Author name code: srivastava ADS astronomy entries on 2022-09-14 author:"Srivastava, N." ------------------------------------------------------------------------ Title: A Comparative Analysis of Machine-learning Models for Solar Flare Forecasting: Identifying High-performing Active Region Flare Indicators Authors: Sinha, Suvadip; Gupta, Om; Singh, Vishal; Lekshmi, B.; Nandy, Dibyendu; Mitra, Dhrubaditya; Chatterjee, Saikat; Bhattacharya, Sourangshu; Chatterjee, Saptarshi; Srivastava, Nandita; Brandenburg, Axel; Pal, Sanchita Bibcode: 2022ApJ...935...45S Altcode: 2022arXiv220405910S Solar flares create adverse space weather impacting space- and Earth-based technologies. However, the difficulty of forecasting flares, and by extension severe space weather, is accentuated by the lack of any unique flare trigger or a single physical pathway. Studies indicate that multiple physical properties contribute to active region flare potential, compounding the challenge. Recent developments in machine learning (ML) have enabled analysis of higher-dimensional data leading to increasingly better flare forecasting techniques. However, consensus on high-performing flare predictors remains elusive. In the most comprehensive study to date, we conduct a comparative analysis of four popular ML techniques (k nearest neighbors, logistic regression, random forest classifier, and support vector machine) by training these on magnetic parameters obtained from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory for the entirety of solar cycle 24. We demonstrate that the logistic regression and support vector machine algorithms perform extremely well in forecasting active region flaring potential. The logistic regression algorithm returns the highest true skill score of 0.967 ± 0.018, possibly the highest classification performance achieved with any strictly parametric study. From a comparative assessment, we establish that magnetic properties like total current helicity, total vertical current density, total unsigned flux, R_VALUE, and total absolute twist are the top-performing flare indicators. We also introduce and analyze two new performance metrics, namely, severe and clear space weather indicators. Our analysis constrains the most successful ML algorithms and identifies physical parameters that contribute most to active region flare productivity. Title: A novel method for lunar elemental abundance estimation using Chandrayaan-2 class and Chandrayaan-1 M3 data Authors: Bhatt, Megha; Wöhler, Christian; Bhardwaj, Anil; Narendranath, Shyama; Pillai, Netra; Srivastava, Neeraj Bibcode: 2022cosp...44..282B Altcode: We report the first employment of the Chandryaan-2 Large Area Soft X-ray Spectrometer (CLASS) data [1] from Chandrayaan-2 mission as ground truth to estimate SiO2, Al2O3, and MgO for understanding the petrological characteristics of the Moon. The algorithm uses multivariate regression between CLASS derived elemental abundances from selected regions spread over mare and highlands and spectral parameters derived using the nearly global coverage of the Moon obtained by the Moon Mineralogy Mapper (M3) [2]. Spectral parameters derived from the two pronounced absorption bands around 1 µm and 2 µm are sensitive to mineral composition [3] and space-weathering effects [4]. We used the same set of M3 spectral parameters as proposed in [5] that is robust with respect to the effects of soil maturity. The M3 spectral parameters have been extracted corresponding to the CLASS footprint size of 12.5 x 12.5 km2. The CLASS derived elemental abundances primarily rely on enhanced solar activity without any dependencies on empirical relationships to lunar returned samples and refer to the top most layer of regolith as M3. We present a first set of global SiO2, Al2O3, and MgO maps constructed by applying a multivariate linear regression (MLR) model to the CLASS footprints and a M3 global mosaic of 20 pixels per degree resolution [5, 6]. The M3 global reflectance mosaic is derived using the framework in [6]. The results are based on a comparative analysis considering independent techniques [5, 7, 8] applied on regional and global scales. We found that the absolute values of CLASS derived MgO matches well with the technique of [5] and also at Apollo landing sites. The absolute values in the case of SiO2 and Al2O3 systematically differ when compared to [5]. The absolute values will be refined and FeO, TiO2, and CaO maps will be derived once a higher coverage of CLASS footprints is available. References: [1] Pillai N. S. et al. (2021) Icarus 363, 114436. [2] Pieters C. M. et al. (2009) Current Science 96, 500-505; [3] Burns R., Remote geochemical analysis: Elemental and mineralogical composition (1993); [4] Morris, R.V. (1978) Lunar Planet. Sci. Conf. Proc., pp. 2287-2297; [5] Bhatt M. et al. (2019) A&A 627, A155. [6] Wöhler, C. et al. (2017) Science Advances 3, e1701286. [7] Lucey P. G. et al. (2000) JGR 105, 20297-20306; [8] Bhatt M. et al. (2015) Icarus 248, 72-88. Title: Modelling the magnetic vectors of ICMEs detected by radially aligned multiple spacecraft using INFROS Authors: Srivastava, Nandita; Kilpua, Emilia; Sarkar, Ranadeep Bibcode: 2022cosp...44.2434S Altcode: Interplanetary flux rope simulator (INFROS) is an observationally constrained analytical model dedicated for forecasting the strength of southward component (Bz) of magnetic field embedded in interplanetary coronal mass ejections (ICMEs). In this work, we validate the model for six ICME events which were sequentially observed by the radially aligned multiple spacecraft at two different heliocentric distances. The six selected ICME events in this study comprise of cases associated with isolated CME evolution as well as the adverse heliospheric conditions that include the interaction of the ICMEs with the high-speed streams (HSS) and high- density streams (HDS). For the isolated CMEs, our results show that the model outputs at both the spacecraft are in remarkably good agreement with the in-situ observations. However, for the interacting events, the model could capture the CME evolution at the first spacecraft until the interaction occurs and subsequently under-estimate the field strength at the second spacecraft as the ICME evolution ceases to be self-similar due to its interaction with the HSS and HDS. Our results show that INFROS can be used as an efficient tool to forecast the magnetic vectors of ICMEs for the cases of isolated CMEs. This work also presents a quantitative estimation of the enhanced field strength of the ICMEs due to interaction which may lead to severe space weather conditions. We conclude that the assumption of self-similar expansion provides the lower limit for the magnetic field strength estimated at any heliocentric distance, based on the remote sensing observations. Title: Venus Radiation environment monitor (VeRad) for the Venus Orbiter Mission Authors: Shanmugam, M.; Chakrabarty, D.; Bhardwaj, Anil; Sheel, Varun; Vadawale, Santosh; Srivastava, Nandita; Patel, Arpit; Ladiya, Tinkal; Mishra, Sanjay K.; Sarkar, Aveek; Kumar, Sushil; Painkra, Deepak Kumar Bibcode: 2022cosp...44..331S Altcode: Venus, being an un-magnetized planet, is continually bombarded with the solar wind and energetic particles. Modelling studies indicate that the ionization, properties and dynamics of Venusian ionosphere are greatly modulated by the injection of energetic particles into the Venusian upper atmosphere. Further, despite a significantly longer duration of night, ionization in the night side of Venus sustains and show substantial variability. The processes that cause the sustenance and variabilities in the nightside ionosphere are poorly understood till date. Supra-thermal and solar energetic particles (SEP) particles can play important roles in this regard. Therefore, it is important to understand and quantify the role of supra-thermal and solar energetic particles (SEP) particles in the modulation of Venusian ionosphere. In order to achieve these objectives, systematic observations of energetic particles around Venus are needed. This, in turn, will help to construct a radiation model and consequently, an impact scenario by combining with ionospheric / thermospheric observations. Keeping these objectives in mind, a Venus Radiation environment monitor (VeRad) on-board a future Indian Venus Orbiter is being envisaged. To detect these energetic particles, VeRad uses a stack of Si PIN detectors and a scintillator to cover the particles in the energy range 20 keV to 100 MeV. The Si PIN detector stack consists of 50, 300 and 1500 micron thick detectors and a 20 mm thick CsI(Tl) Scintillator at the bottom of the stack. CsI(Tl) scintillator is readout using Silicon Photo multiplier (Si PM) detectors. This detector stack is surrounded by 5 plastic scintillators at all the sides to identify the particles coming out of field of view and these detectors are also readout using Si PMs. VeRad is made of two units namely detector unit and electronics unit. The detector unit consists of detector assembly and the electronics unit consists of front-end, back-end electronics and also the electronics for VeRad interfaces with spacecraft. The brief science issues and the major design aspects of the VeRad instrument will be presented. Title: Recent volcanism and tectonism in the pre-Nectarian basins Grimaldi and Crüger-Sirsalis: Shreds of evidence from LRO, Chandrayaan-1, and Kaguya Authors: Srivastava, Neeraj; Bhardwaj, Anil; Bhatt, Megha Bibcode: 2022cosp...44..270S Altcode: Datasets from remote sensing missions such as Kaguya, LRO, GRAIL, and Chandrayaan-1 have substantially improved our understanding of the geology of the Moon by revealing new details about impact cratering, volcanism, and tectonism. Most of the late-stage (< 2.8 Ga) volcanic activities on the Moon occurred in the Procellarum KREEP Terrain (PKT). It is understood that the heat energy required to drive these internal activities can be accounted for by the enrichment of radioactive elements in the PKT. However, some of these activities have also been reported far from the PKT, such as in the Orientale Basin, Moscoviense Basin, and SPA Basin, which indicates that the radioactive heating may not be the only driving force for their occurrences. Also, recent tectonic activities, primarily manifested in the form of fresh lobate scarps, have been revealed from several locations across the Moon with the help of LROC-NAC high-resolution images. In view of the above, to understand the driving force, it is vital to investigate the global distribution of such geologically young volcanic and tectonic formations and study their geological context in detail. Here, we have carried out a comprehensive geological investigation of the area situated near the western boundary of the PKT between the Oceanus Procellarum and the Orientale Basin. The region is comprised of two pre-Nectarian aged old degraded impact basins Grimaldi and Crüger-Sirsalis. Surface topography, geomorphology, spectral reflectance studies, and crater chronology have been carried out to decipher the geological evolution of these basins especially focusing on their volcanic and tectonic history. It has been found that both these basins experienced unexpectedly prolonged volcanism and tectonism. Whereas the volcanism continued from approximately 4.2 Ga to 1.4 Ga in the older Crüger-Sirsalis Basin, it extended from about 3.5 Ga to 700 Ma in the Grimaldi Basin. Also, shreds of evidence of Copernican aged tectonic features have been found in both these basins suggesting that the Moon is geologically active and has a much more complex geological evolution than previously understood. Title: Detection and Classification of Potential Caves on the Flank of Elysium Mons, Mars Authors: Sharma, Ravi; Srivastava, Neeraj Bibcode: 2022RAA....22f5008S Altcode: Martian caves have revived interest in the field of subsurface exploration because they are the potential destinations for future human habitats and astrobiological research. There are many pits on Mars, but some of them look like collapsed cave roofs. These special pits are formed by the collapse of surface materials into the subsurface void spaces. The signature of life is probable in a subsurface cave on Mars as the subsurface environment can protect life from the harsh and dangerous radiation environment of the surface. In a cave, there may be an abundance of minerals, fluids, and other key resources. Therefore, locating the access point of the subsurface cave is essential and crucial for formulating plans for robotic/human explorations of the Red Planet, Mars. We have used remote sensing data from Mars Reconnaissance Orbiter (MRO; NASA), Mars Global Surveyor (MGS; NASA), and Mars Odyssey (NASA) for identifying, mapping, and classifying selected special pit candidates on the flank of Elysium Mons, Mars. A total of 32 special pit candidates has been identified and classified based upon morphology and geological context. Out of these, 26 are newly discovered ones. The thermal behavior of 23 special pit candidates confirms that the special pits are radiating heat energy at nighttime, similar to potential caves. Also, cave entrances have been detected in nine candidates using data from the HiRISE camera onboard MRO. These sites could be important destinations for future robotic/human exploration and the search for life on Mars. Title: A holistic approach to understand helium enrichment in interplanetary coronal mass ejections: new insights Authors: Yogesh; Chakrabarty, D.; Srivastava, N. Bibcode: 2022MNRAS.513L.106Y Altcode: 2022MNRAS.tmpL..45Y; 2022arXiv220201722Y; 2022MNRAS.513L.106C Despite helium abundance (AHe = nH/nHe) being ~8 per cent at the solar photospheric/chromospheric heights, AHe can be found to exceed 8 per cent in interplanetary coronal mass ejections (ICMEs) on many occasions. Although various factors like interplanetary shocks, chromospheric evaporation, and 'sludge removal' have been separately invoked in the past to address the AHe enhancements in ICMEs, none of these processes could explain the variability of AHe in ICMEs comprehensively. Based on an extensive analysis of 275 ICME events, we show that there is a solar activity variation of ICME averaged AHe values. We also found that the first ionization potential effect and localized coronal heating due to magnetic reconnection are not the major contributing factors for AHe enhancements in ICMEs. Investigation on concurrent solar flares and ICME events for 63 cases reveals that chromospheric evaporation in tandem with gravitational settling determines the AHe enhancements and variabilities beyond 8 per cent in ICMEs. While chromospheric evaporation releases the helium from chromosphere into the corona, the gravitationally settled helium is thrown out during the ICMEs. We show that the intensity and timing of the preceding flares from the same active region from where the CME erupts are important factors to understand the AHe enhancements in ICMEs. Title: Geology of the Crüger-Sirsalis Basin: Evidence for prolonged volcanism in the southwestern near side of the Moon Authors: Singh, Tanu; Srivastava, Neeraj; Bhatt, Megha; Bhardwaj, Anil Bibcode: 2022Icar..37614875S Altcode: The Pre-Nectarian Crüger-Sirsalis Basin (centered at 16.0°S, 293.0°E; ~ 475 km in diameter) is a primarily degraded and obscured impact basin on the Moon. This study presents the first geological description of the Crüger-Sirsalis Basin using remote sensing datasets from Lunar Reconnaissance Orbiter (LRO), Chandrayaan-1, and Kaguya missions. An inner depression ring (IDR) with a diameter of ~243 km has been identified, besides two of its outer rings with diameters of ~425 km and ~ 475 km. We report two new floor fractured craters, and a new concentric crater, suggesting the presence of shallow magmatic intrusions. A new pyroclastic deposit has been found within the Crüger-Sirsalis Basin. Our spectral assessment of the cryptomaria and mare basalt reveals two different types of cryptomaria in the region. The cryptomare inside the basin possesses similar olivine-pyroxene composition as basalt within the basin. However, the cryptomare outside the Crüger-Sirsalis Basin, towards the Oceanus Procellarum, is predominantly composed of high-Ca pyroxene. The spectral signature of pure anorthosite (PAN) has been found in crater Darwin C, located along the inner ring of the basin. The Byrgius Crater along the outer ring of the basin shows the spectral signature of olivine or Fe-rich glass mixed with orthopyroxene. Crater chronology has revealed that the basin experienced main phase and late phase volcanism, down to ~1.4 Ga. Thus, the Crüger-Sirsalis Basin uniquely experienced prolonged mare volcanism from the pre-cataclysmic stage to the late stage of lunar history. Title: First Global Lunar Magnesium and Aluminum Abundance Maps Derived Using Chandrayaan-1 and Chandrayaan-2 Data Authors: Bhatt, M.; Narendranath, S.; Wöhler, C.; Pillai, N. S.; Srivastava, N.; Bhardwaj, A. Bibcode: 2022LPICo2678.2253B Altcode: CLASS-derived abundances of Mg and Al were used as ground truth and an empirical multivariate linear regression model developed for M3 global coverage. Title: Identification and Characterisation of Potential Lunar Analogues Within India Authors: Durga Prasad, K.; Bhatt, M.; Kalyana Reddy, P.; Kumar, J.; Srivastava, N.; Ray, D.; Verma, A.; Shukla, A. D.; Sheel, V.; Bhardwaj, A. Bibcode: 2022LPICo2678.1865D Altcode: Terrestrial analogues for lunar basalts and Anorthosites identified within India. Positive comparison with lunar soils qualify them as potential lunar analogues. Title: SHARAD detection of sedimentary infilling within an unnamed crater near Mangala Fossa region, Mars Authors: Bharti, Rajiv R.; Smith, Isaac B.; Mishra, S. K.; Srivastava, N.; Shukla, Shital H. Bibcode: 2022Icar..37114713B Altcode: We present the first Shallow Radar (SHARAD) based observations of subsurface reflections within an unnamed crater centered at 21.0° S, 150.6° W. It is situated south of the Mangala Fossa and Mangala Valles, a major fluvial outflow channel system. We informally name the crater Mangala crater for this paper. In contrast with adjacent Tharsis lava flow, our analysis of radar propagation in the Mangala crater reveals a low loss tangent (0.008-0.009) and lower dielectric subsurface material (average 5.6) for a subsurface unit that is ~40 m thick. These values are unexpected in this region. Lava flows dominate the surface and surrounding region, and SHARAD investigations of lava flows in the Tharsis region have detected higher values, creating a discrepancy that we discuss. Based on observed stratigraphy, and subsurface geophysical properties, we propose that the crater infilling is composed of moderate density sedimentary material buried by a layer of lava in the eastern portion of Mangala crater but left exposed in the west. Our measurements are also supported by previously done geologic mapping. We identify two subsurface reflections that provide details to determine one of the layers is sediment rather than lava. Detection of multiple reflections also indicates that infilling occurred in at least four successive events. These results are significant because it adds more context to this highly studied region and provides compelling evidence that water moved large volumes of sediment into this basin. Title: Editorial: Space Weather Prediction: Challenges and Future prospects Authors: Srivastava, Nandita; Mierla, Marilena; Zhang, Jie Bibcode: 2021FrASS...8..230S Altcode: No abstract at ADS Title: Correction to: Understanding the Origins of Problem Geomagnetic Storms Associated with "Stealth" Coronal Mass Ejections Authors: Nitta, Nariaki V.; Mulligan, Tamitha; Kilpua, Emilia K. J.; Lynch, Benjamin J.; Mierla, Marilena; O'Kane, Jennifer; Pagano, Paolo; Palmerio, Erika; Pomoell, Jens; Richardson, Ian G.; Rodriguez, Luciano; Rouillard, Alexis P.; Sinha, Suvadip; Srivastava, Nandita; Talpeanu, Dana-Camelia; Yardley, Stephanie L.; Zhukov, Andrei N. Bibcode: 2021SSRv..217...84N Altcode: No abstract at ADS Title: Differential behaviors of suprathermal $^4$He and Fe populations in the interplanetary medium during solar cycle 24 Authors: Dalal, Bijoy; Chakrabarty, Dibyendu; Srivastava, Nandita Bibcode: 2021arXiv211213242D Altcode: Investigations on the solar cycle variation of the properties of suprathermal populations (H and other heavy ions like $^4$He, $^3$He, C, O and Fe) in the solar wind are sparse and hence, poorly understood. In the present investigation, solar cycle variations of "quiet" time suprathermal elements are investigated using $<$ $\sim$ 1 MeV/n particle flux data obtained from Ultra-Low Energy Isotope Spectrometer on board Advanced Composition Explorer satellite during the solar cycle 23 and 24. The analysis reveals that helium ($^4$He) shows zero or positive lags with respect to sunspot numbers in solar cycle 23 while it shows zero or negative lag in solar cycle 24. On the contrary, although iron (Fe) shows zero or positive lag in cycle 23 similar to $^4$He, it shows only zero lag in cycle 24 and no negative lag is seen. Further, significant differences in the spectral indices are seen between $^4$He and Fe in cycle 24 compared to the cycle 23. These results suggest that generation mechanisms responsible for suprathermal $^4$He and Fe underwent changes in cycle 24 and these mechanisms are probably dependent on the first ionization potential and mass to charge ratio. This proposition gets credence from the fact that changes in the lag and spectral slopes for C and O are not significantly different in cycle 23 and 24. Title: Understanding the Origins of Problem Geomagnetic Storms Associated with "Stealth" Coronal Mass Ejections Authors: Nitta, Nariaki V.; Mulligan, Tamitha; Kilpua, Emilia K. J.; Lynch, Benjamin J.; Mierla, Marilena; O'Kane, Jennifer; Pagano, Paolo; Palmerio, Erika; Pomoell, Jens; Richardson, Ian G.; Rodriguez, Luciano; Rouillard, Alexis P.; Sinha, Suvadip; Srivastava, Nandita; Talpeanu, Dana-Camelia; Yardley, Stephanie L.; Zhukov, Andrei N. Bibcode: 2021SSRv..217...82N Altcode: 2021arXiv211008408N Geomagnetic storms are an important aspect of space weather and can result in significant impacts on space- and ground-based assets. The majority of strong storms are associated with the passage of interplanetary coronal mass ejections (ICMEs) in the near-Earth environment. In many cases, these ICMEs can be traced back unambiguously to a specific coronal mass ejection (CME) and solar activity on the frontside of the Sun. Hence, predicting the arrival of ICMEs at Earth from routine observations of CMEs and solar activity currently makes a major contribution to the forecasting of geomagnetic storms. However, it is clear that some ICMEs, which may also cause enhanced geomagnetic activity, cannot be traced back to an observed CME, or, if the CME is identified, its origin may be elusive or ambiguous in coronal images. Such CMEs have been termed "stealth CMEs". In this review, we focus on these "problem" geomagnetic storms in the sense that the solar/CME precursors are enigmatic and stealthy. We start by reviewing evidence for stealth CMEs discussed in past studies. We then identify several moderate to strong geomagnetic storms (minimum Dst <−50 nT) in solar cycle 24 for which the related solar sources and/or CMEs are unclear and apparently stealthy. We discuss the solar and in situ circumstances of these events and identify several scenarios that may account for their elusive solar signatures. These range from observational limitations (e.g., a coronagraph near Earth may not detect an incoming CME if it is diffuse and not wide enough) to the possibility that there is a class of mass ejections from the Sun that have only weak or hard-to-observe coronal signatures. In particular, some of these sources are only clearly revealed by considering the evolution of coronal structures over longer time intervals than is usually considered. We also review a variety of numerical modelling approaches that attempt to advance our understanding of the origins and consequences of stealthy solar eruptions with geoeffective potential. Specifically, we discuss magnetofrictional modelling of the energisation of stealth CME source regions and magnetohydrodynamic modelling of the physical processes that generate stealth CME or CME-like eruptions, typically from higher altitudes in the solar corona than CMEs from active regions or extended filament channels. Title: Radial sizes and expansion behavior of ICMEs in solar cycles 23 and 24 Authors: Mishra, Wageesh; Doshi, Urmi; Srivastava, Nandita Bibcode: 2021FrASS...8..142M Altcode: We attempt to understand the influence of the heliospheric state on the expansion behavior of coronal mass ejections (CMEs) and their interplanetary counterparts (ICMEs) in solar cycles 23 and 24. Our study focuses on the distributions of the radial sizes and duration of ICMEs, their sheaths, and magnetic clouds (MCs). We find that the average radial size of ICMEs (MCs) at 1 AU in cycle 24 is decreased by $\sim$33\% ($\sim$24\%) of its value in cycle 23. This is unexpected as the reduced total pressure in cycle 24 should have allowed the ICMEs in cycle 24 to expand considerably to larger sizes at 1 AU. To understand this, we study the evolution of radial expansion speeds of CME-MC pairs between the Sun and Earth based on their remote and \textit{in situ} observations. We find that radial expansion speeds of MCs at 1 AU in solar cycles 23 and 24 are only 9\% and 6\%, respectively, of their radial propagation speeds. Also, the fraction of radial propagation speeds as expansion speeds of CMEs close to the Sun are not considerably different between solar