The impact of stochastically perturbing the terminal velocities of hydrometeors on convective-scale ensemble forecasts of precipitation was examined. An idealized supercell storm case was first used to determine the terminal velocity error characteristics for a one-moment microphysics scheme in terms of the terminal velocities from a two-moment scheme. Two real cases were employed to evaluate the forecast skills resulting from perturbing the terminal velocities with real data. The results indicated that the one-moment scheme produced terminal velocities that were approximately three times higher than those of the two-moment scheme for snow and hail, which often resulted in overpredictions of hourly precipitation and areal accumulated precipitation. Therefore, stochastically perturbing the terminal velocities according to their error characteristics matched the observed hourly precipitation and areal accumulated precipitation better than the symmetrical perturbations. For the two-moment scheme, the symmetrical perturbations of the terminal velocities tended to produce lower falling speeds of precipitation hydrometeors; therefore, more light rain was produced. Compared to the unperturbed two-moment scheme, symmetrically perturbing the terminal velocities resulted in smaller precipitation errors when precipitation was overestimated but comparable or slightly larger precipitation errors when precipitation was underestimated. This work demonstrates the sensitivity of precipitation ensemble forecasts to terminal velocity perturbations and the potential benefits of adopting these perturbations; however, whether the perturbations actually result in significant improvements in precipitation forecast skill needs further study.

中文翻译：

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随机扰动终末速度对降水对流尺度集合预报的影响

研究了随机扰动水凝结物的最终速度对对流尺度集合降水的影响。首先使用理想化的超级单元风暴情况，根据两步法的终极速度来确定一步微物理方案的终极速度误差特征。使用两个实际案例来评估由于用实际数据干扰终端速度而产生的预测技能。结果表明，单时刻方案产生的终速大约是雪和冰雹两时刻方案的终极速度的三倍，这常常导致每小时降水和面积累积降水的高估。因此，根据终端速度的误差特征随机地扰动终端速度，使其与观测的小时降水量和面积累积降水量相匹配，优于对称扰动。对于两矩方案，终端速度的对称扰动趋向于导致降水水凝物的下降速度降低。因此，产生了更多的小雨。与无扰动的两矩方案相比，对称地扰动最终速度会导致高估降水时的降水误差较小，而低估降水时的降水误差则相当或稍大。这项工作证明了降水集合预报对终极速度扰动的敏感性以及采用这些扰动的潜在好处；然而，