Understanding the dependence of storm splitting on numerical models: Comparing UM and WRF,Quarterly Journal of the Royal Meteorological Society

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Understanding the dependence of storm splitting on numerical models: Comparing UM and WRF
Quarterly Journal of the Royal Meteorological Society ( IF 3.0 ) Pub Date : 2021-03-23 , DOI: 10.1002/qj.4025
Anurag Dipankar ₁ , Ragi Rajagopalan ₁ , Xiang‐Yu Huang ₁

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This article performs a systematic study to understand the dependence of the splitting of an initially axisymmetric storm on the various components of the Unified Model (UM) and Weather Research and Forecasting model (WRF). The models are adapted to keep their differences at a minimum. Results at km-scale grid resolution show that the models differ significantly even under a controlled environment with no surface and radiative forcing. The initial storm in UM splits into two within the first hour. WRF also produces two separate updraughts, but it does not split entirely because of a secondary downdraught that falls just ahead of the original updraught. The cold pool from this downdraught converges with the oncoming winds at lower levels to generate a ring of updraughts connecting the two. UM also shows a similar secondary downdraught, but it is relatively weak. Experiments with the successive reduction in complexity of the microphysics scheme show that the models start to differ with the inclusion of rain processes. Sensitivity experiments with the magnitude of turbulent mixing length do not impact this aspect of model behaviour. Resolution sensitivity experiments show that the storm does not split in UM for a horizontal resolution of O(100 m), whereas WRF behaves consistently across all the resolutions. Through further analyses, we argue that the formal accuracy of the model dynamical core has no control in deciding whether the initial storm will undergo a split or not.

中文翻译：

理解风暴分裂对数值模型的依赖：比较 UM 和 WRF

本文进行了系统研究，以了解初始轴对称风暴的分裂对统一模型 (UM) 和天气研究与预报模型 (WRF) 的各个组成部分的依赖性。这些模型经过调整以将它们的差异保持在最低限度。公里级网格分辨率的结果表明，即使在没有表面强迫和辐射强迫的受控环境下，模型也存在显着差异。UM 的初始风暴在第一个小时内分裂成两个。WRF 也产生两个独立的上升气流，但它并没有完全分裂，因为第二个下降气流刚好在原始上升气流之前下降。来自这种下降气流的冷池与较低层迎面而来的风会聚，产生一圈连接两者的上升气流。UM 也显示出类似的二次下降，但它相对较弱。随着微物理方案复杂性的不断降低，实验表明模型开始随着降雨过程的加入而不同。具有湍流混合长度大小的灵敏度实验不会影响模型行为的这方面。分辨率敏感性实验表明，对于 O(100 m) 的水平分辨率，风暴不会在 UM 中分裂，而 WRF 在所有分辨率上表现一致。通过进一步的分析，我们认为模型动力核心的形式准确性无法控制决定初始风暴是否会发生分裂。具有湍流混合长度大小的灵敏度实验不会影响模型行为的这方面。分辨率敏感性实验表明，对于 O(100 m) 的水平分辨率，风暴不会在 UM 中分裂，而 WRF 在所有分辨率上表现一致。通过进一步的分析，我们认为模型动力核心的形式准确性无法控制决定初始风暴是否会发生分裂。具有湍流混合长度大小的灵敏度实验不会影响模型行为的这方面。分辨率敏感性实验表明，对于 O(100 m) 的水平分辨率，风暴不会在 UM 中分裂，而 WRF 在所有分辨率上表现一致。通过进一步的分析，我们认为模型动力核心的形式准确性无法控制决定初始风暴是否会发生分裂。

更新日期：2021-03-23

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