PowerPoint Presentation

Simulation of the

Bohai Sea Circulation and

Thermohaline Structure

Using a Coupled

Hydrodynamical-Ecological Model

LCDR Rodrigo Obino

Brazilian Navy

Thesis Presentation – Naval Postgraduate School

Outline

 Objectives

 Background

 Model Features

 Experiments

 Case Analysis

 Turbulence Study

 Conclusions

 Recommendations

Objectives

 Simulation of the Bohai Sea using

COHERENS model

 Sensitivity studies with different forcing

functions

 Physical mechanisms for the Bohai Sea

circulation and thermohaline structure

 Comparison between two turbulence

schemes

Background

$E:\IMAGES\map\ysmap.jpeg$

Bohai

Sea

China

Korean

Peninsula

Yellow

Sea

East China

Sea

 Eastern China

 Mid latitude

 Semi-Enclosed

sea

 Connected to the

Yellow Sea

The Bohai Sea

LiaodongGulf

Huanghe

River

Central Basin

Haihe R.

Huanhe R.

Laizhou Bay

Yellow

Sea

Bohai Strait

Bohai Gulf

Liaodong

Peninsula

Liaohe R

 Surrounded by the Chinese mainland and

Liaodong Peninsula

 Connected to the northern Huanghai Sea

(Yellow Sea) through the Bohai Strait

 Divided in four parts: Liaodong Gulf, Bohai

Gulf, Laizhou Bay and Central Basin

 Area of 80,000 km square, width of 300 km and

length of 500 km

 Relatively shallow waters

Characteristics

Topography

$D:\Matlab53\work\Thesis\Graph\bohaice.tif$

 Average depth – 18 m

 Maximum depth at Bohai Strait – 60 m

 Open boundary relatively deep

 Gulfs are shallow

$D:\Thesis\bohai_topo.jpg$

Circulation

 Winter current –

surface mainly wind-

driven transport

 Anticyclonic pattern

in central basin

winter monsoon

 Driven by strong monsoon winds, large buoyancy

forces, active tidal mixing, strong open ocean forcing

Circulation

summer monsoon

 Weaker in summer

than in winter due to

weaker winds

 Counterclockwise gyre

in central-northern part

of Bohai Sea

Monsoon

$D:\Thesis\winmosoon 001.jpg$

$D:\Thesis\sumosoon 001.jpg$

summer monsoon

Jun - Sep

winter monsoon

Nov - Mar

 Siberian High

 Relatively strong, cold

and dry NW-NE winds

 Low over East Asia

 Relatively weak, warm

and moist SE-SW winds

Tidal Harmonics

$D:\Thesis\bohai_tide.jpg$

Model Features

 COHERENS – Coupled Hydrodynamical-

Ecological Model for Regional and Shelf Seas

 3-D hydrodynamical model coupled to

sediment, contaminant, and biological models

 Flexibility

Developer: EU Marine Science and Technology

(MAST)

Hydrohynamical Equations

 Governing Primitive Equations derived from

Navior-Stokes Equations

 Boussinesq approximation, hydrostatic

equilibrium and incompressibility

 Mode-splitting technique – coupling between

external and internal modes

 Sea surface elevation and depth-integrated

velocities – external mode

 Three dimensional currents, temperature

and salinity – internal mode

Discretization

 Formulation in spherical coordinates (λ,φ,z)

 Vertical terrain-following coordinate – σ

 Sigma coordinate – 0 at the bottom and

1 at the surface – 16 levels

, -h  z  

 Horizontal differencing – Arakawa staggered

C-scheme – 2nd order centered

 Horizontal grid – 62x50 points -  9 km

Other Features

 Coastline and bottom topography – DBDB5

5’ resolution

 External time step – 15 sec

Internal time step – 10 min

 Free surface BC and slip bottom BC

Zero gradient open BC

 Spinup – Jul 01 1999 to Jan 01 2000 - 0000Z

 Simulations – Jan 01 2000 to Dec 31 2000

Initialization

 Initial conditions for Spinup – GDEM

climatological data, and zero velocities and

sea surface elevation

 Initial conditions for simulations – last

information obtained in the spinup for all

scalar and vector parameters

$D:\Matlab53\work\Thesis\tinitial.tif$

Initial sea surface temperature

$D:\Matlab53\work\Thesis\sinitial.tif$

Initial sea surface salinity

Forcings

 Tidal harmonics at open boundary

phase and amplitude: M2, S2, N2, K2,

K1, O1, P1 and Sa

 Climatological data at open boundary

monthly GDEM temperature and salinity

 Atmospheric forcing over the sea

surface (Full flux forcing)

