杭州湾北岸一次极端高温过程分析

Analysis of an Extreme Heat Process along North Shore of Hangzhou Bay

利用实时探空场和欧洲中心20:00细网格、NCEP再分析资料对2013年8月6—10日杭州湾北岸极端高温过程进行分析,结果表明:副高脊线稳定在30°N、高层有辐散气流、低层26℃暖气团处于强副高中心影响是持续40℃极端高温发生的大尺度环流背景。副高与南亚高压"相向而行",在垂直方向上产生深厚的次级环流圈,是2013年极端高温持续时间长、影响范围大的一个重要因素。极端高温的出现与空气异常干燥有密切关系,北方高层干空气南下叠加在中低层副高暖干气团之上,从高层到近地层受一致下沉气流的绝热压缩增温,以及低空暖平流输送的综合影响,是导致7—9日杭州湾北岸多地最高气温屡破记录的原因。经检验,极端高温期间,业务参考使用的4个主要数值模式对最高气温的预报,EC模式误差较小且稳定,绝对误差为1℃,而GFS、JMA和T639误差分别达3℃、4℃和5℃,应用时需订正,以上结果可供夏季高温预报参考。

The real-time altitude fields, ECMWF nest grid data at 12UTC and NCEP reanalysis data are used to analyze the extreme heat process from August 6 to 10 in 2013 along the north shore of the Hangzhou Bay. The results show that the large-scale circulation background of the persistent extreme high temperature （40 ℃） weather include the subtropical ridge steadily at 30°N, divergence at upper levels, 26 ℃ warm air mass at lower levels under the strong subtropical high center. The subtropical high extended westwards and the South Asia high moved eastwards, which produced a profound secondary circulation loop in the vertical direction, which was an important reason for the extreme high temperature lasted longer and wider. The emergence of extreme heat was closely related with the exceptionally dry air. The reasons for more extreme temperature records have been broken along the north shore of the Hangzhou Bay are： those high-level dry air superimposed on the southward lower-level subtropical dry warm mass, the adiabatic heating effect of sinking airflow from top to ground, and the warm advection at lower levels. The prediction verification of four major numerical models for high temperature service indicates： the error of EC model prediction is small and and 5 ℃, respectively, which need summer high temperature forecast. stable, about 1 ℃, and the errors of GFS, JMA, to correct in service. These results can be used and T639 are 3, 4, as references in the summer high temperature forecast.