Nov 18
0

Estimación de la bondad del ajuste métrico de las medidas a largo plazo del oleaje derivado del Seasonde en el NO de España

Por | Publicaciones científicas
Resumen

Enlace al libro

Long-term skill assessment of SeaSonde radarderived wave parameters in the Galician coast (NW Spain)

A long-term multi-parameter skill assessment of a 5-MHz Coastal Ocean Dynamics Applications Radar (CODAR) SeaSonde High-Frequency radar (HFR) network deployed along the Galician Coast (NW Iberian Peninsula) was attempted for 2014–2016. To this aim, wave estimations from two HFR sites, obtained directly by the CODAR radar proprietary software, were independently validated against hourly in situ observations from two moored buoys for two different periods. The accuracy assessment of significant wave height (Hs) revealed a consistent agreement with Pearson´s
correlation coefficients (r) above 0.75 and normalized root mean squared errors below 0.4. An overall slight overestimation of Hs radar estimations was evidenced, likely due to spurious contributions to the directional spectra.

The seasonal analysis revealed that the performance of this low mono-frequency radar was more precise for high-sea states during wintertime, whereas the quality and availability of radar data decreased under summer less energetic conditions, in accordance with previous works. In the case of the centroid wave period, HFR performance was consistent through the different years, with r values emerging in the range
of 0.61–0.74. The directional accuracy was moderately good, with NW and W-NW as predominant sectors. Despite r values above 0.74, a tendency for CODAR HFR-derived incoming mean wave direction to be aligned more perpendicular to the coast compared to offshore in situ data was also observed. Furthermore, the relationship between the North Atlantic Oscillation (NAO) and HFR wave estimations was explored. A subtle but statistically significant connection was found, with Hs and centroid wave period being positively correlated with NAO daily index.

Complementarily, the skill of the Galician HFR system was evaluated under positive and negative NAO conditions in order to elucidate whether the radar accuracy is or is not NAO-phase dependent. No substantial differences could be found for each of the three parameters analysed as HFR accuracy remained mostly unaffected by swings in the NAO index. Finally, it can be concluded that properly treated CODAR radar-derived wave estimations
can be potentially employed for operational coastal monitoring across a wide range of sea states.

Enlace al libro

Nov 18
0

Monitorización a largo plazo del chorro del Atlántico a través del Estrecho de Gibraltar con observaciones Radar HF

Por | Publicaciones científicas
Resumen

Enlace al libro

Long-Term Monitoring of the Atlantic Jet through the Strait of Gibraltar with HF Radar Observations

The present work focuses on the long-term coastal monitoring of the Atlantic surface inflow into the Mediterranean basin through the Strait of Gibraltar. Hourly current maps provided during 2016–2017 by a High Frequency radar (HFR) system were used to characterize the Atlantic Jet (AJ) since changes in its speed and direction modulate the upper-layer circulation of the Western Alboran Gyre (WAG). The AJ pattern was observed to follow a marked seasonal cycle. A stronger AJ flowed
north-eastwards during autumn and winter, while a weaker AJ was directed more southwardly during the middle of the year, reaching a minimum of intensity during summertime.

A strong relationship between AJ speeds and angles was evidenced: the AJ appeared to be frequently locked at an angle around 63, measured clockwise from the North. The AJ speed usually fluctuated between 50 cms-1 and 170 cms-1, with occasional drops below 50 cms-1 which were coincident with abrupt modifications in AJ orientation. Peaks of current speed clearly reached values up to 250 cms-1, regardless of the season. A number of persistent full reversal episodes of the surface inflow were analyzed in terms of triggering synoptic conditions and the related wind-driven circulation patterns.

High sea level pressures and intense (above 10 ms-1), permanent and spatially-uniform easterlies prevailed over the study domain during the AJ collapse events analyzed. By contrast, tides seemed to play a secondary role by partially speeding up or slowing down the westward currents, depending on the phase of the tide. A detailed characterization of this unusual phenomenon in the Strait of Gibraltar is relevant from diverse aspects, encompassing search and rescue operations, the management of
accidental marine pollution episodes or efficient ship routing.

Enlace al libro

Nov 18
0

Análisis comparativo de eventos de afloramiento y afloramiento de verano en el NO de España

Por | Publicaciones científicas
Resumen

Enlace al libro

Comparative Analysis of Summer Upwelling and Downwelling Events in NW Spain: A Model-Observations Approach

Upwelling and downwelling processes play a critical role in the connectivity between o shore waters and coastal ecosystems, having relevant implications in terms of intense biogeochemical activity and global fisheries production. A variety of in situ and remote-sensing networks were used in concert with the Iberia–Biscay–Ireland (IBI) circulation forecast system, in order to investigate two persistent upwelling and downwelling events that occurred in the Northwestern (NW) Iberian coastal system during summer 2014. Special emphasis was placed on quality-controlled surface currents provided by a high-frequency radar (HFR), since this land-based technology can e ectively monitor the upper layer flow over broad coastal areas in near-real time.

The low-frequency spatiotemporal response of the ocean was explored in terms of wind-induced currents’ structures and immediacy of reaction. Mean kinetic energy, divergence and vorticity maps were also calculated for
upwelling and downwelling favorable events, in order to verify HFR and IBI capabilities, to accurately resolve the prevailing surface circulation features, such as the locus of a persistent upwelling maximum in the vicinity of Cape Finisterre. This integrated approach proved to be well-founded to eciently portray the three-dimensional characteristics of the NW Iberian coastal upwelling system regardless of few shortcomings detected in IBI performance, such as the misrepresentation of the most energetic
surface dynamics or the overestimation of the cooling and warming associated with upwelling and downwelling conditions, respectively.

Finally, the variability of the NW Iberian upwelling system was characterized by means of the development of a novel ocean-based coastal upwelling index (UI), constructed from HFR-derived hourly surface current observations (UIHFR). The proposed UIHFR was validated against two traditional UIs for 2014, to assess its credibility. Results suggest that UIHFR
was able to adequately categorize and characterize a wealth of summer upwelling and downwelling events of diverse length and strength, paving the way for future investigations of the subsequent biophysical implications.

Enlace al libro