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MAJ Ong Ah Chuan RSN, USW

Diagnostic Initialization Generated Extremely Strong Thermohaline Sources & Sinks in South China Sea. MAJ Ong Ah Chuan RSN, USW. SCOPE. Problems of the Diagnostic Initialization Proposed Research in this Thesis Environment of the South China Sea Experiment Design

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MAJ Ong Ah Chuan RSN, USW

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  1. Diagnostic Initialization Generated Extremely Strong Thermohaline Sources & Sinks in South China Sea MAJ Ong Ah Chuan RSN, USW

  2. SCOPE • Problems of the Diagnostic Initialization • Proposed Research in this Thesis • Environment of the South China Sea • Experiment Design • Sensitivity Study Result and Analysis • Conclusion

  3. NUMERICAL OCEAN MODELING • Ocean modeling - Need reliable data for specifying initial condition • Past observations - Contributed greatly to T & S fields • (Tc, Sc) obtained from NODC or GDEM as initial T & S fields • Initial Vc usually not available • Initialization of Vc important • To accurately predict ocean – need a reliable initialization  N Equatorial Current South China Sea Model output

  4. PROBLEMS OF DIAGNOSTIC INITIALIZATION • Widely used model initialization - diagnostic mode • Integrates model from (Tc, Sc), zero Vc & holding (Tc, Sc) unchanged • After diagnostic run, a quasi-steady state & Vc is established   • (Tc, Sc, Vc) are treated as the initial conditions

  5. PROBLEMS OF DIAGNOSTIC INITIALIZATION • Initial condition error can drastically affect the model • Diagnostic mode initialization extensively used - need to examine reliability   • Chu & Lan [2003, GRL] has pointed out the problems: • - Artificially adding extremely strong heat/salt sources or sinks

  6. PROBLEMS OF DIAGNOSTIC INITIALIZATION • Horizontal momentum equation   – (1) • Temp & Salinity equations – (2) and (3) ----- (1) ------------------ (2) ------------------ (3) • (KM, KH) – Vertical eddy diffusivity • (Hv, HT, HS) – Horizontal diffusion & subgrid processes causing change (V, T, S )

  7. PROBLEMS OF DIAGNOSTIC INITIALIZATION ------- (1) ------------------ (2) ------------------ (3) • Diagnostic initialization integrate (1)-(3): • with T and S unchanged

  8. ------------------ (5) ------------------ (6) PROBLEMS OF DIAGNOSTIC INITIALIZATION • Analogous to adding heat & salt source/sink terms (FT, FS) • (2) & (3) becomes: Keeping : ------------------ (7) • Combining (5), (6) & (7):

  9. , PROBLEMS OF DIAGNOSTIC INITIALIZATION ------------------- (8) ------------------- (9) are artificially generated at each time step • Examine these source/sink terms • POM is implemented for the SCS

  10. PRINCETON OCEAN MODEL(Alan Blumberg & George Mellor, 1977) • POM: time-dependent, primitive equation numerical model on a 3-D • Includes realistic topography & a free surface • Sigma coordinate model s ranges from s = 0 at z = h to s = -1 at z = -H • Sigma coordinate - Dealing with significant topographical variability

  11. CRITERIA FOR STRENGTH OF SOURCE/SINK • Chu & Lan [2003, GRL] had proposed criteria for strength of artificial source & sink • Based on SCS, maximum variability of T, S: 35oC & 15 ppt • Max rates of absolute change of T, S data: • These values are used as standard measures for ‘source/sink’ ----- (10)

  12. CRITERIA FOR STRENGTH OF SOURCE/SINK • Twenty four times of (10) represents strong ‘source/sink’ : ----- (11) • Ten times of (11) represents extremely strong ‘source/sink’ ------ (12) • (10), (11) & (12) to measure the heat/salt ‘source/sink’ terms generated

  13. AREAS OF RESEARCH IN THIS THESIS • Chu & Lan [2003] found the problem: • Generation of spurious heat/salt sources and sinks • Did not analyze uncertainty of initialized V to the uncertainty of horizontal eddy viscosity & duration of initialization • Thesis Demonstrate: • -Duration of diagnostic initialization needed to get initial V ? • - Uncertainty of C affect artificial heat & salt sources/sinks ? • - Uncertainty of C affect initial V from diagnostic initialization ? • - Uncertainty of V due to uncertain duration ?

