Operational Oceanography and the Use of Numerical Models for the Basque Coast (Se Bay of Biscay): New Implementations and Future Work

Integrating observations and models to improve predictions of ecosystem response to physical variability ICES CM 2007/Session B: 08

OPERATIONAL OCEANOGRAPHY AND THE USE OF NUMERICAL MODELS FOR THE BASQUE COAST (SE BAY OF BISCAY): NEW IMPLEMENTATIONS AND FUTURE WORK.

V. VALENCIA, A. FONTÁN, L. FERRER, J. MADER, M. GONZÁLEZ. AZTI Foundation Marine Research Division Herrera Kaia, Portualdea, z/g 20110 – Pasaia (Spain) Tel: +34-943-004800; fax: +34-943-004801 E-mail: [email protected]

Abstract A coastal oceanographic-meteorological instrumentation network in the Basque Country (six coastal stations, combining atmospheric and oceanographic sensors) has been implemented recently, with two offshore buoys (Wavescan); these are moored off Cape Matxitxako and San Sebastián, at 550 m and 630 m water depth, respectively. These buoys provide real-time data of meteorological variables (air temperature, atmospheric pressure, vectorial wind, solar and net radiation) and oceanographic parameters (directional waves, current profile in the upper 200 m of the water column, and eight temperature and salinity measurement points from the surface down to 200 m water depth). Both the coastal stations and offshore buoys belong to the Department of Transport and Civil Works of the Basque Government. The network of sensors provides high-frequency, coupled data sets of oceanographic and meteorological variables. Enlargement of the network, in terms of distance offshore and width of the water column covered, will provide new data for input and hindcasting calibration of hydrodynamic and dispersion models. An IBM (Individual Based Model), coupled to ROMS hydrodynamic model (Regional Ocean Modelling System), is used in the Basque Coast for descriptive and forecasting purposes on the transport of oil spills, sediments, fish eggs and larvae, etc. Moreover, high-frequency temperature and salinity profiles, together with the atmospheric and dynamical variables, permit the high- resolution tracking of shelf and slope processes, such as thermocline fluctuations related to wind fields, Ekman transport, and the expansion of river plumes. Examples of applications and results are presented in this contribution. Keywords: Operational oceanography, ROMS, IBM, Bay of Biscay.

Introduction One of the main objectives of Operational Oceanography is to obtain organised and long-term routine measurements of the seas, oceans and atmosphere, and provide their rapid interpretation and dissemination (Dahlin et al., 2003; Flemming et al., 2002; Behrens et al., 1997). Variables measured include: marine current, sea temperature and salinity profiles; wave height and period; wind stress; heat fluxes, between atmosphere and ocean; evaporation and precipitation; and, river runoff. Such data are fundamental to obtain an accurate description of the marine and atmospheric environment, and therefore, to establish an efficient Operational Oceanography System. This information can be obtained by means of appropriate instrumentation together with numerical tools, mainly hydrodynamic models feeding Eulerian or Lagrangian dispersion models (Ferrer et al., 2007a; 2007b). In addition, this information must be accurate and robust quality; this requires routine maintenance and quality tasks. Operational Oceanography Systems are procedures used to study and control the spatio-temporal evolution of a specific phenomenon at sea or, simply, to provide information about the general circulation patterns within an area of interest (González et al., in press). Within this context, the published literature available on water circulation in the Basque coastal area is scarce (González et al., 2004; Fontán et al., 2006). General descriptions of the marine currents over the Basque shelf are confined, almost exclusively, to the surface currents (Ibáñez, 1979). In recent years, several studies have been undertaken over the Basque coastal area concerning wave climate and water level fluctuations and currents (González et al., 2002, 2004, 2006). As a result, exhaustive oceanographic and meteorological data recording and compilation is still required, in order to describe oceanic circulation over the Basque coastal area. In order to fulfil the above-mentioned requirements, a pilot oceanographic- meteorological station was set up in August 2001, in front of the entrance to the harbour of Pasaia (Figure 1). This was followed by the establishment of five more littoral stations in the Basque Country region, in August 2003. Nowadays, the coastal oceanographic-meteorologial instrumentation network in the Basque Country consists of six coastal stations located at Bilbao, Bermeo, Ondarroa, Getaria, Pasaia, and Hondarribia (for locations, see Figure 1). Recently, in December 2006, two offshore buoys have been moored off Matxitxako Cape and San Sebastián, at 550 and 630 m water depth, respectively (Figure 1). Both the coastal stations and offshore buoys provide high-frequency real-time data of the main oceanic and meteorological variables at specific locations, providing reference information for the Basque coastal and oceanic regions (http://www.azti.es; http://www.euskalmet.net). Both the coastal stations and the offshore buoys belong to the Department of Transport and Civil Works of the Basque Government. The instrumentation network system will be implemented soon with the acquisition of a high-frequency radar system, which will provide high spatio-temporal resolution information of wave parameters and the marine surface current field, with a resolution of 5 km. In this context, this contribution describes the present state of the Operational Oceanography System and numerical models within the Basque coast (southeastern Bay of Biscay), together with some applications and results.

