DETECTION OF SUPERSONIC DOWNFLOWS AND ASSOCIATED HEATING EVENTS IN THE TRANSITION REGION ABOVE SUNSPOTS

• Published in: Astrophysical journal. Letters Vol. 789; no. 2; pp. 1 - 7
• Main Authors: KLEINT, L, Antolin, P, Tian, H, Judge, P, Testa, P, DE PONTIEU, B, Martinez-Sykora, J, Reeves, K K, WUELSER, J P, McKillop, S
• Format: Journal Article
• Language: English; Norwegian
• Published: United States Institute of Physics Publishing Ltd 10.07.2014
• Subjects: ASTRONOMY; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Bursts; CARBON IONS; Density; DOPPLER EFFECT; Flares; HEATING; Imaging; INTERFACES; MAGNESIUM IONS; Rain; Ribbons; SOLAR ACTIVITY; SOLAR CORONA; SPATIAL RESOLUTION; SUN; SUNSPOTS; VELOCITY
• ISSN: 2041-8205; 2041-8213
• DOI: 10.1088/2041-8205/789/2/L42

Interface Region Imaging Spectrograph data allow us to study the solar transition region (TR) with an unprecedented spatial resolution of 0".33. On 2013 August 30, we observed bursts of high Doppler shifts suggesting strong supersonic downflows of up to 200 km s super(-1) and weaker, slightly slower upflows in the spectral lines Mgii h and k, C II 1336, Si IV 1394 [Angstrom], and 1403 [Angstrom], that are correlated with brightenings in the slitjaw images (SJIs). The bursty behavior lasts throughout the 2 hr observation, with average burst durations of about 20 s. The locations of these short-lived events appear to be the umbral and penumbral footpoints of EUV loops. Fast apparent downflows are observed along these loops in the SJIs and in the Atmospheric Imaging Assembly, suggesting that the loops are thermally unstable. We interpret the observations as cool material falling from coronal heights, and especially coronal rain produced along the thermally unstable loops, which leads to an increase of intensity at the loop footpoints, probably indicating an increase of density and temperature in the TR. The rain speeds are on the higher end of previously reported speeds for this phenomenon, and possibly higher than the free-fall velocity along the loops. On other observing days, similar bright dots are sometimes aligned into ribbons, resembling small flare ribbons. These observations provide a first insight into small-scale heating events in sunspots in the TR.