The Association between Latitudinal Temperature Gradient and Eddy Transport. Part I: Transport of Sensible Heat in Winter

Abstract

When the total eddy transport of sensible heat in middle latitudes of the Northern Hemisphere increases in winter, the zonally averaged temperature gradient in the subtropics tends to increase, while the temperature gradient decreases in the same latitude as, and north of, the given total eddy flux. This effect is associated mainly with the flux in the quasi-stationary or mean waves. In agreement with this relationship between temperature gradient and heat transport, the correlation between the total eddy flux divergence and zonally averaged temperature in middle latitudes is strongly negative; and the main contribution to this negative correlation also comes from the quasi-stationary eddies. When the mean-eddy flux increases at middle latitudes, the transient-eddy flux tends to decrease over the region of weaker gradients to the north of the stronger mean-eddy flux and to increase to the south of it; and conversely when the mean-eddy flux weakens. From the association between total eddy transport and temperature gradients it follows that the gradients at lower latitudes are negatively correlated with those at higher latitudes. In the Southern Hemisphere, where the quasi-stationary eddies in temperate latitudes transport little sensible heat, the relationship between total eddy flux and zonally averaged temperature gradient is determined principally by the transient-eddy flux. All the associations above refer to seasonal averages.