Evaluating the impact of atmospheric forcing and air–sea coupling on near-coastal regional ocean prediction

• Main Authors: H. W. Lewis, J. Siddorn, J. M. Castillo Sanchez, J. Petch, J. M. Edwards, T. Smyth
• Format: Article
• Language: English
• Published: Copernicus Publications 2019-06-01
• Series: Ocean Science
• Online Access: https://www.ocean-sci.net/15/761/2019/os-15-761-2019.pdf
• ISSN: 1812-0784; 1812-0792

<p>Atmospheric forcing applied as ocean model boundary conditions can have a critical impact on the quality of ocean forecasts. This paper assesses the sensitivity of an eddy-resolving (1.5&thinsp;km resolution) regional ocean model of the north-west European Shelf (NWS) to the choice of atmospheric forcing and atmosphere–ocean coupling. The analysis is focused on a month-long simulation experiment for July 2014 and evaluation of simulated sea surface temperature (SST) in a shallow near-coastal region to the south-west of the UK (Celtic Sea and western English Channel). Observations of the ocean and atmosphere are used to evaluate model results, with a particular focus on the L4 ocean buoy from the Western Channel Observatory as a rare example of co-located data above and below the sea surface.</p> <p>The impacts of differences in the atmospheric forcing are illustrated by comparing results from an ocean model run in forcing mode using operational global-scale numerical weather prediction (NWP) data with an ocean model run forced by a convective-scale regional atmosphere model. The value of dynamically representing feedbacks between the atmosphere and ocean state is assessed via the use of these model components within a fully coupled ocean–wave–atmosphere system.</p> <p>Simulated SSTs show considerable sensitivity to atmospheric forcing and to the impact of model coupling in near-coastal areas. A warm ocean bias relative to in situ observations in the simulation forced by global-scale NWP (0.7&thinsp;K in the model domain) is shown to be reduced (to 0.4&thinsp;K) via the use of the 1.5&thinsp;km resolution regional atmospheric forcing. When simulated in coupled mode, this bias is further reduced (by 0.2&thinsp;K).</p> <p>Results demonstrate much greater variability of both the surface heat budget terms and the near-surface winds in the convective-scale atmosphere model data, as might be expected. Assessment of the surface heat budget and wind forcing over the ocean is challenging due to a scarcity of observations. However, it can be demonstrated that the wind speed over the ocean simulated by the convective-scale atmosphere did not agree as well with the limited number of observations as the global-scale NWP data did. Further partially coupled experiments are discussed to better understand why the degraded wind forcing does not detrimentally impact on SST results.</p>