Autores:
RAMIREZ, E.; SILVA DIAS, P.; RAUPP, C. F. M.

Revista:
Journal of Atmos. Science, v. 74(8), p. 2503–2523, 2017

DOI:
https://doi.org/10.1175/JAS-D-15-0325.1

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In the present study a simplified multiscale atmosphere–ocean coupled model for the tropical interactions among synoptic, intraseasonal, and interannual scales is developed. Two nonlinear equatorial β-plane shallow-water equations are considered: one for the ocean and the other for the atmosphere. The nonlinear terms are the intrinsic advective nonlinearity and the air–sea coupling fluxes. To mimic the main differences between the fast atmosphere and the slow ocean, suitable anisotropic multispace/multitime scalings are applied, yielding a balanced synoptic–intraseasonal–interannual–El Niño (SInEN) regime. In this distinguished balanced regime, the synoptic scale is the fastest atmospheric time scale, the intraseasonal scale is the intermediate air–sea coupling time scale (common to both fluid flows), and El Niño refers to the slowest interannual ocean time scale. The asymptotic SInEN equations reveal that the slow wave amplitude evolution depends on both types of nonlinearities. Analytic solutions of the reduced SInEN equations for a single atmosphere–ocean resonant triad illustrate the potential of the model to understand slow-frequency variability in the tropics. The resonant nonlinear wind stress allows a mechanism for the synoptic-scale atmospheric waves to force intraseasonal variability in the ocean. The intraseasonal ocean temperature anomaly coupled with the atmosphere through evaporation forces synoptic and intraseasonal atmospheric variability. The wave–convection coupling provides another source for higher-order atmospheric variability. Nonlinear interactions of intraseasonal ocean perturbations may also force interannual oceanic variability. The constrains that determine the establishment of the atmosphere–ocean resonant coupling can be viewed as selection rules for the excitation of intraseasonal variability (MJO) or even slower interannual variability (El Niño).

Autores:
ALVIM, D. S., et al.

Revista:
Atmospheric Pollution Research, v. 8 (4), p. 718-728, 2017

DOI:
https://doi.org/10.1016/j.apr.2017.01.008

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The accurate representation of the impacts of natural and anthropogenic aerosols in the climate system presents a challenge in General Circulation Models. This paper analyzes the performance of the aerosol component of two Atmospheric General Circulation Models (AGCM): the Europe Centre Hamburg Model – Hamburg Aerosol Model (ECHAM-HAM), and the Community Atmosphere Model – Modal Aerosol Model (CAM5-MAM3) and their comparison with aerosol observations. We analyzed the spatial distribution of aerosols over Brazil represented in terms of the aerosol optical depth (AOD) simulated by these models. The model results are compared to measurements from Aerosol Robotic Network (AERONET) ground station, and satellite observations provided by the Moderate Resolution Imaging Spectroradiometer (MODIS). While both the models provide AODs at 550 nm, only HAM provides the Angström exponent that is compared with AERONET measurements. The comparison between the model simulations and the satellite observations of AOD show that the models can reproduce the spatial and temporal distributions, however models underestimate AOD for the four cities and for almost every South American continent during all seasons. During the dry season, characterized by intense biomass burning, CAM5-MAM3 shows inconsistent, but comparatively better results that ECHAM-HAM, with negative biases over Northern and Northeastern regions of Brazil. The Angström parameter is reasonably reproduced by ECHAM-HAM, except for Cuiabá, indicating that the particle size distribution is correctly represented in most cities.

Autores:
LACERDA, F. F.; NOBRE, P.; SOBRAL, M. C.; LOPES, G. M. B.; CHOU, S. C.; ASSAD, E. D.; BRITO, E.

