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Ram Ajor Maurya

Publications and source records attributed to Ram Ajor Maurya.

5 recordsLinked to original sources

Morphology of Solar Filaments During the Solar Maximum of Cycle 24: A Study of 35 Filaments Focusing on Chirality, Barb Orientation, Skewness, and Eruptive Behavior

Filaments in the solar atmosphere are plasma structures held aloft by magnetic fields, counteracting the pull of gravity. Analyzing their magnetic structure is challenging due to the lack of direct observations of their magnetic fields. However, through multi-wavelength intensity observations, one can infer their morphology. We identified 35 solar filaments during the maximum period of the solar cycle 24. In order to ascertain their chirality, we analyzed H$α$ intensity observations. Using coronal ultraviolet intensity images, we also determined the skewness of the related coronal arcades. Furthermore, based on adjacent active regions, we classified filaments as quiescent or active, according to strength of nearby photospheric magnetic fields. We followed every filament over time to estimates their characteristics. The hemispheric chirality preference is followed by 27 (77%) filaments across all categories, based on observed bearing sense. We examined the skewness of the coronal arcades connected to 19 filaments, and they all complied with the hemisphere helicity criterion. The morphology of 16 filaments was also ascertained by integrating the skewness and bearing sense. There were two filaments with sheared arcade morphology and fourteen with flux rope shape. Additionally, by analyzing the changes in the skewness of coronal arcades and the bearing sense of filament barbs over time, we examined the variation in filament magnetic structure. Further, we examine the temporal evolution of selected filaments, which exhibit peculiar characteristics during the observational period. Lastly, we investigated the eruptive characteristics of these filaments. We did not find filaments that are more likely to explode because they do not adhere to the hemispheric chirality preference.

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Hard X-Ray Quasi-Periodic Pulsations in X-Class Solar Flares Observed by Aditya-L1/HEL1OS

We present the catalogue of quasi-periodic pulsations (QPPs) detected in hard X-ray (HXR) observations of X-class solar flares obtained with the HEL1OS instrument onboard Aditya-L1 during July 2024 - March 2026. The catalogue comprises 34 flares spanning GOES classes X1.1 - X7.1. QPPs are detected and studied using a uniform procedure based on Ensemble Empirical Mode Decomposition (EEMD) and wavelet analyses. Statistically significant QPPs are identified in 25 events (~74%), demonstrating that QPPs are a common property of X-class flares. The detected periods range from approximately 1 to 3 min, with a pronounced concentration between 1.3 and 1.7 min, suggesting the existence of a preferential timescale that may be associated with kink or slow magnetohydrodynamic oscillations in the flaring region. The dominant periods remain nearly independent of photon energy across the 8 - 20 keV range, while the modulation depth increases systematically with photon energy following a power-law relation with an exponent of about 1.5. QPPs detected in different HXR energy channels exhibit strong phase coherence and positive cross-correlation coefficients, indicating modulation by a common physical mechanism. Several intense flares display HXR modulation depths of up to 25%, providing evidence for nonlinear effects. The observed statistical properties support models in which QPPs are generated by repetitive magnetic reconnection, either spontaneous or periodically modulated by magnetohydrodynamic oscillations. This study establishes HEL1OS as a powerful instrument for quantitative studies of flare QPPs during Solar Cycle 25.

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Strong Blue Asymmetry in Hα line as a Preflare Activity

Chromospheric activities prior to solar flares provide important clues to solar flare initiation, but are as yet poorly understood. We report a significant and rapid H$α$ line broadening before the solar flare SOL2011-09-29T18:08, that was detected using the unprecedented high-resolution H$α$ imaging spectroscopy with the Fast Imaging Solar Spectrograph (FISS) installed on the 1.6 m New Solar Telescope (NST) at Big Bear Solar Observatory.The strong H$α$ broadening extends as a blue excursion up to -4.5 A and as a red excursion up to 2.0 A, which implies a mixture of velocities in the range of -130 km/s to 38 km/s by applying the cloud model, comparable to the highest chromospheric motions reported before. The H$α$ blueshifted broadening lasts for about 4 minutes, and is temporally and spatially correlated with the start of a rising filament, which is later associated with the main phase of the flare as detected by the Atmosphere Imaging Assembly (AIA) onboard Solar Dynamics Observatory (SDO). The potential importance of this H$α$ blueshifted broadening as a preflare chromospheric activity is briefly discussed within the context of the two-step eruption model.

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Chromospheric Sunspot Oscillations in H-alpha and Ca II 8542A

We study chromospheric oscillations including umbral flashes and running penumbral waves in a sunspot of active region (AR) using scanning spectroscopy in H-alpha and Ca II 8542A, with the Fast Imaging Solar Spectrograph (FISS) at the 1.6 meter New Solar Telescope at Big Bear Solar Observatory. A bisector method is applied to spectral observations to construct chromospheric Doppler velocity maps. Temporal sequence analysis of these shows enhanced high-frequency oscillations inside the sunspot umbra in both lines. Their peak frequency gradually decreases outward from the umbra. The oscillation power is found to be associated with magnetic-field strength and inclination, with different relationships in different frequency bands.

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Spectral Line Profile Changes Associated with Energetic Solar Transients

Solar energetic transients occurring in solar atmosphere are associated with catastrophic release of energy in the solar corona. These transients inject a part of their energy by various physical processes to the deeper, denser photospheric layer at which velocity and magnetic fields are measured using suitable spectral lines. Serious questions have been raised about the nature of the observed magnetic (and velocity) field changes associated with energetic transients as their measurements are expected to be affected by flare-induced line profile changes. In this paper, we shall discuss some recent progress on our understanding of the physical processes associated with such events.

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