Asymmetries of the Upper Stratospheric Ozone Distribution Between Two Hemispheres

Abstract

Based on the Nimbus-7 solar backscattered UV-radiation (SBUV) data which are free from the instrumental background noise (dark-current) produced by magnetospheric particles, it is found that the southern winter hemispheric ozone densities in the upper stratosphere are nearly 20% higher than their counterparts in the Northern Hemisphere; i.e., the ozone mixing ratios at the 1.5 mb (?45 km) level are 10.2 ?g g?1 at 60°S in July 1979 versus 8.5 ?g g?1 at 60°N in December 1979. This is in significant contrast to the well-known hemispheric asymmetry of the total ozone content which is higher in the northern hemispheric winter than in the southern hemispheric winter. Comparisons of those findings with the previously obtained similar results from the Nimbus-4 backscattered UV radiation (BUV) experiment have manifested that the dark-current effect on the latter was negligible. Therefore, using the stratospheric temperature which was observed by means of the selective chopper radiometer (SCR) simultaneously with the BUV experiments on the Nimbus-4 for 1970 and 1972, the cause of these asymmetries due to the temperature dependent photo-chemistry is examined. The result indicates: The hemispheric asymmetries of the ozone distribution in the summer mesosphere and upper stratosphere are fully ascribable to the hemispheric temperature differences due to the combined effects of the earth's orbital ellipticity and its tilted spin axis from the ecliptic plane. On the other hand, the wintertime hemispheric asymmetries imply the presence of additional effects such as stronger dynamic heating in the Northern Hemisphere resulting from orographic differences between the two hemispheres.