EVIDENCE FOR A TRANSITION REGION RESPONSE TO PENUMBRAL MICROJETS IN SUNSPOTS

Abstract

Penumbral microjets are short-lived, fine-structured and bright jets that are\ngenerally observed in chromospheric imaging of the penumbra of sunspots. Here\nwe investigate their potential transition region signature, by combining\nobservations with the Swedish 1-m Solar Telescope (SST) in the Ca II H and Ca\nII 8542{\\AA} lines with ultraviolet imaging and spectroscopy obtained with the\nInterface Region Imaging Spectrograph (IRIS), which includes the C II\n1334/1335{\\AA}, Si IV 1394/1403{\\AA} and Mg II h & k 2803/2796{\\AA} lines. We\nfind a clear corresponding signal in the IRIS Mg II k, C II and Si IV slit-jaw\nimages, typically offset spatially from the Ca II signature in the direction\nalong the jets: from base to top, the penumbral microjets are predominantly\nvisible in Ca II, Mg II k and C II/Si IV, suggesting progressive heating to\ntransition region temperatures along the jet extent. Hence, these results\nsupport the suggestion from earlier studies that penumbral microjets may heat\nto transition region temperatures.\n