Circulation Pattern and Moisture Transport for Summertime Persistent Heavy Precipitation in Eastern China
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摘要: 利用1957~2011年我国502个测站逐日降水资料,定义区域平均降水量连续5 d超过1个标准差为1次区域性持续强降水,分析了我国东部(105°E以东)长江流域、华北和东北地区夏季(6~8月)的强降水,共得到74个个例,并探讨了造成长江流域和华北地区持续性强降水的主要环流与水汽输送模态。结果表明,中高纬出现阻塞形势是造成我国东部夏季区域性持续强降水的主要环流型,占比86%。其中影响长江流域强降水的主要阻塞形势为中阻型(贝加尔湖为高压脊)和双阻型(乌拉尔山和鄂霍次克海同时出现高压脊);影响华北地区强降水的主要阻塞形势为中阻型。同时,必须建立一条自热带海洋至降雨区的水汽通道,长江流域强降水的水汽通道为印度洋-孟加拉湾-南海;对于华北地区,除此水汽通道外,西北太平洋水汽输送也是一个重要水汽来源。长江流域强降水的异常水汽输送在菲律宾北部出现反气旋中心,导致从南海有异常水汽输送并在长江流域辐合,这一反气旋中心对应500 hPa上西太平洋副热带高压的加强;华北地区强降水的异常水汽输送在渤海-朝鲜半岛出现反气旋中心,异常水汽来自南海和西北太平洋。渤海-朝鲜半岛在500 hPa出现正高度异常对维持华北地区持续降水有重要作用。深厚的上升运动或低层辐合高层辐散是华北与长江流域持续强降水发生的共同特点。中阻型和双阻型的长江流域强降水在水汽输送上没有明显差异,而是动力上升条件的分布差异决定了雨带主要位置的不同。Abstract: Based on daily precipitation data collected at 502 gauge stations in China during 1957-2011, regional-persistent heavy precipitation is defined to be the precipitation with regional mean precipitation larger than one standard deviation for five consecutive days. In total there are 74 regional-persistent heavy precipitation events in the Yangtze River basin, North China, and Northeast China in the summer (June to August). The main circulation pattern and moisture transport corresponding to the regional-persistent heavy precipitation events in the Yangtze River basin and North China are analyzed. The results show that the blocking high in the middle and high latitudes of Eurasia is the main circulation pattern for the regional-persistent heavy precipitation. The blocking high in the 500-hPa geopotential height field appeared in 86% of the heavy precipitation events. The main blocking patterns for heavy precipitation in the Yangtze River basin are central-blocking (there is a ridge near the Baikal Lake) and double-blocking (there are ridges near the Ural Mountains and the Okhotsk Sea at the same time). For heavy precipitation in North China, the main circulation pattern is central-blocking. The moisture transport from the tropical ocean to the regions of heavy precipitation is vital. For the Yangtze River basin, the moisture is largely from the Indian Ocean-Bay of Bangal-South China Sea. For North China, in addition to the moisture transport from the Indian Ocean-Bay of Bangal-South China Sea, moisture from the western North Pacific is also important. There is an anticyclonic center in the region to the north of the Philippines, which is favorable for abnormal moisture transport from the South China Sea to the Yangtze River basin. Corresponding to the anticyclonic center, the western North Pacific subtropical high at the 500 hPa strengthens. For the heavy precipitation in North China, the anticyclonic center favorable for abnormal moisture transport is located at the Bohai Sea-Korean Peninsula, and more moisture is pulled from the South China Sea and the western North Pacific. The positive geopotential height anomalies in the Bohai Sea-Korean Peninsula at 500 hPa are important for persistent heavy precipitation in North China. One common feature for the heavy precipitation in the Yangtze River basin and North China is the deep upward movement or divergence at upper levels and convergence at lower levels. There is no obvious difference in the moisture transport between central-blocking and double-blocking circulation patterns for heavy precipitation over the Yangtze River basin. However, the difference in upward movement determines the difference in precipitation location.
