CHARACTERISTICS OF ANTARCTIC STRATOSPHERIC AEROSOLS DURING THE 1987 OZONE DEPLETION EPISODE BASED ON SAGE-II SATELLITE-OBSERVATIONS

The stratospheric aerosols play an important role in the formation of polar stratospheric clouds which are linked to Antarctic ozone depletion. The aerosol extinction profiles for higher latitudes have been monitored by the SAGE II (Stratospheric Aerosol and Gas Experiment II) satellite. In this study, features of Antarctic stratospheric aerosols during the ozone depletion episode of October 1987 are investigated based on the SAGE II data. The study focuses on (1) inferring the aerosol size spectrum using a modified randomized minimization search technique and (2) investigating the vertical, zonal, and columnar averages of aerosol properties such as extinction coefficient, optical depth, mean and effective radii, mass loading, total number concentration, and surface area concentration, together with the ozone concentration. The aerosol size distribution is found to be bimodal in several instances. An enhanced aerosol layer of relatively larger particles at altitudes between 21 and 23 km was found in Antarctic region. The effective radius can be fitted by Angstrom coefficient using either a linear or quadratic equation. On the average, in the region below 18 km, maximum values for the parameters of mass loading, total number, and surface area concentration were found to be located just above the region of the most severe ozone depletion. As to the columnar aerosol properties, bimodal feature in the size distribution is found during the days when the peak values of optical depth are greater than 10(-3). Relatively abundant population of smaller particles is associated with the region of severe ozone depletion. The distinct latitudinal gradients of these aerosol parameters suggest that the stratospheric aerosols are separated into two regimes near 62-degrees-S-63-degrees-S, probably as a result of the dynamics introduced by polar vortex. Smaller and larger particles dominate at higher and lower latitudes, respectively. The standard deviation for both mean and effective radii are about 20-25% of the mean values. The fluctuation of the mass loading is about 50% from the mean and about 90% for the total number. The mean optical depth in 15-30 km layer is of the order of 10(-3). The average columnar ozone amount is about 95 DU (Dobson unit) with the amplification of about 48 DU. It is pointed out that the reported features of the stratospheric aerosols in the Antarctic region are useful in providing insights into the mechanisms for ozone depletion.