The South American Monsoon System and the 1970s climate transition

The South American Monsoon System (SAMS) is characterised by intense convective activity and precipitation during austral summer. This study investigates changes in the onset, demise and duration of SAMS during 1948-2008. The results show a significant change in these characteristics in the early 1970s. Onset becomes steadily earlier from 1948 to early 1970s and has occurred earlier than 23-27 October after 1972-1973. Demise dates have remained later than 21-25 April after the mid-to-late 1970s. SAMS duration shows a statistical changepoint in the summer of 1971-1972 such that the mean duration was similar to 170 days (1948-1972) and 195 days (1972-1982). Vertically integrated moisture flux is used to diagnose changes in mean state and reveal statistically significant increases over South America after 1971-1972. Copyright. (C) 2010 Royal Meteorological Society

Origin of Convectively Coupled Kelvin Waves over South America

Convectively coupled Kelvin waves over the South American continent are examined through the use of temporal and spatial filtering of reanalysis, satellite, and gridded rainfall data. They are most prominent from November to April, the season analyzed herein. The following two types of events are isolated: those that result from preexisting Kelvin waves over the eastern Pacific Ocean propagating into the continent, and those that apparently originate over Amazonia, forced by disturbances propagating equatorward from central and southern South America. The events with precursors in the Pacific are mainly upper-level disturbances, with almost no signal at the surface. Those events with precursors over South America, on the other hand, originate as upper-level synoptic wave trains that pass over the continent and resemble the ""cold surges`` documented by Garreaud and Wallace. As the wave train propagates over the Andes, it induces a southerly low-level wind that advects cold air to the north. Precipitation associated with a cold front reaches the equator a few days later and subsequently propagates eastward with the characteristics of a Kelvin wave. The structures of those waves originating over the Pacific are quite similar to those originating over South America as they propagate to eastern South America and into the Atlantic. South America Kelvin waves that originate over neither the Pacific nor the midlatitudes of South America can also be identified. In a composite sense, these form over the eastern slope of the Andes Mountains, close to the equator. There are also cases of cold surges that reach the equator yet do not form Kelvin waves. The interannual variability of the Pacific-originating events is related to sea surface temperatures in the central-eastern Pacific Ocean. When equatorial oceanic conditions are warm, there tends to be an increase in the number of disturbances that reach South America from the Pacific.

A neve em Palmas/PR: da reconstituição histórica à abordagem dinâmica

Pós-graduação em Geografia - IGCE

Variabilidade da precipitação pluviométrica nas regiões Sudeste e Sul do Brasil

Pós-graduação em Agronomia (Energia na Agricultura) - FCA

Sobre o sinal de um downscaling dinâmico às oscilações intrassazonais de precipitação no setor norte do Nordeste do Brasil

Oscilações intrassazonais são fatores controladores da variabilidade pluviométrica interanual de áreas tropicais. O conhecimento de como os modelos numéricos reproduzem suas variabilidades é importante para entender melhor suas atuações e subsidiar operações de previsão de tempo e clima. Neste artigo investiga-se a sensibilidade de um modelo de downscaling dinâmico de precipitação na reprodução das oscilações intrassazonais observadas no setor norte do Nordeste do Brasil (SNNEB - 45ºW-37ºW e 2ºS-12ºS) no período de 1974 a 2000. Os resultados mostraram que a precipitação simulada sobre o SNNEB explicou aproximadamente 70% da variabilidade da precipitação observada no trimestre fevereiro a abril nesta região. Estatísticas de médias, desvios normalizados e percentuais neste trimestre, nessa região, em anos de contrastes climáticos nos Oceanos Pacífico e Atlântico Tropicais, também foram bem capturadas pela precipitação simulada através do downscaling. Análises espectrais com uso de ondeletas mostraram que o downscaling dinâmico tem potencial para reproduzir picos espectrais de precipitação observada no SNNEB nas escalas acima de 8 dias, e nas escalas entre 64 e 128 dias para o período de 01 de janeiro a 30 de junho.

