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					Assimilation of Sea Surface Temperature
   into a Northwest Pacific Ocean Model
        using an Ensemble Kalman Filter


                                               B.-J. Choi
                          Kunsan National University, Korea
           Gwang-Ho Seo, Yang-Ki Cho, Chang-Sin Kim
                         Chonnam National University, Korea
                                             Sangil Kim
                               Oregon State University, USA
                                         Young-Ho Kim
                                             KORDI, Korea
Assimilation of Sea Surface Temperature into a Northwest
Pacific Ocean Model using an Ensemble Kalman Filter



                       Contents
       1. Northwest Pacific Ocean Model with ROMS

       2. Ensemble Kalman Filter

       3. Assimilation of Sea Surface Temperature

       4. Assimilation of Temperature Profiles

       Summary
Assimilation of Sea Surface Temperature into a Northwest
Pacific Ocean Model using an Ensemble Kalman Filter

Objectives of current research
(1) setup a Northwest Pacific Ocean Circulation Model
(2) develop an Ensemble Kalman Filter
(3) assimilate Sea Surface Temperature
(4) assimilate temperature profiles
(5) assimilate sea surface height data
(6) evaluate assimilative model output

 Long Term Goal
 • Developing a Regional Ocean Prediction System for the
 Northwest Pacific Ocean and its marginal seas
 • Providing initial condition and open boundary data for
 high resolution (10km, 3km, 1km) coastal ocean models
Nesting of a coastal ocean modeling system




                                     25 km
      Nesting
                                     10 km

                                     3 km

                                     1 km
Nesting of a coastal ocean modeling system




                                     25 km
Assimilation of Sea Surface Temperature into a Northwest
Pacific Ocean Model using an Ensemble Kalman Filter




       1. Northwest Pacific Ocean Model with ROMS

       2. Ensemble Kalman Filter

       3. Assimilation of Sea Surface Temperature

       4. Assimilation of Temperature Profiles

       Summary
Ocean Circulation Model for the
Northwest Pacific Ocean and its Marginal Seas

50˚                                                                     ROMS (Regional Ocean
                                                                            Modeling System)
45˚                                                                     1. Grid size:
          CHINA                                                             - Horizontal: ¼ degree
40˚                                                                         - Vertical: 20 layers
                         KO




                                                                        2. Topography - ETOPO5 data
                           RE




      Hanghe
      River                                 JAPAN
                              A




35˚                                                                     3. Initial - WOA2001
                                                                        4. Surface forcing
         Changjiang
30˚
         River                                                            - ECMWF daily wind
                                                                          - Heat flux : Bulk Flux
25˚                                                                         parameterization
                AN
              IW




                                               Pacific Ocean            5. River: Changjiang, Hanghe
            TA




20˚                                                                         Yellow rivers
                                                                        6. Tidal forcing along the
15˚                                                                         boundary
  115˚     120˚       125˚    130˚   135˚     140˚   145˚   150˚   155˚
                                                                        7. open boundary data: ECCO
Ocean Circulation Model for the
Northwest Pacific Ocean and its Marginal Seas


                                                Wind
                                                Forcing
Ocean Circulation Model for the
Northwest Pacific Ocean and its Marginal Seas
FEB   MAY



            MODEL
            SST




FEB   MAY




            SATELLITE
            SST
AUG   NOV



            MODEL
            SST




AUG   NOV



            SATELLITE
            SST
Transport through Korea Strait
                           Transport through Korea Strait
                 5
                               Korea Strait
                               Obs. (Takikawa)
                 4             Obs. (Teague)
Transport (Sv)




                 3



                 2



                 1



                 0
                     97   98          99          00    01   02
                                                 Year
Northwest Pacific Ocean Model has problems to be
resolved:

1. Overshooting of western boundary currents

2. Temperature bias – model temperature is
warmer than observed temperature
Assimilation of Sea Surface Temperature into a Northwest
Pacific Ocean Model using an Ensemble Kalman Filter




       1. Northwest Pacific Ocean Model with ROMS

       2. Ensemble Kalman Filter

       3. Assimilation of Sea Surface Temperature

       4. Assimilation of Temperature Profiles

       Summary
Data Assimilation in an Ocean
Modeling System

Ensemble Kalman Filter (EnKF)
The technical methods are based on the original
algorithm of Evensen (1994) and the modified algorithm
of Burgers et al. (1996).

