Effects of the August 1972 solar particle events on stratospheric ozone

Abstract

The spatial extent and the ionization profiles within the extended oval‐shaped regions irradiated by the intense solar particle events (SPE) of August 1972 have been derived from high‐energy proton data obtained with the 1971‐089A polar‐orbiting satellite and from several balloon flights. The particle ionization during the most intense 10‐hour period of the event on August 4 greatly enhanced the concentrations of short‐lived HO x and long‐lived NO x constituents, which in turn were responsible for the creation of a polar ozone cavity (POC) that has been identified and tracked with the backscattered ultraviolet (BUV) ozone sensors on the Nimbus 4 satellite. At the end of the peak irradiation period the ozone concentrations within the northern hemisphere POC were reduced by 46, 16, and 4% at altitudes of 49.5, 41, and 32 km, respectively. The total columnar ozone is estimated to have been reduced by ∼2% at this time. Above ∼45 km the ozone recovered on the time scale of several days. At 38.7 km in the northern hemisphere, however, the POC persisted and rotated as a semirigid mass in an east‐to‐west direction for some 53 days until the autumnal changes in wind patterns finally prevented further tracking. Time‐dependent chemistry calculations have been performed to explain the cause, magnitude, and temporal features of the ozone reductions. Using the calculated diurnal and particle‐induced behavior of the ozone during the SPE, the changes in heating rate and temperature expected in the stratosphere have been estimated. As a result of the initial large HO x ‐caused ozone reduction, the temperature at 45 km should have decreased by ∼4°K several days after the event. Attempts to verify the predicted temperature changes have been unsuccessful due to limitations in the temperature measurement techniques.