Radiative and Dynamic Controls on Atmospheric Heat Transport

Abstract:

Atmospheric heat transport is an important piece of our climate system, yet we lack a complete theory for its magnitude or changes. Atmospheric dynamics and radiation play different roles in controlling the total atmospheric heat transport (AHT) and its partitioning into components associated with eddies and mean meridional circulations. This work focuses on understanding the roles of individual factors controlling AHT. We use idealized atmospheric global climate models to separate the relative roles of radiative-heating tendency, planetary rotation rate, and orography. We find that rotation rate controls the latitudinal extent of the Hadley cell and the planetary-scale heat transport efficiency of eddies. Both rotation rate and radiative tendency influence the strength of the Hadley cell and the strength of equator-to-pole energy differences that are important for AHT by eddies. These controls do not always operate independently and can reinforce or oppose each other.

In addition, we examine how the individual components of AHT, which each have strong spatial patterns, nonetheless sum to a total AHT that varies smoothly with latitude. We employ a novel framework to fix total AHT at climatological values, allowing for easier comparison of how AHT components sum to a smoothly varying total under different dynamical regimes. At slow rotation rates, the mean meridional circulation is most important in ensuring total AHT varies smoothly with latitude, while eddies are most important at rotation rates similar to, and faster than, our current climate. In instances where orography creates robust stationary eddies, there is a high degree of compensation between stationary and transient eddies, such that total AHT remains nearly constant.