nliwiSCS

Nonlinear Internal Waves in the South China Sea: 

Nonlinear Internal Waves in the South China Sea Yuliya Kanarska, James C. McWilliams, Alexander Shchepetkin IGPP, UCLA

Outline: 

Outline LES studies of internal wave generation and transformation; Regional studies of the SCS circulation.

Internal tide generationParameter space diagram from Garrett and Kunze (2006): 

Internal tide generation Parameter space diagram from Garrett and Kunze (2006) Luzon strait is in the limit of 4-5 regimes

Idealized runs for NLIW generationin SCS: 

Idealized runs for NLIW generation in SCS Resolution 100-500m; Gaussian bump H=1.8 km, L=50 km; Stratification profile

Slide5: 

Tidally generated Internal Waves

Nonlinear generation of internal waves:excursion parameter varies from 0.0014(a) to 0.014(c): 

Nonlinear generation of internal waves: excursion parameter varies from 0.0014(a) to 0.014(c) varies from 1000 (a) to 100 (c)

Residual currents due to nonlinear generation and propagation of NLIW: 

Residual currents due to nonlinear generation and propagation of NLIW Tidally averaged over M2 period current u (cm/s) --10.00

Slide8: 

From Orr Mignerey JGR (2003) Elevation-dispersion waves transformation on the China shelf slope Elevation-dispersion waves due to mode interaction U-velocity (cm/s) Temperature (C) U-velocity (m/s) Density 200m 200 km

Conclusion 1: 

Conclusion 1 Generation of nonlinear waves for the idealized parameters of the South China Sea domain is characterized by -- overturning and mixing in the generation area; -- multiple vertical harmonics which may interact and produce different wave shapes in the upper pycnocline; -- residual currents; The obtained internal waves characteristics from idealized simulations are closed to ‘realistic’ SCS values

Slide10: 

Regional simulations Pacific domain: 1/80 resolution South China sea domain: 1/300 and 1/500 resolutions --tidal forcing (idealized and from TPXO6); --climatological runs (Levitus) --topography (ETOPO2) --surface forcing (COADS)

South China Sea domain: 

South China Sea domain

Free surface signature of tidally generated internal waves: 

Free surface signature of tidally generated internal waves Simulations Satellite image of free surface near the Dong Sha area

Slide13: 

Internal waves in cross-section along 210 N in the SCS March, 2000 September, 2000 Temperature at 120.2 0E 210N, at the depth 200m 1km 2 km 700 km

Slide14: 

Internal waves and barotropic tide at 120.2 0E 210N , at the depth 200m Tidal componenets M2+S2+N2+O1+K1

Slide15: 

Non-hydrostatic pressure for simulations with tides only (resolution 1/500; 14,4 million gridpoints) units

Slide16: 

Hydrostatic Non-Hydrostatic Temperature (C) Temperature (C) U-velocity (cm/s) U-velocity (cm/s) Non-hydrostatic pressure is important for dispersive properties of high frequency waves, but wave speed and arrival phase of wave packets can be approximately predicted from hydrostatic models

Conclusion 2: 

Conclusion 2 The mechanism of generation of internal waves in the South China sea is similar to the prediction in idealized configurations; Preliminary simulations show that internal waves are generated at both sides of the Luzon strait, but signal is stronger west from the Luzon strait; Simulations show the evident impact of seasonal circulation on the internal waves properties as well as day-to-day variability of generated internal wave field; More detail study of interaction of waves and currents in regional simulations and importance of small-scale processes are under investigation