Abstract
Abstract. The impact of the assimilation of HFR (high-frequency radar) observations in a high-resolution regional model is evaluated, focusing on the improvement of the mesoscale dynamics. The study area is the Ibiza Channel, located in the western Mediterranean Sea. The resulting fields are tested against trajectories from 13 drifters. Six different assimilation experiments are compared to a control run (no assimilation). The experiments consist of assimilating (i) sea surface temperature, sea level anomaly, and Argo profiles (generic observation dataset); the generic observation dataset plus (ii) HFR total velocities and (iii) HFR radial velocities. Moreover, for each dataset, two different initialization methods are assessed: (a) restarting directly from the analysis after the assimilation or (b) using an intermediate initialization step applying a strong nudging towards the analysis fields. The experiments assimilating generic observations plus HFR total velocities with the direct restart provide the best results, reducing by 53 % the average separation distance between drifters and virtual particles after the first 48 h of simulation in comparison to the control run. When using the nudging initialization step, the best results are found when assimilating HFR radial velocities with a reduction of the mean separation distance by around 48 %. Results show that the integration of HFR observations in the data assimilation system enhances the prediction of surface currents inside the area covered by both antennas, while not degrading the correction achieved thanks to the assimilation of generic data sources beyond it. The assimilation of radial observations benefits from the smoothing effect associated with the application of the intermediate nudging step.
Highlights
High-frequency radar (HFR) is a fast-growing technology, playing an important role in coastal observing systems around the world (Roarty et al, 2019; Rubio et al, 2017)
To evaluate the data assimilation (DA) capabilities to improve the representation of surface currents, we performed an Eulerian analysis in the HFR coverage area
This work has benefitted from the collaborative framework of the Joint European Research Infrastructure of coastal observatories (JERICO)- European research infrastructure initiative (Farcy et al, 2019), which aims at fostering cooperation to build a sustained coastal observing network
Summary
High-frequency radar (HFR) is a fast-growing technology, playing an important role in coastal observing systems around the world (Roarty et al, 2019; Rubio et al, 2017) It allows real-time measurements providing a new, detailed, and quantitative description of physical processes at the marine surface (Paduan and Washburn, 2013). HFR is a cost-effective shore-based remote-sensed technology exploiting the Bragg resonance phenomenon (Crombie, 1955) to map ocean surface currents, wave fields, and increasingly winds in coastal areas. It complements satellite altimeter observations, which are limited to larger scales and suffer limitations when approaching the coast (Vignudelli et al, 2019; Pascual et al, 2013). It has been used to validate geostrophic currents computed from along-track altimetry (Pascual et al, 2015) and to correct sea surface height (SSH) altimeter fields (Roesler et al, 2013)
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