Papers by Arun Kumar Awasthi
Research in Astronomy and Astrophysics, 2022
In this article, we compare the properties of two coronal mass ejections (CMEs) that show similar... more In this article, we compare the properties of two coronal mass ejections (CMEs) that show similar source region characteristics but different evolutionary behaviors in the later phases. We discuss the two events in terms of their near-Sun characteristics, interplanetary evolution and geoeffectiveness. We carefully analyzed the initiation and propagation parameters of these events to establish the precise CME-interplanetary CME (ICME) connection and their near-Earth consequences. The first event is associated with poor geomagnetic storm disturbance index (Dst ≈-20 nT) while the second event is associated with an intense geomagnetic storm of DST ≈-119 nT. The configuration of the sunspots in the active regions and their evolution are observed by Helioseismic and Magnetic Imager (HMI). For source region imaging, we rely on data obtained from Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO) and Hα filtergrams from the Solar Tower Telescope at Aryabhatta Resea...
We explore the temporal evolution of flare plasma parameters including temperature 11 (T ) differ... more We explore the temporal evolution of flare plasma parameters including temperature 11 (T ) differential emission measure (DEM ) relationship by analyzing high spectral and temporal 12 cadence of X-ray emission in 1.6-8.0 keV energy band, recorded by SphinX (Polish) and Solar 13 X-ray Spectrometer (SOXS; Indian) instruments, during a B8.3 flare which occurred on July 14 04, 2009. SphinX records X-ray emission in 1.2-15.0 keV energy band with the temporal and 15 spectral cadence as good as 6 μs and 0.4 keV, respectively. On the other hand, SOXS provides 16 X-ray observations in 4-25 keV energy band with the temporal and spectral resolution of 3 s 17 and 0.7 keV, respectively. We derive the thermal plasma parameters during impulsive phase of 18 the flare employing well-established Withbroe-Sylwester DEM inversion algorithm. 19
Research in Astronomy and Astrophysics, 2021
We study the sunspot activity in relation to spotless days (SLDs) during the descending phase of ... more We study the sunspot activity in relation to spotless days (SLDs) during the descending phase of solar cycle 11-24 to predict the amplitude of sunspot cycle 25. For this purpose, in addition to SLD, we also use the geomagnetic activity (aa index) during the descending phase of a given cycle. A very strong correlation of the SLD (R=0.68) and aa index (R=0.86) during the descending phase of a given cycle with the maximum amplitude of next solar cycle has been estimated.The empirical relationship led us to deduce the amplitude of cycle 25 to be 99.13± 14.97 and 104.23± 17.35 using SLD and aa index, respectively as predictors.Both the predictors provide comparable amplitude for solar cycle 25 and reveal that the solar cycle 25 will be weaker than cycle 24. Further we derive that the maximum of cycle 25 is likely to occur between February and March 2024. While the aa index has been used extensively in the past, this work establishes SLDs as another potential candidate for predicting the characteristics of the next cycle.
Proceedings of the International Astronomical Union, 2015
We explore the temporal evolution of flare plasma parameters including temperature (T) - differen... more We explore the temporal evolution of flare plasma parameters including temperature (T) - differential emission measure (DEM) relationship by analyzing high spectral and temporal cadence of X-ray emission in 1.6-8.0 keV energy band, recorded by SphinX (Polish) and Solar X-ray Spectrometer (SOXS; Indian) instruments, during a B8.3 flare which occurred on July 04, 2009. SphinX records X-ray emission in 1.2-15.0 keV energy band with the temporal and spectral cadence as good as 6 μs and 0.4 keV, respectively. On the other hand, SOXS provides X-ray observations in 4-25 keV energy band with the temporal and spectral resolution of 3 s and 0.7 keV, respectively. We derive the thermal plasma parameters during impulsive phase of the flare employing well-established Withbroe-Sylwester DEM inversion algorithm.
