Validation of UARS microwave limb sounder 183 GHz H₂O measurements

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.