Linking rapid forecast error growth to diabatic processes,Quarterly Journal of the Royal Meteorological Society

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Linking rapid forecast error growth to diabatic processes
Quarterly Journal of the Royal Meteorological Society ( IF 3.0 ) Pub Date : 2020-06-23 , DOI: 10.1002/qj.3861
Claudio Sánchez ₁ , John Methven ₂ , Suzanne Gray ₂ , Mike Cullen ₁

Affiliation

The predictability of high‐impact weather events over the North Atlantic is controlled by synoptic‐scale systems and the mesoscale structures embedded within them. Despite forecast uncertainty being greatest at small scales at the initial time, forecast error projects strongly onto synoptic and larger scales within days. Different stages of error growth have previously been identified including: convective instability, baroclinic instability and the influence of divergent outflow on the tropopause position, and interactions between disturbances at tropopause level. Evidence is presented for "predictability barriers" (PBs) identified with events on certain validation dates during the North Atlantic Waveguide and Downstream impact Experiment (NAWDEX) where ensemble spread grows more quickly than usual, but ensemble‐mean forecast error grows even faster. An advective mechanism for diabatic influence on the development of tropopause ridges is hypothesised to be linked to the PB events. A semi‐geostrophic balance tool is used to attribute the response of the 3D ageostrophic flow to geostrophic and diabatic forcing, enabling a novel diagnostic for Diabatically Induced Ageostrophic Advection (DIAA) of potential vorticity. It is shown that predictability barriers are linked to events with strong diabatic influence on tropopause advection during the NAWDEX period. Error growth exceeds ensemble spread rate by approximately 4/3 during strong DIAA events, showing that predictive skill is considerably lower in these situations.

中文翻译：

将快速的预测误差增长与非绝热过程联系起来

北大西洋高影响天气事件的可预测性受天气尺度系统及其中嵌入的中尺度结构的控制。尽管初始时预测不确定性在小范围内最大，但预测误差会在几天内强烈投射到天气和更大范围内。先前已经确定了误差增长的不同阶段，包括：对流不稳定，斜压不稳定以及发散流出对对流层顶位置的影响，以及对流层顶水平干扰之间的相互作用。提出了在北大西洋波导和下游影响实验（NAWDEX）期间某些验证日期的事件中识别出的“可预测性障碍”（PBs）的证据，其中集合传播比平常增长得更快，但是集合平均预测误差的增长速度甚至更快。假设对对流层顶对流脊发育的非绝热影响的对流机制与PB事件有关。使用半地转平衡工具将3D地转流的响应归因于地转和绝热强迫，从而为潜在的涡度的绝热诱导的地转平流（DIAA）提供了一种新颖的诊断方法。结果表明，可预测性障碍与NAWDEX期间对对流层顶平流具有强烈绝热影响的事件有关。误差增长超过整体传播率大约使用半地转平衡工具将3D地转流的响应归因于地转和绝热强迫，从而为潜在的涡度的绝热诱导的地转平流（DIAA）提供了一种新颖的诊断方法。结果表明，可预测性障碍与NAWDEX期间对对流层顶平流具有强烈绝热影响的事件有关。误差增长超过整体传播率大约使用半地转平衡工具将3D地转流的响应归因于地转和绝热强迫，从而为潜在的涡度的绝热诱导的地转对流（DIAA）提供了一种新颖的诊断方法。结果表明，可预测性障碍与NAWDEX期间对对流层顶平流具有强烈绝热影响的事件有关。误差增长超过整体传播率大约在强烈的DIAA事件中为4/3，表明在这些情况下，预测能力要低得多。

更新日期：2020-06-23

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