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NOPP Review Meeting, 2012, Miami, FL

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NOPP Review Meeting, 2012, Miami, FL

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  1. Advanced coupled atmosphere-wave-ocean modeling for improving tropical cyclone prediction modelsPI: Isaac GinisUniversity of Rhode IslandCo-PIs: T. Hara (URI), E. Andreas (NWR), R. Lukas (UH), A. Soloviev (NSU) Collaborators: J.-W. Bao, C. Fairall (NOAA/ESRL)H. Tolman (NOAA/NCEP) NOPP Review Meeting, 2012, Miami, FL

  2. Long-Term Goals • To understand the physical processes that control the air-sea interaction and their impacts on intensity changes in tropical cyclones. • To develop a physically based and computationally efficient unified air-sea interfacemodule for use in the next generation of research and operational coupled atmosphere-wave-ocean-land models.

  3. Year 2: Work Completed • Evaluation of WAVEWATCH v 3.14 wave model in hurricane conditions. • Investigation of the sea state dependence of drag coefficient in hurricanes with new URI and UM air-sea momentum. • Investigation of the Stokes drift velocity and Coriolis-Stokes forcing due to ocean surface waves under hurricane conditions • Implementation of new methods for coupling the sea-spray parameterization with the surface wave properties.

  4. Year 2: Work Completed (cont’d) • Implementation and testing of the air-sea interface module with URI/ESRL air-sea coupling parameterizations into a research versions of the GFDL and HWRF coupled hurricane-wave-ocean model. • Investigation of the upper and lower limits of the drag coefficient in high wind conditions

  5. Physics of Wind-Wave-Current Interaction Image courtesy of Fabrice Veron

  6. Wave model component - WAVEWATCH III WAVEWATCH III can accurately reproduce observed hurricane surface wave fields if: - Wind forcing is reduced at very high wind speeds. - Ocean current is explicitly included in the simulation. Significant wave height comparison between SRA measurements (during this flight) and WW3 results from experiments A, B (with modified wind stress) and C (with modified wind stress and including ocean currents). WW3 significant wave height field (color) at Sept. 15 2:00 UTC. The thick gray line is the flight track. Comparison between modeled and measured significant wave heights from all flights.

  7. WW3 v3.14: Extending to Finite/Shallow Water . * Previous version of WAVEWATCH III (v2.2.2) did not work well for water depth less than 30m (grey area below) • New version of WAVEWATCH III (v3.1.4) includes improved physics in shallower water. • * We are validating the WAVEWATCH III (v3.1.4) results in shallower water against observations (Scanning Radar Altimeter) in collaboration with Ed Walsh.

  8. Hurricane Ivan (2004) significant wave height predictions WW3 v3.14: Extending to Finite/Shallow Water WW3 2.22 WW3 3.14 Difference

  9. Sea state dependent drag coefficient Isaac Ginis, Tetsu Hara, Brandon Reichl (URI), Mark Donelan (UM) In the fully coupled hurricane-wave-ocean modeling framework, the sea state dependent air-sea momentum flux (drag coefficient) is calculated using the wave model (WAVEWATCH III or others) output. In the air-sea interface module developed during the NOPP project, different flux models (wave boundary layer models) will be available for the flux calculations. We have examined two flux models (new URI and UM) as potential candidates for the air-sea interface module.

  10. pdf

  11. Stokes Drift Isaac Ginis, Tetsu Hara, Colin Hughes, Brandon Reichl, John Bruce (URI) In the fully coupled hurricane-wave-ocean modeling framework, the Stokes drift of surface waves introduces: Langmuir turbulence and enhanced/reduced upper ocean mixing Coriolis-Stokes effect that effectively modifies the momentum flux into subsurface current In addition, the Stokes drift introduces significant near surface mass transport that may affect transport of materials (e.g., oil).

  12. Lagrangian floats deployed ahead of Hurricane Gustav (2008) measured vertical kinetic energy in the mixed layer Courtesy of Eric D’Asaro

  13. Langmuir turbulence D’Asaro et al. suggest that near surface turbulence and upper ocean mixing may be significantly reduced when surface waves are opposing the wind and suppress the Langmuir turbulence. We have examined the Stokes drift (vertical profile) under fetch dependent cases (uniform wind) and under idealized hurricanes (stationary and translating). We are investigating the Langmuir turbulence under hurricanes using LES in collaboration with Tobias Kukulka (U. Del).

  14. Angle difference between wind direction and Stokes drift direction at z=k peak-1 under Idealized hurricane Angle exceeds 90 degrees under a translating hurricane. Left panels: 500x500 km domain Right panels: 100x100 km domain UT

  15. Surface Mass Transport Empirical oil spill models assume drift speed of about 3% of the wind speed. Our calculations under fetch-dependent and hurricane winds show that more than half (around 1.5-2% of the wind speed) is due to the Stokes drift. In a moving hurricane, this ratio varies, with the largest on the rear-right side of the track.

  16. The momentum flux into the ocean may be different from the wind stress. Coriolis–Stokes Effect

  17. Ocean momentum equation with surface wave effects (Mellor 2008) • In meso-scale, deep water, hurricane ocean model: • Momentum equation is unchanged, but • - turbulence closure is modified by (unresolved) Langmuir turbulence. • - surface boundary condition is modified (momentum flux ≠ wind stress). • Air-sea momentum budget Coriolis-Stokes • (Fan et al. 2008) already correction to • included in ASIM wind stress

  18. Coriolis –Stokes effect The momentum flux into the ocean may be different from the wind stress. The difference can be as large as 15% of the wind stress near the radius of maximum wind to the right of the hurricane center, and it exceeds 30% further away. The direction of the Coriolis-Stokes effect (vector) tends to be to the right of the wind stress direction.

