The predictability of near-coastal currents using a baroclinic unstructured grid model |
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Authors: | Cheryl Ann Blain Mustafa Kemal Cambazoglu Robert S Linzell Kendra M Dresback Randall L Kolar |
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Institution: | (1) Oceanography Division, Naval Research Laboratory, Stennis Space Center, MS, 39529, USA;(2) Department of Marine Science, University of Southern Mississippi, Stennis Space Center, MS, 39529, USA;(3) Technology Solutions Group, QinetiQ North America, Stennis Space Center, MS, 39529, USA;(4) School of Civil Engineering and Environmental Science, University of Oklahoma, Norman, OK 73019, USA |
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Abstract: | A limited domain, coastal ocean forecast system consisting of an unstructured grid model, a meteorological model, a regional
ocean model, and a global tidal database is designed to be globally relocatable. For such a system to be viable, the predictability
of coastal currents must be well understood with error sources clearly identified. To this end, the coastal forecast system
is applied at the mouth of Chesapeake Bay in response to a Navy exercise. Two-day forecasts are produced for a 10-day period
from 4 to 14 June 2010 and compared to real-time observations. Interplay between the temporal frequency of the regional model
boundary forcing and the application of external tides to the coastal model impacts the tidal characteristics of the coastal
current, even contributing a small phase error. Frequencies of at least 3 h are needed to resolve the tidal signal within
the regional model; otherwise, externally applied tides from a database are needed to capture the tidal variability. Spatial
resolution of the regional model (3 vs 1 km) does not impact skill of the current prediction. Tidal response of the system
indicates excellent representation of the dominant M
2 tide for water level and currents. Diurnal tides, especially K
1, are amplified unrealistically with the application of coarse 27-km winds. Higher-resolution winds reduce current forecast
error with the exception of wind originating from the SSW, SSE, and E. These winds run shore parallel and are subject to strong
interaction with the shoreline that is poorly represented even by the 3-km wind fields. The vertical distribution of currents
is also well predicted by the coastal model. Spatial and temporal resolution of the wind forcing including areas close to
the shoreline is the most critical component for accurate current forecasts. Additionally, it is demonstrated that wind resolution
plays a large role in establishing realistic thermal and density structures in upwelling prone regions. |
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