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

  • Author(s): Huiyan Xu, Guoqing Zhai, and Xiaofan Li
  • DOI: 10.3319/TAO.2017.10.11.01
  • Keywords: Convective and stratiform rainfall, Surface precipitation budget equation, Vertical velocity, Cloud microphysical budget, 3D WRF model
  • Partition rainfall into eight types in the 3D WRF model
  • Combined those eight rain types into convective-stratiform rainfall
  • Conduct CFAD analysis, surface precipitation and cloud microphysical budgets
Abstract

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 separations 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 stratiform 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 convective 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. 

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