arXiv subjects

Shirsh Lata Soni

Publications and source records attributed to Shirsh Lata Soni.

7 recordsLinked to original sources

arXiv2026

Evolution and Impact of Switchbacks Throughout the Heliosphere

Magnetic switchbacks are large-amplitude fluctuations in the interplanetary magnetic field, and appear frequently in the near-Sun solar wind explored recently by Parker Solar Probe: these new observations have prompted many new studies into their properties and origins. Here, we first review what is known about how switchbacks evolve as they travel away from the Sun: both in terms of their expansion-driven growth and their decay due to various processes like turbulence, reconnection, dispersion, parametric instability, and interaction with interplanetary shocks. We then review the current state of knowledge on how switchbacks impact the physics of the solar wind as a whole: in terms of the turbulent cascade, acceleration and heating of the wind, modification of the open solar flux and scattering of energetic particles. Finally, we suggest future studies to further our understanding of switchback evolution and impacts on the heliosphere.

physics.space-ph↗

arXiv2026

Storm-Time Cusp Precipitation: Insights from TRACERS Multi-Crossing Observations

The dayside cusp provides a direct pathway for solar wind plasma entry into the magnetosphere ionosphere system through magnetic reconnection. Using low altitude ion and electron measurements from TRACERS, together with upstream solar wind and geomagnetic conditions, we investigate the evolution of the cusp during a geomagnetic storm on 30 September 2025, spanning its rising, main, and recovery phases, and compare these with a quiet-time reference. Storm-time observations show broader and more poleward precipitation regions and enhanced electron energy flux, indicating intensified dayside coupling. To interpret these variations, we combine solar wind and IMF measurements with the maximum magnetic shear reconnection model to determine X-line locations and use a Tsyganenko field model to compute event-specific field-line transit distances between the X-line and TRACERS. The results demonstrate that cusp morphology and latitude track IMF-driven reconnection geometry, and that realistic path lengths are essential for quantitative reconnection-rate estimates, highlighting the capability of TRACERS to resolve storm-time cusp evolution. Enhanced cusp precipitation during the recovery phase is consistent with IMF conditions, indicating sustained solar wind driving rather than intrinsic storm-phase effects.

physics.space-ph↗

arXiv2026

Comprehensive MHD modelling of ten successive CMEs driving a historic geomagnetic storm -- The 2024 Mothers Day event

Interacting coronal mass ejections (CMEs) result in complex heliospheric structures that can dramatically enhance their geoeffectiveness compared to isolated events. A striking example of such complex structures is that of the Mothers Day event, which occurred during 10-14 May 2024, leading to the strongest geomagnetic storm in decades. It was driven by at least ten interacting CMEs accompanied by flare and filament eruptions from the solar western hemisphere. We aim to understand its solar and heliospheric origins, variation in plasma and magnetic characteristics, and predict its geoeffectiveness. Furthermore, we focus on bringing to the community the challenges and limitations faced during themodelling of such a complex, yet important environment. We use multi-point remote observations of CMEs and employ different methods to estimate their speeds and geometry. These parameters drive the 3D magnetohydrodynamic simulations of CME evolution and heliospheric propagation in the framework of the EUHFORIA model. The best-performing simulation reproduced the arrival time of the storm and peak intensity with a lead of 2 hours, and estimated the storm strength with about 70% accuracy. This work underscores the requirements and challenges involved in accurately modelling extreme events. The major bottleneck was to constrain the CME input parameters that dictate the accuracy of the data-driven simulations. Predicting the impacts of the complex heliospheric structures during this event required the modelling of the CME-CME interactions accurately. As a community, we need to invest more in observational infrastructure while improving the speed and accuracy of our MHD forecasting models.

astro-ph.SR↗

arXiv2026

Properties of Magnetic Switchbacks in the Near-Sun Solar Wind

Magnetic switchbacks are fluctuations in the solar wind in which the interplanetary magnetic field sharply deflects away from its background direction so as to create folds in magnetic field lines while remaining of roughly constant magnitude. The magnetic field and velocity fluctuations are extremely well correlated in a way corresponding to Alfvénic fluctuations propagating away from the Sun. For a background field which is nearly radial this causes an outwardly propagating jet to form. Switchbacks and their characteristic velocity jets have recently been observed to be nearly ubiquitous by Parker Solar Probe with in situ measurements in the inner heliosphere within 0.3 AU. Their prevalence, substantial energy content, and potentially fundamental role in the dynamics of the outer corona and solar wind motivate the significant research efforts into their understanding. Here we review the in situ measurements of these structures (primarily by Parker Solar Probe). We discuss how they are identified and measured, and present an overview of the primary observational properties of these structures, both in terms of individual switchbacks and their collective arrangement into ``patches''. We identify both properties for which there is a strong consensus and those that have limited or qualified support and require further investigation. We identify and collate several open questions and recommendations for future studies.

