Vo
l.
16
No.4 Joumal
of
Southwest Jiaotong University (English Edition)
Oc
t.
2008
Ar
ticle
ID:
1005-2429
(2008)
04
-0
404-10
Numerical Study
of
Flow Near
Ri
ver
Outlet
in
Namtso
Lake
Diki
Yudron
(德吉玉珍)
1
*,
J
arle
Bemtsen
2
1. School
of
Science , Tibet University , Lhasa
85
α刀
0
,
China
2. Department
of
Mathematics , University
of
Bergen ,
JOM.
Bruns
gt
12
,
N-5ω18
Bergen , Norway
Abstract
A
river
plume
dynamics
analysis
was
made
in
Namtso
Lake
by
using
a
sigma
coordinate
non-hydrostatic
numerical
ocean
model
,
the
Bergen
Ocean
Mode
l.
Simulations
were
carried
out
by
hydrostatic
and
non-hydrostatic
models
with
horizontal
resolution
of 5.00 m, 2.50 m
and
1.
25
m,
respectively.
The
simulation
results
for
the
homogeneous
lake
are
robust
to
也
e
grid
size
,
and
仕
le
non-hydrostatic
pressure
effect
is
not
important
in
由
is
case.
For
也
e
stratified
case
,
the
results
are
sensitive
to
both
the
grid
size
and
non-hydrostatic
press
町
'e
corrections.
Key words
Non-hydrostatics;
Ri
ver
plume;
Numerical
ocean
model;σ-c
∞
rdinate;
Stratified
Introduction
Namtso Lake is the largest lake in Tibet.
It
is
locatβd
in the southem slope
of
the Nyenchen Thangl-
ha
Mountains with an area
of
1980
km
2
and an eleva-
tion
of
4718
m above sea level, covering a domain
of
30
0
30'-30
0
55'N
and
90
0
16'-91
0
03'E.
The drainage
缸
ea
of
Namtso Lake is about 10 610 km
2
with a sup-
ply coefficient
of
5.
53. Namtso Lake has plentiful
sources
of
water supply from glacier and snow melting
in the Nyenchen Thanglha Mountains through several
parallel rivers along the lake which flow into the lake
and from a high amount
of
precipitation in this area.
There are five main rivers which flow into Namt-
so Lake:
Pu
chu River, Eangchu River, Tsechu Riv-
er
, Nyiyachu River, and Kangyasungchu River.
There is no river flowing out
of
the lake. This creates
Received
2008--{)6--{)3
Biography Diki
Yudron
(1
970
寸,
lecturer
,
maste
r.
Her
re-
search
interest
is
in
applied
math
巳
matics:
hydrodynamics
and
oc
巳 an
modeling
*
Corresponding
autho
r.
Te
l.:
+
86
-8
91
叫
6313808;
E-m
创
1:
diki.
yudron@gmai
l.
com
stratification in Namtso Lake, and the lake may be
regarded as a sma
l1
closed sea.
Namtso Lake is stratified and saline.
Wh
en
fresh
river water enters the stratified lake water
, strong gra-
dients between the river water and the ambient water
will develop river plumes and create strong currents
during periods
of
large fluxes
of
fresh water from the
rivers. The plume propagates into the lake.
Th
e prop-
agation speed will be reduced and intemal waves may
propagate away from the front since the lake is
stratified.
At present
, there are many numerical ocean
models. Hydrostatic approximation is made in most
of
the numerical ocean models. This approximation
makes computation less complicated and gives a good
appfûximation for the large scale ocean circulation.
However
, for phenomena involving
1
缸
ge
vertical
speeds
, for many small scale phenomena, and
in
are-
as with weak stratification
, the approximation
becomes not satisfying
[l].
Therefore, the non-hydro-
static effects are becoming more important for the
small scale studies.
It
is now possible to use a fine
resolution to resolve non-hydrostatic processes in
ocean modelling due
to
increasing computer power.