Abstract

MULLER, G. V; REPINALDO, C. R. R; ARANEO, D. C  and  ANDRADE, K. M. Comparison between circulation patterns associated to frost events in the humid Pampa in climatic settings related with the experiments CMIP3 and CMIP5 of the GFDL model. Geoacta [online]. 2014, vol.39, n.2, pp.78-84. ISSN 1852-7744.

The purpose of this study is to investigate the change in the atmospheric circulation associated with frost events in the Wet Pampa (WP) in the future climate for the most critical scenarios projected by the GFDL ocean-atmosphere coupled model. Two versions of the GFDL model are used, the GFDL-CM2 for CMIP3 and GFDL-CM3 for CMIP5. We analyze the model capability to simulate the five most extreme cold events in the present climate (1961-1990), with respect to those obtained with the NCEP/NCAR Reanalysis. Then, we compare the future climate simulations (2081-2100) with the model simulation for the present climate. For the present climate the CMIP3 experiment presents more penetration of the 0°C isotherm in 850 hPa, intensifying the negative temperature anomalies in comparison to the reanalysis. The postfrontal anticyclone is more meridionally extended over the continent, with similar anomalies to those of the reanalysis, mainly over WP. The gradient between the high pressure and the low pressure downwind creates a more intense southerly cold airflow at 850 hPa than the reanalysis, giving place to advective frosts in the studied region. For the future climate, the model projects less penetration of the 0°C isotherm and less intense negative temperature anomalies. The anticyclone maximum is located further north than in the present climate, propitiating radiative frosts. In the upper levels, the subtropical jet shows a more zonally layout and slightly higher intensity than in the present climate simulations. For the present climate the CMIP5 experiment simulates well the incursion of the 0°C isotherm, although with a more intense temperature anomaly in comparison to the reanalysis. The pressure field presents similar characteristics to those shown in the CMIP3 experiment, but with larger anomalies in the southern part of the continent. For the future scenario, the model projects the 0°C isotherm incursion as well as the negative temperature anomalies similar to the present. The post frontal anticyclone is located further north, overestimating its value and the anomaly over WP. The wind field is similar to the present simulation. Summarizing the results of both experiments, the future projections with CMIP3 show significant changes with respect to the present, which is not the case with the CMIP5 experiment. These changes are mainly reflected in the pressure field, in which the position of the anticyclone in CMIP3 (CMIP5) would favor radiative (advective) frosts over WP.

Keywords : Temperature extreme events; Frost; Climate scenarios; GFDL model; Wet Pampa.

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