PAMS 2011 Conference: Taipei, Taiwan
PAMS 2011 Conference: Taipei, Taiwan An Operational Ocean Model for the Northern South China Sea: Forecasting Mesoscale Processes and Internal Tides Authors: Dr. Mark Cobb, Dr. Andrea Mask, Dr. Chris DeHaan, Carl Szczechowski, John Rogers-Cotrone, Lea Locke, and Dr. Charles Horton Naval Oceanographic Office, Oceanographic Department St Stennis i Space S Center, C t MS 39522 Slide 1 Naval Oceanography Approved for public release; distribution unlimited Forecast Systems & Custom Products Ocean Prediction Department CONOPS Observations Ocean Models Forecasts Satellite & In situ Global – Regional Global Regional – Coastal Coastal – Port 14 km 3 km 300 m 5 m ‐ 3D Full Physics ‐ Assimilation ‐ Forecasts to 5 days ‐ Nesting & B.C. NOGAPS/COAMPS / Oceanographers ‐ Interpret models & obs. ‐ Evaluate uncertainty ‐ Tailor forecasts & products to Navy mission. US‐East NCOM Groton Delft3D Groton G t NCOM Global NCOM Slide 2 Naval Oceanography Approved for public release; distribution unlimited Data Assimilation Navy Coupled Ocean Data Assimilation System (NCODA) • Today – MVOI Assimilation • FY11 – transition to 3DVAR – Improvements in processing time but not skill • FY14 – transition to 4DVAR – Major improvement in assimilation skill expected – Need more computational speed to implement • Working on adding current observations to system to system • Cycling of yesterday’s 24‐hr model forecasts provides initial fields for OCNQC and MVOI (Multi‐Variant Optimal Interpolation). • Assimilation performed during model hindcast. Slide 3 Naval Oceanography Approved for public release; distribution unlimited Global Ocean Modeling Global Navy Coastal Ocean Model (G‐NCOM) • Daily 3D Forecasts of ocean – Temperature – Salinity – Currents – Elevation (tides) • Resolution – Horizontal grid: 1/8 deg – 40 vertical layers 40 vertical layers – Including Arctic • Forecast to 96hr @ 3hr increments • Based on Princeton Ocean Model • FNMOC NOGAPS atmosphere forcing p g – Wind stress (momentum) – Heat fluxes (IR/visible/sensible/evaporation) • Tides from OSU (Egbert) model • Coupled with Los Alamos CICE • Assimilates – Sea surface temperature and elevation from satellites (SST / SSH) – Temperature & salinity data from surface observations and profiles (CTD, floats, gliders, marine mammals) lid i l) – NCODA / MVOI assimilation scheme – Employs insitu and synthetic profiles • This is a deep water model – To forecast mesoscale processes p – Order ½ degree features – Use with caution within 2‐3 points of land Naval Oceanography RE G1 7 RE G1 8 RE G1 4 RE G1 5 RE G1 6 Temperature, Salinity, Elevation NRL Stennis graphics (past 30 days) 1/8 deg (~14 km / 7.5 nm) Slide 4 Approved for public release; distribution unlimited Regional Ocean Modeling Regional Navy Coastal Ocean Model – R-NCOM • Same structure / algorithms as GNCOM • Boundary Conditions provided by GNCOM – 1 way nest • FNMOC COAMPS forcing • 3D Forecasts – T, S, Currents, Elevation – Resolution varies (~1 / 36 deg) – Up to 55 vertical layers – Forecast to 96hr @ 3hr increments • Assimilates data from – Satellites (SST, SSH) – insitu obs (XBTs, CTDs, floats, buoys) – Employs synthetic profiles • Tides internal to model – internal tides evident. USEAST-NCOM GNCOM • Eventual transition to COAMPS-OS (coupled atmosphere atmosphere—ocean—waves) ocean waves) 1/36 deg (3 km / 1.7 nm) Slide 5 Naval Oceanography Approved for public release; distribution unlimited Northern South China Sea (NSCS) R-NCOM Model Overview ¾Domain Extent: 105oE -129.9oE, 14oN-23.96oN ¾3 km grid resolution ¾2 min bathymetry from Naval Research Laboratory (NRL) DBDB2_V30 Database ¾1 Hourly H l 18 kkm FNMOC C Coupled l dO Ocean/Atmospheric /At