THE RELATION BETWEEN THE ONSET TIMES OF THE NEGATIVE PHASE OF IONOSPHERIC STORMS AND THE MAIN PHASE OF MAGNETIC STORMS AND A THEORETICAL MODEL

In this paper,major negative phase ionospheric storms occurred from 1969 to 1973 at Manchouli (49.5°N,117.5°E),Billerica (43°N,71.5°W) and Freiburg (48°N,07°E) are analyzed.It is found that if the associated magnetic storm main phase being around noon,the ionospheric storm negative phase begins in the afternoon at Billerica station and at Freiburg station,but the negative phase begins around midnight at Manchouli station.Athearetical model is presented to calculate the negative phase onset time.The model is based on two extended heat sources,one is on the day side of the auroral oval and the other on the night side.When the magnetic storm main phase begins,the molecule enriched air appears at the heat sources.The air is brought to the middle latitudes by the thermospheric winds and the electron loss rate there increases.This gives rise to the occurrence of the negative phase ionospheric storms.The onset times of negative phase is calculated,and the results agree rather well with those of statistics.