摘要
利用NCEP/NCAR逐日再分析资料,提出确定副高双脊线过程的定量指标,之后重点诊断研究1962年“二度梅”期间的双脊线过程。结果表明:1962年“二度梅”期间,由于季风槽的加强东伸,副高外围变形,在其南侧新生一条脊线,呈现双脊线结构。由此,提出亚洲季风槽的发展东移是副高双脊线形成的重要影响因子。分析表明,1962年的双脊线过程与1998年的双脊线过程相比,有同亦有异:两次双脊线过程与长江流域“二度梅”均有关联,但1998年双脊线过程结束后,北侧脊线消失,南侧脊线发展维持,使副高脊线异常偏南,造成“二度梅”的突然出现,而1962年双脊线过程结束后却是南侧脊线消失,北侧脊线维持并异常偏北,从而导致“二度梅”结束;在涡度场上,两次双脊线过程均有一高层对低层的“诱导”效应,同时500 hPa诱导生成的正涡度与低纬度北移而来的正涡度带打通合并、东伸,进而其两侧的负涡度带增强,形成双脊线。这些结果为西太平洋副热带高压双脊线的演变规律和机制的进一步研究提供了新的线索。
The NCEP/NCAR re.analysis data are employed to advance quantitative indicators for confirming the double ridges process of the Western Pacific Subtropical High （WPSH）. The process during the second Meiyu season in 1962 is diagnosed in this paper. The results suggest that, during the second Meiyu season in 1962, a new ridge is rebuilt in the southern part of WPSH, forming a double ridges process, because of the monsoon trough strengthening and extending eastward, making the WPSH distorting strongly. So the monsoon trough development and movement eastward is regarded as an important factor for the double ridges formation. It is indicated that there are both difference and sameness between the double ridges processes in 1962 and 1998： Both of them have essential role in the second Meiyu season of the Yangtze River valley, but in 1998 the northern （original） ridge gets weak and disappears, the southern ridge, in contrast, becomes strong and persists as a single WPSH ridge, causing the location of the WPSH ridge to be much more southward than its normal and an abrupt commencement of the second Meiyu season; in 1962 the southern ridge weakens and vanishes after several days＇ development, the northern （original） ridge then moves northward leading to an end of the second Meiyu season.
It is indicated that the two processes are different from each other on dynamics and thermodynamics. During the persistence period of the process, in terms of the northern ridge, in 1962 it lies to the south of the warm axis all the time and the corresponding ridge axis in the vertical circulation along 120°E also slopes northward all through, however, it coincides with the warm axis and the ridge axis is nearly in plumb in 1998; as to the southern ridge, in 1962 it is thin and not coherent in dynamics, and its relative humidity exceeds 70%, but in 1998 it is thick existing in the whole lower and middle troposphere, and it crosses through dry centers with ascending movement around. When the relative vorticity is concerned
出处
《大气科学》
CSCD
北大核心
2006年第4期682-692,共11页
Chinese Journal of Atmospheric Sciences
基金
国家自然科学基金资助项目40475021
40135020
40233037
关键词
西太平洋副热带高压
双脊线
二度梅
季风槽
the Western Pacific Subtropical High （WPSH）, double ridges, the second Meiyu season, monsoon trough
