Ramesh Chandra

Extreme–Ultraviolet (EUV) waves are large-scale, tsunami-like disturbances on the solar surface associated with eruptive phenomena such as solar flares, filament eruptions, and coronal mass ejections (CMEs). Due to their strong correlation with major solar eruptions, we present here a comprehensive statistical study of EUV waves and their connections to Moreton waves, CMEs, solar flares, type II radio bursts, and solar energetic particle (SEP) events during Solar Cycle 25 (December 2019–December 2025). This study utilizes EUV data from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory and coronagraph data from the Large Angle and Spectrometric Coronagraph onboard Solar and Heliospheric Observatory. Our analysis reveals that 12.3% of the observed EUV waves are associated with Moreton waves, 95% with CMEs, 92.7% associated with flare, 44.3% with metric type II radio bursts, and 11.8% with SEPs. While nearly all EUV waves are linked to CMEs, their association with solar flares varies significantly, ranging from weak B-class events to major X-class flares. Furthermore, the majority of Moreton waves correlate with large- or medium-class flares, with only a small fraction associated with weaker C-class flares. Our findings may contribute to a better understanding of space weather events and, potentially, to their forecasting.

Quiescent filaments are prominent features of the solar atmosphere, and their evolution reflects the coronal magnetic field’s response to photospheric magnetic activity. Here, we report on a quiescent filament observed on 2023 September 28–29, aiming to understand how the magnetic configuration shapes its feet and drives its extension. For this purpose, high-resolution spectral data in H α and Mg II k are used from the Télescope Héliographique pour l’Etude du Magnétisme et des Instabilités Solaires and the Interface Region Imaging Spectrograph, respectively. To track changes in the filament, we utilise long-term data from the Atmospheric Imaging Assembly on the Solar Dynamics Observatory (SDO) and from the Global Oscillation Network Group (GONG). We analyse the longitudinal magnetic field in the photosphere using the Solar Optical Telescope on board Hinode, as well as SDO/Helioseismic and Magnetic Imager data. In addition to this, we use GONG H α data to analyze the longitudinal oscillations in the filament. Observations show that parasitic polarities and canceling flux play a key role in forming and reorganizing the filament feet and in lengthening the filament. A 3D MHD reconstruction using vector magnetograms reveals that its magnetic configuration evolves into a full flux rope (FR), whose extension on the second day matches the observed filament growth. The FR is separated from the surrounding nearly potential field by quasi-separatrix layers, which in turn are separated by current layers. They get more organized around the FR as it grows. Moreover, the longitudinal oscillations in the extended filament are attributed to heating from flux cancellation at underlying bright points.

Quiescent filaments are prominent features of the solar atmosphere, and their evolution reflects the coronal magnetic field's response to photospheric magnetic activity. Here, we report on a quiescent filament observed from 2023 September 28-29, aiming to understand how the magnetic configuration shapes its feet and drives its extension. For this purpose, high-resolution spectral data in H$α$ and Mg II k are used from the Télescope Héliographique pour l'Etude du Magnétisme et des Instabilités Solaires (THEMIS) and the Interface Region Imaging Spectrograph (IRIS), respectively. To track changes in the filament, we utilise long-term data from the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) and from the Global Oscillation Network Group (GONG). We analyse the longitudinal magnetic field in the photosphere using the Solar Optical Telescope (SOT) onboard Hinode, as well as SDO/Helioseismic and Magnetic Imager (HMI) data. In addition to this, we use GONG H$α$ data to analyze the longitudinal oscillations in the filament. Observations show that parasitic polarities and canceling flux play a key role in forming and reorganizing the filament feet and in lengthening the filament. A 3D MHD reconstruction using vector magnetograms reveals that its magnetic configuration evolves into a full flux rope (FR), whose extension on the second day matches the observed filament growth. The FR is separated from the surrounding nearly potential field by quasi-separatrix layers, which in turn are separated by current layers. They get more organized around the FR as it is growing up. Moreover, the longitudinal oscillations in the extended filament are attributed to heating from flux cancellation in underlying bright points.

Solar filaments are cool and dense plasma structures suspended in the solar corona against gravity. We present observations of a quiescent filament eruption that occurs on 13 July 2015. The eruption is associated with a two-ribbon GOES B8.9 class flare. Photospheric magnetic-flux cancellation is present below the filament during days. This builds up a flux rope which progressively rises until it gets unstable, first leading to a confined eruption and pre-flare brightenings, then to an ejection which starts ≈ 20 min later with the flare onset. An interesting feature of this event is the presence of a large circular brightening formed around the erupting region. This brightening is produced due to interchange reconnection of the ejected magnetic configuration with the surrounding open magnetic field. This null-point topology is confirmed by a potential-field extrapolation. The EUV loops located on the southern side of the filament eruption first contract during the null-point reconnection, then expand as the flux rope is ejected. The associated CME has both a classical flux rope shape and plasma ejected along open field lines on the flux rope side (a trace of interchange reconnection). Finally, we set all this disparate observations within a coherent framework where magnetic reconnection occurs both below and above the erupting filament.

We present a comprehensive multiwavelength analysis of a coronal mass ejection (CME) on 2014 January 8 from the active region (AR) NOAA 11947 by analyzing the data from Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory, RHESSI, and Hiraiso Radio Spectrograph. The CME is associated with an M3.6 flare and filament eruption. Observations from the AIA 171 Å images reveal the origin of pre-CME arcade ≈1 hr prior to the eruptive event. Before the onset of event, the hot AIA 131 and 94 Å images exhibit an existence of a hot flux rope, which on eruption results in the activation and eruptive expansion of the pre-CME coronal arcade. The eruptive process of pre-CME arcade consists of a slow rise evolution with a speed ≈3 km s⁻¹, “arcade-to-bubble” transformation, and blowout expansion of the CME-bubble with a fast speed of ≈400 km s⁻¹. A differential emission measure analysis suggests the presence of multithermal plasma in the bubble-structure and strong plasma heating at the core of the AR. A blowout expansion of CME is accompanied with multiple type III and a split-band type II radio bursts in association with X-ray emission up to 50 keV energies from its source region. Our observations reveal that the formation and expansion of the CME-bubble serve as the earliest signatures of the CME, capturing its development in the low corona. Concurrent X-ray and radio emissions further highlight the critical role of large-scale magnetic reconnection in powering both the flare emissions and the early evolution and dynamics of the CME.

The purpose of this paper is to analyze the multi-wavelength and multi-instrument observations of two quiescent filament eruptions as well as the deflection of associated CMEs from the radial direction. The events occurred on 18 October 2017 and 9 May 2021, respectively, in the southern solar hemisphere. Both of them and associated flares were registered by the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory (SDO) and the Solar Terrestrial Relations Observatory-Ahead (STEREO-A) Observatory in different EUV wavebands. Using data from STEREO A COR1 and COR2 instruments and the Large Angle and Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric Observatory (SOHO), we investigated morphology and kinematics of the eruptions and the latitudinal offset of the related CMEs with respect to the erupting filaments. Our observations provide the evidence that the two filament eruptions were highly non-radial. The observed deviations are attributed to the presence of low-latitude coronal holes.