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Comparative Analysis of Two Strong Convections Triggered by Sea-breeze Front in Shandong Peninsula
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摘要: 利用常规地面和高空观测资料、烟台和青岛多普勒天气雷达资料、加密自动气象站等资料分析2014年7月14日(“7·14”)和2009年6月29日(“6·29”)山东半岛两次海风锋引起的强对流天气。结果表明:“7·14”强对流天气发生于冷涡后部前倾槽的环流形势下, 明显的静力不稳定层结、中等大小的对流有效位能及垂直风切变相对偏弱, 是此次对流风暴持续时间短且降雹范围较小的原因; “6·29”过程是东北冷涡影响下的强对流天气。海风锋、阵风锋、地面辐合线是两次过程的触发机制, 两次过程都出现了高悬的强回波、弱回波区、回波悬垂、钩状回波、中气旋等超级单体回波特征; 大冰雹形成期表现为中气旋垂直伸展较大和旋转较强, 两次过程的超级单体风暴均由海风锋触发的靠近山脉的风暴发展加强而成, 即地形与海风锋结合导致的更强抬升在加强对流风暴并演化为超级单体风暴中起了关键作用。但“6·29”强对流天气过程出现了强中气旋, “7·14”强对流天气过程出现了弱中气旋, 因此, 前者对流范围更大、强度更强。Abstract: Using surface and high conventional observations, radar echo data and automatic weather station data of Yantai and Qingdao, two strong convections triggered by sea-breeze front in Shandong Peninsula on 14 July 2014 and 29 June 2009 are analyzed.The convection on 14 July 2014 occurs under circulation patterns of forward-tilting trough in the back of cold vortex, where dry and cold air at middle and upper layer is strong, warm and humid air at low layer is weak, leading to obvious static instability stratification and moderate convective available potential energy.The vertical wind shear is from weak to moderate, therefore the duration of supercell is short, and the range of hail is small.The convection on 29 June 2009 appears under circulation patterns of a typical northeast cold vortex, and strong vertical wind shear is a principal factor in the maintenance of supercell.Sea-breeze front, gust front and convergence line of surface are triggering systems.The high convective available potential energy, temperature and pseudo equivalent potential temperature difference between 850 hPa and 500 hPa, average wind speed of storm bearing layer, wind indices, and potential downside indices are indicative to the intensity of convection.Both processes have supercell storms, showing similar echo characteristics, such as hanging strong echoes, weak echoes regions, echo pendency, hook echoes and mesocyclones.The difference is that there is a strong mesocyclone on 29 June 2009, while the mesocyclone on 14 July 2014 is much weaker, so the former has a larger convection range and stronger intensity.The collision process between sea-breeze front and gust front enhances the mesocyclone, and when one factor weakens the mesocyclone weakens too.Two hail processes appear in the decline phase of cell top and echo top, maximum period of a storm with maximum reflectivity.The strong radar echoes over 50 dBZ in both processes extend to much higher than the height of -20℃.Lower melting level, suitable height of 0℃, thick depth of negative temperature layer are important to large hails.In addition, the formation period of large hails are in the period of low base height, deep thickness, severe rotation intensity of mesocyclone and is simultaneous with the strong period of mesocyclone.Therefore, the size of hail is related to base height, thickness, and rotation intensity of mesocyclone.Supercell storms of two processes occur to storms of the sea-breeze front which is close to the mountains.The stronger uplift triggering caused by combination of terrain and sea-breeze front is critical to strengthen original convective storms and evolve into supercell storms.
