Lidar observation of Mid-Latitude water vapor layers near the tropopause

Atmospheric water vapor profiles have been measured up to the mid-latitude tropopause using a Raman lidar optimized for high altitude measurements. A series of 9 measurements made from San Nicolas Island (33.25N, 119.54W) from June to November 1998 show water vapor layering near the tropopause, strongly correlating with layering observed in wind profiles. The average mixing ratio at 16 km was four times larger than expected from prior climatology. Typical profiles included water vapor layers with 0.4-2 km thickness, at or near saturation vapor pressure, located near the tropopause. The moist layers were often located above thin dry layers. Layers near the tropopause were uncorrelated with mid-tropospheric water vapor. The latter varied from extremely dry (<10 percent relative humidity) above the planetary boundary layer, to relatively moist up to 12 km. The results will be compared with satellite microwave water vapor imagery.