When and where do Radiative-Convective and Radiative-Advective Equilibrium regimes occur on modern Earth?

Abstract:

Conceptual models of an atmospheric column provide a basis to understand the vertical temperature profile and its response to climate change. Specifically, Radiative-Convective Equilibrium (RCE) and Radiative-Advective Equilibrium (RAE) are the standard idealized models for investigating tropical and polar climate change, respectively. Currently we do not have a complete understanding of the spatio-temporal structure of RCE and RAE. Here we use the vertically-integrated Moist Static Energy budget to define a non-dimensional number that quantifies when and where RCE and RAE are approximately satisfied in observations and models. We find RCE exists year-round in the deep tropics and in the northern midlatitudes during summertime. RAE exists year-round poleward of ~60 degrees latitude. We show the observed stratification in RCE and RAE regimes are consistent with a moist adiabatic and stable near-surface temperature profile, respectively. Finally, we vary the mixed layer depth in idealized aquaplanet model simulations with thermodynamic sea ice to test the following hypotheses: 1) the RCE regime occurs during midlatitude summer for land-like (small heat capacity) surface conditions and 2) the equatorward edge of the RAE regime is determined by the sea ice edge.