Impact of ocean model resolution on CCSM climate simulations

• Published in: Climate Dynamics
• Other Authors: Kirtman, Ben (author), Bitz, Cecilia (author), Bryan, Frank (author), Collins, William (author), Dennis, John (author), Hearn, Nathan (author), Kinter, James (author), Loft, Richard (author), Rousset, Clement (author), Siqueira, Leo (author), Stan, Christiana (author), Tomas, Robert (author), Vertenstein, Mariana (author)
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer 2012
• Subjects: Arctic; Southern Ocean; North Atlantic; Sea ice
• Online Access: http://nldr.library.ucar.edu/repository/collections/OSGC-000-000-011-373; https://doi.org/10.1007/s00382-012-1500-3

The current literature provides compelling evidence suggesting that an eddy-resolving (as opposed to eddy-permitting or eddy-parameterized) ocean component model will significantly impact the simulation of the large-scale climate, although this has not been fully tested to date in multi-decadal global coupled climate simulations. The purpose of this paper is to examine how resolved ocean fronts and eddies impact the simulation of large-scale climate. The model used for this study is the NCAR Community Climate System Model version 3.5 (CCSM3.5)—the forerunner to CCSM4. Two experiments are reported here. The control experiment is a 155-year present-day climate simulation using a 0.5° atmosphere component (zonal resolution 0.625 meridional resolution 0.5°; land surface component at the same resolution) coupled to ocean and sea-ice components with zonal resolution of 1.2° and meridional resolution varying from 0.27° at the equator to 0.54° in the mid-latitudes. The second simulation uses the same atmospheric and land-surface models coupled to eddy-resolving 0.1° ocean and sea-ice component models. The simulations are compared in terms of how the representation of smaller scale features in the time mean ocean circulation and ocean eddies impact the mean and variable climate. In terms of the global mean surface temperature, the enhanced ocean resolution leads to a ubiquitous surface warming with a global mean surface temperature increase of about 0.2 °C relative to the control. The warming is largest in the Arctic and regions of strong ocean fronts and ocean eddy activity (i.e., Southern Ocean, western boundary currents). The Arctic warming is associated with significant losses of sea-ice in the high-resolution simulation. The sea surface temperature gradients in the North Atlantic, in particular, are better resolved in the high-resolution model leading to significantly sharper temperature gradients and associated large-scale shifts in the rainfall. In the extra-tropics, the interannual temperature variability is ...