How East Asian westerly jet’s meridional position affects the summer rainfall in Yangtze-Huaihe River Valley?
How East Asian westerly jet’s meridional position affects the summer rainfall in Yangtze-Huaihe River Valley?
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DOI：
10.1007/s00382-017-3591-3
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发表时间：
2018-12
期刊：
影响因子：
4.6
通讯作者：
Shixin Wang;H. Zuo;Shuman Zhao;Jiankai Zhang;Sha Lu
中科院分区：
文献类型：
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作者：
Shixin Wang;H. Zuo;Shuman Zhao;Jiankai Zhang;Sha Lu
已有的研究表明，东亚西风急流纬向位置的变化与江淮流域夏季降水异常有关。然而，其动力机制尚未得到解决。本研究分别揭示了初夏和仲夏这种影响的潜在机制。机制一：与东亚西风急流的异常南移相联系，通过对流层中层水平环流异常，加强了YHRV上空的500 hPa西风，这种西风异常与YHRV上空暖平流异常的形成有关，通过绝热上升运动和对流活动，使降水增加;初夏和盛夏的主要区别是对流层中部环流异常型。机制二：与EAWJ的强烈南移相联系，中纬度对流层中层温度平流的大的逐日变率被急流的捕获瞬变涡旋向南移动，这一变化增强了YHRV上空温度平流的逐日变率，从而通过“下界效应”导致YHRV大部分地区的降水增加（降水量不可能变为负值），初夏和盛夏的降水过程差别不大。
Existing studies show that the change in the meridional position of East Asian westerly jet (EAWJ) is associated with rainfall anomalies in Yangtze-Huaihe River Valley (YHRV) in summer. However, the dynamic mechanism has not been resolved yet. The present study reveals underlying mechanisms for this impact for early summer and midsummer, separately. Mechanism1: associated with EAWJ’s anomalously southward displacement, the 500-hPa westerly wind over YHRV is strengthened through midtropospheric horizontal circulation anomalies; the westerly anomalies are related to the formation of warm advection anomalies over YHRV, which cause increased rainfall through adiabatic ascent motion and convective activities; the major difference in these processes between early summer and midsummer is the midtropospheric circulation anomaly pattern. Mechanism 2: associated with EAWJ’s anomalously southward displacement, the large day-to-day variability of midtropospheric temperature advection in midlatitudes is displaced southward by the jet’s trapping transient eddies; this change enhances the day-to-day variability of temperature advection over YHRV, which in turn causes the increased rainfall in most part of YHRV through “lower-bound effect” (rainfall amount can not become negative); there is not much difference in these processes between early summer and midsummer.