cycles 23 and 24. We also find a constant (0.63 $\pm$ 0.1) dimensionless expansion parameter of MCs at 1 AU for both the solar cycles 23 and 24. We suggest that the reduced heliospheric pressure in cycle 24 is compensated by the reduced magnetic content inside CMEs/MCs, which did not allow the CMEs/MCs to expand enough in the later phase of their propagation. Further, the average radial sizes of sheaths are the same in both cycles, which is unexpected given the weaker CMEs/ICMEs in cycle 24. We discuss the possible causes and consequences of our findings relevant for future studies. Title: Multipoint remote and in situ observations of interplanetary coronal mass ejection structures during 2011 and associated geomagnetic storms Authors: Mishra, Wageesh; Dave, Kunjal; Srivastava, Nandita; Teriaca, Luca Bibcode: 2021MNRAS.506.1186M Altcode: We present multipoint remote and in situ observations of interplanetary coronal mass ejection (ICME) structures during the year 2011. The selected ICMEs arrived at Earth on 2011 March 11 and 2011 August 6, and led to geomagnetic storms. Around the launch of these CMEs from the Sun, the coronagraphs onboard STEREO-Aand-B and SOHO enabled the CMEs to be imaged from three longitudinally separated viewpoints. We attempt to identify the in situ plasma and magnetic parameters of the ICME structures at multiple locations, for example at both STEREO spacecraft and also at the ACE/Wind spacecraft near the first Sun-Earth Lagrangian point (L1), to investigate the global configuration, interplanetary propagation, arrival times and geomagnetic response of the ICMEs. The near-Earth identified ICMEs of March 11 and August 6 formed as a result of the interaction of two successive CMEs observed in the inner corona on March 7 (for the March 11 ICME) and on August 3-4 (for the August 6 ICME). Our study suggests that the structures associated with interacting CMEs, possibly as a result of deflection or large sizes, may reach to even larger longitudinally separated locations in the heliosphere. Our multipoint in situ analysis shows that the characteristics of the same shock, propagating in a pre-conditioned medium, may be different at different longitudinal locations in the heliosphere. Similarly, multiple cuts through the same ejecta/complex ejecta, formed as a result of CME-CME interaction, are found to have inhomogeneous properties. The study highlights the difficulties in connecting the local observations of an ICME from a single in situ spacecraft to its global structures. Title: Investigating Remote-sensing Techniques to Reveal Stealth Coronal Mass Ejections Authors: Palmerio, Erika; Nitta, Nariaki V.; Mulligan, Tamitha; Mierla, Marilena; O'Kane, Jennifer; Richardson, Ian G.; Sinha, Suvadip; Srivastava, Nandita; Yardley, Stephanie L.; Zhukov, Andrei N. Bibcode: 2021FrASS...8..109P Altcode: 2021arXiv210607571P Eruptions of coronal mass ejections (CMEs) from the Sun are usually associated with a number of signatures that can be identified in solar disc imagery. However, there are cases in which a CME that is well observed in coronagraph data is missing a clear low-coronal counterpart. These events have received attention during recent years, mainly as a result of the increased availability of multi-point observations, and are now known as 'stealth CMEs'. In this work, we analyse examples of stealth CMEs featuring various levels of ambiguity. All the selected case studies produced a large-scale CME detected by coronagraphs and were observed from at least one secondary viewpoint, enabling a priori knowledge of their approximate source region. To each event, we apply several image processing and geometric techniques with the aim to evaluate whether such methods can provide additional information compared to the study of "normal" intensity images. We are able to identify at least weak eruptive signatures for all events upon careful investigation of remote-sensing data, noting that differently processed images may be needed to properly interpret and analyse elusive observations. We also find that the effectiveness of geometric techniques strongly depends on the CME propagation direction with respect to the observers and the relative spacecraft separation. Being able to observe and therefore forecast stealth CMEs is of great importance in the context of space weather, since such events are occasionally the solar counterparts of so-called 'problem geomagnetic storms'. Title: Evidence for distinctive changes in the solar wind helium abundance in solar cycle 24 Authors: Yogesh; Chakrabarty, D.; Srivastava, N. Bibcode: 2021MNRAS.503L..17Y Altcode: 2021arXiv210205395Y; 2021MNRAS.tmpL..16Y; 2021MNRAS.503L..17C; 2021MNRAS.503L...7Y The relative abundance of alpha particles with respect to protons, usually expressed as AHe = (nα/np)*100, is known to respond to solar activity, although changes in its behaviour in the last four solar cycles are not known. In this letter, by systematically analysing inter-calibrated AHe data obtained from the first Lagrangian point of the Sun-Earth system, we show that AHe variations are distinctively different in solar cycle 24 as compared to the last three cycles. The frequency of AHe = 2-3 per cent events is significantly higher in slow/intermediate solar winds in solar cycle 24 as opposed to the dominance of the typical AHe = 4-5 per cent events in the previous three cycles. Further, the occurrence of AHe > 10 per cent events is significantly reduced in cycle 24. Not only that the changes in delay of AHe with respect to peak sunspot numbers are less sensitive to changes in solar wind velocity in cycle 24. The investigation suggests that the coronal magnetic field configuration started undergoing systematic changes starting from cycle 23 and this altered magnetic field configuration affected the way helium got processed and depleted in the solar atmosphere. Title: INterplanetary Flux ROpe Simulator (INFROS): Predicting the magnetic-field vectors of ICMEs Authors: Srivastava, Nandita; Gopalswamy, Nat; Sarkar, Ranadeep Bibcode: 2021cosp...43E1029S Altcode: We have developed an observationally constrained analytical model, the INterplanetary Flux ROpe Simulator (INFROS), for predicting the magnetic-field vectors of interplanetary coronal mass ejections (ICMEs). The main architecture of INFROS uses the near-Sun flux rope properties obtained from the observational parameters that are evolved through the model to estimate the magnetic field vectors of ICMEs at any heliocentric distance. As a proof of concept, we present the case study of an Earth-impacting CME which occurred on 2013 April 11. The predicted magnetic field profiles of the associated ICME show good agreement with those observed by the in-situ spacecraft. We further validated INFROS model for the ICMEs detected by the radially aligned multiple spacecraft orbiting the Sun at different heliocentric distances. The in-situ observations of those ICMEs as detected in MESSENGER at ∼ 0.3 AU or VEX at ~0.7 AU and STEREO at ~1 AU , help us to constrain the INFROS model parameters in order to predict the magnetic field-vectors of the ICME at 1 AU. INFROS shows promising results in the forecasting of Bz in near real-time. It is a simple less time-consuming and computationally inexpensive compared to other models and has the potential to be implemented as a practical space-weather forecasting tool. Title: Lorentz force evolution reveals the energy build-up processes during recurrent eruptive solar flares Authors: Srivastava, Nandita; Veronig, Astrid; Sarkar, Ranadeep Bibcode: 2021cosp...43E1773S Altcode: The energy release and build-up processes in the solar corona have significant implications in particular for the case of large recurrent flares in the same active region (AR), which pose challenging questions about the conditions that lead to the episodic energy release processes. It is not yet clear whether these events occur due to the continuous supply of free magnetic energy to the solar corona or because not all of the available free magnetic energy is released during a single major flaring event. In order to address this question, we report on the evolution of photospheric magnetic field and the associated net Lorentz force changes in ARs 11261 and 11283, each of which gave rise to recurrent eruptive M- and X-class flares. Our study reveals that after the abrupt downward changes during each flare, the net Lorentz force increases significantly between the successive flares. This distinct rebuild-up of net Lorentz forces is the first observational evidence found in the evolution of any nonpotential parameter of solar ARs, which suggests that new energy was supplied to the ARs in order to produce the recurrent large flares. The rebuild-up of magnetic free energy of the ARs is further confirmed by the observations of continuous shearing motion of moving magnetic features of opposite polarities near the polarity inversion line. The evolutionary pattern of the net Lorentz force changes reported in this study has significant implications, in particular, for the forecasting of recurrent large eruptive flares from the same AR and hence the chances of interaction between the associated CMEs. Title: Geology of Grimaldi Basin on the Moon: Evidence for volcanism and tectonism during the Copernican period Authors: Singh, Tanu; Srivastava, Neeraj Bibcode: 2020Icar..35113921S Altcode: The Grimaldi Basin, centered at (5.2° S, 68.6° W), is a ~400 km diameter highly degraded, Pre-Nectarian double-ring impact structure on the Moon located near the western edge of the Oceanus Procellarum. Hyperspectral data from Moon Mineralogy Mapper (M3), FeO estimates from Kaguya Lunar Multiband Imager (MI) data and TiO2 estimates from WAC 321/415 nm ratio have been used to study the compositional make-up of the Grimaldi mare basalt. Additionally, morphological studies and crater chronology have been carried out using moderate to very high-resolution images from Lunar Reconnaissance Orbiter (LRO) to decipher the geological evolution of the Grimaldi Basin. Mare Grimaldi are dominantly composed of clino-pyroxenes with olivine and/or of feldspathic mixing with lateral as well as depth-wise variations in composition. In the south central part, the basin experienced Copernican aged volcanism ~700 Ma ago resulting in the formation of olivine bearing basalts with high FeO and TiO2 content. Cross-cutting of small Copernican craters by fresh wrinkle ridges and lobate scarps has been observed at several places in the basin suggesting that tectonic activities occurred in the basin within the past ~50 Ma-1 Ga. Thus, similar to the Oceanus Procellarum region, Grimaldi Basin was also geologically active during the Copernican period. Title: A Comparison of Elemental Abundances Derived from Chandrayaan-2 Class and Chandrayaan-1 M3 from the Western Nearside of the Moon Authors: Bhatt, M.; Narendranath, S.; Srivastava, N.; Pillai, N. S.; Wöhler, C.; Bhardwaj, A. Bibcode: 2020LPI....51.2270B Altcode: We present a comparison of the abundance of Al, Mg, and Si estimated using the Chandrayaan-2 CLASS with the elemental abundance estimation derived using M3. Title: Geological characterization of Chandrayaan-2 landing site in the southern high latitudes of the Moon Authors: Sinha, Rishitosh K.; Sivaprahasam, Vijayan; Bhatt, Megha; Harish; Kumari, Nandita; Srivastava, Neeraj; Varatharajan, Indhu; Ray, Dwijesh; Wöhler, Christian; Bhardwaj, Anil Bibcode: 2020Icar..33713449S Altcode: ISRO's lunar orbiter-lander-rover mission Chandryaan-2 is scheduled to be launched in the mid of 2019. In this contribution, we have carried out detailed geological characterization of the prime landing site (70.9°S, 22.8°E) of the Chandrayaan-2 lander - "Vikram". The proposed landing site is located amidst the nearside lunar highlands at high southern latitudes, which is ~350 km north of South Pole Aitken (SPA) basin rim. Topography of the region is generally flat and it is largely confined by craters of varying diameter. The majority (94%) of the landing ellipse (~15 × 8 km) is within the boundary of intercrater plains with a slope <15° and yields a crater retention age of ~3.7-0.04+0.03 Ga. Craters (diameter: ~2.28 m to ~1.13 km) consistent with morphologies varying from fresh to degraded are common within the landing ellipse, though the ellipse center is devoid of craters with significant depth. Analysis of the spectral reflectance data suggests that the landing ellipse is dominantly feldspathic/highland material. The estimated average abundance of elements within the landing ellipse are Fe: 4.2 wt%, Mg: 5.4 wt%, Ca: 10 wt%, and Ti: 0.3 wt%. Results indicate that the surface composition might correspond to FAN dominated material. Based on elemental and spectral analysis results, we envisage possible mixing of highland material with ejecta from multiple craters surrounding the landing ellipse and/or SPA basin, resulting in hybridisation of highland regolith. Together, the results provide a contextual framework for in situ investigations at the proposed landing site. Title: An Observationally Constrained Analytical Model for Predicting the Magnetic Field Vectors of Interplanetary Coronal Mass Ejections at 1 au Authors: Sarkar, Ranadeep; Gopalswamy, Nat; Srivastava, Nandita Bibcode: 2020ApJ...888..121S Altcode: 2019arXiv191203494S We report on an observationally constrained analytical model, the INterplanetary Flux ROpe Simulator (INFROS), for predicting the magnetic field vectors of coronal mass ejections (CMEs) in the interplanetary medium. The main architecture of INFROS involves using the near-Sun flux rope properties obtained from the observational parameters that are evolved through the model in order to estimate the magnetic field vectors of interplanetary CMEs (ICMEs) at any heliocentric distance. We have formulated a new approach in INFROS to incorporate the expanding nature and the time-varying axial magnetic field strength of the flux rope during its passage over the spacecraft. As a proof of concept, we present the case study of an Earth-impacting CME which occurred on 2013 April 11. Using the near-Sun properties of the CME flux rope, we have estimated the magnetic vectors of the ICME as intersected by the spacecraft at 1 au. The predicted magnetic field profiles of the ICME show good agreement with those observed by the in situ spacecraft. Importantly, the maximum strength (10.5 ± 2.5 nT) of the southward component of the magnetic field (Bz) obtained from the model prediction is in agreement with the observed value (11 nT). Although our model does not include the prediction of the ICME plasma parameters, as a first-order approximation, it shows promising results in forecasting of Bz in near real time, which is critical for predicting the severity of the associated geomagnetic storms. This could prove to be a simple space-weather forecasting tool compared to the time-consuming and computationally expensive MHD models. Title: Lorentz Force Evolution Reveals the Energy Build-up Processes during Recurrent Eruptive Solar Flares Authors: Sarkar, Ranadeep; Srivastava, Nandita; Veronig, Astrid M. Bibcode: 2019ApJ...885L..17S Altcode: 2019arXiv191013264S The energy release and build-up processes in the solar corona have significant implications in particular for the case of large recurrent flares, which pose challenging questions about the conditions that lead to the episodic energy release processes. It is not yet clear whether these events occur due to the continuous supply of free magnetic energy to the solar corona or because not all of the available free magnetic energy is released during a single major flaring event. In order to address this question, we report on the evolution of photospheric magnetic field and the associated net Lorentz force changes in ARs 11261 and 11283, each of which gave rise to recurrent eruptive M- and X-class flares. Our study reveals that after the abrupt downward changes during each flare, the net Lorentz force increases by (2-5) × 1022 dyne in between the successive flares. This distinct rebuild-up of net Lorentz forces is the first observational evidence found in the evolution of any nonpotential parameter of solar active regions (ARs), which suggests that new energy was supplied to the ARs in order to produce the recurrent large flares. The rebuild-up of magnetic free energy of the ARs is further confirmed by the observations of continuous shearing motion of moving magnetic features of opposite polarities near the polarity inversion line. The evolutionary pattern of the net Lorentz force changes reported in this study has significant implications, in particular, for the forecasting of recurrent large eruptive flares from the same AR and hence the chances of interaction between the associated CMEs. Title: Solar Filament Eruptions as Precursors to Flare-CME Events: Establishing the Temporal Connection Authors: Sinha, Suvadip; Srivastava, Nandita; Nandy, Dibyendu Bibcode: 2019ApJ...880...84S Altcode: Elongated structures on the Sun’s surface known as filaments are known to have a connection with energetic events of space weather consequence (flares and coronal mass ejections (CMEs)). In this work, we explore the connection between the eruptive dynamics of filaments and the initiation of solar flares and CMEs. We estimate the filament eruption start time by tracking the filament throughout its eruption phase. We define the filament eruption start time as the time from which the filament area starts to decrease as observed in Hα images. A total of 33 eruptive filament events are reported in this study, out of which 73% are CME associated and 76% are related to solar flares. We find a good correlation between area decay rate of the quiescent filaments and the speed of the associated CMEs with a correlation coefficient of 0.75. By analyzing the time delay of the extreme ultraviolet brightening of solar flares relative to the start time of associated filament eruption, we show that in 83% of cases, filament eruption precedes the flare brightening, which indicates that eruptive filaments can be considered as one of the precursors for the occurrence of a solar flare. Finally, we study the time delay of the CME onset from the time of initiation of the filament eruption process and show that for most of the cases, CMEs occur within 2 hr from the start time of the filament eruptions. This study would be useful for space weather assessment and characterization based on automated trackers of solar filament dynamics. Title: Resource potential and planning for exploration of the Hebrus Valles, Mars Authors: Sharma, Ravi; Srivastava, Neeraj; Yadav, Santosh Kumar Bibcode: 2019RAA....19..116S Altcode: Mars is the only extraterrestrial body which could host primitive lifeforms and also has the potential to host a human base in the near future. Towards fulfilling these objectives, several remote sensing missions and rover based missions have been sent to Mars. Still, confirmation of existing or extinct life on this planet in any form has not been achieved and possibly human missions at selected sites in the future are the key to addressing this problem. Here, we have used remote sensing data from Mars Reconnaissance Orbiter (MRO; NASA), Mars Global Surveyor (MGS; NASA), Mars Odyssey (NASA) and Mars Express (MEX; ESA) to devise an exploration strategy for one such area known as Hebrus Valles, which is a potential site for human exploration of the surface of Mars. A geological context map of the Hebrus Valles and Hephaestus Fossae region has been prepared and a candidate landing site has been proposed in the Hebrus Valles region. Suitable rover paths have been worked out from the proposed landing site for harnessing the science and resource potential of the region. The proposed landing site is located in the equatorial region at (20^\circ {40}^{\prime } N, 126^\circ {23}^{\prime } E) and due to its proximity to the Potential Subsurface Access Candidates (PSACs) in the region, such as sinkholes and skylights and also other resources such as crater ejecta, silicate material and fluvial channels, the site is appropriate for exploration of the region. Title: Mass loss via solar wind and coronal mass ejections during solar cycles 23 and 24 Authors: Mishra, Wageesh; Srivastava, Nandita; Wang, Yuming; Mirtoshev, Zavkiddin; Zhang, Jie; Liu, Rui Bibcode: 2019MNRAS.486.4671M Altcode: 2019MNRAS.tmp.1056M; 2019arXiv190409898M Similar to the Sun, other stars shed mass and magnetic flux via ubiquitous quasi-steady wind and episodic stellar coronal mass ejections (CMEs). We investigate the mass loss rate via solar wind and CMEs as a function of solar magnetic variability represented in terms of sunspot number and solar X-ray background luminosity. We estimate the contribution of CMEs to the total solar wind mass flux in the ecliptic and beyond, and its variation over different phases of the solar activity cycles. The study exploits the number of sunspots observed, coronagraphic observations of CMEs near the Sun by SOHO/LASCO, in situ observations of the solar wind at 1 AU by WIND, and GOES X-ray flux during solar cycles 23 and 24. We note that the X-ray background luminosity, occurrence rate of CMEs and ICMEs, solar wind mass flux, and associated mass loss rates from the Sun do not decrease as strongly as the sunspot number from the maximum of solar cycle 23 to the next maximum. Our study confirms a true physical increase in CME activity relative to the sunspot number in cycle 24. We show that the CME occurrence rate and associated mass loss rate can be better predicted by X-ray background luminosity than the sunspot number. The solar wind mass loss rate which is an order of magnitude more than the CME mass loss rate shows no obvious dependency on cyclic variation in sunspot number and solar X-ray background luminosity. These results have implications for the study of solar-type stars. Title: Evolution of the Coronal Cavity From the Quiescent to Eruptive Phase Associated with Coronal Mass Ejection Authors: Sarkar, Ranadeep; Srivastava, Nandita; Mierla, Marilena; West, Matthew J.; D'Huys, Elke Bibcode: 2019ApJ...875..101S Altcode: 2019arXiv190400899S We present the evolution of a coronal cavity encompassing its quiescent and eruptive phases in the lower corona. Using multiple vantage-point observations from the SDO/AIA, STEREO SECCHI/EUVI, and PROBA2/Sun Watcher with the APS and Image Processing (SWAP) extreme ultraviolet (EUV) imagers, we capture a sequence of quasi-static equilibria of the quiescent cavity, which exhibited a slow rise and an expansion phase during its passage on the solar disk from 2010 May 30 to June 13. By comparing the decay-index profiles of the cavity system during the different stages of its quiescent and pre-eruptive phases, we find that the decay-index value at the cavity centroid height can be used as a good indicator to predict the cavity eruption in the context of torus instability. Combining the observations of SWAP and the Large Angle and Spectrometric Coronagraph Experiment C2/C3, we show the evolution of the EUV cavity into the white-light cavity as a three-part structure of the associated coronal mass ejection that was observed to erupt on 2010 June 13. By applying successive geometrical fits to the cavity morphology, we find that the cavity exhibited non-self-similar expansion in the lower corona, below 2.2 ± 0.2 R S, which points to the spatial scale for the radius of the source surface where the coronal magnetic field lines are believed to become radial. Furthermore, the kinematic study of the erupting cavity captures both the “impulsive” and “residual” phases of acceleration along with a strong deflection of the cavity at 1.3 R S. We also discuss the role of driving forces behind the dynamics of the morphological and kinematic evolution of the cavity. Title: Geological Insights into Chandrayaan-2 Landing Site in the Southern High Latitudes of the Moon Authors: Sinha, R. K.; Vijayan, S.; Bhatt, M.; Nandal, H.; Kumari, N.; Srivastava, N.; Varatharajan, I.; Ray, D.; Wöhler, C.; Bhardwaj, A. Bibcode: 2019LPI....50.1493S Altcode: Pre-Chandrayaan-2 understanding of lunar morphology, topography, mineralogy, and chronology at the Vikram Landing site. Title: Study of reconnection rates and light curves in solar flares from low and mid chromosphere Authors: Sindhuja, G.; Srivastava, Nandita; Veronig, A. M.; Pötzi, W. Bibcode: 2019MNRAS.482.3744S Altcode: 2018MNRAS.tmp.2748S We study the flare evolution process using both H α and Ca-K data sets to understand the variations between the two. The reconnection rates and fluxes from low and mid chromosphere using the high cadence Ca-K and H α time lapse images and low-noise 720-s Helioseismic Magnetic Imager line-of-sight magnetograms, respectively, are studied. From the past studies it is understood that the surface magnetic flux swept by the flare ribbons relates to a global reconnection rate. Therefore in order to measure the abovesaid parameters, the observables like the newly brightened area and magnetic field of the area are calculated. We report the results of the analysis carried out for nine flare events observed during 2010-2015 from Kanzelhöhe Solar Observatory for Solar and Environmental Research. The parameters like reconnection flux and reconnection rate estimated using Ca-K and H α images are compared. We infer that the reconnection flux parameter estimated from Ca-K and H α follow a similar trend and shows a linear relation in the log-log plot. Further our study also reveals that Ca-K light curve during the course of the flare is dominated by impulsive and gradual components and follows the trend of the non-thermally dominated Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) (25-50 