Mean meridional distributions of ozone in different seasons calculated from Umkehr observations and probable vertical transport mechanisms

Abstract

The paper contains a study of the mean meridional distributions of ozone in different seasons. The vertical distributions of ozone at a number of stations at different latitudes in the Northern Hemisphere were worked out from the intensities of light scattered from the zenith sky on individual clear days using method B, i.e., the method of curve fitting, with suitable correction for secondary scattering. Diagrams of vertical distribution corresponding (1) to high ozone amounts (frequent in winter and spring) and (2) to low ozone amounts (frequent in summer and autumn) are shown. Mean distribution diagrams are also given for the months of March, July and November. An important feature of the distribution is the strong increase in ozone amount in March below 18 km when the latitude increases beyond 30° . The results are discussed in relation to the idea of a poleward flow of air from the lower stratosphere and the neighbourhood of the equatorial tropopause, as suggested by Dobson and Brewer from frost-point measurements over the United Kingdom. The existence of a stratospheric warm air pool over the middle latitude in winter and spring as revealed by sounding-balloon ascents is confirmatory evidence of this. The influence of the pool of cold air which exists in winter above 20 km in the stratosphere of the dark polar night is also considered. It is suggested that in winter and spring there is an ozone-regenerating cycle due to meridional circulation in the stratosphere of tropical and middle latitudes, which carries air from the lower equatorial stratosphere to lower levels in the stratosphere of middle latitudes and puts back some of this accumulated air to higher levels in the equatorial stratosphere above 25 km. The more vigorous this circulation, the greater will be the rate of ozone storage in the lower stratosphere of extra-tropical latitudes.