Speaker
Description
Small-scale impulsive energy events, often attributed to magnetic reconnection, are prime candidates for heating the solar corona to millions of degrees. However, the direct detection of the effect of such events in the corona remains challenging due to fast energy dissipation in the corona. These events, though faint in the corona, can drive significant chromospheric dynamics, leaving detectable imprints in strong resonance lines such as the Ca II K line, which forms over a broad height range from the lower photosphere to the chromosphere. In this study, we analyse high-resolution, full-Stokes spectropolarimetric observations from the Sunrise III/SUSI instrument, capturing an explosive event within an emerging flux region (NOAA AR 13738) on 2024 July 10. Using spectral moments, we characterise the variability of the Ca II K line core, focusing on regions exhibiting extreme line asymmetries and broadening. By comparing these moments with simultaneous photospheric and lower chromospheric observations from SUSI and SDO/AIA, we establish a multi-height context for the event. Our analysis reveals a localized, transient brightening in the AIA 17.1 nm and 9.4 nm channels, indicative of plasma temperatures reaching 1–7 MK and typically associated with coronal loop structures extending from the transition region to coronal heights of order 10 Mm. These coronal signatures are coincident with a strong, spatially-confined enhancement in the Ca II K zeroth, first and second order spectral moments. Notably, the event is associated with mixed-polarity magnetic footpoints and shows a clear loop-like connection between the SUSI field of view and the boundary of a distant sunspot penumbra in the AIA 17.1 nm, AIA 160 nm and AIA 9.4 nm channels. The spectral moment anomalies, coronal brightenings and magnetic connectivity, support the interpretation of this event as a nanoflare-like reconnection burst.