Brazilian Regional Atmospheric Modeling System Research Articles

Stratospheric water vapour budget and convection overshooting the tropopause: modelling study from SCOUT-AMMA

Abstract. The aim of this paper is to study the impacts of overshooting convection at a local scale on the water distribution in the tropical UTLS. Overshooting convection is assumed to be one of the processes controlling the entry of water vapour mixing ratio in the stratosphere by injecting ice crystals above the tropopause which later sublimate and hydrate the lower stratosphere. For this purpose, we quantify the individual impact of two cases of overshooting convection in Africa observed during SCOUT-AMMA: the case of 4 August 2006 over Southern Chad which is likely to have influenced the water vapour measurements by micro-SDLA and FLASH-B from Niamey on 5 August, and the case of a mesoscale convective system over Aïr on 5 August 2006. We make use of high resolution (down to 1 km horizontally) nested grid simulations with the three-dimensional regional atmospheric model BRAMS (Brazilian Regional Atmospheric Modelling System). In both cases, BRAMS succeeds in simulating the main features of the convective activity, as well as overshooting convection, though the exact position and time of the overshoots indicated by MSG brightness temperature difference is not fully reproduced (typically 1° displacement in latitude compared with the overshoots indicated by brightness temperature difference from satellite observations for both cases, and several hours shift for the Aïr case on 5 August 2006). Total water budgets associated with these two events show a significant injection of ice particles above the tropopause with maximum values of about 3.7 ton s−1 for the Chad case (4 August) and 1.4 ton s−1 for the Aïr case (5 August), and a total upward cross tropopause transport of about 3300 ton h−1 for the Chad case and 2400 ton h−1 for the Aïr case in the third domain of simulation. The order of magnitude of these modelled fluxes is lower but comparable with similar studies in other tropical areas based on models. These two estimations exhibit significant differences and highlight variability among the cases of the impact of overshooting convection in hydrating the lower stratosphere. We show that the regional enhancement of water above the tropopause is between 0.21 to 0.67 ppmv between 380 and 400 K, generally in the range of other model estimations. The amount of water which remains in the stratosphere after the overshoot is estimated for both cases. A range of 330 to 507 tons is found for the Chad case and an upper limit of 200 tons is found for the Aïr case. Finally we emphasize that the hydrated area in the LS by overshooting convection can be advected relatively far away from the overshoot initial location, with locally mixing ratios of more than 3 ppmv higher than the background level, which is compatible with the balloon borne measurements performed above Niamey in the same air mass, 30 h after the overshoot.

O uso da energia radiativa do fogo para estimar as emissões de queimadas para a América do Sul

A cada ano grandes extensões terrestres sofrem com a ação antropogênica e natural das queimadas. Estima-se que mais de 100 milhões de toneladas de aerossóis provenientes da fumaça sejam lançados na atmosfera, dos quais 80% ocorrem em regiões tropicais do globo. O processo de combustão da biomassa libera para a atmosfera gases traços e partículas de aerossóis que afetam significativamente a qualidade do ar, a química troposférica e estratosférica, o balanço de radiação e a dinâmica e microfísica das nuvens. O presente trabalho tem como objetivo principal utilizar a energia radiativa do fogo (ERF) derivada do sensor MODIS (Moderate Resolution Imaging Spectroradiometer) e do GOES (Geostationary Operational Environmental Satellite) para estimar as emissões de monóxido de carbono (CO) e de material particulado com diâmetro menor que 2.5µm (PM2,5µm) para o período de queimadas de 2002 na América do Sul, e modelar estas emissões no CCATT-BRAMS (Coupled Chemistry-Aerosol-Tracer Transport model coupled to Brazilian Regional Atmospheric Modeling System). Com uma correlação superior a 86% entre os dados de emissão de aerossóis (kg.s -1) e a ERF (MJ.s -1), originaram-se três coeficientes para os dados provenientes do satélite GOES. O uso da ERF e dos coeficientes de emissão para estimar o PM2,5µm e CO emitido na queimada mostrou uma correlação de aproximadamente 91 % entre os dados estimados e os dados utilizados como verdade terrestre obtidos a partir dos experimentos do LBA (Large Scale Biosphere-Atmosphere Experiment in Amazônia) SMOCC (Smoke, Aerosols, Clouds, rainfall, and Climate) e RaCCI (Radiation, Cloud, and Climate Interactions).