keV) light curves. Whereas, H α light curve is dominated by a gradual component and follows the trend and shape of the thermally dominated RHESSI HXR (6-12 keV) light curves. Title: Dependence of Coronal Mass Ejection Properties on Their Solar Source Active Region Characteristics and Associated Flare Reconnection Flux Authors: Pal, Sanchita; Nandy, Dibyendu; Srivastava, Nandita; Gopalswamy, Nat; Panda, Suman Bibcode: 2018ApJ...865....4P Altcode: 2018arXiv180804144P The near-Sun kinematics of coronal mass ejections (CMEs) determine the severity and arrival time of associated geomagnetic storms. We investigate the relationship between the deprojected speed and kinetic energy of CMEs and magnetic measures of their solar sources, reconnection flux of associated eruptive events, and intrinsic flux-rope characteristics. Our data covers the period 2010-2014 in solar cycle 24. Using vector magnetograms of source active regions, we estimate the size and nonpotentiality. We compute the total magnetic reconnection flux at the source regions of CMEs using the post-eruption arcade method. By forward modeling the CMEs, we find their deprojected geometric parameters and constrain their kinematics and magnetic properties. Based on an analysis of this database, we report that the correlation between CME speed and their source active region size and global nonpotentiality is weak, but not negligible. We find the near-Sun velocity and kinetic energy of CMEs to be well correlated with the associated magnetic reconnection flux. We establish a statistically significant empirical relationship between the CME speed and reconnection flux that may be utilized for prediction purposes. Furthermore, we find CME kinematics to be related with the axial magnetic field intensity and relative magnetic helicity of their intrinsic flux ropes. The amount of coronal magnetic helicity shed by CMEs is found to be well correlated with their near-Sun speeds. The kinetic energy of CMEs is well correlated with their intrinsic magnetic energy density. Our results constrain processes related to the origin and propagation of CMEs and may lead to better empirical forecasting of their arrival and geoeffectiveness. Title: Geomagnetic Consequences of Interacting CMEs of June 13-14, 2012 Authors: Srivastava, Nandita; Mirtoshev, Zavkiddin; Mishra, Wageesh Bibcode: 2018IAUS..335...65S Altcode: We have studied the consequences of interacting coronal mass ejections (CMEs) of June 13-14, 2012 which were directed towards Earth and caused a moderate geomagnetic storm with Dst index ~ -86 nT. We analysed the in-situ observations of the solar wind plasma and magnetic field parameters obtained from the OMNI database for these CMEs. The in-situ observations show that the interacting CMEs arrive at Earth with the strongest (~ 150 nT) Sudden Storm Commencement (SSC) of the solar cycle 24. We compared these interacting CMEs to a similar interaction event which occurred during November 9-10, 2012. This occurred in the same phase of the solar cycle 24 but resulted in an intense geomagnetic storm (Dst ~ -108 nT), as reported by Mishra et al. (2015). Our analysis shows that in the June event, the interaction led to a merged structure at 1 AU while in the case of November 2012 event, the interacted CMEs arrived as two distinct structures at 1 AU. The geomagnetic signatures of the two cases reveal that both resulted in a single step geomagnetic storm. Title: On the Dynamics of the Largest Active Region of the Solar Cycle 24 Authors: Sarkar, Ranadeep; Srivastava, Nandita; Dhara, Sajal Kumar Bibcode: 2018IAUS..335...32S Altcode: We have studied the dynamics of the solar active region (AR) NOAA 12192 using full-disc continuum images and the vector magnetograms observed by the Helioseismic and Magnetic Imager (HMI) onboard Solar Dynamics Observatory (SDO). AR 12192 is the largest region of the solar cycle 24. It underwent a noticeable growth and produced 6 X-class, 22 M-class and 53 C-class flares during its disc passage. But the most peculiar fact of this AR is that it was associated with only one CME in spite of producing several X-class flares. In this work, we present the area evolution of this giant sunspot group during the first three rotations when it appeared as AR 12172, AR 12192 and AR 12209, respectively. We have also attempted to make a comparative study of the flare-related photospheric magnetic field and Lorentz force changes for both the eruptive and non-eruptive flares produced by AR 12192. Title: Magnetic field experiment at L1 point onboard Aditya-L1 mission Authors: Yadav, Vipin K.; Srivastava, Nandita; Ghosh, Suktisama; Srikar, P. T.; Ravindra, H. S.; Krishnamoorthy, Subhalakshmi Bibcode: 2018cosp...42E3726Y Altcode: The Aditya-L1 mission is first Indian solar mission scheduled to be placed in a halo orbit around the first Lagrangian point (L1) of Sun-Earth system in the year 2019. The scientific payloads onboard Aditya-L1 spacecraft includes a Fluxgate magnetometer (FGM) to measure the local magnetic field which is necessary to supplement the outcome of other scientific experiments onboard. The in-situ vector magnetic field data at L-1 is essential for better understanding of the data provided by the particle and plasma analysis experiments, on board Aditya-L1 mission. Also, the dynamics of Coronal Mass Ejections (CMEs) can be better understood with the help of in-situ magnetic field data at the L1 point region. This data will also serve as crucial input for the short lead-time space weather forecasting models.The FGM is a dual range 3-axis magnetic sensor sits on a 6 m boom mounted on the EP-01 [Earth viewing Panel] deck and configured to deploy along the negative roll direction of the spacecraft. Two sets of such sensors are to be mounted- one at the boom tip (6 m from the spacecraft) and other somewhere in between the boom tip and spacecraft. The main science goals of this instrument is to measure the magnitude and nature of interplanetary magnetic field (IMF) locally and to study the disturbed magnetic conditions and extreme solar events by detecting the CME from Sun as a transient event. The secondary science goals are to study the impact of interplanetary structures and shock solar wind interaction on geo-space environment and to detect plasma waves emanating from the solar corona at L1 point.This paper gives the detailed scientific goals of this magnetic field experiment and brief technical details of the proposed FGM onboard Aditya-L1 spacecraft. Title: Editorial: Earth-affecting Solar Transients Authors: Zhang, Jie; Blanco-Cano, Xochitl; Nitta, Nariaki; Srivastava, Nandita; Mandrini, Cristina H. Bibcode: 2018SoPh..293...80Z Altcode: No abstract at ADS Title: Regolith Alteration Processes at Reiner Gamma Shed Light on the Formation of Lunar Swirls Authors: Bhatt, M.; Woehler, C.; Srivastava, N.; Shevchenko, V. V.; Berezhnoy, A. A.; Grumpe, A.; Bhardwaj, A. Bibcode: 2018LPI....49.1765B Altcode: The two different locations of Reiner Gamma can be ascribed to predominant formation mechanisms; regolith compaction and space-weathering effects. Title: Study of Stealth CMEs and associated ICMEs Authors: Bhatt, Miral; Srivastava, Nandita; Jadhav, Ravindra Bibcode: 2018IAUS..340...89B Altcode: Generally Coronal Mass Ejections (CMEs) are large eruptions of plasma and magnetic field from the Sun into interplanetary space. CMEs are most frequently associated with a variety of phenomena occurring in the lower corona before, during and after onset of eruption and generally are visible in coronagraph observation. Stealth CMEs do not obviously exhibit any of the low-coronal signatures (LCS) like solar flares, flows, jets, coronal dimmings or brightenings, filament eruptions or the formation of flare loop arcades. In this study, five stealth CMEs are selected using LASCO/SOHO CME catalogue and associated ICMEs (Interplanetaty CMEs) are identified using data from STEREO, ACE and WIND. Title: Study of Interplanetary and Geomagnetic Response of Filament Associated CMEs Authors: Dave, Kunjal; Mishra, Wageesh; Srivastava, Nandita; Jadhav, R. M. Bibcode: 2018IAUS..340...83D Altcode: 2018arXiv180700809D It has been established that Coronal Mass Ejections (CMEs) may have significant impact on terrestrial magnetic field and lead to space weather events. In the present study, we selected several CMEs which are associated with filament eruptions on the Sun. We attempt to identify the presence of filament material within ICME at 1AU. We discuss how different ICMEs associated with filaments lead to moderate or major geomagnetic activity on their arrival at the Earth. Our study also highlights the difficulties in identifying the filament material at 1AU within isolated and in interacting CMEs. Title: A Comparative Study of the Eruptive and Non-eruptive Flares Produced by the Largest Active Region of Solar Cycle 24 Authors: Sarkar, Ranadeep; Srivastava, Nandita Bibcode: 2018SoPh..293...16S Altcode: 2018arXiv180100473S We investigate the morphological and magnetic characteristics of solar active region (AR) NOAA 12192. AR 12192 was the largest region of Solar Cycle 24; it underwent noticeable growth and produced 6 X-class flares, 22 M-class flares, and 53 C-class flares in the course of its disc passage. However, the most peculiar fact of this AR is that it was associated with only one CME in spite of producing several X-class flares. In this work, we carry out a comparative study between the eruptive and non-eruptive flares produced by AR 12192. We find that the magnitude of abrupt and permanent changes in the horizontal magnetic field and Lorentz force are significantly smaller in the case of the confined flares compared to the eruptive one. We present the areal evolution of AR 12192 during its disc passage. We find the flare-related morphological changes to be weaker during the confined flares, whereas the eruptive flare exhibits a rapid and permanent disappearance of penumbral area away from the magnetic neutral line after the flare. Furthermore, from the extrapolated non-linear force-free magnetic field, we examine the overlying coronal magnetic environment over the eruptive and non-eruptive zones of the AR. We find that the critical decay index for the onset of torus instability was achieved at a lower height over the eruptive flaring region, than for the non-eruptive core area. These results suggest that the decay rate of the gradient of overlying magnetic-field strength may play a decisive role to determine the CME productivity of the AR. In addition, the magnitude of changes in the flare-related magnetic characteristics are found to be well correlated with the nature of solar eruptions. Title: Geometric and magnetic properties of coronal flux ropes associated with CMEs leading to geomagnetic storms Authors: Sarkar, Ranadeep; Srivastava, Nandita Bibcode: 2018IAUS..340..191S Altcode: 2018arXiv180511329S We have studied three Interplanetary Coronal Mass Ejections (ICMEs) having clear signatures of magnetic cloud (MC) arrival at 1 AU and their associated solar sources during 2011 to 2013. Comparing the axial magnetic field strength (B0) of the near-Sun coronal flux-ropes with that of the MC at 1 AU, we have found that the average inferred value of B0 at 1 AU assuming the self-similar expansion of the flux-rope is two times smaller than the value of B0 obtained from the results of MC fitting. Furthermore, by comparing the initial orientation of the flux-rope near the Sun and its final orientation at 1 AU we have found that the three CMEs exhibited more than 80° rotation during its propagation through the interplanetary medium. Our study suggests that although the near-Sun magnetic properties of coronal flux-ropes can be used to infer the field strength of the associated MC at 1 AU, it is difficult to estimate the final orientation of the MC axis in order to predict the geo-effectiveness of the ICMEs. Title: Solar cycle variation of coronal mass ejections contribution to solar wind mass flux Authors: Mishra, Wageesh; Srivastava, Nandita; Mirtoshev, Zavkiddin; Wang, Yuming Bibcode: 2018IAUS..340..175M Altcode: 2018arXiv180507593M Coronal Mass Ejections (CMEs) contribute to the perturbation of solar wind in the heliosphere. Thus, depending on the different phases of the solar cycle and the rate of CME occurrence, contribution of CMEs to solar wind parameters near the Earth changes. In the present study, we examine the long term occurrence rate of CMEs, their speeds, angular widths and masses. We attempt to find correlation between near sun parameters of the CMEs with near the Earth measurements. Importantly, we attempt to find what fraction of the averaged solar wind mass near the Earth is provided by the CMEs during different phases of the solar cycles. Title: Science objectives of the magnetic field experiment onboard Aditya-L1 spacecraft Authors: Yadav, Vipin K.; Srivastava, Nandita; Ghosh, S. S.; Srikar, P. T.; Subhalakshmi, Krishnamoorthy Bibcode: 2018AdSpR..61..749Y Altcode: The Aditya-L1 is first Indian solar mission scheduled to be placed in a halo orbit around the first Lagrangian point (L1) of Sun-Earth system in the year 2018-19. The approved scientific payloads onboard Aditya-L1 spacecraft includes a Fluxgate Digital Magnetometer (FGM) to measure the local magnetic field which is necessary to supplement the outcome of other scientific experiments onboard. The in-situ vector magnetic field data at L1 is essential for better understanding of the data provided by the particle and plasma analysis experiments, onboard Aditya-L1 mission. Also, the dynamics of Coronal Mass Ejections (CMEs) can be better understood with the help of in-situ magnetic field data at the L1 point region. This data will also serve as crucial input for the short lead-time space weather forecasting models.

The proposed FGM is a dual range magnetic sensor on a 6 m long boom mounted on the Sun viewing panel deck and configured to deploy along the negative roll direction of the spacecraft. Two sets of sensors (tri-axial each) are proposed to be mounted, one at the tip of boom (6 m from the spacecraft) and other, midway (3 m from the spacecraft). The main science objective of this experiment is to measure the magnitude and nature of the interplanetary magnetic field (IMF) locally and to study the disturbed magnetic conditions and extreme solar events by detecting the CME from Sun as a transient event. The proposed secondary science objectives are to study the impact of interplanetary structures and shock solar wind interaction on geo-space environment and to detect low frequency plasma waves emanating from the solar corona at L1 point. This will provide a better understanding on how the Sun affects interplanetary space.

In this paper, we shall give the main scientific objectives of the magnetic field experiment and brief technical details of the FGM onboard Aditya-1 spacecraft. Title: Interplanetary and Geomagnetic Consequences of Interacting CMEs of 13 - 14 June 2012 Authors: Srivastava, Nandita; Mishra, Wageesh; Chakrabarty, D. Bibcode: 2018SoPh..293....5S Altcode: 2017arXiv171208408S We report on the kinematics of two interacting CMEs observed on 13 and 14 June 2012. The two CMEs originated from the same active region NOAA 11504. After their launches which were separated by several hours, they were observed to interact at a distance of 100 R from the Sun. The interaction led to a moderate geomagnetic storm at the Earth with minimum Dst index of approximately −86 nT. The kinematics of the two CMEs is estimated using data from the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) instrument onboard the Solar Terrestrial Relations Observatory (STEREO). Assuming a head-on collision scenario, we find that the collision is inelastic in nature. Further, the signatures of their interaction are examined using the in situ observations obtained by Wind and the Advance Composition Explorer (ACE) spacecraft. It is also found that this interaction event led to the strongest sudden storm commencement (SSC) (≈150 nT) of the present Solar Cycle 24. The SSC was of long duration, approximately 20 hours. The role of interacting CMEs in enhancing the geoeffectiveness is examined. Title: MAVEN-Measured Meteoritic Ions on Mars - Tracers of Lower Ionosphere Processes With and Without Analogues On Earth Authors: Benna, M.; Grebowsky, J. M.; Collinson, G.; Plane, J. M. C.; Mitchell, D.; Srivastava, N. Bibcode: 2017AGUFM.P51C2607B Altcode: MAVEN observations of meteoritic metal ion populations during "deep dip" campaigns at Mars have revealed unique non-Earth like behavior that are not yet understood. These deep dip campaigns (6 so far) consisted each of more than a score of repeated orbits through the Martian molecular-ion-dominated lower ionosphere, whose terrestrial parallel (Earth's E-region) has been rather sparcely surveyed in situ by sounding rockets. In regions of weak Mars magnetic fields, MAVEN found ordered exponentially decreasing metal ion concentrations above the altitude of peak meteor ablation. Such an ordered trend has never been observed on Earth. Isolated anomalous high-altitude layers in the metal ion are also encountered, typically on deep dip campaigns in the southern hemisphere where large localized surface remanent magnetic fields prevail. The source of these anomalous layers is not yet evident, although the occurrences of some high-altitude metal ion enhancements were in regions with measured perturbed magnetic fields, indicative of localized electrical currents. Further investigation shows that those currents are also sometimes associated with superthermal/energetic electron bursts offering evidence that that impact ionization of neutral metal populations persisting at high altitudes are the source of metal ion enhancement - a rather difficult assumption to accept far above the ablation region where the metal neutrals are deposited. The relationship of the anomalous layers to the coincident electron populations as well as to the orientation of the magnetic fields which can play a role in the neutral wind generated ion convergences as on Earth is investigated. Title: Distribution of meteoritic ions in the upper atmosphere of Mars as observed by MAVEN's mass spectrometer Authors: Benna, M.; Grebowsky, J. M.; Srivastava, N.; Plane, J. M. C.; Mahaffy, P. R. Bibcode: 2017EPSC...11..163B Altcode: The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission made the first in situ detection of the continuous presence of Sodium, Magnesium, and Iron ions at Mars. The measured density distributions revealed that these metal ions are well-mixed with the neutral atmosphere at altitudes where no mixing process is expected. Additionally, isolated metal ion layers mimicking Earth's sporadic E layers were regularly observed despite the lack of a strong magnetic field as required at Earth. Finally, the metal ion distributions are coherent enough to always reveal the signature of atmospheric gravity wave signatures. Title: Assessing the Nature of Collisions of Coronal Mass Ejections in the Inner Heliosphere Authors: Mishra, Wageesh; Wang, Yuming; Srivastava, Nandita; Shen, Chenglong Bibcode: 2017ApJS..232....5M Altcode: 2017arXiv170708299M There have been several attempts in the past to understand the nature of the collision of individual cases of interacting coronal mass ejections (CMEs). We selected eight cases of interacting CMEs and estimated their propagation and expansion speeds, and direction of impact and masses, by exploiting coronagraphic and heliospheric imaging observations. Using these estimates while ignoring the errors therein, we find that the nature of collisions is perfectly inelastic for two cases (I.e., 2012 March and November), inelastic for two cases (I.e., 2012 June and 2011 August), elastic for one case (I.e., 2013 October), and super-elastic for three cases (I.e., 2011 February, 2010 May, and 2012 September). Including the large uncertainties in the estimated directions, angular widths, and pre-collision speeds, the probability of a perfectly inelastic collision for the 2012 March and November cases drops from 98% to 60% and 100% to 40%, respectively, increasing the probability for other types of collision. Similarly, the probability of an inelastic collision drops from 95% to 50% for the 2012 June case, 85% to 50% for the 2011 August case, and 75% to 15% for the 2013 October case. We note that the probability of a super-elastic collision for the 2011 February, 2010 May, and 2012 September CMEs drops from 90% to 75%, 60% to 45%, and 90% to 50%, respectively. Although the sample size is small, we find good dependence of the nature of collision on the CME parameters. The crucial pre-collision parameters of the CMEs responsible for increasing the probability of a super-elastic collision are, in descending order of priority, their lower approaching speed, expansion speed of the following CME higher than the preceding one, and a longer duration of the collision phase. Title: The Multi Application Solar Telescope Authors: Venkatakrishnan, P.; Mathew, Shibu K.; Srivastava, Nandita; Bayanna, A. R.; Kumar, Brajesh; Ramya, Bireddy; Jain, Naresh; Saradava, Mukesh Bibcode: 2017CSci..113..686V Altcode: No abstract at ADS Title: Validation of the CME Geomagnetic Forecast Alerts Under the COMESEP Alert System Authors: Dumbović, Mateja; Srivastava, Nandita; Rao, Yamini K.; Vršnak, Bojan; Devos, Andy; Rodriguez, Luciano Bibcode: 2017SoPh..292...96D Altcode: Under the European Union 7th Framework Programme (EU FP7) project Coronal Mass Ejections and Solar Energetic Particles (COMESEP, http://comesep.aeronomy.be), an automated space weather alert system has been developed to forecast solar energetic particles (SEP) and coronal mass ejection (CME) risk levels at Earth. The COMESEP alert system uses the automated detection tool called Computer Aided CME Tracking (CACTus) to detect potentially threatening CMEs, a drag-based model (DBM) to predict their arrival, and a CME geoeffectiveness tool (CGFT) to predict their geomagnetic impact. Whenever CACTus detects a halo or partial halo CME and issues an alert, the DBM calculates its arrival time at Earth and the CGFT calculates its geomagnetic risk level. The geomagnetic risk level is calculated based on an estimation of the CME arrival probability and its likely geoeffectiveness, as well as an estimate of the geomagnetic storm duration. We present the evaluation of the CME risk level forecast with the COMESEP alert system based on a study of geoeffective CMEs observed during 2014. The validation of the forecast tool is made by comparing the forecasts with observations. In addition, we test the success rate of the automatic forecasts (without human intervention) against the forecasts with human intervention using advanced versions of the DBM and CGFT (independent tools available at the Hvar Observatory website, http://oh.geof.unizg.hr). The results indicate that the success rate of the forecast in its current form is unacceptably low for a realistic operation system. Human intervention improves the forecast, but the false-alarm rate remains unacceptably high. We discuss these results and their implications for possible improvement of the COMESEP alert system. Title: Probing the heliosphere using in situ payloads on-board Aditya-L1 Authors: Janardhan, P.; Vadawale, Santosh; Bapat, Bhas; Subramanian, K. P.; Chakrabarty, D.; Kumar, Prashant; Sarkar, Aveek; Srivastava, Nandita; Satheesh Thampi, R.; Yadav, Vipin K.; Dhanya, M. B.; Nampoothiri, Govind G.; Abhishek, J. K.; Bhardwaj, Anil; Subhalakshmi, K. Bibcode: 2017CSci..113..620J Altcode: No abstract at ADS Title: Validation of the CME Geomagnetic forecast alerts under COMESEP alert system Authors: Dumbovic, Mateja; Srivastava, Nandita; Khodia, Yamini; Vršnak, Bojan; Devos, Andy; Rodriguez, Luciano Bibcode: 2017EGUGA..1914917D Altcode: An automated space weather alert system has been developed under the EU FP7 project COMESEP (COronal Mass Ejections and Solar Energetic Particles: http://comesep.aeronomy.be) to forecast solar energetic particles (SEP) and coronal mass ejection (CME) risk levels at Earth. COMESEP alert system uses automated detection tool CACTus to detect potentially threatening CMEs, drag-based model (DBM) to predict their arrival and CME geo-effectiveness tool (CGFT) to predict their geomagnetic impact. Whenever CACTus detects a halo or partial halo CME and issues an alert, DBM calculates its arrival time at Earth and CGFT calculates its geomagnetic risk level. Geomagnetic risk level is calculated based on an estimation of the CME arrival probability and its likely geo-effectiveness, as well as an estimate of the geomagnetic-storm duration. We present the evaluation of the CME risk level forecast with COMESEP alert system based on a study of geo-effective CMEs observed during 2014. The validation of the forecast tool is done by comparing the forecasts with observations. In addition, we test the success rate of the automatic forecasts (without human intervention) against the forecasts with human intervention using advanced versions of DBM and CGFT (self standing tools available at Hvar Observatory website: http://oh.geof.unizg.hr). The results implicate that the success rate of the forecast is higher with human intervention and using more advanced tools. This work has received funding from the European Commission FP7 Project COMESEP (263252). We acknowledge the support of Croatian Science Foundation under the project 6212 „Solar and Stellar Variability". Title: Future Scientific Exploration of the Moon: Sample Return from the Lowell Crater, Orientale Basin Authors: Srivastava, N. Bibcode: 2017LPICo1989.8066S Altcode: A case for sample return from