  19. Drag coefficient parameterization by Ed Andreas

  20. The parameterization predicts leveling off of the drag coefficient

  21. We can combine linear relations in the smooth regime and in the rough regime

  22. Air-Sea Interface in Hurricane Conditions Alex Soloviev1, 2, Roger Lukas3 Silvia Matt1, Atsushi Fujimura2 1 Nova Southeastern University 2 University of Miami 3 University of Hawaii In collaboration with Isaac Ginis and Tetsu Hara March 1, 2012 ONR/NOPP Review at UM RSMAS

  23. Introduction • In this work, we further develop the hypothesis that the change of the air-sea interaction regime in hurricane conditions is associated with the mechanism of direct disruption of the air-sea interface by pressure fluctuations working against surface tension. • This disruption can be achieved through the Kelvin-Helmholtz (KH) or Tollmien-Schlichting (TS) instability and leads to formation of two-phase transition layer. • The transition layer has been related to the lower bound on the air-sea drag coefficient in hurricane conditions in an earlier work (Soloviev and Lukas 2010).

  24. Direct Disruption of the Air-Sea Interface A non-dimensional number, which we call here the Koga number, is the criteria for the K-H instability at an interface (Soloviev and Lukas 2010). The instability occurs at K > Kcr, where Kcr ~ 0.26 (corresponding to U10 ~ 30 m s-1). In this formula, u*a is the friction velocity from the air side, g the acceleration due to gravity, ss the surface tension, rw and ra are the water and air density, respectively.

  25. Numerical Simulations • In order to demonstrate the possibility of the direct disruption of the air-sea interface under hurricane conditions, we have used an idealized 3D model set-up. • A series of numerical experiments has been conducted using the computational fluid dynamics software ANSYS Fluent. • Wind stress was applied at the upper boundary of the air layer, ranging from no wind stress to hurricane force wind stress. periodic periodic

  26. Disruption of the air-water interface due to the K-H type instability Elapsed time = 2 s Wind stress 4 N m-2 10 cm The numerical experiment with an initially flat interface illustrates the possibility of the direct disruption of the air-water interface due to the K-H type instability and formation of the two-phase environment under hurricane force winds. Soloviev, Fujimura and Matt, submitted to JGR-Oceans

  27. The numerical experiment with imposed short waves Elapsed time = 0.5 s Wind stress 4 N m-2 The numerical experiment with imposed short waves demonstrates the tearing of wave crests, formation of water sheets and spume ejected into the air Soloviev, Fujimura and Matt, submitted to JGR-Oceans

  28. Averaged vertical density and velocity profiles at the air-sea interface from CFD simulation For air-water density difference, Boussinesq approximation is no longer valid: “Theoretical” value for non Boussinesq: Ricr= 1/2 Cushman-Rosin (1994) Linear profiles for log r and u follow from dimensional analysis:

  29. Schematic representation of density and velocity profiles in the atmospheric and oceanic boundary layers under hurricane conditions The density profile in the atmospheric boundary layer is assumed to obey the log layer law as well but cannot be seen in this diagram scale.

  30. The CFD model has provided a better estimate for the lower bound on the air-sea drag coefficient in hurricane conditions potential local minimum in Cd? The two-phase layer resistance and wave resistance parameterizations in comparison with available laboratory and field data. Transition to hurricane force wind is associated with the drop of the drag coefficient, which then may slowly increase with wind speed.

  31. Thickness of the two-phase transition layer as a function of wind speed The two-phase environment suppresses short waves. This effect can be included in the wave model via the condition: kcutoff is cut-off wavenumber His thickness of the transition layer C is dimensionless constant of the order of 1.

  32. Conclusions • Change of the air-sea interaction regime in hurricane conditions can be linked to the effect of direct disruption of the air-sea interface and formation of a relatively thin two-phase transition layer • Analysis including computational fluid dynamics experiments has provided an estimate for the lower bound on the air-sea drag coefficient Cd in hurricane conditions assuming regime of marginal stability in the transition layer • An ad hoc “sweet spot” type parameterization for Cd can be implemented • Two-phase environment can be included into wave model

  33. Summary

  34. Coupled Atmosphere-Wave-Ocean Framework Red - atmospheric parameters, Green – wave parameters, Blue - ocean parameters • Hurricane model: air-sea fluxes depend on sea state,sea spray and include surface current. • Wave model: forced by sea state dependent wind forcing and includes surface current • Ocean model: forced by sea state dependent wind stress modified by growing or decaying wave fields and Coriolis-Stokes. Turbulent mixing is modified by the Stokes drift (Langmiur turbulence).

  35. Year 3 Plans for the URI Co-PIs • Implement the new URI and UM sea state momentum flux parameterizations into the air-sea interface module (ASIM) • Implement the effect of Coriolis-Stokes forcing into ASIM • Refine the wave-driven sea spray parameterization and implement it into ASIM (in collaboration with ESRL) • Insure that all components of ASIM are modular, so the same codes can be moved between the coupler and component models as needed and different coupled atmosphere-wave-ocean models

  36. Year 3 Plans for the URI Co-PIs • Implement and test ASIM into the HWRF-WAVEWATCH III-POM/HYCOM system (in collaboration with EMC) • Transition components of ASIM into the COAMPS TC-WAVEWATCH III-NCOM system (in collaboration with NRL) • Run test simulations with HWRF-WW3-POM/HYCOM as part of HFIP Stream 2 and evaluate the model results against available observations • Assist in transitioning the HWRF-WW3-POM/HYCOM to the research community via DTC

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