2023年昆明准静止锋对云南的影响

The Impact of Kunming Quasi-Stationary Front on Yunnan in 2023

  • 摘要: 利用地面观测资料和ERA5再分析资料,分析了2023年影响云南的昆明准静止锋概况,选取典型个例,对比分析增强西进型、维持型和减弱东退型昆明准静止锋的锋面天气、锋面结构和环流特征。结果表明:2023年云南共受到27次昆明准静止锋过程影响,其中增强西进型14次共106 d,维持型5次共32 d,减弱东退型8次共27 d;增强西进型一年四季都有出现,维持型主要出现在春、秋两季,减弱东退型主要出现在初冬、春季和秋末;昆明准静止锋增强西进常给云南中东部带来强降温、局部降雪和寒潮天气,长时间维持会造成云南东部持续低温阴雨寡照天气,减弱东退常使云南东部天空状况突变,由阴转为多云或晴;增强西进型锋区内等温线密集且与地面垂直,向上伸展高度最高,冷空气厚度最大,锋后偏东风最强,维持型次之,减弱东退型最弱;三种类型锋后均存在顺时针次级环流,增强西进型强于其他两种类型;当500 hPa东亚大槽呈东北—西南走向,槽后有强冷平流,南支槽位于阿拉伯海,槽前暖平流较弱,700 hPa川滇之间有切变线,800 hPa反气旋位于四川盆地以东,地面冷高压位于(110°E,40°N)附近时,有利于昆明准静止锋增强西进;当500 hPa东亚大槽呈准南北走向,槽后冷平流较弱,南支槽位于孟加拉湾北部,槽前暖平流不强,700 hPa川滇切变线不明显,800 hPa反气旋位于四川盆地以北,地面冷高压位于110°E以东、40°N以北时,昆明准静止锋维持;当500 hPa东亚大槽位于140°E以东,槽后为弱冷平流,南支槽加深,槽前暖平流较强,700 hPa无川滇切变线,800 hPa反气旋位置偏南,地面冷高压偏弱时,昆明准静止锋东退。

     

    Abstract: Utilizing surface observation data and ERA5 reanalysis data, this study analyzed the impact of Kunming quasistationary front (QSF) on Yunnan in 2023. Typical cases were selected to comparatively analyze the frontal weather, frontal structure, and circulation characteristics of the westward-advancing, maintaining, and eastward-retreating Kunming quasistationary fronts. The results indicate that Yunnan was influenced by 27 Kunming quasi-stationary front processes in 2023, including 14 westward-advancing events lasting 106 d, 5 maintaining events lasting 32 d, and 8 eastward-retreating events lasting 27 d. Westward-advancing events occurred throughout the year, maintaining events primarily occurred in spring and autumn, and eastward-retreating events mainly occurred in early winter, spring, and late autumn. Generally speaking, the westwardadvancing Kunming quasi-stationary front often brings strong cooling, localized snowfall, and cold waves to central and eastern Yunnan. The maintenance of the Kunming quasistationary front means persistent low temperatures, overcast, and rainy weather with limited sunshine in eastern Yunnan. And the eastward-retreating type often causes abrupt changes in the weather conditions in eastern Yunnan, transitioning from overcast to cloudy or clear. The isotherms within the frontal zone of the westward-advancing type are densely packed and perpendicular to the ground. Among the 3 types, the westward-advancing type is characterized with the highest upward height, the thickest cold air and the strongest easterly wind behind the front, which is followed by the maintaining type, with the eastward-retreating type as the weakest. All 3 types exhibit clockwise secondary circulation behind the front, with the westward-advancing type being the strongest. The following conditions are favorable for the westward advancement of Kunming quasi-stationary front: The 500 hPa East Asian trough is oriented northeastsouthwest, with strong cold advection behind the trough; the southern branch trough is located in the Arabian Sea with weak warm advection ahead; a shear line exists between Sichuan and Yunnan at 700 hPa; an anticyclone is located to the east of the Sichuan Basin at 800 hPa; and the surface cold high is near (110°E, 40°N). The following conditions are favorable for the maintaining of Kunming quasi-stationary front: The 500 hPa East Asian trough is quasi-north-south oriented, with weak cold advection behind the trough; the southern branch trough is located in the northern Bay of Bengal with moderate warm advection ahead; the Sichuan-Yunnan shear line at 700 hPa is not prominent; the anticyclone at 800 hPa is located to the north of the Sichuan Basin; and the surface cold high is to the east of 110°E and to the north of 40°N. The eastward retreating of Kunming quasi-stationary front is likely to be triggered by the following conditions: The 500 hPa East Asian trough is to the east of 140°E, with weak cold advection behind the trough; the southern branch trough deepens, with strong warm advection ahead of the trough; there is not Sichuan-Yunnan shear line at 700 hPa; the anticyclone at 800 hPa is positioned further south; and the surface cold high is weak.

     

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