Stratospheric response to global warming in the northern hemisphere winter

• Main Author: Hu, Z.
• Format: Report
• Language: English
• Published: 2001
• Subjects: polar night
• Online Access: http://hdl.handle.net/21.11116/0000-0005-9DB7-C; http://hdl.handle.net/21.11116/0000-0005-9DB9-A

Lower stratospheric climate response to global warming in the Northern Hemisphere winter was investigated by a transient greenhouse warming integration with the ECHAM4/OPYC3 coupled global climate model. The dynamics of the response was studied through analyses of kinetic energy of various wavenumbers, vertical propagation of planetary waves, and feedback between transient eddy activity and the zonal mean circulation. It is indicated that the zonal mean circulation, especially at high latitudes and subtropics, becomes stronger in the upper troposphere (300 hPa) than in the current climate, mainly associated with a significant intensification of the meridional temperature gradient. In the lower stratosphere (50 hPa), a cooling occurs with a stronger polar night jet. The kinetic energy in the upper troposphere decreases for wave number 2 and increases for wave number 1. The stratospheric cooling is further enhanced because of a reduction in the vertical wave energy propagation from the troposphere to the stratosphere, which is the result of the zonal mean wind and kinetic energy changes, thus acting as a positive feedback mechanism. In addition, transient eddy activity plays a positive role in the zonal mean wind change in the upper troposphere at increased greenhouse gas forcing.