闽中北一次罕见强对流天气不稳定触发机制分析

利用NCEP再分析资料,对2007年4月1日福建省一次致灾天气过程成因进行分析。结果表明,这次强对流天气过程是地面锋前急流暖区内午后对流雷暴单体发展造成的。中高层的冷平流侵入对该次强对流天气的发生起主要触发作用。θse的倾斜锋区容易出现涡度的倾斜发展,使得对流层中层存在大量的潜热释放,同时有利于中层位涡的下传,从而对强对流区低空涡度的发展和维持起了重要贡献,有利于雷暴的发展和维持。在强对流发生区域对流层中低层出现了类似重力波的中尺度的波列分布,同时散度上也反映了上升运动和下沉运动相间的波动特征。对流层中下层西风扰动、低空和对流层中上层的南风扰动,对强对流天气有重要贡献,对流层顶的东风扰动以及辐散作用加强了垂直运动的发展。强的垂直风切变是该次强对流天气发生的有利条件。

Diagnostic Analysis on an Infrequent Disaster-caused Hail Process in Middle-northern Fujian Province

Using NCEP reanalysis data,the genesis mechanism for a severe convective weather event,which happened in Fujian Province on April 4,2007,was analyzed.The result showed that this process was developed from convective thunderstorm cell in jet warm sector of surface front at afternoon.The invasion of cold advection on middle-high layers was major trigger mechanism to this process.The inclined development of vorticity often occured in tilt frontal zone of θse,which induced a large amount of latent heat released on middle layer of troposphere.Meanwhile,it was good for potential vorticity in middle layer to download,and had a significant contribution to the development and maintenance of low layers vorticity in severe convective area.Then it was favorable for the development and maintenance of thunderstorm.There were mesoscale wavetrains,which were similar to gravity wave,in middle-low layers of troposphere in severe convective area.At the same time,divergence also showed the wave characteristic between ascending and descending motions.As a result,inertia-gravity wave was one of the possible trigger mechanism to this severe convective weather event.Westerly disturbance in middle-low layers of troposphere,southerly disturbance in low air and middle-high layers of troposphere made an important contribution to this process.Easterly disturbance in tropopause and divergence effect on top of severe convective storm strengthened the development of vertical motion.Strong vertical wind shear was favorable condition to the happening of this severe convective weather event.