It is relatively easy to implement the algorithm, the EnKF,
to a sophisticated nonlinear model (e.g. ROMS, POM,
ECOM, FVCOM, HYCOM) since the data assimilation
algorithm is independent of the forecast model.
 Data Assimilation in an Ocean
 Modeling System
Ensemble Kalman Filtering (a stochastic process)

                                      Member1


                                      Member2




                                      Member16
Ensemble Kalman Filter (EnKF)

  k
X new        k
            X old   W      k
                         ( yo       k
                                    yf   )
                                T
                          CH
  k
X new        k
            X old               ( yo  y f )
                                    k     k
                      ( HCH  R)
                            T



X new  X old  CH T ( HCH T  R) 1 ( yo  y k )
  k       k                             k
                                              f

X : state vector(T,S, U, V, zeta) W : weight
  k
yo : observation vector H : measurent function
y f  H X f : measurement vector
  k        k

Superscrip t k represents the kth ensemble member
Subscript f representsforward model
Identical Twin Experiment


  Number of Ensemble: 16 member


        Spin up time                assimilation




                                    True run
start                  2003/01/01   Control run    2003/12/31
                                    Ensemble run
Identical Twin Experiment
               (30 SST observation points)




                                The 30 diamond
                                marks (♦) are
                                the locations for
                                measurement.
Identical Twin Experiment
Surface        Surface      Surface
Currents       Currents     Currents
Identical Twin Experiment

    RMS error of SST
Assimilation of Sea Surface Temperature into a Northwest
Pacific Ocean Model using an Ensemble Kalman Filter




       1. Northwest Pacific Ocean Model with ROMS

       2. Ensemble Kalman Filter

       3. Assimilation of Sea Surface Temperature

       4. Assimilation of Temperature Profiles

       Summary
Assimilation of Satellite-observed SST

   Modeling Domain: Northwest Pacific Ocean
                    and its Marginal Seas
   Duration: November 2003 to June 2004
   SST data: NASA composite SST
            (AVHRR, AMSR, buoy)
   Assimilation method: Ensemble Kalman Filter
   Assimilation interval: every 7 day
   Ensemble number: 16
   Number of observation points: 50
Assimilation of Satellite-observed SST




                                         The 50 red
                                         dots ( ) are the
                                         locations for
                                         SST
                                         measurement
                                         point.
                                                                          Logitude
         2 Mode        50˚
           of 16 ensemble members using EOF analysis of
Initialization
         19.6%
                       45˚    400
model output                p

                                                                                                                           
                       40˚
                                                                                                                                200

                                                                           E ( x)  x                                                      a a
            Latitude


                       35˚                                                                                                      ξ0a        rm em
                       30˚
                                                                                                                           a 1-200
                       25˚
           E (x) is ensemble initial, state vector on November 1, 2003,
                                                -400

           ξa is normal random number, r eigenvalues, e eigenvectors, and p mode number.
              20˚                                    0  300  600   900  1200
                                                            Time(day)
                       15˚
                         115˚ 120˚ 125˚ 130˚ 135˚ 140˚ 145˚ 150˚ 155˚ 160˚
                                                                      Logitude
           50˚
                       1 Mode
                           3 Mode
                       31.7%
                       50˚
                             6.4%                                                                                             400
           45˚
                       45˚
                                                                                                                              200
                                                                                                                                400
           40˚
                       40˚
Latitude




                                                                                                                                0
           Latitude




           35˚                                                                                                                  200
                       35˚
           30˚                                                                                                               -200 0
                       30˚

           25˚                                                                                                                 -200
                                                                                                                             -400
                       25˚
                                                                                                                                   0       300    600    900   1200
           20˚                                                                                                                 -400
                       20˚                                                                                                                        Time(day)
                                                                                                                                       0    300    600   900   1200
           15˚ 15˚                                                                                                                                Time(day)
                   120˚ 125˚ 130˚ 135˚ 140˚ 145˚ 150˚ 155˚ 160˚
             115˚ 115˚ 120˚ 125˚ 130˚ 135˚ 140˚ 145˚ 150˚ 155˚ 160˚
                                                                 Logitude
                                                                   Logitude

           50˚
                       2 Mode                                                                                              (sea surface height)
                             -0.015

                                      -0.011

                                               -0.007

                                                        -0.003

                                                                  0.001

                                                                           0.005

                                                                                   0.009

                                                                                           0.013

                                                                                                   0.017

                                                                                                           0.021

                                                                                                                   0.025




                       19.6%
           45˚                                                                                                                400
                                                              Logitude