  14. AREAS OF RESEARCH IN THIS THESIS • Area of study: SCS • POM implemented for SCS to investigate physical outcome of diagnostic initialization • NODC annual mean (Tc, Sc) • SCS initialized diagnostically for 90 days (C = 0.05, 0.1, 0.2 & 0.3) • 60th Day V with C = 0.2 taken as reference

  15. SCS Area = 3.5 x 106 km2 Sill depth: 2600 m ENVIRONMENT OF SOUTH CHINA SEA • Largest marginal sea in Western Pacific Ocean • Large shelf regions & deep basins • Deepest water confined to a bowl-type trench • South of 5°N, depth drops to 100m

  16. ENVIRONMENT OF SOUTH CHINA SEA Climatological wind stress • Subjected to seasonal monsoon system • Summer: SW monsoon (0.1 N/m2 ) • Winter: NE monsoon (0.3 N/m2) • Transitional periods - highly variable winds & currents Jun Dec

  17. Kuroshio Luzon Strait Sill depth: 2600 m South China Sea Jun ENVIRONMENT OF SOUTH CHINA SEA • Circulation of intermediate to upper layers: local monsoon systems & Kuroshio • Kuroshio enters through southern side of channel, executes a tight, anticyclonic turn • Kuroshio excursion near Luzon Strait, anti-cyclonic rings detached

  18. North: Cold, saline. Annual variability of salinity small • South: Warmer & fresher • Summer: 25-29°C (> 16°N) • 29-30°C (< 16°N) • Winter: 20-25°C (> 16°N) • 25-27.5°C (< 16°N) Winter Summer ENVIRONMENT OF SOUTH CHINA SEA

  19. SCS MODEL INPUT INTO POM FOR DIAGNOSTIC RUN • 125 x 162 x 23 horizontally grid points with 23 s - levels • Model domain: 3.06°S to 25.07°N, & from 98.84°E to 121.16°E • Bottom topography: DBDB 5’ resolution • Horizontal diffusivities are modeled using Smagorinsky form (C = 0.05, 0.1, 0.2 and 0.3) • No atmospheric forcing

  20. SCS MODEL INPUT INTO POM FOR DIAGNOSTIC RUN • Closed lateral boundaries • Free slip condition • Zero gradient condition for temp & salinity • No advective or diffusive heat, salt or velocity fluxes through boundaries • Open boundaries, radiative boundary condition with zero vol transport

  21. EXPERIMENT DESIGN • Analyze impact of uncertainty of C to initialized V • 1 control run, 3 sensitivity runs of POM • Control run: C = 0.2, Sensitivity runs: C = 0.05, 0.1 & 0.3 • Assess duration of initialization & impact on Vunder different C • - diagnostic model was integrated 90 days • - 60th day of model result used as reference • - RRMSD of V between day-60 & day-i (i = 60, 61,62…...90) • Investigate sensitivity of V to uncertainty of initialization period

  22. EXPERIMENT DESIGN • POM diagnostic mode integrated with 3 components of V = 0 • Temp & salinity specified by interpolating annual mean data • FT & FS obtained at each time step • Horizontal distributions of FT & FS derived & compared to measures established earlier • Horizontal mean | FT | & | FS | to identify overall strength of heat & salt source/sink

  23. EXPERIMENT DESIGN • 30 days for mean model KE to reach quasi-steady state Figure 7. Model Day: 90 days with C = 0.05 Figure 8. Model Day: 90 days with C = 0.1

  24. EXPERIMENT DESIGN • (FT, FS) generated on day-30, day-45, day-60 & day-90 • Identify their magnitudes & sensitivity to the integration period Figure 9. Model Day: 90 days with C = 0.2 Figure 10. Model Day: 90 days with C = 0.3

  25. RESULT OF SENSITIVITY STUDY • Horizontal distribution of FT (°C hr-1) • - at 4 levels (surface, subsurface, mid-level, near bottom) • - with 4 different C-values • Show extremely strong heat sources/sinks • Unphysical sources/sinks have various scales and strengths • Reveal small- to meso-scale patterns

