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Strengthening of the Walker circulation under globalwarming in an aqua-planet general circulation model simulation |
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| Authors: | Tim Li Lei Zhang Hiroyuki Murakami |
| Institution: | 1. AORC/IPRC and Department of Atmospheric Sciences, University of Hawaii, 2525 Correa Rd., Honolulu, HI, 96822, USA 2. International Laboratory on Climate and Environment Change and Key Laboratory of Meteorological Disaster, Nanjing University of Information Science and Technology, Nanjing, 210044, China 3. Climate Research Department, Meteorological Research Institute, Tsukuboda, Ibaraki, 305-0052, Japan |
| Abstract: | Most climate models project a weakening of the Walker circulation under global warming scenarios. It is argued, based on a global averaged moisture budget, that this weakening can be attributed to a slower rate of rainfall increase compared to that of moisture increase, which leads to a decrease in ascending motion. Through an idealized aqua-planet simulation in which a zonal wavenumber-1 SST distribution is prescribed along the equator, we find that the Walker circulation is strengthened under a uniform 2-K SST warming, even though the global mean rainfall-moisture relationship remains the same. Further diagnosis shows that the ascending branch of the Walker cell is enhanced in the upper troposphere but weakened in the lower troposphere. As a result, a "double-cell" circulation change pattern with a clockwise (anti-clockwise) circulation anomaly in the upper (lower) troposphere forms, and the upper tropospheric circulation change dominates. The mechanism for the formation of the "double cell" circulation pattern is attributed to a larger (smaller) rate of increase of diabatic heating than static stability in the upper (lower) troposphere. The result indicates that the future change of the Walker circulation cannot simply be interpreted based on a global mean moisture budget argument. |
| Keywords: | Walker circulation global warming aqua-planet simulation |
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