Abstract
Torrential rainfall responses to vertical wind shear, radiation, and ice clouds during the landfall of severe Tropical Storm, Bilis (2006) are investigated via a rainfall partitioning analysis of grid-scale sensitivity experiment data. The rainfall data are partitioned into eight types based on surface rainfall budget. The largest contributions to total rainfall come from local atmospheric moistening, water vapor convergence, and hydrometeor loss/convergence (Type 3; 29%) when the large-scale upward motions occurred only in the upper troposphere on 15 July 2006. When the large-scale upward motion center moved to the mid troposphere on 16 July, Type 3 hydrometeor loss/convergence (26%) plus local atmospheric drying, water vapor divergence, and hydrometeor loss/convergence (Type 5; 25%) show equally important contributions to total rainfall. The exclusion of vertical wind shear primarily reduced Type 5 rainfall because of the weakened hydrometeor loss/ convergence on 16 July. The removal of cloud radiative effects enhances Type 5 rainfall due to increased local atmospheric drying and hydrometeor loss/convergence on 15 July. The elimination of ice clouds generally reduced Type 2 rainfall through the decreases in local atmospheric drying, water vapor convergence, and hydrometeor gain/divergence and Type 3 rainfall over two days.
Highlights
The landfall of typhoons over the southeast coast of China over the summer in the Northern Hemisphere produces a major water resource contributor over southern China, but may cause major floods which lead to tremendous socio-economic losses in southern coast cities
The calculation of daily mean surface rain rate for each rainfall type in the control experiment (C) shows that the highest rain rate comes from the Type 3 rainfall associated with local atmospheric moistening, water vapor convergence and hydrometeor loss/convergence (0.78 mm h-1) on July and from Type 3 (0.79 mm h-1) and the rainfall Type 5 associated with local atmospheric drying, water vapor divergence and hydrometeor loss/convergence (0.76 mm h-1) on July (Fig. 2) because these rainfalls cover the largest areas (Fig. 3)
The fractional coverage is small, the Type 1 rainfall associated with local atmospheric drying, water vapor convergence and hydrometeor loss/convergence contribute more than 10% to total rainfall
Summary
The landfall of typhoons over the southeast coast of China over the summer in the Northern Hemisphere produces a major water resource contributor over southern China, but may cause major floods which lead to tremendous socio-economic losses in southern coast cities. Shen et al (2010) separated 2D grid-scale cloud-resolving model simulation rainfall data during the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE) into eight rainfall types based on different rainfall processes proposed by Gao et al (2005) and Cui and Li (2006) They showed that the largest rainfall contribution is associated with local atmospheric drying, water vapor divergence, and hydrometeor loss/convergence among the eight rainfall types. Unlike previous Bilis studies (Wang et al 2009a, b, 2010b, c) in which convective-stratiform rainfall partitioning scheme is applied for grid-scale analysis, the rainfall separation scheme based on the surface rainfall scheme proposed by Shen et al (2010) is applied to the gridscale model simulation data from various sensitivity experiments of Bilis.
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