D. Pozo-Vázquez

The Association between ENSO and Winter Atmospheric Circulation and Temperature in the North Atlantic Region

The association among ENSO, the Northern Hemisphere sea level pressure (SLP), and temperatures in Europe has been analyzed during the period 1873-1995. In the first part, the SST of the Nino-3 region has been used to select extreme cold and warm ENSO events and periods that can be regarded as normal. The study was carried out for winter with the constraints that the ENSO events were well developed during the winter of study, and that they are extreme events. Composites of winter SLP and temperatures have been made for the selected cold and warm events as well as for normal cases and compared with each other. In the North Atlantic area, no statistically significant SLP anomaly patterns were found associated with warm events, while during cold events a statistically significant anomaly pattern resembling the positive phase of the North Atlantic oscillation (NAO) was found. The temperature analysis shows statistically significant negative anomalies during cold events over the Iberian Peninsula and positive anomalies over the British Isles and southern Scandinavia, consistent with the SLP anomalies. The SLP and temperatures have also been analyzed for spring. The patterns resemble those found for winter but the anomalies have lower amplitudes. For the completion of the composite analysis, the consistency among events of the relationship between ENSO and SLP as well as between ENSO and temperatures was examined. The results show that the significant patterns found in the composite analysis in the North Atlantic area are not the result of a few major events, but rather because both the SLP and temperature anomalies in this area during cold ENSO events are stable and qualitatively similar to those found during the positive phase of the NAO. The possible physical basis for this association between NAO and ENSO is discussed.

A 500‐year precipitation record in Southern Spain

This paper is part of a research programme devoted to the analysis of historical climate in Spain. A reconstruction of rainfall characteristics in Southern Spain from 1500 to the present is described. Weather information was taken from original documentary sources in the region. A numerical index was established to characterize the rainfall and its evolution. Results were calibrated with modern precipitation data and with the results of other studies of historical climate. The main objective is to obtain a long precipitation record. A preliminary analysis of the obtained series shows a fluctuating behavior with alternating dry and wet periods. The wettest periods occurred at the end of 16th century, the beginning of 17th century, and at the end of 19th century. The driest periods in the pre-instrumental era occurred during the first half of the 16th century, and around 1750. A general decreasing trend in precipitation can be observed from 1960 onwards. Copyright

Rainfall variability in southern Spain on decadal to centennial time scales

In this work a long rainfall series in Andalusia (southern Spain) is analysed. Methods of historical climatology were used to reconstruct a 500-year series from historical sources. Different statistical tools were used to detect and characterize significant changes in this series. Results indicate rainfall fluctuations, without abrupt changes, in the following alternating dry and wet phases: 1501–1589 dry, 1590–1649 wet, 1650–1775 dry, 1776-1937 wet and 1938–1997 dry. Possible causal mechanisms are discussed, emphasizing the important contribution of the North Atlantic Oscillation (NAO) to rainfall variability in the region. Solar activity is discussed in relation to the Maunder Minimum period, and finally the past and present are compared. Results indicate that the magnitude of fluctuations is similar in the past and present. Copyright

An analysis of the variability of the North Atlantic Oscillation in the time and the frequency domains

An analysis of the variability of the North Atlantic Oscillation (NAO) since the beginning of the 19th century has been carried out using monthly pressure series from Gibraltar, Lisbon, The Azores and Iceland. In the first part, the combinations of stations that best monitor the NAO at different time intervals (monthly, seasonal and winter-annual) are analysed based on a signal:noise approach. The stability through time of the relationship between the pressures at the different stations is also studied. Based on this analysis, proxy indices of the NAO are obtained and compared with the NAO index resulting from a principal component analysis (PCA) of gridded sea level pressure (SLP) data. In the second part, the cross-spectral characteristics of the data of the northern and southern stations are studied in order to determine for which ranges of periods the pressure undergoes simultaneous coherent and out-of-phase variations. Based on the cross-spectral analysis, several filters are proposed to be applied to the pressure series prior to calculating the NAO index, in order to improve the reliability of the NAO index as an indicator of the NAO. Results show that for a monthly or seasonal index, The Azores must be selected as the southern station, but the strongest relationship is found for winter using Gibraltar as the southern station. The cross-spectral analysis shows, firstly, that the periods that are mainly responsible for coherent and out-of-phase variations are 6 months, 1 year, 2 years and 8 years (the most important). Secondly, several ranges of periods, mainly from 3 to 4 years and less than 6 months, are shown not to contribute to coherent and out-of-phase relationships between stations. Removing these ranges of periods from the pressure series prior to calculating the indices notably improves the reliability of the indices as indicators of the NAO state. The comparison of the filtered and unfiltered indices shows that extreme values of the NAO result from coherent out-of-phase pressure variations between stations. Copyright

The Impact of the North Atlantic Oscillation on Renewable Energy Resources in Southwestern Europe

AbstractEurope is investing considerably in renewable energies for a sustainable future, with both Iberian countries (Portugal and Spain) promoting significantly new hydropower, wind, and solar plants. The climate variability in this area is highly controlled by just a few large-scale teleconnection modes. However, the relationship between these modes and the renewable climate-dependent energy resources has not yet been established in detail. The objective of this study is to evaluate the impact of the North Atlantic Oscillation (NAO) on the interannual variability of the main and primary renewable energy resources in Iberia. This is achieved through a holistic assessment that is based on a 10-km-resolution climate simulation spanning the period 1959–2007 that provides physically consistent data of the various magnitudes involved. A monthly analysis for the extended winter (October–March) months shows that negative NAO phases enhance wind speeds (10%–15%) and, thereby, wind power (estimated around 30% at ...

