Pooja Devi

• Devi, Pooja; Chandra, Ramesh; Miteva, Rositsa; Ibrahim, M. Syed & Joshi, Kamal (2026). Band splitting in m-Type II radio bursts and their role in coronal parameter diagnostics. Advances in Space Research. ISSN 0273-1177. doi: 10.1016/j.asr.2025.10.006. Fulltekst i vitenarkiv Vis sammendrag

  Type II radio bursts are signatures of shock waves generated by solar eruptions, observed at radio wavelengths. While metric (m) type II bursts originate in the lower corona, their longer-wavelength (up to kilometers) counterparts extend into interplanetary space. A rare but valuable feature observed in some type II bursts is band splitting in their dynamic spectra, which provides crucial insights into physical parameters such as shock speed, Alfvén Mach number, Alfvén speed, and coronal magnetic field strength (B). In this study, we investigate band-splitting in 44 m-type II radio bursts observed by the Radio Solar Telescope Network during solar cycle 24 (2009–2019). These events exhibit splitting in both fundamental and harmonic bands and are analyzed under both perpendicular and parallel shocks. All events are associated to solar flares and 41 (93 %) with the coronal mass ejections. Shock speeds, derived using a hybrid coronal density model proposed by Vršnak et al. (2004), range from ~ 350 to 1727 km/s. The relative bandwidth (BDW) of the split bands remains constant with frequency and height. Alfvén Mach numbers indicate moderate shock strength (1.06–3.38), while Alfvén speeds and B vary from 230–1294 km/s and 0.48–7.13 G, respectively. Power-law relationships are established as BDW ∝ f_L^{-0.4} and BDW ∝ R^{~1} , while the coronal magnetic field decreases with height as B ∝ R^{~-3}. These results enhance our understanding of shock dynamics and magnetic field structures in the solar corona.

• Karki, Garima; Schmieder, Brigitte; Démoulin, Pascal; Devi, Pooja; Chandra, Ramesh & Joshi, Reetika (2025). Counter-Streaming Velocities in a Quiescent Filament. Solar Physics. ISSN 0038-0938. 300(7). doi: 10.1007/s11207-025-02509-w. Fulltekst i vitenarkiv Vis sammendrag

  Filaments/prominences are cold plasma (~10^4 K) embedded in the solar corona, two orders of magnitude hotter. Filament plasma is structured by the magnetic field in thin elongated threads. Counter-streaming flows have been observed. The aim of this paper is to characterize these flows. For that, we use high spatial resolution observations of spectral data obtained with THEMIS in Halpha and with IRIS in Mg II k lines on 29 September 2023. We best detect counter-streaming flows in both the blue and red wings of these spectral lines. They are forming long Doppler shifted strands slightly inclined on the filament axis. The blue/red shift alternates across the strands at the arc second scale. H spectral profiles with large widths are interpreted as formed by multi-strands with opposite velocity directions. The absorption in the core of Mg II k line is also broader than in the chromosphere. This corresponds also to counter-streaming velocities. We derive that a fraction of the filament plasma is moving at supersonic speed (of the order of 20 km s−1) with the assumption that the filament is optically thick. We conclude that the counter-directed Doppler shifts might not be magnetic field aligned flows but rather correspond to kink transverse oscillations of the magnetic field with independent motions in nearby strands.

• Devi, Pooja; Mandrini, Cristina H.; Chandra, Ramesh; Cristiani, Germán D.; Démoulin, Pascal & Cormack, Cecilia Mac [Vis alle 7 forfattere av denne artikkelen] (2025). Partial Null-Point Reconnection of an Eruptive Filament. Solar Physics. ISSN 0038-0938. 300(11). doi: 10.1007/s11207-025-02579-w. Fulltekst i vitenarkiv Vis sammendrag

  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.

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