Comment on egusphere-2022-1126

Abstract

This paper analyses the variability of the sea level in the Mediterranean Sea and its reproduction with a barotropic model, with and without applying data assimilation. The impact of data assimilation is considered in hindcast and forecast simulations, considering its usefulness for both reanalysis studies and short-term forecasts. We used a two-dimensional finite element barotropic model with an ensemble Kalman filter, assimilating hourly sea-level observations from 50 stations along all the Mediterranean coasts. The results show a great improvement given by data assimilation in hindcast simulations for the reproduction of astronomical tide, surge and total sea level, even in coastal areas far from the assimilated stations (e.g. the Eastern Mediterranean Sea). The improvement is consistent also in forecasts, especially for the first day (~37 % average error reduction), and in case of storm surge events with a strong presence of seiche oscillations. Since these oscillations depend only on the initial state and not on the boundary conditions, they are corrected very effectively by data assimilation. Finally, based on observations, this article estimates the periods of the normal barotropic modes (seiches) in the Adriatic Sea, where they have been extensively studied, and in the Mediterranean Sea, where the present documentation is scarce.