CHROMOSPHERIC EVAPORATION SHOCK AND REDUCED OPTICAL-THICKNESS DRIFTING IN THE 1-4.5 GHZ RANGE

Using a 1-D numerical hydrodynamic model, the evaporation shock evolut ion is computed in the solar atmosphere having the density profile der ived from radioastronomical observations. Then the optical thickness o f the 1-4.5 GHz plasma emission on harmonic frequency is computed. It is found that the optical thickness of the radio emission is reduced a t the evaporation shock. With a motion of this shock the optical thick ness reduction drifts towards lower frequencies with the frequency dri ft which depends on the evaporation shock speed. The theoretical radio spectrum caused by this optical thickness reduction is presented and discussed in comparison with the July 9, 1996 radio spectrum.