Observations of chromospheric evaporation flows in RHESSI microflares
Berkebile-Stoiser S.1,Gömöry P.1,2,
Veronig A. M.1, Rybak J.2
1 IGAM/Kanzelhoehe Observatory, Institute of Physics, Universiteat Graz,
Universiteatsplatz 5, A-8010 Graz, Austria
2 Astronomical Institute of the Slovak Academy of Sciences,
SK-05960 Tatranská Lomnica, Slovakia
Abstract:
We present the analysis of two homologous microflares of GOES class A9 with respect to mass flows
in the chromosphere and transition region. Both events show non-thermal emission (evidence for beamed
electrons) in RHESSI X-ray spectra. As outlined by observations of the Coronal Diagnostic Spectrometer,
we find for the first event downflows in the He I, O V and Ne VI line reaching speeds up to 40 km/s
at the position of chromospheric flare brightenings. On the other hand, upflows with velocities <40 km/s
are observed for the second microflare. According to hydrodynamic flare simulations, the non-thermal
electron energy density F deposited in the chromosphere determines if chromospheric evaporation is
`gentle' or `explosive'. Thus, we derive rough estimates for F in our microflares and compare the results
to the observed CDS flow properties.