92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Tuesday, 24 January 2012: 2:15 PM
Analysis of the Tropical Vorticity Budget
Room 355 (New Orleans Convention Center )
Ricardo M. Fonseca, Portugal; and B. J. Hoskins and M. Blackburn

Analysis of the vorticity budget in the tropics showed the vorticity forcing to be associated with the vertical mixing of horizontal momentum in towering cumulus, a process known as cumulus momentum transport, and with the transient effect of tropical convection. A simple parameterisation of the momentum source associated with convection was introduced in the IGCM, a dry general circulation model of intermediate complexity. The wind tendencies obtained with this scheme were compared with the forecast tendencies from the more complex scheme in the ECMWF model used for the YOTC analyses and forecasts. It was found that the simple scheme gives wind tendencies that are similar in both phase and amplitude to the forecast tendencies. When the scheme is applied in the model there is a damping of the local response to a tropical heating anomaly and also a change in the remote response. Fluctuations in the amplitude of tropical heating anomalies can be important for the tropical and extra-tropical mean flows, in particular if on longer time-scales. These processes were found to contribute significantly to the vorticity balance and must be accounted for in idealized models and diagnostic calculations. To further stress their importance to the tropical and extra-tropical flows they were applied to an extreme season in Europe, summer 2007.

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