h i M Mesoscale l P Prediction di ti System (COAMPS) wind fields (e.g. surface winds, total precip, radiation forcing) ¾Initialized from 1/8o G-NCOM G NCOM on Oct 15 15, 2008 2008. ¾3 hourly baroclinic G-NCOM boundary conditions. Barotropic tides imposed at the NSCS boundary. boundary ¾42 Sigma levels (50 total). Sigma levels fully extended at ~ 1600 m depth. Slide 6 Naval Oceanography Approved for public release; distribution unlimited R-NCOM vs. G-NCOM Circulation SSHA & Surface Currents 1/36o R-NCOM Kuroshio Current Black box indicates NSCS R-NCOM boundary 1/8o G-NCOM Slide 7 Naval Oceanography Approved for public release; distribution unlimited Northern South China Sea: Regional Oceanography (What is NAVO trying to forecast?) ¾Surface wind effects on mixed layer, radiation heat fluxes, diurnal cycle of heating and cooling, precipitation effects. Mesoscale M l Circulation: Ci l ti ¾NE monsoon circulation: (i) Basin wide cyclonic gyre circulation pattern. (ii) Wind driven southward shelf break current. ¾Cyclonically propagating cold core eddies occur (i.e. Luzon cold eddy) during NE monsoon. ¾SE monsoon circulation: (i) Dual cyclonic/anti-cyclonic gyre circulation pattern (ii) Eddy generation (iii) Vietnam Jet. ¾NSCS typically yp y has a high g thermocline ((relative to Philippine pp Sea)) and mixed layers y between 0-100 m. ¾Frontal structures due to eddies and currents. ¾Kuroshio current (KC) meanders into NSCS. This can generate eddies and filamentary structures in the vicinity of Luzon Strait. Internal Waves: ¾K1 and M2 are primary barotropic tides. M2 weakens away from Luzon whereas K1 intensifies (N to S). ¾Large (10-80 m) internal waves occur in vicinity of Luzon Strait. K1 internal waves dominate the interior of NSCS. Mesoscale Circulation Internal Waves Sea Surface Elevation (m) Slide 8 Naval Oceanography Approved for public release; distribution unlimited NE Monsoon Example: Cold Core Eddy Generation near Luzon Mean COAMPS Wind Stress Mean Ekman pumping Upwelling region Mean Temperature: 62 m Model animation of mean temperature (3-day mean intervals) at 62 m between Dec 31-Feb 23 clearly shows f formation ti and d cyclonic l i propagation ti off cold ld core eddies ddi west of Luzon. Other features: ¾Kuroshio intrusions across Luzon strait are observed. ¾Shelf break current is well established ¾Large warm core eddy in southeast corner of domain Slide 9 Naval Oceanography Approved for public release; distribution unlimited Validating NSCS R-NCOM Mesoscale Circulation with Altimetry ¾24 hr mean model fields of sea surface height (SSH) are compared to previous week’s altimeter along track sea surface height anomaly (SSHA) data. Altimeter data influences model via assimilation of synthetic temperature-salinity profiles derived from SSHA and SST observations observations. ¾Time scales of NSCS eddies (~ several weeks to months) permit valid comparisons to SSHA obs. ¾Cyclonic basin scale movement of cold core eddies eddies, forecast by R-NCOM R NCOM, is in reasonable agreement with altimeter SSHA data. ¾Evolution of warm core/anti-cyclonic structure in SE corner of domain is also in agreement with SSHA obs. Dec 15 15, 2008 Jan 15 15, 2009 F b1 Feb 1, 2009 Feb 22 22, 2009 March 1 1, 2009 April 8 8, 2009 Slide 10 Naval Oceanography Approved for public release; distribution unlimited Validating NSCS R-NCOM Mesoscale Circulation NE Monsoon: January 2010 K10 SST Data + Altimetry NCOM 7 day SST composite Slide 11 Naval Oceanography Approved for public release; distribution unlimited Validating NSCS R-NCOM Mesoscale Circulation SW Monsoon: August 2009 K10 SST Data + Altimetry NCOM 7 day SST composite Slide 12 Naval Oceanography Approved for public release; distribution