The driving of baroclinic anomalies at different timescales

Abstract

This work investigates the internal variability of zonal-mean baroclinicity over the Southern Hemisphere midlatitudes. The first two leading modes describe a meridional baroclinicity shift and a sharpening/broadening of baroclinicity, with the shift becoming more dominant at low frequency. The lifecycles of the baroclinic anomalies, estimated by means of lagged regression analysis, are qualitatively different depending on the frequency range. At high frequency, the zonal-mean baroclinicity simply responds to the fast eddy heat flux forcing. At low frequency, the baroclinicity shift is forced by the eddy momentum flux through an eddy driven mean meridional circulation and damped diabatically. The meridional eddy heat flux by planetary scale eddies also contributes to the low-frequency shift but the synoptic eddy heat flux behaves diffusively and damps the baroclinicity anomalies at low frequency. Copyright 2011 by the American Geophysical Union.