Observations of the overshoot effect during the 2004 EISCAT PMSE campaign

The radar phenomenon PMSE (Polar Mesospheric Summer Echoes), which is associated with charged dust particles, can be affected by artificial electron heating. Chilson et al., (2000) showed that if the heater is run in a cycle with equal, and comparatively, short (10–20 s) off and on periods, the PMSE strength is observed to weaken when the heater is on, and recover to approximately the same strength when the heater is switched off. With a new heater cycling, where the heater is on for a short time and then off for a long enough time for the dusty plasma conditions to return to its undisturbed conditions, a PMSE overshoot effect is produced. In the overshoot the PMSE strength, when the heater is switched off, can increase by a factor of several fold compared to what it was directly before the heater was switched on. By analyzing the shape of the overshoot characteristic curve as the PMSE varies through a weakening as the heater is switched on, an overshoot as it is switched off and a subsequent relaxation back to an unaffected strength, we can obtain a considerable amount of information on the state of the PMSE dusty plasma.In the present paper, we will show results from a large EISCAT overshoot campaign in July 2004 where the PMSE overshoot was observed frequently. The shape of the PMSE power variations in each overshoot cycle is shown to vary considerably with height in the PMSE layer and also from cycle to cycle. We will show that very different PMSE overshoot shapes can occur at various occasions, and heights, and how they can be dependent on the local dust and plasma conditions.