W. Koch

Ocean Forecasting: From Regional to Coastal Scales

In the past years, the Helmholtz Zentrum Geesthacht put in place the Coastal Observing System for the North and Arctic Seas (COSYNA) in the frame of which different aspects of forecasting the marine environment have been developed. This paper describes these developments, which are based on recent advances in coastal ocean forecasting in the field of 10 numerical modelling, data assimilation and observational array design. The region of interest is the North and Baltic Sea; most of the coastal examples discussed in the paper are for the German Bight. Several pre-operational applications are presented exemplifying the outcome of using the best available science in coastal ocean predictions. They help to identify new challenges; most of them are associated with resolving the non-linear behavior of coastal ocean, which for the studied region, is manifested by the tidal distortion and generation of shallow-water tides. Led by the motivation to maximize the 15 benefit from observations, the authors focus on the integration of observations and modelling by using advanced statistical methods. The coastal and regional ocean forecasting systems do not run in isolation, but are linked, either weakly by just using forcing data, or interactively by using two-way nesting or unstructured-grid models. Therefore the problem of downscaling and upscaling, which currently attracts much attention, is also addressed. One example shown is the coupling of the coarse-resolution regional models by using a two-way nesting method with fine resolution in the area of connecting 20 straits. The major part of the paper presents illustrations from assimilation of remote sensing, in situ and HF radar data, prediction of wind waves and storm surges, as well as possible applications to search and rescue operations, and modelling support for assessing the environmental impact of wind parks. Concepts for seamless approaches to link coastal and regional forecasting systems are also presented and the two examples given illustrate (1) an application of unstructured-grid model for the Ems Estuary, and (2) the potential influence of the information from coastal observatories or coastal forecasting 25 systems on the regional models. Ocean Sci. Discuss., doi:10.5194/os-2016-25, 2016 Manuscript under review for journal Ocean Sci. Published: 9 May 2016 c