THE SECULAR TREND VARIATIONS AND ABRUPT CHANGE OF NORTHERN 500 hPa GEOPOTENTIAL HEIGHT
CHEN Hui
Shi Neng
WANG Yong-bo
Abstract：The trends and abrupt variations of Northern hemisphere (NH) 500 hPa seasonal geopotential height are examined using the data for the period 195l～1998. Evidence suggests that low (high) latitude 500 hPa geopotential height displays a remarkably positive (negative) trend; the positive anomaly of the height is maintained over NW Africa, the western Mediterranean Sea and northern North Africa, mid-Pacific at lower latitudes, Lake Baikal and area to the east and NW North America; the height drops significantly over the Aleutians and North pacific, the area to the south of the Greenland and NE North America and the sector to the north of the Arabian sea. Further, analysis of abrupt change shows that the 500 hPa circulations experience noticeable sudden change twice, once around the early 1960s and again in 1976, during which, however, the height exhibits great difference between the Pacific and Atlantic. In the first case it drops (rises) over the mid Atlantic at lower latitudes (NW Africa) in contrast to the height rise (drop) over the mid-Pacific at lower latitudes and Lake Baikal (the North Pacific) in the second abruptness. Statistical test indicates that in the 1976 case the low-latitude positive abrupt change is even more noticeable compared to the negative of the North pacific, thus representing a large-scale jumping event of the northern 500 hPa height.
Keywords：northern 500 hPa heighttrendinterdecadal variationabrupt change
Publication Date：2000-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：10( 272-281 )