Influence of baroclinic eddies on the Hadley cell edge

The Hadley cell (HC) is a thermally direct circulation in the tropics that transports heat from the tropics to the mid-latitudes. HC is known as the primary cause of subtropical desert formation, and with the recent observation of poleward shift of both the HC and desert regions, extensive studies has been made to understand its formation. The most foundational theory on the HC was proposed by Held and Hou (1980). This theory pinpointed the importance of angular momentum conservation and energy flux balance, while providing approximations for the edge and intensity of the HC. However, it did not consider the influence of baroclinic eddies. By extending this theory, the present study incorporates eddy heat fluxes and changes of adiabatic processes induced by eddy momentum fluxes in the subtropical upper troposphere into the energy flux balance HC dynamics. It is proposed that HC contracts when losing heat and expands when gaining heat due to thermal interactions with baroclinic eddies. This finding is verified through a series of dynamical core model experiments with varying baroclinicity.