Major%20currents,%20gyres,%20rings,%20and%20eddies%20(basin%20scale)

1
Major currents, gyres, rings, and eddies (basin
scale)

• Winds and wind-driven basin circulation
• Meanders, rings, eddies and gyres
• The thermohaline circulation

2
Winds and wind-driven basin circulation
Winds
Unevenly heating by the sun
Spinning sphere
3
Subpolar gyre
Strong and narrow western boundary current
Subtropical gyre
Subtropical gyre
4

• The Coriolis force causes the moving water to be
  deflected to the right of the right of the wind
  (in NH). The net effect of winds in the upper
  ocean is a flow perpendicular to the wind (i.e.
  Ekman transport).
• The strong western boundary currents are formed
  due to the variation of the Coriolis parameter
  with latitude.

5
Meanders, rings, eddies and gyres
gyre
6

• Meanders Jet stream develop large oscillations
  caused by its unstable.
• Rings Eddy pinched off from meander as it become
  too large.
• Anticlockwise and clockwise rotating rings are
  cold and warm rings, respectively.
• They contain water from the opposite side of the
  stream having the other sides physical, chemical
  and biological properties.
• The interaction of meander and rings create
  significant vertical transports of nutrient and
  plankton which enhance biological activity

7

• Eddies The closed circulation with horizontal
  scale of 10-100km and time scale of 10-30 days.
  The upward and downward vertical velocities in
  cyclonic and anticyclonic will enhance biological
  productivity, respectively.

8
(No Transcript)
9
High surface Chl-a
10

• Gyres A circular current that is confined by or
  associated with bathymetric features and covers a
  wide range of spatial scales.

11
The Thermohaline Circulation (north-south
vertical circulation
Sinking of dense water due to cooling in mid to
high latitude.
12
(No Transcript)
13
(No Transcript)
14

• The global conveyor belt thermohaline circulation
  is driven primarily by the formation and sinking
  of deep water (from around 1500m to the Antarctic
  bottom water overlying the bottom of the ocean)
  in the Norwegian Sea.

15

• This circulation is thought to be responsible for
  the large flow of upper ocean water from the
  tropical Pacific to the Indian Ocean through the
  Indonesian Archipelogo.

16

• The two counteracting forcings operating in the
  North Atlantic control the conveyor belt
  circulation (1) the thermal forcing
  (high-latitude cooling and the low-latitude
  heating) which drives a polar southward flow and
  (2) haline forcing (net high-latitude freshwater
  gain and low-latitude evaporation) which moves in
  the opposite direction. In today's Atlantic the
  thermal forcing dominates, hence, the flow of
  upper current from south to north.