Solar and Heliospheric Observatory/Coronal Diagnostic Spectrograph and Ground‐based Observations of a Two‐Ribbon Flare: Spatially Resolved Signatures of Chromospheric Evaporation

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Abstract

During a coordinated observing campaign (Solar and Heliospheric Observatory, SOHO JOP 139), we obtained simultaneous spectroheliograms of a solar active region in several spectral lines, sampling levels from the chromosphere to the corona. Ground-based spectroheliograms were acquired at the Dunn Solar Tower of the National Solar Observatory/Sacramento Peak in four chromospheric lines, while the coronal diagnostic spectrograph on board SOHO was used to obtain rasters of the active region in transition region (TR) and coronal lines. Such a complete data set allowed us to compare the development of intensity and velocity fields during a small two-ribbon flare in the whole atmosphere. In particular, we obtained for the first time quasi-simultaneous and spatially resolved observations of velocity fields during the impulsive phase of a flare, in both the chromosphere and upper atmosphere. In this phase, strong downflows (up to 40 km s-1) following the shape of the developing ribbons are measured at chromospheric levels, while strong upward motions are instead measured in TR (up to -100 km s-1) and coronal lines (-160 km s-1). The spatial pattern of these velocities have a common area about 10'' wide. This is the first time that opposite-directed flows at different atmospheric levels are observed in the same spatial location during a flare. These signatures are highly suggestive of the chromospheric evaporation scenario predicted in theoretical models of flares.

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