Analysis of the sulfate aerosol scavenging processes in the metropolitan area of Porto Alegre (MAPA), RS, Brazil

The present work aims to study the in-cloud and below-cloud sulfate (SO42-) scavenging processes by applying numerical models. The BRAMS (Brazilian Regional Atmospheric Modeling System) model was used to simulate the vertical structure of clouds in the metropolitan area of Porto Alegre (MAPA), in southern Brazil, together with the B.V.2 (below-cloud Beheng version 2) scavenging model for wet removal processes, which occur in–cloud (rainout) and below-cloud (washout). Six rainfall events between 2005 and 2007 were selected. They occurred at three sites within the MAPA–Porto Alegre, Canoas, and Sapucaia do Sul–where the SO42- concentrations measured experimentally in wet precipitation, as well as the SO2 concentrations in the air, were measured. The data were used in the modeling. Results of SO42- scavenging process modeling were in good agreement with those observed experimentally, showing a correlation of 0.73. Results also showed a prevalence of in-cloud scavenging processes, which are responsible for about 70 to 90% of the SO42- concentration found in rainwater, corroborating with data found in the literature.

Study on wet scavenging of atmospheric pollutants in south Brazil

The present paper presents the study of in-cloud and below-cloud SO2 and SO42-scavenging processes by applying numerical models in the Candiota region, located in the state of Rio Grande do Sul, South Brazil. The BRAMS (Brazilian Regional Atmospheric Modeling System) model was applied to simulate the vertical structure of the clouds, and the B.V.2 (Below-Cloud Beheng Version 2) scavenging model was applied to simulate in-cloud and below-cloud scavenging processes of the pollutants SO2 and SO42−. Five events in 2004 were selected for this study and were sampled at the Candiota Airport station. The concentrations of SO2 and SO42− sampled in the air and the simulated meteorological parameters of rainfall episodes were used as input data in the B.V.2, which simulates raindrop interactions associated with the scavenging process. Results for the Candiota region showed that in-cloud scavenging processes were more significant than below-cloud scavenging processes for two of the five events studied, with a contribution of approximately 90–100% of SO2 and SO42− concentrations in rainwater. A few adjustments to the original version of B.V.2 were made to allow simulation of scavenging processes in several types of clouds, not only cumulus humilis and cumulus congestus.

Numerical simulation of the 7 to 9 September 2006 AMMA mesoscale convective system: Evaluation of the dynamics and cloud microphysics using synthetic observations

AbstractThis paper presents a numerical simulation of a Mesoscale Convective System (MCS) observed during the AMMA (African Monsoon Multidisciplinary Analysis) experiment with the BRAMS model (Brazilian Regional Atmospheric Modelling System). The aim is to document the life cycle of the MCS and to identify key cloud microphysical processes and their signatures by making use of synthetic observations calculated from the simulated fields. These observations: ARM (Atmospheric Radiation Measurement) 95 GHz equivalent radar reflectivity factor and Doppler velocity and infrared brightness temperatures in three SEVIRI (Spinning Enhanced Visible and InfraRed Imager) channels centred at 8.7, 10.6 and 12 µm are simulated using respectively Mie scattering theory and FASDOM (Fast Discrete Ordinate Method), a fast radiative transfer code. Synthetic observations and model variables are compared to various measurements from several platforms (W‐band and Massachusetts Institute of Technology (MIT) ground‐based Doppler radars, soundings, aircraft measurements, and Meteosat Second Generation) to evaluate the model at different scales and to identify the signatures of microphysical properties with a focus on the anvil part of the MCS. A method using both the ARM and the MIT radar data is used to identify the different regimes within the MCS. A relatively good agreement with direct comparisons is found, as well as discrepancies in the microphysical scheme parametrization that clearly need improvements (using in situ measurements). Microphysical signatures are also studied using joint radar reflectivity/Doppler‐height histograms. Their analysis shows that the model tends to overplay the role of the riming processes, even in the anvil part of the MCS. Comparisons of the Particle Size Distributions (simulated and measured in situ) show the model's ability to reproduce complex PSDs (e.g. a multimodal behaviour). Copyright © 2010 Royal Meteorological Society

Enriched Analyses with Assimilation of SALLJEX Data

Abstract This paper aims at generating a set of enriched analyses by assimilating the data collected during the South American Low-Level Jet Experiment (SALLJEX) in southeastern South America during the summer season 2002/03. The analyses are generated with the Brazilian Regional Atmospheric Modeling System (BRAMS) using all available observations and achieving 20-km horizontal resolution and 3-h temporal resolution. This paper describes the methods used to generate and evaluate the analyses. The results indicate that the method is appropriate because data assimilation provides an improved fit between analyses and observations. In addition, enriched analyses show a better representation of mesoscale structure in case studies. This satisfactory evaluation allows one to use the set of analyses to perform case studies at higher resolution than is currently available, with the certainty that these analyses reproduce the atmospheric conditions better than those that do not assimilate data.

