Shallow Orographic Heavy Rainfall in the Asian Monsoon Region Observed by TRMM PR

Abstract:

In contrast to the dominant view that heavy rainfall results from deep clouds, shallow orographic heavy rainfall has been observed by the TRMM PR over mesoscale mountain ranges of the Asian monsoon regions. The low-level horizontal winds, leading to topographic forced upward motion, are dynamically important for its occurrence. We further examine thermodynamic characters of the atmospheric environment which shallow orographic heavy rainfall may be linked to. Depth of heavy orographic rainfall decreases with relative humidity, in opposite to what were observed for convection over the tropical ocean. In contrast to transient and ubiquitous occurrence of convection over the tropical ocean, orographic convection occurs stationary and thus strongly stabilize their environment. Depth of heavy orographic rainfall decreases with the static stability of mid-troposphere, and therefore the static stability of mid-troposphere is inferred to inhibit cloud growth and promote cloud detrainment.