Characterisation of convective regimes over the British Isles
Characterisation of convective regimes over the British Isles
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不列颠群岛上空对流状况的特征
DOI：
10.1002/qj.2758
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发表时间：
2016
影响因子：
8.9
通讯作者：
G. Craig
中科院分区：
文献类型：
--
作者：
D. Flack;R. Plant;S. Gray;H. Lean;C. Keil;G. Craig
对流允许模型使对流事件的预测发生了重大变化。然而，对流发生在不同的区域内，表现出不同的预测行为。对流调整时间尺度可用于区分这些状态并检查其相关的可预测性。对流调整时间尺度是根据无线电探空仪上升计算得出的，与对流允许模型预测得出的时间尺度一致。然后，对不列颠群岛的三个夏季对模型得出的对流调整时间尺度进行检查，以确定该海域对流状况的特征。不列颠群岛的对流主要处于对流准平衡状态，85%的对流时间尺度小于或等于3小时。这个百分比在空间上有所不同，南部和西南部发生了更多的非平衡事件。对流调整时间尺度表现出陆地上的昼夜循环。非平衡状态在中等风速和风从南风到西风区域更频繁地发生。不列颠群岛的大多数非平衡对流事件都是在大的沿海地形梯度附近或欧洲大陆发起的。因此，当所检查的位置紧邻大地形梯度的下游时，对流调整时间尺度最大，并且随着距对流起始区域的距离而减小。不列颠群岛上空对流准平衡条件的主导地位表明在该地区的概率预测中使用大成员系综。
Convection‐permitting modelling has led to a step change in forecasting convective events. However, convection occurs within different regimes which exhibit different forecast behaviour. A convective adjustment timescale can be used to distinguish between these regimes and examine their associated predictability. The convective adjustment timescale is calculated from radiosonde ascents and found to be consistent with that derived from convection‐permitting model forecasts. The model‐derived convective adjustment timescale is then examined for three summers in the British Isles to determine characteristics of the convective regimes for this maritime region. Convection in the British Isles is predominantly in convective quasi‐equilibrium, with 85% of convection having a timescale less than or equal to 3 h. This percentage varies spatially with more non‐equilibrium events occurring in the south and southwest. The convective adjustment timescale exhibits a diurnal cycle over land. The non‐equilibrium regime occurs more frequently at mid‐range wind speeds and with winds from southerly to westerly sectors. Most non‐equilibrium convective events in the British Isles are initiated near large coastal orographic gradients or on the European continent. Thus, the convective adjustment timescale is greatest when the location being examined is immediately downstream of large orographic gradients and decreases with distance from the convective initiation region. The dominance of convective quasi‐equilibrium conditions over the British Isles argues for the use of large‐member ensembles in probabilistic forecasts for this region.