CHANGES IN LAND COVER AND USE AFFECT THE LOCAL AND REGIONAL CLIMATE IN PIRACICABA, BRAZIL (doi: 10.4090/juee.2008.v2n2.068074)

Land use and changes in land cover play an important role in local and regional climatic conditions, especially in tropical regions. Piracicaba, a city in southeastern Brazil, has an economy that is based primarily on sugar cane cultivation. The seasonality of this crop means that there are marked annual fluctuations in land use and cover in this municipality. In this work, we investigated the seasonal variation in urban heat-islands and local climatic variations by using remote sensing data, geographic information system (GIS) and atmospheric modeling. The urban heat-islands were analyzed by using Landsat 7 (Enhanced Thematic Mapper+) images for the sugar cane crop (January to March) and non-crop (August to November) periods, and these images were subsequently converted to land surface brightness temperature. The average temperature in the non-crop period was 3.5°C higher than in the crop period, which suggested that heat-island intensity may be linked to the seasonality of sugar cane cultivation. In order to examine the influence of urban areas on regional temperature changes and heat fluxes, numerical simulations were done with the Brazilian Regional Atmospheric Modeling System (BRAMS). Overall, the results obtained suggested that local and regional climatic dynamics were related to land use and changes in land cover.

Regional representativity of AERONET observation sites during the biomass burning season in South America determined by correlation studies with MODIS Aerosol Optical Depth

This paper presents an analysis of ground‐based Aerosol Optical Depth (AOD) observations by the Aerosol Robotic Network (AERONET) in South America from 2001 to 2007 in comparison with the satellite AOD product of Moderate Resolution Imaging Spectroradiometer (MODIS), aboard TERRA and AQUA satellites. Data of 12 observation sites were used with primary interest in AERONET sites located in or downwind of areas with high biomass burning activity and with measurements available for the full time range. Fires cause the predominant carbonaceous aerosol emission signal during the dry season in South America and are therefore a special focus of this study. Interannual and seasonal behavior of the observed AOD at different sites were investigated, showing clear differences between purely fire and urban influenced sites. An intercomparison of AERONET and MODIS AOD annual correlations revealed that neither an interannual long‐term trend may be observed nor that correlations differ significantly owing to different overpass times of TERRA and AQUA. Individual anisotropic representativity areas for each AERONET site were derived by correlating daily AOD of each site for all years with available individual MODIS AOD pixels gridded to 1° × 1°. Results showed that for many sites a good AOD correlation (R2 > 0.5) persists for large, often strongly anisotropic, areas. The climatological areas of common regional aerosol regimes often extend over several hundreds of kilometers, sometimes far across national boundaries. As a practical application, these strongly inhomogeneous and anisotropic areas of influence are being implemented in the tropospheric aerosol data assimilation system of the Coupled Chemistry‐Aerosol‐Tracer Transport Model coupled to the Brazilian Regional Atmospheric Modeling System (CCATT‐BRAMS) at the Brazilian National Institute for Space Research (INPE). This new information promises an improved exploitation of local site sampling and, thus, chemical weather forecast.

Changes in land cover and use affect the local and regional climate in Piracicaba, Brazil

Land use and changes in land cover play an important role in local and regional climatic conditions, especially in tropical regions. Piracicaba, a city in southeastern Brazil, has an economy that is based primarily on sugar cane cultivation. The seasonality of this crop means that there are marked annual fluctuations in land use and cover in this municipality. In this work, we investigated the seasonal variation in urban heat-islands and local climatic variations by using remote sensing data, geographic information system (GIS) and atmospheric modeling. The urban heat-islands were analyzed by using Landsat 7 (Enhanced Thematic Mapper+) images for the sugar cane crop (January to March) and non-crop (August to November) periods, and these images were subsequently converted to land surface brightness temperature. The average temperature in the non-crop period was 3.5°C higher than in the crop period, which suggested that heat-island intensity may be linked to the seasonality of sugar cane cultivation. In order to examine the influence of urban areas on regional temperature changes and heat fluxes, numerical simulations were done with the Brazilian Regional Atmospheric Modeling System (BRAMS). Overall, the results obtained suggested that local and regional climatic dynamics were related to land use and changes in land cover.