Índices de extremos climáticos e tendências da precipitação anual e sazonal na Amazônia Oriental

Baseado no conjunto de dados diários de precipitação e temperatura do ar de oito estações meteorológicas sobre o Pará, pertencentes ao INMET, disponíveis no período 1961-2007, foram calculados índices de extremos climáticos através da metodologia estatística do software RClimdex. Utilizando-se ainda um conjunto de dados mensais de precipitação de 134 estações pluviométricas da Amazônia oriental, provenientes da ANA e INMET, foram analisadas as tendências anual e sazonal num período de 25 a 37 anos (1970-2009), através da aplicação da estatística não-paramétrica (teste de Mann-Kendall e método de Sen). E por fim, utilizaram-se dados de desmatamento do PRODES/INPE no período 2000-2007, para analisar a possível influência do desmatamento nas tendências de precipitação anual e sazonal do Pará. Considerando os índices de extremos climáticos referentes aos dados diários de precipitação, constatou-se que a variabilidade interanual dos índices possui relações com os episódios ENOS e as fases do Dipolo do Atlântico. Para os extremos climáticos de temperatura evidenciaram-se reduções sistemáticas dos dias frios (TX10p) e aumentos sistemáticos da mínima da máxima temperatura (TXN), da percentagem de noites quentes (TX90p) e da temperatura máxima da máxima (TXX). Os resultados das tendências da precipitação anual usando os testes não-paramétricos evidenciaram que do total de 134 estações, em torno de 51% apresentam tendências positivas e 41% tendências negativas sobre a Amazônia oriental. Contudo, essas tendências anuais “mascararam” de certa forma as tendências sazonais, cujos resultados mostraram-se mais diversificados, explicando melhor os aspectos da variabilidade climática regional. Para o trimestre MAM, observaram-se 99 estações (74%) com tendências positivas, indicando que a quantidade de precipitação durante o período chuvoso principal vem aumentando sistematicamente durante a última década. Em DJF, notaram-se 45 estações (34%) com tendências positivas e 78 estações (58%) com tendências negativas. Por outro lado, nos trimestres que englobam o período seco ou menos chuvoso verificaram-se tendências sazonais predominantemente negativas, com 84 estações (62%) em JJA e 89 estações (66%) em SON. Portanto, a evidência observacional de que a precipitação do período seco encontra-se em diminuição gradativa nas últimas décadas corrobora com a hipótese de que o desmatamento associa-se com a redução da precipitação em escala regional, porém sugere-se que isso ocorra em escala de tempo sazonal.

Subtropical Cyclones over the Southwestern South Atlantic: Climatological Aspects and Case Study

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Análise da variabilidade das chuvas e sua relação com a produtividade da soja na vertente paranaense da bacia do Paranapanema

Pós-graduação em Geografia - FCT

Re-analysis of pluvial precipitation in southern Brazil

This study examined precipitation in southern Brazil based on a data set provided by the Brazilian National Water Agency, covering the period from 1976 to 2010. Data were homogenized using the R software and the Climatol subroutine, which allow completing missing data. Isohyets were drawn using the Geostatistics software to obtain a semivariogram for each analysis. There was a remarkable interannual variability in this region, with positive anomalies in the warm phase (El Nino) and negative anomalies in the cold phase (La Nina) of ENSO. Also, the responses of this variability were not uniform in the entire region, since there was variability from year to year and from event to event.

Temporal changes in benthic megafaunal abundance and composition across the West Antarctic Peninsula shelf: Results from video surveys

