PPT - Tide Simulation Using ROMS

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					                   Tide Simulation
 Regional Ocean Modeling System (ROMS)

                      Xiaochun Wang

Co-author: Changming Dong, Yi Chao, Zhijin Li, James McWillams
Contributions from: Koji Matsumoto, John Farrara,
Jei-kook Choi, Quoc Vu

    ROMS/TOMS Workshop Oct. 24-26 2005
Three Level Nested ROMS

                 3-Level Nested Model
              Grid Size   Time Step     Res.
           L1: 85*170*32 900s           17km
           L2: 95*191*32 300s           6km
           L3: 83*179*32 100s           2km

          16 Processors on SGI Altix 3000
          1 hour integration takes 1min cpu time.
 Boundary Conditions

 • Open Boundary Condition
      SSH: Chapman condition
      Tangential Barotropic Velocity: Oblique radiation
      Normal Barotropic Velocity: Flather condition

  • Closed Boundary Condition
      SSH: Zero gradient
      Tangential Velocity: Free slip
      Normal Velocity: Zero

Tide SSH and transport are from the barotropic tide data
assimilation system of Oregon State University (TPXO.6).

Atmospheric Forcing: Hourly wind stress and heat flux.
Tide Solution in Nested ROMS (M2)

               Tide constituents used:
               M2 K1 O1 S2 N2 P1 K2 Q1
 Comparison with T/P Tide Estimation

                                         Away from the coast
Courtesy of Dr. Koji Matsumoto (Japan)
Comparison with Tide Gauges (Amp)

                                                 RSS: 5.41cm

        M2 K1 O1 S2 N2 P1 K2 Q1
 RMS   4.59 1.29 0.92 2.00 0.64 0.93 0.54 0.29

 Coastal region, 10 stations.
Comparison with Tide Gauges (Phase)
         M2 K1 O1 S2                     N2 P1 K2 Q1

Blue: Tide Gauge            M2 K1 O1 S2 N2 P1 K2 Q1
Green: ROMS            RMS 3.42 2.39 3.75 4.06 2.53 5.10 3.08 7.28
  Comparison with Tide Gauges

RMS of one month sea surface height from
model and 10 tide gauges.
  Comparison around Monterey Bay

                                             Monterey Bay
                                             3 Gauges

                                             L1 Domain
                                             10 Gauges

Three stations: Moss Landing, Santa Cruz, Monterey Bay
Nested Tide Solution for One Station

Tide solution is improved in finer resolution model domain.
    Quadratic Bottom Drag Coefficient

   1.e-3                      3.e-3

   30e-3                      100e-3

Tide Solution is more robust in OGCMs than in barotropic models.
               Future Plan

• Tidal Data Assimilation
    Find optimal boundary condition
• Tidal Current Simulation
    How to improve the tide current
• Forced by tidal signal along the open boundaries
    in west, north and south directions, ROMS can
    simulate tide reasonably well for US west coast
•   Comparing with barotropic tide models, the tide
    simulation is not sensitive to bottom drag
    coefficient in ROMS.
•   Addition of tide into ROMS is a significant step
    toward an operational ocean forecasting system
    of the region.
       Tide Current Estimation
• Tide current changes with stratification
• Missing data
• Subtidal current influence

Sheme: The data is 8-28-hour band-pass filtered to
remove the subtidal signal. When the length of missing
data is less than 12 hours, a linear interpolation is used to
fill the gap. When the missing data is longer than 12
hours, the longest segment of data is used to estimate
tide current ellipses.
             Tide Current:
A long journey with a humble beginning

  HF Radar Surface Current   ROMS Surface Current
Stratification (M1 Mooring)

August, September, October 2003
     HF Radar Tidal Current (M2)

  August                 September             October   2003

Tidal current is sensitive to stratification
   Tidal Current (M1 ADCP)

August           September       October   2003

Tidal current is sensitive to stratification
     Spatial Comparison (M2 K1 O1 S2)
         ROMS SSH          TPXO (SSH)

M2           K1     M2         K1

O1            S2    O1          S2
Spatial Comparison (Vbar)
 ROMS               TPXO
Spatial Comparison (Ubar)
 ROMS             TPXO
 RMS of ROMS (L1) and TPXO
    SSH                    Ubar                 Vbar

Difference of SSH is small. Difference of transport is large.
Influence of Bottom Drag Coefficient

           0                          3*10^-4

       30*10^-4                    300*10^-4                       Linear Case

Compared with barotropic tidal models, the ROMS tidal solution is not
sensitive to Bottom Drag Coefficient (<300*10^-4).
Influence of Boundary Condition

Tidal Solution is a combined effect of boundary conditions.
Tide in ROMS and TPXO(M2)
Comparison with Tide Gauges (Amp)

                           RSS: 5.41cm

                           RSS: 2.72cm

Coastal region
Comparison with Tide Gauges (Phase)
       M2 K1 O1 S2
                      N2 P1 K2 Q1

  Blue: Tide Gauge
  Green: ROMS
  Red: TPXO

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