arXiv subjects

B Lekshmi

Publications and source records attributed to B Lekshmi.

3 recordsLinked to original sources

arXiv2026

Temporal variations of solar inertial mode parameters from GONG (2002-2024) and HMI (2010-2024): Rossby modes ($3 \leq m \leq 16 $) and $m=1$ high-latitude mode

We studied the temporal evolution of solar inertial modes over the solar cycle using observations from GONG and SDO/HMI. We focused on the high-latitude mode with azimuthal wavenumber $m=1$ and the equatorial Rossby modes with $3 \le m \le 16$. We used horizontal flow maps near the solar surface from GONG and HMI ring-diagram pipelines at a cadence of approximately one day, covering the period 2002-2024. The data were divided into overlapping 4-year windows, with central times separated by six months. Within each time window and for each inertial mode, we measured the frequency and power of the mode from GONG and HMI data. We find good agreement between GONG and HMI measurements throughout their overlapping period from 2010 to 2024. In general, the magnitude of the frequency variations increases with increasing $m$, and relative changes in mode power typically exceed 100%. For the $m=1$ high-latitude mode, the measured power is anticorrelated with the sunspot number (SSN), while its frequency shows no significant temporal variation. For the equatorial Rossby modes, the frequencies are generally anticorrelated with the SSN, whereas the mode powers tend to correlate positively with the SSN. An exception is the $m=3$ equatorial Rossby mode, whose mode power is strongly anticorrelated with the SSN, in contrast to the other equatorial Rossby modes, highlighting its distinct behavior. We find that the frequencies and power of the Sun's inertial modes have varied significantly on solar-cycle timescales over the past 23 years. The mode parameters are however not uniformly synchronized with the SSN; variations are observed both between modes and from one solar cycle to the next, with some of the differences likely reflecting observational uncertainties. The sensitivity of inertial modes to solar-cycle changes indicates their potential as a diagnostic of solar interior dynamics and magnetism.

astro-ph.SR↗

arXiv2025

Dynamics of Subsurface Flows in Solar Active Regions During the May 2024 Storm

In May 2024, the Sun exhibited intense magnetic activity, marked by numerous high-intensity flares resulting from the interaction and merging of NOAA ARs 13664 and 13668 in the southern hemisphere and AR 13663 in the northern hemisphere. Notably, AR 13664 displayed an extended lifetime, remaining visible after a full solar rotation and continuing to produce significant flaring activity. In this study, we investigate the evolution of sub-photospheric plasma flows associated with these ARs during their disk passage using ring-diagram analysis of SDO/HMI Dopplergrams. We analyze flow divergence, vorticity, and kinetic helicity across depths from the surface to 25 Mm, revealing pronounced temporal and depth-dependent variations. Our observations indicate that the majority of flares occur on the days when the Normalized Helicity Gradient Variance, a measure of kinetic helicity spread, peaks or on the following day. Furthermore, we examine the relationship between subsurface flow dynamics and surface magnetic properties of these complex active regions to understand the interaction between them.

astro-ph.SR↗

arXiv2022

Sub-surface Plasma Flows and the Flare Productivity of Solar Active Regions

The extreme space weather conditions resulting from high energetic events likes solar flares and Coronal Mass Ejections (CMEs) demand for reliable space weather forecasting. The magnetic flux tubes while rising through the convection zone gets twisted by the turbulent plasma flows, energizing the system and resulting in flares. We investigate the relationship between the subsurface plasma flows associated with flaring active regions and their surface magnetic flux and current helicity. The near-surface horizontal velocities derived from the ring-diagram analysis of active region patches using Global Oscillation Network Group (GONG) Doppler velocity measurements are used to compute the fluid dynamics descriptors like vertical divergence, vorticity and kinetic helicity used in this work. The flaring active regions are observed to have large value of vertical vorticity and kinetic helicity. Also, the horizontal flow divergence, vorticity, flux, kinetic and current helicities are observed to be significantly correlated and evolve in phase with each other. We observe that the integrated values of the above flow and magnetic parameters observed one day prior to the flare are significantly correlated with the integrated flare intensity of the active region. Hence, we show that strong vorticity/kinetic helicities lead to larger active region twisting, presumably generating high-intensity flares.

astro-ph.SR↗