Asymmetry in the seasonal cycle of zonal-mean surface air temperature

The asymmetry varies spatially, with the cooling season being similar to 40 days shorter than the warming season in the subtropics and the warming season being similar to 100 days shorter than the cooling season at the poles. Furthermore, the asymmetry differs between the Northern Hemisphere and the Southern Hemisphere.

Here, we show that these observed features are broadly captured in a simple model for the evolution of temperature forced by realistic insolation. The model suggests that Earth's orbital eccentricity largely determines the hemispheric contrast, and obliquity broadly dictates the meridional structure. Clouds, atmospheric heat flux convergence, and time-invariant effective surface heat capacity have minimal impacts on seasonal asymmetry.