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新论文介绍:Opposite annular responses of Northern and Southern Hemisphere to Indian Ocean warming

[发布日期: 2014-12-31 浏览量 857]

Atmospheric circulation changes during boreal winter of the second half of the 20th century exhibit a trend toward the positive polarity of both the Northern Hemisphere Annular Mode (NAM) and the Southern Hemisphere Annular Mode (SAM). This has occurred in concert with other trends in the climate system, most notably a warming of the Indian Ocean. This study explores whether the tropical Indian Ocean warming played a role in forcing these annular trends. Five different atmospheric general circulation models (AGCMs) are forced with an idealized, transient warming of Indian Ocean sea surface temperature anomalies (SSTA), the results of which indicate that the warming contributed to the annular trend in the Northern Hemisphere (NH) but offset the annular trend in the Southern Hemisphere (SH). The latter result implies that the Indian Ocean warming may have partly cancelled the influence of the stratospheric ozone depletion over the southern polar area which itself forced a trend toward the positive phase of the SAM. Diagnosis of the physical mechanisms for the annular responses indicates that the direct impact of the diabatic heating induced by the Indian Ocean warming does not account for the annular response in the extratropics. Instead, interactions between the forced stationary wave anomalies and transient eddies is key for the formation of annular structures.