Azken hamarkadetako itsas tenperaturaren joerak Bizkaiko Golkoan

Bizkaiako Golkoan azken hamarkadetan itsasoko tenperaturak erakutsi dituen joerak aztertu dira lan honetan, horretarako satelite bidez jasotako itsas gaineko tenperaturen neurketak erabiliz bai tokian bertan, gainazalean, bai sakonera desberdinetan, bildutako tenperatura-neurketak erabiliaz. Bi denbora tarte aztertu dira lan honetan:1955-2010 eta 1985-2008. Tokiko neurketen multzoa 1955-2010 eperako dago eskuragarri eta epe hori neurketa mota horrekin soilik aztertu da. 1985-2008 tarterako berriz, tokiko zein sateliteko neurketak daude eskuragarri eta beraz, analisian bi datu motak hartu dira kontuan. Datu horietatik ondoriozta daiteke gainazalean zein aztertutako gainontzeko sakoneretan beroketa-joera ageri bat dagoela, baina bere balioa aukeratzen den denbora tartearekiko menpekoa dela. Horretaz gain, itsas gainazalean eta lehenengo metroetan ageri da beroketa handiena, hortik behera beroketa txikitzen doalarik

Daily scale wintertime sea surface temperature and IPC-Navidad variability in the southern Bay of Biscay from 1981 to 2010

The combination of remotely sensed gappy Sea surface temperature (SST) images with the missing data filling DINEOF (data interpolating empirical orthogonal functions) technique, followed by a principal component analysis of the reconstructed data, has been used to identify the time evolution and the daily scale variability of the wintertime surface signal of the Iberian Poleward Current (IPC), or Navidad, during the 1981-2010 period. An exhaustive comparison with the existing bibliography, and the vertical temperature and salinity profiles related to its extremes over the Bay of Biscay area, show that the obtained time series accurately reflect the IPC-Navidad variability. Once a time series for the evolution of the SST signal of the current over the last decades is well established, this time series is used to propose a physical mechanism in relation to the variability of the IPC-Navidad, involving both atmospheric and oceanic variables. According to the proposed mechanism, an atmospheric circulation anomaly observed in both the 500 hPa and the surface levels generates atmospheric surface level pressure, wind-stress and heat-flux anomalies. In turn, those surface level atmospheric anomalies induce mutually coherent SST and sea level anomalies over the North Atlantic area, and locally, in the Bay of Biscay area. These anomalies, both locally over the Bay of Biscay area and over the North Atlantic, are in agreement with several mechanisms that have separately been related to the variability of the IPC-Navidad, i.e. the south-westerly winds, the joint effect of baroclinicity and relief (JEBAR) effect, the topographic beta effect and a weakened North Atlantic gyre.ERA-Interim data were obtained from the ECMWF data server (http://data.ecmwf.int/data). Pathfinder v5.2 data were provided by GHRSST and the US National Oceanographic Data Center. AMSR-E data are produced by Remote Sensing Systems and sponsored by the NASA Earth Science MEaSUREs DISCOVER Project and the AMSR-E Science Team. Data are available at www.remss.com. The altimeter products were produced by Ssalto/Duacs and distributed by Aviso, with support from Cnes (http://www.aviso.oceanobs.com/duacs/). ICOADS data for this study have been retrieved from the Research Data Archive (RDA) which is maintained by the Computational and Information Systems Laboratory (CISL) at the National Center for Atmospheric Research (NCAR). Word Ocean Database data were obtained from http://www.nodc.noaa.gov/OC5/WOD/pr_wod.html. DINEOF source code is freely available at http://modb.oce.ulg.ac.be/mediawiki/index.php/DINEOF. G. Esnaola is supported by a research grant (Interaccion Atmosfera-Oceano en el Golfo de Bizkaia) from Fundacion Centros Tecnologicos Inaki Goenaga. Jon Saenz would like to thank the financial support from project CGL2008-03321 (Spanish National R+D+I Programme). He also thanks funding provided by the University of the Basque Country (UFI 11/55, PPH12/01 and GIU 11/01). The Basque Government (Department of Agriculture, Fisheries and Food) has funded the project VARIACIONES. The authors want to express their gratitude to A. Caballero from AZTI-Tecnalia for her help with the Altimetry data and to B. Le Cann from UBO-CNRS-IRD-IFREMER for his useful comments on an early draft of this document. This is contribution number 649 of the Marine Research Division of AZTI-Tecnalia