Methodology The study area is located in the innermost part of the Bay of Biscay (Basque coast), between the west-east oriented coast of Spain and the north-south oriented coast of France (Figure 1). The Basque coast is clearly a marginal area of the northeastern Atlantic and even of the Bay of Biscay itself; it has some distinctive climatic and geographic characteristics. Thus, the concavity of the southeastern corner of the Bay of Biscay results in a continental influence in this region and, consequently, the shelf waters of the area are colder in winter and warmer and less saline in summer, than the waters of western areas at equivalent latitudes (Valencia et al., 2003, 2004b). The Basque continental shelf, located within the eastern section of the northern Iberian Peninsula shelf, is the most complex of the three shelves bordering the Bay of Biscay (Armorican, Aquitaine and Northern Iberian Peninsula shelf). The Basque shelf is characterised by its narrowness. It ranges from 7 km in width in front of the Matxitxako Cape, to 20 km in front of Orio; this can be compared to the neighbouring shelf of Aquitaine, which ranges from 60 to over 200 km (Pascual et al., 2004). The anthropogenic pressure on the coastline is higher than the average for the Spanish Cantabrian coast, over this particular area. This factor explains the need to understand the water circulation patterns and associated transport mechanisms of terrestrial pollutants, or those discharged accidentally from ships within this sensitive area (González et al., 2004, 2006).

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43.2º N 3.2º W 3.0º W 2.8º W 2.6º W 2.4º W 2.2º W 2.0º W 1.8º W 1.6º W 1.4º W 1.2º W Figure 1. Location of the study area and the coastal section between Hondarribia and Bilbao (shaded rectangle), showing the position of the coastal stations and offshore buoys. Bathymetry in metres.

The coordinates, depths and sampling intervals of the coastal stations and offshore buoys are summarised in Table 1. The oceanographic-meteorological stations feature the meteorological sensors for wind (direction, speed and maximum gust), atmospheric pressure and air temperature. The oceanographic information is provided with an ADCP, which carries out measurements of the speed and direction of currents at 6 layers within the water column. The system incorporates also a tide gauge, together with a set of thermistors with sensors at 5 layers. The offshore buoys are equipped also with meteorological sensors (air temperature, atmospheric pressure, vectorial wind, solar and net radiation) and a wave sensor, providing directional wave data. The current profile and temperature and salinity, from the surface down to 200 m depth, are provided by a surface current meter and downlooking ADCP, and CTs (conductivity and temperature recorders), respectively.

