doi:  10.3878/j.issn.1006-9895.1807.18134
46年京津冀地区“夏雨秋下”现象及其成因初探

A Study on the Phenomenon of Midsummer Precipitation Delays until Early Autumn and Associated Reasons in Beijing-Tianjin-Hebei during 1970-2015
摘要点击 260  全文点击 181  投稿时间:2018-03-05  
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基金:  国家自然科学基金青年科学基金项目41805058,公益性行业气象国家自然科学基金青年科学基金项目41805058,公益性行业(气象)科研专项GYHY201506001-1,天津市应用基础与前沿技术研究计划一般项目15JCYBJC22300,天津市气象局博士基金项目201628bsjj01
中文关键词:  京津冀  降水  盛夏  初秋  东亚夏季风
英文关键词:  Beijing-Tianjin-Hebei  Precipitation  Midsummer  Early autumn  East Asian summer monsoon
              
作者中文名作者英文名单位
梁苏洁LIANG Sujie天津市气候中心,天津300074
丁一汇DING Yihui国家气候中心,北京100081
段丽瑶DUAN Liyao天津市气象台,天津300074
郝立生HAO Lisheng天津市气候中心,天津300074
李明财and LI Mingcai天津市气候中心,天津300074
引用:梁苏洁,丁一汇,段丽瑶,郝立生,李明财.2019.近46年京津冀地区“夏雨秋下”现象及其成因初探[J].大气科学,43(3):655-675,doi:10.3878/j.issn.1006-9895.1807.18134.
Citation:LIANG Sujie,DING Yihui,DUAN Liyao,HAO Lisheng,and LI Mingcai.2019.A Study on the Phenomenon of Midsummer Precipitation Delays until Early Autumn and Associated Reasons in Beijing-Tianjin-Hebei during 1970-2015[J].Chinese Journal of Atmospheric Sciences (in Chinese),43(3):655-675,doi:10.3878/j.issn.1006-9895.1807.18134.
中文摘要:
      基于京津冀地区逐日和逐时降水资料,对1970年以来变暖背景下该地区盛夏(7月和8月)和初秋(9月)降水的变化特征分析后:近46年京津冀地区盛夏降水显著减少,在1990年代末由多雨转为少雨位相,降水日变化上,不同时段的降水皆明显减少,其中持续性降水事件的变化对总降水量减少的贡献更大。而初秋降水明显增加,且在2000年代初发生跃变,由少雨转为多雨位相,夜间降水明显增加,并且持续性降水的增加和跃变是初秋降水增加的主要原因。进一步分析发现,日最高气温的变化与短时降水有较好的时间关系,盛夏时最高气温在1997年发生跃变,从较低位相跃变为较高位相,对应的,盛夏短时降水也同年发生跃变,由多雨转为少雨位相。而初秋的最高气温变化不明显,短时降水也没有发生跃变,无明显的变化趋势。此外,在环流场上,2000年代后,盛夏时欧亚中高纬阻高活动加强,阻碍了中纬度西风扰动输送水汽到京津冀地区,东亚急流偏南,京津冀地区上升气流受到抑制,不利于降水产生;而初秋时,输送至京津冀地区的水汽增加,东亚急流偏北,京津冀地区上升气流加强,贝加尔湖地区低槽受到东部高压阻挡,经向环流加强,有利于冷空气的活动,同时,西太平洋副高强度增强位置偏北,有利于降水的形成。东亚海陆热力差指数在初秋的增强反映出东亚夏季风在夏末秋初的南撤过程发生延迟,形成了以上有利于初秋降水的环流形势,导致了“夏雨秋下”的现象的出现。
Abstract:
      Based on daily and hourly precipitation data collected at 33 meteorological observational stations in Beijing-Tianjin-Hebei during 1970-2015, spatial and temporal characteristics of midsummer (July and August) and early Autumn (September) precipitation are analyzed. It is found that the midsummer precipitation decreases significantly during the past 46 years, and the midsummer shifts from rainy phase to rainless phase at the end of the 1990s. From the point of view of diurnal precipitation variation, accumulated precipitation at any intervals and individual hours of the day has been decreasing since the late 1990s. Decreases in long-duration precipitation make more contribution to the decreasing trend of total midsummer precipitation. On the other hand, precipitation in early autumn exhibits an increasing trend, and early autumn shifts from rainless phase to rainy phase at the beginning of the 2000s. There is an obvious increase of nocturnal precipitation during the recent decade. And increases in long-duration precipitation are largely responsible for the phase shift and increases in total precipitation in early autumn. Further analysis reveals that monthly mean daily maximum temperature shifts from low-temperature phase to high-temperature phase at 1997, accordingly, short-duration precipitation shifts from rainy phase to rainless phase in the midsummer. Note that monthly mean daily maximum temperature and short-duration precipitation in early autumn show no obvious trend. Also, it is found that the retreat of the East Asian summer monsoon delays during late summer and early autumn, leading to the phenomenon of delays of midsummer precipitation until early autumn in Beijing-Tianjin-Hebei. The results show that the blocking high has intensified over the mid-high latitudes of Eurasia in the midsummer since early 2000s, resulting in less water vapor transport by the mid-latitude westerly jet to Beijing-Tianjin-Hebei. Meanwhile, the East Asian jet shifts southward while the ascending motions over Beijing-Tianjin-Hebei become weak. The above circulation patterns lead to less precipitation in the midsummer. In contrast, more water vapor can be transported to Beijing-Tianjin-Hebei in early autumn due to the northward shift of the East Asia jet and intensified ascending motions over Beijing-Tianjin-Hebei since early 2000s. Meridional circulation also strengthens since the low trough in Lake Baikal is blocked by the high pressure system to its east, which is in favor of cold air activities. Meanwhile, the western Pacific subtropical high intensifies and shifts further north. The above circulation changes lead to more precipitation in early autumn in Beijing-Tianjin-Hebei. Besides, the index of land-sea thermal difference shows a significant increasing trend in early autumn, which may reflects a delayed southward retreat of the East Asian summer monsoon.
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