The Role of Diabatic Heating in Ferrel Cell Dynamics

Abstract:

The main features of the midlatitude circulation – the storm track, jet stream and Ferrel cell - are dynamically coupled. It is often assumed that the eddy-driven jet and the poleward eddy heat flux, which is a metric for the storm track, are both located between the ascending and descending branches of the Ferrel cell. In this study, we examine the necessary conditions for the collocation of the eddy-driven jet and eddy heat flux maxima, and focus in particular on the condition that diabatic heating is negligible in the midlatitude tropospheric heat budget. Using the JRA55 reanalysis data, we show that the diabatic heating rate is significant close to the center of the Ferrel cell during winter and at the ascending branch during summer in both hemispheres. We analyze the interannual variability of the latitudes of maximum eddy-driven jet and poleward eddy heat flux. The variability of the latitudinal separation between the eddy heat flux and the eddy-driven jet maxima is larger during winter than summer in both hemispheres. The large separation during winter in certain years is due partly to the tilted structure of the Ferrel cell, and partly to strong diabatic heating at the ascending branch of the Ferrel cell. These findings imply that the dry dynamics are insufficient in describing the connection between the basic features of the midlatitude circulation. It is expected that diabatic heating will increase in response to warming due to increased greenhouse gas concentration. Increased diabatic heating in the midlatitude mid-troposphere might affect the relative latitudinal shifts of the storm track and eddy-driven jet in response to climate change.