Duration and decay of Arctic stratospheric vortex events in the ECMWF seasonal forecast model
Duration and decay of Arctic stratospheric vortex events in the ECMWF seasonal forecast model
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DOI：
10.1002/qj.3417
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发表时间：
2018-10
影响因子：
8.9
通讯作者：
Y. Orsolini;K. Nishii;H. Nakamura
中科院分区：
文献类型：
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作者：
Y. Orsolini;K. Nishii;H. Nakamura
以前的研究已经记录了极端的平流层极涡事件，但影响其持续时间的因素很少受到关注。在这里，我们调查弱和强平流层极涡事件模拟集合再预报的北方半球冬季与欧洲中期天气预报中心的季节预报模型（系统4），与欧洲再分析中期数据集。将单个强涡旋事件和弱涡旋事件分为短事件和长事件。对四类事件中的每一类事件的开始或结束日期进行了综合分析。我们检查了预报模式和再分析中每个类别的特征，包括异常纬向平均纬向风，热量和波活动通量，低对流层温度和地面气压，以及对流层上层异常在出现和衰减阶段的天气演变。主要调查结果如下：（a）对于所考虑的四种类型，预报系统4产生的短、长异常涡事件的振幅与再分析相当，但极纬向风异常更持久;（B）短事件在开始时的穿透深度与长事件一样深，但在持续性不如长事件的波浪强迫下，它们迅速衰减;（c）在两个大洋盆地或北方欧亚大陆或美洲上空阻塞高压和低压的天气演变的细微差别似乎决定了强迫的持续时间;（d）在这种短事件期间，由平流层向下影响引起的环形模态范例的特征地面或低对流层特征没有足够的时间发展。
Previous studies have documented extreme stratospheric polar vortex events, but the factors governing their duration have received little attention. Here, we investigate weak and strong stratospheric polar vortex events simulated in ensemble reforecasts for the Northern Hemisphere winter with the seasonal forecast model (System 4) of the European Centre for Medium‐Range Weather Forecasting, in comparison with the European Reanalysis Interim dataset. The individual strong and weak vortex events are classified into short and long events. A composite analysis is conducted for each of the four categories of events with respect to their initial or end days. We examine the characteristics of each category in the forecast model and reanalyses, including anomalous zonal‐mean zonal winds, heat and wave‐activity fluxes, lower‐tropospheric temperature and surface pressure, as well as the synoptic evolution of upper‐tropospheric anomalies during the precursory and decaying stages. The main findings are: (a) the forecast System 4 is found to produce both short and long anomalous vortex events in comparable amplitude to the reanalyses, but the polar zonal wind anomalies are more persistent, for each of the four categories considered; (b) short events penetrate as deep as the long events right at their onset, but they rapidly decay under a wave forcing that is less sustained than in the long events; (c) subtle differences in the synoptic evolution of blocking Highs and Lows over both oceanic basins or over Northern Eurasia or America appear to condition the duration of the forcing; and (d) during such short events, characteristic surface or lower‐tropospheric signatures of the annular mode paradigm arising from the downward stratospheric influence are not allowed sufficient time to develop.