            50˚
                  2 Mode
                  19.6%
            45˚                                                                                                 400
            40˚
                                                                                                                200
 Latitude



            35˚
                                                                                                                  0
            30˚
                                                                                                                -200
            25˚
                                                                                                                -400
            20˚                                                                                                        0   300   600    900   1200
                                                                                                                                 Time(day)
            15˚
              115˚ 120˚ 125˚ 130˚ 135˚ 140˚ 145˚ 150˚ 155˚ 160˚
                                                          Logitude

            50˚
                  3 Mode
                  6.4%
            45˚
                                                                                                                400
            40˚
Latitude




                                                                                                                200
            35˚
                                                                                                                  0
            30˚
                                                                                                                -200
            25˚
                                                                                                                -400
            20˚
                                                                                                                       0   300   600    900   1200
            15˚                                                                                                                  Time(day)
              115˚ 120˚ 125˚ 130˚ 135˚ 140˚ 145˚ 150˚ 155˚ 160˚
                                                              Logitude

                                                                                                               (sea surface height)
                  -0.015

                           -0.011

                                    -0.007

                                             -0.003

                                                      0.001

                                                               0.005

                                                                       0.009

                                                                               0.013

                                                                                       0.017

                                                                                               0.021

                                                                                                       0.025
Assimilation of Satellite-observed SST
Ensemble Kalman Filtering (a stochastic process)

                                      Member1


                                      Member2




                                      Member16
                3.0
                               Control rmse
                               Assimilation rmse
                               Control rmse Avg.
                               Assimilation rmse Avg.



   RMS ERROR
                2.5




                2.0
                                                                                       Sea Surface
                                                                                       Temperature
                1.5
                      0   30         60         90       120   150   180   210   240
                                                        TIME (day)
               0.24
RMS ERROR




               0.20




               0.16
                               Control rmse                                            Sea Surface
                               Assimilation rmse
                               Control rmse Avg.                                       Height
                               Assimilation rmse Avg.
               0.12
                      0   30          60         90      120   150   180   210   240
                                                        TIME (day)
        East Sea
      (Japan Sea)
YS

ECS                 KE
                RMSE in Sea Surface Temperature
                Yellow Sea Area ( 122E~126E , 34N~38N )                         East China Sea Area ( 122E~130E , 25N~32N )
            5                                                               5
                           Control rmse                                                   Control rmse
                           Assimilation rmse                                              Assimilation rmse
            4                                                               4




                                                                RMS ERROR
RMS ERROR




            3                                                               3

            2                                                               2

            1                                                               1
                0     30   60     90      120 150 180 210 240                   0    30   60      90     120 150 180 210 240
                                         TIME                                                           TIME
                    East Sea Area ( 129E~139E , 36N~42N )                   Kuroshio extention Area ( 140E~155E , 30N~40N )
            5                                                               5

            4                                                               4
RMS ERROR




                                                                RMS ERROR


            3                                                               3

            2              Control rmse                                     2
                                                                                          Control rmse
                           Assimilation rmse
                                                                                          Assimilation rmse
            1                                                               1
                0     30   60     90      120 150 180 210 240                   0    30   60      90     120 150 180 210 240
                                         TIME                                                           TIME
             RMSE in Sea Surface Height
                  Yellow Sea Area ( 122E~126E , 34N~38N )                            East China Sea Area ( 122E~130E , 25N~32N )
                              Control rmse
            0.4               Assimilation rmse                                0.4




                                                                   RMS ERROR
RMS ERROR




            0.3                                                                0.3

            0.2                                                                0.2

                                                                                               Control rmse
            0.1                                                                0.1             Assimilation rmse


                  0      30   60      90     120 150 180 210 240                     0   30   60       90     120 150 180 210 240
                                            TIME                                                             TIME


                      East Sea Area ( 129E~139E , 36N~42N )                     Kuroshio extention Area ( 140E~155E , 30N~40N )
                              Control rmse
            0.4                                                                0.4
                              Assimilation rmse
                                                                   RMS ERROR
RMS ERROR




            0.3                                                                0.3

            0.2                                                                0.2

                                                                                               Control rmse
            0.1                                                                0.1             Assimilation rmse


                  0      30   60      90     120 150 180 210 240                     0   30   60       90     120 150 180 210 240
                                            TIME                                                             TIME
RMSE of SST with respect to in-situ observation




