Observed solar-cycle responses and trends in mesospheric water vapor

Time series of the Halogen Occultation Experiment (HALOE) water vapor have been analyzed for their seasonal, interannual, 11-yr, and linear trend terms. Analyses were conducted on time series of profile data within 20-degree wide latitude bins from 45S to 45N and in the upper mesosphere (0.1 to 0.02 hPa). The 11-yr variation in water vapor is related inversely to the changes in Lyman-á photolysis. Those 11-yr responses for water vapor show increases with latitude and with pressure-altitude, in accord with model simulations. On the other hand, the observed, 11-yr responses at middle latitudes are significantly larger in the northern than the southern hemisphere, most likely a result of greater decadal variations for the wave activity in the mesosphere of the northern hemisphere. The linear trends for the HALOE water vapor also increase with latitude, but remain rather steady with pressure altitude and are similar for both hemispheres. At middle latitudes those trends for the period of HALOE (1991-2005) are of the order of 10%/decade.