Stratospheric Water Vapor Information from Laser-Radar Scattering Measurements

Abstract

A method is proposed whereby it should be possible to obtain valuable information about the amount of water vapor in the lower stratosphere from high-latitude observing locations in winter. Laser-radar scattering returns vs height would be examined for regions exhibiting enhanced returns (over the background due to stratospheric aerosols and atmospheric density fluctuations). These data would be compared with water vapor saturation mixing ratios calculated from radiosonde measurements. Climatological aspects of cold regions of the stratosphere are reviewed and possible locations for such observations are presented. The best such locations will be in Antarctica in winter months. Estimates of the stratospheric condensation particle radii and concentrations suggest that existing laser-radar systems used in studies of stratospheric aerosols have the sensitivity needed to undertake the proposed measurements. Aircraft-borne laser-radar systems would provide particularly interesting information, especially in flight across the winter Antarctic. Careful interpretation of the data should yield upper limits on the stratospheric water vapor mixing ratio on days when no enhanced scattering returns are received, and should provide detailed information on the spatial and temporal variation of the mixing ratio when enhanced returns are observed.