The West Antarctic Peninsula (WAP) shelf experiences intense seasonal and interannual variability in phytoplankton production and particulate-organic-carbon flux to the seafloor. To explore the response of the megabenthic community to this production variability, we conducted video surveys of epibenthic megafauna at three stations on the WAP shelf in Nov-Dec 1999, Mar 2000, Jun 2000, Oct-Nov 2000, and Feb-Mar 2001. The epibenthic megafauna was dominated (>90%) by elasipod holothurians, irregular urchins and anthozoans, with total abundances ranging from 19 to 152 ind. 1 00 m(-2). The abundance of three of the dominant taxa (Protelpidia murrayi, Peniagone vignomi, and Amphipneustes spp.) varied significantly across seasons (p <0.05), although variations were not tightly correlated with the summer bloom cycle. The irregular urchins in the genus Amphipneustes varied 5-fold in abundance at single stations, with maximum densities (an average of 10.1 ind. 100 m(-2)) attained in Jun 2000. Abundances of the elasipod holothurians P. murrayi (1-121 ind. 100 m(-2)) and P. vignoni (0.7-27.5 ind. 100 m(-2)) fell within the range for elasipod holothurians from other bathyal regions measured using image analysis. The abundance of P. murrayi increased up to 6-fold from a single Jun-Oct recruitment pulse, while changes in the abundance of P. vignoni (over 2-fold higher in Feb-Mar 2001) apparently resulted from immigration during the presence of a 1-2 cm thick carpet of fresh phytocletritus. Based on the ratio of the number of fecal casts per individual, elasipod holothurians increased surface-deposit feeding rates by >= 2-fold while phytocletritus was present at the seafloor. Nonetheless, these surface-deposit feeders appeared to feed and egest sediments throughout the winter, which is consistent with year-round persistence of a labile food bank in surficial sediments on the deep WAP shelf.

A biophysical model of Sugarcane growth

Scientists predict that global agricultural lands will expand over the next few decades due to increasing demands for food production and an exponential increase in crop-based biofuel production. These changes in land use will greatly impact biogeochemical and biogeophysical cycles across the globe. It is therefore important to develop models that can accurately simulate the interactions between the atmosphere and important crops. In this study, we develop and validate a new process-based sugarcane model (included as a module within the Agro-IBIS dynamic agro-ecosystem model) which can be applied at multiple spatial scales. At site level, the model systematically under/overestimated the daily sensible/latent heat flux (by -10.5% and 14.8%, H and E, respectively) when compared against the micrometeorological observations from southeast Brazil. The model underestimated ET (relative bias between -10.1% and 12.5%) when compared against an agro-meteorological field experiment from northeast Australia. At the regional level, the model accurately simulated average yield for the four largest mesoregions (clusters of municipalities) in the state of Sao Paulo, Brazil, over a period of 16 years, with a yield relative bias of -0.68% to 1.08%. Finally, the simulated annual average sugarcane yield over 31 years for the state of Louisiana (US) had a low relative bias (-2.67%), but exhibited a lower interannual variability than the observed yields.

The Southern Ocean and Its Climate in CCSM4

The new Community Climate System Model, version 4 (CCSM4), provides a powerful tool to understand and predict the earth's climate system. Several aspects of the Southern Ocean in the CCSM4 are explored, including the surface climatology and interannual variability, simulation of key climate water masses (Antarctic Bottom Water, Subantarctic Mode Water, and Antarctic Intermediate Water), the transport and structure of the Antarctic Circumpolar Current, and interbasin exchange via the Agulhas and Tasman leakages and at the Brazil-Malvinas Confluence. It is found that the CCSM4 has varying degrees of accuracy in the simulation of the climate of the Southern Ocean when compared with observations. This study has identified aspects of the model that warrant further analysis that will result in a more comprehensive understanding of ocean-atmosphere-ice dynamics and interactions that control the earth's climate and its variability.

Root niche separation can explain avoidance of seasonal drought stress and vulnerability of overstory trees to extended drought in a mature Amazonian forest

