基于观测资料和数值模拟的对流云冰晶繁生过程研究

Ice multiplication has strong impacts on the fast ice generation in convective clouds, however, the relative contributions of different ice multiplication mechanisms to the ice generation are still poorly understood. Aircraft measurements can hardly partition different ice multiplication processes, while the representation of ice multiplication in models is over simplified, such as Weather Research and Forecast（WRF）, which is widely used to study cloud microphysics, only contains the riming-splinter process in the spectral bin microphysics (SBM) scheme, other ice multiplication processes are not included. Therefore, the modelled ice concentration in convective clouds is often underestimated by WRF.. This proposal aims to develop a parameterization for the fragmentation of freezing drops based on airborne observations and previous laboratory studies. This parameterization, as well as the parameterization of ice-ice collisional breakup developed before, will be implemented in WRF SBM scheme. Using high-resolution simulations, the relative contributions of three different ice multiplication processes to the ice generation in convective cloud will be explored, including riming-splinter process, fragmentation of freezing drops, and ice-ice collisional breakup. The modelled results will be evaluated using airborne observations. Comparison between model simulations and observations will be made to illustrate whether the three ice multiplication mechanisms can explain the observed high ice concentration in convective clouds.

在对流云中，冰晶繁生过程对冰晶的快速生成起到了关键作用，然而，目前人们对不同繁生机制对冰晶生成的相对贡献还存在较大争议。飞机观测难以区分不同的冰晶繁生过程，而数值模式对冰晶繁生过程的处理还较为简单，如Weather Research and Forecast（WRF）是研究云物理常用的模式，但是WRF只在分档云微物理方案中考虑了淞附-破碎过程，其他繁生机制未被考虑，因此常常低估对流云中的冰晶数浓度。. 本项目旨在利用公开的实验室研究和飞机观测资料，为液滴冻结破碎建立参数化方案，并将该方案与已有的冰晶碰撞破碎参数化方案加入WRF分档云微物理方案。利用高精度数值模拟，探究淞附-破碎过程、液滴冻结破碎、冰晶碰撞破碎三种繁生机制在对流云中对冰晶生成的相对贡献。同时，利用飞机观测资料对模拟结果进行验证，阐明此三种冰晶繁生机制是否能解释在对流云中观测到的高冰晶数浓度。

在对流云中，冰晶繁生对冰晶的快速生成起到了关键作用，然而，目前人们对不同繁生机制对冰晶生成的相对贡献还存在较大争议。飞机观测难以区分不同的冰晶繁生过程，而数值模式对冰晶繁生过程的处理还较为简单，如Weather Research and Forecast（WRF）是研究云物理常用的模式，但是WRF只在分档云微物理方案中考虑了淞附-破碎过程，其他繁生机制未被考虑，因此常常低估对流云中的冰晶数浓度。本研究利用公开的实验室研究和飞机观测资料，为液滴冻结破碎建立了参数化方案，并将该方案与已有的冰晶碰撞破碎参数化方案加入了WRF分档云微物理方案。利用高精度数值模拟，探究了淞附-破碎过程、液滴冻结破碎、冰晶碰撞破碎三种繁生机制在海洋和陆地对流云中对冰晶生成的相对贡献。同时，利用飞机观测资料对模拟结果进行验证。结果表明冰晶繁生的加入可以明显增加对流云内的冰晶数浓度，可以较好地解释在对流云中观测到的高冰晶数浓度。在发展期对流云中，液滴冻结破碎机制对次生冰晶的贡献最大。本研究的结果加深了对对流云内冰晶生成的认识，为改进对流云微物理和降水的模拟提供了支撑。