Warm rain features causing heavy rainfall under the humid East Asian environment and associated problems in estimating rain rate from space

Heavy rainfall over the Korean peninsula is often thought to be associated with the convection system with high and cold cloud top and strong updrafts. By contrast, the analysis of satellite observations including TRMM, MODIS, and CloudSat indicates that heavy rainfall over the Korean peninsula can also be related to relatively low-level clouds whose cloud top temperature is warmer. Prevalent water clouds are also evident. Large-scale weather conditions related to such low-level warm-type clouds causing heavy rainfall over the Korean peninsula (and/or surrounding areas) were deduced from a clustering analysis of MODIS cloud products and by relating obtained results to ERA-Interim reanalysis fields. It is found that low-level warm-type clouds producing heavy rainfall over Korea appear to be associated with large-scale conditions in which a feature like 'water vapor transporting river' is established along the northwestern periphery of the North Pacific high. Much of water vapor under the humid East Asian condition is transported through the river and converges on the area of Korea and surrounding regions. Because of excessive water vapor, it may be possible to produce heavy rainfall even with a small updraft within the lower tropospheric layer. This is much different from what can be expected from the typical convective clouds causing flash flood over the Great Plains of US. These warm rain features cause problems of estimating rain rate from space, missing substantial amount of rainfall.