Seasonal precipitation in eastern Amazon during rainy season: regional observations and RegCM3 simulations

This paper presents a contribution on the climate modelling studies with emphasis on seasonal rainfall variability in eastern Amazonia, during the austral summer and autumn seasons (DJF and MAM). Based on RegCM3 regional climate simulations for a 26 years period (1982/83 to 2007/08) using high resolution domain scale (30 km) and two different convection schemes (Grell and MIT), it was investigated the model performance to simulate the regional pluviometric distribution in eastern Amazon, with reference to a new observational data base containing regional aspects extracted from a dense rain gauge station network. The quantitative analysis showed that RegCM3 presents systematic errors, especially those related to the dry bias in the Amapá and north/northeast of Pará using both schemes Grell and MIT, which indicate that the model does not reproduce ITCZ characteristics over equatorial Atlantic. The simulations using MIT also indicated wet bias in the southwest/south/southeast of Pará and north of Tocantins. Moreover, through composites technique, it was also investigated RegCM3 response to reproduce the anomalous spatial rainfall patterns in association with ENSO episodes and interhemispheric SSTa gradient phases across the intertropical Atlantic. The results showed that the model represented realistically well the spatial pattern related to the rainfall anomalies above (below) than normal in most of eastern Amazonia, during the known favourable scenarios, i.e., La Niña and south Atlantic SSTa gradient (unfavourable, i.e., El Niño and north Atlantic SSTa gradient).O presente trabalho apresenta uma contribuição aos estudos de modelagem climática com ênfase na variabilidade pluviométrica sazonal da Amazônia oriental, durante as estações de verão e outono (DJF e MAM). Baseado nos resultados das simulações regionais do RegCM3 para um período de 26 anos (1982/83 a 2007/08) e usando domínio em alta resolução espacial (30 Km) e dois diferentes esquemas de convecção (Grell e MIT), foi investigado o desempenho do modelo em simular a distribuição regional de precipitação sazonal na Amazônia oriental, com referência a um novo conjunto de dados observacional compilado com informações de uma ampla rede integrada de estações pluviométricas. As análises quantitativas evidenciaram que o RegCM3 apresenta erros sistemáticos, sobretudo aqueles relacionados com viés seco no Amapá e norte/nordeste do Pará usando ambos os esquemas Grell e MIT, os quais apontam que o modelo não reproduz as características da ZCIT sobre o Atlântico equatorial. As simulações usando MIT, também apresentaram viés úmido no sudoeste/sul/sudeste do Pará e norte do Tocantins. Além disso, através da técnica de composições, também foi investigado o desempenho do RegCM3 em reproduzir os padrões espaciais anômalos de precipitação sazonal em associação aos episódios ENOS, e as fases do gradiente térmico sobre o Atlântico intertropical. Os resultados demonstraram que o modelo conseguiu representar realisticamente bem o padrão espacial das anomalias pluviométricas acima (abaixo) do normal em grande parte da Amazônia oriental, durante os conhecidos cenários favoráveis, i.e., condições de La Niña e gradiente de aTSM para o Atlântico sul (desfavoráveis, i.e., El Niño e gradiente de aTSM para o Atlântico norte

Variação Sazonal da TSM do Atlântico Equatorial Ocidental a partir do Sensor AVRHH

The sea surface temperature (SST) in the equatorial Atlantic has variability over the years with many interacting processes in the region that is influenced by the dynamics of winds, currents, tides and discharge of the Amazon River. The present study is an analysis of SST near the northern coastal region, using AVHRR sensor monthly data aboard the NOAA satellite for the period of January 1998 to December 2007. It was possible to avaliate through this time series the SST behavior in space and time with an objective description of the images and quantify the time-scale variability by wavelets transformed. It was also analysed the correlations of SST data with OLR (Outgoing Longwave Radiation) and the flow of the Óbidos station to represent the Amazon River flow, in order to understand the processes that are related. The correlation between SST and OLR weren´t significant for the study period, the correlation between SST and low flow, indicating that the flow is not a dominant factor for the variability of SST of the northern waters of Brazil. The correlation between the SST anomalies for the three points, and the SST anomalies in the basin of the North and South Atlantic have clearly shown the influence of the dipole in the study area, suggesting that they are strongly associated.Pages: -781

Interannual variations of storm tracks in the Southern Hemisphere and their connections with the Antarctic oscillation

Interannual variations of storm tracks in the Southern Hemisphere (SH) are studied. Large interannual variations are found in the enveloping function of meridional wind nu(c), and these suggest some dominant periodicities. Some of these periodicities are a quasi-biennial oscillation in the subtropical branch of the winter storm track and the midlatitude spring storm track. a 3 year period and a long period of 8 years. The Antarctic oscillation (AAO) seems to be connected to the interannual variation of storm tracks in the SH. A significant negative correlation between nu(e) and the AAO index in the high latitudes. a positive correlation in the midlatitudes and again a negative correlation in the subtropics are found throughout the year. During the high index phase of the AAO, the low-level zonal wind shear increases in the region of midlatitude storm tracks and the static stability decreases, increasing the growth rate of baroclinic eddies, i.e. increase of nu(e) (the opposite occurs during the negative phase). This explains the positive correlation in the midlatitudes between nu(c) and the AAO index. In the region of the subtropical storm track during the high index phase the wind shear decreases and the static stability increases. decreasing the growth rates, thus explaining the negative correlation between nu(c) and the AAO index.Pages: 1537-154