physics.space-ph↗

arXiv2024

Switchback Patches Evolve into Microstreams via Magnetic Relaxation

Magnetic switchbacks are distinct magnetic structures characterized by their abrupt reversal in the radial component of the magnetic field within the pristine solar wind. Switchbacks are believed to lose magnetic energy with heliocentric distance. To investigate this switchbacks originating from similar solar source regions are identified during a radial alignment of the Parker Solar Probe (PSP; 25.8 solar radii) and Solar Orbiter (SolO; 152 solar radii). We found that 1) the dynamic and thermal pressures decrease at the switchback boundaries by up to 20% at PSP and relatively unchanged at SolO and magnetic pressure jump across the boundary remains negligible at both distances, and 2) bundles of switchbacks are often observed in switchback patches near the Sun, and in microstreams farther away. Background proton velocity (vp) is 10% greater than the pristine solar wind (vsw) in microstreams, whereas vp ~ vsw in switchback patches. Microstreams contain an average of 30% fewer switchbacks than switchback patches. It is concluded that switchbacks likely relax magnetically and equilibrate their plasma with the surrounding environment with heliocentric distance. Switchback relaxation can, in turn, accelerate the surrounding plasma. Therefore, it is hypothesized that magnetic relaxation of switchbacks may cause switchback patches to evolve into microstreams with heliocentric distance. Statistical analysis of PSP and SolO switchbacks is underway to further test our hypothesis.

astro-ph.SR↗

arXiv2020

Exhaustive study of three-time periods of solar activity due to single active regions: sunspot, flare, CME, and, geo-effective characteristics

In this paper, we present the multi-wavelength study of a high level of solar activity during which a single active region produced multiple flares/CMEs. According to the sunspot observations, the current solar cycle 24 manifest to be less intense in comparison with the previous recent sunspot cycles. In the course of the current sunspot cycle 24, several small and large sunspot groups have produced various moderate and intense flare/CME events. There are a few active regions with a large number of flaring activities passed across the visible disk of the Sun during 2012-2015. In this study, we consider the three periods 22-29 Oct 2013, 01-08 Nov 2013, and 25 Oct- 08-Nov 2014, during which 228 flares have been observed. Considering only active regions near the central part of the disk, 59 CMEs (halo or partial) have been reported among which only 39 events are associated with flares. We conclude that an active region with a larger area, more complex morphology and stronger magnetic field has a comparatively higher possibility of producing extremely fast CMEs (speed > 1500 km/sec). So that among the 5 X class flares of the reported periods, 3 of them (60%) are associated with a CME. The lift-off time for CME-flare associated events has a +15 to+30 minute time interval range after the occurrence time of associated flares suggesting that the flares produce the CMEs. Additionally, we compiled the geomagnetic storms occurring within1-5 days after the CME onset. 10% of the 59 CMEs are related to a magnetic storm but all are moderate storms.

astro-ph.SR↗

arXiv2020

Multi-wavelength Study of Energetic Processes during Solar Flares occurrence

This paper is an attempt to understand the physical processes occurring in different layers of solar atmosphere during a solar flare. For a complete understanding of the flare we must analyze multi-wavelength datasets, as emission at different wavelength originates from different layers of the solar atmosphere. Also, flares are transient and localized events observed to occur at all longitudes. With these considerations, we have carried out multi-wavelength analysis of two representative flare events. One event occurred close to the centre of the solar disk and other occurred close to the limb. In the former case, we examine the emission from the lower layers of the solar atmosphere. Therefore the chromospheres, transition region and also the photospheric magneto-gram can be analyzed. On the other hand, in near-limb event, coronal features can be clearly studied. In this paper, the first event studied is the M 1.1 class flare from the active region NOAA 10649 located at S10E14 and the second event is the M 1.4 class flare from the active region NOAA 10713 located at S12W90. In both cases, we have observed the excellent multi-wavelength data sets. The observations from multi-instrumental data clearly shows that flares occur in the vicinity of sunspots. These are regions of strong magnetic field with mixed polarity.

astro-ph.SR↗