Terrestrial evaporation and global climate: lessons from Northland, a planet with a hemispheric continent

Abstract

From a climate perspective, land differs from the ocean in several fundamental physical ways, including albedo, heat capacity, amount of water storage, and differences in resistance to evaporation. These differences alter the surface energy and water budgets over land compared to ocean, with implications for both surface climate and atmospheric circulation. In this study, we use an idealized general circulation model (Isca) to explore the climate state of Northland, a planet with a northern land hemisphere and a southern ocean hemisphere. These idealized simulations are motivated by the asymmetry of continental distribution on the globe, with a greater concentration of landmasses in the northern hemisphere and a larger area of ocean in the southern hemisphere, and further illuminate the basic role that land-sea contrasts play in global atmospheric dynamics. We find a much larger seasonal cycle of temperature over land compared to ocean, as expected. The continent is seasonally wet in the tropics, has a subtropical desert, and a moist high-latitude ``swamp'', where moisture transported from the tropics accumulates. Decreasing the land albedo leads to warming. In contrast to past studies, suppressing evaporation from the land surface cools the climate, resulting from decreased atmospheric water vapor and reduced trapping of longwave radiation, which dominates over the warming associated with reduced evaporative cooling at the surface. The ITCZ in the Northland simulations extends farther polewards over both the land and ocean hemispheres than the ITCZ in an aquaplanet. Our results demonstrate the potential for land and hemispheric asymmetries in controlling the large-scale axisymmetric atmospheric circulation.