Abstract
Abstract. The accurate parameterisation of momentum and heat transfer across the air–sea interface is vital for realistic simulation of the atmosphere–ocean system. In most modelling applications accurate representation of the wind stress is required to numerically reproduce surge, coastal ocean circulation, surface waves, turbulence and mixing. Different formulations can be implemented and impact the accuracy of the instantaneous and long-term residual circulation, the surface mixed layer, and the generation of wave-surge conditions. This, in turn, affects predictions of storm impact, sediment pathways, and coastal resilience to climate change. The specific numerical formulation needs careful selection to ensure the accuracy of the simulation. Two wind stress parameterisations widely used in the ocean circulation and the storm surge communities respectively are studied with focus on an application to the NW region of the UK. Model–observation validation is performed at two nearshore and one estuarine ADCP (acoustic Doppler current profiler) stations in Liverpool Bay, a hypertidal region of freshwater influence (ROFI) with vast intertidal areas. The period of study covers both calm and extreme conditions to test the robustness of the 10 m wind stress component of the Coupled Ocean–Atmosphere Response Experiment (COARE) bulk formulae and the standard Charnock relation. In this coastal application a realistic barotropic–baroclinic simulation of the circulation and surge elevation is set-up, demonstrating greater accuracy occurs when using the Charnock relation, with a constant Charnock coefficient of 0.0185, for surface wind stress during this one month period.
Highlights
For realistic simulation of the atmosphere–ocean system an accurate parameterisation of momentum and heat transfer across the air–sea interface is required
We focus on an application to Liverpool Bay, which is in the NW region of the UK and a case study of specific interest for improving the understanding of sediment pathways around the UK
The time-varying results of the differential accuracy metric are shown in Figs. 3–5 for each study site, along with the model wind forcing at that location
Summary
For realistic simulation of the atmosphere–ocean system an accurate parameterisation of momentum and heat transfer across the air–sea interface is required. We focus on an application to Liverpool Bay, which is in the NW region of the UK and a case study of specific interest for improving the understanding of sediment pathways around the UK At this location both the Charnock (1955) relation and the COARE (Coupled Ocean–Atmosphere Response Experiment) bulk formulae (Fairall et al, 2003) have previously been used in separate studies of storm surge extremes (Brown and Wolf, 2009) and freshwater influence (O’Neill et al, 2012), but not compared. The standard Charnock relation used in operational barotropic surge modelling to capture increased surface roughness due to the presence of waves on the surface stress due to the 10 m wind components In this coastal application, a high-resolution (∼ 180 m) Liverpool Bay model is nested within models of decreasing resolution.
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