ElNio夏季太平洋上空垂直环流特征及我国汛期降水

THE EFFECT OF EL NINO EVENT ON VERTICAL CIRCULATION OVER THE PACIFIC AND PRECIPITATION FOR THE RAINY SEASON IN CHINA

本文利用NCAR(美国国家大气研究中心)1976年太平洋各层风场资料,计算了0°—50°N,105°E—110°W范围内,7月850hPa,700hPa,500hPa,300hPa,250hPa和200hPa各层上的垂直运动,并与叶笃正等所作的太平洋上空夏季平均环流特征作比较得出:(1)常年Walker环流明显,而E1 Ni(?)o发生年热带西太平洋上升运动减弱,东太平洋空气下沉区变成了强上升区,Walker环流下沉区东移至110°W以东;(2)常年热带西太平洋Hadley环流不明显,沿160°E以东Hadley环流越来越清楚,呈向东递增的趋势,而E1 Ni(?)o年Hadley环流东西变化甚为复杂,Hadley环流的上升支并不在赤道附近,而移至10°N左右,明显较常年偏北,Hadley环流也变成自热带向副热带倾斜的环流圈;(3)E1 Ni(?)o发生年,夏季以淮河为中心的空气上升区变成下沉区,而37°N以北的华北地区仍是上升区,华北多雨,所以出现Ⅰ型降水。

In this paper, the data of NCAR's 1976 wind tields over the Pacific have been used, and after calculation and comparison the results showed that: (1) Walker circulation evidently exists in general years, but in El Nino year the air current's upward speed decreases over tropical western Pacific. The downward zone of Eastern Pacific becomes a strong upward air current, and the downward zone moves to the east up to about 110W. (2 ) In general years Hadley circulation is not evident in tropical western Pacific, but from 160°E to farther east, Hadley circulation becomes more evident, and in El Nino years Hadley circulation becomes complex, and moves to about 10°N, evidently slanting to the north than its general position. ( 3 ) In the summer of El Nino years, the zone of upward air current of the Huai river becomes a downward air current, but in the north (37°N) of China, it is still an upward zone, bringing unstable weather with rain.