the Lowell crater has been made stating its geological importance and uniqueness on the Moon. Such an endeavor would provide samples essential for making significant advancements in lunar science and exploration. Title: On Understanding the Nature of Collisions of Coronal Mass Ejections Observed by STEREO Authors: Mishra, Wageesh; Wang, Yuming; Srivastava, Nandita Bibcode: 2016ApJ...831...99M Altcode: 2016arXiv160707692M We attempt to understand the collision characteristics of two coronal mass ejections (CMEs) launched successively from the Sun on 2013 October 25. The estimated kinematics, from three-dimensional (3D) reconstruction techniques applied to observations of CMEs by the SECCHI/Coronagraphic (COR) and Heliospheric Imagers, reveal their collision around 37 {R} from the Sun. In the analysis, we take into account the propagation and expansion speeds, impact direction, and angular size as well as the masses of the CMEs. These parameters are derived from imaging observations, but may suffer from large uncertainties. Therefore, by adopting head-on as well as oblique collision scenarios, we have quantified the range of uncertainties involved in the calculation of the coefficient of restitution for expanding magnetized plasmoids. We show that the large expansion speed of the following CME compared with that of the preceding CME results in a higher probability of super-elastic collision. We also infer that a relative approaching speed of the CMEs lower than the sum of their expansion speeds increases the chance of a super-elastic collision. The analysis under reasonable errors in the observed parameters of the CME reveals a larger probability of occurrence of an inelastic collision for the selected CMEs. We suggest that the collision nature of two CMEs should be discussed in 3D, and the calculated value of the coefficient of restitution may suffer from a large uncertainty. Title: Lowell crater: A region of prime geological importance on the Moon Authors: Srivastava, Neeraj Bibcode: 2016EGUGA..1812570S Altcode: Detailed surface topography, morphology, morphometry, spectral reflectance studies, and crater chronology of the Lowell crater region have been carried out using data from Kaguya (JAXA), LRO (NASA) and Chandrayaan-1(ISRO) missions. The study has revealed that the Lowell crater is characterized with several peculiarities. Some of these include: a) conspicuous W-E asymmetries in the morphological make-up of the central peak, crater wall and floor constituents; b) low albedo proximal ejecta blanket mainly confined to the northern areas; c) distribution of exterior melt pools only on the northeastern side; d) possible exposures of olivine bearing undifferentiated mantle rocks; e) a Copernican age of formation, even though characteristic rays are absent; and, f) possibility of recent volcanism inside it. Most of these observed specialties in the case of the Lowell crater are related to variations in the pre-existing topography and target material properties, which are related to its broad geological context i.e. its location inside the Orientale basin and the nature of the Lowell forming impact event. It has been deciphered that the Lowell crater formed in the Montes Rook region of the Orientale basin during Younger Copernican period (374±28 Ma old) due to an oblique impact of a ~5.7 km diameter projectile from the S-SW direction, at an angle of ~30-45 degrees. Thus, the Moon was hit by at least four projectiles of ~6 km diameter during the Younger Copernican period, the others three being those responsible for the formation of craters Jackson, Ohm and Tycho. In addition to these, the morphology of the Lowell crater favors much debated extent of the Orientale transient cavity to lie between the ORR & the IRR. Thus, the study establishes the Lowell crater as a site of prime geological importance on the Moon that has the potential to address several important issues related to lunar geology such as basin and crater forming process, nature of the mantle, and relationship between impact cratering and volcanism. Title: Geomorphology of Lowell crater region on the Moon Authors: Srivastava, N.; Varatharajan, I. Bibcode: 2016Icar..266...44S Altcode: Surface topography, surface morphology and crater chronology studies have been carried out for the Lowell crater region (occupying ∼198 × 198 km2 in the northwestern quadrant of the Orientale basin) using Kaguya TC-DTM, LRO-WAC data, and Chandrayaan-1 M3-750 nm image, to characterize and date Lowell impact event and to identify and assess the geological importance of the Lowell crater and effect of pre-existing geological conditions on the present day appearance of Lowell crater. The Lowell crater has been found to be polygonal in shape with an average diameter of 69.03 km. Its average rim height and depth from pre-existing surface are 1.02 km and 2.82 km respectively. A prominent central peak with average height of 1.77 km above the crater floor is present, which could have exposed undifferentiated mantle rocks. The peak exhibits a pronounced ;V; shaped slumped zone on the eastern side and a distinct ;V; shaped depression in the adjacent region on the crater floor. Several other peculiarities noticed and mapped here include W-E asymmetry in the degree of slumping of the walls and height of the topographic rim, N-S asymmetry in the proximal ejecta distribution with most of the material lying in the northern direction, concentration of exterior melt pools in the northeastern direction only, presence of several cross cutting pre-existing lineaments on the crater walls, presence of a superposed rayed crater on the eastern wall, and a geologically interesting resurfaced unit, which could be an outcome of recent volcanic activity in the region. It has been inferred that the Lowell crater formed due to impact of a ∼5.7 km diameter bolide in the Montes Rook region. The impact occurred at an angle of ∼30-45° from the S-SW direction. The age of the Lowell crater has been estimated as 374 ± 28 Ma, therefore it is a Younger Copernican crater consistent with the possibility expressed by McEwen et al. (McEwen, A.S., et al. [1993]. J. Geophys. Res. 98(E9), 17207-17231). Pre-existing topography and morphology has played a key role in shaping up the present day Lowell crater. Title: Kinematics of interacting CMEs of 25 and 28 September 2012 Authors: Mishra, Wageesh; Srivastava, Nandita; Singh, Talwinder Bibcode: 2015JGRA..12010221M Altcode: 2015arXiv151106970M We have studied two coronal mass ejections (CMEs) that occurred on 25 and 28 September 2012 and interacted near the Earth. By fitting the Graduated Cylindrical Shell model on the SECCHI/COR2 images and applying the Stereoscopic Self-Similar Expansion method on the SECCHI/HI images, the initial direction of both the CMEs is estimated to be west of the Sun-Earth line. Further, the three-dimensional (3-D) heliospheric kinematics of these CMEs have been estimated using Self-Similar Expansion (SSE) reconstruction method. We show that the use of SSE method with different values of angular extent of the CMEs leads to significantly different kinematics estimates for the CMEs propagating away from the observer. Using the estimated kinematics and true masses of the CMEs, we have derived the coefficient of restitution for the collision which is found to be close to elastic. The in situ measurements at 1 AU show two distinct structures of interplanetary CMEs, heating of the following CME, and ongoing interaction between the preceding and the following CME. We highlight the signatures of interaction in remote and in situ observations of these CMEs and the role of interaction in producing a major geomagnetic storm. Title: Understanding the Nature of Collision of CMEs in the Heliosphere Authors: Mishra, W.; Wang, Y.; Srivastava, N. Bibcode: 2015AGUFMSH53A2465M Altcode: Understanding the propagation of coronal mass ejections (CMEs) in the heliosphere is important to estimate their arrival time at Earth. The kinematics of CMEs can change when they interact or collide with each other as they propagate in the heliosphere. The knowledge about nature of collision of CMEs can be utilized to predict their post-collision kinematics and relatively accurate arrival time at the Earth. To calculate the coefficient of restitution for the colliding CMEs, we need to estimate the propagation and expansion speeds, impact direction and the masses of the CMEs. Although, these parameters could be derived from heliospheric imaging observations, but have large uncertainties. In the present study, we have thoroughly discussed the uncertainties involved in the calculation of coefficient of restitution. Our results suggest that calculated value of coefficient of restitution, from mere use of kinematics from STEREO/COR and HI observations, should also be validated with simulation before making a reliable conclusion for nature of collision for the CMEs. We also highlight the significance of HI observations in studying CME-CME collision for the purpose of improved space weather forecasting. Title: Heliospheric tracking of enhanced density structures of the 6 October 2010 CME Authors: Mishra, Wageesh; Srivastava, Nandita Bibcode: 2015JSWSC...5A..20M Altcode: 2015arXiv150504871M A Coronal Mass Ejection (CME) is an inhomogeneous structure consisting of different features which evolve differently with the propagation of the CME. Simultaneous heliospheric tracking of different observed features of a CME can improve our understanding about relative forces acting on them. It also helps to estimate accurately their arrival times at the Earth and identify them in in-situ data. This also enables finding any association between remotely observed features and in-situ observations near the Earth. In this paper, we attempt to continuously track two density enhanced features in the CME of 6 October 2010, one at the front and another at the rear edge. This is achieved by using time-elongation maps constructed from STEREO/SECCHI observations. We derive the kinematics of the tracked features using various reconstruction methods. The estimated kinematics are used as inputs in the Drag Based Model (DBM) to estimate the arrival time of the tracked features of the CME at L1. On comparing the estimated kinematics as well as the arrival times of the remotely observed features with in-situ observations by Advanced Composition Explorer (ACE) and Wind, we find that the tracked bright feature at the rear edge of 6 October 2010 CME corresponds most probably to the enhanced density structure after the magnetic cloud detected by ACE and Wind. In-situ plasma and compositional parameters provide evidence that the rear edge density structure may correspond to a filament associated with the CME while the density enhancement at the front corresponds to the leading edge of the CME. Based on this single event study, we discuss the relevance and significance of Heliospheric Imager (HI) observations in identification of the three-part structure of the CME. Title: Evolution and Consequences of Interacting CMEs of 9 - 10 November 2012 Using STEREO/SECCHI and In Situ Observations Authors: Mishra, Wageesh; Srivastava, Nandita; Chakrabarty, D. Bibcode: 2015SoPh..290..527M Altcode: 2014arXiv1408.0352M Understanding the kinematic evolution of coronal mass ejections (CMEs) in the heliosphere is important to estimate their arrival time at Earth. The kinematics of CMEs can change when they interact or collide with each other as they propagate in the heliosphere. In this article, we analyze the collision and post-interaction characteristics of two Earth-directed CMEs that were launched successively on 9 and 10 November 2012. To do this, we used white-light imaging observations from STEREO/SECCHI and in situ observations taken from the Wind spacecraft. We tracked two density-enhancement features associated with the leading and trailing edge of the 9 November CME and one density enhanced feature associated with the leading edges of the 10 November CME by constructing J-maps. We found that the leading edge of the 10 November CME interacted with the trailing edge of the 9 November CME. We also estimated the kinematics of these features of the CMEs and found a significant change in their dynamics after interaction. In in situ observations, we identified distinct structures associated with interacting CMEs and also observed heating and compression as signatures of their interaction. Our analysis shows an improvement in the arrival-time prediction of CMEs when their post-collision dynamics are used instead of the pre-collision dynamics. By estimating the true masses and speeds of these colliding CMEs, we investigated the nature of the observed collision, which is found to be almost perfectly inelastic. The investigation also places in perspective the geomagnetic consequences of the two CMEs and their interaction in terms of occurrence of geomagnetic storms and triggering of magnetospheric substorms. Title: Narrow-Band Imaging System for the Multi-application Solar Telescope at Udaipur Solar Observatory: Characterization of Lithium Niobate Etalons Authors: Raja Bayanna, A.; Mathew, Shibu K.; Venkatakrishnan, P.; Srivastava, N. Bibcode: 2014SoPh..289.4007R Altcode: 2014arXiv1407.7627R; 2014SoPh..tmp...96R The Multi-application Solar Telescope is a 50 cm off-axis Gregorian telescope that has been installed at the lake site of Udaipur Solar Observatory. For quasi-simultaneous photospheric and chromospheric observations, a narrow-band imager has been developed as one of the back-end instruments for this telescope. Narrow-band imaging is achieved using two lithium niobate Fabry-Perot etalons working in tandem as a filter. This filter can be tuned to different wavelengths by changing either voltage, tilt, or temperature of the etalons. To characterize the etalons, a Littrow spectrograph was set up in conjunction with a 15 cm Carl Zeiss Coudé solar telescope. The etalons were calibrated for the solar spectral lines Fe I 6173 Å, and Ca II 8542 Å. In this work, we discuss the characterization of the Fabry-Perot etalons, specifically, the temperature and voltage tuning of the system for the spectral lines proposed for observations. We present the details of the calibration set-up and various tuning parameters. We also present solar images obtained using the system. Title: Morphological and Kinematic Evolution of Three Interacting Coronal Mass Ejections of 2011 February 13-15 Authors: Mishra, Wageesh; Srivastava, Nandita Bibcode: 2014ApJ...794...64M Altcode: 2014arXiv1408.4604M During 2011 February 13-15, three Earth-directed coronal mass ejections (CMEs) launched in succession were recorded as limb CMEs by STEREO/SECCHI coronagraphs (COR). These CMEs provided an opportunity to study their geometrical and kinematic evolution from multiple vantage points. In this paper, we examine the differences in geometrical evolution of slow and fast CMEs during their propagation in the heliosphere. We also study their interaction and collision using STEREO/SECCHI COR and Heliospheric Imager (HI) observations. We have found evidence of interaction and collision between the CMEs of February 15 and 14 in the COR2 and HI1 field of view (FOV), respectively, while the CME of February 14 caught up with the CME of February 13 in the HI2 FOV. By estimating the true mass of these CMEs and using their pre- and post-collision dynamics, the momentum and energy exchange between them during the collision phase are studied. We classify the nature of the observed collision between the CMEs of February 14 and 15 as inelastic, reaching close to the elastic regime. Relating imaging observations with in situ WIND measurements at L1, we find that the CMEs move adjacent to each other after their collision in the heliosphere and are recognized as distinct structures in in situ observations. Our results highlight the significance of HI observations in studying CME-CME collision for the purpose of improved space weather forecasting. Title: Mineralogy of young lunar mare basalts: Assessment of temporal and spatial heterogeneity using M3 data from Chandrayaan-1 Authors: Varatharajan, Indhu; Srivastava, Neeraj; Murty, Sripada V. S. Bibcode: 2014Icar..236...56V Altcode: A comparative assessment of the mineralogy of young basalts (∼1.2 Ga to ∼2.8 Ga) from the western nearside, Moscoviense basin, and the Orientale basin of the Moon has been made using Level 2 Moon Mineralogy Mapper (M3) data from the Chandrayaan-1 mission. Spectral data characteristics of the individual units have been generated from fresh small craters to minimize the complications due to space weathering. Representative spectra for individual units and the derived spectral parameters (band centers and integrated band depth ratio) have been used to study composition of these young basalts. A modified approach of Gaffey et al. (Gaffey, M.J., Cloutis, E.A., Kelley, M.S., Reed, K.L. [2002]. Mineralogy of asteroids. In: Asteroids III. The University of Arizona Press, Tucson, pp. 183-204) (for olivine-pyroxene mixtures) and the methodology of Adams (Adams, J.B. [1974]. J. Geophys. Res. 79, 4829-4836. http://dx.doi.org/10.1029/JB079i032p04829) (for interpreting pyroxene type) have been used to improve our understanding of the spectral behavior of these basalts. Most of the young basalts of Oceanus Procellarum are characterized by abundant olivines and they show complex volcanic history. Vast exposures of olivine concentrated units having higher abundance of olivine content than high-Ca pyroxenes are emplaced in the northern Oceanus Procellarum region. Mostly, they show distinct stratigraphic gradation with the immediately underlying units of relatively lower olivine content. The Moscoviense unit shows signatures of Fe-rich glasses along with clinopyroxenes. The basalts of Orientale basin are typically devoid of olivine and are rich in high-Ca pyroxene. Thus, mineralogy of these mare basalts which erupted during the late stage volcanism vary across the Moon’s surface; however, broader observations reveal apparently higher FeO content in the younger basalts of western nearside and Orientale region. Title: A Comparison of Reconstruction Methods for the Estimation of Coronal Mass Ejections Kinematics Based on SECCHI/HI Observations Authors: Mishra, Wageesh; Srivastava, Nandita; Davies, Jackie A. Bibcode: 2014ApJ...784..135M Altcode: 2014arXiv1407.8446M A study of the kinematics and arrival times of coronal mass ejections (CMEs) at Earth, derived from time-elongation maps (J-maps) constructed from STEREO/heliospheric imager (HI) observations, provides an opportunity to understand the heliospheric evolution of CMEs in general. We implement various reconstruction techniques, based on the use of time-elongation profiles of propagating CMEs viewed from single or multiple vantage points, to estimate the dynamics of three geo-effective CMEs. We use the kinematic properties, derived from analysis of the elongation profiles, as inputs to the Drag Based Model for the distance beyond which the CMEs cannot be tracked unambiguously in the J-maps. The ambient solar wind into which these CMEs, which travel with different speeds, are launched, is different. Therefore, these CMEs will evolve differently throughout their journey from the Sun to 1 AU. We associate the CMEs, identified and tracked in the J-maps, with signatures observed in situ near 1 AU by the WIND spacecraft. By deriving the kinematic properties of each CME, using a variety of existing methods, we assess the relative performance of each method for the purpose of space weather forecasting. We discuss the limitations of each method, and identify the major constraints in predicting the arrival time of CMEs near 1 AU using HI observations. Title: A Statistical Study on Characteristics of Disappearing Prominences Authors: Joshi, Anand D.; Bong, Su-Chan; Srivastava, Nandita Bibcode: 2014IAUS..300..422J Altcode: Real-time monitoring of filaments is essential for the prediction of their eruption and the ensuing coronal mass ejection (CME). We apply an automated algorithm for the detection and tracking of filaments in full-disc Hα images to obtain their physical attributes. This provides an accurate onset time of the eruption, and also allows us to study the physical characteristics of the erupting filaments in an objective manner. Title: On the onset of recurrent eruptions of a filament observed during August 2012 Authors: Srivastava, Nandita; Joshi, Anand D.; Mathew, Shibu K. Bibcode: 2014IAUS..300..495S Altcode: We report observations of a long filament that underwent recurrent partial eruptions on August 4, 6, and 8, 2012. The filament reappeared in the subsequent rotation of the Sun, and disappeared completely on August 31, 2012. We implemented an automated filament detection algorithm developed by us for estimating different attributes of these filaments few hours prior to its disappearance in Hα and studied their evolution. Based on these attributes, we determine the onset time of the disappearance of Hα filaments. We then compared these onset times with that of the associated CMEs observed by LASCO/SOHO coronagraphs. This is also useful to understand temporal relationship of EUV and X-ray flux variation associated with filament disappearances in Hα. Our results show the importance of such studies in understanding the mechanism of CME initiation, particularly the role of eruptive filaments, in this process. Title: Role of filament plasma remnants in ICMEs leading to geomagnetic storms Authors: Sharma, Rahul; Srivastava, Nandita; Chakrabarty, D. Bibcode: 2014IAUS..300..493S Altcode: We studied three interplanetary coronal mass ejections associated with solar eruptive filaments. Filament plasma remnants embedded in these structures were identified using plasma, magnetic and compositional signatures. These features when impacted the Earth's terrestrial magnetosphere - ionosphere system, resulted in geomagnetic storms. During the main phase of associated storms, along with high density plasma structures, polarity reversals in the Y-component (dawn-to-dusk) of the interplanetary electric field seem to trigger major auroral substorms with concomitant changes in the polar ionospheric electric field. Here, we examine the cases where plasma dynamics and magnetic structuring in the presence of the prompt penetration of the electric field into the equatorial ionosphere affected the space weather while highlighting the complex geomagnetic storm-substorm relationship. Title: Rapid Formation and Disappearance of a Filament Barb Authors: Joshi, Anand D.; Srivastava, Nandita; Mathew, Shibu K.; Martin, Sara F. Bibcode: 2013SoPh..288..191J Altcode: We present observations of an activated quiescent filament obtained in Hα from the high-resolution Dutch Open Telescope (DOT) on 20 August 2010. The filament developed a barb in 10 min, which disappeared within the next 35 min. A data set from the DOT spanning 2 h was used to analyse this event. Line-of-sight velocity maps were constructed from the Doppler images, which reveal flows in filament spine during this period. Photospheric magnetograms were used from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) to determine the changes in magnetic flux in the region surrounding the barb location. The analysis shows flows in the filament spine towards the barb location preceding its formation, and flows in the barb towards the spine during its disappearance. Magnetograms reveal patches of minority polarity flux close to the end of the barb at its greatest elongation. The flows in the spine and barbs are along numerous threads that compose these typical filament structures. The flows are consistent with field-aligned threads and demonstrate that the replacement time of the mass in barbs, and by inference, in the spine is very rapid. Title: Young viscous flows in the Lowell crater of Orientale basin, Moon: Impact melts or volcanic eruptions? Authors: Srivastava, N.; Kumar, D.; Gupta, R. P. Bibcode: 2013P&SS...87...37S Altcode: Topographical, morphological and spectral reflectance studies have been carried out for a distinct resurface event inside Copernican aged Lowell crater (13.00°S 103.40°W), Orientale basin, using high resolution TC, MI-VIS, LROC-NAC, and M3 data from Kaguya, Lunar Reconnaissance Orbiter (LRO) and Chandrayaan-1 missions. The resurfacing is predominantly gabbroic/basaltic in composition and is confined to nearly a linear ~17 km long, a 3-6 km wide and a ~100 m deep channel, possibly a graben. It is characterised with distinct surface features such as small uplift with melt pond, several lava-like flows, cracks going up to decimetre size, 20-80 m pits/craters with small central uplifts or depressions and ~100 m craters that emanate liquid. A minimum of three generations of flows have been identified within the unit, the oldest one being less viscous and the subsequent younger ones showing well developed lobes due to the high viscosity. There is a conspicuous absence of unambiguously identified primary impact craters on these flows suggesting their fresh nature. On the basis of these integrated observations we hypothesise that at least the younger portions of this amazingly carved resurfaced unit might be composed of volcanic flows erupted from single or multiple sources subsequent to the emplacement of impact melts from a ~9 km diameter crater on the edge of Lowell crater. Gabbroic/basaltic signatures have also been identified at several other locations inside Lowell crater indicating that it would have impacted on a pre-existing basaltic surface or on a gabbroic pluton. These findings have implications to lunar magmatism and understanding of the genesis of young flows on the lunar surface. Title: Estimating the Arrival Time of Earth-directed Coronal Mass Ejections at in Situ Spacecraft Using COR and HI Observations from STEREO Authors: Mishra, Wageesh; Srivastava, Nandita Bibcode: 2013ApJ...772...70M Altcode: 2013arXiv1306.1397M Predicting the arrival time and transit speed of coronal mass ejections (CMEs) near the Earth is critical to understanding the solar-terrestrial relationship. Even though STEREO observations now provide multiple views of CMEs in the heliosphere, the true speeds derived from stereoscopic reconstruction of SECCHI coronagraph data are not quite sufficient for accurate forecasting of the arrival time at Earth of a majority of CMEs. This uncertainty is due to many factors that change CME kinematics, such as the interaction of two or more CMEs or the interaction of CMEs with the pervading solar wind. In order to understand the propagation of CMEs, we have used the three-dimensional triangulation method on SECCHI coronagraph (COR2) images and geometric triangulation on the J-maps constructed from Heliospheric Imagers HI1 and HI2 data for eight Earth-directed CMEs observed during 2008-2010. Based on the reconstruction, and implementing the drag-based model for the distance where the CMEs could not be tracked unambiguously in the interplanetary (IP) medium, the arrival time of these CMEs have been estimated. These arrival times have also been compared with the actual arrival times as observed by in situ instruments. The analysis reveals the importance of heliospheric imaging for improved forecasting of the arrival time and direction of propagation of CMEs in the IP medium. Title: Interplanetary and geomagnetic consequences of 5 January 2005 CMEs associated with eruptive filaments Authors: Sharma, Rahul; Srivastava, Nandita; Chakrabarty, D.; Möstl, Christian; Hu, Qiang Bibcode: 2013JGRA..118.3954S Altcode: On 5 January 2005, SoHO/LASCO observed the launch of two successive coronal mass ejections (CMEs) associated with the filament (active region and quiescent) structures. The eruptions resulted in two distinct magnetic clouds whose embedded flux-rope topology is modeled by the Grad-Shafranov (G-S) reconstruction technique. Filament plasma remnants in these magnetic clouds were identified using a combination of in situ plasma, magnetic, and composition signatures. In situ spacecraft (ACE and Wind) measurements suggest interaction between two magnetic clouds with complex magnetic structures at interface region separated by magnetic holes. These features impacted the Earth's terrestrial magnetosphere-ionosphere system and resulted in a moderate geomagnetic storm (peak Dst ≈-96 nT). During the main phase of this storm on 7 January 2005, polarity reversals in the Y component (dawn to dusk) of interplanetary electric field triggered two major auroral substorms with concomitant changes in the polar ionospheric electric field. However, similar polarity reversal on 8 January 2005 during the recovery phase of the storm did not trigger any auroral substorm activity. The results provide clues for the interplanetary interaction of the two CMEs and its possible role in the development of the geomagnetic storm and substorms. Title: Prototype Spectro-Polarimeter for the India's National Large Solar Telescope Authors: Elayavalli Rangarajan, Komandur; Sankarasubramanian, Kasiviswanathan; Srivastava, Nandita; Venkatakrishnan, Parameswaran; Mathew, Shibu; Bayanna, Raja; Hasan, Sirajul; Prabhu, Kesavan Bibcode: 2013EGUGA..15.6932E Altcode: India's National Large Solar Telescope (NLST) of two meter aperture size is proposed to be set up in Ladakh region of Himalayas at a height of around 4300 meters. A high resolution spectrograph along with a polarimeter is planned as one of the backend instruments for NLST. Prototype development of the NLST Spectro-Polarimeter (SP) is proposed to be designed and developed for usage at the back focal plane of the Multi-Application Solar Telescope (MAST) recently installed at the Udaipur Solar Observatory. Design of the prototype SP is discussed in detail along with the scientific goals. The SP is designed to be operated in three wavelengths to observe photospheric and chromospheric layers of the solar atmosphere simultaneously. Vector magnetic fields will be calculated in these layers. High resolution of the designed SP will provide accurate estimates of velocities. Highly resolved polarized line profiles will allow us to obtain the height variation of vector magnetic fields when used along with suitable inversion codes (like SPINOR or SIR). Title: Onset time estimation of eruptive filaments using Halpha line center and Doppler images. Authors: Srivastava, Nandita Bibcode: 2013EGUGA..15..937S Altcode: A dual-beam H-alpha Doppler system is being developed at the Udaipur Solar Observatory (USO) in order to record images of quiet, activated and erupting filaments on the Sun, with special emphasis on the study of those that are associated with geoeffective coronal mass ejections. These H-alpha line center images will be complemented with near co-temporal Doppler images. These images can also be compared with multi-wavelength images obtained from space missions such as STEREO, SOHO and Hinode. In order to understand the potential of these observations, we have used the existing data-sets from different ground based observatories and implemented our analysis technique. The technique involves implementation of an automated detection algorithm developed by us for estimation of different attributes of a filament and study its evolution during its eruption using full disk H-alpha and Doppler images. The analysis is important for determining the exact onset time of the filament eruption based on these attributes. We also compare the onset time of eruptive filament with that of the associated CMEs observed by LASCO coronagraphs and EUV images. In this paper, we present our results to highlight the importance of such studies in understanding the mechanism of CME initiation and possible role of eruptive filaments for the same. This work contributes to the research for European Union Seventh Framework Programme (FP7/2007-2013) for the Coronal Mass Ejections and Solar Energetic Particles (COMESEP) project under Grant Agreement No. 263252. Title: Solar activity and its evolution across the corona: recent advances Authors: Zuccarello, Francesca; Balmaceda, Laura; Cessateur, Gael; Cremades, Hebe; Guglielmino, Salvatore L.; Lilensten, Jean; Dudok de Wit, Thierry; Kretzschmar, Matthieu; Lopez, Fernando M.; Mierla, Marilena; Parenti, Susanna; Pomoell, Jens; Romano, Paolo; Rodriguez, Luciano; Srivastava, Nandita; Vainio, Rami; West, Matt; Zuccarello, Francesco P. Bibcode: 2013JSWSC...3A..18Z Altcode: Solar magnetism is responsible for the several active phenomena that occur in the solar atmosphere. The consequences of these phenomena on the solar-terrestrial environment and on Space Weather are nowadays clearly recognized, even if not yet fully understood. In order to shed light on the mechanisms that are at the basis of the Space Weather, it is necessary to investigate the sequence of phenomena starting in the solar atmosphere and developing across the outer layers of the Sun and along the path from the Sun to the Earth. This goal can be reached by a combined multi-disciplinary, multi-instrument, multi-wavelength study of these phenomena, starting with the very first manifestation of solar active region formation and evolution, followed by explosive phenomena (i.e., flares, erupting prominences, coronal mass ejections), and ending with the interaction of plasma magnetized clouds expelled from the Sun with the interplanetary magnetic field and medium. This wide field of research constitutes one of the main aims of COST Action ES0803: Developing Space Weather products and services in Europe. In particular, one of the tasks of this COST Action was to investigate the Progress in Scientific Understanding of Space Weather. In this paper we review the state of the art of our comprehension of some phenomena that, in the scenario outlined above, might have a role on Space Weather, focusing on the researches, thematic reviews, and main results obtained during the COST Action ES0803. Title: Narrow-band Imager for Multi-Application Solar Telescope (MAST) at Udaipur Solar Observatory Authors: Raja Bayanna, A.; Mathew, Shibu K.; Venkatakrishnan, Parameswaran; Srivastava, Nandita Bibcode: 2013EGUGA..15.7618R Altcode: Multi-Application Solar Telescope (MAST) is an off-axis Gregorian solar telescope of 50 cm clear aperture installed at the lake site of Udaipur solar observatory (USO). A narrow band imager is being developed for near simultaneous observations of the solar atmosphere at different heights. The heart of the system is two Fabry-Perot (FP) etalons working in tandem. The substrate of the etalons is made of Lithium Niobate electro-optic crystal. The filter is tuned by changing the refractive index of the crystal with the application of the voltage. It is important to know the voltage required per unit wavelength shift to tune the system for different wavelength regions for near simultaneous observations. A littrow spectrograph was set up to calibrate the FP etalons. The achieved spectral resolution with the spectrograph at 6173 Å is 35 mÅ. Calibration is carried-out for the Fe I 6173 Å, H-alpha 6563 Å and Ca K 8542 Å. Free spectral range (FSR) obtained for FP1 and FP2 in tandem for 6173 Å is 6.7Å and 150 mÅ respectively. Voltage range of the system allows us to scan the entire line profile of 6173 in the range of ±220 mÅ with a sampling of 20 mÅ. We also performed temperature tuning and voltage tuning of the system. Similar exercise is performed for other two wavelengths. Here we present the details of the calibration set-up and obtained parameters and first-light results of the system. Title: Spatial Distribution of Spinel in the Orientale Basin: New Insights from M^3 Data Authors: Srivastava, N.; Gupta, R. P. Bibcode: 2013LPI....44.1509S Altcode: 2013LPICo1719.1509S M^3 derived spinel distribution and litho-associations in non-mare units of Orientale basin favor its origin from melt-wall rock reaction during ancient magmatism. Title: Spectral Reflectance Studies of Selected Young Basalts on the Moon Using M^3 Datasets from Chandrayaan-1 Authors: Indhu, V.; Srivastava, N.; Murty, S. V. S. Bibcode: 2013LPI....44.1185I Altcode: 2013LPICo1719.1185I L- 2 M^3 data have revealed that young basalts near Litchenberg crater may have slightly higher olivine content than the ones near Aristarchus crater. Title: Indicators of solar filament remnants in ICMEs Authors: Sharma, Rahul; Srivastava, Nandita Bibcode: 2013ASInC..10..143S Altcode: Coronal mass ejections (CMEs) associated with solar filament eruptions expel huge amount of mass, energy and magnetic helicity in interplanetary medium as part of interplanetary coronal mass ejections (ICMEs). Despite of the fact that around 70% of CMEs are associated with filament eruptions, identification of filament (cold) material are rare in in-situ measurements. Only few earlier studies report in-situ observations of filament material by the ACE and Wind spacecraft at L1 point. We examined 10 ICMEs with filament remnants during the last solar cycle for which cold filament material was identified as periods of density enhancements, temperature depressions and low ionic charge states with depressed deviations in RMS parameters (magnetic and plasma). We further attempt to determine the threshold magnitudes of relative changes in magnetic, plasma and compositional parameters associated with in-situ observations which could serve as indicators for filament plasma. Title: Solar eruptive filament studies at USO for the COMESEP project Authors: Srivastava, N.; Crosby, N.; Veronig, A.; Robrrecht, E.; Vršnak, B.; Vennerstrom, S.; Malandraki, O.; Dalla, S.; Rodriguez, L.; Hesse, M.; Odstrcil, D. Bibcode: 2013ASInC..10...67S Altcode: The Coronal Mass Ejections and Solar Energetic Particles (COMESEP) project is developing tools for forecasting geomagnetic storms and solar energetic particle (SEP) radiation storms. By analysis of historical solar and interplanetary data, complemented with the extensive data coverage of solar cycle 23, the key ingredients that lead to geomagnetic storms, SEP events and the factors that are responsible for false alarms are being identified. Based on the insights gained, and making use of algorithms for the automated detection of CMEs, forecasting tools for geomagnetic and SEP radiation storms will be developed and optimised. Validation and implementation of the developed tools into an operational Space Weather Alert system will be performed. COMESEP is a unique cross collaboration effort and bridges the gap between the SEP, CME and terrestrial effects scientific communities. The role of the Udaipur Solar Observatory (USO) in addressing some of the goals of this project are highlighted in this paper. In particular, USO is engaged in studying the CMEs associated with eruptive filaments. We describe the studies undertaken to understand space weather effects related to these CMEs. Title: Estimating arrival time of 10 October 2010 CME using STEREO/SECCHI and in-situ observations Authors: Mishra, Wageesh; Srivastava, Nandita Bibcode: 2013ASInC..10..127M Altcode: The prediction of arrival time of Coronal Mass Ejections (CMEs) at the Earth is one of the prime objectives of solar-terrestrial physicist. In the present work, we applied the tie-pointing method on STEREO/SECCHI coronagraph (COR2) images to obtain the true 3D coordinates of CME feature of 10 October 2010 and estimated its arrival time at 1AU. Further, we tracked this CME in the interplanetary medium using COR2 and HI images from SECCHI instruments and obtained its true kinematics using geometric triangulation technique. In order to estimate the arrival time of the CME, the drag based model is used for the remaining distance where CME could not be tracked with good accuracy in HI field of view. We identified the interplanetary counterpart of 10 October 2010 CME in in-situ data and marked its arrival time which is then compared with the arrival time estimated using remote sensing observations. It is shown that a better prediction of arrival time and transit velocity of CME at 1AU is possible by implementing geometric triangulation technique on HI observations combined with drag based model than using only SECCHI coronagraph images. Title: Using heliospheric imaging observations to forecast the arrival time of CMEs Authors: Mishra, Wageesh; Srivastava, Nandita Bibcode: 2013ASInC...9...70M Altcode: The estimation of arrival time of coronal mass ejections (CMEs) near 1 AU is a crucial problem in the development of any space weather prediction model. For more than twenty years such studies are being done mainly using coronagraphs (SOHO/LASCO) observations near the sun or using empirical, statistical or numerical arrival time models. In both the approaches, we utilize the in-situ measurements of ICMEs as a reference of the actual arrival time of CMEs. But the identification of ICMEs near the earth is based on many signatures and they usually have unclear boundaries, resulting in uncertainties in the actual arrival time too. In this way, our understanding about CME kinematics and estimation of its arrival time based on two point measurements, are not sufficient. In order to understand the CME kinematics throughout the interplanetary medium, we have analyzed the coronagraph (2.5 -15 Rs) and heliospheric imager (15-330 Rs) (SECCHI/HI) data. We applied different methods on imaging (COR and HI) observations to estimate the true kinematics of CMEs in interplanetary medium. We used these estimates as inputs to the drag based model to predict the arrival time as well as transit velocity of CMEs at 1 AU. We also compare the accuracy of different methods implemented on imaging (COR and HI) data on our studied events. Our analysis reveals the importance of heliospheric imager observations in forecasting the CME arrival time near 1 AU. Title: The Build-Up to Eruptive Solar Events Viewed as the Development of Chiral Systems Authors: Martin, S. F.; Panasenco, O.; Berger, M. A.; Engvold, O.; Lin, Y.; Pevtsov, A. A.; Srivastava, N. Bibcode: 2012ASPC..463..157M Altcode: 2012arXiv1212.3646M When we examine the chirality or observed handedness of the chromospheric and coronal structures involved in the long-term build-up to eruptive events, we find that they evolve in very specific ways to form two and only two sets of large-scale chiral systems. Each system contains spatially separated components with both signs of chirality, the upper portion having negative (positive) chirality and the lower part possessing positive (negative) chirality. The components within a system are a filament channel (represented partially by sets of chromospheric fibrils), a filament (if present), a filament cavity, sometimes a sigmoid, and always an overlying arcade of coronal loops. When we view these components as parts of large-scale chiral systems, we more clearly see that it is not the individual components of chiral systems that erupt but rather it is the approximate upper parts of an entire evolving chiral system that erupts. We illustrate the typical pattern of build-up to eruptive solar events first without and then including the chirality in each stage of the build-up. We argue that a complete chiral system has one sign of handedness above the filament spine and the opposite handedness in the barbs and filament channel below the filament spine. If the spine has handedness, the observations favor its having the handedness of the filament cavity and coronal loops above. As the separate components of a chiral system form, we show that the system appears to maintain a balance of right-handed and left-handed features, thus preserving an initial near-zero net helicity. We further argue that the chiral systems allow us to identify key sites of energy transformation and stored energy later dissipated in the form of concurrent CMEs, erupting filaments and solar flares. Each individual chiral system may produce many successive eruptive events above a single filament channel. Because major eruptive events apparently do not occur independent of, or outside of, these unique chiral systems, we hypothesize that the development of chiral systems: (1) are fundamental to the occurrence of eruptive solar events and (2) preserve an approximate balance between positive and negative helicity (right and left-handed chirality) while preparing to release energy in the form of CMEs, erupting filaments, and flares. Title: Estimating Travel Times of Coronal Mass Ejections to 1 AU Using Multi-spacecraft Coronagraph Data Authors: Kilpua, E. K. J.; Mierla, M.; Rodriguez, L.; Zhukov, A. N.; Srivastava, N.; West, M. J. Bibcode: 2012SoPh..279..477K Altcode: We study the relationship between the speeds of coronal mass ejections (CMEs) obtained close to the Sun and in the interplanetary medium during the low solar-activity period from 2008 to 2010. We use a multi-spacecraft forward-modeling technique to fit a flux-rope-like model to white-light coronagraph images from the STEREO and SOHO spacecraft to estimate the geometrical configuration, propagation in three-dimensions (3D), and the radial speeds of the observed CMEs. The 3D speeds obtained in this way are used in existing CME travel-time prediction models. The results are compared to the actual CME transit times from the Sun to STEREO, ACE, and Wind spacecraft as well as to the transit times calculated using projected CME speeds. CME 3D speeds give slightly better predictions than projected CME speeds, but a large scatter is observed between the predicted and observed travel times, even when 3D speeds are used. We estimate the possible sources of errors and find a weak tendency for large interplanetary CMEs (ICMEs) with high magnetic fields to arrive faster than predicted and small, low-magnetic-field ICMEs to arrive later than predicted. The observed CME transit times from the Sun to 1 AU show a particularly good correlation with the upstream solar-wind speed. Similar trends have not been observed in previous studies using data sets near solar maximum. We suggest that near solar minimum a relatively narrow range of CME initial speeds, sizes, and magnetic-field magnitudes led to a situation where aerodynamic drag between CMEs and ambient solar wind was the primary cause of variations in CME arrival times from the Sun to 1 AU. Title: Acceleration of CMEs Observed from SECCHI/STEREO Authors: Joshi, Anand; Srivastava, Nandita Bibcode: 2012cosp...39..842J Altcode: 2012cosp.meet..842J A study on acceleration profiles of six coronal mass ejections (CMEs) that occurred in the period from 2007 to 2010 was carried out using images from coronagraphs COR1 and COR2 on board the twin STEREO spacecraft. Eruptive prominences (EPs) associated with three of the CMEs were also analysed using 304 Å images from the Extreme UltraViolet Imager (EUVI). A stereoscopic reconstruction technique developed by us was used to determine the 3D coordinates of features in the CME leading edge (LE) and the EP, from which their true velocity and acceleration were determined. One of the main conclusions of our analysis is that the CME LE undergoes maximum acceleration typically below 2 R_{⊙}, while earlier studies have reported this height to be 2--4 R_{⊙}. Our analysis also reveals that while the CMEs associated with flares show a bimodal acceleration profile, those associated with prominences do not. This suggests that the driving mechanism for the CMEs associated with flares and those associated with EPs may be different. Title: High-Resolution Observations of a Filament showing Activated Barb Authors: Joshi, Anand; Martin, Sara F.; Mathew, Shibu; Srivastava, Nandita Bibcode: 2012cosp...39..841J Altcode: 2012cosp.meet..841J Analysis of a filament showing an activated barb using observations from the Dutch Open Telescope (DOT) on 2010 August 20 are presented. The DOT takes Doppler images in Hα, among other wavelengths, in a region about 110 × 110 arcsec^{2} in area, at a cadence of 30~seconds. The offline image restoration technique of speckle reconstruction is applied to obtain diffraction limited images. The filament developed a new barb in 10~minutes, which disappeared within the next 35~minutes. Such a rapid formation and disappearance of a filament barb is unusual, and has not been reported earlier. Line-of-sight velocity maps were constructed from the Doppler images of the target filament. We observe flows in the filament spine towards the barb location prior to its formation, and flows in the barb towards the spine during its disappearance. Photospheric magnetograms from Heliospheric Magnetic Imager on board the Solar Dynamics Observatory, at a cadence of 45~seconds, were used to determine the changes in magnetic flux in the region surrounding the barb location. The variation of magnetic flux in this duration supports the view that barbs are rooted in minor magnetic polarity. Our analysis shows that barbs can be short-lived and formation and disappearance of the barb was associated with cancellation of magnetic flux. Title: Presence of solar filament plasma detected in interplanetary coronal mass ejections by in situ spacecraft Authors: Sharma, Rahul; Srivastava, Nandita Bibcode: 2012JSWSC...2A..10S Altcode: Aims: To identify the solar filament plasma at 1 AU by using in situ spacecraft data. Methods: We used magnetic, plasma and compositional parameters to identify the presence of filamentary material within and outside magnetic clouds. Results: We report two cases of observed filament plasma embedded in interplanetary coronal mass ejections (ICMEs) related to a flare-associated eruptive filament and a quiescent filament eruption at different phases of solar cycle by using magnetic, plasma, and compositional parameters. Conclusions: Analysis of in situ multi-spacecraft observations of ICME structures and substructures confirms the presence of solar filament material. Title: Compositional Diversity inside Lowell Crater, Orientale Basin: Evidences for Extensive Spinel Rich Deposits Authors: Srivastava, N.; Gupta, R. P. Bibcode: 2012LPICo1677...55S Altcode: Extensive exposures of spinel rich rocks have been found inside Lowell Crater (12.9°S 103.1°W) and in other adjoining areas of Montes Rook, Orientale basin, indicating their pervasive presence in the crust at depth prior to the Orientale impact. Title: On the estimation of true speeds and arrival times of CMEs observed during 2007-2011 Authors: Srivastava, Nandita Bibcode: 2012cosp...39.1884S Altcode: 2012cosp.meet.1884S I will present results on a study of the relationship between the speeds of a few coronal mass ejections (CMEs) measured in the corona close to the Sun and in the interplanetary medium during the ascending phase of the solar cycle 24, i.e. from 2007 to 2011. Close to the Sun, we use different techniques like forward modeling, 3D height-time and triangulation to estimate the true speeds and direction of propagation from images taken by COR1 & 2 white-light coronagraphs and also Heliospheric Imagers (HI) aboard STEREO. The 3D speeds obtained in this way are used in the CME travel time prediction models to determine the actual CME transit times from the Sun to STEREO, ACE or Wind spacecraft. These are then compared with the transit times calculated using projected CME speeds. We find CME 3D speeds give improved predictions than that obtained from projected CME speeds for most of the events. The sources of errors will be discussed and interpretation of the results in the wake of the solar minimum phase will also be highlighted. Title: