Javier Soto-Navarro

Accuracy assessment of high frequency radar current measurements in the Strait of Gibraltar

An assessment of accuracy of a three site short-range (27 MHz) CODAR SeaSonde HF radar network deployed in the Strait of Gibraltar is attempted by comparing its surface current estimates with measurements from a moored point current meter. Radial and total current vectors are compared for a 47 day period from 19 October to 4 December 2013, yielding angular offsets, root mean square errors and correlations in the range 2ͦ–30ͦ, 8–22 cm s-1 and 0.31–0.81, respectively. Statistics improve when the measured antenna pattern is used, except at one radar site. A self-consistency check in overwater baseline reveals that the dominant source of velocity differences is HF radar variance error.

Evaluation of regional ocean circulation models for the Mediterranean Sea at the Strait of Gibraltar: volume transport and thermohaline properties of the outflow

Abstract A set of simulations from different configurations of the NEMOMED8, NEMOMED12 and NEMOMED36 ocean regional circulation models for the Mediterranean Sea has been studied in order to assess the accuracy of their representation of the exchange through the Strait of Gibraltar. The model volume transport and thermohaline properties of the Mediterranean outflow have been compared with observational data collected at Espartel sill, the westernmost sill of the strait, by a permanent station moored since October 2004 in the frame of the INGRES projects. Results show that, in terms of volume transport, NEMOMED8 simulations perform a better representation of the exchange, while NEMOMED12/36 underestimate both the mean inflow and outflow. The reason for this underestimation is a too low velocity of the flow, which could be consequence of an enhanced roughness effect due the flow-bathymetry interaction. An important improvement in the representation of the exchange seasonality is achieved by the simulations including sea surface height variability of the Atlantic area of the domain. The results for the themohaline characteristics of the Mediterranean outflow are better for NEMOMED12 and NEMOMED36, as a consequence of their better representation of the local dynamical processes that leads to a more realistic composition of the Mediterranean waters comprising the flow.

Ocean model skill assessment in the NW Mediterranean using multi-sensor data

ABSTRACT This paper showcases the one year-long (2014) multi-parameter skill assessment of Iberia-Biscay-Ireland (IBI) operational ocean forecasting system. The investigation is focused on a specific subdomain in the Northwestern Mediterranean where several observational networks encompassing both in situ and remote sensing instruments are available. This region is relevant since it includes two harbours and a marine protected area, the Ebro River Delta. Class-1 and class-2 skill metrics are used in concert to quantitatively evaluate the quality of hourly IBI surface fields. The impact of riverine discharges on the coastal circulation is investigated by comparing the signal of the Ebro River freshwater outflow in both observed (high-frequency radar (HFR)) and modelled (IBI) current maps. The ability of the HFR and IBI to detect the presence of coastal eddies is also qualitatively estimated by calculating surface vorticity maps. According to the results, basic circulation features are statistically reproduced by IBI in reference to mean and variance, despite some model drawbacks in terms of reduced energy content in surface currents. IBI has proven to be a robust model solution in the study area, able to act as a consistent large-scale ‘father’ system in future downscaling approaches by providing coherent open boundary conditions to nested high-resolution coastal models.

Surface circulation at the Strait of Gibraltar: A combined HF radar and high‐resolution model study

Observations from a high frequency radar system and outputs from a high resolution operational ocean model working at the Strait of Gibraltar have been analyzed and compared during the period February 2013 to September 2014 in order to evaluate their capability to resolve the surface circulation of the region. The description of the mean circulation patterns has been statistically assessed, showing good agreement, particularly in the central region of the strait corresponding with the Atlantic Jet (AJ) stream, although some short scale features are not reproduced by the model. In the frequency domain very high concordance is observed. Tidal maps of diurnal and semidiurnal constituents are in good agreement with previous observations. The analysis of the model and radar response to the wind forcing reveals that the low resolution of the model wind-forcing field and its deeper superficial level smoothes the wind effect on the simulated currents. The first three EOF modes account for the 86% of model and radar variances. The coincidence between the observed and simulated patterns is very significant for the first two modes, which account for the mean velocity field and the latitudinal shifting of the AJ consequence of the flow-topography interaction. The third mode captures the wind-induced circulation, and greater discrepancies are found in this case. Results underline the complementary character of both systems: radar observations improve the model description, resolving short scale processes, while the model completes the radar information when the time or spatial coverage is poorer.