unlimited Luzon Transit: Ship of Opportunity Sept 10-11, 2009 ¾A ship of opportunity can be an excellent way of obtaining a transect of observations with relatively high spatial resolution (~ 20 km intervals). ¾Large change in thermocline depth from the Philippine Sea to the NSCS is reproduced quite well by R-NCOM model. ¾Signature of internal waves is apparent in isotherms of obs as well as R-NCOM. 118 120 122 124 126 Ship transit Slide 13 Naval Oceanography Approved for public release; distribution unlimited NSCS R-NCOM vs. Insitu Observations ¾Profiling floats (temperature and salinity data) provided extensive coverage of NSCS model domain during Jan (09 NE monsoon) and Aug (09 SW monsoon). ¾R-NCOM is in reasonable agreement g with T-S data from floats spanning p g the model domain during g NE and SW M Monsoons (black (bl k circles-red i l d centers). t ) ¾Model produces the correct transition from Philippine Sea to NSCS with regard to thermocline and T-S curves. ¾NCOM sonic layer depths (SLD) (first max of sound speed profile) are in good agreement with SLD derived from observations (all NSCS float data are used). Model tends to over-predict depth of shallow SLD. Locations Temperature T-S Diagram Sonic Layer Depth Slide 14 Naval Oceanography Approved for public release; distribution unlimited Forecasting Internal Waves within the NSCS ¾R-NCOM barotropic tides generate baroclinic hydrostatic internal waves at the Luzon Strait. Note: RNCOM cannot simulate non-linear internal waves. ¾This example shows internal waves, generated by a sill at 800 m depth, along a longitudinal transect at 20 deg north. Internal waves propagate away from Luzon Strait. 3-Hourly model output. ¾Power spectrum analysis of sea glider results indicate that K1 baroclinic internal tides dominate SW of Luzon Strait as expected from other studies of this region region. ¾R-NCOM results are in fair to good agreement with observed internal wave power spectrum Slide 15 Naval Oceanography Approved for public release; distribution unlimited NSCS R-NCOM vs. Glider Observations Virtual Mooring: Mooring April 5-12, 2009 Depth vs. Temperature (oC) R-NCOM Sea Surface Height (m) Model SSH indicates diurnal tidal signal in vicinity of glider. Glider performed Glid f d 3-hourly 3h l dives at the same approximate location for 1 week. T-S Diagram OBS R-NCOM G-NCOM G NCOM R-NCOM R NCOM Depth vs. temperature plots indicate reasonable agreement between the model d l and d observations b ti with regard to phase and amplitude of internal waves. T-S diagram reveals a RNCOM bias towards slightly higher salinity at temperatures > 20oC/100C/100 150m OBS Slide 16 Naval Oceanography Approved for public release; distribution unlimited NSCS R-NCOM vs. Glider Observations: Power Spectra April 5-12, 2009 ¾Fourier analysis of glider and R-NCOM temperature time series at model output depths ¾Overall good agreement between model and observations observations. ¾ Majority of R-NCOM baroclinic energy is centered around the thermocline depth (100-200 m) at the diurnal tidal frequency. ¾R-NCOM under-predicts surface energy (< 70 m) in the diurnal frequency band. Precise reason for this is not clear. Low frequency surface energy may be due to synoptic weather events. Slide 17 Naval Oceanography Approved for public release; distribution unlimited NSCS R-NCOM vs. Glider Observations: Power Spectra at 100 m: m April 5-12, 2009 ¾R-NCOM has a diurnal and semi-diurnal peak in the power spectrum. ¾Observations clearly show a diurnal peak in the power spectrum. spectrum 25 hours 12.5 hours ¾Observations indicate a step or small peak at frequencies between diurnal and semi-diurnal frequencies. No well defined semi-diurnal peak. Possibly due to 3-hour glider dive interval. ¾Primary internal tide peak occurs at ~25 hours in both model and observations. 