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Abstract:
As a contribution towards improving the climate mean states of the atmosphere and the ocean in Earth System Models (ESMs), we compare several coupled simulations conducted with the Max Planck Institute for Meteorology Earth System Model (MPI-ESM) following the HighResMIP protocol. Our simulations allow to analyse the separate effects of increasing the horizontal resolution of the ocean (0.4° to 0.1°) and atmosphere (T127 to T255) submodels, and the effects of substituting the Pacanowski and Philander (PP) vertical ocean mixing scheme with the K-Profile Parameterization (KPP).
The results show clearly distinguishable effects from all three factors. The eddy-resolving ocean removes biases in the ocean interior and in the atmosphere. This leads to an important conclusion that ocean eddies have a major impact on the large-scale temperature distribution in the atmosphere, and on temperature and salinity distributions in the ocean. The near-surface wind forcing reduces with a T255 atmosphere and improves ocean mixed layer depths in both hemisphere. The reduced wind forcing further slows the Antarctic Circumpolar Current (ACC) and reduces the transport through Drake Passage to observed values. In the North Atlantic, however, it causes a slow down of the Atlantic Meridional Overturning Circulation (AMOC) due to a slower subpolar gyre, when the PP scheme is used. The KPP scheme causes stronger open-ocean convection that spins up the gyres and leads to a stronger and stable AMOC, when coupled to the T255 atmosphere, maintaining all the positive effects of a higher resolved atmosphere.