Satelite bidezko itsas gainazaleko tenperatura eta klorofila kontzentrazioen berreraikitzea. Azken hamarkadetako eta urtaroen zikloaren bilakaera Bizkaiko Golkoan

Satelite bidezko itsas gainazaleko tenperatura eta klorofila kontzentrazio irudiei lainoek eragindako zuloak betetzeko DINEOF teknika aplikatu zaie, zulorik gabeko eguneroko maiztasuneko hamarkadetako irudi sortak sortzeko asmoarekin. Irudi sorta horien azterketa egin da ondoren bi aldagaietan urtaroen zikloa aztertzeko, bai bere anplitudeari zein bere faseari dagokienez. Azterketak erakusten du tenperaturaren urtaro zikloaren anplitudeak 0,11 °C/hamarkada balioko joera gorakor adierazgarria duela baina ez horrela klorofila kontzentrazioarenak. Faseari dagokionez, berriz, ez da joera adierazgarririk detektatu bi aldagaietako batean ere.; Satellite sea surface temperate and chlorophyll concentration images have been processed using DINEOF technique to fill the gaps created by the presence of clouds in satellite images. This set of satellite temperature and chlorophyll images have then been used to analyse their respective seasonal cycles, both regarding the amplitude of the cycle and its phase. The results show a significant growing trend in the amplitude of the seasonal cycle with a value of 0.11 ºC/decade in the case of the temperature, but no significant trend for chlorophyll. Again, no significant trend is observed in the phase of the cycle in both variables

CMIP6 projections for global offshore wind and wave energy production (2015–2100)

Three-hourly CMIP6 projections have been used in conjuction with the CSIRO WaveWatchIII wave model to calculate the global trends in offshore wind and wave energy for the SSP585 and SSP126 scenarios until 2100. The results indicate that moderate yet significant changes are expected in the theoretical electricity generated from wind and waves at fewer than 10–15% of coastal locations. While this implies a generally stable outlook for the future, certain coastal regions with existing or planned wind farms may experience a slight reduction in production by 2100. Regarding wave energy, given its early stage of development, a more cautious approach is advisable, although a similar conclusion may be reached. Considering the decreasing installation costs on the horizon and accounting for both climatic scenarios, this provides a reliable context for most ongoing feasibility studies, technological developments, and offshore facility investments.This study is part of project PID2020-116153RB-I00 funded by the Spanish Ministry of Science and Innova- tion/National Research Agency MCIN/AEI/ 10.13039/501100011033. The authors acknowledge funding for the research groups by the University of the Basque Country (UPV/EHU, GIU20/08). All the authors have contributed equally to this paper

Performance variations of wave energy converters due to global long-term wave period change (1900–2010)

Long-term ocean climate effects on wave energy are often analysed from the viewpoint of the well-known increment of wave height over the decades. However, this increment associated with the increase of wave energy flux and absorbed power does not consider the influence of variations in the wave period, whose contribution is more important according to an adimensional performance analysis given by the capture width ratio. This study identifies significant past variations in wave periods during the 20th and 21st centuries using the reanalysis ERA-20C globally and at specific locations, such as Ireland, via calibration with ERA5. A more specific analysis developed in this area shows very significant performance variations (up to 20%) for two types of wave energy converters: oscillating water column devices and a floating body, in which laboratory empirical equations have been used to compute their performance loss due to the deviation from its natural resonance frequency or optimum working wave period. Thus, the performance measured as capture width ratio is highly sensitive to wave period changes, even losing productivity for regions where the wave energy potential is being incremented during the last decades.This study is part of project PID2020-116153RB-I00 funded by Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación, Spain MCIN/AEI/ 10.13039/501100011033. The authors acknowledge the funding of the research groups by the University of the Basque Country, Spain (UPV/EHU, GIU20/08)

Electricity production, capacity factor, and plant efficiency index at the Mutriku wave farm (2014–2016)