  26. Max Value = 2.331 Min Value = - 0.987 Unit: C/hr Max Value = 1.872 Min Value = - 2.983 Unit: C/hr Max Value = 1.682 Min Value = - 0.591 Unit: C/hr Max Value = 0.374 Min Value = - 0.367 Unit: C/hr HORIZONTAL DISTRIBUTION OF FT • Max Heat Source = 2778 Wm-3 • Features consistent for different C-values Max Heat Sink = -3555 Wm-3 On day-60 with C = 0.05

  27. Max Value = 2.338 Min Value = - 0.595 Unit: C/hr Max Value = 1.724 Min Value = - 2.001 Unit: C/hr Max Value = 1.627 Min Value = - 0.595 Unit: C/hr Max Value = 0.314 Min Value = - 0.364 Unit: C/hr HORIZONTAL DISTRIBUTION OF FT Max Heat Source = 2787 Wm-3 Max Heat Sink = -2385 Wm-3 On day-60 with C = 0.1

  28. Max Value = 2.337 Min Value = - 0.348 Unit: C/hr Max Value = 1.332 Min Value = - 1.016 Unit: C/hr Max Value = 1.632 Min Value = - 0.602 Unit: C/hr Max Value = 0.287 Min Value = - 0.369 Unit: C/hr HORIZONTAL DISTRIBUTION OF FT Max Heat Source = 2785 Wm-3 Max Heat Sink = -1211 Wm-3 • C-value increases, FT weakens • Still above extremely strong heat source criterion On day-60 with C = 0.2

  29. Max Value = 2.331 Min Value = - 0.346 Unit: C/hr Max Value = 1.013 Min Value = - 0.908 Unit: C/hr Max Value = 1.661 Min Value = - 0.607 Unit: C/hr Max Value = 0.277 Min Value = - 0.363 Unit: C/hr HORIZONTAL DISTRIBUTION OF FT Max Heat Source = 2778 Wm-3 Max Heat Sink = -1082 Wm-3 • large C cause unrealistically strong diffusion in ocean model On day-60 with C = 0.3

  30. RESULT OF SENSITIVITY STUDY • Horizontal distribution of FS (ppt hr-1) • - at 4 levels (surface, subsurface, mid-level, near bottom) • - with 4 different C-values • Show strong salinity sources/sinks • Unphysical sources/sinks have various scales and strengths • Reveal small- to meso-scale patterns

  31. Max Value = 0.372 Min Value = - 0.115 Unit: ppt/hr Max Value = 0.134 Min Value = - 0.198 Unit: ppt/hr Max Value = 0.019 Min Value = - 0.067 Unit: ppt/hr Max Value = 0.014 Min Value = - 0.016 Unit: ppt/hr HORIZONTAL DISTRIBUTION OF FS • Max Salinity Source = 0.372 ppt hr-1 • Features similar for different C-values Max Salinity Sink = -0.198 ppt hr-1 On day-60 with C = 0.05

  32. when C-value increases, FS weakens Max Value = 0.372 Min Value = - 0.085 Unit: ppt/hr Max Value = 0.079 Min Value = - 0.198 Unit: ppt/hr Max Value = 0.018 Min Value = - 0.066 Unit: ppt/hr Max Value = 0.011 Min Value = - 0.012 Unit: ppt/hr HORIZONTAL DISTRIBUTION OF FS Max Salinity Source = 0.372 ppt hr-1 Max Salinity Sink = -0.198 ppt hr-1 On day-60 with C = 0.1

  33. Max Value = 0.373 Min Value = - 0.075 Unit: ppt/hr Max Value = 0.065 Min Value = - 0.199 Unit: ppt/hr Max Value = 0.013 Min Value = - 0.067 Unit: ppt/hr Max Value = 0.009 Min Value = - 0.011 Unit: ppt/hr HORIZONTAL DISTRIBUTION OF FS Max Salinity Source = 0.373 ppt hr-1 Max Salinity Sink = -0.199 ppt hr-1 On day-60 with C = 0.2

