Fourth Study Conference on BALTEX Scala Cinema Gudhjem

- 110 -
Simulation of Bottom Water Inflow in the Bornholm Basin
Valeriy Tsarev
Russian State Hydrometeorological University, 98, Malookhtinsky Ave., 195196, St.Petersburg, Russia, e-mail:
tsarev@rshu.ru
1. Introduction
Possible features of bottom flow from the Bornholm
Straight into the Bornholm Basin are investigated by
numerical simulation.
2. Model
The vertical salinity distribution in the Bornholm Basin is
excepted to be in form of two horizontal layers. Salinity
of upper and down layer was set 8 pml and 16 pml.
consequently. At the boundary with the Bornholm
Straight salinity was 20 pml. Salinity difference at this
boundary generates bottom saline water inflow. A set of
the model governing equations describing bottom water
inflow from the Bornholm Straight involves treedimensional
non-stationary non-linear equations of
motion for the horizontal and vertical directions (Tsarev
V.). It also includes equations of mass and salinity
conservation and equation of the state. Equations of
motion and mass conservation are transformed with the
method of vector potential to three-dimensional equation
of vector vorticity and equation of vector potential.
Resulting currents velocity u is found from vector ψ
potentials accordingly.
u = ∇×ψ.
ψ is connected with vorticity Ω by equation ∇ 2 ψ=−Ω.
Ω is calculated from equation of vorticity
2
∂Ω
∂u
∂ Ω
+ u z
z 2 l l
∂t
∂z
∂z
2
( ⋅∇)
Ω − ( Ω ⋅ ∇)
u − f − k − k ∇ Ω = g × ∇ρ.
For calculation of water salinity and density the
following equations are used
2
∂s
∂s
∂s
∂s
∂ s 2
+ u + v + w = kz
+ kl∇
s
2
∂t
∂x
∂y
∂z
∂z
ρ = ρ + α s.
0
s
u, v, w are velocity components along coordinate axes x,
y, z; ρ 0,ρ are standard and real sea water density
respectively; s is salinity; k z, k l are coefficiens of vertical
and horizontal eddy viscosity ,k s,k l are coefficients of
vertical and horizontal diffusivity respectively; α s is a
coefficient of the saline contribution to density; g is
gravitational acceleration; f is the Coriolis coefficient.
Evolution of density boundary disturbance caused by
bottom saline water spreading is simulated by model of
baroclinic mode for two layer environment (Gill A).
The accounts were carried out for rectangular area
located in the central part of the Bornholm Basin (fig. 1).
The lateral border was considered as solid except for its
small parts in area of the Bornholm Stright and the Stolp
Channel . Initial vorticity was kept equel to 0. Initial
density boundary between layers was horizontal. The
vertical and horizontal viscosity coefficients were
accepted equal k z= 10 -4 м 2 с -1 , k l = 10 м 2 с -1 . The vertical
and horizontal diffusivity were as follows k sz = 10 -5 м 2 с -1 ,
ksl = 10 м 2 с -1 . The domain was covered by 33х37x30
grid with 30 levels in vertical direction. The spatial steps
was 3 kms. In a vertical direction first ten steps from the
bottom were 2 м, and above equaled (Н-20м) /19, where
Н bottom depth in meters.
Figure 1: Model area location
3. Model results
The Bornholm Deep
From the model run initially inflowing saline bottom
water spreads in the Bornholm Basin in form of narrow
flow (fig.1.). Spreadding bottom water lifts down layer
and in such way disturbs density boundary.
35.00
30.00
25.00
20.00
15.00
10.00
5.00
0.00
0.00 5.00 10.00 15.00 20.00 25.00 30.00
Figure2: Distribution of bottom water salinity and
density boundary disturbance (isoclines) in a day after
inflow
The density boundary disturbance spreads in form of
inner waves racially at a distance close to baroclinic radii
of deformation. Because of bottom slope influence it