AMS Forum: Climate Change Manifested by Changes in Weather


A Mass Circulation Paradigm for the Annular Mode Variability

Ming Cai, Florida State Univ., Tallahassee, FL; and R. -. C. Ren

This paper reports a diagnostics study of circulation anomalies in a semi-Lagrangian ?-PVLAT coordinate generated by following contours of daily potential vorticity (PV) field on isentropic (?) surfaces using the NCEP/NCAR reanalysis II dataset from 1979 to 2003. The leading EOF mode, which explains about 69% of the total variance of daily Northern Hemisphere PV anomalies in the ?-PVLAT coordinate and is highly correlated with the stratosphere Northern Annular Mode (NAM) index, is used to construct a composite life cycle of the NAM variability. The composite circulation anomalies of both signs propagate poleward in the stratosphere and equatorward in the troposphere with an average traveling time of 40-70 days from the equator to the pole. Accompanying with the meridional propagation, there exists a simultaneous downward propagation of circulation anomalies from the stratosphere to the troposphere in both the tropics and extratropics. A global mass circulation paradigm is proposed to explain the simultaneous meridional and vertical propagation of global circulation anomalies that appears to be responsible for the annular mode variability. The global mass circulation paradigm for the annular mode is analogous to the frontal circulation system for weather. We will discuss the role of the stratosphere bridge that links tropical thermal forcing and high-latitude circulation in winter season as well as its implications for climate predictions. .

Session 3, THORPEX Special Session: Impacts of Processes over the Tropical Pacific and Indian Oceans on Mid-Latitude Weather and Predictability
Wednesday, 17 January 2007, 1:30 PM-5:15 PM, 214A

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