Assessment of Wind Pattern Accuracy from the QuikSCAT Satellite and the WRF Model along the Galician Coast (Northwest Iberian Peninsula)

Surface wind along the Galician coast is a key factor allowing the analysis of important oceanographic features that are related to the great primary production in this area, as upwelling events. A comparative analysis between surface winds obtained from the Quick Scatterometer (QuikSCAT), the Weather Research and Forecasting (WRF) Model, and in situ observations from buoys along the Galician coast is carried out from November 2008 to October 2009. This comparison evaluates the accuracy of satellite and modeled data. The results show that the wind speeds derived from QuikSCAT and the WRF Model are similar along the coast, with errors ranging from 1.5 to 2 m s(-1). However, QuikSCAT tends to overestimate wind speeds when compared to the buoys measurements. Regarding the wind direction, the RMSE values are about 358 for the stations under analysis. The bias presents a similar pattern between satellite and modeled data, with positive values at the western coast and negative values at the middle and northern coasts, the satellite data always being lower in absolute value than the modeled data. A spatial comparison between QuikSCAT and WRF data is also performed over the whole Galician coast to evaluate the differences between the two datasets. This comparison shows that the modeled wind speed tends to be lower than satellite winds over the entire domain, with the highest RMSE and bias values found for the wind speed and direction observed near the shoreline

Variability of Iberian upwelling implied by ERA-40 and ERA-Interim reanalyses

The Regional Ocean Modeling System ocean model is used to simulate the decadal evolution of the regional waters in offshore Iberia in response to atmospheric fields given by ECMWF ERA-40 (1961–2001) and ERA-Interim (1989–2008) reanalyses. The simulated sea surface temperature (SST) fields are verified against satellite AVHRR SST, and they are analysed to characterise the variability and trends of coastal upwelling in the region. Opposing trends in upwelling frequency are found at the northern limit, where upwelling has been decreasing in recent decades, and at its southern edge, where there is some evidence of increased upwelling. These results confirm previous observational studies and, more importantly, indicate that observed SST trends are not only due to changes in radiative or atmospheric heat fluxes alone but also due to changes in upwelling dynamics, suggesting that such a process may be relevant in climate change scenarios

Unusual circulation patterns of the rias baixas induced by minho freshwater intrusion (NW of the Iberian Peninsula)

The Minho River, situated 30 km south of the Rias Baixas, is the most important freshwater source flowing into the Western Galician coast (NW of the Iberian Peninsula). The buoyancy generated by the Minho estuarine plume can reverse the normal circulation pattern inside the Rias Baixas affecting the exchange between the Rias and the ocean, changing the input of nutrients. Nevertheless, this inversion of the circulation patterns is not a well-monitored phenomenon. The only published results based on in situ data related to the presence of the Minho River plume inside the Rias de Vigo and Pontevedra correspond to an event measured on spring 1998. In this case unexpectedly higher inflow surface current velocities were found at the Ria de Pontevedra, located further away from Minho River. Thus, the main aim of this study is to research the main factors inducing this unusual pattern on the circulation of the Rias de Vigo and Pontevedra. A numerical model implementation of MOHID previously developed, calibrated, and validated for this coastal area was used. Several scenarios were performed in order to explain the individual effect of the Minho River, rivers discharging into each Rias, and estuarine morphology changes. According to the model results, the Minho River discharge is a key factor in the establishment of the negative circulation, while small rivers inside the Rias slightly attenuate this circulation. The negative circulation was stronger in Ria de Pontevedra independently of the distance of this coastal system from the Minho River mouth, showing that morphologic estuarine features are the main factor justifying the different local circulation patterns

Summer upwelling frequency along the western Cantabrian coast from 1967 to 2007

Upwelling events have been analyzed along the western part of the Cantabrian coast from 1967 to 2007. This analysis shows that the highest number of days under upwelling favorable conditions was observed from June to September (12–14 days per month) with a probability of finding consecutive days under upwelling favorable conditions decreasing from 47% to 17% when events between 1 and 5 consecutive days were considered respectively. This situation was also corroborated by Sea Surface Temperature data which revealed the presence of cold water over the continental shelf, near coast, associated with upwelling favorable winds. This cold water was also observed inside the estuaries located in this area. The water temperature signal measured at the inner part of the Ria de O Barqueiro (NW Iberian Peninsula) from June to September 2008 showed to be negatively correlated with the Upwelling Index calculated in front of the northern Galician coast. This correlation tends to increase as the number of lag days between both variables increases. The maximum value of − 0.8 corresponds to a lag of 5 days.publishe