Forecasting Geomagnetic Storms and Solar Energetic Particle Events: the COMESEP Project Authors: Crosby, N.; Veronig, A.; Robbrecht, E.; Vrsnak, B.; Vennerstrøm, S.; Malandraki, O.; Dalla, S.; Srivastava, N.; Hesse, M.; Odstrcil, D. Bibcode: 2012EGUGA..1412544C Altcode: COMESEP (COronal Mass Ejections and Solar Energetic Particles), funded by the European Union Framework 7 programme, is a three-year collaborative project that has been running for one year. Tools for forecasting geomagnetic storms and solar energetic particle (SEP) radiation storms are being developed under the project. By analysis of historical data, complemented by the extensive data coverage of solar cycle 23, the key ingredients that lead to magnetic storms and SEP events and the factors that are responsible for false alarms are being identified. To enhance our understanding of the 3D kinematics and interplanetary propagation of coronal mass ejections (CMEs), the structure, propagation and evolution of CMEs are being investigated. In parallel, the sources and propagation of SEPs are being examined and modeled. Based on the insights gained, and making use of algorithms for the automated detection of CMEs, forecasting tools for geomagnetic and SEP radiation storms are being developed and optimised. Validation and implementation of the produced tools into an operational Space Weather Alert system will be performed. Geomagnetic and SEP radiation storm alerts will be based on the COMESEP definition of risk. COMESEP is a unique cross-collaboration effort and bridges the gap between the SEP and CME scientific communities. For more information about the project, see the COMESEP website http://www.comesep.eu/ . This work has received funding from the European Commission FP7 Project COMESEP (263252). Title: Acceleration of Coronal Mass Ejections from Three-dimensional Reconstruction of STEREO Images Authors: Joshi, Anand D.; Srivastava, Nandita Bibcode: 2011ApJ...739....8J Altcode: 2011arXiv1107.1769J We employ a three-dimensional (3D) reconstruction technique for the first time to study the kinematics of six coronal mass ejections (CMEs), using images obtained from the COR1 and COR2 coronagraphs on board the twin STEREO spacecraft, and also the eruptive prominences (EPs) associated with three of them using images from the Extreme UltraViolet Imager. A feature in the EPs and leading edges (LEs) of all the CMEs was identified and tracked in images from the two spacecraft, and a stereoscopic reconstruction technique was used to determine the 3D coordinates of these features. True velocity and acceleration were determined from the temporal evolution of the true height of the CME features. Our study of the kinematics of the CMEs in 3D reveals that the CME LE undergoes maximum acceleration typically below 2 R sun. The acceleration profiles of CMEs associated with flares and prominences exhibit different behaviors. While the CMEs not associated with prominences show a bimodal acceleration profile, those associated with prominences do not. Two of the three associated prominences in the study show a high and increasing value of acceleration up to a distance of almost 4 R sun, but acceleration of the corresponding CME LE does not show the same behavior, suggesting that the two may not be always driven by the same mechanism. One of the CMEs, although associated with a C-class flare, showed unusually high acceleration of over 1500 m s-2. Our results therefore suggest that only the flare-associated CMEs undergo residual acceleration, which indicates that the flux injection theoretical model holds well for the flare-associated CMEs, but a different mechanism should be considered for EP-associated CMEs. Title: Rolling motion in erupting prominences observed by STEREO Authors: Panasenco, Olga; Martin, Sara; Joshi, Anand D.; Srivastava, Nandita Bibcode: 2011JASTP..73.1129P Altcode: We analyze the large-scale dynamical forms of three erupting prominences (filaments) observed by at least one of the two STEREO spacecraft and which reveal evidence of sideways rolling motion beginning at the crest of the erupting filament. We find that all three events were also highly non-radial and occurred adjacent to large coronal holes. For each event, the rolling motion and the average non-radial outward motion of the erupting filament and associated CME were away from a neighboring coronal hole. The location of each coronal hole was adjacent to the outer boundary of the arcade of loops overlying the filaments. The erupting filaments were all more non-radial than the CMEs but in the same general direction. From these associations, we make the hypothesis that the degree of the roll effect depends on the level of force imbalances inside the filament arcade related to the coronal hole and the relative amount of magnetic flux on each side of the filament, while the non-radial motion of the CME is related to global magnetic configuration force imbalances. Our analyses of the prominence eruption best observed from both STEREO-A and STEREO-B shows that its spine retained the thin ribbon-like topology that it had prior to the eruption. This topology allows bending, rolling, and twisting during the early phase of the eruption. Title: Actors of the main activity in large complex centres during the 23 solar cycle maximum Authors: Schmieder, B.; Démoulin, P.; Pariat, E.; Török, T.; Molodij, G.; Mandrini, C. H.; Dasso, S.; Chandra, R.; Uddin, W.; Kumar, P.; Manoharan, P. K.; Venkatakrishnan, P.; Srivastava, N. Bibcode: 2011AdSpR..47.2081S Altcode: During the maximum of Solar Cycle 23, large active regions had a long life, spanning several solar rotations, and produced large numbers of X-class flares and CMEs, some of them associated to magnetic clouds (MCs). This is the case for the Halloween active regions in 2003. The most geoeffective MC of the cycle (Dst = -457) had its source during the disk passage of one of these active regions (NOAA 10501) on 18 November 2003. Such an activity was presumably due to continuous emerging magnetic flux that was observed during this passage. Moreover, the region exhibited a complex topology with multiple domains of different magnetic helicities. The complexity was observed to reach such unprecedented levels that a detailed multi-wavelength analysis is necessary to precisely identify the solar sources of CMEs and MCs. Magnetic clouds are identified using in situ measurements and interplanetary scintillation (IPS) data. Results from these two different sets of data are also compared. Title: On three-dimensional aspects of CMEs, their source regions and interplanetary manifestations: Introduction to special issue Authors: Srivastava, Nandita; Mierla, Marilena; Rodriguez, Luciano Bibcode: 2011JASTP..73.1077S Altcode: No abstract at ADS Title: On 3D reconstruction of coronal mass ejections: II. Longitudinal and latitudinal width analysis of 31 August 2007 event Authors: Mierla, M.; Inhester, B.; Rodriguez, L.; Gissot, S.; Zhukov, A.; Srivastava, N. Bibcode: 2011JASTP..73.1166M Altcode: In an earlier work, Mierla et al. (2009) applied four different reconstruction techniques to three coronal mass ejections (CMEs) at a given time. This study is a follow up of the above work in which we apply a local correlation tracking and tie-point reconstruction technique (LCT-TP) to the CME observed on 31 August 2007 by the COR1 and COR2 coronagraphs onboard the STEREO spacecraft at different times. The results show considerable scatter in the direction parallel to the line of sight, which is a direct indication of the CME depth. We derive the longitudinal and latitudinal sizes of the CME as a function of time. We find that a reasonable lower estimate of the longitudinal size is 18°-44° with an absolute largest extent of 78°-110°. We also find that a reasonable lower estimate for the latitudinal size of the CME is 18°-32° with an absolute largest extent of 44°-56°. In general, the latitudinal size is smaller than the longitudinal size, indicating an elliptical cone like structure or a flux rope like structure with very little tilt relative to the ecliptic. Self-similar expansion is observed above a height of 6.9R. As our analysis is based on a statistical approach, large scatter is expected. In order for the method to be validated, more cases have to be studied. Title: Kinematics of Two Eruptive Prominences Observed by EUVI/STEREO Authors: Joshi, Anand D.; Srivastava, Nandita Bibcode: 2011ApJ...730..104J Altcode: 2011arXiv1101.4543J Two large northern polar crown prominences that erupted on 2010 April 13 and 2010 August 1 were analyzed using images obtained from the Extreme UltraViolet Imager on the twin Solar Terrestrial Relations Observatory spacecraft. Several features along the prominence legs were reconstructed using a stereoscopic reconstruction technique developed by us. The three-dimensional changes exhibited by the prominences can be explained as an interplay between two different motions, namely helical twist in the prominence spine, and overall non-radial equatorward motion of the entire prominence structure. The sense of twist in both the prominences is determined from the changes in latitudes and longitudes of the reconstructed features. The prominences are observed starting from a few hours before the eruption. Increase in height before and during the eruption allowed us to study the kinematics of the prominences in the two phases of eruption, the slow-rise and the fast-eruptive phase. A constant value of acceleration was found for each reconstructed feature in each phase, but it showed a significant change from one leg to the other in both the prominences. The magnitude of acceleration during the eruptive phase is found to be commensurate with the net effect of the two motions stated above. Title: Studies of Lunar Dark Halo Craters in North Western Mare Nectaris Using High Resolution Chandrayaan-1 Data Authors: Chauhan, P.; Kaur, P.; Srivastava, N.; Bhattacharya, S.; Lal, D.; Ajai; Kiran Kumar, A. S. Bibcode: 2011LPI....42.1338C Altcode: In this study, we present the results from remote sensing data of very high resolution (both spatial and spectral) for localized dark mantle deposits (LDMD) around crater Beaumont-L in the northwestern part of Mare Nectaris from Chandrayaan-1. Title: Evidences of Multiphase Modification over the Central Peak of Tycho Crater on Moon from High Resolution Remote Sensing Data Authors: Chauhan, P.; Srivastava, N.; Kaur, P.; Bhattacharya, S.; Ajai; Kiran Kumar, A. S.; Goswami, J. N.; Navalgund, R. R. Bibcode: 2011LPI....42.1341C Altcode: Results of an integrated analysis of the central peak of Tycho from TMC data onboard Chandrayaan-1, NAC images of LROC, and Multi-band Imager (MI) data from SELENE are presented to understand processes involved in multiphase modifications of the central peak of Tycho. Title: Proposed visible emission line space solar coronagraph Authors: Singh, Jagdev; Prasad, B. Raghavendra; Venkatakrishnan, P.; Sankarasubramanian, K.; Banerjee, Dipankar; Bayanna, Raja; Mathew, Shibu; Murthy, Jayant; Subramanian, Prasad; Ramesh, R.; Kathiravan, S.; Nagabhushana, S.; Mahesh, P. K.; Manoharan, P. K.; Uddin, Wahab; Sriram, S.; Kumar, Amir; Srivastava, N.; Rao, Koteswara; Nagendra, C. L.; Chakraborthy, P.; Sriram, K. V.; Venkateswaran, R.; Krishnamurthy, T.; Sreekumar, P.; Sarma, K. S.; Murthy, Raghava; Navalgund, K. HJ.; Samudraiah, D. R. M.; Babu, P. Narayan; Patra, Asit Bibcode: 2011CSci..100..167S Altcode: The outer atmosphere of the sun - called the corona - has been observed during total solar eclipse for short periods (typically <6 min), from as early as the eighteenth century. In the recent past, space-based instruments have permitted us to study the corona uninterruptedly. In spite of these developments, the dynamic corona and its high temperature (1-2 million K) are yet to be fully understood. It is conjectured that their dynamic nature and associated energetic events are possible reasons behind the high temperature. In order to study these in detail, a visible emission line space solar coronagraph is being proposed as a payload under the small-satellite programme of the Indian Space Research Organisation. The satellite is named as Aditya-1 and the scientific objectives of this payload are to study: (i) the existence of intensity oscillations for the study of wave-driven coronal heating; (ii) the dynamics and formation of coronal loops and temperature structure of the coronal features; (iii) the origin, cause and acceleration of coronal mass ejections (CMEs) and other solar active features, and (iv) coronal magnetic field topology and three-dimensional structures of CMEs using polarization information. The uniqueness of this payload compared to previously flown space instruments is as follows: (a) observations in the visible wavelength closer to the disk (down to 1.05 solar radii); (b) high time cadence capability (better than two-images per second), and (c) simultaneous observations of at least two spectral windows all the time and three spectral windows for short durations. Title: 3D reconstruction and kinematics of eruptive prominences using STEREO observations Authors: Srivastava, Nandita; Joshi, Anand D. Bibcode: 2011ASInC...3R.100S Altcode: We present observations of two large northern polar crown prominences that erupted on 2010 April 13 and 2010 August 1 on the Sun. For 3D studies of these events, we developed a stereoscopic reconstruction technique for the images obtained from the SECCHI suite of instruments on board the twin Solar TErrestrial RElations Observatory (STEREO) spacecraft. This technique was applied to images obtained from the Extreme UltraViolet Imager to reconstruct several features along the prominences. The three-dimensional changes exhibited by the prominences can be explained as an interplay of two different motions, namely, the twist in the prominence spine, and the overall non-radial motion of the entire prominence structure. The sense of twist in both the prominences is determined from the changes in latitudes and longitudes of the reconstructed features. The study of kinematics of these features reveals crucial information of the early phase of eruptive prominences and initiation of the associated CMEs. Our results from 3D reconstruction of observations from two view points (STEREO) provide a better understanding of the physical mechanism in the lower corona as compared to previous results obtained using observation from a single vantage point, for e.g. SOHO. Title: Prediction of space weather based on a statistical model Authors: Srivastava, Nandita Bibcode: 2010EGUGA..12..567S Altcode: Space weather prediction involves predicting the magnitude and the time of onset of intense geomagnetic storms at the earth. In this paper, I describe a new statistical prediction model for predicting major geomagnetic storms, which was developed using only solar variables. The input variables for the model were identified through an exhaustive statistical investigation of the solar origins and interplanetary characteristics of major geomagnetic storms that occurred during 1996-2002, based mainly on observations of coronal mass ejections from LASCO/SoHO. This model was then used to predict the occurrence of major geomagnetic storms during 1996-2009. The results of this study reveal that solar variables contribute relatively less in the prediction of major geomagnetic storms, as compared to interplanetary parameters. The model also shows the relative importance of each solar variable for the prediction of major geomagnetic storms. Amongst the solar variables, the speed and location of the source region of the CME was found to be the most important factor controlling the geo-effectiveness. With the launch of STEREO in 2006, albeit it is possible to measure the true speed and direction of propagation of the CMEs in general using SECCHI coronagraph observations, however only a few cases of geo-effective events have been recorded till now. The results obtained using STEREO observations thus far and their implications on the space weather prediction model will also be discussed. Title: Automated Detection of Filaments and Their Disappearance Using Full-Disc Hα Images Authors: Joshi, A. D.; Srivastava, N.; Mathew, S. K. Bibcode: 2010SoPh..262..425J Altcode: 2009arXiv0905.3055J; 2010SoPh..tmp...54J; 2010SoPh..tmp...42J A new algorithm is presented that automatically detects filaments on the Sun in full-disc Hα images. Pre-processing of Hα images includes corrections for limb darkening and foreshortening. Further, by applying suitable intensity and size thresholds, filaments are extracted, while other solar features, e.g. sunspots and plages, are removed. Filament attributes such as their position on the solar disc, total area, length, and number of fragments are determined. In addition, every filament is also labelled with a unique number for identification. The algorithm is capable of following a particular filament through successive images, which allows us to detect their changes and disappearance. We have analysed ten cases of filament eruption from different observatories, and the results obtained are presented. The algorithm will eventually be integrated with an upcoming telescope at the Udaipur Solar Observatory for real-time monitoring of activated/eruptive filaments. This aspect should prove to be of particular importance in studies pertaining to space weather. Title: Integrated Analysis of Topographically High Mafic Exposures at Apollo-17 Landing Site Using Data from Imaging Sensors on Chandrayaan-1 Authors: Chauhan, P.; Srivastava, N.; Pieters, C. M.; Ajai; Kiran Kumar, A. S.; Navalgund, R. R.; Head, J. W.; Petro, N.; Runyon, C.; Goswami, J. N. Bibcode: 2010LPI....41.1606C Altcode: Mafic exposures at topographically high locations surrounding Apollo 17 landing site have been studied using imaging sensors onboard Chandrayaan -1 (TMC, HySI, and M3). Compositionally, most of them have been found to be noritic. Title: Three-dimensional reconstruction of solar features using triangulation technique Authors: Joshi, Anand; Srivastava, Nandita Bibcode: 2010cosp...38.1910J Altcode: 2010cosp.meet.1910J We present a new technique to obtain the true coordinates of features seen on the solar disc or in the corona, from the SECCHI suite of instruments on the twin STEREO spacecraft. The reconstruction is carried out in the heliocentric Earth-ecliptic (HEE) coordinate system, which is fixed with respect to the Sun-Earth line. The HEE system is rotated to align with the line of sight of the two STEREO spacecraft. The corresponding rotation matrices are then solved to obtain the true coordinates of the feature identified by employing the epipolar constraint. Using this technique we can determine true speeds of erupting prominences/filaments as well as coronal mass ejections. Results from the technique applied to some such events will be presented. Title: CME Observations from STEREO Authors: Srivastava, N. Bibcode: 2010ASSP...19..308S Altcode: 2010mcia.conf..308S; 2009arXiv0903.3477S Coronal mass ejections (CMEs) are spectacular ejections of material from the Sun as seen in the coronal field of view. Regular observations are possible with both ground-based and space-based coronagraphs. I present our current understanding of CMEs based on multi-wavelength observations from ground-based instruments as well as from space missions such as SoHO. Based on the continuous and multi-wavelength observations of CMEs from SoHO over a period of more than a solar cycle, the physical properties of CMEs are described. Recent observations of CMEs with the SECCHI coronagraphs, namely COR1 and COR2, aboard the twin STEREO spacecrafts A and B are also presented. STEREO surpasses previous missions by providing a 3D view of CME structure from two vantage points. Applications of STEREO observations to 3D reconstructions of the leading edge of CMEs are described. Title: Acceleration of CMEs Associated with Eruptive Prominences Authors: Joshi, A. D.; Srivastava, N. Bibcode: 2010ASSP...19..485J Altcode: 2010mcia.conf..485J The association of coronal mass ejections (CMEs) with erupting prominences has been known for a long time. However, most studies focus on CMEs that cannot be observed close to the solar surface. We present a study of two CMEs that were associated with eruptive prominences, using data from the STEREO and SOHO space missions to study the CME accelerations. Our results confirm the scaling law proposed by Chen and Krall (2003). Title: On the 3-D reconstruction of Coronal Mass Ejections using coronagraph data Authors: Mierla, M.; Inhester, B.; Antunes, A.; Boursier, Y.; Byrne, J. P.; Colaninno, R.; Davila, J.; de Koning, C. A.; Gallagher, P. T.; Gissot, S.; Howard, R. A.; Howard, T. A.; Kramar, M.; Lamy, P.; Liewer, P. C.; Maloney, S.; Marqué, C.; McAteer, R. T. J.; Moran, T.; Rodriguez, L.; Srivastava, N.; St. Cyr, O. C.; Stenborg, G.; Temmer, M.; Thernisien, A.; Vourlidas, A.; West, M. J.; Wood, B. E.; Zhukov, A. N. Bibcode: 2010AnGeo..28..203M Altcode: Coronal Mass ejections (CMEs) are enormous eruptions of magnetized plasma expelled from the Sun into the interplanetary space, over the course of hours to days. They can create major disturbances in the interplanetary medium and trigger severe magnetic storms when they collide with the Earth's magnetosphere. It is important to know their real speed, propagation direction and 3-D configuration in order to accurately predict their arrival time at the Earth. Using data from the SECCHI coronagraphs onboard the STEREO mission, which was launched in October 2006, we can infer the propagation direction and the 3-D structure of such events. In this review, we first describe different techniques that were used to model the 3-D configuration of CMEs in the coronagraph field of view (up to 15 R⊙). Then, we apply these techniques to different CMEs observed by various coronagraphs. A comparison of results obtained from the application of different reconstruction algorithms is presented and discussed. Title: 3D Reconstruction of the Leading Edge of the 20 May 2007 Partial Halo CME Authors: Srivastava, N.; Inhester, B.; Mierla, M.; Podlipnik, B. Bibcode: 2009SoPh..259..213S Altcode: We have reconstructed the leading edge of a coronal mass ejection (CME) observed on 20 May 2007 by COR1 and COR2 of the SECCHI suite onboard the twin STEREO spacecraft. The reconstruction of the leading edge of this CME was achieved using the tie-pointing method based on epipolar geometry. The true speeds derived from the reconstruction of the leading edge were estimated. These estimated true speeds were compared with the projected plane-of-sky speeds of the leading edge of the CME derived from LASCO aboard SoHO as well as from STEREO A and B images individually. The results show that a better estimation of the true speed of the CME in the Sun - Earth direction is achieved from the 3D reconstruction and therefore has an important bearing on space weather prediction. Title: A Dual Beam H-alpha Doppler System to Acquire, Analyse and Anticipate Solar Eruptive Events Directed towards Earth Authors: Joshi, Anand D.; Mathew, Shibu K.; Srivastava, Nandita; Martin, Sara F.; Gupta, Sudhir K. Bibcode: 2009arXiv0905.3037J Altcode: A new instrument with a dual-beam H-alpha Doppler system is being developed at the Udaipur Solar Observatory (USO) in order to improve the quality and quantity of data on quiet, activated and erupting filaments and prominences on the Sun, especially those associated with geo-effective coronal mass ejections. These data can be potentially used to construct three-dimensional topology of erupting filaments as they leave the surface of the Sun and can be compared with multi-wavelength data obtained from space missions such as STEREO, SOHO, and Hinode. The characterization of various optical components for the instrument is being carried out, and some preliminary results are described in the paper. Title: Source region of the 18 November 2003 coronal mass ejection that led to the strongest magnetic storm of cycle 23 Authors: Srivastava, Nandita; Mathew, Shibu K.; Louis, Rohan E.; Wiegelmann, Thomas Bibcode: 2009JGRA..114.3107S Altcode: 2008arXiv0812.5046S; 2009JGRA..11403107S The superstorm of 20 November 2003 was associated with a high-speed coronal mass ejection (CME) which originated in the NOAA AR 10501 on 18 November. This coronal mass ejection had severe terrestrial consequences leading to a geomagnetic storm with Dst index of -472 nT, the strongest of the current solar cycle. In this paper, we attempt to understand the factors that led to the coronal mass ejection on 18 November. We have also studied the evolution of the photospheric magnetic field of NOAA AR 10501, the source region of this coronal mass ejection. For this purpose, the Michelson Doppler Imager line-of-sight magnetograms and vector magnetograms from Solar Flare Telescope, Mitaka, obtained during 17-19 November 2003 were analyzed. In particular, quantitative estimates of the temporal variation in magnetic flux, energy, and magnetic field gradient were estimated for the source active region. The evolution of these quantities was studied for the 3-day period with an objective to understand the preflare configuration leading up to the moderate flare which was associated with the geoeffective coronal mass ejection. We also examined the chromospheric images recorded in H α from Udaipur Solar Observatory to compare the flare location with regions of different magnetic field and energy. Our observations provide evidence that the flare associated with the CME occurred at a location marked by high magnetic field gradient which led to release of free energy stored in the active region. Title: Spectral Reflectance Studies for Maturation Trends in a Mare and Highland Swirl Authors: Srivastava, N. Bibcode: 2009LPI....40.1577S Altcode: Regions shielded by maximum magnetic field intensity in the proto type swirl Reiner Gamma and the one near Airy Crater, have been investigated for maturity trends. Both the cases show differences (though of reversed nature) from the trend seen in nearby unshielded areas. Title: A Quick Method for Estimating the Propagation Direction of Coronal Mass Ejections Using STEREO-COR1 Images Authors: Mierla, M.; Davila, J.; Thompson, W.; Inhester, B.; Srivastava, N.; Kramar, M.; St. Cyr, O. C.; Stenborg, G.; Howard, R. A. Bibcode: 2008SoPh..252..385M Altcode: 2008SoPh..tmp..170M We describe here a method to obtain the position of a coronal moving feature in a three-dimensional coordinate system based on height - time measurements applied to STEREO data. By using the height - time diagrams from the two SECCHI-COR1 coronagraphs onboard STEREO, one can easily determine the direction of propagation of a coronal mass ejection (i.e., if the moving plasma is oriented toward or away from the Earth). This method may prove to be a useful tool for space weather forecasting by easily identifying the direction of propagation as well as the real speed of the coronal mass ejections. Title: Chapter 10: Coronal Mass Ejections and Associated Phenomena Authors: Srivastava, Nandita Bibcode: 2008psa..book..193S Altcode: Coronal mass ejections or CMEs were first classified as a distinct class of solar phenomena soon after the launch of Skylab mission in space in 1973 which carried a coronagraph onboard... Title: Titanium estimates of the central peaks of lunar craters: Implications for sub-surface lithology of moon Authors: Srivastava, Neeraj Bibcode: 2008AdSpR..42..281S Altcode: Central peaks of 24 lunar craters, having mafic rocks, were studied to estimate their average titanium content and infer the nature of the subsurface lithologies. Titanium contents were derived from Clementine UV Vis data (415, 750 nm) following the approach of Lucey et al. [Lucey, P.G., Blewett, D.T. and Jolliff, B.L., Lunar iron and titanium abundance algorithms based on final processing of Clementine ultraviolet visible images, J. Geophys. Res.106 (E8), 20297 20,305, 2000]. TiO2 content exceeding 1 wt% suggests presence of mantle derived mafic sub-surface rock types (plutonic/volcanic) within the central peaks. Even though, the algorithm used for deriving titanium content is susceptible to variation in topography and sun angle, especially at higher latitudes, careful selection and analyses of data for regions within the central peaks revealed compositional heterogeneities. The results indicate a preponderance of mafic lithologies with low TiO2 content (<1 wt%) in the central peaks of lunar craters populating the equatorial region. Average titanium content of central peaks can serve as a useful tracer for distinguishing mantle derived mafic subsurface lithologies from those formed during global magma ocean episode. Title: STEREO observations of solar energetic particles: a case study Authors: Bucik, R.; Gomez-Herrero, R.; Inhester, B.; Korth, A.; Mall, U.; Mason, G. M.; Mierla, M.; Srivastava, N. Bibcode: 2008EGUGA..10.7760B Altcode: 2008EGUGA..1007760B The STEREO mission gives an opportunity to combine stereoscopic observations of the Sun, providing the CME characteristics for example speed and propagation direction from the close vicinity of the Sun, when particles are accelerated, with in-situ particle data measurements. This information is important for timing analysis of the solar energetic particle (SEP) events. As expected for the declining phase of the solar cycle, during the year 2007, the energetic particle increases were dominated by CIR events. One opportunity to study the solar energetic particles occurred between 18 May and 27 May 2007, a period with a quite complex temporal profile of particle enhancement in intensity. During this period the twin STEREO spacecrafts, A and B, were at heliocentric distances of 0.96 and 1.06 AU, respectively, with a separation angle of about 9 degrees. The time-of-flight mass spectrometer SIT measured the initial CIR increases in energetic ions (up to 1 MeV/nucleon) on 18 May and 24 May 2007, first on the B and then on the A spacecraft. The SEPT instrument observed a rapid rise of 100 keV electrons on 19, 20, and 23 May 2007, most likely indicating small SEP events. Associated flares were B9.5, B6.7 and B5.3 classes, as recorded by the GOES X-ray data. The source regions of the two CMEs were well seen by a 3-D reconstruction of SECCHI observations, one on 20 May 2007 in an active region around the disk centre and the second on 23 May 2007 on the west limb of the Sun. We survey the abundances of H, He and heavier elements, such C to Fe, to separate the CIR and SEP ions. A preliminary analysis shows that the He/H ratio (measured at a fixed MeV/nucleon) on 20 May and 23 May 2007 is consistent with average values measured in the CME-related SEP events. The radio data from ground-based stations clearly indicates type II radio emissions, which are well correlated with 19 May and 23 May 2007 events, suggesting the presence of the shock propagating in the corona and thus supporting the idea of the shock-associated (gradual) nature for these events. Title: On the study of kinematics of eruptive quiescent prominences observed in He 304 Å Authors: Joshi, V.; Srivastava, N. Bibcode: 2007BASI...35..447J Altcode: The observations taken in He 304 Å by the EIT telescope aboard SoHO reveals that these images are extremely useful in tracing prominences because of the relatively sharper spine which is better visible in 304 Å than in H_α. We have developed a geometric technique of measuring the height of prominences. The technique was applied to six eruptive quiescent prominence images recorded by EIT in He 304 Å during January 2000-July 2003 in an attempt to identify the precursors of geo-effective caronal mass ejections (CMEs) that are associated with eruptive prominences. Our analyses show that prominence eruptions evolve through a pre-eruptive phase and an eruptive phase, which are characterized by lower velocities of several km s^{-1} and eruptive velocities of several tens to hundreds of km s^{-1}, respectively. The analyses also show that during the pre-eruptive phase, a prominence rises at a constant acceleration of several cm s^{-2} and not at constant velocity as reported by previous workers. We suggest that this phase is indicative of the precursor of prominence eruption. This might be useful in predicting the occurrence of an associated coronal mass ejection. Title: Geochemical Estimation of Iron and Titanium for Central Peaks of Lunar Craters Authors: Srivastava, N. Bibcode: 2007LPI....38.2188S Altcode: Central peaks of 26 lunar craters have been observed for average FeO and TiO2 concentration using Clementine UVVIS data. The results have shown a distinct correlation with lithological assemblage obtained earlier by Tompkins and Pieters (1999). Title: On the Slow-Rise Phase of Eruptive Quiescent Solar Prominences Authors: Srivastava, N. Bibcode: 2006ihy..workE..45S Altcode: The observations taken in He 304 Å reveal that these images are extremely useful to trace prominences because of the relatively sharper spine which is better visible in 304 Å than in H-alpha. In this paper, we have studied several eruptive quiescent prominence images recorded by EIT in He 304 Å during January 2000 - July 2003 in an attempt to identify the precursors of CMEs that are associated with eruptive prominences. Our analyses show that erupting prominences evolve through a pre-eruptive phase and an eruptive phase which are characterized by lower velocities of several km/s and eruptive velocities of several tens to hundreds of km/s, respectively. The analyses also show that during the pre-eruptive phase, a prominence rises at a constant acceleration ranging between 4-12 cm/s2 and not at constant velocity as reported by previous workers. The values of acceleration are found to be lower in comparison to that measured during the eruptive phase which ranges between 10-80 m/s2. A comparison of height-time profiles of various features of prominences and associated CMEs provides information on their role in the eruption process. We suggest that the characteristic slow rise of eruptive prominences might be considered as reliable amongst all CME precursors. The kinematics of slowly rising filaments/prominences also helps in understanding the nature of propagation of the associated CMEs. We further investigated if the filaments which rise slowly are the ones which are associated with a slow expansion of the corona and/or slow outward motion before the phase of rapid mass expulsion. Such distinctions are extremely useful in identifying the eruption of CMEs directed toward the Earth, when they are associated with erupting filaments. Title: The Challenge of Predicting the Occurrence of Intense Storms Authors: Srivastava, Nandita Bibcode: 2006JApA...27..237S Altcode: Geomagnetic super-storms of October and November 2003 are compared in order to identify solar and interplanetary variables that influence the magnitude of geomagnetic storms. Although these superstorms (DST < -300 nT) are associated with high speed CMEs, their DST indices show large variation. The most intense storm of November 20, 2003 (DSt∼ - 472 nT) had its source in a comparatively small active region and was associated with a relatively weaker, M-class flare, while the others had their origins in large active regions and were associated with strong X-class flares. An attempt has been made to implement a logistic regression model for the prediction of the occurrence of intense/superintense geomagnetic storms. The model parameters (regression coefficients) were estimated from a training data-set extracted from a data-set of 64 geo-effective CMEs observed during 1996-2002. The results indicate that logistic regression models can be effectively used for predicting the occurrence of major geomagnetic storms from a set of solar and interplanetary factors. The model validation shows that 100% of the intense storms (-200 nT < DSt < -100 nT) and only 50% of the super-intense (DST < -200 nT) storms could be correctly predicted. 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: How good is the prediction of space weather based on solar and interplanetary properties? Authors: Srivastava, N. Bibcode: 2006ilws.conf..102S Altcode: Space weather prediction involves advance forecasting of the magnitude and the on-set time of major geomagnetic storms at the earth. In a previous attempt, a logistic regression model based on solar and interplanetary variables was developed which was based on an exhaustive study of the solar origins of major geomagnetic storms recorded during 1996- 2002. In this paper, the logistic regression model developed earlier is refined using a new database of the solar and interplanetary characteristics of the major geomagnetic storms recorded during 2003-2004, which leads to better prediction results. The model is also used to estimate the relative importance of each solar and interplanetary variable in predicting major geomagnetic storms. In an attempt aimed at an early prediction of the occurrence of geomagnetic storms, the interplanetary variables are excluded and a new model based only on the solar variables is developed. The new model did not perform well, which indicates that the solar variables responsible for geomagnetic activity at the Earth are not well-understood. Title: Propagation Characteristics of Geo-Effective Coronal Mass Ejections Authors: Srivastava, N.; Mathew, S. K. Bibcode: 2005ESASP.592..311S Altcode: 2005ESASP.592E..47S; 2005soho...16E..47S No abstract at ADS Title: Can flux rope model explain the dynamics of eruptive solar prominences? Authors: Srivastava, N.; Chen, J.; Krall, J. Bibcode: 2005AGUSMSH53A..07S Altcode: Coronal mass ejections usually occur in association with eruptive prominences or flares. The kinematics of flare-associated CMEs are generally characterised by fast speeds with little or no observable acceleration beyond the occulting disk. On the other hand, CMEs associated with eruptive prominences tend to attain lower speeds and have discernible acceleration beyond the occulting disk. It has been suggested that the two classes of CMEs correspond to a common magnetic flux-rope geometry but differ in the amount of magnetic energy that drives the eruption. The acceleration profiles are also critically influenced by the Alfven speed in the erupting flux rope. This paper analyzes a number of eruptive solar prominences in H-alpha which were associated with CMEs in the frame-work of flux-rope model in order to specifically understand the dynamics of erupting prominences. The geometrical properties of prominences viz. the footpoint separation and the apex height are the key parameters of this model which influence the acceleration and the height at which maximum acceleration of the prominence occurs. The comparative study of model and observations using Hα and SECCHI observations will shed new light on the geometrical relationship between the flux rope, the prominence, and the bright rim of the CME during the eruption. Title: Predicting Intensity of Major Geomagnetic Storms from Solar and Interplanetary Properties of CMEs: A Statistical Model Authors: Srivastava, N. Bibcode: 2004AGUFMSH53B0317S Altcode: This paper describes a statistical model based on logistic regression for predicting the occurrence of intense geomagnetic storms. Previous studies show that the strength of the resulting geomagnetic storms depend upon various solar and interplanetary properties. During 1996-2002, 64 geo-effective events were recorded which were used for determining the parameters influencing the strength or the magnitude of the resulting geomagnetic storms. 60% of the events recorded were used for determining the model parameters while the rest 40% were used for validating the model. Independent variables which include a number of solar and interplanetary factors were provided as input to the model and regressed against a binary dependent variable viz. occurrence of the intense geomagnetic storms. The present model predicts 90% of the training events correctly and 90% of the validation events correctly. The results indicate that the logistic regression model can be effectively used for space weather prediction i.e. the strength of the geomagnetic storms. Title: Solar and interplanetary sources of major geomagnetic storms during 1996-2002 Authors: Srivastava, Nandita; Venkatakrishnan, P. Bibcode: 2004JGRA..10910103S Altcode: During the 7-year period of the current solar cycle, 64 geoeffective coronal mass ejections (CMEs) were found to produce major geomagnetic storms (DST < -100 nT) at the Earth. In this paper we examine solar and interplanetary properties of these geoeffective coronal mass ejections (CMEs). The observations reveal that full-halo CMEs are potential sources of intense geomagnetic activity at the Earth. However, not all full-halo CMEs give rise to major geomagnetic storms, which complicates the task of space weather forecasting. We examine solar origins of the geoeffective CMEs and their interplanetary effects, namely, solar wind speed, interplanetary shocks, and the southward component of the interplanetary magnetic field, in order to investigate the relationship between the solar and interplanetary parameters. In particular, the present study aims at ascertaining solar parameters that govern important interplanetary parameters responsible for producing major geomagnetic storms. Our investigation shows that fast full-halo CMEs associated with strong flares and originating from a favorable location, i.e., close to the central meridian and low and middle latitudes, are the most potential candidates for producing strong ram pressure at the Earth's magnetosphere and hence intense geomagnetic storms. The results also show that the intensity of geomagnetic storms depends most strongly on the southward component of the interplanetary magnetic field, followed by the initial speed of the CME and the ram pressure. Title: Chandrayaan-1 Lunar Polar Orbiter: Science Goals And Payloads (AAS 03-703) Authors: Bhandari, N.; Adimurthy, V.; Banerjee, D.; Srivastava, N.; Dhingra, D. Bibcode: 2004ilc..conf...33B Altcode: No abstract at ADS Title: Conditions Leading to Eruptions of CMEs Associated with Eruptive Filaments Authors: Srivastava, N.; Burkepile, J. T.; Darnell, J. A. Bibcode: 2003AGUFMSH42B0504S Altcode: We report on a few recent and interesting observations of coronal mass ejections associated with eruptive filaments recorded in multiwavelengths using various data sets obtained from ground- and space-based observatories. These include chromospheric observations in H-alpha and the inner coronal data recorded from Mauna Loa Solar observatory (MLSO). The CME recorded in white light observations from the LASCO/SoHO is included in the analysis. In this paper, we attempt to investigate the pre-eruptive scenario of these events leading up to the eventual eruption. The role of the restructuring of the magnetic field and changes in the magnetic field due to the emergence and cancellation of magnetic flux in the source region of the CME will be discussed. Title: Performance Evaluation of Adaptive Optics Systems Authors: Sridharan, Rengaswamy; Raja Bayanna, A.; Srivastava, Nandita; Kumar, Brajesh; Ravindra, B.; Gupta, S. K.; Jain, Naresh; Ambastha, A.; Venkatakrishnan, P. Bibcode: 2003BASI...31..455S Altcode: Adaptive Optics (AO) systems improve the resolution of ground based telescopes and allow for long exposure images. Their performance depends on the seeing conditions at the time of observations. In this paper, we evaluate the performance of an AO system under various seeing conditions through simulations. Then we present the wave-front sensing and correction schemes that would be used in the first phase of the AO system to be developed at the Udaipur Solar Observatory. Title: Propagation Characteristics of Geo-Effective CMES Authors: Srivastava, Nandita; Venkatakrishnan, P. Bibcode: 2003IAUJD...7E..19S Altcode: The expansion speeds of halo CMEs observed by LASCO aboard SoHO duirng 1996-2002 which were geo-effective (Dst <-100 nT) have been measured. The radial propagation profiles of these CMEs have been inferred from the measured expansion speeds. We also investigate if the propagation profiles of these geoeffective CMEs is of blast wave nature. It is found that the profiles of geoeffective CMEs associated with the flares and eruptive prominences are distinctly different. This provides a crucial clue to the initial trigger mechanism of geo-effective halo CMEs and their nature of propagation which in turn has important implication on forecasting of the space weather. Title: The Source of a coronal mass ejection in a decayed solar active region Authors: Prasad Choudhary, Debi; Srivastava, Nandita; Gosain, Sanjay Bibcode: 2002A&A...395..257P Altcode: 2002A&A...395..257C We have studied the source of a coronal mass ejection (CME), which occurred in a decayed active region NOAA 7978 on 19 October, 1996. The active region NOAA 7978 first appeared on the solar disk on 2 June, 1996 and made more than five disk passages before it decayed. The event analysed in this paper was observed during fifth disk passage. We have attempted to identify the mechanism responsible for triggering this CME based on the analysis of photospheric magnetograms (MDI/SoHO), chromospheric filtergrams (Meudon and Big Bear Observatories) and coronal images (SXT/Yohkoh). We found that the emergence of new bipoles in the active region led to the eruption of a low-lying sheared filament observed in SXT images, subsequently followed by filament eruption observed both in Halpha and EUV wavelengths (EIT/SoHO). The study aims at chronologically investigating the occurrence of the events in different wavelengths, in order to have a comprehensive understanding of the mechanism involved in the launch of the CME. Title: Relationship between CME Speed and Geomagnetic Storm Intensity Authors: Srivastava, Nandita; Venkatakrishnan, P. Bibcode: 2002GeoRL..29.1287S Altcode: 2002GeoRL..29i...1S In this paper, we discuss the solar origin and interplanetary consequences of the coronal mass ejection of March 29, 2001 that was responsible for the most intense geomagnetic storm (DST ~ -377 nT) of the current solar cycle to date. A comparison of the CME of March 29, 2001, with a set of geo-effective halo CMEs associated with X-class flares showed that the strength of the geomagnetic storm at the earth is well correlated with the speed of the halo. Our study shows that the fast ejection is responsible for building up the ram pressure at the earth's magnetosphere. This may serve as a useful tool in the forecasting of intense geomagnetic storms. Title: Solar and interplanetary signatures of intense geomagnetic storms during 1997-2000 Authors: Srivastava, Nandita Bibcode: 2001BASI...29..249S Altcode: During the ascending phase of the recent solar cycle, the solar and interplanetary signatures of coronal mass ejections (CMEs) observed by Large Angle Spectrometric Coronagraphs (LASCO) aboard SOHO, have been examined. These CMEs were responsible for causing intense geomagnetic storms (Dst ? -100 nT) on the earth. In this paper, the relationship of these CMEs with halos, long-duration events, flares and eruptive prominences have been studied. In addition, investigation of the role of the initial expansion speeds of halos in determining the time of their arrival at the earth has also been made. Title: Model Prediction for an Observed Filament Authors: Aulanier, G.; Srivastava, N.; Martin, S. F. Bibcode: 2000ApJ...543..447A Altcode: This paper presents the results of a ``blind test'' for modeling the structure of an observed filament using the three-dimensional magnetohydrostatic model recently developed by Aulanier et al. in 1999. The model uses a constant shear α, and it takes into account the effects of pressure and gravity. The test consisted of predicting the structure of a filament (observed in the southern hemisphere) with a minimum observational input: only a line-of-sight magnetogram, with a straight line drawn on it to show the location of the filament, was provided. The filament was chosen by the observers (N. S. and S. F. M.) because it had a definite overall left-handed structural pattern known as sinistral, but the direction of component of the magnetic field along the filament axis was uncertain from the combination of Hα data and magnetograms. The modeler (G. A.) evaluated and fixed the values of some of the free parameters of the model while some others were varied in reasonable ranges. The Hα image of the filament was revealed only after the modeling. For α>0, the three-dimensional distribution of magnetic dips computed by the model fairly well reproduces the structure of the filament and its barbs. Moreover, the models for which α<0 do not match well the observations. This study then shows the first successful theoretical prediction for the magnetic field of an observed filament. It shows that the method based on the Aulanier et al. model is a powerful tool, not only for purposes of modeling, but also for prediction of the chirality, helicity, and morphology of observed filaments. Title: The origin of the solar wind: an overview Authors: Srivastava, Nandita; Schwenn, Rainer Bibcode: 2000ohbp.conf...13S Altcode: A tutorial review of the origin of the solar wind is presented in this chapter. At the outset, the concept of the solar wind is introduced and its various components and their charactertistics are discussed. Also outlined are some of the important space missions dedicated to the study of the solar wind and a review of their observations. The salient features of a three-dimensional model of the inner heliosphere are presented on the basis of the observations. From these space-based observations, it is now well established that there exists a close relation between the 3D heliosphere and the underlying coronal structure. Around solar activity minimum, large polar coronal holes dominate the major part of the heliosphere through which emanates the high-speed solar wind. On the other hand, another type of solar wind which is relatively slow, is restricted to a narrow equatorial belt of about ±30° width in latitude. The magnetic topology is dominated by strong multipole components and multiple current sheets in the upper corona and by a large-scale dipole field further outside, respectively. In this review, the emphasis is laid on the new observations and findings by several sophisticated instruments aboard SOHO which observe both, the inner and outer corona. These have revealed several clues to the solar origins or the source regions of the two types of solar wind, viz., the fast and the slow solar wind. The observations also unravel the finer details of the processes that are responsible for their generation. Finally, we summarize the present status of our knowledge on the origin of solar wind. Title: Factors Related to the Origin of a Gradual Coronal Mass Ejection Associated with an Eruptive Prominence on 1998 June 21-22 Authors: Srivastava, Nandita; Schwenn, Rainer; Inhester, Bernd; Martin, Sara F.; Hanaoka, Yoichiro Bibcode: 2000ApJ...534..468S Altcode: We present observations of a coronal mass ejection (CME) associated with an eruptive prominence during 1998 June 21-22 by LASCO (Large Angle Spectroscopic Coronagraph) aboard SOHO (Solar and Heliospheric Observatory). Various features in the three-part structured, white-light CME