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图 2 长江流域(a、c)中阻型和(b、d)双阻型持续性强降水环流形势的(a、b)500 hPa高度场(等值线,单位:dagpm)及其标准化距平(填色),(c、d)降水量标准化距平
Figure 2. (a, b) The geopotential heights (contour, units: dagpm) and anomalies (shaded) at 500 hPa, and (c, d) precipitation anomalies under (a, c) central-blocking and (b, d) double-blocking circulation patterns for the regional-persistent heavy precipitation in the Yangtze River basin
图 3 长江流域中阻型(左列)和双阻型(右列)持续强降水:(a、b)垂直积分水汽输送;(c、d)沿122.5°E水汽输送高度—纬度剖面;(e、f)水汽输送标准化距平(填色区域表示水汽异常的辐合区)
Figure 3. (a, b) Vertically integrated moisture transport, (c, d) latitude-height cross sections of moisture transport along 122.5°E, and (e, f) normalized anomalies of vertically integrated moisture transport (the shaded area illustrates the abnormally convergent region) under central-blocking (left column) and double-blocking (right column) circulation patterns for the regional-persistent heavy precipitation in the Yangtze River basin
图 4 长江流域(a、c)中阻型和(b、d)双阻型持续强降水(a、b)200 hPa纬向风标准化距平(填色)(黑色等值线为高空急流,单位:m/s)以及(c、d)850 hPa风场标准化距平
Figure 4. (a, b) Normalized anomalies of zonal winds (colored) at 200 hPa (colored) (solid lines illustrate the jet stream, units: m/s), and (c, d) normalized anomalies of winds at 850 hPa under (a, c) central-blocking and (b, d) double-blocking circulation patterns for the regional-persistent heavy precipitation in the Yangtze River basin
图 5 长江流域中阻型强降水环流型(a)200 hPa散度标准化距平(黑色等值线)及纬向风分布(粗灰实线,单位:m/s)、(b)850 hPa散度标准化距平、(c)沿115°E的垂直速度标准化距平纬度—高度剖面(箭头分别表示上升/下沉运动,横坐标上粗黑线表示雨带的主要纬度范围)
Figure 5. (a) Standardized divergence anomaly (black contour) and the zonalwind (thick grey solid lines) at 200 hPa, (b) standardized divergence anomaly at 850 hPa, and (c) latitude-height cross sections of vertical velocity along 115°E under the central-blocking circulation pattern for the regional-persistent heavy precipitation in the Yangtze River basin (arrows illustrate ascending/ descending motion; the very thick black line along the x-axis illustrates the rainbelt)
图 7 华北地区中阻型持续性强降水环流形势的(a)500 hPa高度(等值线,单位:dagpm)及其标准化距平(填色),(b)降水量标准化距平
Figure 7. (a) The geopotential heights (contour, units: dagpm) and standardized anomalies (shaded) at 500 hPa, and (b) standardized precipitation anomalies under central-blocking circulation pattern for the regional-persistent heavy precipitation in North China
图 8 华北地区中阻型持续强降水:(a)垂直积分水汽输送;(b)沿122.5°E水汽输送高度—纬度剖面;(c)水汽输送标准化距平(填色区域表示水汽异常的辐合区)
Figure 8. (a) Vertically integrated moisture transport, (b) latitude-height cross sections of moisture transport along 122.5°E, and (c) normalized anomalies of vertically integrated moisture transport (the shaded area illustrates the abnormally convergent region) under central-blocking pattern for the regional-persistent heavy precipitation in North China
图 9 华北地区中阻型持续性强降水环流形势的(a)200 hPa纬向风标准化距平(填色)(黑色等值线为高空急流,单位:m/s)、(b)850 hPa风场标准化距平(粗灰线表示赤道辐合带位置)
Figure 9. (a) Standardized anomalies of zonal winds at 200 hPa (colored) (solid lines illustrate the jet stream, units: m/s), and (b) standardized anomalies of winds at 850 hPa under the central-blocking pattern for the regional-persistent heavy precipitation in North China (the heavy line in gray indicates the intertropical convergence zone)
表 1 不同环流形势的区域性持续强降水个例及比例
Table 1. Numbers of regional-persistent heavy precipitation events under different circulations and their percentages in the total number for different regions
区域 持续强降水个例(比例) 中阻型 双阻型 双阻过渡型 持续西风波动型 长江流域 15(36.6%) 15(36.6%) 8(19.5%) 3(7.3%) 华北 7(33.3%) 5(23.8%) 6(28.6%) 3(14.3%) 东北 4(33.3%) 3(25.0%) 1(8.3%) 4(33.3%) 注:双阻过渡型指乌拉尔阻塞和鄂霍茨克阻塞。 -
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