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Key words:
- sea-breeze front;
- gust front;
- supercell;
- terrain triggering
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图 1 2014年7月14日08:00(a)和2009年6月29日08:00(b)500 hPa天气图
(叠加850 hPa槽线, 红色圆圈处为冰雹发生区)
Fig. 1 500 hPa analysis at 0800 BT 14 Jul 2014(a) and 0800 BT 29 Jun 2009(b)
(superimposed 850 hPa trough, the red circle denotes hail area)
图 2 2014年7月14日14:00(a)和2009年6月29日14:00(b)地面风场实况
(黑色虚线为地面辐合线, 橘色虚线为海风锋位置)
Fig. 2 The surface wind observation at 1400 BT 14 Jul 2014(a) and 1400 BT 29 Jun 2009(b)
(the black dotted line denotes convergence line of surface, the orange dotted line denotes sea-breeze front)
图 3 2014年7月14日烟台雷达回波
(a)11:04 0.5°仰角反射率因子, (b)13:22 0.5°仰角反射率因子, (c)13:46 0.5°仰角反射率因子,
(d)15:26 6.2°仰角反射率因子, (e)15:20 4.3°仰角径向速度, (f)15:36 10.0°仰角径向速度Fig. 3 Refelectivity and radial velocity of Yantai radar on 14 Jul 2014
(a)reflectivity of 0.5° elevation at 1104 BT, (b)reflectivity of 0.5° elevation at 1322 BT,
(c)reflectivity of 0.5° elevation at 1346 BT, (d)reflectivity of 6.2° elevation at 1526 BT,
(e)radial velocity of 4.3° elevation at 1520 BT, (f)radial velocity of 10.0° elevation at 1536 BT
图 4 2009年6月29日青岛雷达回波
(a)13:56 0.5°仰角反射率因子, (b)14:33 0.5°仰角反射率因子, (c)15:46 0.5°仰角反射率因子,
(d)15:52 9.9°仰角反射率因子, (e)15:34 9.9°仰角径向速度, (f)15:46 0.5°仰角径向速度Fig. 4 Refelectivity and radial velocity of Qingdao radar on 29 Jun 2009
(a)reflectivity of 0.5° elevation at 1356 BT, (b)reflectivity of 0.5° elevation at 1433 BT,
(c)reflectivity of 0.5° elevation at 1546 BT, (d)reflectivity of 9.9° elevation at 1552 BT,
(e)radial velocity of 9.9° elevation at 1534 BT, (f)radial velocity of 0.5° elevation at 1546 BT
图 5 2014年7月14日(a)和2009年6月29日(b)回波顶高、风暴单体高度及最大反射率因子演变
Fig. 5 Temporal evolution of echo top, storm with cell top and maximum reflectivity on 14 Jul 2014(a) and 29 Jun 2009(b)
图 6 2014年7月14日(a)和2009年6月29日(b)中气旋底高、中气旋顶高、最大切变及所在高度演变趋势
Fig. 6 Temporal evolution of base height, top height, maximum shear and the height of maximum shear with mesocyclone on 14 Jul 2014(a) and 29 Jun 2009(b)
表 1 青岛站探空要素
Table 1 Sounding elements at Qingdao Station
探空要素 2014-07-14T08:00 2014-07-14T14:00 2009-06-29T08:00 2009-06-29T14:00 850 hPa与500 hPa 温度差/℃ 29 26 850 hPa与500 hPa假相当位温之差/K 9 15 11 20 对流有效位能/(J·kg-1) 230 1800 170 1300 抬升凝结高度/km 829 950 959 945 0～6 km风矢量差/(m·s-1) 11.4 12.5 21.7 21.1 风暴承载层平均风速/(m·s-1) 12.4 18.3 大风指数/(m·s-1) 28 32 潜在下冲指数 4.2 3.2 抬升指数/℃ -0.5 -5.7 -1.4 -1.4 沙氏指数/℃ -1.4 -1.2 -2.0 -1.8 
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表 2 青岛站高度和湿度条件
Table 2 Height and humidity conditions at Qingdao Station
探空要素 2014-07-14T08:00 2014-07-14T14:00 2009-06-29T08:00 2009-06-29T14:00 地面和850 hPa温度露点差平均值/℃ 6 6 2 2 对流层中上层干空气强度/℃ 19 32 0℃层高度/km 4.1 4.6 -20℃层高度/km 7.1 7.8 融化层高度/km 3.4 2.95 地面露点温度/℃ 19 22 23 23
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