Evaluating high-frequency radar data assimilation impact in coastal ocean operational modelling

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.

Sea Storm Analysis: Evaluation of Multiannual Wave Parameters Retrieved from HF Radar and Wave Model

“…In particular, the results presented in [70] proved that a synergistic observational and modeling approach can provide a comprehensive characterization of severe wave conditions in coastal areas, merging the benefits of the complementary natures of both systems. HFr wave parameters can also be assimilated in wave models [71,72], solving local dynamics mainly in intricate geographical areas.…”

EuroGOOS roadmap for operational coastal downstream services

“…Capet et al (2020) provide a recent review of the operational modelling and predictive capacities in European Seas in terms of hydrodynamics, waves and biogeochemistry. Recent examples demonstrate the benefit of assimilating HF radar, gliders, CTDs and tide gauge observations in European coastal models (Vandenbulcke et al, 2017;Hernańdez-Lasheras and Mourre 2018;Schulz-Stellenfleth et al, 2021;Hernańdez-Lasheras et al, 2021). Other options for data assemblage/blending relies on the use of statistical and variational methods directly on complementary observational data sets, based on different techniques like optimal interpolation, variational analysis, Self-Organizing Maps, Data Interpolating Empirical Orthogonal Functions (DINEOF), or the combination of observations and outputs of numerical models.…”

Coastal HF radars in the Mediterranean: status of operations and a framework for future development

“…The implementation of consistent data assimilation schemes has constituted a quantum leap in terms of realistic forecast predictions in the Mediterranean Sea since they maximize the interconnection of ocean observing systems and numerical models (Teruzzi et al, 2018;Dobricic and Pinardi, 2008). In this context, the benefits of assimilating HFR current data to improve ocean model forecasts in the Mediterranean region have been also demonstrated (Hernández-Lasheras et al, 2021;Vandenbulcke et al, 2017;Marmain et al, 2014).…”

“…On the other hand, the implementation of data assimilation schemes could provide the integrative framework for maximizing the joint utility of HFR-derived observations and numerical models with the aim of improving model predictive skills in coastal areas. Although few valuable initiatives have been already carried out in the Mediterranean with positive results in the modelling of the upper layer circulation (Hernández-Lasheras et al, 2021;Vandenbulcke et al, 2017;Marmain et al, 2014), we should further strive to develop robust, fully operational assimilation schemes for HFR data, encompassing both radial and total current vectors. Equally, some previous works outside the Mediterranean study area have reported the benefits of assimilating HFR-derived wave parameters into SWAN wave models (Siddons et al, 2009) or the high-resolution coastal Wavewatch III model (Waters et al, 2013).…”