Improved Atmosphere-Ocean Coupled Simulation by Parameterizing Sub-Diurnal Scale Air-Sea Interactions

The atmosphere-ocean is a highly coupled system with significant diurnal and hourly variations. However, current coupled models usually lack sub-diurnal scale processes at the air-sea interface due to the finite vertical resolution for ocean discretization. Previous modeling studies showed that sub-diurnal scale air-sea interaction processes are important for ocean mixing. Here, by designing an integrated sub-diurnal parameterization (ISDP) scheme which combines different temperature profiling functions, we stress sub-diurnal air-sea interactions to better represent the local ocean mixing. This scheme has been implemented into two coupled models which contributed to the Climate Model Intercomparison Project (CMIP), referenced by the Intergovernmental Panel on Climate Change-Community Earth System Model and Coupled Model version 2. The results show that the ISDP scheme improves model simulations with better climatology and more realistic spectra, especially in the tropics and North Pacific Ocean. With the scheme, the tropical cold tongue bias is significantly relaxed by reducing the overestimation of ocean upper mixing, and the cold bias of North Pacific Ocean is reduced due to the improvement on currents and net heat fluxes. Our scheme may help better the simulation and prediction skills of coupled models when their horizontal resolution becomes fine but vertical resolution remains relatively coarse as it describes high-frequency air-sea interactions more realistically.