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The Heavy Rainfall Event Leading to the Large Debris Flow at Zhouqu
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摘要: 利用自动气象站观测资料、MTSAT卫星红外亮温资料、NCEP/NCAR再分析资料、AIRS卫星大气温湿资料、MODIS卫星气溶胶光学厚度资料和ECMWF模式预报的地面风、压、温、湿资料，对2010年8月7—8日甘肃省甘南州舟曲县引发特大泥石流灾害的强降雨天气过程的成因进行了天气动力学诊断分析，结果表明：由于地表强烈增温与高空槽后冷空气平流作用，8月7日午后舟曲及其上游 (西北方向) 地区大气不稳定性极强，区域平均对流有效位能 (CAPE) 值为4393 J·kg-1、对流零浮力层 (LNB) 高度达16.54 km；南北气流交汇与局地复杂小地形使得近地面形成多个中小尺度辐合线和辐合中心，于8月7日14：00(北京时) 左右触发了对流的产生；强盛的西北太平洋副热带高压与台风电母之间的偏南气流在23°~30°N纬度带转向西输送水汽直达青藏高原东缘，在高原地形作用下转为向北传输到达舟曲附近区域，为该区域对流发展提供水汽条件；对流云团形成后，在高空西北气流的引导下向东南方向移动，于8月7日夜间到达舟曲地区造成该地区强降雨，引发特大泥石流灾害。Abstract: Heavy rainfall occurs abruptly at Zhouqu, Gansu Province at night of 7 August 2010, causing disastrous debris flow and bringing about more than a thousand casualties. To find out the possible triggering mechanism of this rainfall, observations by Automatic Meteorological Stations are used to analyze temporal variation of the surface temperature and spatial distribution of rainfall; brightness temperature data from MTSAT satellite are adopted to reveal evolution of convective clouds; NCEP/NCAR 1°×1° reanalysis data are used to investigate the large-scale atmospheric conditions; AIRS satellite observations are examined to analyze the atmospheric instability; and ECMWF 0.125°×0.125° forecast data are employed to study the convection. First, over Zhuoqu and its upstream (northwest) region, the rapid increase of surface air temperature and the cold air advection in the rear area of the upper-level trough significantly enhanced the conditional instability in the morning of 7 August, favoring formation and development of deep convection. Second, several small-scale convergence centers and lines at the ground surface, generated by interactions among the southerly warm and northerly cold air flow near the ground surface and the complex terrain elevation, triggered the formation of the precipitating convective clouds around 14:00 7 August 2010 (Beijing Time). Third, the southerly air flow between the strong Northwest Pacific Subtropical High and the typhoon "Dianmu" changed to easterly at 23°—30°N, transporting water vapor toward the west until reaching the eastern side of Tibetan Plateau, and then changed to northward, supplying abundant moisture for the raining storm over Zhouqu and its upstream region. At last, the convective clouds moved toward southeast following the upper-level air flow, arrived at Zhouqu and produced heavy rainfall at night of 7 August, leading to the large debris flow at Zhouqu.Satellite remote sensing observations play an important role in the diagnosis of this synoptic process. The infrared brightness temperature (TBB) from the MTSAT satellite reveals the occurrence, development, movement and weakening of the convective clouds which directly produced the heavy rainfall at Zhouqu. The air column temperature and moisture data observed by the AIRS satellite around 14:30 7 August 2010 are used to analyze convective available potential energy (CAPE) and level of neutral buoyancy (LNB) height. The results indicate that atmosphere over Zhouqu—Qinghai Lake region is strongly unstable with the area-averaged CAPE of 4393 J·kg-1 and LNB height of 16.54 km.
