Assessment of Upper Tropospheric Water Vapor Monthly Variation in Reanalyses With Near-Global Homogenized 6.5-mu m Radiances From Geostationary Satellites

The monthly variation of upper tropospheric water vapor (UTWV) simulated by six reanalysis data sets is evaluated with homogenized water vapor radiance observations from international geostationary (GEO) weather satellites by using a profile-to-radiance approach over 45 degrees N to 45 degrees S regions for the period 2015-2017. Results show that reanalysis data sets have an overall good agreement with observations. However, a widespread wet bias is found in all reanalyses and is more dominant in large-scale subsidence regions. JRA55 has the smallest wet bias while MERRA-2 exhibits the most humid upper troposphere. The temporal variation of brightness temperatures in response to the warm phase of El Nino-Southern Oscillation (ENSO) in 2015-2016 indicates that the UTWV field is regulated by both ascending and descending branches of the large-scale circulation. All six reanalyses roughly capture the temporal variation of UTWV in the developing and decay year of this ENSO event. However, they tend to overestimate the eastward propagation of high UTWV in the developing year, especially MERRA-2. The UTWV gradient over the tropical Pacific in the decay year is underestimated, with a dry bias over the convective western Pacific and a wet bias over the eastern Pacific in reanalysis data sets. These results may provide a useful tool for the climate modeling community for identifying and solving problems associated with UTWV simulation.