Global water vapor trend from 1988 to 2011 and its diurnal asymmetry based on GPS, radiosonde, and microwave satellite measurements

This study analyzes trends in precipitable water (PW) over land and ocean from 1988 to 2011, the PW-surface temperature T_s relationship, and their diurnal asymmetry using homogenized radiosonde data, microwave satellite observations, and ground-based global positioning system (GPS) measurements. It is found that positive PW trends predominate over the globe, with larger magnitudes over ocean than over land. The PW trend is correlated with surface warming spatially over ocean with a pattern correlation coefficient of 0.51. The PW percentage increase rate normalized by T_s expressed as is larger and closer to the rate implied by the Clausius-Clapeyron (C-C) equation over ocean than over land. The 2-hourly GPS PW data show that the PW trend from 1995 to 2011 is larger at night than during daytime. Nighttime PW monthly anomalies correlate positively and significantly with nighttime minimum temperature T_min at all stations, but this is not true for daytime PW and maximum temperature T_max. The ratio of relative PW changes with T_min (dlnPW/dT_min) is larger and closer to the C-C equation's implied value of ~7% K^-1 than. This suggests that the relationship between PW and T_s at night is a better indicator of the water vapor feedback than that during daytime, when clouds and other factors also influence T_s.