Can wave coupling improve operational regional ocean forecasts for the North-West European Shelf?

Abstract

Operational ocean forecasts are typically produced by modelling systems run using a forced mode approach. The evolution of the ocean state is not directly influenced by surface waves, and the ocean dynamics are driven by an external source of meteorological data which is independent of the ocean state. Model coupling provides one approach to increase the extent to which ocean forecast systems can represent the interactions and feedbacks between ocean, waves and the atmosphere seen in 15 nature. This paper demonstrates the impact of improving how the effect of waves on the momentum exchange across the ocean-atmosphere interface is represented through ocean-wave coupling on the performance of an operational regional ocean prediction system. This study focuses on the eddy-resolving (1.5 km resolution) Atlantic Margin Model (AMM15) ocean model configuration for the North-West European Shelf (NWS) region.A series of two-year duration forecast trials of the Copernicus Marine Environment Monitoring Service (CMEMS) North-20 West Shelf regional ocean prediction system are analysed. The impact of including ocean-wave feedbacks via dynamic coupling on the simulated ocean is discussed. The main interactions included are the modification of surface stress by wave growth and dissipation, Stokes-Coriolis forcing and wave height dependent ocean surface roughness. Given the relevance to operational forecasting, trials with and without ocean data assimilation are considered.Summary forecast metrics demonstrate that the ocean-wave coupled system is a viable evolution for future operational 25 implementation. When results are considered in more depth, wave coupling was found to result in an annual cycle of relatively warmer winter and cooler summer sea surface temperatures for seasonally stratified regions of the NWS. This is driven by enhanced mixing due to waves, and a deepening of the ocean mixed layer during summer. The impact of wave coupling is shown to be reduced within the mixed layer with assimilation of ocean observations. Evaluation of salinity and ocean currents against profile measurements in the German Bight demonstrates improved simulation with wave coupling relative to control 30 simulations. Further, evidence is provided of improvement to simulation of extremes of sea surface height anomalies relative to coastal tide gauges.Ocean Sci. Discuss., https://doi.

Impacts of the Assimilation of Satellite Sea Surface Temperature Data on Volume and Heat Budget Estimates for the North Sea

“…This work follows that of Lewis et al. (2019), who showed that model coupling alone is not a sufficient strategy for improving all aspects of model performance. The 3DVAR scheme is implemented with the assumption that the model SST errors are strongly correlated with the temperature errors inside the mixing layer.…”

The impact of a new high-resolution ocean model on the Met Office North-West European Shelf forecasting system

“…The AMM15 system described in this paper has been already tested in an ocean-wave coupled configuration (Lewis et al, 2019a) which is planned to become operational in 2020. We hope to add the biogeochemical components in a few years, but a precise plan is not yet available.…”

The impact of a new high-resolution ocean model on the Met Office North-West European Shelf forecasting system

“…The AMM15 system described in this paper, has been already tested in an ocean-wave coupled configuration (Lewis et al 2018a) which is planned to become operational in 2020. We hope to add the biogeochemical components in a few years, but a precise plan is not yet available.…”

“…The increase of resolution to 1.5 km is therefore a fundamental step change in the ability to resolve key processes and features in the NWS region (Guihou et al, 2017). As well as being developed for ocean forecasting operations, the AMM15 is being used within a coupled ocean-wave-atmosphere research system (Lewis et al, 2018a and.…”