Large areas of Amazonian evergreen forest experience seasonal droughts extending for three or more months, yet show maximum rates of photosynthesis and evapotranspiration during dry intervals. This apparent resilience is belied by disproportionate mortality of the large trees in manipulations that reduce wet season rainfall, occurring after 2-3 years of treatment. The goal of this study is to characterize the mechanisms that produce these contrasting ecosystem responses. A mechanistic model is developed based on the ecohydrological framework of TIN (Triangulated Irregular Network)-based Real Time Integrated Basin Simulator + Vegetation Generator for Interactive Evolution (tRIBS+VEGGIE). The model is used to test the roles of deep roots and soil capillary flux to provide water to the forest during the dry season. Also examined is the importance of "root niche separation," in which roots of overstory trees extend to depth, where during the dry season they use water stored from wet season precipitation, while roots of understory trees are concentrated in shallow layers that access dry season precipitation directly. Observational data from the Tapajo's National Forest, Brazil, were used as meteorological forcing and provided comprehensive observational constraints on the model. Results strongly suggest that deep roots with root niche separation adaptations explain both the observed resilience during seasonal drought and the vulnerability of canopy-dominant trees to extended deficits of wet season rainfall. These mechanisms appear to provide an adaptive strategy that enhances productivity of the largest trees in the face of their disproportionate heat loads and water demand in the dry season. A sensitivity analysis exploring how wet season rainfall affects the stability of the rainforest system is presented. Citation: Ivanov, V. Y., L. R. Hutyra, S. C. Wofsy, J. W. Munger, S. R. Saleska, R. C. de Oliveira Jr., and P. B. de Camargo (2012), Root niche separation can explain avoidance of seasonal drought stress and vulnerability of overstory trees to extended drought in a mature Amazonian forest, Water Resour. Res., 48, W12507, doi:10.1029/2012WR011972.

Soil carbon balance in a tropical grassland: Estimation of soil respiration and its partitioning using a semi-empirical model

In savannah and tropical grasslands, which account for 60% of grasslands worldwide, a large share of ecosystem carbon is located below ground due to high root:shoot ratios. Temporal variations in soil CO2 efflux (R-S) were investigated in a grassland of coastal Congo over two years. The objectives were (1) to identify the main factors controlling seasonal variations in R-S and (2) to develop a semi-empirical model describing R-S and including a heterotrophic component (R-H) and an autotrophic component (R-A). Plant above-ground activity was found to exert strong control over soil respiration since 71% of seasonal R-S variability was explained by the quantity of photosynthetically active radiation absorbed (APAR) by the grass canopy. We tested an additive model including a parameter enabling R-S partitioning into R-A and R-H. Assumptions underlying this model were that R-A mainly depended on the amount of photosynthates allocated below ground and that microbial and root activity was mostly controlled by soil temperature and soil moisture. The model provided a reasonably good prediction of seasonal variations in R-S (R-2 = 0.85) which varied between 5.4 mu mol m(-2) s(-1) in the wet season and 0.9 mu mol m(-2) s(-1) at the end of the dry season. The model was subsequently used to obtain annual estimates of R-S, R-A and R-H. In accordance with results reported for other tropical grasslands, we estimated that R-H accounted for 44% of R-S, which represented a flux similar to the amount of carbon brought annually to the soil from below-ground litter production. Overall, this study opens up prospects for simulating the carbon budget of tropical grasslands on a large scale using remotely sensed data. (C) 2012 Elsevier B.V. All rights reserved.

Estimating the monthly pCO2 distribution in the North Atlantic using a self-organizing neural network

[EN] Here we present monthly, basin-wide maps of the partial pressure of carbon dioxide (pCO2) for the North Atlantic on a latitude by longitude grid for years 2004 through 2006 inclusive. The maps have been computed using a neural network technique which reconstructs the non-linear relationships between three biogeochemical parameters and marine pCO2. A self organizing map (SOM) neural network has been trained using 389 000 triplets of the SeaWiFSMODIS chlorophyll-a concentration, the NCEP/NCAR reanalysis sea surface temperature, and the FOAM mixed layer depth. The trained SOM was labelled with 137 000 underway pCO2 measurements collected in situ during 2004, 2005 and 2006 in the North Atlantic, spanning the range of 208 to 437atm. The root mean square error (RMSE) of the neural network fit to the data is 11.6?atm, which equals to just above 3 per cent of an average pCO2 value in the in situ dataset. The seasonal pCO2 cycle as well as estimates of the interannual variability in the major biogeochemical provinces are presented and discussed. High resolution combined with basin-wide coverage makes the maps a useful tool for several applications such as the monitoring of basin-wide air-sea CO2 fluxes or improvement of seasonal and interannual marine CO2 cycles in future model predictions. The method itself is a valuable alternative to traditional statistical modelling techniques used in geosciences.