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Mesoscale convective systems (MCSs) are severe disaster-producing weather systems. Previous attempts of MCS census are made by examining infrared satellite imageries artificially, with subjectivity involved in the process unavoidably. This method is also inefficient and time-consuming. The disadvantages make it impossible to do MCS census over Asia and western Pacific region (AWPR) with an extended span of time, which is not favorable for gaining a deeper insight into these systems. In this paper, a fire-new automatic MCS identification (AMI) method is used to capture four categories of MCSs with different sizes and shapes from numerical satellite infrared data. 47,468 MCSs are identified over Asia and western Pacific region during the warm season (May to October) from 1995 to 2008. Based on this database, MCS characteristics such as shape, size, duration, velocity, geographical distribution, intermonthly variation, and lifecycle are studied. Results indicate that the number of linear MCSs is 2.5 times that of circular MCSs. The former is of a larger size while the latter is of a longer duration. The 500 hPa steering flow plays an important role in the MCS movement. MCSs tend to move faster after they reach the maximum extent. Four categories of MCS have similar characteristics of geographical distribution and intermonthly variation. Basically, MCSs are zonally distributed, with three zones weakening from south to north. The intermonthly variation of MCSs is related to the seasonal adjustment of the large-scale circulation. As to the MCSs over China, they have different lifecycle characteristics over different areas. MCSs over plateaus and hill areas, with only one peak in their lifecycle curves, tend to form in the afternoon, mature at nightfall, and dissipate at night. On the other hand, MCSs over plains, which have several peaks in their lifecycle curves, may form either in the afternoon or at night, whereas MCSs over the oceans tend to form at midnight. Affected by the sea-land breeze circulation, MCSs over coastal areas of Guangdong and Guangxi always come into being at about 1500 or 1600 (local time), while MCSs over the Sichuan Basin, affected by the mountain-valley breeze circulation, generally initiate nocturnally. 相似文献
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Single-Doppler Radar Observations of a High Precipitation Supercell Accompanying the 12 April 2003 Severe Squall Line in Fujian Province 下载免费PDF全文
In this study,single Doppler radar data were used to examine the structure and evolution of a high precipitation(HP) supercell embedded in a cold front near Jianyang,Fujian Province on 12 April 2003.The synoptic environment was characterized by high humidity at low levels,moderate CAPE(convective available potential energy;1601 J kg~(-1)),moderate wind shear(22 m s~(-1) in 0-5 km),and veering of the horizontal winds with height,similar to those HP supercells previously observed in midlatitudes.In additio... 相似文献
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淮河流域东北部一次异常特大暴雨的数值模拟研究 Ⅱ:
不稳定条件及其增强和维持机制分析 总被引:3,自引:1,他引:2
利用"淮河流域东北部一次异常特大暴雨的数值模拟研究Ⅰ"的数值模拟结果,分析了几种不稳定对流涡度矢量(CVV)与中尺度深湿对流系统之间的关系,并分析了不稳定条件的增强和维持机制,结果表明:(1)中低层对流不稳定是深湿对流系统发生的先决条件,由于低层存在辐合,使得周围湿空气向暴雨区集中,对流单体在暴雨区汇聚,且发生合并增强,台风左前方向暴雨区输送对流不稳定能量等,是使得暴雨区对流不稳定重新建立和加强的重要机制.(2)深湿对流系统的中低层不仅有对流不稳定,而且还有斜压不稳定、条件对称不稳定,而中高层必须有湿斜压不稳定和条件对称不稳定.深湿对流系统中高层西(北)侧为负MPV2柱,东(南)侧为正MPV2柱;(3)深湿对流系统中惯性不稳定柱与惯性稳定柱相间分布,西(南)侧为负CVV柱,东(北)侧为正CVV柱,负CVV柱对深湿对流起激发作用;(4)惯性不稳定、湿倾斜不稳定和条件不稳定产生强的倾斜式对流,而强的倾斜式上升运动加强了深对流系统北侧高层的南风分量,因深对流系统南侧低层出现补偿性下沉气流,因而低层南风加强,高低空急流中心的加强会进一步加强对流的发展,使得惯性不稳定、湿倾斜不稳定及条件不稳定增强和维持,这是一个正反馈过程.(5)在暴雨中心以东维持一顺切变环流,同时暴雨中心的浅对流单体吸收来自南方的水汽和不稳定能量,中尺度辐合线与β中尺度涡旋对对流单体起组织和增强作用,对流系统中辐合、辐散柱相间分布,强散度柱与强涡柱互伴互耦,都有利于形成中尺度深湿对流系统,使不稳定向纵深方向发展,从而使得不稳定得到增强和维持. 相似文献
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2011年6月23日沿淮强对流天气中尺度辐合特征模拟研究 总被引:2,自引:1,他引:1
利用常规地面、高空气象观测资料、安徽和江苏两省自动站观测资料、NCEP/NCAR再分析资料,对2011年6月23日江苏、安徽两省沿淮(简称沿淮)地区发生的一次强对流天气过程进行天气形势分析,并结合卫星、多普勒雷达资料进行综合分析,且运用中尺度数值模式WRF对本次过程进行数值模拟。结果表明:(1) 西南地区鞍型场中激发的对流单体东移使得强对流天气能够增强和维持;(2) 北方高空冷空气的下沉造成沿淮地区的雷雨大风;(3) 本次强对流天气过程中的对流单体来源路径有3条:一是西南地区鞍型场激发的对流单体沿高空西南气流向东北方向输送到沿淮地区,二是源于南海产生于副高边缘的对流单体沿偏南气流向北输送到沿淮地区,三是西北方向高空槽前产生的对流单体沿西北气流向沿淮地区集中;(4) 中低层切变线和地面辐合线对强对流系统起组织和加强作用。 相似文献