Seasonality of precipitation for the Amazon using the RegCM3 model: evaluating only the forcing of equatorial Atlantic

The present study tries to bring a new perspective of the Equatorial Atlantic Ocean importance on seasonal pattern, during the summer and fall on the Amazon region. It contributes in a different way for studies in the area of climate modeling and variability of rainfall over the region. For this study, we used the model RegCM3 with Grell convection scheme, applying the donwscaling technique and using, as initial condition, NCEP/NCAR reanalysis data. After the simulations statistical method of the Bias was applied to evaluate how the accurately the model can reproduce the reanalysis seasonal rainfall. In a first analysis, it appears that the model is sensitive to FS or SAZC occurrences, as well as approaching the dynamics of the tropics and extratropics. The results suggest that the low resolution and the Grell parameterization are the main factors for inadequate quality of the simulations. Although the Grell scheme is suitable for areas with intense convection and strong vertical movements, an adjustment to the physical characteristics of the region is required. This study contributed to the improvement of regional climate models for the Amazon region, considering the contribution of ocean-atmosphere processes, during the summer and autumn in the southern hemisphere.O presente estudo tenta trazer um novo ponto de vista sobre a importância do Oceano Atlântico Equatorial no padrão sazonal, durante o período de verão e de outono da região Amazônica. Desta maneira, contribui de uma forma diferente para os estudos na área de modelagem climática e variabilidade pluviométrica na região. Para isto, foi utilizado o modelo RegCM3, com esquema de convecção Grell, aplicando a técnica donwscaling e utilizando como condição inicial os dados de reanalise do NCEP/NCAR. Após a obtenção das simulações foi aplicado o método estatístico Viés para avaliar o quanto o modelo consegue reproduzir a precipitação sazonal. Em uma primeira análise, constata-se que o modelo é sensível a entrada de SF ou ZCAS, bem como, aproxima-se da dinâmica dos trópicos e extratropicos. Os resultados sugerem que a baixa resolução e a parametrização Grell são os principais fatores para a inadequação da qualidade das simulações. Apesar de o esquema Grell ser indicado para regiões com intensa convecção e fortes movimentos verticais, o mesmo necessita ser ajustado com as características físicas da região. Este estudo contribuiu para o aprimoramento dos modelos climáticos regionais para a região amazônica, considerando a contribuição dos processos oceano-atmosfera, durante o período de verão e outono do hemisfério sul

Desligamentos de sistemas elétricos produzidos por relâmpagos nuvem-solo na Amazônia oriental

Operational records of power outages of the electric energy distribution systems in eastern Amazonia presented a large number of events attributed to lightning strikes, during the 2006 to 2009 period. The regional electricity concessionary data were compared to actual lightning observations made by SIPAM’s LDN system, over two areas where operational sub systems of transmission lines are installed. Statistical relations were drawn between the monthly lightning occurrence density and the number of power outages of the electric systems for both areas studied. The results showed that, although with some delays between these variables peaks, the number of power disruptions has a tendency to follow the behavior of the lightning occurrence densities variations. The numerical correlations were positive and may be useful to the transmission lines maintenance crews at least for the Belém-Castanhal electricity distribution sub system. Evidence was found, that the SST’s over certain areas of the Pacific and Atlantic Oceans, influence convection over the area of interest, and may help to prognosticate the periods of intense electric storms, requiring repair readiness for the regional electric systems.Os registros de desligamentos dos sistemas de distribuição de energia elétrica, na Amazônia oriental, apresentaram um grande número de eventos atribuídos à incidência de raios, durante o período de 2006 a 2008. Dados da concessionária regional de energia foram comparados com observações de raios feitas pelo sistema de detecção do SIPAM sobre áreas que abrangem dois subsistemas de linhas de transmissão. Relações estatísticas, entre a densidade mensal de ocorrência de raios e o número de desligamentos dos sistemas elétricos, foram deduzidas para ambos os subsistemas estudados. Os resultados mostraram que apesar de alguns atrasos entre os picos dessas variáveis e o número de desligamentos de energia apresentam uma tendência de acompanhar as variações das densidades de eventos de raios. As correlações numéricas foram positivas e podem ser úteis às equipes de manutenção, pelo menos para o subsistema de Belém-Castanhal. Evidência foi encontrada de que anomalias de TSM, sobre certas áreas dos oceanos Pacífico e Atlântico, influenciam a convecção sobre a área de interesse, e consequentemente, podem ajudar a prognosticar os períodos de intensas tempestades, que necessitam de prontidão para reparos dos sistemas elétricos regionais