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Oliveira F.N.M.,University of Sao Paulo | Oliveira F.N.M.,National Institute of Meteorology | Carvalho L.M.V.,University of California at Santa Barbara | Ambrizzi T.,University of Sao Paulo
International Journal of Climatology

This study presents 53-year climatology of Southern Hemisphere (SH) blockings in the winter using daily 500-hPa geopotential height data from NCEP-NCAR reanalysis. The variability of SH blocking events and their relationships with combined phases of El Niño/southern oscillation (ENSO) and the southern annular mode (SAM) are examined. Conventional indices were revised and a slightly modified index is proposed to detect latitudinal variations of SH blockings. The South Pacific region is examined in detail. There is no statistically significant long-term trend in the SH blockings. During moderate El Niño, the preferred location SH blocking is observed over East Pacific, and we show that the blocking frequency increases during negative SAM phases. During moderate La Niña the SH blockings are significantly suppressed over Central Pacific, with lower blocking frequency during positive SAM phases. These results indicate that the daily variability of SH blocking is strongly modulated by both ENSO and SAM phases. © 2013 Royal Meteorological Society. Source

de Carvalho Alves M.,Federal University of Mato Grosso | de Carvalho L.G.,Federal University of Lavras | Vianello R.L.,National Institute of Meteorology | Sediyama G.C.,Federal University of Vicosa | And 2 more authors.
Theoretical and Applied Climatology

The objective of the present study was to use the simple cokriging methodology to characterize the spatial variability of Penman-Monteith reference evapotranspiration and Thornthwaite potential evapotranspiration methods based on Moderate Resolution Imaging Spetroradiometer (MODIS) global evapotranspiration products and high-resolution surfaces of WordClim temperature and precipitation data. The climatic element data referred to 39 National Institute of Meteorology climatic stations located in Minas Gerais state, Brazil and surrounding states. The use of geostatistics and simple cokriging technique enabled the characterization of the spatial variability of the evapotranspiration providing uncertainty information on the spatial prediction pattern. Evapotranspiration and precipitation surfaces were implemented for the climatic classification in Minas Gerais. Multivariate geostatistical determined improvements of evapotranspiration spatial information. The regions in the south of Minas Gerais derived from the moisture index estimated with the MODIS evapotranspiration (2000-2010), presented divergence of humid conditions when compared to the moisture index derived from the simple kriged and cokriged evapotranspiration (1961-1990), indicating climate change in this region. There was stronger pattern of crossed covariance between evapotranspiration and precipitation rather than temperature, indicating that trends in precipitation could be one of the main external drivers of the evapotranspiration in Minas Gerais state, Brazil. © 2012 Springer-Verlag Wien. Source

Manhique A.J.,National Institute of Meteorology | Manhique A.J.,University of Cape Town | Reason C.J.C.,University of Cape Town | Rydberg L.,Gothenburg University | Fauchereau N.,University of Cape Town
International Journal of Climatology

An analysis of the inter-annual frequency of the main summer rainfall producing synoptic system [tropical temperate troughs (TTTs)] over Mozambique and the Southwest Indian Ocean and their relationships with regional sea surface temperatures and circulation patterns is presented for the January-March season. Correlations and composite anomalies based on annual frequency of occurrence of TTTs over Mozambique suggest that TTT occurrence is related to La Niña and Southern Hemisphere planetary waves (wavenumber-3 or -4) that modulate the subtropical high pressure cells in the three oceanic basins. These modulations lead to enhanced easterly winds over the South Indian Ocean and onshore moisture fluxes towards southeastern Africa. A stronger than average Angola low, particularly linked to La Niña, also plays an important role in the frequency and intensity of the TTT, by enhancing the wind and moisture convergence over southeastern Africa. Moisture fluxes over the warm Agulhas current and tropical southeast Atlantic also affect the rainfall variability over southern Africa to some extent during summers with a high frequency of TTT. Positive sea surface temperature (SST) anomalies over the tropical and subtropical South Indian Ocean that are linked to El Niño-Southern Oscillation appear to play a significant role in causing dry conditions over Mozambique. These positive SST anomalies help promote convective activity offshore, and also weaken the northern half of the South Indian Ocean high pressure cell. As a result, the easterly winds are weakened leading to less onshore moisture fluxes than in the wet seasons. Copyright © 2009 Royal Meteorological Society. Source