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图 1 2010年8月7日08：00—8日08：00自动气象站24 h累积降水量
(灰色阴影：地形高度；白色圆圈：舟曲位置；黑色曲线：青海湖)
Fig. 1 Precipitation accumulated during 08:00 7 August—08:00 8 August in 2010 at individual AMS stations
(gray area: terrain elevation; white circle: Zhouqu; Qinghai Lake is circled by black solid line)
图 2 2010年8月7日14：00大尺度环流 (×：舟曲位置)(a) 700 hPa位势高度场 (黑线，单位：gpm) 和风场 (矢量)(灰色阴影：地形在700 hPa以上的区域)，(b) 500 hPa位势高度场 (黑线，单位：gpm)、08：00—14：00负变温区 (彩色阴影)、风场 (矢量)，(c) 200 hPa位势高度场 (黑线，单位：gpm)、正辐散区 (彩色阴影)、风场 (矢量)
Fig. 2 Synoptic background at 14:00 7 August 2010 (×: Zhouqu) (a) geopotential height (black line, unit: gpm) and wind (arrow) at 700 hPa (gray shaded represents the area with terrain elevation above 700 hPa), (b) geopotential height (black line, unit: gpm), decrease in temperature from 08:00 to 14:00 (color shaded) and wind (arrow) at 500 hPa, (c) geopotential height (black line, unit: gpm), positive divergence (color shaded) and wind (vector) at 200 hPa
图 3 MTSAT卫星观测的红外亮温水平分布的时间演变
(彩色阴影：红外亮温；灰色阴影：地形高度；×：舟曲位置)
Fig. 3 Temporal evolution of horizontal distribution of TBB observed by the MTSAT satellite
(color shaded: TBB; gray shaded: terrain elevation; ×: Zhouqu)
图 4 2010年8月7日12：00与08：00的近地面空气温度差 (单位：℃)
(灰色阴影：地形高度；×：舟曲位置)
Fig. 4 Differences in surface air temperature between 12:00 and 08:00 on 7 August 2010 (unit: ℃)
(gray shaded: terrain elevation; ×: Zhouqu)
图 5 2010年8月7日08：00—8日08：00 34°~37.5°N, 100°~104°E区域内近地面气温时间演变
Fig. 5 Time series of surface air temperature at the area of 34°—37.5°N, 100°—104°E from 08:00 7 August to 08:00 8 August in 2010
图 6 2010年8月7日14：35对流有效位能的水平分布
(灰色阴影：地形高度；白色圆圈：舟曲位置；黑色轮廓：青海湖)
Fig. 6 Horizontal distribution of CAPE at 14:35 7 August 2010
(gray shaded: terrain elevation; white circle: Zhouqu; Qinghai Lake is circled by black solid line)
图 7 2010年8月7日14：35对流零浮力层高度的水平分布
(灰色阴影：地形高度；白色圆圈：舟曲位置；黑色轮廓：青海湖)
Fig. 7 Horizontal distribution of LNB height at 14:35 7 August 2010
(gray shaded: terrain elevation; white circle: Zhouqu; Qinghai Lake is circled by black solid line)
图 8 大气湿静力能 (a)、感热 (b)、潜热 (c) 的垂直廓线
(灰线：四川盆地 (28°~32°N, 104°~106°E)；黑线：青海湖—舟曲地区 (32°~37°N, 100°~105°E))
Fig. 8 Vertical distributions of moist static energy (a), sensible heat (b) and latent heat (c)
(gray line: Sichuan Basin (28°—32°N, 104°—106°E); black line: Qinghai Lake—Zhouqu (32°—37°N, 100°—105°E))
图 9 2010年8月7日地面辐合和红外亮温、700 hPa温度和比湿、地面风、海平面气压、地形高度的水平分布
(图9b，9c中白线：地面风辐合线；图9b，9c中白色方框：地面风辐合区；×：舟曲位置；左上方黑实线：青海湖轮廓) (a)14：30 MTSAT卫星红外亮温水平分布 (彩色阴影)、地形高度 (灰色阴影)，(b)14：00 700 hPa温度场 (灰色阴影)、地面风场 (矢量)、海平面气压场 (彩线)，(c)14：00 700 hPa比湿场 (灰色阴影)、地面风场 (矢量)、海平面气压场 (彩线)，(d)14：00地面风场 (矢量)、地形高度 (彩色阴影)
Fig. 9 Horzontal distribution of surface wind convergence, TBB, temperature and specific humidity at 700 hPa, surface wind, and sea level pressure on 7 August 2010 and terrain elevation
(white lines and white boxes in Fig. 9b, 9c represent surface wind convergence lines and surface wind convergence areas, respectively; ×: Zhouqu; black solid line at the left-upper of each panel: Qinghai Lake) (a) horizontal distribution of TBB (color shaded) observed by MTSAT satellite at 14:30 with terrain elevation (gray shaded), (b) temperature (gray shaded) at 700 hPa, surface wind (arrow), sea level pressure (color line) at 14:00, (c) specific humidity (gray shaded) at 700 hPa, surface wind (arrow), sea level pressure (color line) at 14:00, (d) surface wind (arrow) at 14:00 and terrain elevation (color shaded)
图 10 2010年8月7日14：00地面至100 hPa积分的水汽通量(矢量)和水汽通量辐合区(虚线,单位：10-5s-1·hPa)
(灰色阴影：地形高度在700 hPa以上的区域； ×：舟曲位置； 黑粗箭头：水汽输送通道)
Fig. 10 Water vapor flux integrated vertically from ground to 100 hPa (arrow) and convergence of the water vapor flux (dashed line, unit: 10-5s-1·hPa) at 14:00 7 August 2010(gray shaded: area with terrain elevation above 700 hPa; ×: Zhouqu; black thick arrow: water vapor channel)
表 1 2010年8月7日14：35青海湖—舟曲地区与四川盆地对流有效位能、对流零浮力层高度、2.5~5.0 km高度的大气湿静力能、感热和潜热的平均值与标准偏差
Table 1 Means and standard deviations of CAPE, LNB height, and MSE, SHE, LHE at the heights of 2.5 to 5.0 km over Qinghai-Zhouqu region and Sichuan Basin at 14:35 7 August 2010
物理量 青海湖—舟曲地区 四川盆地 平均值 标准偏差 平均值 标准偏差 对流有效位能/(J·kg-1) 4393 2669 847 616 对流零浮力层高度/km 16.54 1.32 12.89 1.33 大气湿静力能/(J·kg-1) 352740 10209 339784 4132 感热/(J·kg-1) 286445 5687 284212 4555 潜热/(J·kg-1) 25886 10302 18905 6183 
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