The Astrophysical Journal, 2016
We investigate the evolution of differential emission measure distribution (DEM[T]) in various ph... more We investigate the evolution of differential emission measure distribution (DEM[T]) in various phases of a B8.3 flare, which occurred on July 04, 2009. We analyze the soft X-ray (SXR) emission in 1.6-8.0 keV range, recorded collectively by Solar Photometer in X-rays (SphinX; Polish) and Solar X-ray Spectrometer (SOXS; Indian) instruments. We make a comparative investigation of the best-fit DEM[T] distributions derived by employing various inversion schemes viz. single gaussian, power-law, functions and Withbroe-Sylwester (W-S) maximum likelihood algorithm. In addition, SXR spectrum in three different energy bands viz. 1.6-5.0 keV (low), 5.0-8.0 keV (high) and 1.6-8.0 keV (combined) is analyzed to determine the dependence of the best-fit DEM[T] distribution on the selection of energy interval. The evolution of DEM[T] distribution, derived using W-S algorithm, reveals the plasma of multi-thermal nature during the rise to the maximum phase of the flare, while of isothermal nature in the post-maximum phase of the flare. Thermal energy content is estimated considering the flare plasma to be of 1) iso-thermal and 2) multi-thermal nature. We find that the energy content during the flare, estimated from the multi-thermal approach, is in good agreement with that derived using the iso-thermal assumption except during the maximum of the flare. Further, (multi-) thermal energy estimated employing low-energy band of the SXR spectrum result in higher values than that derived from the combined-energy band. On the contrary, the analysis of high-energy band of SXR spectrum lead to lower thermal energy than that estimated from the combined-energy band.
Proceedings of the International Astronomical Union, 2012
We investigate 10 M-class flares observed by the SOXS mission to study the influence of the solar... more We investigate 10 M-class flares observed by the SOXS mission to study the influence of the solar flare plasma cooling on the Neupert effect. We study the temporal evolution of 1s cadence X-ray emission in 7-10 keV and 10-30 keV representing the SXR and HXR emission respectively. We model the cooling as a function of time by the ratio of time-derivative of SXR with the HXR flux. We report that the ratio is exponentially decaying in rise phase of the flare, which, however, saturates after the impulsive phase. We estimate the cooling time scale in the rise phase for the flares and found to be varying between 39 and 525 s.
In order to study the origin of precursor phase emission in solar flares and its relation to main... more In order to study the origin of precursor phase emission in solar flares and its relation to main phase energy release, we employ X-ray and EUV wavebands observations in 13 flare events observed during the years 2003-2004. The X-ray spectral mode observations are taken from "Solar X-ray Spectrometer (SOXS)" as well as RHESSI missions and EUV observations from TRACE mission. The X-ray emission spectral mode analysis revealed that, during precursor phase emission, the plasma temperature (T) and emission measure (EM) vary between 7-15 MK and 0.002-0.08 times 10^$$49$$ cm^$$-3$$ respectively. We report two major conclusions: (1) The precursor phase emission is originated from low-temperature and moderately dense plasma. (2) the precursor phase emission corresponds to low-altitude coronal loops, however, in co-spatial with the main phase energy release site. Further, during the study, we have also found some preliminary conclusions viz. (1) Isothermal plasma behavior in precurs...
Proceedings of the International Astronomical Union, 2012
We study the temporal and spatial evolution of magnetic field parameters, and multiwavelength obs... more We study the temporal and spatial evolution of magnetic field parameters, and multiwavelength observations of the AR 11226 and AR 11261, observed during 02-09 June 2011 and 31 July to 06 August 2011 respectively, to probe the origin of the associated solar energetic particles (SEPs). The magnetic-field toplogy of both ARs shows complex magnetic structure of β and βγ configuration. The X-ray observations by GOES and RHESSI reveal that the AR 11226 as well as AR 11261 has been most turbulent to produce flares accompanying CMEs and SEPs. We restrict our study of magnetic field evolution of ARs to helio-longitudes E20-W70. The AR 11226 produced 28 flares (GOES C-class) and 8 CMEs as well as 5 SEPs. On the other hand, the AR 11261 produced 29 flares (GOES C class), 8 CMEs as well as 5 SEPs. We study the temporal evolution of magnetic field parameters viz. gradient, shear, rotation to probe the origin of the energy release in the flare and associated CME and SEP. We do not find convincing relationship in view of predicting SEPs.
