Infrared and Visible Satellite Rain Estimation. Part II: A Cloud Definition Approach

Abstract
This study examines the relationships between satellite infrared clouds and rainfall, and infrared-threshold visible clouds and rainfall. Clouds are defined by the outline of the 253 K isotherm. Cloud infrared area was highly correlated with rain area (ρ = 0.85) and with volume rainrate (ρ = 0.81). It was poorly correlated with mean cloud rainrate (ρ = −0.28). One-parameter models were as effective in explaining the variance of cloud volume rainrate as multiparameter methods, due to the high correlations between visible brightness, mean cloud temperature and cloud area. An exception was found for clouds >10 000 km2, where area and temperature were uncorrelated, and mean temperature was more effective in discriminating among classes of volume rain than was cloud area. Statistical separation of five- of six-volume rain classes was achieved with mean temperature; however, the probability of occurrence of the classes effectively reduced this to a four-class problem. Due to the high correlation betwee... Abstract This study examines the relationships between satellite infrared clouds and rainfall, and infrared-threshold visible clouds and rainfall. Clouds are defined by the outline of the 253 K isotherm. Cloud infrared area was highly correlated with rain area (ρ = 0.85) and with volume rainrate (ρ = 0.81). It was poorly correlated with mean cloud rainrate (ρ = −0.28). One-parameter models were as effective in explaining the variance of cloud volume rainrate as multiparameter methods, due to the high correlations between visible brightness, mean cloud temperature and cloud area. An exception was found for clouds >10 000 km2, where area and temperature were uncorrelated, and mean temperature was more effective in discriminating among classes of volume rain than was cloud area. Statistical separation of five- of six-volume rain classes was achieved with mean temperature; however, the probability of occurrence of the classes effectively reduced this to a four-class problem. Due to the high correlation betwee...