Revista:
Journal of Earth Science & Climatic Change, v. 06, p. 1-8, 2015

DOI:
10.4172/2157-7617.1000296

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This study investigates long-term climate trends in Pernambuco, Northeast Brazil (Nordeste), and in the Tropical Atlantic islands of Fernando de Noronha and Cape Verde. The study is based on meteorological station time series and model simulations of present and future climates. Past trends are compared with numerical simulations of present and future climate scenarios for the periods of 1960-2000 and 2010-2050. Both the station data analyses and numerical simulations revealed trends of increasing temperature maxima and diminishing precipitation. While station data analyses showed modest warming in Fernando de Noronha they revealed strong warming and drying trends in Cape Verde similar to the trends detected over the semiarid Nordeste. The water-balance calculations for the study sites showed reduced soil moisture availability and total rainfall in all areas. The observed temperature and precipitation trends are indicative that aridification processes are underway in Pernambuco and Cape Verde. The atmospheric model simulations were consistent with the station data regarding the present warming; the climate change scenarios for 2010-2050 indicated a faster increase of daily temperature maxima over Nordeste compared to that simulated for the recent past

Autores:
GIAROLLA, E.; SIQUEIRA, L. S. P.; BOTTINO, M. J.; MALAGUTTI, M.; CAPISTRANO, V. B.; NOBRE, P.

Revista:
Ocean Dynamics, v. 65 (6), p. 831-843, 2015

DOI:
10.1007/s10236-015-0836-8

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The ocean temperatures and zonal currents at the equatorial Atlantic simulated by an improved version of the Brazilian earth system model (BESM), with changes in the cloud cover scheme and optical properties of the atmospheric component, are analyzed and compared to those obtained from a previous version of BESM and also from other seven selected CMIP5 models. It is shown that this updated version of BESM, despite some persistent biases, more accurately represents the surface temperature variation at the Equator and the equatorial thermocline east–west slope. These improvements are associated to a more realistic seasonal cycle achieved for the Atlantic equatorial undercurrent, as well as sea surface temperatures and zonal wind stress. The better simulation of the equatorial undercurrent is, in its turn, credited to a more realistic representation of the surface wind position and strength at the tropical Atlantic by the coupled model. With many of the systematic errors noticed in the previous version of the model alleviated, this version of BESM can be considered as a useful tool for modelers involved in Atlantic variability studies.

Autores:
CHOU, S. C.; LYRA, A.; MOURÃO, C.; DERECZYNSKI, C.; PILOTTO, I.; GOMES, J.; BUSTAMANTE, J.; TAVARES, P.; SILVA, A.; RODRIGUES, D.; CAMPOS, D.; CHAGAS, D.; SUEIRO, G.; SIQUEIRA, G.; Nobre, P.; MARENGO, J.

Revista:
American Journal of Climate Change, v. 03, p. 438-454, 2014.

DOI:
10.4236/ajcc.2014.35039

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To provide long-term simulations of climate change at higher resolution, Regional Climate Models (RCMs) are nested in global climate models (GCMs). The objective of this work is to evaluate the Eta RCM simulations driven by three global models, the HadGEM2-ES, BESM, and MIROC5, for the present period, 1961-1990. The RCM domain covers South America, Central America, and Caribbean. These simulations will be used for assessment of climate change projections in the region. Maximum temperatures are generally underestimated in the domain, in particular by MIROC5 driven simulations, in summer and winter seasons. Larger spread among the simulations was found in the minimum temperatures, which showed mixed signs of errors. The spatial correlations of temperature simulations against the CRU observations show better agreement for the MIROC5 driven simulations. The nested simulations underestimate precipitation in large areas over the continent in austral summer, whereas in winter overestimate occurs in southern Amazonia, and underestimate in southern Brazil and eastern coast of Northeast Brazil. The annual cycle of the near-surface temperature is underestimated in all model simulations, in all regions in Brazil, and in most of the year. The temperature and precipitation frequency distributions reveal that the RCM and GCM simulations contain more extreme values than the CRU observations. Evaluations of the climatic extreme indicators show that in general hot days, warm nights, and heat waves are increasing in the period, in agreement with observations. The Eta simulations driven by HadGEM2-ES show wet trends in the period, whereas the Eta driven by BESM and by MIROC5 show trends for drier conditions.