TTaiwanaiwan SStraittrait NOWNOWcastcast ssystemystem

NNational ational CCenter for enter for OOcean cean RResearchesearchTaiwan, ROCTaiwan, ROC

P01

• 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

P02

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)

P03

• 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

P04

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

P05

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

P06

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

P07

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

P08

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

P09

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

P10

),(),,(

)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.

P11

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

P12

DeterminationDetermination of boundary conditionsof boundary conditionsTake advantage of a larger-domain 2D tidal model results

P13

Model simulated resultsModel simulated results

P14

Black-observedRed -calculated

ModelModel validation – sea levelsvalidation – sea levels

Kaohsiung

Dongee

P15

ModelModel validation – tidal currentsvalidation – tidal currents

P16

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.

P17

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:

P18

0 +24-24

PenghuIslands

Dongee

Demonstration of model productsDemonstration of model products

P19

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.

P20

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.

P21

Thank you Thank you for your attention!for your attention!

P22