Environmental Engineering Reference
In-Depth Information
Origin and Evolution of Ocean Surface
Current System
The water mass of the marine compartment
remains constantly under the in
same shows negative (debit side)
gures. Under
such differential heating process as a natural
course, heat redistribution from areas of credit side
(i.e., from lower latitudes) to that of debit side (i.e.,
towards higher latitudes) establishes both wind
fl
fl
uence of some
types of
'
surface forces
'
as well as some form of
'
body forces
'
, which cause acceleration of that
ow system in the atmospheric and water
fl
ow
system in the oceanic environment.
The different thermal capacities of the conti-
nental mass and that of its oceanic counterpart
greatly in
water mass.
These forces are basically of the following
types:
￿
Differential (latitude-wise) solar heating (or
cooling)
uence the actual global pattern of
above-stated interacting
fl
which in turn develops density
the
idealized situation. Again the distributions of
land areas
fl
ow system
vis à vis
variation
both
horizontally
as well
as
vertically.
that of the oceans as at present
vary greatly between the two hemispheres and
hence exercise differing complex control.
Moreover, huge quantity of heat either is left
locked up or is released (known as latent heat),
whenever any change of state takes place in the
hydrosphere (by way of evaporation from ocean
surface, condensation during cloud/rain forma-
tions, freezing by some form of ice formation and
their melting), they behave as hidden
vis à vis
Wind
ow system (which also varies with
latitude), with its frictional coupling imparts
motion to the oceanic water mass, in a varying
degree spatially.
fl
￿
￿
Atmospheric pressure gradient (inverted baro-
metric effect) in
uencing the water level at the
oceanic surface, which in turn brings in asso-
ciated oceanic water circulation.
fl
Earth
'
s spin and gravitational attraction also
source and
sinks ' , in this heat redistribution system.
With the establishment of the wind
'
￿
uencing the movement of ocean waters.
Besides these forces, other parameters that
exercise control on ocean water circulation pat-
tern are as follows:
1. Seasonal changes in the atmospheric wind set-
up and differing degrees of evaporation/pre-
cipitation/ice (or snow) melting/freshwater
in
in
fl
fl
ow sys-
tem, the wind
ow pattern over ocean region
transfers a part of the energy to the surface layers
of the ocean. A part of this energy is utilized to
generate oceanic currents. The wind
fl
fl
ow drags
the ocean waters to
ow along with it, the rate of
energy transfer on an average being about 3 % of
the wind speed. In ideal situation under the
in
fl
ow, etc.
2. Position and shape of continental boundaries.
3. Topography of the ocean
fl
'
fl
oor.
s spin, the oceanic surface
current in the Northern Hemisphere gets de
fl
uence of earth
Atmosphere
ocean
earth system is a coupled
fl
ec-
-
-
ted at an angle of about 40
45 to the right-hand
'
heat engine
'
with appropriate
'
sources
'
and
-
'
. In this heat engine, differential heating
takes place. Sun remains closer to the zenith in the
Tropical region all the year round and conse-
quently receives more heat, which progressively
decreases polewards with increasing obliquity of
sun
sinks
'
side of
ow direction (and in the
Southern Hemisphere by about the same amount
to the left-hand side of the wind
the wind
fl
ow direction).
Each layer of moving water sets the layer below
it
fl
uence of Coriolis
force, deeper layers exhibit gradually shifting
direction of
in motion. Under the in
fl
'
s rays. A part of the heat under reradiation
from earthly environment gets lost in space, at the
same time. The balance sheet of the available solar
energy shows positive (credit
ow with slower speeds (Ekman
transport). The net
fl
fl
ow on an average exhibits a
°
side)
gures
de
to the right (or to the left) with
respect to the wind
fl
ection by 90
between equator and 40
°
latitude (N and S).
ow direction in the Northern
(or Southern) Hemisphere (Fig. 1.23 ).
fl
Beyond 40
°
latitude towards polar region, the
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