  34. Max Salinity Sink = -0.200 ppt hr-1 when C-value increases, FS weakens But above criterion Max Value = 0.378 Min Value = - 0.075 Unit: ppt/hr Max Value = 0.055 Min Value = - 0.200 Unit: ppt/hr On day-60 with C = 0.3 Max Value = 0.011 Min Value = - 0.068 Unit: ppt/hr Max Value = 0.008 Min Value = - 0.011 Unit: ppt/hr HORIZONTAL DISTRIBUTION OF FS Max Salinity Source = 0.378 ppt hr-1

  35. RESULT OF SENSITIVITY STUDY • Horizontal mean | FT | : • Identify overall strength of heat source/sink • Figure 21 to 24: temporal evolution at 4 levels: • Near surface ( = –0.0125) • Subsurface ( = –0.15) • Mid-level ( = –0.5) • Near bottom ( = –0.95) ----- (17)

  36. HORIZONTAL MEAN | FT | • Mean |FT| increases rapidly with time • Oscillate around quasi-stationary value • Large - Mean |FT| based on horizontal average Figure 21. Temporal evolution at 4 different levels with C = 0.05

  37. HORIZONTAL MEAN | FT | • Mean |FT| increases rapidly with time • Oscillate around quasi-stationary value • Similar features observed at other C-values Figure 22. Temporal evolution at 4 different levels with C = 0.1

  38. HORIZONTAL MEAN | FT | • Mean |FT| increases rapidly with time • Oscillate around quasi-stationary value • Strength mean |FT| decreases across corresponding level when C increases Figure 23. Temporal evolution at 4 different levels with C = 0.2

  39. HORIZONTAL MEAN | FT | • Mean |FT| increases rapidly with time • Oscillate around quasi-stationary value • Strength mean |FT| decreases across corresponding level when C increases Figure 24. Temporal evolution at 4 different levels with C = 0.3

  40. DEPTH PROFILE OF MEAN | FT | • Max mean |FT| at subsurface • Min at mid-level • Different C values, max & min mean |FT| occurred at different levels Figure 25. Depth Profile with C = 0.05

  41. DEPTH PROFILE OF MEAN | FT | • Max mean |FT| at subsurface • Min at surface • Different C values, max & min mean |FT| occurred at different levels Figure 26. Depth Profile with C = 0.1

  42. DEPTH PROFILE OF MEAN | FT | • Max near bottom • Higher value indicates a greater heat sources & sinks problem • Min at surface Figure 27. Depth Profile with C = 0.2

  43. DEPTH PROFILE OF MEAN | FT | • Max at bottom • Higher value indicates a greater heat sources & sinks problem • Min at surface Figure 28. Depth Profile with C = 0.3

  44. RESULT OF SENSITIVITY STUDY • Horizontal mean | FS | : • Identify overall strength of salt source/sink • Figure 29 to 32: temporal evolution at 4 levels: • Near surface ( = –0.0125) • Subsurface ( = –0.15) • Mid-level ( = –0.5) • Near bottom ( = –0.95)

  45. HORIZONTAL MEAN | FS | • Mean |FS| increases rapidly with time • Peak value of 0.0137 ppt hr-1 • Oscillate around quasi-stationary value Figure 29. Temporal evolution at 4 different levels with C = 0.05

  46. HORIZONTAL MEAN | FS | • Mean |FS| increases rapidly with time • Peak value of 0.0127 ppt hr-1 • Oscillate around quasi-stationary value Figure 30. Temporal evolution at 4 different levels with C = 0.1

  47. HORIZONTAL MEAN | FS | • Mean |FS| increases rapidly with time • Peak value of 0.0124 ppt hr-1 • Oscillate around quasi-stationary value Figure 31. Temporal evolution at 4 different levels with C = 0.2

  48. HORIZONTAL MEAN | FS | • Peak value of 0.0121 ppt hr-1 • Strength of Mean |FS| decreases across corresponding level when C increases Figure 32. Temporal evolution at 4 different levels with C = 0.3

  49. DEPTH PROFILE OF MEAN | FS | • Mean |FS| - max value at surface • Oscillates with decreasing value as depth increases • Higher value indicates a greater salt sources & sinks problem • Min occurred at bottom Figure 33. Depth Profile with C = 0.05

  50. DEPTH PROFILE OF MEAN | FS | • Max value at surface • Oscillates with decreasing value as depth increases • Min occurred at bottom • Similar pattern for other C-values Figure 34. Depth Profile with C = 0.1

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