华北区域冰雹天气分型及云系特征

Classification and Satellite Nephogram Features of Hail Weather in North China

  • 摘要: 基于地面加密观测资料、FY-2E静止气象卫星观测资料和NCEP分析资料,选取2010—2012年华北区域内27次冰雹过程,按大气环流背景、主要影响系统和云系的云型特征等将其分为冷涡云系尾部型、低涡槽前型和偏北气流控制型3种类型。分析结果表明:3种天气型下冰雹对流云系特征存在差异,但90%以上的冰雹过程发生在对流云团的快速发展阶段中,降雹集中出现于准圆形或椭圆形对流云团边缘或带状对流云系的传播前沿区域,对应于云顶亮温梯度的大值区。在掌握背景环境的前提下,综合分析红外图像中对流系统的发展演变、水汽图像暗带和暗区变化等信息,对冰雹的监测和预警有一定的参考价值。定量统计分析表明,大的亮温梯度值 (不低于8 ℃/0.05°) 是辅助判断冰雹能否发生的重要参量,而当冰雹云同时具备低云顶亮温和大亮温梯度的情况下,更有利于大于10 mm大冰雹的发生。

     

    Abstract: Based on conventional observations, automatic weather station data, geostationary satellite data and NCEP FNL data, meso-scale features of 27 hail processes occurred over Northern China during 2010-2012 are analyzed. According to synoptic circulation and cloud characteristics, these hail processes are divided into three types.The first type of hail convective storm is often embedded in the westerly trough of cold vortex system. The place where the severe convective storms initiated is frequently on the rear of the cloud band corresponding to the synoptic system. The cold front provides a strong lifting for convective initiation, while the anticyclone dry air intrusion triggers the intensive development of the hail storm. Whenever the water vapor content is plenty, heavy rainfall can also occur.The hail shooting zone of the second type convective storm is in the front of the cold vortex. The range of affected area is highly related to the southward movement of the cold vortex system. The front system often presents a forward-tilting structure, which is the main characteristic of this type of hail convective storm. The middle layer cold air mass become superimposed above 850 hPa warm ridge, which causes a wide range of potential instability, and also a continuous hail shooting weather, accompany with heavy rainfall in North China. The life span of the convective system is as long as 10 to 16 hours. The third type of hail convective storm generally occurs in a stable synoptic background, which is different from the other two. The hail storm initiates within the cold air mass, while the northerly air stream dominates the upper layer. Due to the poor moisture condition, the main disaster is hail and wind gale rather than short-during heavy rainfall. The short-wave trough at 500 hPa and the weak convective instability in the afternoon locally may be the cause for this kind of convective storm, and it is still difficult to forecast.On satellite-based (infrared and water vapor) images, over 90% of hail events produce hail when the convective storm growing rapidly. The main hail shooting zone is near the edge of a storm propagation frontal side, corresponding to a large gradient of TBB area in infrared image. The convective storm with both the low TBB (≤-40 ℃) and large gradient of TBB (≥8 ℃/0.05°) features seems an important threshold for short-range forecasting a bigger hail stone.

     

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