Gabriel Clauzet

Last Glacial Maximum and Holocene Climate in CCSM3

Abstract The climate sensitivity of the Community Climate System Model version 3 (CCSM3) is studied for two past climate forcings, the Last Glacial Maximum (LGM) and the mid-Holocene. The LGM, approximately 21 000 yr ago, is a glacial period with large changes in the greenhouse gases, sea level, and ice sheets. The mid-Holocene, approximately 6000 yr ago, occurred during the current interglacial with primary changes in the seasonal solar irradiance. The LGM CCSM3 simulation has a global cooling of 4.5°C compared to preindustrial (PI) conditions with amplification of this cooling at high latitudes and over the continental ice sheets present at LGM. Tropical sea surface temperature (SST) cools by 1.7°C and tropical land temperature cools by 2.6°C on average. Simulations with the CCSM3 slab ocean model suggest that about half of the global cooling is explained by the reduced LGM concentration of atmospheric CO2 (∼50% of present-day concentrations). There is an increase in the Antarctic Circumpolar Current an...

Climate Sensitivity of Moderate and Low Resolution Versions of CCSM3 to Preindustrial Forcings

Preindustrial (PI) simulations of the Community Climate System Model version 3 (CCSM3) at two resolutions, a moderate and a low resolution, are described and compared to the standard controls for present-day (PD) simulations. Because of computational efficiency, the moderate- and low-resolution versions of CCSM3 may be appropriate for climate change studies requiring simulations of the order of hundreds to thousands of years. The PI simulations provide the basis for comparison for proxy records that represent average late Holocene conditions. When forced with PI trace gases, aerosols, and solar irradiance estimates, both resolutions have a global cooling of 1.2°–1.3°C, increased sea ice in both hemispheres, and less precipitation near the equator and at midlatitudes as compared to simulations using PD forcing. The response to PI forcings differs in the two resolutions for North Atlantic meridional overturning circulation (MOC), the Antarctic Circumpolar Current (ACC), and ENSO. The moderate-resolution CCSM3 has enhanced ACC, North Atlantic MOC, and tropical Pacific ENSO variability for PI forcings as compared to PD. The low-resolution CCSM3 with more extensive sea ice and colder climate at high northern latitudes in the PD simulation shows less sensitivity of the North Atlantic MOC to PI forcing. ENSO variability and the strength of the ACC do not increase with PI forcing in the low-resolution CCSM3.

Identificação da variabilidade de baixa freqüência em algumas regiões da costa sudeste-nordeste do Brasil

Neste trabalho, series temporais de 35 anos, dos parâmetros de superficie marinha da costa SE do Brasil e em particular das regioes de Cananeia e Ubatuba sao examinadas. Procurou-se situar, num contexto global de larga escala, as variacoes climaticas locais. A variabilidade de baixa frequencia nas estacoes costeiras brasiieiras esta relacionada, com fenomenos climaticos de larga escala como o ENSO (El Niiio -Southem Oscillation) e o dipolo do Atlântico. Concluiu-se que o fenomeno ENSO tem influencias diretas sobre as. series temporais ao longo de toda costa, mas nao as determina. O dipolo do Atlântico tem pouca influencia na costa SE do Brasil. Na regiao Nordeste o impacto do dipolo do Atlântico e significativo na escala decadal.