Rodrigo Caballero, Timothy M Merlis 

We develop a novel single-column model of clear-sky radiative-advective equilibrium where advective heating is internally determined by relaxing the column temperature and humidity toward fixed midlatitude profiles, consistent with an air-mass transformation perspective. The model reproduces observed polar temperature and advective heating rate profiles, and also captures many of the climate-change responses found in climate models. Exploring the model's physics, we show that the surface-based temperature inversion develops by ceding energy downwards to the surface, which then radiates this energy to space; we name this the ``surface radiator fin'' effect. We use the model to address three outstanding questions regarding polar climate change: (i) What mechanisms control polar lapse-rate change? (ii) What determines the known compensation between changes in dry and moist energy transport? and (iii) What is the most physically consistent way to decompose forcing and feedbacks at the poles? In answer to these questions, we show that: (i) Three mechanisms control the lapse-rate response to warming: weakening of the surface radiator fin, increased radiative cooling by free-tropospheric water vapor emission, and relaxation toward the external profile anomaly; all three increase the lapse rate as climate warms. (ii) Compensation between dry and moist advective heating results from a delicate balance between changes in the boundary layer and the free troposphere, with no constraints imposing precise compensation. (iii) Remote advective influence on the poles should be considered a forcing, while lapse-rate and advective heating changes should not be treated as separate feedbacks but rather as part of the temperature feedback.