Friction Torque Dynamics Associated with Intraseasonal Length-of-Day Variability

This investigation examines the dynamical processes that drive the anomalous friction torque associated with intraseasonal length-of-day fluctuations. Diagnostic analyses with National Centers for Environmental Protection– National Center for Atmospheric Research reanalysis and National Oceanic and Atmospheric Administration outgoing longwave radiation data are performed. The approach adopted is to use the mean meridional circulation (MMC) as a proxy for the friction torque, and then to examine the MMC that is driven both by eddy fluxes and zonal mean diabatic heating. The following simple picture emerges from this analyses. For the austral winter (May through September), the anomalous friction torque in both hemispheres is driven by anomalous zonal mean convection. For the boreal winter (November through March), the anomalous friction torque in the Northern Hemisphere is driven primarily by eddy fluxes, whereas in the Southern Hemisphere the anomalous friction torque is also driven by anomalous zonal mean convection. However, the dynamics associated with this convection for the Southern Hemisphere boreal winter may be rather subtle, as the results suggest that this convection may in turn be driven by eddies within the Northern Hemisphere.