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Session 73 - Solar Space Observations, SOHO & SERTS.
Display session, Friday, January 09
Exhibit Hall,
Observations of the Sun at microwave, EUV and X-ray wavelengths have shown that solar active regions exhibit compact, flare-like brightenings lasting a few tens of seconds to minutes. These phenomena appear to be the signatures of small-scale heating and particle acceleration that can be triggered by magnetic reconnection in the transition region and corona. In this paper we discuss the results of recent collaborative investigations of evolving solar active regions that combine VLA images at 3.5, 6.2,20.7 and 91.6 cm with SOHO EIT and CDS spectroheliograms at several wavelengths. The main objective of these observations was to study the spatial and temporal relationship of transient events in both the radio and EUV domains and to constrain physical parameters such as electron temperature, electron density and magnetic field strength in the emitting regions. Observations made during eight different periods show that only some EUV events have counterparts in microwaves. The EUV transient events seem to occur throughout the target active regions while the evolving microwave sources predominantly overlie regions of high magnetic field strength near sunspots. Our VLA 91 cm observations also show changes in the brightness of Type I noise storm sources around the time of some EUV events. In one case, a new decimetric source appeared about 15 minutes prior to a transient EUV brightening and may have been created by nonthermal electrons produced during impulsive magnetic reconnection events seen earlier in the day. Other 91 cm source changes suggest an interaction between large and small-scale loops at different levels in the corona.
