Tiwari, Sanjiv ; Hansteen, Viggo ; De Pontieu, Bart ; Panesar, Navdeep K ; Berghmans, David

Poster presented at Hinode-14 / IRIS-11 Joint Science Meeting on 2021-10-25

Abstract: We report on the presence of numerous tiny bright dots in and around an emerging ephemeral bipolar region observed with SOLO HRIEUV in 174 Å, emitted by the coronal plasma at ∼1 MK. These dots are roundish, have a diameter of 615±306 km, a lifetime of 40±30 seconds, and intensity enhancement of 30% ± 11% from their immediate surroundings. While some dots remain isolated during their evolution, most dots extend explosively to become a small loop or show a jet-like activity. Some dots form at the end of a fine-scale explosion (i.e., a loop, surge/jet). Many of the bigger and brighter EUI dots are also discernible in SDO/AIA 171 channel, have significant EM in the temperature range of 1–2 MK, and are often located at polarity inversion lines observed in HMI LOS magnetograms. Although not as pervasive as in observations, Bifrost MHD simulations of an ephemeral bipolar region do show the presence of dots in synthetic Fe IX/X emissions. These dots show distinct Doppler signatures – have redshifts of the order of 10 km s−1, often followed by blueshifts of similar or higher magnitudes. Occasionally, blueshifts and redshifts coexist. These scenarios suggest that dots are plausibly formed by magnetic reconnection between emerging and pre-existing magnetic field. Further, the synthetic images of O V/VI and Si IV lines, which form in the transition region, also show the dots observed in Fe IX/X emission, often expanded in size, or extended as a loop, similar to that in HRIEUV observations. Thus, although most dots are consistent with them being a result of magnetic reconnection in the lower solar atmosphere, the possibility of magneto-acoustic shocks (driven from the lower atmosphere) manifesting themselves as dots through Fe IX/X emission can not be ruled out.

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