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Casado M.J.,Agencia Estatal de Meteorologia AEMET | Pastor M.A.,Agencia Estatal de Meteorologia AEMET | Doblas-Reyes F.J.,ECMWF
Physics and Chemistry of the Earth | Year: 2010

This paper illustrates the ability of a set of different atmospheric circulation classifications from the COST733 Action " Harmonisation and Applications of Weather Types Classifications for European Regions" to describe the variability of winter precipitation over different climatic regions of Spain for the period 1961-1990. A Principal Component Analysis was first applied to identify the three regions (Atlantic, Mediterranean and Northern) with similar precipitation climatology. Different metrics such as the explained variation (EV), Pseudo-F index (PF) and the standard deviation (STD) have been used to evaluate the discriminatory power of the circulation classifications. A ranking of circulation classifications has been established for each region and for each metric. In the Atlantic and Northern regions, classifications that show a better performance correspond to the same type of algorithms, i.e. derived types with non-hierarchical cluster analysis. Instead, in the Mediterranean region, classifications using pre-defined types based on thresholds perform better. The classifications with the worst performance in every region belong to the subjective type. An analysis of the impact of the number of CTs on the discrimination ability of the classifications has also been carried out. Depending on the metric used, a different sensitivity of the classifications to the number of CTs has been found. The EV index shows an improvement when the number of CTs increases. Instead, the PF and the STD metrics showed a negative impact with an increasing number of CTs. © 2010 Elsevier Ltd.


Vicente-Serrano S.M.,CSIC - Pyrenean Institute of Ecology | Azorin-Molina C.,CSIC - Pyrenean Institute of Ecology | Sanchez-Lorenzo A.,University of Girona | Moran-Tejeda E.,University of Geneva | And 4 more authors.
Climate Dynamics | Year: 2014

We analyzed the evolution of surface relative humidity (RH) and specific humidity (q) in Spain, based on complete records available from the State Meteorological Agency of Spain. The surface RH records used span the period 1920-2011, but because of spatial and temporal constraints in the dataset we used a subset of the data, covering the period 1961-2011. The subset contained 50 monthly series of RH, which were created through a process of quality control, reconstruction and homogenization. The data shows that there was a large decrease in RH over mainland Spain from 1961 to 2011, which was greatest in spring and summer. In contrast, there was no overall change in the specific humidity in this period, except in spring, when an increase was observed. The decrease in RH affected the entire country, but the changes in specific humidity were less homogeneous. For specific humidity there was a general increase in the northern and eastern parts of Spain, whereas negative trends dominated in the central and southern areas, mainly during the summer months. The results suggest that an increase in the water holding capacity of the atmosphere as a consequence of warming during recent decades has not been accompanied by an increase in the surface water vapor content, probably because the supply of water vapor from the main terrestrial and oceanic areas has been constrained. We discuss the implications of these findings for evapotranspiration processes, precipitation and water management in Spain. © 2013 Springer-Verlag Berlin Heidelberg.


Garcia-Mozo H.,University of Cordoba, Spain | Mestre A.,Agencia Estatal de Meteorologia AEMET | Galan C.,University of Cordoba, Spain
Agricultural and Forest Meteorology | Year: 2010

The impact of climate change, and particularly of climate warming, is being tracked in many physical and biological systems. Plant phenology is seen as one of the most important bio-indicators, since trends can provide considerable temporal and spatial information regarding ongoing changes. Analyses performed at six sites in southern Spain from 1986 to the present have focused on vegetative and overall reproductive phenology in Olea europaea L., and Vitis vinifera L. and in various species of Quercus spp. and Poaceae. Early results suggest that trends in flowering patterns derived from field phenological observations were similar to trends in aerobiological data for most study species, and indicate a trend towards earlier foliation, flowering and fruit ripening. This advance is more evident in arboreal than in herbaceous species. Statistical analysis showed temperature increase was the major factor affecting earlier foliation, flowering and fruit ripening, as well as prompting delayed leaf fall. Herbaceous species were more affected than trees by changes in rainfall records. © 2010 Elsevier B.V. All rights reserved.


Pons M.R.,Agencia Estatal de Meteorologia AEMET | San-Martin D.,University of Cantabria | Herrera S.,University of Cantabria | Gutierrez J.M.,University of Cantabria
International Journal of Climatology | Year: 2010

In this study we analyze and simulate (with statistical downscaling techniques) the snow trends observed in the Northern Iberian Peninsula using daily snow occurrence (DSO) data from a network of 33 stations ranging from 60 to 1350 m. We first analyze the annual snow frequency measured as the annual number of snow days (NSD), obtaining a significant decreasing trend since the mid-seventies with a NSD reduction of about 50%; moreover, this magnitude is similar for low and high stations and for winter and spring separately. Then, we analyze the existing correlations with mean temperature and precipitation occurrence obtaining different relationships depending on the season and elevation. Finally, we simulate the observed trends using the connection of DSO with large-scale fields simulated by a General Circulation Model; for this purpose we apply an analog-based statistical downscaling method to obtain an estimation of DSO, working in perfect prognosis conditions using reanalysis data. On the one hand, the downscaling method is able to estimate/predict the DSO with typical values of hit and false alarm rates around 60% and 2%, respectively. On the other hand, the annual frequency obtained by averaging the DSO estimations reproduces very well both the observed trends and the high inter-annual variability. These promising results open the possibility to future research in seasonal or climate change projections of snow frequency. © 2009 Royal Meteorological Society.


