Quantifying contributions to polar warming amplification in an idealized coupled general circulation model |
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Authors: | Jianhua Lu Ming Cai |
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Institution: | (1) Department of Meteorology, Florida State University, Tallahassee, FL 32306, USA; |
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Abstract: | An idealized coupled general circulation model is used to demonstrate that the surface warming due to the doubling of CO2 can still be stronger in high latitudes than in low latitudes even without the negative evaporation feedback in low latitudes
and positive ice-albedo feedback in high latitudes, as well as without the poleward latent heat transport. The new climate
feedback analysis method formulated in Lu and Cai (Clim Dyn 32:873–885, 2009) is used to isolate contributions from both radiative and non-radiative feedback processes to the total temperature change
obtained with the coupled GCM. These partial temperature changes are additive and their sum is convergent to the total temperature
change. The radiative energy flux perturbations due to the doubling of CO2 and water vapor feedback lead to a stronger warming in low latitudes than in high latitudes at the surface and throughout
the entire troposphere. In the vertical, the temperature changes due to the doubling of CO2 and water vapor feedback are maximum near the surface and decrease with height at all latitudes. The simultaneous warming
reduction in low latitudes and amplification in high latitudes by the enhanced poleward dry static energy transport reverses
the poleward decreasing warming pattern at the surface and in the lower troposphere, but it is not able to do so in the upper
troposphere. The enhanced vertical moist convection in the tropics acts to amplify the warming in the upper troposphere at
an expense of reducing the warming in the lower troposphere and surface warming in the tropics. As a result, the final warming
pattern shows the co-existence of a reduction of the meridional temperature gradient at the surface and in the lower troposphere
with an increase of the meridional temperature gradient in the upper troposphere. In the tropics, the total warming in the
upper troposphere is stronger than the surface warming. |
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