Periodicities in the X-Ray Emission from the Solar Corona
The Astrophysical Journal, 2013
Monthly Notices of the Royal Astronomical Society, 2013
We study the temporal, spatial and spectral evolution of the M1.8 flare, which occurred in the ac... more We study the temporal, spatial and spectral evolution of the M1.8 flare, which occurred in the active region 11195 (S17E31) on 2011 April 22, and explore the underlying physical processes during the precursor phase and their relation to the main phase. The study of the source morphology using the composite images in 131 Å wavelength observed by the Solar Dynamics Observatory/Atmospheric Imaging Assembly and 6-14 keV [from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)] revealed a multiloop system that destabilized systematically during the precursor and main phases. In contrast, hard X-ray emission (20-50 keV) was absent during the precursor phase, appearing only from the onset of the impulsive phase in the form of foot-points of emitting loops. This study also revealed the heated looptop prior to the loop emission, although no accompanying foot-point sources were observed during the precursor phase. We estimate the flare plasma parameters, namely temperature (T), emission measure (EM), power-law index (γ) and photon turnover energy (to), and found them to be varying in the ranges 12.4-23.4 MK, 0.0003-0.6 × 10 49 cm −3 , 5-9 and 14-18 keV, respectively, by forward fitting RHESSI spectral observations. The energy released in the precursor phase was thermal and constituted ≈1 per cent of the total energy released during the flare. The study of morphological evolution of the filament in conjunction with synthesized T and EM maps was carried out, which reveals (a) partial filament eruption prior to the onset of the precursor emission and (b) heated dense plasma over the polarity inversion line and in the vicinity of the slowly rising filament during the precursor phase. Based on the implications from multiwavelength observations, we propose a scheme to unify the energy release during the precursor and main phase emissions in which the precursor phase emission was originated via conduction front that resulted due to the partial filament eruption. Next, the heated leftover S-shaped filament underwent slow-rise and heating due to magnetic reconnection and finally erupted to produce emission during the impulsive and gradual phases.
Icarus, 2012
We probe the lethality of X-rays from solar flares to organisms on Mars based on the observations... more We probe the lethality of X-rays from solar flares to organisms on Mars based on the observations of 10 solar flares. We, firstly, estimate the doses produced by the strong flares observed by the RHESSI and GOES missions during the descending phase of sunspot cycle 23. Next, in order to realize the dependence of dose on flux and steepness of spectra, we model the incident spectra over a wide range of spectral index to estimate dose values and compare them with the observed doses. We calculate the distribution of surficial spectra visible to organisms on the martian surface by employing attenuation of X-rays due to CO 2 column densities distribution over the South Pole. The surficial flux distribution after folding with the opacity of water enables us to estimate the dose distribution over the South Pole. The dose measured from the surficial spectrum produced by the observed 10 flares corresponding to the latitudes 50-60°, 60-70°, 70-80°and 80-90°S varies in the range of 6.39 Â 10 À9-1.80 Â 10 À6 ; 4.89 Â 10 À10-5.21 Â 10 À8 ; 5.10 Â 10 À11-5.20 Â 10 À9 and 4.42 Â 10 À10-4.89 Â 10 À12 gray (1 gray = 10 4 erg/g) respectively. Comparing the measured as well as the modeled doses with those proposed to be lethal for various organisms by Smith and Scalo (Smith, D.S., Scalo, J. [2007]. Planet. Space Sci. 55, 517-527); we report that the habitability of life on the South Pole remains unaffected even by the strongest solar flare occurred during descending phase of solar cycle 23. Further, the monthly integrated energy released by the solar flares in the most productive month viz. October 2003 and January 2005 from the GOES soft X-ray observations is estimated to be 8.43 and 3.32 Â 10 32 ergs respectively, which is almost equal in order to the typical energy released by a single strong X-class flare. Therefore, we propose the life near the South Pole region on the Mars remain uninfluenced by X-ray emission even during monster phenomena of energy release on the Sun and/or Star.
Advances in Space Research, 2013
We use multiwavelength data from space and ground based instruments to study the solar flares and... more We use multiwavelength data from space and ground based instruments to study the solar flares and coronal mass ejections (CMEs) on January 23, 2012 that were responsible for one of the largest solar energetic particle (SEP) events of solar cycle 24. The eruptions consisting of two fast CMEs (≈1400 km s −1 and ≈2000 km s −1) and M-class flares that occurred in active region 11402 located at ≈N28 W36. The two CMEs occurred in quick successions, so they interacted very close to the Sun. The second CME caught up with the first one at a distance of ≈11-12 R sun. The CME interaction may be responsible for the elevated SEP flux and significant changes in the intensity profile of the SEP event. The compound CME resulted in a double-dip moderate geomagnetic storm (Dst ∼ −73nT). The two dips are due to the southward component of the interplanetary magnetic field in the shock sheath and the ICME intervals. One possible reason for the lack of a stronger geomagnetic storm may be that the ICME delivered a glancing blow to Earth.
