Relationship between AIRS and SSM/I Water Vapor and TRMM Precipitation

This study evaluates the relationship between water vapor and precipitation over tropical land (Amazon Basin, Sahel, Congo Basin), tropical ocean (Niño 3, Niño 4, Atlantic Ocean, Indian Ocean, Kwajalein Island), and subtropical land south of the Amazon. Total column water vapor from AIRS and SSM/I, and vertical profiles of relative and mixing ratio are from AIRS considered in the analysis. TRMM data were used for precipitation. We find regional differences where there are linear or exponential relationships between total column water vapor and precipitation over land. The Sahel featured an exponential curve relationship between precipitation and total column water vapor, relative humidity, and water vapor mixing ratio. Precipitation over the Amazon and Congo Basins, and southern South America all had slight linear dependence on total column water vapor and on relative humidity and mixing ratio profiles. Precipitation is also weakly linear with total column water vapor, relative humidity, and water vapor mixing ratio over tropical ocean. However, there is more variability in ocean regions. Niño 4 and Kwajalein Island demonstrate similar results to southern South America. Results from tropical land and some ocean regions imply a strong relationship between precipitation and column vapor.

Comparing AIRS and SSM/I, this study finds that SSM/I measures total column water vapor with more fidelity than the AIRS, with an apparent dry sampling bias in the AIRS data. This is important to consider in future analyses. Overall, this study depicts a strong regional relationship between water vapor and precipitation over southern South America and the Sahel in Africa. The relationship over tropical ocean need to be explored further.