Dissipation Scaled Internal Wave Drag in a Global Heterogeneously
Coupled Internal/External Mode Total Water Level Model
Abstract
This study showcases a global, heterogeneously coupled total water level
system wherein salinity and temperature outputs from a coarse-resolution
($\sim$12 km) ocean general circulation model are used
to calculate density-driven terms within a global, high-resolution
($\sim$2.5 km) depth-averaged total water level model.
We demonstrate that the inclusion of baroclinic forcing in the
barotropic model requires careful treatment of the internal wave drag
term in order to maintain the fidelity of tidal results from the purely
barotropic model. By accurately capturing the internal tide dissipation
within the coupled system, the resulting heterogeneously coupled model
has deep-ocean tidal errors of 2.27 cm, outperforming global,
depth-resolving ocean models in representing global tides. Moreover,
global median root mean square errors as compared to observations of
total water levels, 30-day sea levels, and non-tidal residuals improve
by 1.86, 2.55, and 0.36 cm respectively. The drastic improvement in
model performance highlights the importance of including density-driven
effects within global hydrodynamic models and will help to improve the
results of both hindcasts and forecasts in modeling extreme and nuisance
flooding. With only an 11\% increase in computational
time as compared to the fully barotropic total water level model, this
efficient approach paves the way for high resolution coastal water level
and flood models to be used directly alongside climate models, improving
operational forecasting of total water levels.