50 h hours 10 hours ¾R-NCOM has more power at diurnal and semi-diurnal peaks than observations. Perhaps due to lack of non-linear dissipation mechanisms mechanisms. Slide 18 Naval Oceanography Approved for public release; distribution unlimited Summary and Conclusions 3 km R-NCOM model demonstrates ability to forecast (96 hrs) 3-D mesoscale circulation and internal wave environment of NSCS. NSCS Overall good agreement between R-NCOM NSCS model and un-assimilated insitu observations. Because observations are assimilated through NCODA MVOI process, directly or via synthetic profiles, model is pushed towards obs at their locations. Slow moving gliders will rapidly remove model bias in their vicinity. Note: MVOI assimilation process can create temporary shocks to the system! Assimilation A i il ti off synthetic th ti profiles fil derived d i d from f SSHA and d SST strongly t l iinfluence fl proper location of mesoscale eddies. Model will diverge from reality without remotely sensed observations (that span the domain) after several weeks. Model over-predicts energy in diurnal and semi-diurnal bands, but is in reasonable agreement with amplitude and phase of observed internal waves. Future F t virtual i t l mooring i studies t di with ith gliders lid should h ld be b 2 2-3 3 weeks k att lleastt ffor proper resolution of internal wave power spectrum. Naval Oceanography Approved for public release; distribution unlimited Slide 19 References • Barron, C., A.B. Kara, H. E. Hurlburt, C. Rowley, L. Smedstad, JAOT, 21, 1876-1893 (2004). • Chao, S-Y, D-S Ko, R-C Lien, P-T Shaw, Assessing the West Ridge of Luzon Strait as an Internal Wave Mediator, J. Ocn, 63, 897-911 (2007). • Hu, J., H. Kawamura, H. hong, Y. Qi, A Review of the Currents in the South China Sea: Seasonal Circulation, South China Sea Warm Current and Kuroshio Intrusion, J. Ocn, 56 , 607-624 (2000). • Jan, S., C-S Chern, J. Wang, g S-Y Chao, Generation of diurnal K1 internal tide in the Luzon Strait and its influence on the surface tide in the South China Sea, JGR, 112, C06019 (2007). • Jia, Y., Q. Liu, Eddy Shedding from the Kuroshio Bend at Luzon Strait, J. Ocn, 60, 1063-1069 (2004). • Qu T Qu, T., Upper-Layer Upper Layer Circulation in the South China Sea Sea, JPO JPO, 30 30, pp pp.1450 1450-1460 1460 (2000). (2000) • Qu, T., Y.T. Song, T. Yamagata, An introduction to the South China Sea throughflow: Its dynamics, variability, and application for the climate, Dyn. Atmos. and Ocns, 47, 3-14 (2009). • Wang, G., W G Dake D k Chen, Ch Jilan Jil Su, S Mesoscale M l eddies ddi in i the th South S th China Chi Sea S observed b d with ith altimeter lti t data, Geo. Res. Lett, 30, 21, 2121 (2003). Slide 20 Naval Oceanography Approved for public release; distribution unlimited References • Wang, G., Dake Chen, Jilan Su, Generation and life cycle of the dipole in the South China Sea summer circulation, JGR, 111, C06002 (2006). • Yang, g, H.,, Q. Liu,, Forced Rossby y wave in the northern South China Sea,, Deep-Sea p Res. 1,, 50,, 917-926 (2003). Slide 21 Naval Oceanography Approved for public release; distribution unlimited Backup Slides Slide 22 Naval Oceanography Approved for public release; distribution unlimited NSCS R-NCOM vs. Glider observations Feb 8-18, 2009 Slide 23 Naval Oceanography Approved for public release; distribution unlimited NSCS R-NCOM vs. Glider observations Feb 8-18, 2009 Slide 24 Naval Oceanography Approved for public release; distribution unlimited Slide 25 Naval Oceanography Approved for public release; distribution unlimited
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