GFDL's CM2 Global Coupled Climate Models. Part II: The Baseline Ocean Simulation

Abstract

The current generation of coupled climate models run at the Geophysical Fluid Dynamics Laboratory (GFDL) as part of the Climate Change Science Program contains ocean components that differ in almost every respect from those contained in previous generations of GFDL climate models. This paper summarizes the new physical features of the models and examines the simulations that they produce. Of the two new coupled climate model versions 2.1 (CM2.1) and 2.0 (CM2.0), the CM2.1 model represents a major improvement over CM2.0 in most of the major oceanic features examined, with strikingly lower drifts in hydrographic fields such as temperature and salinity, more realistic ventilation of the deep ocean, and currents that are closer to their observed values. Regional analysis of the differences between the models highlights the importance of wind stress in determining the circulation, particularly in the Southern Ocean. At present, major errors in both models are associated with Northern Hemisphere Mode Waters and outflows from overflows, particularly the Mediterranean Sea and Red Sea.

Changes in severe thunderstorm environment frequency during the 21st century caused by anthropogenically enhanced global radiative forcing

“…2 was applied only after some initial criteria are satisfied: CAPE Ն 100 J⅐kg Ϫ1 , V ជ 6  Ն V ជ 0 , and S06 Ն 5 m⅐s Ϫ1 . The preceding calculations also were made using integrations of three GCMs: GFDL CM2.1 (27,28), MPI ECHAM5 (29)(30)(31), and NCAR CCSM3 (32). The members of this limited ensemble were chosen based on the availability of the subdaily, 3D atmospheric data necessary to perform the CAPE, S06, and NDSEV calculations.…”

Global Warming Pattern Formation: Sea Surface Temperature and Rainfall*

“…Xie et al (2000) discuss interdecadal changes in North Pacific mode waters and show that they can be the dominant mechanism for ocean temperature variability in the central subtropical gyre. Gnanadesikan et al (2006) analyze a CM control simulation under constant GHG forcing and show that the model produces spuriously thick mode waters in the density range 26.5-27.5 s u , possibly associated with the southward recirculation of the model North Atlantic Current south of the British Isles. It is quite remarkable that changes in North Atlantic water mass ventilation have significant effects on SST in the subtropics.…”

The Role of Volcanic Activity in Climate and Global Change

“…The land cover type in the model uses a classification scheme with 10 different land cover types. The ocean model [73,74] has a nominal grid spacing of 1 in latitude and longitude, with meridional grid spacing decreasing in the tropics to 1/3 near the equator, and uses a tripolar grid to avoid polar filtering over the Arctic. The model has 50 vertical levels, including 22 levels with 10-m thickness each in the top 220 m. A novel aspect is the use of a true freshwater-flux boundary condition.…”