The structure of low frequency phenomena in the tropics and its interaction with the extratropics |
| |
| Authors: | Peter J Webster Min Dong |
| |
| Institution: | Department of Meteorology, The Pennsylvania State University, PA 16802 USA,Academy of Meteorological Science, State Meteorological Administration, Beijing 100081, PRC |
| |
| Abstract: | The structure of planetary scale low frequency phenomena in the tropics is studied, and an attempt is made to determine its
influence and interactions with phenomena at higher latitudes.
In the tropics, it is found that the majority of the variance in the zonal wind structure is made up in wave numbers 1 and
2. During warm events in the Pacific Ocean, when the Southern Oscillation Index is negative, almost all of the variance resides
in the gravest mode which undergoes a 40° eastward phase shift. Meanwhile, the second logitudinal mode almost disappears.
On the other hand, the meridional wind field possesses maximum amplitude at higher wave numbers. However, near the equator,the
amplitude is small with extreme values occurring in the subtropics. The difference in scale and the location of extrema of
the meridional and zonal wind components indicate that the tropical atmosphere is responding to two different driving mechanisms.
Correlation analyses between variations of the zonal wind at reference points along the equator with variations of component
elsewhere show that there are strong logitudinal connections. The strongest correlations between the tropics and higher latitudes
exist in the region of the equatorial westerlies. In fact, stronger correlations occur between variations in U anywhere along
the equator and the middle latitudes to the north and south of the equatorial westerlies than to the latitudes immediately
to the north and south of the reference points. We interpret this “remote” correlation pattern as indicating a two-stage teleconnection
process which emphasizes the importance of the equatorial tropical westerlies of the Pacific Ocean as a “corridor” of communication
between the low and high latitudes. The regionality of the correlations confirms, to some extent, recent theoretical development
regarding trapped equatorial modes. Finally, time lagged correlations from plus and minus six months between variations of
U and OLR indicate that the interactions between the extratropics and low latitudes possess an organized sequence. The extratropical
influence appears to propagate into the tropics followed by an eastward propagation along the equator. Finally, a propagation
from the tropics to the extratropics in the upper troposphere occurs in the eastern Pacific Ocean. The time-lagged correlation
sequence does not appear to be symmetric about the equator. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
| 点击此处可从《大气科学进展》浏览原始摘要信息 |
| 点击此处可从《大气科学进展》下载免费的PDF全文 |
|