Differences in coastal and oceanic SST trends due to the strengthening of coastal upwelling along the Benguela current system

Coastal and oceanic sea surface temperature (SST) trends were analyzed in the Benguela upwelling ecosystem from the seventies on. Monthly SST data were obtained from the UK Meteorological Office, Hadley Center at two transects in front of the Namibia coast and the western coast of South Africa. A positive SST trend (0.06 °C dec−1) is observed at open sea locations and a negative one (−0.13 °C dec−1) near shore. The observed negative ΔSST (SSTcoast−SSTocean) trend (−0.18 °C dec−1) is linked to the strengthening of upwelling (87 m3 s−1 km−1 dec−1) during the same period. For this purpose, Ekman transport was directly obtained from the Pacific Fisheries Environmental Laboratory in the area under study and calculated from reanalysis wind data from NCEP/NCAR at six locations in front of the Namibia coast and the western coast of South Africa. This coastal upwelling enhancement is in good agreement with changes in the intensity and location of the South Atlantic High, which are also reflected in the Southern Annular Mode (SAM) index.publishe

Modeling the Minho River plume intrusion into the Rias Baixas (NW Iberian Peninsula)

The Minho River discharge is recognized as particularly important in driving the circulation and hydrography of Rias Baixas, which are highly productive fishery and aquaculture regions extremely sensitive to environmental characteristics. The intrusion of the Minho River plume inside these Rias can reverse the normal circulation pattern and affect the macronutrient concentrations, imposing a control on new production within the estuarine environment. Consequently, detailed knowledge of the propagation of the plume in this zone facilitates largely the management of many exploited and protected local species. Thus, the main purpose of this work is to study the propagation and influence of Minho estuarine plume in Rias Baixas circulation and hydrography through the development and validation of an application of MOHID numerical model including a local coastal nesting configuration fed by Minho River discharge predicted by an estuary model. The nesting configuration and the Minho estuary model were validated and then applied to research the role of the wind and Minho River discharge effects on the circulation reversal. The spring of 1998 was chosen as the validation period for Minho estuarine plume propagation, considering there were field data available for this period confirming the intrusion of the Minho River plume in Rias Baixas and reversing the normal circulation pattern. Predictions replicate accurately the hydrodynamics and thermohaline patterns in Minho estuary and Rias Baixas under these conditions showing that the developed model application reproduces the dynamics of the coupled estuarine-near coastal systems under research. Results showed that a buoyancy intrusion caused by the Minho River reverses the normal estuarine salinity longitudinal gradient and estuarine circulation of the Rias de Vigo and Pontevedra. Moreover, it was found that a continuous moderate Minho River discharge combined with southerly winds is enough to reverse the Rias Baixas circulation pattern, reducing the importance of the occurrence of specific events of high runoff values

Influence of the Minho River plume on the Rias Baixas (NW of the iberian peninsula)

The buoyancy generated by the Minho estuarine plume can flood the Rias Baixas for long periods, reversing the normal salinity gradients. Thus, the main purpose of this work was to study the propagation of Minho estuarine plume to the Rias Baixas, establishing the wind and river discharge conditions in which this plume affects the circulation and hydrography features of these coastal systems as well as the plume characteristics under the most probable forcing conditions, through the application of the numerical model MOHID. For this purpose, several scenarios with different river discharges and wind were simulated. The numerical results revealed that the Minho estuarine plume responds rapidly to wind variations and is influenced by coastline geometry. Under Minho River discharges higher than 700m3s-1 and weak northward winds (3ms-1) the circulation patterns of the Rias de Vigo and Pontevedra are reversed. On the other hand, moderate northward winds (6ms-1) combined with Minho River discharges higher than 200m3s-1, 300m3s-1 and 700m3s-1 reverse the circulation pattern of the Rias de Vigo, Pontevedra and Arousa, respectively. Under the same conditions, the water exchange between Rias Baixas was analyzed using a particle-tracking model following the trajectories of particles released close to the Minho River mouth. Over 5days, under Minho River discharges higher than 2100m3s-1 combined with northward winds of 6ms-1, an intense water exchange between Rias was observed. However, only 20% of the particles found in Ria de Pontevedra come directly from the Minho River

