The processes which drive the anomalous friction torque associated with intraseasonal (30-70 day) atmospheric angular momentum fluctuations are examined with NCEP-NCAR Reanalysis data. For this purpose, we first examine the relative angular momentum budget at the lowest sigma level in the Reanalysis model, followed by an examination of the eddy momentum flux, eddy heat flux, and diabatic heating anomalies regressed against the global angular momentum tendency. These quantities are then used as forcing terms in the quasi-geostrophic, elliptic partial differential equation for the mean meridional circulation.
It is found that the anomalous friction torque is driven by the anomalous Coriolis torque acting on the low level branch of the anomalous mean meridional circulation, rather than direct eddy forcing of the friction torque.
The inversion of the equation for the mean meridional circulation shows that the anomalous meridional circulation is primarily driven by both eddy momentum fluxes and diabatic heating, with eddy heat fluxes playing a negligible role. In midlatitudes and in the subtropics, the anomalous meridional circulation is directly driven by the eddy momentum fluxes, and in the deep tropics the anomalous meridional circulation is driven by diabatic heating. However, by assuming that diabatic heating is balanced by adiabatic cooling in the deep tropics, it is shown that the diabatic heating is indirectly driven by the eddy momentum fluxes.
Hypotheses are presented for which atmospheric dynamical processes drive the anomalous meridional circulation. Dominant processes involve 1) the interaction between a poleward propagating Rossby wavetrain and the climatological stationary eddies, and 2) storm track eddies which have been re-organized by the poleward propagating Rossby wavetrain.
Close window or click on previous window to return to the Conference Program.
12th Conference on Atmospheric and Oceanic Fluid Dynamics