Presentation on theme: "INTERNAL WAVE GENERATION, BREAKING, MIXING AND MODEL VALIDATION ALAN DAVIES (POL) JIUXING XING (POL) JARLE BERNTSEN (BERGEN)"— Presentation transcript:
INTERNAL WAVE GENERATION, BREAKING, MIXING AND MODEL VALIDATION ALAN DAVIES (POL) JIUXING XING (POL) JARLE BERNTSEN (BERGEN)
EXTERNAL FORCING Tides (Moon, Sun ), with stratification (T or S origin) + topography gives internal waves. Meterological, solar heating gives stratification, with wind forcing + stratification internal waves
LOCAL MIXING INFLUENCE LARGE SCALE CIRCULATION Significant Ocean circulation in lateral boundary layers Topographic gradients + Density gradients in these regions, source of internal wave generation, + mixing which influences their lateral extent, Hence boundary layer flow.
MIXING SOURCES Energy cascade through breaking internal waves Internal waves generated in one region propagate to another Energy loss to mixing during propagation Energy loss to mixing, due to non-linear processes giving rise to wave breaking
HOW DO WE VALIDATE THAT WE HAVE CORRECT INTERNAL WAVE + MIXING INTERNAL WAVE SPECTRA AT KEY LOCATIONS DETAILED + COMPREHENSIVE TURBULENCE MEASUREMENTS
MODEL NEEDS DETAILED SMALL SCALE TOPOG. PRECISE SPECTRA OF FORCING AND ITS AMPLITUDE ACCURATE INITIAL STRATIFICATION AND DETAILS OF ITS EVOLUTION FOR VALIDATION
HOW TO PARAMETERIZE AND UPSCALE TO LARGE AREA MODELS Topographic gradients dh/dx Details of stratification Details of small scale wind forcing
TWO EXAMPLES INTERNAL WAVE MIXING Wind forced internal waves trapped in cold water dome Tidally forced internal waves over a sill.
Format (A) Internal Wave trapping in Domes (B) Mixing over abrupt topog. Conclusions and future Developements
BAROCLINIC IRISH SEA MODEL Simulation 3D baroclinic model Dome formation and breakdown Dome circulation published JPO
Non-Linear effects on Inertial Oscillations Unbounded Ocean Eqts Effect of external shear is to change Amp. + Freq. of I.O. Frontal Shear Changes I.O. amp./Freq at depth so conv/divg. Gives internal wave at level of thermocline. Freq. int. wave above inertial propogates away, if below trapped
Super-inertial wind forcing
Wavelength λf from Dispersion Relation ωf = forcing frequency So λf/Leff gives nodal structure where Leff is effective length of dome
Sub-inertial wind forcing
CONCLUSIONS 1.Non-linear effects associated with along frontal flows produce near-inertial internal waves in presence of wind forcing 2.Super-inertial internal waves propagate away from generation region (front) 3.Sub-inertial are trapped and enhance mixing in frontal region 4.In a cold water bottom dome, super-inertial internal waves are trapped as standing waves, can modify GM spectrum 5.Response in centre of dome different from 1D model, must account for internal wave 6.Sub-inertial wave confined to front, and response in centre of dome as in 1D model
TIDAL MIXING AT SILLS Idealized Loch Etive Recent measurements Inall et al Non-hydrostatic model High resolution Idealized M2 forcing + idealized T profile Example of internal tidal mixing
Influence of small scale topog. Lee wave characteristics influenced by Buoyancy frequency Velocity over sill….. Froude Number Fourier transform of topog. So How small scale effect mixing ?????
CONCLUSIONS….. Sill Internal tide little mixing Lee Wave not advected back over sill Lee Wave major source of mixing Lee wave distribution influenced by non- hydro. nature of model Lee wave spectrum/mixing influenced by small scale topog. Assumptions in b.b.l. also infulence lee wave hence mixing
Future Role surface stratification / fresh water, wind mixing Detailed distribution of Topog. Sill b.b.l effects Lateral + across sill form drag
Model Skill Assessment Model Validation in highly variable undersampled domain. Spectral Decompostion.. Hans van Haren
Conclusions Details of wind field frequency composition Precision in stratification Accurate tidal forcing Precise small scale topog. Variations. MAJOR PROBLEMS IN VALIDATION HOW TO UPSCALE WITHOUT LOOSING ACCURACY !!!!!!!!!