Abstract. We compare atmospheric total precipitable water (TPW) derived from SSM/I (Special Sensor Microwave Imager) and SSMIS (Special Sensor Microwave Imager Sounder) radiometers and WindSat to collocated TPW estimates derived from COSMIC (Constellation System for Meteorology, Ionosphere and Climate) radio occultation (RO) under clear and cloudy conditions over the oceans from June 2006 to December 2013. Results show that the mean microwave (MW) radiometer – COSMIC TPW differences range from 0.06–0.18 mm for clear skies, 0.79–0.96 mm for cloudy skies, 0.46–0.49 mm for cloudy but non-precipitation conditions, and 1.64–1.88 mm for precipitation conditions. Because RO measurements are not significantly affected by clouds and precipitation, the biases mainly result from MW retrieval uncertainties under cloudy and precipitating conditions. All COSMIC and MW radiometers detect a positive TPW trend over these eight years. The trend using all COSMIC observations collocated with MW pixels is 1.79 mm/decade, with a 95 % confidence interval of (0.96, 2.63), which is in close agreement with the trend estimated by all MW observations (1.78 mm/decade with a 95 % confidence interval of 0.94, 2.62). These two trends from independent observations are larger than previous estimates and are a strong indication of the positive water vapor-temperature feedback in a warming planet.
A Total Precipitable Water Product and Its Trend Analysis in Recent Years Based on Passive Microwave Radiometers
