srivastava

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Author name code: srivastava
ADS astronomy entries on 2022-09-14
author:"Srivastava, N."

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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
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.

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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
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&amp;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.

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Title: Modelling the magnetic vectors of ICMEs detected by radially
aligned multiple spacecraft using INFROS
Authors: Srivastava, Nandita; Kilpua, Emilia; Sarkar, Ranadeep
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.

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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
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.

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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
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 (&lt;
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.

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Title: Detection and Classification of Potential Caves on the Flank
of Elysium Mons, Mars
Authors: Sharma, Ravi; Srivastava, Neeraj
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.

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Title: A holistic approach to understand helium enrichment in
interplanetary coronal mass ejections: new insights
Authors: Yogesh; Chakrabarty, D.; Srivastava, N.
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.

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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
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.

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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.
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.

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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.
2022LPICo2678.1865D Altcode:
Terrestrial analogues for lunar basalts and Anorthosites identified
within India. Positive comparison with lunar soils qualify them as
potential lunar analogues.

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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.
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.

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Title: Editorial: Space Weather Prediction: Challenges and Future
prospects
Authors: Srivastava, Nandita; Mierla, Marilena; Zhang, Jie
2021FrASS...8..230S Altcode:
No abstract at ADS

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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.
2021SSRv..217...84N Altcode:
No abstract at ADS

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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
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 $&lt;$
$\sim$ 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.

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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.
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 &lt;−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.

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Title: Radial sizes and expansion behavior of ICMEs in solar cycles
23 and 24
Authors: Mishra, Wageesh; Doshi, Urmi; Srivastava, Nandita
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.

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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
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.

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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.
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'.

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Title: Evidence for distinctive changes in the solar wind helium
abundance in solar cycle 24
Authors: Yogesh; Chakrabarty, D.; Srivastava, N.
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 &gt; 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.

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Title: INterplanetary Flux ROpe Simulator (INFROS): Predicting the
magnetic-field vectors of ICMEs
Authors: Srivastava, Nandita; Gopalswamy, Nat; Sarkar, Ranadeep
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
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.

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Title: Geology of Grimaldi Basin on the Moon: Evidence for volcanism
and tectonism during the Copernican period
Authors: Singh, Tanu; Srivastava, Neeraj
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.

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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.
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.

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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
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 &lt;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
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.
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
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.

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Title: Resource potential and planning for exploration of the Hebrus
Valles, Mars
Authors: Sharma, Ravi; Srivastava, Neeraj; Yadav, Santosh Kumar
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.

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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
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.

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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
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.
2019LPI....50.1493S Altcode:
Pre-Chandrayaan-2 understanding of lunar morphology, topography,
mineralogy, and chronology at the Vikram Landing site.

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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.
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.

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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
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.

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Title: Geomagnetic Consequences of Interacting CMEs of June 13-14,
2012
Authors: Srivastava, Nandita; Mirtoshev, Zavkiddin; Mishra, Wageesh
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
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.

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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
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.

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Title: Editorial: Earth-affecting Solar Transients
Authors: Zhang, Jie; Blanco-Cano, Xochitl; Nitta, Nariaki; Srivastava,
Nandita; Mandrini, Cristina H.
2018SoPh..293...80Z Altcode:
No abstract at ADS

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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.
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
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.
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
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
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
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
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.
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.
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.
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
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
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
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.
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
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.
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
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
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 &amp; 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.
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
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.
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
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.
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.
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
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.

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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.
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.

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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.
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.

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Title: A Statistical Study on Characteristics of Disappearing
Prominences
Authors: Joshi, Anand D.; Bong, Su-Chan; Srivastava, Nandita
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.

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Title: On the onset of recurrent eruptions of a filament observed
during August 2012
Authors: Srivastava, Nandita; Joshi, Anand D.; Mathew, Shibu K.
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.
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.
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.

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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.
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
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
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
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
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.
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
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.

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Title: Spatial Distribution of Spinel in the Orientale Basin: New
Insights from M^3 Data
Authors: Srivastava, N.; Gupta, R. P.
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.
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.

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Title: Indicators of solar filament remnants in ICMEs
Authors: Sharma, Rahul; Srivastava, Nandita
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.
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
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
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.

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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.
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.
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
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
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
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.
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
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 &amp; 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.
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
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
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.
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
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.
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
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.
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.
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
2011CSci..100..167S Altcode:
The outer atmosphere of the sun - called the corona - has been observed
during total solar eclipse for short periods (typically &lt;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.
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
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.
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.
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
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.
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.
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.
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.
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.
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
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.
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.
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
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
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 (&lt;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.
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.
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.
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.
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
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 &lt; -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 &lt;
DSt &lt; -100 nT) and only 50% of the super-intense (DST &lt;
-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.
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.
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.
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.
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.
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.
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.
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.
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.
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 &lt; -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.
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.
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.
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.
2003IAUJD...7E..19S Altcode:
The expansion speeds of halo CMEs observed by LASCO aboard SoHO
duirng 1996-2002 which were geo-effective (Dst &lt;-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
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.
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
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.
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&gt;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&lt;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
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
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.
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
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.
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.
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.
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
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 (&gt;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.
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.
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.
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.
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
1999SSRv...87..303S Altcode:
The slow solar wind (&lt; 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
1998SoPh..183..419S Altcode:
Intense geomagnetic storms with DST index &lt;= -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
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
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
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.
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.
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.
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
1995BASI...23..427D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Three-Dimensional Velocity Structure of Surge and Quiescent
Prominences
Authors: Srivastava, N.; Mathew, S. K.
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
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.
1993ASPC...46..351B Altcode: 1993IAUCo.141..351B; 1993mvfs.conf..351B
No abstract at ADS

---------------------------------------------------------
Title: Dynamic phenomena on the sun
Authors: Srivastava, Nandita
1993PhDT.......429S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Filament Eruptions Flaring Arches and Eruptive Flares
Authors: Bhatnagar, A.; Ambastha, A.; Srivastava, N.
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.
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.
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
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.
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.

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Title: Notes and News
Authors: Srivastava, N.
1991BASI...19..163S Altcode:
No abstract at ADS

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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.
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).

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Title: On impulsive and gradual optical solar flares.
Authors: Bhatnagar, A.; Ambastha, A.; Jain, R. M.; Srivastava, N.
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.