Mutriku has recently become the first commercial wave farm to release its operating data. The plant has 14 OWC operating turbines, and this study has conducted an analysis of hourly data corresponding to the 2014–2016 period. The plant's capacity factor has been calculated for this period, and its seasonal evolution characterized. Additionally, a plant efficiency index has been defined as the ratio between the wave energy flux at a reference buoy and the average power generation across the active turbines. The Mutriku wave farm's annual output in the period analysed has been 246,468.7 kW-h, with an average of around ten working turbines. The results indicate that Mutriku's average capacity factor is around 0.11, with higher values in winter than in summer. These values are below the capacity factors reported for other renewable energy sources. The plant efficiency index is 0.26, and further advances in regulation and control may also raise this parameter's values, as may lower rated power alternators. This will also help to improve the Mutriku wave plant's capacity factor, and OWC technology in general.MINECO CGL2016-76561-R (MINECO/EU ERDF), University of the Basque Country UPV/EHU (GIU14/03 and PES17/23

The Sailor diagram – A new diagram for the verification of two-dimensional vector data from multiple models

A new diagram is proposed for the verification of vector quantities generated by multiple models against a set of observations. It has been designed with the objective, as in the Taylor diagram, of providing a visual diagnostic tool which allows an easy comparison of simulations by multiple models against a reference dataset. However, the Sailor diagram extends this ability to two-dimensional quantities such as currents, wind, horizontal fluxes of water vapour and other geophysical variables by adding features which allow us to evaluate directional properties of the data as well. The diagram is based on the analysis of the two-dimensional structure of the mean squared error matrix between model and observations. This matrix is separated in a part corresponding to the bias and the relative rotation of the two orthogonal directions (empirical orthogonal functions; EOFs) which best describe the vector data. Since there is no truncation of the retained EOFs, these orthogonal directions explain the total variability of the original dataset. We test the performance of this new diagram to identify the differences amongst the reference dataset and a series of model outputs by using some synthetic datasets and real-world examples with time series of variables such as wind, current and vertically integrated moisture transport. An alternative setup for spatially varying time-fixed fields is shown in the last examples, in which the spatial average of surface wind in the Northern and Southern Hemisphere according to different reanalyses and realizations from ensembles of CMIP5 models are compared. The Sailor diagrams presented here show that it is a tool which helps in identifying errors due to the bias or the orientation of the simulated vector time series or fields. The R implementation of the diagram presented together with this paper allows us also to easily retrieve the individual diagnostics of the different components of the mean squared error and additional diagnostics which can be presented in tabular form.This research has been supported by the Spanish Government’s MINECO grant and ERDF (grant no. CGL2016- 76561-R) and the UPV/EHU (grant no. GIU17/02)

The power flow and the wave energy flux at an operational wave farm: Findings from Mutriku, Bay of Biscay

Mutriku is a wave farm on the Spanish coast of the Bay of Biscay that has now been continuously supplying electricity for more than nine years. Since 1979, there has been a growing trend in wave energy flux for the whole Bay of Biscay. ERA5 data at the grid point nearest to Mutriku indicate an increase of 0.146 kW/m per decade for the 1979–2019 period. In this paper, a Self-Organizing Map (SOM) with a 2X5 architecture has been fitted to identify ten major sea-state types, each with a distinctive electricity generation pattern at a daily scale. This rendered it possible to reconstruct the daily electric power that would have been generated if the Mutriku wave farm had been operational over the entire 1979–2019 period and, accordingly, evaluate the impact that the observed changes in the wave climate and associated wave energy flux would have had on the electricity production. The results indicate that the electricity production or power flow would have remained constant during that period despite the increasing trend in wave energy flux. This is due to the regulation procedures and mechanisms used in the operation of Mutriku's Oscillating Water Column (OWC) wave energy converters, which dampen the effect of the increasing trend observed. The main conclusion is that the power flow levels off above a given threshold, making it more stable than the wave energy flux.This work has been financially supported by the Spanish Government through the MINECO project CGL2016-76561-R (MINECO/ERDF, UE) and the University of the Basque Country (UPV/EHU, GIU 17/002). ERA5 data have been downloaded at no cost from the Copernicus Climate Data Store. The authors want to express their gratitude to the Basque Energy Agency for kindly providing with operational records from Mutriku wave farm. All the calculations and plots have been carried out in the framework of R (R Core Team, 2020; Wehrens and Kruisselbrink, 2018; Komsta, 2019)

Wave energy flux vectorial prediction at three coastal buoys in Spain

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