Climatology Analysis of Global Climate Models from HiGEM Family Over South America.

Abstract:

General Circulation Models (GCMs) have shown difficulties to correctly simulate some atmospheric patterns, especially the precipitation over South America (SA), which is often attributed to the low resolution of these models. The increased horizontal resolution of climate models aims to improve the simulations accuracy and to understand the non-linear processes during interactions between different spatial scales within the climate system. Up to this moment, these interactions did not have a good representation on low horizontal resolution GCMs. The purpose of this study was to understand the impact of the horizontal resolution in high resolution coupled and atmospheric global models of HiGEM project in simulating atmospheric patterns and processes of interaction between spatial scales. The simulations were validated using different reanalysis data and compared with observations in order to understand the impact of horizontal resolution on the precipitation systems over SA. Three different horizontal resolutions for HiGEM family models were compared ≈ 60, 90 and 135 km. Precipitation estimations from CMAP, CPC and GPCP are used for validation. Both coupled and uncoupled simulations consistently represent the observed spatial patterns related to seasonal march of the Inter-tropical Convergence Zone (ITCZ), the formation and location of the South Atlantic Convergence Zone (SACZ) and the subtropical high pressure systems in the Pacific and Atlantic Oceans. However, they overestimate the precipitation rate, especially in the ITCZ and western border regions of higher elevation, as in southern Chile. The fine horizontal resolution contributed to the large similarity between the seasonal patterns of global models and observations, with coupled models representing better these patterns than the atmospheric models in many regions of SA. The simulated annual cycles are in phase with estimations of rainfall for most of the six regions considered. An important result is that these models eliminate a common problem of coarse resolution CGCMs, which is the simulation of a semiannual cycle of precipitation due to the semiannual solar forcing. These results show, although still with some problems, that the increased resolution improves the representation of the annual precipitation cycle in South America.