1987Ap&SS.137...23S Altcode: It is proved that the only circulation preserving magnetogeostrophic flows whose current density is lamellar, and bears a constant on a current density vector have (1) a plane motion of constant current density (on which certain unsteady potential motions may be superposed) and (2) a particular circular helical motion. Title: Cross sections for ionization of ions by electron impact. Authors: Tripathi, D. N.; Rai, D. K. Bibcode: 1971JQSRT..11.1665T Altcode: No abstract at ADS Title: Electronic ionization and recombination coefficients for atmospheric molecules-I. Electron impact ionization cross-sections. Authors: Sharma, V. N.; Tripathi, D. N.; Rai, D. K. Bibcode: 1971JQSRT..11..283S Altcode: No abstract at ADS