Impact of model upgrades on diabatic processes in extratropical cyclones and downstream forecast evolution
Impact of model upgrades on diabatic processes in extratropical cyclones and downstream forecast evolution
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DOI：
10.1002/qj.3739
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发表时间：
2020-02
影响因子：
8.9
通讯作者：
J. Maddison;S. Gray;O. Martínez‐Alvarado;K. Williams
中科院分区：
文献类型：
--
作者：
J. Maddison;S. Gray;O. Martínez‐Alvarado;K. Williams
数值天气预报中心不断发展模式，以提高预报技巧，并每隔几年采用新的操作模式配置。绝热过程的参数化可能是NWP模式中最常更新的部分，因为它们对准确的天气预报至关重要，并且在其公式中包含不确定性。在2016年秋季，英国气象局的天气预报模型在北大西洋波导和下游影响实验场活动期间初始化，对模型发展的影响进行了评估。计划中的模式参数化发展，连同每日更新的海面温度和海冰比例的“廉价耦合”预报，都被考虑在内。从耦合系统产生的预报，平均而言，与控制预报没有区别，这表明耦合的大气-海洋NWP系统的好处可能很小。相比之下，使用升级对流方案产生的预报误差减少了（约4%）。在研究期间，预报技能较低的时期与阻塞事件的发生和衰减以及到达对流层上层的气团的非绝热加热增加有关。在一个特定的块体发展情况的预测中，在任何实验中都没有准确预测，也没有在气象局的业务整体预测中得到准确预测，上游气旋温暖传送带中的绝热加热表示被证明可以缓和随后的块体发展；在加热较强的预报中，通常会有一个被放大的阻塞脊，并且通过使用绝热示踪剂诊断，所有参数化对加热的贡献都会被放大。因此，我们证明了模式中几种不同非绝热过程表示的合理变化可以通过上游气旋内部的变化影响预测块体的发展。
Models are continuously developed at numerical weather prediction (NWP) centres to improve forecast skill, with new operational model configurations adopted every few years. The parametrizations of diabatic processes are probably the most frequently updated part of NWP models as they are crucial for accurate weather predictions and contain uncertainties in their formulation. The impact of model developments is assessed here in forecasts from the Met Office's weather forecast model initialised throughout the North Atlantic Waveguide and Downstream Impact Experiment field campaign period in autumn 2016. Planned model parametrization developments are considered, together with an ‘inexpensive coupled’ forecast with daily updating of the sea surface temperature and sea‐ice fraction. Forecasts produced from the coupled system have, on average, indistinguishable skill from the control forecasts, suggesting the benefits of coupled atmosphere–ocean NWP systems can be small. In contrast, a reduction in forecast error (∼4%) is identified in forecasts produced using an upgraded convection scheme. Periods of low forecast skill during the study period are shown to be associated with the onset and decay of blocking events and increased diabatic heating of air masses reaching the upper troposphere. In forecasts of a specific block development case that was not accurately predicted in any of the experiments or in the operational ensemble forecast from the Met Office, the representation of diabatic heating in the warm conveyor belt of an upstream cyclone is shown to moderate the subsequent block development; forecasts in which the heating is stronger generally have a more‐amplified blocking ridge and amplified heating contributions from all parametrizations as diagnosed using diabatic tracers. Hence, we demonstrate that plausible changes to the representation of several different diabatic processes in models can impact forecast block development via changes within upstream cyclones.