 No river runoff

Atmospheric Forcing Function

 National Center for Environmental Prediction

(NCEP) Reanalysis Data – 2.5° global grid

(4 times daily) and interpolated to model grid

 Parameters: wind components at 10 m,

air temperature, sea surface pressure,

relative humidity, precipitation rate and

cloudiness

 Interpolated on each time step

$D:\Matlab53\work\Thesis\airtemp.tif$

Air Temperature at Sea Surface

15 January 2000

15 July 2000

$D:\Matlab53\work\Thesis\wind.tif$

Wind Field at 10 m

15 January 2000

15 July 2000

Sea Surface Pressure

$D:\Matlab53\work\Thesis\pressure.tif$

15 January 2000

15 July 2000

$D:\Matlab53\work\Thesis\humid.tif$

Relative Humidity

15 January 2000

15 July 2000

$D:\Matlab53\work\Thesis\cloud.tif$

Cloudiness

15 January 2000

15 July 2000

$D:\Matlab53\work\Thesis\prate.tif$

Precipitation Rate

15 January 2000

15 July 2000

Experiments

 Control Run – all forcing functions

 Non-Fluxes Run – exclude heat and salt fluxes

 Non-Tidal Run – tide effect not considered

 Non-Wind Run – no surface stress due to winds

Adopted same settings for all runs – types of

turbulence scheme, advection and diffusion

Control Run

$D:\Matlab53\work\Thesis\cross.tif$

 Most complete case

 Analysis based on T, S and V fields

 Plots only January and July

Zonal and Meridional

Vertical Cross-Sections

surface

Horizontal Temperature and Velocity Vectors

$F:\Thesis\Figure\tempuvsurf.tif$

 Head of Gulfs are colder

 Northern Bohai Strait warmer

 Velocities are S-SE and strong

 Inflow at open boundary and

outflow at the southern part

January 2000

July 2000

 Head of Gulfs are warmer

 N Bohai Strait relatively cold

 Open boundary is colder

 Currents flow NE

 Still strong current at N Bohai

Strait

$F:\Thesis\Figure\tempuvmid.tif$

mid-depth

January 2000

July 2000

 Confirms warmer N Bohai

Strait

 Relatively low temperature

at central basin

 Currents weaker than at surf

 Warm region at central basin

 Penetration of sub-surface

cold water mass from YS

 Currents weaker than at surf

 Anticyclonic gyre at central

basin

bottom

$F:\Thesis\Figure\tempuvbot.tif$

January 2000

July 2000

 Temperature almost the same

as the SST field

 Currents are more N-NE,

but weaker

 Temperature different from

the SST field

 Presence of cold water mass

from YS – North YS Bottom

Cold Water

Vertical Temperature Cross-Sections

$D:\Matlab53\work\Thesis\verttemplon.tif$

Along meridian 121º01’E

January 2000

July 2000

 Vertically uniform

 Shallow regions are colder

 Some stratification

 North YS Bottom Cold

Water

 Surface and shallow regions

are warmer

$D:\Matlab53\work\Thesis\verttemplat.tif$

Along parallel 38º35.5’N

January 2000

July 2000

 No stratification

 Some stratification

Horizontal Salinity Field

$D:\Matlab53\work\Thesis\saltsurf.tif$

surface

15 January 2000

15 July 2000

 Fresher region near

Huanghe River delta

 Saltier at central basin

 Saltier at Bohai Gulf head

 Values have increased

slowly along the year

 No river runoff

Vertical Salinity Cross-Sections

$D:\Matlab53\work\Thesis\vertsaltlon.tif$

Along meridian 121º01’E

 Vertically uniform

 Little stratification

15 January 2000

15 July 2000

$D:\Matlab53\work\Thesis\vertsaltlat.tif$

Along parallel 38º35.5’N

 Vertically uniform

 Little stratification

15 July 2000

15 January 2000

Effects of Surface Thermohaline

Forcing (Control – No Fluxes)

 Winter (January): cooling, reduction of the

circulation, minor effect on salinity.

The effects are vertically uniform.

 Summer (July): warming, saline, enhancement

of the circulation.

The effects decrease with depth except in the

shallow water regions.

There is no effect on temperature in the deeper

layer connecting to the Yellow Sea.

