T T aiwan aiwan S S trait trait NOW NOW cast cast s s ystem ystem N N ational ational C C enter for enter for O O cean cean R R esearch esearch Taiwan, ROC Taiwan, ROC P01
Jan 21, 2016
TTaiwanaiwan SStraittrait NOWNOWcastcast ssystemystem
NNational ational CCenter for enter for OOcean cean RResearchesearchTaiwan, ROCTaiwan, ROC
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• promotion of cutting-edge oceanographic promotion of cutting-edge oceanographic researchresearch
• promotion of the use of satellite remote-sensing promotion of the use of satellite remote-sensing technology in oceanographic researchtechnology in oceanographic research
• Promotion of international collaboration in Promotion of international collaboration in oceanographic researchoceanographic research
• coordination of the use of oceanographic coordination of the use of oceanographic research vesselsresearch vessels
• establishment of an oceanographic databankestablishment of an oceanographic databank
National Center for Ocean ResearchNational Center for Ocean Research (NCOR) was (NCOR) was established on August 1, 1997, by the National established on August 1, 1997, by the National Science Council of Taiwan. The major missions of Science Council of Taiwan. The major missions of NCOR includeNCOR include
Introduction to NCORIntroduction to NCOR
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Sen Jan and Yu-Huai WangNational Center for Ocean Research, Taiwan, National Center for Ocean Research, Taiwan,
R.O.C.R.O.C.
Shenn-Yu ChaoUniversity of Maryland Center for Environmental Sciences, U.S.A.University of Maryland Center for Environmental Sciences, U.S.A.
Dong-Ping WangMarine Science Research Center, SUNY, Stony Brook, U.S.A.Marine Science Research Center, SUNY, Stony Brook, U.S.A.
Development of a Nowcast System Development of a Nowcast System for the Taiwan Strait (TSNOW)for the Taiwan Strait (TSNOW)
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• is necessary because 90% of Taiwan’s is necessary because 90% of Taiwan’s population, industry and economy lies in her west population, industry and economy lies in her west coastcoast
• is based on the extensive hydrographic data is based on the extensive hydrographic data acquired in the strait during the past two decadesacquired in the strait during the past two decades
• is aimed for both practical and scientific is aimed for both practical and scientific applicationsapplications
• takes a balanced approach relying equally on takes a balanced approach relying equally on models and observationsmodels and observations
• will have the capacity of real-time observational will have the capacity of real-time observational data assimilationdata assimilation
The Taiwan Strait nowcast systemThe Taiwan Strait nowcast system
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Taipei
Kaohsiung
Taichung
Keelung
Matsu
Maopitou
Dongshan
Nowcast system model domainNowcast system model domain
CY Rise
KY D
epre
ssio
n
WC D
epre
ssion
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For TNOW, ”nowcast” is defined asFor TNOW, ”nowcast” is defined as
timetime
T = 0 T = 24 hrs
sea levelssea levels
currentscurrents
Definition of nowcastDefinition of nowcast
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Short-termShort-term
• Disaster warningDisaster warning
• Marine rescueMarine rescue
• Pollutant dispersion Pollutant dispersion
predictionprediction
Long-termLong-term
• Scientific studyScientific study
• Environmental Environmental
policy makingpolicy making
• Marine resources Marine resources
managementmanagement
ObservationsObservations PredictionPrediction DemonstrationDemonstration ApplicationsApplications
Conceptual modelConceptual model for for TSNOWTSNOW
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WWWWWW
11stst Stage Stage: to establish the capability and demonstrate : to establish the capability and demonstrate success in doing good hindcast for the barotropic success in doing good hindcast for the barotropic tidestides
22ndnd Stage Stage: to incorporate wind-driven part in the : to incorporate wind-driven part in the modelmodel
33rdrd Stage Stage: to consider the seasonal/monthly mean : to consider the seasonal/monthly mean circulation and baroclinic effect in the flow fieldcirculation and baroclinic effect in the flow field
Development of the TSNOW Development of the TSNOW systemsystem
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ObservationsObservations•To determine initial and boundary conditionsTo determine initial and boundary conditions•To validate model resultsTo validate model results
Tide-gage stations Tide-gage stations established by NCORestablished by NCOR
Tide-gage stations Tide-gage stations established by CWBestablished by CWB
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Mooring stations of Mooring stations of bottom-mount ADCPbottom-mount ADCP
Velocities measured using SB-ADCP
ObservationsObservations
Velocities acquired by long-term moored BM-ADCP
Spring Summer
Temperature SalinityTemperatureSalinity
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),(),,(
)cos( ),(
yxyxAA
tAyxn
nn
28 ,2 , /0.9
1306.6 , 3
1
1
kZZ
mZkmyx
kk
Numerical modelNumerical model
Model resolutionModel resolution Boundary conditionsBoundary conditions
A 3D general circulation model with free surface is used for the nowcast system.The bottom slope is quite large and the baroclinic effect is strong in the Taiwan Strait, justifying the choice of a z-level model over a sigma-coordinate model (e.g., POM). Five major tidal constituents O1, K1, N2, M2 and S2 were run together in the model.
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Observations-- real-time-- near real-time
Malfunction?
2D adjoint modelassimilating sea levelsat 9 tide-gage stations
Transfer function forharmonics derived fromlarger-domain 2D model
Boundaryconditions
Complex 3D model
DeterminationDetermination of boundary conditionsof boundary conditions
NoNo
YesYes
WebWeb
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DeterminationDetermination of boundary conditionsof boundary conditionsTake advantage of a larger-domain 2D tidal model results
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Model simulated resultsModel simulated results
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Black-observedRed -calculated
ModelModel validation – sea levelsvalidation – sea levels
Kaohsiung
Dongee
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ModelModel validation – tidal currentsvalidation – tidal currents
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Blue - ship-board ADCP Blue - ship-board ADCP measured velocitiesmeasured velocities
Red - model calculatedRed - model calculatedvelocitiesvelocities
ModelModel validation – tidal currentsvalidation – tidal currents
Errors of calculated speed: < 40% of measured speed.
Errors of calculated current direction: 30º of measured directions.
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Tidal Constituents M2 S2 N2 K1 O1
ADJM rms(cm) 6.5
2.2 2.6 3.8 2.0
TSNOW-2D
rms(cm) model skill
12.30.99
11.50.84
2.50.98
9.40.75
2.50.97
TSNOW-ADJM
rms(cm) model skill
14.90.98
11.40.84
4.60.94
8.80.77
9.20.63
AssessmentAssessment of model performanceof model performance
station
2O)-M(T
1
station of no.
1RMSMean
varianceobs.
anceerror vari-1skill Model
Define:
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0 +24-24
PenghuIslands
Dongee
Demonstration of model productsDemonstration of model products
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SummarySummary
• In the first stage of model development, barotropic tides were successfully simulated in a hindcast mode.
• The model performed well as the open boundary conditions were determined using either an adjoint model or a larger-domain two-dimensional model results.
• The coexistence of a southward propagating Kelvin wave and a nearly standing wave respectively in the eastern and western halves of the Taiwan Strait has also been examined using the model.
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Future workFuture work
• The two approaches of determining open boundary conditions will be adopted when the model is used in an operational mode.
• The wind-driven part, remote-controlled larger-scale circulation and buoyancy-driven circulation will be incorporated in the model step by step.
• The observational work will include strait-wide hydrographic surveys, current measurements using bottom-mounted ADCP moorings and real-time sea-level observations.
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Thank you Thank you for your attention!for your attention!
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