Observational Constraints of Humidity Climatology From GPS Radio Occultation measurements

Abstract:

Recent studies have shown large differences in the humidity climatology of the upper troposphere (UT) region between global models and observations. Such discrepancies can lead to large differences in the water vapor feedback estimations between models, reanalyses and satellite observations, and therefore climate projection uncertainties. Global Circulation Models (GCMs) could also mischaracterize the middle troposphere moist convection leading to erroneous conclusions about the water vapor vertical distribution and horizontal transport. We observationally constrain the UT humidity by employing high accuracy (<1.0%) and high vertical resolution (100-200 m) Global Positioning System Radio Occultation (GPSRO) refractivity measurements. Preliminary results from GPSRO reveal a significantly drier tropical boundary layer than both ECMWF and MERRA reanalyses. In the middle and upper troposphere, GPSRO is moister than ECMWF but drier than MERRA. These features are more pronounced at equatorial latitudes. These differences could have greater repercussions with regards to the water vapor feedback estimation. Also, zonally varying distributions of relative humidity (RH) from GPSRO, MERRA and ECMWF were also correlated with precipitation measurements from the Global Precipitation Climatology Project (GPCP). We found latitudinal differences between maxima of precipitation and RH, which could imply that large-scale horizontal transport in the boundary layer plays a critical role to governing the coupling strength between precipitation and RH. The application of GPSRO data in constraining the underlying model physics will be discussed.