A Total Flow Representation of Atmospheric Mass and Angular Momentum Circulations: Part I. Boreal Winter Mean State

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Thursday, 6 February 2014
Hall C3 (The Georgia World Congress Center )
Ming Cai, Florida State Univ., Tallahassee, FL; and C. S. shin

Following the theoretical framework of Johnson and his collaborators, we here report a comprehensive diagnostic analysis of diabatic and adiabatic mass and angular momentum fluxes and their sources/sinks in boreal winter using 32-year daily NCEP-NCAR reanalysis (1979-2010). The diagnosis is performed using instantaneous total flows before taking time and zonal average without decomposition of time mean and transient flows and separation of zonal mean and wavy flows. We put forward a conceptual model that substantiates Hadley's original view on the atmospheric general circulation. The conceptual model attempts qualitatively to explain 1) how diabatic heating/cooling is coupled with adiabatic mass transport and its companion angular momentum transport in the tropical Hadley cell; 2) how diabatic heating/cooling, adiabatic mass and its companion angular momentum transport and the pressure torque associated with westward titled waves are coupled in giving rise to the extratropical zonally asymmetric Hadley cell; 3) the origins of surface westerly in the extratropics and easterly in the tropics by considering the angular momentum circulation in conjunction with the mass circulation. Because the mass circulation cannot cause a net divergence of mass anywhere in long time mean and the Earth's angular momentum decreases towards the poles, the companion angular momentum transport in the equatorward cold air branch inevitably has to be divergent. The downward transfer of westerly angular momentum to the cold air branch by the pressure torque of westward tilted baroclinic waves dominates such divergence in the extratropics, explaining the prevailing surface westerly there. In the tropics and polar region where the meridional circulation is nearly zonally symmetric, the dominance of this divergence results in a surface easterly there.