Brands S.,MeteoGalicia Xunta de Galicia
Geophysical Research Letters | Year: 2017
Assuming that atmosphere general circulation models (AGCMs) provide realistic estimates of the atmosphere's response to external forcing, it is here tested whether teleconnections triggered by the El Niño–Southern Oscillation (ENSO) are robust to internal atmospheric variability. To this aim, the AGCM ensemble from the European Centre for Medium-Range Weather Forecasts ERA-20CM project is used, whose 10 members are here seen as surrogates for the atmosphere's response to the observed external forcing. Results for 1900–2010 indicate that ENSO teleconnections in the tropics and in areas affected by the Pacific-North American and Pacific-South American patterns are robust, whereas in the extratropics they are otherwise generally not. Then, shorter periods are assessed during which particularly strong or weak teleconnections were found in previous studies based on observations. Results reveal that the late twentieth century teleconnections to North America, coinciding with the positive phase of the Pacific Decadal Oscillation, are robust in the southern United States and Mexico and to the south of Aleutian Islands. In contrast, according to the model experiments and methods applied here, teleconnections to the climate in southern Europe are not robust at all. ©2017. American Geophysical Union. All Rights Reserved.
Saavedra S.,University of Santiago de Compostela |
Rodriguez A.,University of Santiago de Compostela |
Taboada J.J.,MeteoGalicia Xunta de Galicia |
Souto J.A.,University of Santiago de Compostela |
Casares J.J.,University of Santiago de Compostela
Science of the Total Environment | Year: 2012
High levels of ozone are frequently measured at the Galicia (NW Iberian Peninsula) air quality monitoring stations from March to October. However, there have been very few studies on surface ozone in the northwestern Iberian Peninsula, most likely because the climate of this region is not favourable to photochemical ozone generation. The occurrence of these episodes may be related to either local-scale photochemical pollution or regional-scale transport from other polluted regions. In addition, high ozone episodes usually are developed under specific synoptic conditions. The main purposes of this study are to characterise the atmospheric conditions that lead to the ozone episodes in this region and to identify possible advection paths of ozone and precursors. A surface hourly ozone dataset (2002-2007) measured at rural sites in Galicia was analysed to identify high ozone episodes together with their associated synoptic patterns using a subjective classification with 23 different synoptic types. The synoptic weather patterns revealed that most of the episodes occur with high surface pressures centred over the British Isles and/or Central Europe while a high-altitude anticyclonic ridge crosses the Peninsula from North Africa, causing easterly or southeasterly winds. This analysis was completed with 3-day backward air mass trajectories obtained with HYSPLIT to assess the contribution of long-range transport, resulting in the following main routes: Mediterranean-Peninsular, South Atlantic-Portuguese, local and French-Cantabric. © 2012 Elsevier B.V..
Lorenzo M.N.,University of Vigo |
Taboada J.J.,Meteogalicia Xunta de Galicia |
Iglesias I.,University of Vigo |
Gomez-Gesteira M.,University of Vigo
Climatic Change | Year: 2011
The influence of sea surface temperature (SST) of the ocean on seasonal rainfall in Northwestern Iberian Peninsula is studied for the period 1951-2006. Seasonal correlations were calculated for all seasons and different lags applied on SST. A test for field-significance considering the properties of finiteness and interdependence of the spatial grid was applied to avoid correlations by chance. The most significant and repetitive correlation is found between SST over Equatorial Pacific and spring rainfall. The correlation is maintained for different lags, and the common area that satisfies the criteria for statistical field significance is coincident with ENSO area. A forecast scheme is developed to predict spring rainfall anomalies based in SST over ENSO area in precedent seasons. An analysis of principal components was also carried out to obtain the main modes of the Pacific Ocean and their influence on spring rainfall in NWIP. This study concludes that for the period 1951-2006 the negative phase of ENSO, "La Niña", almost always announces dry springs in NW Iberian Peninsula. However, the positive phase of ENSO, "El Niño", does not anticipate the appearance of wet springs. © 2010 Springer Science+Business Media B.V.