STORM SUDDEN COMMENCEMENTS OBSERVED IN IONOSPHERIC ABSORPTION

Particle precipitation events coinciding with storm sudden commencements were studied for 328 events occurring during 1970-1979. The study was based on data recorded at seven riometer stations between L = 3.3 and 6.0, on ionosonde data and on IMF Bz data. At L > 5, the probability of occurrence of a precipitation event is greater at night than during the day. South of this the probability is almost equal during the day and night. Generally precipitation increases when IMF Bz is negative. The effect of the precipitation was limited to the D-region of the ionosphere, and no effects on foE or foF2 were detected. © 1990.