Papers by nandita srivastava
Frontiers in Astronomy and Space Sciences, 2021
We attempt to understand the influence of the heliospheric state on the expansion behavior of cor... more 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 ∼33% (∼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 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 Su...
Monthly Notices of the Royal Astronomical Society, 2019
Similar to the Sun, other stars shed mass and magnetic flux via ubiquitous quasi-steady wind and ... more 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 ph...
Space Science Reviews, 2021
Geomagnetic storms are an important aspect of space weather and can result in significant impacts... more 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 steal...
The outer atmosphere of the sun-called the corona-has been observed during total solar eclipse fo... more The outer atmosphere of the sun-called the corona-has been observed during total solar eclipse for short periods (typically < 6 min), from as early as the eighteenth century. In the recent past, space-based instruments have permitted us to study the corona uninterruptedly. In spite of these developments, the dynamic corona and its high temperature (1-2 million K) are yet to be fully understood. It is conjectured that their dynamic nature and associated energetic events are possible reasons behind the high temperature. In order to study these in detail, a visible emission line space solar coronagraph is being proposed as a payload under the small-satellite programme of the Indian Space Research Organisation. The satellite is named as Aditya-1 and the scientific objectives of this payload are to study: (i) the existence of intensity oscillations for the study of wavedriven 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.
The Astrophysical Journal
Investigations on the solar cycle variation of the properties of suprathermal populations (H and ... more Investigations on the solar cycle variation of the properties of suprathermal populations (H and other heavy ions like 4He, 3He, 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 <∼ 1 MeV n−1 particle flux data obtained from the Ultra-Low Energy Isotope Spectrometer on board the Advanced Composition Explorer satellite during solar cycles 23 and 24. The analysis reveals that helium (4He) 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 a zero or positive lag in cycle 23 similar to 4He, it shows only a zero lag in cycle 24 and no negative lag is seen. Further, significant differences in the spectral indices are seen between 4He and Fe in cycle 24 compared to cycle 23. These results suggest that generation mechanisms responsi...
The Astrophysical Journal
Solar flares create adverse space weather impacting space- and Earth-based technologies. However,... more 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 th...
Astronomical Society of India Conference Series, 2013
Bulletin of the Astronomical Society of India
Bulletin of the Astronomical Society of India
Coronal Mass Ejections (CMEs) associated with solar filament eruptions expel huge amount of mass,... more 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, observations of filament (cold) material are rare when sampled by the in situ spacecraft (ACE/Wind) at L1 point and were reported quantitatively in only few earlier studies. We examine cases where cold material is identified as a direct consequence of eruptive filaments during last solar cycle as 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.
AIP Conference Proceedings, 2012
The FP7 COronal Mass Ejections and Solar Energetic Particles (COMESEP) project is developing tool... more The FP7 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 data, complemented by the extensive data coverage of solar cycle 23, the key ingredients that lead to magnetic storm and SEP events and the factors that are responsible for false alarms are being identified. To enhance our understanding of the 3-D 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 modelled. COMESEP is a unique cross-collaboration effort and bridges the gap between the SEP, CME and terrestrial effects scientific communities.
The launch of STEREO spacecraft with the capability of heliospheric imaging alongwith in-situ obs... more The launch of STEREO spacecraft with the capability of heliospheric imaging alongwith in-situ observations have provided us an opportunity to track and understand the propagation of CMEs from the Sun to the Earth and beyond. We present the results of a study based on several cases of CME-CME interaction observed by STEREO/HI instruments. These CMEs were launched in quick succession and interacted as they propagated in the inner heliosphere. We estimate the 3D kinematics of these interacting CMEs using stereoscopic observations and examine the nature of their collision /interaction and exchange of momentum during interaction. We also compare the actual arrival times of these CMEs with that estimated from the 3D kinematics. This would help us to understand the role of the post-collision kinematics dependence on the actual arrival time of these CMEs at the in-situ spacecraft. Further, we examine the signatures of collision/interaction of CMEs in in-situ observations. The consequences of interaction in strengthening the geoeffectiveness of CMEs will also be presented.
We propose a space based solar coronagraph for the vector magnetic field measurements. A space ba... more We propose a space based solar coronagraph for the vector magnetic field measurements. A space based coronagraph is highly desirable in order to avoid the earth’s atmospheric scattered light related problems in coronal magnetic field measurements. There are several interesting problems which could be addressed by knowing the vector magnetic field in the corona. Some of the most interesting problems are, the magnetic field configuration for the origin of coronal mass ejections, role of magnetic field in the coronal heating, and solar g-mode detection. There are a handful of lines in the infrared wavelength which could be used for the coronal magnetic measurements, among those Fe XIII line is the most suitable line for this purpose. For the magnetic field measurements using this line, we describe the expected polarization signal level and the measurement technique employed to retrieve the polarization signals. Towards the end, we discuss the optical layout of a space based coronagraph...
Frontiers in Astronomy and Space Sciences, 2021
Eruptions of coronal mass ejections (CMEs) from the Sun are usually associated with a number of s... more 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 analyze 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...
Current Science, 2017
Aditya-L1, the first ever Indian scientific space mission dedicated to probe the Sun, our nearest... more Aditya-L1, the first ever Indian scientific space mission dedicated to probe the Sun, our nearest star, is slated for launch by the Indian Space Research Organisation (ISRO) most likely in 2020, the year coinciding with the expected start of the rising phase of solar cycle 25. Of the seven science payloads on-board Aditya-L1, three are in situ instruments, namely the Aditya Solar wind Particle EXperiment, the Plasma Analyser Package for Aditya and a magnetometer package. These three payloads will sample heliospheric data from the L1 Lagrangian point of the Sun-Earth system, at a distance of ~1% of the distance to the Sun, along the Sun-Earth line. This is therefore a unique opportunity for the solar physics community to gain a better understanding of the inner heliosphere and predict space weather more accurately.
Advances in Space Research, 2018
The Aditya-L1 is first Indian solar mission scheduled to be placed in a halo orbit around the fir... more 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 insitu 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 insitu 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.
Monthly Notices of the Royal Astronomical Society, 2018
We study the flare evolution process using both H α and Ca-K data sets to understand the variatio... more 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.
Solar Physics, 2018
This Topical Collection (TC) is devoted to the recent advancement in the study of Earthaffecting ... more This Topical Collection (TC) is devoted to the recent advancement in the study of Earthaffecting solar transients. Earth-affecting solar transients encompass a broad range of phenomena, including major solar flares, coronal mass ejections (CMEs), interplanetary CMEs (ICMEs), solar energetic particle (SEP) events, and corotating interaction regions (CIRs). In the past decade, nearly continuous observations of the Sun and the inner heliosphere Earth-affecting Solar Transients
AIP Conference Proceedings, 1999
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Papers by nandita srivastava