Multi-wavelength fine structure and mass flows in solar microflares
Authors:
S. Berkebile-Stoiser, P. Gomory, A. M. Veronig, J. Rybak, P. Sutterlin
Image & caption:
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Image caption::
AR 10898 as observed by TRACE, MDI and DOT before the 08:26 UT microflare occurred. Panel a): TRACE WL image with the position of the CDS slit and the DOT FoV. Panel b) shows an MDI high resolution longitudinal magnetogram recorded ~45 min before the other images and rotated to 08:21:36 UT. In Panel c), a TRACE 17.1 nm image (inverse grey scale). Panels d) to f) show the DOT G Band, Ca II H and H alpha images nearest in time to the TRACE white light map.
Description:
We study the multi-wavelength characteristics at high spatial resolution, as well as chromospheric evaporation signatures of solar microflares. To this end, we analyze the fine structure and mass flow dynamics in the chromosphere, transition region and corona of three homologous microflares (GOES class 3 keV) was carried out. EUV line spectra provided by the CDS/SOHO spectrometer are searched for Doppler shifts in order to study associated plasma flows at chromospheric (He I, T~39000 K), transition region (O V, T~260000 K), and coronal temperatures (Si XII, T~2MK). RHESSI X-ray spectra provide information about non-thermal electrons.
The multi-wavelength appearance of the microflares is in basic agreement with the characteristics of large flares. We find the flow dynamics associated with the events to be very complex. For all three microflares, multi-component fitting is needed for several profiles of He I, O V, and Ne VI lines observed at the flare peaks, which indicate spatially unresolved, oppositely directed flows of 180 km/s. We interpret these flows as twisting motions of the flare loops. RHESSI X-ray spectra show evidence of non-thermal bremsstrahlung for two of the three microflares. The electron beam flux density deposited in the chromosphere for these events is estimated to straddle the threshold heating flux between gentle and explosive evaporation.
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