Pons M.R.,Agencia Estatal de Meteorologia AEMET | Herrera S.,University of Cantabria | Gutierrez J.M.,Institute Fisica Of Cantabria Uc Csic
Climate Dynamics | Year: 2015

In a previous study Pons et al. (Clim Res 54(3):197–207, 2010. doi:10.3354/cr01117g) reported a significant decreasing trend of snowfall occurrence in the Northern Iberian Peninsula since the mid 70s. The study was based on observations of annual snowfall frequency (measured as the annual number of snowfall days NSD) from a network of 33 stations ranging from 60 to 1350 m. In the present work we analyze the skill of Regional Climate Models (RCMs) to reproduce this trend for the period 1961–2000 (using both reanalysis- and historical GCM-driven boundary conditions) and the trend and the associated uncertainty of the regional future projections obtained under the A1B scenario for the first half of the twenty-first century. In particular, we consider the regional simulation dataset from the EU-funded ENSEMBLES project, consisting of thirteen state-of-the-art RCMs run at 25 km resolution over Europe. While ERA40 severely underestimates both the mean NSD and its observed trend (−2.2 days/decade), the corresponding RCM simulations driven by the reanalysis appropriately capture the interannual variability and trends of the observed NSD (trends ranging from −3.4 to −0.7, −2.1 days/decade for the ensemble mean). The results driven by the GCM historical runs are quite variable, with trends ranging from −8.5 to 0.2 days/decade (−1.5 days/decade for the ensemble mean), and the greatest uncertainty by far being associated with the particular GCM used. Finally, the trends for the future 2011–2050 A1B runs are more consistent and significant, ranging in this case from −3.7 to −0.5 days/decade (−2.0 days/decade for the ensemble mean), indicating a future significant decreasing trend. These trends are mainly determined by the increasing temperatures, as indicated by the interannual correlation between temperature and NSD (−0.63 in the observations), which is preserved in both ERA40- and GCM-driven simulations. © 2015 Springer-Verlag Berlin Heidelberg


Simarro J.,Agencia Estatal de Meteorologia AEMET | Homar V.,University of the Balearic Islands | Simarro G.,CSIC - Institute of Marine Sciences
Tellus, Series A: Dynamic Meteorology and Oceanography | Year: 2013

Most of the dynamical cores of operational global models can be broadly classified according to the spatial discretisation into two categories: spectral models with mass-based vertical coordinate and grid point models with height-based vertical coordinate. This article describes a new non-hydrostatic dynamical core for a global model that uses the spectral transform method for the horizontal directions and a height-based vertical coordinate. Velocity is expressed in the contravariant basis (instead of the geographical orthonormal basis pointing to the East, North and Zenith directions) so that the expressions of the boundary conditions and the divergence of the velocity are simpler. Prognostic variables in our model are the contravariant components of the velocity, the logarithm of pressure and the logarithm of temperature. Covariant tensor analysis is used to derive the differential operators of the prognostic equations, such as the curl, gradient, divergence and covariant derivative of the contravariant velocity. A Lorenz type grid is used in the vertical direction, with the vertical contravariant velocity staggered with respect to the other prognostic variables. High-order vertical operators are constructed following the finite difference technique. Time stepping is semi-implicit because it allows for long time steps that compensates the cost of the spectral transformations. A set of experiments reported in the literature is implemented so as to confirm the accuracy and efficiency of the new dynamical core. © 2013 J. Simarro et al.


Herrera S.,University of Cantabria | Gutierrez J.M.,University of Cantabria | Ancell R.,Agencia Estatal de Meteorologia AEMET | Pons M.R.,Agencia Estatal de Meteorologia AEMET | And 2 more authors.
International Journal of Climatology | Year: 2012

