Development of a coastal modeling system

Transcription

1 Development of a coastal modeling system John Warner US Geological Survey Coastal and Marine Geology Program Woods Hole, MA U.S. Department of the Interior U.S. Geological Survey Jeff List Rob Thieler Brandy Armstrong Ruoying He Joseph Zambon USGS Woods Hole USGS Woods Hole USGS Woods Hole North Carolina State University North Carolina State University

2 Carolinas Coastal Change Processes Project Observations Modelling Sea Floor Mapping 1. Improve our understanding of the processes leading to coastal change at sub-regional to regional scales. 2. Quantify interactions between the geology and physical processes that control coastal behavior. 3. Develop an improved capability for predicting coastal change and vulnerability to coastal hazards. 4. Provide regional information to understand processes of coastal change relevant to the Carolinas.

3 Carolinas Coastal Change Processes Project Observations Modelling Sea Floor Mapping 1. Improve our understanding of the processes leading to coastal change at sub-regional to regional scales. 2. Quantify interactions between the geology and physical processes that control coastal behavior. 3. Develop an improved capability for predicting coastal change and vulnerability to coastal hazards. 4. Provide regional information to understand processes of coastal change relevant to the Carolinas.

4 COAWST Modeling System We are developing a Coupled Ocean Atmosphere Wave Sediment Transport (COAWST ) Modeling System to investigate the impacts of storms on coastal environments. Modeling System C = Coupled MCT O = Ocean ROMS A = Atmosphere WRF W = Wave SWAN ST = Sediment Transport CSTMS

5 Latitude Model setup ATMOSPHERE m Longitude WRF wind speed 5000 m H sig, L wave, D wave, 5000 m T surf, T bott,q b, W dissip, U b MCT u s, v s, h, bath ROMS SST SWAN Hsig OCEAN WAVE

6 Grid refinement Grid refinement Latitude Model setup ATMOSPHERE m Longitude WRF wind speed 5000 m H sig, L wave, D wave, 5000 m T surf, T bott,q b, W dissip, U b MCT u s, v s, h, bath ROMS SST SWAN Hsig OCEAN WAVE

7 CSTMS - 'Sediment Transport' Warner, J.C., Sherwood, C.R., Signell, R.P., Harris, C.K., and Arango, H.G. (2008). Development of a three-dimensional, regional, coupled wave, current, and sediment-transport model, Computers & Geosciences 34,

8 Storm surge use a 3D model consider 2D balance for simplicity (for now) dp/dx t surface P atm ds xx /dx + ds xy /dy tide t bottom concentrate on processes for surface and bottom stress

9 Hurricane Isabel USGS Oblique aerial photography of the breach caused by Hurricane Isabel. Use the COAWST modeling system to hindcast Hurricane Isabel. Track of Hurricane Isabel making landfall on the Outer Banks on 18 Sept 2003.

10 Model setup WRF (Atmosphere) 27 vertical levels dt 36 s Physics Lin microphysics RRTM longwave, Dudhia shortwave Mellor-Yamada-Janjic (MYJ) PBL Kain-Fritsch (KF) cumulus scheme 50 WRF Grid ROMS (Ocean) 16 vertical levels dt 240, 48, 9.6 Physics GLS turbulence closure COARE bulk fluxes BC's from HYCOM Timestep = 240s SWAN (Wave) Spectral dt 600 s Physics Komen wave growth km grid spacing Simulation 12 Sept to 21 Sept, ROMS and SWAN Grid(s) 5000m, 1000m, 200m grid spacings

11 Sensitivity experiments Surface Stress Effect of model coupling on SST and surface stress Bottom Stress Effect of model coupling on bottom stress?

12 Observed Modelled Effects of SST "3 Way Coupling" WRF ROMS SWAN Ocean SST as seen by the ATM model "2 Way Coupling" "Uncoupled" WRF ROMS WRF combined ROMS + RTG_SST combined ROMS + RTG_SST 0.5 x 0.5 deg RTG_SST ( daily update GOES coupled system provides a more consistent SST than uncoupled

13 Modelled Response of the Atm model Effects of SST "3 Way Coupling" WRF ROMS SWAN Ocean SST as seen by the ATM model "2 Way Coupling" "Uncoupled" WRF ROMS WRF combined ROMS + RTG_SST combined ROMS + RTG_SST 0.5 x 0.5 deg RTG_SST ( daily update But coupled system tends track southward. Need better init for WRF.

14 wind speed magnitude (m/s) Different SST creates different wind speed "3 Way Coupling" Difference of 3 Way - 2 Way Difference of 3 Way - 1 Way Diff in wind speed surf stress wave generation surge Need both accurate SST and track to get correct surge.

15 t mean /(t current +t wave ) Bottom properties different formulations to include bottom stress in circulation models. Non-linear enhancement wave-mean bottom stress Linear drag Quadratic drag Logarithmic: Zo Zo + bedforms (ripples) Zo + bedforms + waves t current /(t current +t wave ) Look at waves as an example. Winds - > waves -- > bottom stress --> currents --> surge Grant and Madsen (1986) Ann. Rev. Fluid Mech. 18:

16 Wind wave growth formulations SWAN wave model has several options for wave growth

17 Surge Model results at Sept 18 at 12:00 near peak of storm surge Water level from simulation with enhanced bottom stress due to combined waves+ currents. Difference in water level: wave enhanced bottom stress - constant Zo.

18 Summary Developing a coastal modeling system that can be used to investigate storm impacts. Model coupling allows interaction of physical processes. We are running some tests to identify impact of the interactions. Modeling system can be used to address issues such as wave dynamics, storm surge, ocean circulation, surface stress, Coupling of atm-ocean provides better SST fields but alters storm track and intensity. Coupling of ocean-wave model modifies bottom stress and storm surge.

19 Issues Atm model: - initialization - physics Wav model: - bottom roughness - wave gen. formulations Ocn model: - surface stress - bottom stress - grain sizes - waves - bedforms (ripples) - stratification (t, s, ssc) - sediment spatial variability - bathy - sediment thickness - topography