as observed by LASCO-C2 and C3 coronagraphs were compared with features in the other wavelengths, for example, in Fe XIV and Fe X emission lines obtained from LASCO C1, in Hα from Helio-Research and at 17 GHz obtained from Nobeyama Radioheliograph. We have investigated conditions in several data sets to understand the eruptive and the pre-eruptive scenario of the CME. The CME and the eruptive prominence accelerate up to ~20 Rsolar and then decelerate to the velocity of the ambient slow solar wind. The analysis clearly shows that this particular CME is a typical case of a very slow or gradual CME for which it is difficult to define an exact onset time. The CME could be tracked for about 30 hours until it crossed a distance of 30 Rsolar and disappeared from the field of view of the LASCO-C3 coronagraph. The height-time profiles of various features of this CME suggest that the leading edge of the CME and the top of the prominence or the core follow similar pattern, implying a common driver for both the CME and the eruptive prominence. The observations provide strong evidence that the CME and the prominence eruption resulted from a common cause which is the global restructuring of the magnetic field in the corona in an extensive volume of space near and including the CME. The restructuring in turn was a consequence of newly emerging flux regions near and within the neighboring active regions close to the base of the CME. Title: On the Rotation Rate of the Emission Solar Corona Authors: Stenborg, G.; Schwenn, R.; Inhester, B.; Srivastava, N. Bibcode: 1999ESASP.448.1107S Altcode: 1999mfsp.conf.1107S; 1999ESPM....9.1107S No abstract at ADS Title: Comparative Study of Coronal Mass Ejections Associated with Eruptive prominences Authors: Srivastava, Nandita; Schwenn, Rainer; Stenborg, Guillermo Bibcode: 1999ESASP.446..621S Altcode: 1999soho....8..621S Coronal mass ejections associated with eruptive prominences often display a classical 3-part structure in white light, viz., a bright leading edge followed by a dark cavity devoid of material and an embedded prominence or core. However, the initiation of such CMEs and nature of their acceleration as they propagate outward in the corona are some of the basic questions that remain unsolved. In particular, the question of role of the prominence in triggering or driving the CME has not been settled yet. In this paper, we report observations of coronal mass ejections (CMEs) associated with eruptive quiescent prominences that occurred on June 2,1998 and June 21-22, 1998. A comparative study based on multi-wavelength observations is presented. Various features in three part structured, white-light CME as observed by LASCO C2 and C3 coronagraphs aboard SOHO were compared with features in other wavelengths, for example, in FeXIV green and FeX red emission lines by LASCO-C1 coronagraph. These observations were combined with other data-sets in H-alpha, X-ray and radio wavelengths. The comparison provides an important clue to the understanding, the origin or the initiation of the CMEs. Measurements of speed and acceleration of these CMEs have also been made in order to understand the nature of propagation of the CMEs in the outer corona and the driver that triggers the onset of the CMEs. Title: MICA Observations of Coronal Transients Authors: Stenborg, G.; Schwenn, R.; Srivastava, N. Bibcode: 1999ESASP.446..627S Altcode: 1999soho....8..627S Dynamical processes are well known to occur in the inner solar atmosphere, many of them giving origin to spectacular eruptions known as coronal mass ejections. The projected velocity of propagation of these events ranges from less than 100 km/sec to greater than 1200 km/sec. In order to study the initial evolution of the faster processes it is necessary to image the inner corona at a very high cadence. Although ground-based observations of the corona are strongly affected by sky conditions they allow imaging at a high temporal resolution as compared to coronagraphic observations from space. In the recently inaugurated German-Argentinean Solar-Observatory at El Leoncito, San Juan, Argentina, a mirror coronagraph (MICA) daily images the inner solar corona with high temporal and spatial resolution in two spectral ranges: the well known green (~1.8 MK) and red (~1.0 MK) coronal lines at 5303 A and 6374 A respectively. It is essentially similar in design to LASCO-C1 on board SOHO, its field-of-view ranging from 1.05 to 2.0 solar radii from the sun center. Thus, it is ideally suited to observe the hot material and reveal the fast processes that occur in the coronal plasma. In the last year MICA has recorded several fast and not so fast green line transients at a high temporal resolution. In this work we will present observations of a few such events. This study would allow us to have a better understanding of the conditions that trigger the coronal mass ejections and their propagation in the inner solar corona. Title: LASCO FeXIV and FeX observations of the solar coronal rotation during the recent solar activity minimum Authors: Inhester, B.; Stenborg, G.; Schwenn, R.; Srivastava, N.; Podlipnik, B. Bibcode: 1999AIPC..471..297I Altcode: 1999sowi.conf..297I We investigate the periodicity and recurrence of FeXIV and FeX emission structures with heliospheric latitude and distance above the Sun's surface. The data was observed by the LASCO C1 coronagraph on board the SOHO spacecraft during the solar minimum activity from April 1996 to March 1997. For the green FeXIV emission line, reliable estimates of the solar rotation period could be obtained between -60 and 60 degrees in latitude and between 1.1 and 2 solar radii. Our investigation confirms the results of (3) of an almost ridgidly rotating equatorial streamer belt with a rotation period of about 27.5+/-0.5 days. Even coronal emissivity structures with a shorter life time between 14 and 27 days do not seem to rotate differentially. The FeX observations on the other hand do yield some indication of a reduced rotation for coronal structures over the solar poles. However, the error of the derived rotation period estimates is considerable so that the analysis of the FeX data does not allow a definite conclusion. Title: Recent observations of the solar corona with a new ground-based Coronagraph in Argentina (MICA) Authors: Stenborg, G.; Schwenn, R.; Srivastava, N.; Inhester, B.; Podlipnik, B.; Rovira, M.; Francile, C. Bibcode: 1999AIPC..471..561S Altcode: 1999sowi.conf..561S As part of the new German-Argentinian Solar-Observatory in El Leoncito, San Juan, Argentina, a new ground-based solar telescope (MICA: Mirror Coronagraph for Argentina) began to operate in August 1997. MICA is an advanced mirror coronagraph, its design being an almost exact copy of the LASCO-C1 instrument. Since its installation, it has been imaging the inner solar corona (1.05 to 2.0 solar radii) in two spectral ranges, corresponding to the emission lines of the Fe XIV and Fe X ions. The instrument can image the corona as fast as every minute. Thus, it is ideally suited to study fast processes in the inner corona. In this way it is a good complement for the LASCO-C1 instrument. We present a brief review of the characteristics of the instrument, and some recent observations. Title: Measurements of flow speeds and acceleration in gradually evolving solar mass ejections as observed by LASCO Authors: Srivastava, Nandita; Schwenn, Rainer; Inhester, Bernd; Stenborg, Guillermo; Podlipnik, Borut Bibcode: 1999AIPC..471..115S Altcode: 1999sowi.conf..115S We present observations of slowly evolving, balloon-type solar mass ejections observed by the LASCO coronagraphs aboard SOHO. These mass ejections are typically observed to rise gradually in the solar corona for several hours (>20 hours) as large loops or balloons crossing the entire field of view of the coronagraphs. Usually, their angular extent does not change much. Analysis of several such cases of balloon-type mass ejections show that they rise with very slow speeds (less than 50 km s-1) up to a distance of 2 Rsolar and then are accelerated to higher speeds until 5 Rsolar. From a distance of about 20 Rsolar, the mass ejecta attain almost a constant speed ranging between 300 and 500 km s-1. The speed profiles obtained for individual mass ejections indicate that they trace out the slow solar wind and, thus, provide an insight into the initiation and the propagation of the CMEs into the solar wind. Title: Multi-wavelength observations of the onset phase of a coronal mass ejection Authors: Innes, D. E.; Inhester, B.; Srivastava, N.; Brekke, P.; Harrison, R. A.; Matthews, S. A.; Noëns, J. C.; Schmieder, B.; Thompson, B. J. Bibcode: 1999SoPh..186..337I Altcode: The structure and dynamics of the initial phases of a coronal mass ejection (CME) seen in soft X-ray, extreme ultraviolet and optical emission are described. The event occurred on the SW limb of the Sun in active region AR 8026 on 9 April 1997. Just prior to the CME there was a class C1.5 flare. Images taken with the Extreme Ultraviolet Imaging Telescope (EIT) reveal the emergence of a candle-flame shaped extreme ultraviolet (EUV) cavity at the time of the flare. Yohkoh images, taken about 15 min later, show that this cavity is filled with hot X-ray emitting gas. It is most likely that this is the site of the flare. Almost simultaneous to the flare, an Hα surge or small filament eruption occurs about 50 arc sec northwards along the limb from the EUV cavity. At both the site of the core of the hot, EUV cavity and the filament ejection are X-ray jets. These jets seem to be connected by hot loops near their bases. Both jets disappear within a few minutes of one another. Title: A Digital Imaging Multi-Slit Spectrograph for Measurement of Line-of-Sight Velocities on the sun Authors: Srivastava, Nandita; Mathew, Shibu K. Bibcode: 1999SoPh..185...61S Altcode: A multi-slit digital imaging spectrograph has been installed at Udaipur Solar Observatory, Udaipur (India) to measure the line-of-sight velocities in Hα associated with the mass motions of the dynamic phenomena on the solar surface viz. solar flares, eruptive prominences and surges. This spectrograph is being used in conjunction with a 15 cm aperture Coudé telescope to obtain the Hα spectra at a high rate of a specific region of interest on the Sun. In this paper, we describe the principal features of this instrument and the data acquisition method. We also present spectral observations of a surge and a quiescent prominence recorded using this instrument. Title: The Rotation of the Fe XIV Solar Corona During the Recent Solar Activity Minimum Authors: Inhester, B.; Stenborg, G.; Schwenn, R.; Srivastava, N.; Podlipnik, B. Bibcode: 1999SSRv...87..211I Altcode: We analyze data observed by the LASCO C1 coronagraph on board the SOHO spacecraft during the solar minimum activity from April 1996 to March 1997. Using the phase dispersion technique, we investigate the periodicity and recurrence of Fe XIV emission structures with heliospheric latitude and distance above the Sun's surface with high spatial resolution. We find no significant deviation from a rigidly rotating Fe XIV corona with latitude or with distance from the Sun even on these small scales. In agreement with earlier work, the coronal rotation period at solar minimum is about 27.5 ± 1 days. Title: MICA: The Mirror Coronagraph for Argentina Authors: Stenborg, G.; Schwenn, R.; Srivastava, N.; Inhester, B.; Podlipnik, B.; Rovira, M.; Francile, C. Bibcode: 1999SSRv...87..307S Altcode: As part of the new German-Argentinian Solar Observatory in El Leoncito, San Juan, Argentina, a new ground-based solar telescope (MICA) began to operate in August 1997. MICA is an advanced mirror coronagraph, its design being an almost exact copy of the LASCO-C1 instrument. Since its installation, it has been imaging the inner solar corona (1.05 to 2.0 solar radii) in two spectral ranges corresponding to the emission lines of the Fe XIV and Fe X ions. The instrument can image the corona as fast as every minute. Thus, it is ideally suited to study fast processes in the inner corona. In this way, it is a good complement for the LASCO-C1 instrument. After a brief review of the instrument, we present some recent observations showing the capabilities of the instrument. Title: Acceleration Profile of the Slow Solar Wind as Inferred from Gradual Mass Ejections Observed by LASCO Authors: Srivastava, Nandita; Schwenn, Rainer; Inhester, Bernd; Stenborg, Guillermo; Podlipnik, Borut Bibcode: 1999SSRv...87..303S Altcode: The slow solar wind (< 400 km s-1) appears to initiate from the regions in the corona where magnetic fields are closed, or from the interface between streamers and other coronal regions. The nature of the acceleration of slow solar wind is not yet well known. LASCO observations of gradually evolving mass ejections offer us a good opportunity to study the speed and acceleration profiles of the slow solar wind from a distance of 1.1 up to 30 R. We present speed and acceleration profiles of slow solar wind, derived on the basis of measurements of mass flows in several cases of gradual mass ejections and present them in perspective of earlier work. Title: On the Solar Origins of Intense Geomagnetic Storms Observed During 6-11 March 1993 Authors: Srivastava, Nandita; Gonzalez, Walter D.; Gonzalez, Alicia L. C.; Masuda, Satoshi Bibcode: 1998SoPh..183..419S Altcode: Intense geomagnetic storms with DST index <= -100nT were recorded on 9March and 11March 1993 associated with solar activity on 6March and 9-10March, respectively. In this paper, we discuss the characteristic features of the solar origins of the two events that gave rise to coronal and interplanetary disturbances and as a consequence produced strong geomagnetic activity at the Earth. The source of the activity in one case is attributed to a major 3M7.0 flare that occurred on 6March 1993 and in the other case, to two large filament disruptions on the disk during 9-10March, 1993. Both these sources were found to be located near changing or varying low-latitude coronal holes. They were also located close to the heliospheric currents sheets. Distinct X-ray activity was observed for both the events as observed by the Yohkoh SXT telescope. The detailed evolution and a comparison of these events on the basis of Yohkoh soft X-ray observations are presented here. Title: Dynamics of Helically Twisted Prominence of January 22, 1979 Authors: Srivastava, Nandita; Ambastha, Ashok Bibcode: 1998Ap&SS.262...29S Altcode: 1999Ap&SS.262...29S We have studied the dynamics of a macroscopically twisted helical prominence observed in Hα line on January 22, 1979 from Udaipur Solar Observatory. The analysis carried out is similar to that of March 11, 1979 event (Srivastava et al., 1991) wherein we had studied the role of twisted force-free magnetic fields in the prominence system. In the present study, it is found that of the two helically braided prominence tubes, one was dynamically more active. We have examined the temporal evolution of force-free parameter alpha, and the axial currents associated with the prominence system that decreased with time. We find that the magnitude of the electric currents and also the rate of energy release during the untwisting of the prominence was of comparatively higher order ~ 10^30 ergs s^-1 than that of March 11, 1979 event, in agreement with the physical dimensions of the two prominences. Title: Photospheric and Chromospheric Activity Associated with 3B Flare of February 27, 1992 Authors: Debi Prasad, C.; Srivastava, Nandita Bibcode: 1998Ap&SS.262..363D Altcode: 1999Ap&SS.262..363D We have analyzed the Hα filtergrams and vector magnetograms of the active region NOAA 7070, in which a 3B/X3.3 flare occurred on February 27, 1992. The average area per sunspot of this active region was in declining phase at the time of the flare. The vector magnetograms indicate that the magnetic field was non-potential at the flaring site. Besides non-potentiality, the longitudinal field gradient was found to be the highest at the region showing initial Hα brightening. Further, in Hα filtergrams no appreciable change in the morphology of the filament tracing the magnetic neutral line was noticed in the post-flare stage. Also, the photospheric vector magnetograms show considerable shear in post-flare magnetic field of the active region. In this paper we present the observations and discuss the possible mechanism responsible for the 3B/X3.3 flare. Title: On the Characteristics of Solar Origins of Geoeffective CMEs Observed during August 1992 - April 1993 Authors: Srivastava, N.; Gonzalez, Walter D.; Gonzalez, A. L. C.; Masuda, Satoshi Bibcode: 1997ESASP.415..443S Altcode: 1997cpsh.conf..443S No abstract at ADS Title: Chromospheric Evolution and the Flare Activity of Super-Active Region NOAA 6555 Authors: Debi Prasad, C.; Ambastha, Ashok; Srivastava, Nandita; Tripathy, Sushanta C.; Hagyard, Mona J. Bibcode: 1997JApA...18...39D Altcode: Super-active region NOAA 6555 was highly flare productive during the period March 21st-27th, 1991 of its disk passage. We have st udied its chromospheric activity using high spatial resolution Hα filtergrams taken at Udaipur along with MSFC vector magnetograms. A possible relationship of flare productivity and the variation in shear has been explored. Flares were generally seen in those subareas of the active region which possessed closed magnetic field configuration, whereas only minor flares and/or surges occurred in subareas showing open magnetic field configuration. Physical mechanisms responsible for the observed surges are also discussed. Title: Radio observations of total solar eclipse of November 3, 1994 at Chapecó (Brzil) Authors: Sawant, H. S.; Srivastava, N.; Trigoso, H. E.; Sobral, J. H. A.; Fernandes, F. C. R.; Cecatto, J. R.; Subramanian, K. R. Bibcode: 1997AdSpR..20.2359S Altcode: Radio observations of the eclipse on November 3, 1994, were carried out at Chapecó, Brazil by using a decimetric spectrograph having high spectral and time resolution. The light curve shows that: (1) Time variation of the radio flux before the totality was more compared to that after. (2) During the totality radio emission at 1.5 GHz was observed. Advantage of high spatial resolution (~ 3.2 arc sec) possible during solar eclipse enabled us to determine the height of radio emission at 1.5 GHz. (3) Microwave bursts were observed associated with metric Type III-RS bursts. The source size of one of the microwave bursts was ~ 7 arc sec and its physical parameters have been estimated. (4) The time difference between radio and optical contacts suggested for the first time asymmetrical limb brightening at 1.5 GHz. Title: On the association of eruptive prominences, coronal holes and current sheets with the coronal mass ejections Authors: Srivastava, N.; Gonzalez, W. D.; Sawant, H. S. Bibcode: 1997AdSpR..20.2355S Altcode: In this paper, a study of the coronal mass ejections (CMEs) observed by Solar Maximum Mission satellite (SMM) during the period March - September, 1980, is presented. An attempt to identify various possible associations of the solar phenomena, for example, the location of coronal holes, the role of eruptive filaments or prominences, and current-sheets with the CMEs is carried out. It is shown that the combined associations of these three play an important role in the occurrence of geoeffective CMEs and also act as a tool to predict the associated geomagnetic activity. Title: Chromospheric, photospheric, magnetic field evolution and flare activity of the super active region NOAA 6555 Authors: Debi Prasad, C.; Srivastava, Nandita; Tripathy, Sushantha C.; Ambastha, Ashok Bibcode: 1995BASI...23..427D Altcode: No abstract at ADS Title: Three-Dimensional Velocity Structure of Surge and Quiescent Prominences Authors: Srivastava, N.; Mathew, S. K. Bibcode: 1995JApAS..16..382S Altcode: No abstract at ADS Title: A Possible Explanation of Reversed Magnetic Field Features Observed in NOAA AR 7321 Authors: Liu, Yang; Srivastava, Nandita; Prasad, Debi; Li, Wei; Ai, Guoxiang Bibcode: 1995SoPh..158..249L Altcode: Observations of reversed-polarity features in the chromosphere as well as in the photosphere in the form of magnetic gulfs or islands of opposite polarity have been reported recently. In this paper, we present a possible explanation for the appearance of reversed-polarity features observed in the chromospheric magnetograms of the NOAA AR 7321 observed during October 25-27, 1992. It is suggested that the large-scale reversed-polarity features may occur due to the twisting of the smaller-scale magnetic flux tubes in the layer between the photosphere and the chromosphere. Title: Magnetic Field Configuration in H alpha Flare Loops and Flaring Arches Authors: Bhatnagar, A.; Srivastava, N. Bibcode: 1993ASPC...46..351B Altcode: 1993IAUCo.141..351B; 1993mvfs.conf..351B No abstract at ADS Title: Dynamic phenomena on the sun Authors: Srivastava, Nandita Bibcode: 1993PhDT.......429S Altcode: No abstract at ADS Title: Filament Eruptions Flaring Arches and Eruptive Flares Authors: Bhatnagar, A.; Ambastha, A.; Srivastava, N. Bibcode: 1992LNP...399...59B Altcode: 1992esf..coll...59B; 1992IAUCo.133...59B Several cases of erupting filaments showing distinctly their feet have been studied. Role of the feet and their anchorage with the photosphere in maintaining filament stability is established; apart from the footpoint separation and height criteria. Further, a homologous series of more energetic events, namely, the flaring arches and eruptive flares of March 5-7, 1991, suggest a repetitive restoration of magnetic field conditions and energy build-up within a day. High resolution H-alpha observations of these events indicate that large amount of ejected material was siphoned out from the chromosphere through, the top. of a low-lying compact emission loop within the active region. Title: Helically twisted prominence eruption event of 1979 March 11. Authors: Srivastava, N.; Ambastha, A.; Bhatnagar, A. Bibcode: 1991BASI...19..208S Altcode: No abstract at ADS Title: Results of GONG site survey program at the Udaipur Solar Observatory. Authors: Ambastha, A.; Bhatnagar, A.; Srivastava, N.; Jain, R. M.; Gupta, S. K.; Sharma, R.; Agrawal, G. Bibcode: 1991BASI...19..211A Altcode: No abstract at ADS Title: GONG site evaluation program at Udaipur Solar Observatory Authors: Ambastha, Ashok; Bhatnagar, Arvind; Jain, Rajmal; Srivastava, Nandita; Gupta, Sudhir; Sharma, Richa; Agrawal, Gopal; Kumawat, Vishnu; Hill, Frank; Fischer, George Bibcode: 1991BASI...19..215A Altcode: The Global Oscillations Network Group (GONG) project to study the internal structure and dynamic of the sun is discussed. The GONG project will measure waves that penetrate throughout the sun's core. Power spectra of the monthly average transparency for each calendar month were obtained and analyzed. The resulting clear and dark time distributions and monthly average extinction coefficients and transparency power spectra are shown and discussed. The various possible networks from the candidate sites participating in the GONG project are compared. Title: Evolution of helically twisted prominence structures of March 11, 1979 Authors: Srivastava, N.; Ambastha, A.; Bhatnagar, A. Bibcode: 1991SoPh..133..339S Altcode: Helical structures are generally associated with many eruptive solar prominences. Thus, study of their evolution in the solar atmosphere assumes importance. We present a study of a flare-associated erupting prominence of March 11, 1979, with conspicuous helically twisted structure, observed in Hα line center. We have attempted to understand the role played by twisted force-free magnetic fields in this event. In the analysis, we have assumed that the helical structures visible in Hα outline the field lines in which prominence tubes are embedded. Untwisting of observed prominence tubes and later, formation of open prominence structures provide evidence of restructuring of the magnetic field configuration over the active region during the course of prominence eruption. Temporal evolution of the force-free parameter α is obtained for two main prominence tubes observed to be intertwined in a rope-like structure. Axial electric currents associated with the prominence tubes are estimated to be of the order of 1011 A which decreased with time. Correspondingly, it is estimated that the rate of energy release was ≈ 1028 erg s−1 during the prominence eruption. Title: Notes and News Authors: Srivastava, N. Bibcode: 1991BASI...19..163S Altcode: No abstract at ADS Title: Intensity variation of O i λ5577 Å line of atomic oxygen at allahabad during morning and evening twilight Authors: Srivastava, S.; Srivastava, N.; Dixit, S. D.; Srivastava, A. N. Bibcode: 1990Ap&SS.166..151S Altcode: Intensity variation of O i green line observed at Allahabad (25°32' N, 81°53' E) by a laboratorymade photometer has been reported here for the period January 1988 to December 1988. During the summer period of observation, slight enhancement in the intensity of evening and morning twilight emission is observed for a short duration of 4 min. However, winter observations show less pronounced enhancement in the intensity of evening twilight, while it does not occur during morning twilight. These observations are closely in agreement with those of Schaffer (1975). Title: On impulsive and gradual optical solar flares. Authors: Bhatnagar, A.; Ambastha, A.; Jain, R. M.; Srivastava, N. Bibcode: 1989sasf.confP.207B Altcode: 1988sasf.conf..207B; 1989IAUCo.104P.207B A comparative study of H-alpha intensity and area development of several flares is presented in an attempt to investigate characteristic features of various types of optical solar flares.