Estimation of precipitable water and relative humidity over the Tibetan Plateau from GMS-5 water vapor channel data

The brightness temperature of the Geostationary Meteorological Satellite (GMS) -5 water vapor channel (Tb-6.7) and relative humidity, precipitable water, specific humidity and temperature observed by radiosondes over the Tibetan Plateau are compared for the summer of 1995. A wavelength of 6.7 mum was employed, so most of the radiation sensed by the satellite comes from the atmospheric layer between 300 and 600 hPa. The plateau altitude is 3,000 to 4,000 m, and GMS-5 Tb-6.7 over the Plateau represents the moisture information above that. The regression equations of upper tropospheric humidity (UTH) and precipitable water with Tb-6.7 are presented in this paper. The relationships between Tb-6.7 and observed temperature and specific humidity at the standard pressure levels are then compared to each other. Results show that, over the Plateau, Tb-6.7 is sensitive to the moisture information around 200 to 300 hPa height. The results demonstrate that Tb-6.7 is useful for not only qualitatively analyzing the moisture transporting field over and around the Tibetan Plateau, but also quantitatively inferring UTH and precipitable water above 100 hPa (W-400). Estimates of W-400 for July and August 1995 and its diurnal variability over and around the Tibetan Plateau are presented.