Stratospheric water vapor at a mid-latitude location has been shown to be increasing over the past 45 years [Rosenlof et al., 2001]. A clear reason for this increase has not been established. Throughout the measurement lifetime of the Upper Atmosphere Research Satellite (UARS), 1992-2001, global increases of total potential water (2CH4+H2O) are evident, however there is significant spatial structure in the lower stratosphere. Anti-correlated decreases in methane and increases in water vapor are noted in the upper stratosphere; these appear to be associated with a slowing of the mass flux into the upper stratosphere and a concomitant increase in residence time above 10 hPa. Increases greater than those due to the surface increase in methane are more difficult to explain. One possibility is changes in the water vapor flux into the middle and upper stratosphere associated with a widening of the tropical upwelling. Results of a study using the operational sonde network extending back to the late 1940s will be presented. Both zonal averages and longitudinal structure in changes in the vertical temperature structure in the tropics will be discussed. An analysis using NCEP temperatures will be compared with the sonde results.

Rosenlof, K. H., et al., 2001,Stratospheric water vapor increases over the past half century, Geophys. Res. Lett.,28,1195-1199.