In this paper, we present a new publicly available high-resolution daily precipitation gridded dataset developed for peninsular Spain and the Balearic islands using 2756 quality-controlled stations (this dataset is referred to as Spain02). The grid has a regular 0.2° (approx. 20 km) horizontal resolution and spans the period from 1950 to 2003. Different interpolation methods were tested using a cross-validation approach to compare the resulting interpolated values against station data: kriging, angular distance weighting, and thin plane splines. Finally, the grid was produced applying the kriging method in a two-step process. First, the occurrence was interpolated using a binary kriging and, in a second step, the amounts were interpolated by applying ordinary kriging to the occurrence outcomes. This procedure is similar to the interpolation method used to generate the E-OBS gridded data-the state-of-the-art publicly available high-resolution daily dataset for Europe-which was used in this study for comparison purposes. Climatological statistics and extreme value indicators from the resulting grid were compared to those from the 25 km E-OBS dataset using the observed station records as a reference. Spain02 faithfully reproduces climatological features such as annual precipitation occurrence, accumulated amounts and variability, whereas E-OBS has some deficiencies in the southern region. When focusing on upper percentiles and other indicators of extreme precipitation regimes, Spain02 accurately reproduces the amount and spatial distribution of the observed extreme indicators, whereas E-OBS data present serious limitations over Spain due to the sparse data used in this region. As extreme values are more sensitive to interpolation, the dense station coverage of this new data set was crucial to get an accurate reproduction of the extremes. © 2010 Royal Meteorological Society.


Casado M.J.,Agencia Estatal de Meteorologia AEMET | Pastor M.A.,Agencia Estatal de Meteorologia AEMET
International Journal of Climatology | Year: 2016

This paper is concentrated on the evaluation of circulation type classifications (CTCs) from the European Action COST733 catalogue version 2.0 in terms of their ability to capture winter precipitation, expressed as percentage, over Spanish Iberia and the Balearic Islands. The explained variation, the pseudo-F statistics and the Brier skill score are used to quantify the explanatory power of circulation classifications. As secondary aims, the impact of using different number of circulation types, additional types of variables and 4-day sequences in the generation of classifications is analysed.Although no optimal method has been found, nevertheless, the results suggest that the use of CTCs based on optimization algorithms are, in general, performing better than those which are based on other algorithms (i.e. leader algorithms). Distinct variations in skill exist not only among classifications from different groups of basic methods but as well between classifications from the same method group; being remarkable the behaviour of the optimum random centroid method. Results are very dependent on the metric, for the explained variation, and the Brier skill score, the larger the number of circulation types, the better the performance; contrary to the behaviour of the pseudo-F statistic. The inclusion of 500 hPa vorticity in the generation of classifications improves results while a general deterioration is observed when considering 4-day sequences. These results are only valid for the selected season and cannot be transferred to other locations and seasons. © 2016 Royal Meteorological Society.


Casado M.J.,Agencia Estatal de Meteorologia AEMET | Pastor M.A.,Agencia Estatal de Meteorologia AEMET
Climate Dynamics | Year: 2012

This paper analyzes the ability of the multi-model simulations from the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) to simulate the main leading modes of variability over the Euro-Atlantic region in winter: the North-Atlantic Oscillation (NAO), the Scandinavian mode (SCAND), the East/Atlantic Oscillation (EA) and the East Atlantic/Western Russia mode (EA/WR). These modes of variability have been evaluated both spatially, by analyzing the intensity and location of their anomaly centres, as well as temporally, by focusing on the probability density functions and e-folding time scales. The choice of variability modes as a tool for climate model assessment can be justified by the fact that modes of variability determine local climatic conditions and their likely change may have important implications for future climate changes. It is found that all the models considered are able to simulate reasonably well these four variability modes, the SCAND being the mode which is best spatially simulated. From a temporal point of view the NAO and SCAND modes are the best simulated. UKMO-HadGEM1 and CGCM3. 1(T63) are the models best at reproducing spatial characteristics, whereas CCSM3 and CGCM3. 1(T63) are the best ones with regard to the temporal features. GISS-AOM is the model showing the worst performance, in terms of both spatial and temporal features. These results may bring new insight into the selection and use of specific models to simulate Euro-Atlantic climate, with some models being clearly more successful in simulating patterns of temporal and spatial variability than others. © 2011 Springer-Verlag.


Pastor M.A.,Agencia Estatal de Meteorologia AEMET | Casado M.J.,Agencia Estatal de Meteorologia AEMET
Climate Dynamics | Year: 2012

This paper presents an evaluation of the multi-model simulations for the 4th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) in terms of their ability to simulate the ERA40 circulation types over the Euro-Atlantic region in winter season. Two classification schemes, k-means and SANDRA, have been considered to test the sensitivity of the evaluation results to the classification procedure. The assessment allows establishing different rankings attending spatial and temporal features of the circulation types. Regarding temporal characteristics, in general, all AR4 models tend to underestimate the frequency of occurrence. The best model simulating spatial characteristics is the UKMO-HadGEM1 whereas CCSM3, UKMO-HadGEM1 and CGCM3. 1(T63) are the best simulating the temporal features, for both classification schemes. This result agrees with the AR4 models ranking obtained when having analysed the ability of the same AR4 models to simulate Euro-Atlantic variability modes. This study has proved the utility of applying such a synoptic climatology approach as a diagnostic tool for models' assessment. The ability of the models to properly reproduce the position of ridges and troughs and the frequency of synoptic patterns, will therefore improve our confidence in the response of models to future climate changes. © 2012 Springer-Verlag.

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