Advances in Space Research, 2013
Emergence of complex magnetic flux in the solar active regions lead to several observational effe... more Emergence of complex magnetic flux in the solar active regions lead to several observational effects such as a change in sunspot area and flux embalance in photospheric magnetograms. The flux emergence also results in twisted magnetic field lines that add to free energy content. The magnetic field configuration of these active regions relax to near potential-field configuration after energy release through solar flares and coronal mass ejections. In this paper, we study the relation of flare productivity of active regions with their evolution of magnetic flux emergence, flux imbalance and free energy content. We use the sunspot area and number for flux emergence study as they contain most of the concentrated magnetic flux in the active region. The magnetic flux imbalance and the free energy are estimated using the HMI/SDO magnetograms and Virial theorem method. We find that the active regions that undergo large changes in sunspot area are most flare productive. The active regions become flary when the free energy content exceeds 50% of the total energy. Although, the flary active regions show magnetic flux imbalance, it is hard to predict flare activity based on this parameter alone.
Advances in Space Research, 2013
Employing coronagraphic and EUV observations close to the solar surface made by the Solar Terrest... more Employing coronagraphic and EUV observations close to the solar surface made by the Solar Terrestrial Relations Observatory (STEREO) mission, we determined the heliocentric distance of coronal mass ejections (CMEs) at the starting time of associated metric type II bursts. We used the wave diameter and leading edge methods and measured the CME heights for a set of 32 metric type II bursts from solar cycle 24. We minimized the projection effects by making the measurements from a view that is roughly orthogonal to the direction of the ejection. We also chose image frames close to the onset times of the type II bursts, so no extrapolation was necessary. We found that the CMEs were located in the heliocentric distance range from 1.20 to 1.93 solar radii (Rs), with mean and median values of 1.43 and 1.38 Rs, respectively. We conclusively find that the shock formation can occur at heights substantially below 1.5 Rs. In a few cases, the CME height at type II onset was close to 2 Rs. In these cases, the starting frequency of the type II bursts was very low, in the range 25 -40 MHz, which confirms that the shock can also form at larger heights. The starting frequencies of metric type II bursts have a weak correlation with the measured CME/shock heights and are consistent with the rapid decline of density with height in the inner corona.
Coronal mass ejections and type II radio bursts
Page 1. Coronal Mass Ejections and Type II Radio Bursts Nat Gopalswamy Solar System Exploration D... more Page 1. Coronal Mass Ejections and Type II Radio Bursts Nat Gopalswamy Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland ... 17 Page 18.peak in the outer corona, and then slowly declines in the IP medium. ...
Active region NOAA 11158 produced many flares during its disk passage. At least two of these flar... more Active region NOAA 11158 produced many flares during its disk passage. At least two of these flares can be considered as homologous: the C6.6 flare at 06:51 UT and C9.4 flare at 12:41 UT on February 14, 2011. Both flares occurred at the same location (eastern edge of the active region) and have a similar decay of the GOES soft X-ray light curve. The associated coronal mass ejections (CMEs) were slow (334 km/s and 337 km/s) and of similar apparent widths (43° and 44°), but they had different radio signatures. The second event was associated with a metric type II burst while the first one was not. The COR1 coronagraphs on board the STEREO spacecraft clearly show that the second CME propagated into the preceding CME that occurred 50 minutes before. These observations suggest that ., On the origin of solar metric type II bursts, Solar Physics, v. 187, Issue 1, p. 89-114, 1999. Gaizauskas, V., The relation of solar flares to the evolution and proper motions of magnetic fields, Advances in Space Research, 2, 11-30, 1982.
The energetic relationship among geoeffective solar flares, associated CMEs and SEPs
Research in Astronomy and Astrophysics, 2013
ABSTRACT Major solar eruptions (flares, coronal mass ejections (CMEs) and solar energetic particl... more ABSTRACT Major solar eruptions (flares, coronal mass ejections (CMEs) and solar energetic particles (SEPs)) strongly influence geospace and space weather. Currently, the mechanism of their influence on space weather is not well understood and requires a detailed study of the energetic relationship among these eruptive phenomena. From this perspective, we investigate 30 flares (observed by RHESSI), followed by weak to strong geomagnetic storms. Spectral analysis of these flares suggests a new power-law relationship (r ~ 0.79) between the hard X-ray (HXR) spectral index (before flare-peak) and linear speed of the associated CME observed by LASCO/SOHO. For 12 flares which were followed by SEP enhancement near Earth, HXR and SEP spectral analysis reveals a new scaling law (r ~ 0.9) between the hardest X-ray flare spectrum and the hardest SEP spectrum. Furthermore, a strong correlation is obtained between the linear speed of the CME and the hardest spectrum of the corresponding SEP event (r ~ 0.96). We propose that the potentially geoeffective flare and associated CME and SEP are well-connected through a possible feedback mechanism, and should be regarded within the framework of a solar eruption. Owing to their space weather effects, these new results will help improve our current understanding of the Sun-Earth relationship, which is a major goal of research programs in heliophysics.
