Predictability of the stratospheric polar vortex breakdown: An ensemble reforecast experiment for the splitting event in January 2009
Predictability of the stratospheric polar vortex breakdown: An ensemble reforecast experiment for the splitting event in January 2009
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DOI：
10.1002/2015jd024581
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发表时间：
2016-04
期刊：
影响因子：
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通讯作者：
S. Noguchi;H. Mukougawa;Y. Kuroda;R. Mizuta;Shoukichi Yabu;Hiromasa Yoshimura
中科院分区：
文献类型：
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作者：
S. Noguchi;H. Mukougawa;Y. Kuroda;R. Mizuta;Shoukichi Yabu;Hiromasa Yoshimura
为了研究2009年1月下旬发生的一次典型的极地涡旋分裂事件的平流层突然增温的可预测性和发生机制，开展了一系列集合重预报实验。为了全面考察涡旋分裂的快速演化和可预测性变化，2009年1月期间每天进行集合预报。通过涡旋分裂前6天后初始化的预报，对涡旋分裂事件进行了可靠的预测。研究还发现，行星波在平流层内的传播特性是成功预测涡分裂事件的关键。对于失败的预报，来自对流层的行星波会反射回对流层，而对于成功的预报，它们会被平流层吸收。综合分析揭示了预测失败时行星波的以下反射过程： 在初始预测期间，来自阿拉斯加上空对流层阻挡的行星波活动向上传播较弱；随后，欧洲上空平流层上层纬向风的减速作用减弱，为波浪反射创造了良好的条件；因此，随后来自欧洲上空对流层的入射波活动被反射回西伯利亚，引起行星波向东的相位倾斜，从而阻止行星波进一步向上传播，从而导致涡旋分裂。因此，本研究表明，除了对流层异常环流强制行星波向上传播之外，平流层条件将是涡分裂事件发生的另一个重要控制因素。
A series of ensemble reforecast experiments is conducted to investigate the predictability and the occurrence mechanism of a stratospheric sudden warming occurred in late January 2009, which is a typical polar vortex splitting event. To fully examine the rapid vortex splitting evolution and predictability variation, ensemble forecasts are carried out every day during January 2009. The vortex splitting event is reliably predicted by forecasts initialized after 6 days prior to the vortex breakup. It is also found that the propagating property of planetary waves within the stratosphere is a key to the successful prediction for the vortex splitting event. Planetary waves incoming from the troposphere are reflected back into the troposphere for failed forecasts, whereas they are absorbed within the stratosphere for succeeded forecasts. Composite analysis reveals the following reflection process of planetary waves for the failed forecast: Upward propagation of planetary wave activity from a tropospheric blocking over Alaska is weaker during initial prediction periods; then, the deceleration of the zonal wind in the upper stratosphere becomes weaker over Europe, which produces a preferable condition for the wave reflection; hence, subsequently incoming wave activity from the troposphere over Europe is reflected back over the Siberia inducing the eastward phase tilt of planetary waves, which shuts down the further upward propagation of planetary waves leading to the vortex splitting. Thus, this study shows that the stratospheric condition would be another important control factor for the occurrence of the vortex splitting event, besides anomalous tropospheric circulations enforcing upward propagation of planetary waves.