摘要
对1998年华南暴雨试验加密观测期间(IOP)5月23日强降水个例的数值模拟结果分析指出,锋面对于中尺度对流系统而言除了提供对流运动的触发机制外,两者之间还可能存在复杂的相互作用。华南前汛期中伴随对流活动的冷锋具有独特的垂直环流结构。它主要表现为暖湿气流不是沿锋面上滑,而是在冷锋前沿的对流雨团中直接上升到高空,锋面上方上滑的暖空气完全被对流雨团北侧的补偿性下沉气流所代替;而在锋后以及锋前暖区内均有对流活动发生的情况下,低空流入锋区前沿和锋区上方雨团的空气不是来自锋前暖区,而是来自锋后。对对流系统内部雨团进行的三维轨迹追踪也揭示出锋面上空对流雨团内存在一部分来自锋后并穿越锋区的上升气流。这是因为锋面并不是真正意义上的物质面,它只是大气温、湿属性有显著差别的界面,因此存在穿越锋区的运动并不是完全不可能发生的。在华南前汛期中,锋区两侧温度对比比通常意义上的锋面要小,这也是可能发生穿越锋面运动的原因之一,表明中尺度对流系统由于具有与梅雨锋在跨锋方向相类似的尺度而有可能对梅雨锋的流场结构发生影响。
Based on the results of the numerical simulation for a heavy rainfall case occurring on May 23, 1998 during the IOP period of HUAMEX, the relation of front-related vertical circulation with convection was investigated. In addition to the convection trigger mechanism provided by cold front, there is a possible interaction between cold front and MCS. In case convection occurs on front, the structure of vertical circulation on the cross section of front may change significantly. In stead of sliding upward along the slant front, the warm and wet stream in the MCS in front of the cold front ascents to the upper air directly. However, in case that there are MCSs occurring on both sides of the cold front simultaneously, there are stream coming from the rear of the cold front and penetrate it. The trajectory of the air mass from the convection also reveals the phenomena. These results reveal that the front is not an exact ‘material＇ surface as its definition. Actually, it is just an interface in atmosphere with significantly different temperature and moisture attributions. In the pre-flooding season in South China, the temperature difference is not so obvious as that of common sense, which could be regarded as a reason of the existence of the penetrating upstream of front. MCS should be able to affect the vertical stream structure of cold front due to its similar scale with that of front on cross-front direction.
出处
《气象学报》
CAS
CSCD
北大核心
2007年第5期785-791,共7页
Acta Meteorologica Sinica
基金
国家自然科学基金项目(40505020)
北京市科技新星计划A类(2006A02)
