High frequency radar observing system simulation experiment in the Western Mediterranean Sea. A Lagrangian assessment approach

The potential impact of the inclusion of new antenas in a HFR system is evaluated through an Observing System Simulation Experiment (OSSE) in the Ibiza Channel (Western Mediterranean Sea). Two different configurations of the same model are used: (i) a Nature Run considered as the real ocean state, is used to generate pseudo-observations, and (ii) a Control Run , where the pseudo-observations are assimilated. The OSSE is first validated by comparison against a previous Observing System Experiment (OSE). The impact of the new antennas for forecasting surface currents is evaluated in two different periods with different levels of agreement between NR and CR. The HFR expansion is found to contribute to significantly correct the circulation patterns in the Channel, leading to surface meridional velocity error reductions up to 19%. The improvement on surface transport in the area is analyzed in the Lagrangian framework, taking advantage of the full ocean state knowledge given by the OSSE. Results show that DA can help to better represent the Lagrangian Coherent Structures present in the NR.