A reconstruction of the winter North Atlantic Oscillation index back to A.D. 1501 using documentary data in southern Spain

In this work a reconstruction of seasonal rainfall in Andalusia (southern Spain) from 1501 to 1997 is presented. This reconstruction is based on the analysis of a wide variety of documentary data. Qualitative data arc translated into numerical indices to elaborate time series of rainfall for each season of the year. Because of the strong relationship between Andalusian rainfall and the North Atlantic Oscillation (40% of the winter rainfall variance is explained by the NAO index behavior), it is possible to use these rainfall series to reconstruct the seasonal NAO index back to 1501. The results are compared with other analyses reported in the literature.

Analysis of WRF Model Wind Estimate Sensitivity to Physics Parameterization Choice and Terrain Representation in Andalusia (Southern Spain)

AbstractThis paper reports on an evaluation of the relative roles of choice of parameterization scheme and terrain representation in the Weather Research and Forecasting (WRF) mesoscale model, in the context of a regional wind resource assessment. As a first step, 32 configurations using two different schemes for microphysics, cumulus, planetary boundary layer (PBL), or shortwave and longwave radiation were evaluated. In a second step, wind estimates that were obtained from various experiments with different spatial resolution (1, 3, and 9 km) were assessed. Estimates were tested against data from four stations, located in southern Spain, that provided hourly wind speed and direction data at 40 m above ground level. Results from the first analysis showed that wind speed standard deviation (STD) and bias values were mainly sensitive to the PBL parameterization selection, with STD differences up to 10% and bias differences between −15% and 10%. The second analysis showed a weak influence of spatial resoluti...

Analysis of Spatiotemporal Balancing between Wind and Solar Energy Resources in the Southern Iberian Peninsula

AbstractElectricity from wind and, to a lesser extent, solar energy is intermittent and not controllable. Unlike conventional power generation, therefore, this electricity is not suitable to supply base-load electric power. In the future, with greater penetration of these renewable sources, intermittency and control problems will become critical. Here, the authors explore the use of canonical correlation analysis (CCA) for analyzing spatiotemporal balancing between regional solar and wind energy resources. The CCA allows optimal distribution of wind farms and solar energy plants across a territory to minimize the variability of total energy input into the power supply system. The method was tested in the southern half of the Iberian Peninsula, a region covering about 350 000 km2. The authors used daily-integrated wind and solar energy estimates in 2007 from the Weather Research and Forecasting (WRF) mesoscale model, at a spatial resolution of 9 km. Results showed valuable balancing patterns in the study r...

North Atlantic Winter SLP Anomalies Based on the Autumn ENSO State

The winter sea level pressure (SLP) anomalies in the Northern Hemisphere have been analyzed over the period 1873-2000 based on the ENSO state during the previous autumn. First, a set of extreme cold and warm ENSO events and periods that may be regarded as normal is selected using the SST data of the Nino-3 region. This selection is carried out for autumn and with the constraint that the ENSO event is well developed. For the winters following these selected autumn events, composites of Northern Hemisphere SLP anomalies have been obtained and compared to each other. A study of the consistency among events of the relationship between ENSO and SLP anomalies was also carried out. Results show the preference for a positive NAO-like SLP anomaly pattern in the North Atlantic region during the winters following autumns of strong cold ENSO events and, thus, suggest the existence of a potential source of predictability for the North Atlantic climate. An additional analysis of the winter North Atlantic Oscillation (NAO) index confirms this finding. The possible physical basis of this source of predictability for the North Atlantic climate is discussed.

Optimal management of wind and solar energy resources

This paper presents a portfolio-based approach to the harvesting of renewable energy (RE) resources. Our examined problem setting considers the possibility of distributing the total available capacity across an array of heterogeneous RE generation technologies (wind and solar power production units) being dispersed over a large geographical area. We formulate the capacity allocation process as a bi-objective optimization problem, in which the decision maker seeks to increase the mean productivity of the entire array while having control on the variability of the aggregate energy supply. Using large-scale optimization techniques, we are able to calculate - to an arbitrary degree of accuracy - the complete set of Pareto-optimal configurations of power plants, which attain the maximum possible energy delivery for a given level of power supply risk. Experimental results from a reference geographical region show that wind and solar resources are largely complementary. We demonstrate how this feature could help energy policy makers to improve the overall reliability of future RE generation in a properly designed risk management framework.