Abstract Simulations of a mesoscale convective system (MCS), which propagated across northern India on 2nd May 2018 - leading to many fatalities when the gust front knocked down homes and tore apart building roofs - have been performed using the National Centre for Medium Range Weather Forecasting (NCMRWF) Unified Model – Regional (4 km horizontal grid spacing), to evaluate the model’s convective treatments. Though the model captures many of the qualitative and quantitative features, it slightly lags behind the observed MCS organisation and movement, produces lesser precipitation, and lacks the spatial separation between two adjacent organised convective systems in the satellite observations – leading to a faintly offset MCS track. Sensitivity simulations are then performed, for this non-equilibrium MCS case, with different partitioning between parameterised and explicit convection to assess the reliance of the convective treatments on the large-scale environment, as well as to test the notion of a breakdown of convective parameterisation at the mesoscale model resolution. Fully parametrized (FP) convection produces even lesser rainfall and are dominated by orographic precipitations along the foot hills of Himalayas with no any traces of the MCS. Fully explicit (FE) convection realistically simulates most of the prominent convective cells and enhance precipitation along the MCS track that agree better with the observations, though the ‘two lobes’ of intense precipitation are not resolved; instead it produces a squall line of precipitation. The FE configuration generates the most vigorous convective updraft, along with a vertical shear that is tilted westward. The simulation with partially parametrized and partially explicit convection resembles the fashion in the FP and FE scenarios, with a transition over the duration of the run from parametrized to explicit precipitation. The results are in line with the notion from previous studies; that the majority of successful explicit simulations of mesoscale organisation are those associated with strong large-scale forcing for convection, wherein resolved vertical motions are sufficient to minimise delays in onset.

中文翻译：

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印度北部中尺度对流系统的模拟：区域 NWP 模型中对流分区的敏感性

摘要 使用国家中期天气预报中心对 2018 年 5 月 2 日在印度北部传播的中尺度对流系统 (MCS) 进行了模拟——当阵风锋吹倒房屋并撕裂建筑物屋顶时，导致许多人死亡。 (NCMRWF) 统一模型 – 区域（4 公里水平网格间距），用于评估模型的对流处理。尽管该模型捕获了许多定性和定量特征，但它略微滞后于观测到的 MCS 组织和运动，产生的降水较少，并且在卫星观测中缺乏两个相邻的有组织的对流系统之间的空间分离——导致微弱的 MCS 轨迹偏移. 然后执行灵敏度模拟，对于这种非平衡 MCS 情况，在参数化对流和显式对流之间进行不同划分，以评估对流处理对大尺度环境的依赖，并测试对流参数化在中尺度模型分辨率下分解的概念。完全参数化 (FP) 对流产生的降雨量甚至更少，并且以沿喜马拉雅山脚下的地形降水为主，没有任何 MCS 痕迹。完全显性 (FE) 对流真实地模拟了大多数突出的对流单元，并增强了沿 MCS 轨迹的降水，这与观测结果更吻合，尽管强降水的“两瓣”没有得到解决；相反，它会产生一条飑线降水。FE 配置产生最强的对流上升气流，伴随着向西倾斜的垂直剪切。部分参数化和部分显式对流的模拟类似于 FP 和 FE 场景中的时尚，在运行期间从参数化到显式降水过渡。结果与先前研究的概念一致；大多数成功的中尺度组织显式模拟都与强烈的大规模对流强迫有关，其中解析的垂直运动足以最大限度地减少开始的延迟。