摘要
用H40°N-H65°N即40°N和65°N纬圈平均位势高度的差来定义西风指数,可以很好地反映温带地区西风的强弱。西风环流强的年份,北半球气温通常偏高,主要是中纬度大陆变暖明显,这可能与中高纬度西风强时,向北的经向热量输送也加强有关。在长期变化的趋势上,1950年代以前北半球偏暖时期的指数偏低,而偏冷时期的指数偏高。但近30多年来,伴随全球加速变暖,西风指数也持续加强,这是否与温室效应的加强有关还有待深入研究。
The dominant modes of northern hemispheric zonally-mean wind (u) and 500 hPa geopotential height in winter demonstrate two centers with opposite sign. Thus the zonal index can be defined as H40 °N-H65 °N or U35 °N?U55 °N, i.e., the difference in geopotential height (or zonal wind) between 40 °N and 65 °N (or between 35 °N and 55 °N). In this paper the zonal index of H40 °N-H65 °N is applied. This kind of zonal index correlate with westerly of 55 °N at 0.96. The anomalous variation of the westerly can impact the winter surface temperature significantly. During the high-index years, the northern continent becomes warmer and during the low-index years become colder. The changes in temperature are more significant over the middle-high latitudes. Correlation between the zonal index and the meridional heat flux show that there are more heat transporting to the higher latitudes through the intensified eddies activity with the stronger westerlies. On the interdecadal time scale, the temperature and zonal index vacillate out of phase before the 1950s, i.e., the low-index associate with warmer periods and high-index with colder periods. But during the last three decades, both the northern hemispheric mean temperature and zonal index demonstrate significant upward trends. Analysis indicates the increasing greenhouse effect may trigger the recent positive trend in zonal index.
出处
《热带气象学报》
CSCD
北大核心
2002年第2期104-110,共7页
Journal of Tropical Meteorology
基金
国家自然科学基金(40105007)
国家重点基础研究发展规划首批项目(G1998040900)资助
关键词
西风指数
变率
温度
zonal index
variability
temperature
