Using an arbitrary moment predictor to investigate the optimal choice of prognostic moments in bulk cloud microphysics schemes

Most bulk cloud microphysics schemes predict up to three standard properties of hydrometeor size distributions, namely, the mass mixing ratio, number concentration, and reflectivity factor in order of increasing scheme complexity. However, it is unclear whether this combination of properties is optimal for obtaining the best simulation of clouds and precipitation in models. In this study, a bin microphysics scheme has been modified to act like a bulk microphysics scheme. The new scheme can predict an arbitrary combination of two or three moments of the hydrometeor size distributions. As a first test of the arbitrary moment predictor (AMP), box model simulations of condensation, evaporation, and collision‐coalescence are conducted for a variety of initial cloud droplet distributions and for a variety of configurations of AMP. The performance of AMP is assessed relative to the bin scheme from which it was built. The results show that no double‐ or triple‐moment configuration of AMP can simulta...绝大多数块体云微物理方案（bulk cloud microphysics schemes）最多可预测水凝物粒径分布的3种标准属性，按方案复杂度递增排序分别为质量混合比、数浓度与反射率因子（reflectivity factor）。然而，目前尚不明确该组属性组合是否为模式中实现最优云与降水模拟的最佳选择。本研究对一款分档云微物理方案（bin microphysics scheme）进行改进，使其可充当块体云微物理方案。改进后的新方案可预测水凝物粒径分布的2阶或3阶矩的任意组合。作为对任意矩预测器（Arbitrary Moment Predictor, AMP）的首次测试，本研究针对多种初始云滴分布与多种AMP配置，开展了凝结、蒸发及碰撞并合过程的箱式模型（box model）模拟。以其构建所基于的分档方案为参照，评估了AMP的模拟性能。结果表明，尚无任何双矩或三矩配置的AMP可同时……