Stratospheric Sudden Cooling after Solar Proton Event over Syowa Station, Antarctica.

Forty-three solar proton events (SPEs) with energies of greater than 30MeV, whose time-integrated proton flux throughout an event is above 107/cm2, are selected from four solar cycles of 1956 to 1990, and their influences on the lower stratospheric temperature have been investigated by using radiosonde data from Syowa Station, Antarctica. It is shown that 64% of the 33 SPEs in which the radiosonde data were available are followed by a sudden cooling of -2.4°C on average at 20-30km altitude. Also 69% of the 13 SPEs recorded the proton flux beyond 108/cm2 gives the mean value of -3.5°C. Fifteen events accompanied with the GLE (Ground Level Enhancement, with the order of GeV protons) exhibit significant coolings except for two.