The combined effect of two westerly jet waveguides on heavy haze in the North China Plain in November and December 2015
The combined effect of two westerly jet waveguides on heavy haze in the North China Plain in November and December 2015
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DOI：
10.5194/acp-2019-826
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发表时间：
2019-11
影响因子：
6.3
通讯作者：
Xiadong An;L. Sheng;Qian Liu;Chun Li;Yang Gao;Jianping Li
中科院分区：
文献类型：
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作者：
Xiadong An;L. Sheng;Qian Liu;Chun Li;Yang Gao;Jianping Li
. 2015年11 - 12月，华北平原出现了严重的灰霾天气，且空间范围广、持续时间长。利用能见度观测资料和NCEP/NCAR再分析资料，研究了两个西风急流波导对华北地区灰霾天气的共同影响。结果表明，来自地中海的西风急流中的两个Rossby波导是造成华北地区霾的主要原因。Rossby波沿着副热带西风急流和极锋急流向东传播，在日本海上空形成异常反气旋，并在NCP上空形成850 hPa反气旋风速切变，增强了对流层中低层异常下降气流，导致大气稳定。此外，Rossby波减弱了东亚大槽和乌拉尔山脊，加强了我国东部沿海850 hPa异常偏南风，使东亚冬季风减速。上述气象条件调节了二零一五年十一月及十二月的灰霾天气。与此同时，由于Rossby波沿着副热带西风急流传播，使华南大范围出现了与上升运动有关的持续性降水。降水释放的潜热作为热源，在华南地区诱发对流。这进一步加强了华南上空的上升气流，使华北平原上空的下降气流得以维持，有利于严重烟霞的维持。该研究对揭示华北平原秋末冬季大范围灰霾的形成和维持机制具有重要意义。
. Severe haze occurred in the North China Plain (NCP) from November to December 2015, with a wide spatial range and long duration. In this paper, the combined effect of two westerly jet waveguides on haze in the NCP was investigated based on visibility observational data and NCEP/NCAR reanalysis data. The results showed that the two Rossby waveguides within the westerly jet originating from the Mediterranean were responsible for the haze formation in the NCP. The Rossby wave propagated eastward along the subtropical westerly jet and the polar front jet, causing an anomalous anticyclone over the Sea of Japan and anticyclonic wind speed shear at 850 hPa over the NCP, which enhanced the anomalous descending air motion in the middle and lower troposphere and subsequently resulted in a stable atmosphere. Furthermore, the Rossby wave weakened the East Asia trough and Ural ridge, and strengthened the anomalous southerly wind at 850 hPa over the coastal areas of east China, decelerating the East Asia winter monsoon. The above meteorological conditions modulated haze accumulation in November and December 2015. Meanwhile, continuous rainfall related to ascending motion due to Rossby wave propagation along the subtropical westerly jet occurred in a large area of southern China. The latent heat released by rainfall acted as a heat source, inducing convection over South China. This further strengthened the ascending motion over South China so that the descending motion over the NCP was maintained, favoring the maintenance of severe haze. This study is of great significance to elucidate the formation and maintenance mechanism of large-scale haze in the NCP in late fall and boreal winter.