The severe zonda wind event of 11 July 2006 east of the Andes Cordillera (Argentine): a case study using the BRAMS model

The zonda is a wind that exhibits the so-called foehn effect: a warm, dry, strong wind related to adiabatic compression upon descending in the lee of the Andes. This phenomenon occurs mostly in winter and spring over the entire length of the extratropical Andes. It is frequently detected near the cities of Mendoza and San Juan, the most important urban regions of western Argentina. The aim of this work is to understand why a zonda wind event, occurring on 11 July 2006, reached and maintained the higher category Z4 during several hours. A secondary aim is to evaluate the ability of a Brazilian regional atmospheric modeling system (BRAMS) model to represent the features of this extreme episode and to explore if it can be used to predict a zonda event. The difference found with respect to other severe zonda wind episodes analyzed was that the wind registered the highest category (Z4) with extreme gusts during a long period. This condition was registered in particular on southern plain areas of San Juan province. The phenomenon had a great impact on the community, with residences and buildings being affected or destroyed, trees being felled, power supply and communications being shutdown, and several rural and urban fires being reported. The event was characterized through surface and upper-level information and model results. The synoptic surface and upper-air conditions were those typically associated with a severe zonda wind occurrence: a surface cold front approaching the region, driven by a 500 hPa trough, a strong upper-air jet stream, and a deep low-pressure surface system at higher latitudes over the Atlantic Ocean. The North West Argentine Low in central west Argentina during the following hours could be observed centered approximately at 31°S 66°W. in a few lower latitude than the location observed by National Center of Environmental Prediction (NCEP) reanalysis. On the other hand, it is the authors’ impression that the BRAMS model achieved an acceptable representation of some aspects of this zonda wind event. This is the first study on BRAMS model performance in predicting a zonda event. Further and thorough research is required to study the application of BRAMS to contribute to the analysis of the three-dimensional structure and the related physical mechanisms, and to enable skillful comparison with others models. To apply this sophisticated high-resolution model in a region with complex topography and without a dense surface and upper-air observational network is a challenge.

Impact of TMI SST on the Simulation of a Heavy Rainfall Episode over Mumbai on 26 July 2005

In this study the simulation of a severe rainfall episode over Mumbai on 26 July 2005 has been attempted with two different mesoscale models. The numerical models used in this study are the Brazilian Regional Atmospheric Modeling System (BRAMS) developed originally by Colorado State University and the Advanced Research Weather Research Forecast (WRF-ARW) Model, version 2.0.1, developed at the National Center for Atmospheric Research. The simulations carried out in this study use the Grell–Devenyi Ensemble cumulus parameterization scheme. Apart from using climatological sea surface temperature (SST) for the control simulations, the impact of the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) SST on the simulation of rainfall is evaluated using these two models. The performances of the models are compared by examining the predicted parameters like upper- and lower-level circulations, moisture, temperature, and rainfall. The strength of convective instability is also derived by calculating the convective available potential energy. The intensity of maximum rainfall around Mumbai is significantly improved with TMI SST as the surface boundary condition in both the models. The large-scale circulation features, moisture, and temperature are compared with those in the National Centers for Environmental Prediction analyses. The rainfall prediction is assessed quantitatively by comparing the simulated rainfall with the rainfall from TRMM products and the observed station values reported in Indian Daily Weather Reports from the India Meteorological Department.

Mesoscale modelling of water vapour in the tropical UTLS: two case studies from the HIBISCUS campaign

Abstract. In this study, we evaluate the ability of the BRAMS (Brazilian Regional Atmospheric Modeling System) mesoscale model compared to ECMWF global analysis to simulate the observed vertical variations of water vapour in the tropical upper troposphere and lower stratosphere (UTLS). The observations are balloon-borne measurements of water vapour mixing ratio and temperature from micro-SDLA (Tunable Diode Laser Spectrometer) instrument. Data from two balloon flights performed during the 2004 HIBISCUS field campaign are used to compare with the mesoscale simulations and to the ECMWF analysis. The observations exhibit fine scale vertical structures of water vapour of a few hundred meters height. The ECMWF vertical resolution (~1 km) is too coarse to capture these vertical structures in the UTLS. With a vertical resolution similar to ECMWF, the mesoscale model performs better than ECMWF analysis for water vapour in the upper troposphere and similarly or slightly worse for temperature. The BRAMS model with 250 m vertical resolution is able to capture more of the observed fine scale vertical variations of water vapour compared to runs with a coarser vertical resolution. This is mainly related to: (i) the enhanced vertical resolution in the UTLS and (ii) to the more detailed microphysical parameterization providing ice supersaturations as in the observations. In near saturated or supersaturated layers, the mesoscale model predicted relative humidity with respect to ice saturation is close to observations provided that the temperature profile is realistic. For temperature, the ECMWF analysis gives good results partly attributed to data assimilation. The analysis of the mesoscale model results showed that the vertical variations of the water vapour profile depends on the dynamics in unsaturated layer while the microphysical processes play a major role in saturated/supersaturated layers. In the lower stratosphere, the ECMWF model and the BRAMS model give very similar water vapour profiles that are significantly drier than micro-SDLA measurements. This similarity comes from the fact that BRAMS is initialised using ECMWF analysis and that no mesoscale process acts in the stratosphere leading to no modification of the BRAMS results with respect to ECMWF analysis.