On the Performance of High Frequency Radar in the Western Mediterranean During the Record-Breaking Storm Gloria

Abstract

Storm Gloria (January 19–24, 2020) hit the NW Mediterranean Sea with heavy rainfall, strong easterly winds, and very high waves, causing structural damages and 13 fatalities. The low-lying Ebro Delta (ED) region was severely inundated, ruining rice fields and seaside promenades. A variety of Copernicus Marine Environment Monitoring Service (CMEMS) modeling and observational products were jointly used to examine the fingerprint of Gloria and the response of the upper oceanic layer. According to the results, Gloria can be interpreted as a high-impact once-in-a-decade metocean event where various historical records were beaten. The 99th percentile of several parameters (wind speed, significant wave height, wave period, and surface current velocity), derived from long-term observational time series, was persistently exceeded. The atmospheric surge, albeit not negligible, exerted a secondary role in ED. The ability of a high-frequency radar deployed in this region (HFR-ED) to characterize the striking features of the storm was quantified from both waves and circulation aspects. Consistent radar current observations were subsequently compared against the 5-day-ahead forecast of CMEMS Iberia-Biscay-Ireland (IBI) regional ocean model to determine, from an Eulerian perspective, the strengths and shortcomings in its predictive capabilities. Time-averaged maps of surface circulation, superimposed with fields of Instantaneous Rate of Separation (IROS), were derived to resolve flow features and identify areas of elevated particles dispersion, respectively. The mean and P99 values of IROS almost doubled the historical statistics in the vicinity of the northern Ebro hemidelta. Although IBI predicted moderately well basic features of the storm-induced circulation, results suggests that coastal transport processes, likely modulated by wave-current interactions, were not fully captured. Furthermore, current estimations from other two radar systems, overlooking immediate choke points like the Ibiza Channel and the Strait of Gibraltar, evidenced Gloria’s remote-effect in the anomalous circulation patterns observed, that altered the usual water exchanges between adjacent sub-basins. Finally, three-dimensional outcomes from IBI were used to elucidate the impact of this moving storm at different depth levels. Data analyses illustrated that Gloria caused a large increase in kinetic energy and a significant deepening of the mixed layer depth.

Storm Gloria: Sea State Evolution Based on in situ Measurements and Modeled Data and Its Impact on Extreme Values

“…The direction of the wind-induced currents, during Storm Gloria, was similar to the mean wave direction (Sotillo et al, 2021). On the contrary, the Ebro River outflow currents had an opposite direction to the waves (Lorente et al, 2021). Hence, a suitable option for modifying the overprediction of the wave heights may be to couple a circulation model with PORTUS-wana.…”

“…This large, albeit thin, low-pressure system remained in the same position until January 22nd, allowing for the warm and moist unstable air to continue claiming the Mediterranean Spanish coast, promoting heavy precipitation and snow in low levels in Tarragona, Castellón, and Teruel provinces (located from northern Spanish Mediterranean to middle Spanish Mediterranean). More details about the atmospheric condition can be found in Lorente et al (2021).…”

“…The wave heights might have had been affected by concomitant currents. For instance, in the Ebro Delta, there might have been an interaction between high incoming waves, intense Ebro river outflow currents (reinforced by rain), and the wind-forced flow to the south-west, over the inner continental shelf (Lorente et al, 2021). High-frequency radars can help detect this interaction, as well as to complement the buoys in the monitoring of extreme coastal hazards in near real time.…”

“…For a more in-depth study of the associated surge or the surface dynamics, please refer to Pérez- Gómez et al (unpublished) and Sotillo et al (2021), respectively. With respect to the coastal impacts, especially on the Ebro Delta region (Figure 1), please refer to Lorente et al (2021). The manuscript is structured as follows: Section 2 outlines the materials and the methods employed in this study, Section 3 shows the results, and Section 4 discusses the intricacies of the results, as well as stating the conclusions for the study.…”

Wind Direction Data from a Coastal HF Radar System in the Gulf of Naples (Central Mediterranean Sea)

“…The first-order echoes are typically used to retrieve surface currents, while second order ones are analyzed to reconstruct the wave field [4]. While the analysis of surface currents is well established and the retrieval of wave parameters is an emerging topic [6][7][8][9], the use of first-order peaks to measure wind direction is still poorly explored in the SeaSonde system, while in the literature some investigation on acquisition and validation using phased-array systems are available. The first numerical model to extract the wind direction from HFr backscatter was suggested by Long and Trizna [10].…”