中尺度低涡发展时高层流场特征及能量学研究

The Features of Flow Pattern in Upper Level Troposphere and Energy Conversion During the Development of Meso-Scale Low Vortex

本文通过对一次长江中游中尺度低涡的分析发现,在这类斜压性低涡发展时,低涡西侧冷区对流顶明显下降,在低涡区发生折叠现象.与大位涡值相联系的平流层空气从该处下沉至对流层,对流顶下陷比对流活动区对流顶高度变化要早且明显.中尺度涡旋发展所需要之动能主要取自辐散风动能,在对流层高层和低层这种正向转换最为清晰,而整个气柱中位能向辐散风动能转换,以支持它在涡旋发展过程中之消耗.但高层与低层的情况不同.在100hPa高空辐散风动能既支持了涡旋动能,又向总位能转换.分析表明,高层对流层流场在中尺度系统发展过程中是十分活跃的,必须引起足够的重视.

A case of heavy rain occurred in a baroclinic meso-low in the middle reaches of the Yangtze River is analyzed. The height of the tropopause in the colder sector of the vortex descends clearly when the tropopause folding occurs in that area during the development of the low. The stratospheric air with larger potential vorticity moves downward to the troposphere through the folding zone. The dropping of the tropopause in the colder sector is stronger and earlier than the lifting in warmer sector . The rotational component of kinetic energy (K) needed for the vortex development obtains mainly from divergence wind kinetic energy (Kx). The potential energy P in a whole air column in the heavy rain area transfers to Kx. In other words, the conversion function C(P, Kx) is positive in the whole air column as well as at lower levels. However, the situation seems different at 100 hPa that the divergent wind kinetic energy transfers both to K and P in the vortex region . The results indicate that the flow pattern in the upper troposphere plays an important role in the development of meso-low at lower levels.