Convective-stratiform rainfall separation of typhoon Fitow (2013): A 3D WRF modeling study

Surface precipitation budget equation in a three-dimensional (3D) WRF model framework is derived. By applying the convective-stratiform partition method to the surface precipitation budget equation in the 3D model, this study separated convective and stratiform rainfall of typhoon Fitow (2013). The eparations are further verified by examining statistics of vertical velocity, surface precipitation budget, and cloud microphysical budget. Results show that water vapor convergence moistens local atmosphere and offsets hydrometeor divergence, and producing convective rainfall, while hydrometeor convergence primarily supports stratiform rainfall, since water vapor divergence and local atmospheric drying generally cancelled out. Mean ascending motions are prevailing in the entire troposphere in the convective region, whereas mean descending motions occur below 5 km and mean ascending motions occur above in the tratiform region. The frequency distribution of vertical velocity shows vertical velocity has wide distribution with the maximum values up to 13 m s-1 in the convective regions, whereas it has narrow distribution with absolute values confined within 7 m s-1 in the stratiform region. Liquid cloud microphysics is dominant in onvective regions and ice cloud microphysics is dominant in stratiform regions. These indicate that the statistics results are generally consistent with the corresponding physical characteristics of the convective-stratiform rainfall structures generalized by previous studies.

推导了三维（3D）WRF模型框架下的地面降水收支方程。通过将对流 - 层状云分离方法应用于三维模型中的地面降水收支方程，本研究分离了台风菲特（2013）的对流性降水和层状云降水。通过检验垂直速度、地面降水收支和云微物理收支的统计数据，进一步验证了这种分离。结果表明，水汽辐合使局部大气增湿并抵消水汽凝结物的辐散，从而产生对流性降水，而水汽凝结物辐合主要支持层状云降水，因为水汽辐散和局部大气干燥通常相互抵消。在对流区域，整个对流层盛行平均上升运动，而在层状云区域，平均下沉运动出现在5公里以下，平均上升运动出现在5公里以上。垂直速度的频率分布表明，在对流区域垂直速度分布较宽，最大值可达13米/秒，而在层状云区域分布较窄，绝对值限制在7米/秒以内。液态云微物理过程在对流区域占主导地位，冰态云微物理过程在层状云区域占主导地位。这些表明统计结果与先前研究总结的对流 - 层状云降水结构的相应物理特征基本一致。