The Partitioning of Poleward Heat Transport between the Atmosphere and Ocean

Abstract

Abstract Observations of the poleward heat transport of the earth (H) suggest that the atmosphere is the primary transporting agent poleward of 30°, that oceanic (HO) and atmospheric (HA) contributions are comparable in the tropical belt, and that ocean transport dominates in the deep Tropics. To study the partition we express the ratio HA/HO aswhere Ψ (with subscripts A and O denoting atmosphere and ocean, respectively) is the meridional mass transport within θ layers (moist potential temperature for the atmosphere, potential temperature for the ocean), and CΔθ (C being the specific heat) is the change in energy across the circulation defined by Ψ. It is argued here that the observed partitioning of heat transport between the atmosphere and ocean is a robust feature of the earth's climate and reflects two limits: (i) dominance of atmospheric mass transport in mid-to-high latitudes (ΨA ≫ ΨO with CAΔθA ∼ COΔθO and hence HA/HO ≫ 1) and (ii) dominance of oceanic energy contrast in the Tropics (COΔθO ≫ CAΔθA with ΨA ∼ ΨO and hence HA/HO ≪ 1). Motivated by simple dynamical arguments, these ideas are illustrated through diagnosis of atmospheric reanalyses, long simulations of an ocean model, and a coupled atmosphere–ocean model of intermediate complexity.