Energy-dependent nature of thermal emission in solar flares
Proceedings of the 29th Meeting of the …, Jan 1, 2011
ABSTRACT Our study of 10 M - class solar flares observed by the SOXS mission reveals breakthrough... more ABSTRACT Our study of 10 M - class solar flares observed by the SOXS mission reveals breakthrough nature of multi-thermal X-ray emission in 6-20 keV with temperatures of 15-50 MK. The multi-thermal power-law index ($gamma$) and the flare plasma cooling time vary between 2.7 - 4.3 and 22 - 310 s respectively. Further the break-energy point between thermal and non-thermal emission is found to vary between 17 and 22 keV.
Solar Physics, Jan 1, 2011
We carried out a multi-wavelength study of a Coronal Mass Ejection (CME) and an associated flare ... more We carried out a multi-wavelength study of a Coronal Mass Ejection (CME) and an associated flare occurring on 12 May 1997. We present a detailed investigation of magnetic-field variations in the NOAA Active Region 8038 which was observed on the Sun during 7--16 May 1997. This region was quiet and decaying and produced only very small flare activity during its disk passage. However, on 12 May 1997 it produced a CME and associated medium-size 1B/C1.3 flare. Detailed analyses of Hα filtergrams and MDI/SOHO magnetograms revealed continual but discrete surge activity, and emergence and cancellation of flux in this active region. The movie of these magnetograms revealed two important results that the major opposite polarities of pre-existing region as well as in the emerging flux region were approaching towards each other and moving magnetic features (MMF) were ejecting out from the major north polarity at a quasi-periodicity of about ten hrs during 10--13 May 1997. These activities were probably caused by the magnetic reconnection in the lower atmosphere driven by photospheric convergence motions, which were evident in magnetograms. The quantitative measurements of magnetic field variations such as magnetic flux, gradient, and sunspot rotation revealed that in this active region, free energy was slowly being stored in the corona. The slow low-layer magnetic reconnection may be responsible for the storage of magnetic free energy in the corona and the formation of a sigmoidal core field or a flux rope leading to the eventual 2 eruption. The occurrence of EUV brightenings in the sigmoidal core field prior to the rise of a flux rope suggests that the eruption was triggered by the inner tether-cutting reconnection, but not the external breakout reconnection. An impulsive acceleration revealed from fast separation of the Hα ribbons of the first 150 seconds suggests the CME accelerated in the inner corona, which is also in consistent with the temporal profile of the reconnection electric field. Based on observations and analysis we propose a qualitative model, and we conclude that the mass ejections, filament eruption, CME, and subsequent flare were connected with one another and should be regarded within the framework of a solar eruption.
Solar Physics, Jan 1, 2011
We report solar flare plasma to be multi-thermal in nature based on the theoretical model and stu... more We report solar flare plasma to be multi-thermal in nature based on the theoretical model and study of the energy-dependent timing of thermal emission in ten M-class flares. We employ high-resolution X-ray spectra observed by the Si detector of the "Solar X-ray Spectrometer" (SOXS). The SOXS onboard the Indian GSAT-2 spacecraft was launched by the GSLV-D2 rocket on 8 May 2003. Firstly we model the spectral evolution of the X-ray line and continuum emission flux F (ε) from the flare by integrating a series of isothermal plasma flux. We find that the multi-temperature integrated flux F (ε) is a power-law function of ε with a spectral index (γ ) ≈ −4.65. Next, based on spectral-temporal evolution of the flares we find that the emission in the energy range E = 4 -15 keV is dominated by temperatures of T = 12 -50 MK, while the multi-thermal power-law DEM index (δ) varies in the range of −4.4 and −5.7. The temporal evolution of the X-ray flux F (ε, t) assuming a multi-temperature plasma governed by thermal conduction cooling reveals that the temperature-dependent cooling time varies between 296 and 4640 s and the electron density (n e ) varies in the range of n e = (1.77 -29.3) × 10 10 cm −3 . Employing temporal evolution technique in the current study as an alternative method for separating thermal from nonthermal components in the energy spectra, we measure the break-energy point, ranging between 14 and 21 ± 1.0 keV.
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Papers by Arun Kumar Awasthi