Southern Hemisphere atmospheric circulation: role of teleconnections, sea surface temperatures, horizontal resolution, physical parameterizations and topography on the simulated climate in a Global Climate Model

SAURRAL, R.; CAMILLONI, I.; AMBRIZZI, T.

Noumea

Congreso; 10th International Conference on Southern Hemisphere Meteorology and Oceanography; 2012

American Meteorological Society y IRD

In this work the atmospheric climate model CAM was used to explore the role of different horizontal resolutions, physical parameterization schemes, sea surface temperature (SST) distributions and simulated teleconnection skills in the simulated climate of temperature and precipitation of the Southern Hemisphere. A series of simulations were performed to explore the role of the size of the grid mesh, varying it from about 2.8º to 1.4º. In another simulation the Andes Cordillera was removed to study up to what extent the representation of this topographic barrier determines the horizontal moisture flux fields in the atmospheric model and their impacts on precipitation over South America in particular. SST representation and influence on the Southern Hemisphere circulation were assessed by performing three different simulations. In the first one, the SST gradient over the South Pacific was modified in order to increase the low-level atmospheric baroclinicity and upper jets strength. In the second one, the SST distribution along the South Pacific Convergence Zone was altered to enhance Rossby wave genesis in that region and analyze the teleconnection representation between that region and -mainly- South America and Africa. The third simulation consisted of modifying the SST distribution over the South Atlantic Convergence Zone and analyzing the changes in the teleconnection patterns resulting from this modification. The impact of the convective parameterization selection was assessed by changing the original Zhang-McFarlane scheme used by CAM. In one simulation the convective precipitation was suppressed while in a second one a parameterization for the vertical transport of horizontal momentum due to convection was added. Results show that the representation of convection is the most important feature in the skill of the climate simulations, followed by the horizontal resolution. Although important, the teleconnection patterns appear to have second-order impacts on the accuracy of the simulations of temperature and precipitation.