A Study of SSM/I-Derived Columnar Water Vapor over the Global Oceans

Abstract

Four years of columnar water vapor (CWV) data from July 1987 through June 1991 derived from a satellite-based physical retrieval method are analysed using microwave observations from the Special Sensor Microwave/Imager. This retrieval along with three statistically based retrievals were compared to radiosonde data compiled for the GEWEX Water Vapor Project. It is shown that the root-mean-square (rms) difference (R) between the radiosonde data and these satellite retrievals ranges from 4.66 kg m?2 to 5.08 kg m?2. The rms difference was found to have a seasonal variability of up to 1.0 kg m?2 with the highest R in JJA. It was also found to significantly depend on the specified time and spatial coincidence of the satellite pixels with the radiosonde observation. The rms difference decreased by about 0.65 kg m?2 when the time constraint was reduced from 2 h to 0.5 h, but R increased by about 0.3 kg m?2 when the spatial coincidence was reduced from 50 to 20 km. The relationship between 4 yr of CWV and SST data was found to vary significantly with season and hemisphere. The correlation between 4 yr of monthly mean, globally averaged SST and CWV was approximately 0.95 for the hemispheric means and 0.65 for the global means. The 4-yr correlation of SST and CWV was found to be strongest in the subtropical regions and weakest in several tropical regions.