B. Vrsnak
Hvar Observatory, Faculty of Geodesy, Kaciceva 26, HR-10000
Zagreb, Croatia
It is demonstrated that the source-process that causes a particular coronal large-scale MHD shock cannot be reliably identified without confronting detailed multiwavelength observations and measurements with careful consideration of theoretical constraints. Bearing this in mind, physics of various processes related to CMEs and flares, capable of launching large-scale coronal MHD shocks, is presented. We present basic characteristics of the shock formation caused by the expanding 3-D piston (driven either by the CME ``over-expansion'' or the flare energy release), a moving-expanding piston (CME), a supersonic rigid-blunt-body-analog (e.g., current sheet plasmoid), variable reconnection rate in the current sheet, the interaction of the downward directed reconnection jet (or plasmoid) with the flare loops, etc. Advantages and drawbacks of each mechanism are discussed. Special attention is paid to observable signatures and measurable parameters that could be used in a real situation to distinguish which of the described scenarios is the most probable one in a particular event. Some examples are presented.