AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 78. TRACE and Coronal Heating
Solar, Display, Wednesday, June 2, 1999, 10:00am-6:30pm, Southeast Exhibit Hall

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[78.03] Plasma Streaming and Explosive Events in the Solar Transition Region: Theory and Observations

M. Ryutova (LLNL/IGPP), T. Tarbell (LMSAL)

As shown by Tarbell et al. (ApJ, 514, L47, 1999 ) a sporadic excess of temperature and wide variety of plasma jets observed in the chromosphere and transition region overlying quiet sun regions may be explained by hydrodynamic cumulation resulted from the acoustic shocks generated by the reconnecting small scale network magnetic elements in the solar photosphere. Here we study magneto-hydrodynamic cumulation resulted from post-reconnection MHD shocks generated in complex magnetic field geometries typical to upper chromosphere and low corona. We present the results for the observed regularities obtained from simultaneous measurements taken by TRACE in chromospheric, transition region and coronal images and MDI on SOHO showing time series of high resolution magnetograms. We find that

(1) All the essential features of the hydrodynamic cumulation remain in place: the MHD shocks driven by the post-reconnection sling-shot effect and self-focusing of these shocks lead to several well observed signatures of the energy release.

(2) The evolution of generated flows depends on the geometry of intermittent magnetic fields and the height of jet formation. In regions of open magnetic structures plasma flows have tendency to accelerate and reach supersonic and super-Alfvènic velocities. Due to linear KH instability such flows may generate high frequency Alfvén waves propagating along the magnetic structures.

(3) In those regions where cumulative effects result in the predominant heating which is accompanied by generation of "moderate" (sub-Alfvénic) velocity jets, there are conditions when high velocity explosive events are driven. Our theoretical model shows that the explosive events proceeded by appearance of the bright transients are caused by the development of shear flow dissipative (nonlinear) instabilities. We also suggest that "non-bright"explosive events may be driven by rare effect of the cylindrical focusing of the MHD shocks (the Guderley's effect).

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