The Structure and Origin of a Rainstorm-inducing Mesoscale Convective System on Western Coast of Bohai Bay
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摘要: 利用卫星、雷达和加密自动站等监测资料,结合VDRAS系统资料和1°×1° NCEP再分析资料,对造成黑昼和暴雨的中尺度对流系统的空间、热动力结构特征和发生、发展及维持原因进行了分析。结果表明:2004—2009年渤海西岸圆形α-中尺度对流系统有别于南方,其中只有16%可发展为中尺度复合体;黑昼现象是影响系统的特殊性所致。突发性暴雨的制造者是α-中尺度对流系统西端不断新生的β-中尺度对流系统,其发生、发展、维持与边界层内冷池外流、对流层低层 (1.3~2.4 km) 侵入的西北气流与西南气流形成的辐合线或交汇线有密切关系。α-中尺度对流系统的上升速度中心在500 hPa附近,多个β-中尺度对流系统分别具有独自的垂直气流和弱边界层环流。α-中尺度对流系统内部扰动温度呈下负上正的垂直分布,促使了不稳定层结趋于稳定;冷池呈东厚西薄的楔形结构,有利于β-中尺度对流系统发展维持。Abstract: Black day phenomenon and sudden hard rain occur in Tianjin on 16 June 2009. Based on several monitoring data such as FY-2 satellites data, multi-radar composite and intensive automatic stations data, combing with VDRAS data, the origins of black day and the rainstorm are analyzed. The thermal and dynamical structure which leads to the occurrence and development of meso-β-scale, meso-γ-scale convective systems in circular meso-α-scale convective system are also studied. 31 circle-shape MCSs which lead to severe weather on western coast of Bohai Bay in 2004—2009 are preliminarily sorted and summed up in size and life-circle.Less than 16% circular MαCS on the western coast of Bohai Bay develop into MCC with no more than 15×104 km2 large (where the TBB is equal to or below-52 ℃). The MCCs generally last no more than 8 hours and always happen in night. But in the South China, it's common to see MCC larger than 20×104 km2 which last more than 10 hours."6.16" MαCS has special characteristics in range, time of occurrence and precipitation echoes on the thickness, which are the main causes for black day phenomenon. New MβCS and MγCS develop constantly in the west of MαCS move eastward into the high-energy region with warm-moisture intensively and maintain, leading to rainstorm in Tianjin.Cold air intrudes into MαCS from its back at the height of 1.3—2.4 km, flows out from rain echoes convergence line or close-gradually line, and triggers the development of MβCS with southwestern warm-moisture flow.In the ascending center of MαCS, the vertical velocity is 0.7 Pa·s-1 at height of 500 hPa. Below the height of 700 hPa (about 3 km), ascending vertical velocity reaches 1.8 m·s-1, and each of MβCS1—3 has independent vertical circle. Under the height of 1 km, there is corresponding boundary layer circulation for MβCS1—3. With evolution of MβCS1—3, cold pool (the areas of negative perturbation temperature) appears under the height of 2 km and the area of positive perturbation temperature appears above it, so the vertical structure is stable.
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图 2 2009年6月16日08:00天气形势
(a) 850 hPa高度场 (实线, 单位:dagpm)、风场和水汽通量 (虚线, 单位:106 g·cm-2·hPa-1), (b) 1000 hPa高度场 (实线, 单位:dagpm)、风场和水汽通量 (虚线, 单位:106 g·cm-2·hPa-1), (c) 500 hPa高度场 (实线, 单位:dagpm)、700 hPa风场和850 hPa假相当位温 (虚线, 单位:℃)
Fig. 2 Weather charts at 08:00 16 June 2009
with 850 hPa (a), 1000 hPa (b) height (solid line, unit: dagpm), wind field and water flux (dashed line, unit: 106 g·cm-2·hPa-1), and 500 hPa height (solid line, unit: dagpm), 700 hPa wind field, 850 hPa potential pseudo-equivalent temperature (dashed line, unit: ℃)(c)
图 4 2009年6月16日FY-2C卫星资料TBB≤-52℃范围 (实线,单位:℃) 和同时刻组合反射率因子 (阴影) 叠加图
(a)12:00, (b)13:00, (c)14:00, (d)15:00, (e)16:00, (f)17:00, (g) 沿图 4b中AB直线所作的剖面
Fig. 4 Composed radar reflectivity (shaded area) and FY-2C satellite TBB≤-52℃(solid line, unit:℃) on 16 June 2009 (a)12:00, (b)13:00, (c)14:00, (d)15:00, (e)16:00, (f)17:00, (g) cross section of radar reflectivity along line AB in Fig. 4b
图 7 2009年6月16日不同尺度环流垂直剖面图 (a)14:00沿117°E做垂直速度剖面 (单位:Pa·s-1,“━”为MαCS位置), (b)14:29沿图 4b中AB做剖面得到3 km内垂直速度图 (单位:m·s-1),(c)14:29 3 km内垂直环流与扰动温度叠加图 (阴影为扰动温度)
Fig. 7 Vertical velocity in cross section along 117°E at 14:00 (unit: Pa·s-1, "━" is position of MαCS)(a), vertical velocity cycle in cross section (unit:m·s-1) along line AB in Fig. 4b at 14:29 (b) and its vertical circulation with perturb temperature (shaded area, unit:℃) at 14:29 (c) on 16 June 2009
表 1 2004—2009年渤海西岸圆型MαCS (云顶TBB≤-52℃的面积在5×104 km2以上) 参数
Table 1 Features of circular MαCS (the area of cloud top with TBB≤-52℃ is more than 5×104 km2) during 2004—2009 on western coast of Bohai Bay
出现时间 TBB≤-62℃的面积/104 km2 TBB≤-52℃的面积/104 km2 云顶最低TBB/℃ 维持时间/h 2005-06-23T17:00 7.15 12.45 -71 6 2005-07-13T23:00 0.92 6.89 -68 4 2005-08-16T17:00 0.97 6.83 -76 4 2006-06-27T22:00 1.99 13.51 -67 8 2007-06-25T22:00 4.66 7.42 -74 6 2007-07-18T08:00 5.27 14.56 -80 6 2007-07-31T00:00 7.44 14.4 -72 7 2008-06-25T22:00 2.10 8.35 -71 5 2009-06-16T12:00 2.98 10.45 -67 4 2009-07-22T21:00 0.72 6.03 -64 2 注:2005-05-31过程达到标准,但TBB资料缺失;2007-07-18和2009-06-16过程中由圆型变形后继续强烈发展。 -
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