Validation of UARS microwave limb sounder 183 GHz H₂O measurements

Abstract

The Upper Atmosphere Research Satellite (UARS) microwave limb sounder (MLS) makes measurements of thermal emission at 183.3 GHz which are used to infer the concentration of water vapor over a pressure range of 46 – 0.2 hPa (∼20 to ∼60 km). We provide a validation of MLS H 2 O by analyzing the integrity of the measurements, by providing an error characterization, and by comparison with data from other instruments. It is estimated that version 3 MLS H 2 O retrievals are accurate to within 20–25% in the lower stratosphere and to within 8–13 % in the upper stratosphere and lower mesosphere. The precision of a single profile is estimated to be ∼0.15 parts per million by volume (ppmv) in the midstratosphere and 0.2 ppmv in the lower and upper stratosphere. In the lower mesosphere the estimate of a single profile precision is 0.25–0.45 ppmv. During polar winter conditions, H 2 O retrievals at 46 hPa can have a substantial contribution from climatology. The vertical resolution of MLS H 2 O retrievals is ∼5 km.