Table 1. The stations and buoys presented including location, record length and sampling rate. For locations, see Figure 1. Note: AWS is Aanderaa Weather Station. Location Mean depth of Water Sampling rate Station reference (geographical Platform sensors below surface Start date depth (m) (minutes) coordinates) (m) 43º 23,5' N, HONDARRIBIA AWS 14 0 - 2 - 4 - 6 - 8 - 10 August 2003 10 1º 47.2' W 43º 20.3' N, PASAIA AWS 24 0 - 3 - 7 - 10 - 13 - 17 August 2001 10 1º 55.5' W 43º 18.4' N, GETARIA AWS 9 0 - 2 - 3 - 4 - 5 - 7 August 2003 10 2º 11.7' W 43º 19.6 N, ONDARROA 2º 24.8' W AWS 13 0 - 2 - 4- 6 - 7 - 9 August 2003 10 43º 25.4' N, BERMEO 2º 42.5' W AWS 17 0 - 2 - 4 - 7 - 9 - 11 August 2003 10 43º 22.7' N, BILBAO AWS 30 0 - 4 - 9 - 13 - 17 - 22 August 2003 10 3º 04.9' W SAN SEBASTIÁN 43º 33.8' N, 0 - 10 - 20 - 30 - 50 – WAVESCAN 630 January 2007 60 BUOY 2º 01.4' W 75 – 100 - 200 MATXITXAKO 43º 37.9' N, 0 - 10 - 20 - 30 - 50 – WAVESCAN 550 January 2007 60 BUOY 2º 41.6' W 75 – 100 - 200

Results The coastal oceanographic-meteorological instrumentation network in the Basque Country has a broad range of marine applications, such as numerical modelling and descriptive oceanography. In terms of numerical modelling, the implementation of such a network in the Basque Country has established a Operational Oceanography System, together with hindcasting of past events and a forecasting capacity. Within this context, two hydrodynamic models are used in the Basque Country: TRIMODENA and ROMS (developed using finite element and finite difference techniques, respectively). These models, fed by appropriate atmospheric forcing, provide daily forecasts of current, temperature and salinity fields (http://www.azti.es and http://www.eseoo.org/servicios/azti), as well as hindcasts of past events. The model results are tested against buoy data (hindcast) in Figure 2. The model results compare very well, for both eastward and northward current components, with the buoy observations. 50 50

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-30 -20 -10 0 10 20 30 40 50 -30 -20 -10 0 10 20 30 40 50 Matxitxako buoy Matxitxako buoy Figure 2. Comparison of current components between the Matxitxako buoy (see Figure 1) and output from the ROMS model, for the period 10-Mar-2007 to 20-Mar-2007. The results of hydrodynamic models are used as input to dispersion models (Eulerian or Lagrangian type), which allow the transport description of particles or individuals (sediments, oil spills, containers, fish eggs and larvae, etc.). These models have been validated and calibrated with the field data from the aforementioned instruments (Figure 3).

Figure 3. The model calibration by means of sea level time-series.

In shallow waters and harbours, these tools are fundamental from a technical viewpoint (management and design of dredging activities, maritime traffic, structure design, etc.), as well as for environmental analysis such as coastal water quality and pollution events management. The buoys provide also data for descriptive purposes, since high-temporal resolution data are obtained. Air-sea interaction and climate modelling is one of the main applications. With reference to the coupling between air temperature and sea temperature, at 4 m depth at the Pasaia coastal station, the hourly average air temperature correlates significantly (r = 0.8; α <0.0001; for the period 2004-2006), with the hourly sea temperature at 4 m depth. In addition, a regression analysis undertaken between wind and sea surface current components, from January 2004 to December 2006, shows that eastward and northward wind components explain of about 74% of the variability of the corresponding sea surface current components, respectively (α <0.0001).

Other applications and future work Features and events such as the effect of precipitation and rives plumes or storms can be identified easily (Figures 4 and 5). Thus, high-frequency monitoring of coastal and oceanic waters can be undertaken by means of the data provided by the oceanographic- meteorological network.

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In terms of numerical modelling, the implementation of such a network in the Basque Country has established an Operational Oceanography System, together with hindcasting of past events and a forecasting capacity. For descriptive purposes, the network provides high-frequency, well coupled, oceanographic and meteorological data. In addition to the monitoring of coastal and oceanic waters, local processes related with river plumes, Ekman transport, wind-induced mixed layer, storms, etc. can be identified easily and compared with similar mesoscale processes.

Acknowledgements The coastal stations and offshore buoys belong to the Department of Transport and Civil Works of the Basque Government. A part of this work has been supported by the ETORTEK R. & D. Program of the Department of Industry of the Basque Government. We are very grateful to the sampling staff of the Marine Research Division (AZTI Tecnalia), for the high quality of the work performed. Professor Michael Collins (SOES, UK and AZTI- Tecnalia, Spain) is thanked for his comments on the text.

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