Monday, 10 January 2005
Response of the wintertime sea level pressure with A0-like pattern to the global warming — Implication of stratospheric origin
The Arctic Oscillation (AO) is the most dominant variability in the northern hemisphere atmospheric circulation, and its change in response to the global warming is attracting many concerns. A global warming scenario experiment is performed with a coupled atmosphere-ocean GCM. In the experiment, the northern wintertime sea level pressure exhibits a long-term trend with a pattern similar to the positive phase of AO. The associated meridional-vertical structure of zonal wind reveals an intensification at the midlatitude lower stratosphere, which shares a feature with the month-to-month AO as an internal variability of the model, although the vertical structure of temperature change is different in many aspects. In response to the surface warming, the enhanced tropical convective activity leads to a warming of tropical upper troposphere and an upward shift of the tropopause height. In the stratosphere, on the other hand, the temperature decreases due to radiative cooling by the increased greenhouse gases. This structure of diabatic heating change increases the poleward geopotential height gradient at the midlatitude, and intensifies zonal wind in the lower stratosphere. An experiment with a momentum flux forcing in the midlatitude stratosphere with the same model exhibits a sea level pressure pattern similar to that in the global warming experiment. It is implied that the change in stratospheric zonal wind influences on the tropospheric circulation through changes in wave propagation and coherent meridional circulation.