Iracema F. A. Cavalcanti

Annual variation of rainfall over Brazil and water vapor characteristics over South America

A large region in central Brazil is characterized by summer rainfall and winter dry conditions. During the 6-month period of September, October, November, December, January, and February (SONDJF) this region receives 70% or more of its annual rainfall. Calculations of vertically integrated water vapor flux and its divergence are made for South America. The results suggest that the Amazon basin is the principal source of moisture for central Brazil during the period SONDJF. Water vapor flux from the equatorial Atlantic associated with trade winds is the main moisture source for the Amazon basin.

Note on “Predictability of Northeast Brazil Rainfall and Real-Time Forecast Skill, 1987–98”

The predictability of rainy season rainfall over northeast Brazil for the relatively long period 1912‐98 is analyzed using dynamical and empirical techniques. The dynamical assessments are based on the HadAM2b atmospheric model forced with the Met Office Global Sea Ice and Sea Surface Temperature Dataset (GISST3). Ensembles of simulations and hindcasts starting from real initial conditions for 1982‐93 made under the European Community Prediction of Climate Variations on Seasonal to Interannual Timescales (PROVOST) program are analyzed. The results demonstrate a relatively high degree of predictability. Its source lies mostly in tropical Atlantic and Pacific sea surface temperatures. The results confirm the less extensive evidence of other authors that northeast Brazil is a region where two separate ocean basins influence seasonal climate to a comparable extent. Overall, the sea surface temperature gradient between the northern and southern tropical Atlantic appears

Global Climatological Features in a Simulation Using the CPTEC–COLA AGCM

Abstract The Center for Weather Forecasting and Climate Studies–Center for Ocean–Land–Atmosphere Studies (CPTEC–COLA) atmospheric general circulation model (AGCM) is integrated with nine initial conditions for 10 yr to obtain the model climate in an ensemble mode. The global climatological characteristics simulated by the model are compared with observational data, and emphasis is given to the Southern Hemisphere and South America. Evaluation of the models performance is presented by showing systematic errors of several variables, and anomaly correlation and reproducibility are applied to precipitation. The model is able to simulate the main features of the global climate, and the results are consistent with analyses of other AGCMs. The seasonal cycle is reproduced well in all analyzed variables, and systematic errors occur at the same regions in different seasons. The Southern Hemisphere convergence zones are simulated reasonably well, although the model overestimates precipitation in the southern porti...

The Life Cycle of the South American Monsoon System

Abstract The South American monsoon system (SAMS) life cycle plays an important role in the distribution and duration of the rainy season mainly over southwestern Amazonia, and the central west and southeast Brazil regions, affecting the economy through impacts on the agriculture and hydrology sectors. In this study a new criterion is applied to identify the monsoon onset and demise that was not used before in the SAMS region. This criterion is based on the atmospheric humidity flux over an area recognized as the monsoon core because of zonal wind reversal and changes in humidity from the transition seasons to summer and winter. Areas in Brazil that have a monsoon regime are identified, and several features associated with the life cycle are discussed. The climatological onset and demise are identified as the end of October and the end of March, respectively, and an interannual variability is found in the times of onset/demise. The main observed features in the two phases are discussed, such as the role o...

Extended range forecasts over South America using the regional eta model

An 80-km National Centers for Environmental Prediction eta model was configured to run over the South America continent. This limited area model has 38 layers in the atmosphere, and its domain includes part of the adjacent Atlantic and Pacific Oceans. The model was setup to perform 1 month forecasts. The version used in these preliminary experiments uses a bucket model to describe water in the ground and a modified Betts-Miller scheme for producing convective precipitation. The experiments used constant sea surface temperature field and initial soil moisture from climatology. Results obtained from a dry season month and a rainy season month over South America in 1997 show that the reinitialization of model at short range forecasts is not necessary as was done with the previous version of the model. These results show no obvious drying of the atmosphere or tendency with time of the domain average surface pressure. In both cases (dry and wet) the model seems to have reproduced the climatological signal of the forecast months. The monthly accumulated total precipitation agrees well with the observations. These runs showed that the current configuration of the eta model is stable and capable of producing continuous extended range runs over South America.

Apportionment of black carbon in the South Shetland Islands, Antarctic Peninsula

concentration of 8.3 ng m � 3 was consistent with global model estimates for this region. The intermittent coupling mechanism between the regional circulation of the low-level jets and the passages of the frontal systems explained the transport of BC from areas of burning biomass in Brazil to the northern Antarctic Peninsula. Principal component analysis applied to BC, Radon, ANC, and meteorological data presented significant factor loadings linking BC with 222 Rn and with wind velocity corroborating with this hypothesis.