Assessment of chlorophyll variability along the northwestern coast of Iberian Peninsula

The northwestern coast of the Iberian Peninsula is characterized by a high primary production mainly supported by coastal upwelling, creating an extraordinary commercial interest for fisheries and aquaculture. Considering chlorophyll- a (Chl- a) as an indicator of primary production, its spatio-temporal variability was researched in this study in the surface water of this upwelling region from 1998 to 2007. Satellite derived Chl- a, Sea Surface Temperature (SST) and Ekman transport data as well as the inflow of the main rivers discharging into the study area were used to investigate the origin of the Chl- a concentration. Empirical Orthogonal Function (EOF) analysis of weekly Chl- a images was performed, as well as correlation analysis between Chl- a concentration, Ekman transport and river discharge. EOF results suggest that the highest Chl- a concentration occurs near the coast up to 60. km offshore. The interannual variability of Chl- a, SST and Ekman transport was also studied considering summer and winter months. Generally, 2005, 2006 and 2007 were the most productive years during the summer months with high Chl- a concentrations along the coast associated to the strong upwelling conditions observed. Otherwise, 1998 seemed to be the most productive year during winter. The absence of upwelling favorable conditions together with localized low SST and considerable discharges, suggests that the high Chl- a concentrations observed during this period are mainly due to the entrance of nutrients through river runoff. However, in winter, high concentrations of colored dissolved organic matter (CDOM), associated with river runoff, are present in the ocean surface, leading to an erroneous strong signal of the satellite. During winter correlations of 0.58 and 0.49 were found between Chl- a concentration and Douro and Minho discharges, respectively, evidencing that high Chl- a concentration was related with river runoff. Otherwise, during summer, Chl- a and Ekman transport exhibited a correlation of - 0.38 indicating that high Chl- a is associated to upwelling events. In summary, it was found that the spatio-temporal variability of Chl- a along the northwestern coast of Iberian Peninsula exhibited the clear influence of upwelling events during summer. Conversely, the variability during winter was mainly due to entrance of nutrients through the rivers discharge which flow into the area

Comparative analysis of upwelling influence between the western and northern coast of the Iberian Peninsula

Upwelling conditions have been simultaneously analyzed along the western and northern coast of the Iberian Peninsula in terms of wind forcing and water temperature response. The wind forcing analysis showed that the season under more upwelling favorable conditions corresponds to spring–summer (April–September) along the western coast and only to summer (June–August) along the northern one. Taking into account the upwelling period common to both coasts (June–August), it was observed that the occurrence of upwelling events simultaneously along both coasts is the most probable situation (∼46%) followed by upwelling unfavorable conditions also along both coasts (∼26%). The analysis of sea surface temperature data also showed the existence of an upwelling season in spring–summer along both coasts, although upwelling events are more frequent and intense along the western coast than along the northern one. Chlorophyll concentrations showed a high seasonal variability at the western coast with the highest concentrations values in spring–summer months while at the northern coast the maximum values were observed in spring and autumn.This work is supported by the Ministerio de Ciencia e Innovacion under projects CTM2007-62546-C03-03/MAR and CGL2009-09143 and by Xunta de Galicia under projects PGIDIT06PXIB383285PR and PGIDIT06PXIB383288PR. Authors thank the valuable comments of Dr. M. Varela and Dr. J.L. Gomez-Gesteira which helped to improve the quality of the manuscript. One of us (I.A.) has been supported by the Fundação para a Ciência e a Tecnologia through a post-doctoral grant (SFRH/BPD/38292/2007).publishe