                    February               April                   June
                 Assi.   Control   Assi.       Control     Assi.      Control
   YELLOW SEA   1.393     1.507    1.412           1.547   2.289          2.423
     EAST SEA   0.953     1.447    1.547           1.865   1.902          2.274
Comparison with observed Temperature (100 m)
            Depth (   -40                         -40                                             -40                    Temperature (oc)             Temperature (oc)
                                                                                          Temperature (oc)
                                                                                          0    5 10 15 20 25             0   5 10 15 20 25            0   5 10 15 20 25
                      -60
                                      Feb.
                                                  -60           (a)                  0
                                                                                          Apr.       -60         (b) 0 June                 (c) 0
                      -80
                                      YS          -80                     -20
                                                                                          YS         -80           -20 YS                      -20




                                                                        Depth (m)
                            0   5 10 15 20 25           0               5 10 15 20 25                      0   5 10 15 20 25
                  of
      Comparison (e) 0
    (d) 0                                                                                          (f) 0
                                                                                    -40                            -40                         -40
                  Temperature
                  -100                           -100                                               -100
     Depth (m)




                                                                                    -60                            -60                         -60
                  Profile
                  -200                           -200                                               -200Feb.                       Apr.                        June
                                                                                                        YS         -80
                                                                                                                                   YS          -80
                                                                                                                                                               YS
                  -300                           -300                               -80
                                                                                           0   5 10 -300 20 25
                                                                                                     15                  0   5 10 15 20 25            0   5 10 15 20 25

                                      Feb.                      (d)                  0                           (e) 0 June                  (f) 0
                  -400                           -400                                     Apr.      -400

                  -500
                                      EJS        -500
                                                                         -100
                                                                                      -500
                                                                                          EJS                    -100    EJS                  -100
                            0   5 10 15 20 25           0               5 10 15 20 25                      0   5 10 15 20 25
                                                                 Depth (m)


                                                (h) 0                    -200                                    -200                         -200
    (g)                0                                                                 0        (i)
                  -200                           -200                           -300               -200           -300                        -300
Depth (m)




                  -400                           -400                           -400               -400 Feb.      -400             Apr.       -400              June
                                                                                -500
                                                                                                        EJS       -500
                                                                                                                                   EJS        -500
                                                                                                                                                                EJS
                  -600                           -600                                              -600
                                                                                          0    5 10 15 20 25             0   5 10 15 20 25            0   5 10 15 20 25

                  -800                Feb.       -800           (g)                  0
                                                                                          Apr.     -800          (h) 0 June                 (i)   0

                                      KE                                       -200       KE                      -200 KE                     -200
              -1000                             -1000                                             -1000
                                                            Depth (m)




                                      ASSIM.                                   -400                               -400                        -400
                                      CON.
                                      OBS.                                     -600                               -600                        -600

                                                                               -800                     Feb.      -800             Apr.       -800             June
                                                                           -1000
                                                                                                        KE       -1000
                                                                                                                                   KE        -1000
                                                                                                                                                               KE
                                                                                                        ASSIM.
Assimilation of Sea Surface Temperature into a Northwest
Pacific Ocean Model using an Ensemble Kalman Filter




       1. Northwest Pacific Ocean Model with ROMS

       2. Ensemble Kalman Filter

       3. Assimilation of SST

       4. Assimilation of Temperature Profiles

       Summary
  Subsurface temperature data from CDT, XBT, and
  ARGO floats.




 we assimilated temperature data at 5, 10, 30, 50, 100, 200,
500 m depths every 7 day. The observation data within 7 days of
time window are sampled on the day of assimilation.
t = 7 day    t = 14 day   t = 21 day




t = 28 day   t = 35 day   t = 42 day




t = 49 day   t = 56 day   t = 63 day
 RMSE of Sea Surface Height (m)


RMSE(meter) Control   SST Assi.   SST & Hydro Assi.
2004/5/27    0.222    0.187       0.181
Comparison of
Temperature
Profile
(May 2004)
Summary
•   Setup a Northwest Pacific Ocean Circulation Model
•   Developed an Ensemble Kalman Filter
•   Performed an identical twin experiment to evaluate the
    performance of Ensemble Kalman Filter
•   Assimilation of SST
Work in Progress
• Assimilation of Subsurface Temperature Data from CDT,
  XBT and ARGO Floats
Future Plan
• Setup a higher resolution model and assimilate Sea
   Surface Height in order to resolve eddies and current
   meandering
• Provide initial condition and open boundary data for
   (3km and/or 1km resolution) coastal ocean models
Assimilation of Sea Surface Temperature into a Northwest
Pacific Ocean Model using an Ensemble Kalman Filter




                       Thank you !

				
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