资源环境科技发展态势分析平台

The impacts of Asian orography on the wintertime atmospheric circulation over the Pacific are explored using altered-orography, semi-idealized, general circulation model experiments. The latitude of orography is found to be far more important than height. The Mongolian Plateau and nearby mountain ranges, centered at similar to 488 degrees N, have an impact on the upper-level wintertime jet stream that is approximately 4 times greater than that of the larger and taller Tibetan Plateau and Himalayas to the south. Key contributing factors to the importance of the Mongolian mountains are latitudinal variations in the meridional potential vorticity gradient and the strength of the impinging wind-both of which determine the amplitude of the atmospheric response-and the structure of the atmosphere, which influences the spatial pattern of the downstream response. Interestingly, while the Mongolian mountains produce a larger response than the Tibetan Plateau in Northern Hemisphere winter, in April-June the response from the Tibetan Plateau predominates. This result holds in two different general circulation models. In experiments with idealized orography, varying the plateau latitude by 20 degrees, from 43 degrees to 63 degrees N, changes the response amplitude by a factor of 2, with a maximum response for orography between 48 degrees and 53 degrees N, comparable to the Mongolian mountains. In these idealized experiments, the latitude of the maximum wintertime jet increase changes by only similar to 6 degrees. It is proposed that this nearly invariant spatial response pattern is due to variations in the stationary wavenumber with latitude leading to differences in the zonal versus meridional wave propagation.