Teleconnection patterns orographically induced in model results and from observational data in the austral winter of the Southern Hemisphere

Low frequency disturbances in the Southern Hemisphere are investigated through an observational study and numerical model experiments. The orography of the Andes and Antarctica in the Southern Hemisphere are the forcing of numerical experiments, submitted to zonal climatological austral winter conditions. The large-scale pattern forced by the Andes orography shows a high level wavetrain from the southeast of the mountain to the South Atlantic and two jet streams at high levels. The Antarctic case presents a wavenumber three horizontal structure around the hemisphere and three regions of jet stream. Characteristics of this wavenumber three model results are discussed based on analysis of streamfunction, vorticity and temperature, and related to blocking regions in the Southern Hemisphere. Empirical orthogonal function analysis of the low frequency filtered streamfunction at 250 hPa also shows, for the austral winter season, a wavenumber three structure and a wavetrain over the South Pacific and the South Atlantic, similar to the Pacific South American Pattern (PSA). Parts of the low frequency teleconnection patterns are identified in both the observational data and the model results, supporting the influence of the orography on the Southern Hemisphere atmospheric circulation. Analyses of periods with extreme amplitudes of the eigenvectors also show the influence of tropical convection on the anomalies over South America.

A sensitivity study using two different convection schemes over south america

The sensitivity of cumulus convection parameterizations is investigated using the CPTEC/COLA Atmospheric General Circulation Model (AGCM) with T62L28 resolution. This model has been used at CPTEC/INPE since 1995 with the Kuo convective scheme for weather and seasonal climate forecasts. In this study, two sets of integrations are performed using climatological Sea Surface Temperature (SST) of the Southern Hemisphere summer season (December, January and February) as bottom boundary conditions. Five integrations with different initial conditions are applied for each ensemble. The study was divided in two groups, one using the adjusted Relaxed Arakawa-Schubert convection scheme considering modifications in the convection physics (ARAS) and the other one using the Kuo convection scheme (KUO). The atmospheric circulation and precipitation model results are compared with NCEP/NCAR reanalysis data and CMAP precipitation data. The results are analyzed mainly over South America and also for the Southern Hemisphere to verify the model response compared to observed data when different convection scheme is applied. The adjusted scheme for RAS suggested in this study, reduced errors in several areas of South America, when comparing with the previous version. Over most of South America areas KUO gives smaller errors than ARAS. Over tropical Pacific Ocean, Southeastern Brazil and south of northeast Brazil, ARAS scheme shows better results.

Impacts of a New Solar Radiation Parameterization on the CPTEC AGCM Climatological Features

The impacts of improved atmospheric absorption on radiative fluxes, atmospheric circulation, and hydrological cycle for long-term GCM integrations are investigated. For these runs the operational version of the Centro de Previsao de Tempo e Estudos Climaticos (CPTEC) AGCM and its enhanced version with a new solar radiation scheme are used. There is an 8% increase in the annual mean global average atmospheric absorption in the enhanced integration as compared with the operational model integration. The extra absorption is due to gases (0.5%), the water vapor continuum (1.5%), and background aerosols (6%), which were not considered in the operational solar radiation scheme. Under clear-sky conditions the enhanced model atmospheric absorption is in agreement with observations to within 3Wm 2 , while for all-sky conditions the remaining errors are related to unaccounted-for cloud absorption. There is a general warm-up of the atmosphere in the enhanced model with temperatures increasing up to 3Ki n the troposphere and 5–8 K in the stratosphere, bringing the model closer to the reference values. The intensities of the tropospheric jets are reduced by 7%–8%, while that of the polar night stratospheric jet is increased by 5%–10%, reducing the model systematic error. The reduced availability of latent energy for the saturated convective processes weakens the meridional circulation and slows down the hydrological cycle. The model overestimation of December–February precipitation over the South Pacific convergence zone (SPCZ) and the South Atlantic convergence zone (SACZ) is reduced by 0.5–1.0 mm day 1 , and that over the Northern Hemisphere storm-tracks region is reduced by 0.5 mm day 1 . On a monthly time scale, the changes in the precipitation distribution over the SACZ are found to be much larger, 2–3 mm day 1 .

Monthly Mean Solar Radiative Fluxes and Cloud Forcing over South America in the Period of 1986–88: GCM Results and Satellite-Derived Data

Abstract The incident solar radiative fluxes, simulated by an atmospheric general circulation model over South America for the period 1986–88, are compared with the satellite-derived surface fluxes provided by the Surface Radiation Budget (SRB) datasets. The comparison shows that the model systematically overestimates both all-sky and clear-sky SRB fluxes while representing well their latitudinal variations. In order to analyze the reasons for the bias, the shortwave radiation code employed in the model is tested with more comprehensive techniques in a stand-alone mode. The results of testing demonstrate that the code underestimates solar radiation absorption in the clear-sky atmosphere due to trace gases and aerosols. The underestimation of the absorption due to aerosols contributes noticeably to the surface flux bias. The impact of clouds on the surface fluxes is estimated by calculating cloud radiative forcing, defined as the difference between the net surface fluxes in all-sky and clear-sky conditions...