Luu T.N.M.,University Pierre and Marie Curie | Luu T.N.M.,Vietnam Academy of Science and Technology | Garnier J.,University Pierre and Marie Curie | Billen G.,University Pierre and Marie Curie | And 6 more authors.
Journal of Asian Earth Sciences

The Red River Delta (RRD) in Northern Vietnam represents a complex hydrological network of tributaries and distributaries that receive a large and seasonally fluctuating flow of water from the upper Red River basin and is also subjected to tidal influence. In this study, we attempted to assemble a database of discharge estimates within the RRD for 1996-2006 to elucidate the water circulation patterns in the system, enable quantification of major water fluxes and assess the water resources availability. Regular discharge measurements in the RRD are available for three upstream stations, while the other hydrological stations provide only water level records; however, the MIKE 11 model allowed overall calibration curves to be established, which enabled the conversion of available daily mean water level data into discharge values. Four gauging surveys were conducted under flood and dry season in 2007 and 2008 to experimentally validate these calibration curves. After the database was generated, a water balance was established for two years with contrasting climatic and hydrological characteristics. During the wet year (1996), the main branch of the Red River represented the largest input of freshwater to the sea (approximately 60%). Conversely, during the dry year (2006), the inputs were more evenly distributed among the three main fluvial branches. The total volume annually delivered to the sea from the RRD was approximately 140 and 100 km3 for 1996 and 2006, respectively. When the five sub-basins within the RRD were evaluated, it was shown that the water resources were far from evenly distributed within the area. In particular, the Bui sub-basin, which has the highest population density and the lowest water resources per unit area, is experiencing a critical situation in terms of pressure on water resources. © 2009 Elsevier Ltd. All rights reserved. Source

van Drooge B.L.,CSIC - Institute of Environmental Assessment And Water Research | Fernandez P.,CSIC - Institute of Environmental Assessment And Water Research | Grimalt J.O.,CSIC - Institute of Environmental Assessment And Water Research | Stuchlik E.,Charles University | And 2 more authors.
Environmental Science and Pollution Research

Background, aim and scope: Ambient air concentrations of polycyclic aromatic hydrocarbons (PAH) were determined at five elevated mountain sites on the European continent and the Atlantic Ocean. All sites can be considered remote background areas since they are situated above the timberline and they lack local emission sources of these compounds. Results and discussion: Average gas phase concentrations of ΣPAH were 165, 1,475, 1,553, 1,822 and 4,443 pg m-3 for Tenerife, Pyrenees, Central Norway, Tyrolean Alps and High Tatras, respectively. Particulate phase concentrations were 55, 70, 383, 196 and 708 pg m-3, respectively. The PAH profiles of samples from the different sites are very similar, being typical of PAH mixtures after long-range atmospheric transport. Part of the fluctuations in PAH concentrations are explained by the influence of temperature on the particulate/gas phase partitioning. Conclusion: The differences in PAH levels between sites, with the lowest concentrations found in Tenerife and the highest in the High Tatras, suggest the geographical influence of regional emissions on the sites, especially in the cold periods and for the sites in the eastern sector of the European continent. This is supported by air mass back-trajectories analysis for the samples on the different sites. The influence of the continent is not detectable in the case of the elevated site of Tenerife where the free troposphere has been sampled. The results in this study are consistent with the PAH levels found in soils and/or high mountain lake sediments from these areas. © 2010 Springer-Verlag. Source

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