Articles | Volume 11, issue 6
Research article
16 Nov 2015
Research article |  | 16 Nov 2015

Evaluation of numerical models by FerryBox and fixed platform in situ data in the southern North Sea

M. Haller, F. Janssen, J. Siddorn, W. Petersen, and S. Dick

Abstract. For understanding and forecasting of hydrodynamics in coastal regions, numerical models have served as an important tool for many years. In order to assess the model performance, we compared simulations to observational data of water temperature and salinity. Observations were available from FerryBox transects in the southern North Sea and, additionally, from a fixed platform of the MARNET network. More detailed analyses have been made at three different stations, located off the English eastern coast, at the Oyster Ground and in the German Bight. FerryBoxes installed on ships of opportunity (SoO) provide high-frequency surface measurements along selected tracks on a regular basis. The results of two operational hydrodynamic models have been evaluated for two different time periods: BSHcmod v4 (January 2009 to April 2012) and FOAM AMM7 NEMO (April 2011 to April 2012). While they adequately simulate temperature, both models underestimate salinity, especially near the coast in the southern North Sea. Statistical errors differ between the two models and between the measured parameters. The root mean square error (RMSE) of water temperatures amounts to 0.72 °C (BSHcmod v4) and 0.44 °C (AMM7), while for salinity the performance of BSHcmod is slightly better (0.68 compared to 1.1). The study results reveal weaknesses in both models, in terms of variability, absolute levels and limited spatial resolution. Simulation of the transition zone between the coasts and the open sea is still a demanding task for operational modelling. Thus, FerryBox data, combined with other observations with differing temporal and spatial scales, can serve as an invaluable tool not only for model evaluation, but also for model optimization by assimilation of such high-frequency observations.

Short summary
Automated measurement systems called FerryBox are installed on cargo ships in the North Sea. Operational model forecasts have been compared to FerryBox data of water temperature and salinity. We wanted to know how well the simulations agree with the observations. We found out that water temperature simulation gives satisfying results, while salinity simulation still could be improved. It turned out that assimilation of observational data into operational models gives strong benefits.