$F:\Thesis\Figure\fluxtempuvbot.tif$

$F:\Thesis\Figure\fluxtempuvsurf.tif$

Temperature and Velocity Differences

July 2000

January 2000

surface

bottom

$F:\Thesis\Figure\fluxverttemplon.tif$

$F:\Thesis\Figure\fluxverttemplat.tif$

 In winter vertically uniform, while in summer

some stratification

July 2000

January 2000

$F:\Thesis\Figure\fluxsaltsurf.tif$

Salinity Differences

surface

 Differences increase along

the year

 Head of Gulfs present

highest differences

 Bohai Strait and eastern

boundary have smaller

differences

15 July 2000

15 January 2000

$F:\Thesis\Figure\fluxvertsaltlat.tif$

$F:\Thesis\Figure\fluxvertsaltlon.tif$

 Surface layer more affected by salt fluxes and

even more in July

15 July 2000

15 January 2000

Wind Effect (Control – No Wind)

 Winter (January): cooling in deeper region,

warming at southern Bohai Strait, enhancement

of the circulation, presence of salty and fresher

spots in the central basin.

The effects are vertically uniform.

 Summer (July): warming in central basin and

in shallow regions, cooling in deeper region,

enhancement of the circulation, fresher at surface

layer.

There is some variability in the surface layer.

Temperature and Velocity Differences

$F:\Thesis\Figure\windtempuvsurf.tif$

$F:\Thesis\Figure\windverttemplat.tif$

July 2000

January 2000

surface

Salinity Differences

$F:\Thesis\Figure\windsalsurf.tif$

$F:\Thesis\Figure\windvertsaltlat.tif$

15 July 2000

surface

15 January 2000

Tidal Mixing (Control - No Tides)

 Winter (January): reduction of the circulation

in the central basin, variable effect on

temperature.

The effects are vertically uniform.

 Summer (July): warming close to the bottom

and cooling in surface layer, enhancement of

the circulation in the central basin.

There is no effect on temperature in the deeper

layer connecting to the Yellow Sea.

Temperature and Velocity Differences

$F:\Thesis\Figure\tidetempuvsurf.tif$

$F:\Thesis\Figure\tideverttemplon.tif$

July 2000

surface

January 2000

Salinity Differences

$F:\Thesis\Figure\tidsalsurf.tif$

$F:\Thesis\Figure\tidevertsaltlon.tif$

15 July 2000

15 January 2000

surface

Turbulence Study

 Vertical eddy viscosity and diffusion

coefficients parameterized by turbulence scheme

 Study = “k-l” x “k-”

 Spatial and Seasonal comparisons

 Observed parameter – TKE

 Selected 6 points

 January and July

$D:\Matlab53\work\Thesis\staturbo.tif$

July – Sta # 3

$D:\Matlab53\work\Thesis\Turbo\janavr3.tif$

$D:\Matlab53\work\Thesis\Turbo\janavr1.tif$

January – Sta # 2

Spatial and Seasonal Comparison

“k-l” (green) > “k-” (blue)

Diurnal and Seasonal Variation

$D:\Matlab53\work\Thesis\Turbo\luysea2.tif$

“k-” Turbulence Closure Scheme

15 January 2000

15 July 2000

 Summer reaches higher values

 Summer has weak turbulence in

deeper layer

Sta # 4

$D:\Matlab53\work\Thesis\luyten5.tif$

15 January 2000

15 July 2000

Sta # 5

$D:\Matlab53\work\Thesis\Turbo\melsea4.tif$

15 January 2000

15 July 2000

“k-l” Turbulence Closure Scheme

Sta #1

$D:\Matlab53\work\Thesis\mellor6.tif$

Sta # 6

15 January 2000

15 July 2000

 Summer is highly turbulent at

mid-depth

 Summer has weak turbulence in

deeper layer

Pattern of TKE Profiles

$D:\Matlab53\work\Thesis\pattern.tif$

Conclusions

 Seasonal circulation patterns and temperature fields

are reasonably well simulated

 Salinity is not as well simulated as temperature,

probably due to no river runoff

 Winter monsoon season presents vertically uniform

thermohaline structure, while summer monsoon season

presents a multi-layer structure

 Wind effect is the major forcing for driving surface

currents

 The Heat fluxes are the predominant driving force for

the thermal structure

Conclusions

Tidal mixing is responsible for deep layer characteristics.

It cools the surface layer and warms the deeper layer in

the summer (i.e., vertical mixing)

 “k-l” scheme provides higher TKE than “k-” scheme

 Summer has weaker turbulence at deeper layer than in

winter

Recommendations

 Extend simulation to Yellow Sea, East China

Sea and South China Sea

 Include river runoff

 Assimilate MCSST and Scatterometer Winds

 Detailed study of the tidal effect on surface

elevation and main harmonics

Questions ?