1. The basic concepts of oceanography
Lecture 1
The basic concepts of oceanography
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

2. Oceanography is a multi-discipline science studying the World ocean.
It includes:
Physical oceanography
Marine geology
Marine chemistry
Marine biology
Marine technology
etc.
In this course, we restrict our study to the topics that include instruments, measuring ocean properties and mounted on earth-orbiting satellites.
As such, we do not touch the problems of marine geology and chemistry, because satellite sensors cannot help much in these studies. Most satellite observations of the ocean are related to physical oceanography. Another topic of satellite oceanography is the measurements of ocean color, which can be used as assessments of phytoplankton biomass and are of great interest to marine biologists.
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

3. The basic topic of physical oceanography is ocean circulation.
This image of MODIS satellite illustrates a plume of polluted water discharged after rainstorm from the mouth of Santa Clara River and transported by coastal current to Santa Monica Bay.
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4. 1. What drives ocean currents?
Two external forces influence the World Ocean generating ocean currents - gravitation and the energy flux from the sun.
Gravitation includes tidal forces resulting from the interaction of water mass with the moon and the sun, and rotation of the Earth.
The radiation flux from the sun results in wind stress, heating and cooling of the ocean surface, and evaporation and precipitation of water.
A complex process of interaction between these forces results in a complex and variable pattern of ocean circulation.
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5. 1. What drives ocean currents?
Solar heating is different at different latitudes, because equal amounts of sunlight are spread over a greater surface area near the poles than in the tropics.
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

6. 1. What drives ocean currents?
The amount of solar energy also varies with time, resulting from the annual rotation of the earth around the sun on an axis tilted by 23º27’ and earth diurnal rotation.
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

7. 1. What drives ocean currents?
Warm air rises and cool air sinks; a convection current forms in a room resulting from uneven heating and cooling.
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

8. 1. What drives ocean currents?
The amount of heat radiation is of maximum at the equator. The cold air at the poles is denser than the warm air at the equator; hence, air pressure at sea level is higher at the poles than at the equator. In other words, the pressure gradient at sea level is directed from the poles toward the equator, and the pressure gradient in the upper part of the atmosphere has the opposite sign.
In fluid and gases pressure gradients produce flow from regions of high pressure to regions of low pressure. If the earth were not rotating, the response to these pressure gradients would be direct and simple.
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

9. 1. What drives ocean currents?
At the higher latitude each location travels a shorter path on the rotating Earth than at the equator.
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

10. 1. What drives ocean currents?
A cannonball shot north from the cannon located at the equator is also moving east at the speed of the Earth rotation at the equator and veers to the right from its northward path.
A cannonball shot south travels over portions of the Earth that are moving increasingly faster in an eastward direction and also veers to the right.
This effect is called “Coriolis effect”.
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11. 1. What drives ocean currents?
The rotation of the Earth modifies the pattern of atmospheric circulation. As air moves toward the equator, the rotation of the earth shifts ocean and land eastward under it. The result is "easterly" winds (Polar Easterlies and Trade winds).
Traveling from the equator to the pole air in the upper atmospheric layer cools. About 30ºN and 30ºS the air becomes dense enough to fall back to earth surface, forming two Hadley cells of atmospheric circulation. Similar cells are created between the poles and 60º latitude. The zones between 30º and 60º are called Ferrel cells, where "westerly" winds dominate.
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12. 1. What drives the ocean currents?
Atmospheric circulation pattern is modulated by the difference between the heat balance over land and sea zones.
During summer land accepts more heat and onshore wind dominates.
During winter land is cooler than sea and offshore wind dominates.
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

13. 1. What drives ocean currents?
Surface winds over the World Ocean
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

14. 1. What drives ocean currents?
Surface winds over the World Ocean
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

15. 1. What drives ocean currents?
Surface winds over the World Ocean
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

16. 1. What drives ocean currents?
Surface winds over the World Ocean
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

17. 1. What drives ocean currents?
Surface winds over the World Ocean
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

18. 1. What drives ocean currents?
Surface winds over the World Ocean
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

19. 1. What drives ocean currents?
Surface winds over the World Ocean
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

20. 1. What drives ocean currents?
Surface winds over the World Ocean
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

21. 1. What drives ocean currents?
Surface winds over the World Ocean
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

22. 1. What drives ocean currents?
Surface winds over the World Ocean
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

23. 1. What drives ocean currents?
Surface winds over the World Ocean
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

24. 1. What drives ocean currents?
Surface winds over the World Ocean
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25. Cd is the dimensionless "drag coefficient" (about 0.0013),
1. What drives the ocean currents?
1.2. Wind stress
Wind stress t (kg m-1 s-2 or Newton per m2) is an important quantity in the process of wind driving ocean currents.
|t | = Cd  raU2, where
Cd   is the dimensionless "drag coefficient" (about ),
ra  is air density (about 1.2 kg m-2),
U  is wind speed at 10 m above sea level (m s-1).
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26. 1. What drives the ocean currents?
Wind stress is a square function of wind speed because the wind forcing depends on wind speed and sea roughness, which in turn depends on wind speed.
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27. 1. What drives ocean currents?
Horizontal circulation - Ekman drift
The movement of water as influenced by the Coriolis effect and gravity.
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28. 1. What drives ocean currents?
Horizontal circulation - Ekman drift
The Ekman spiral. The top layer is driven forward be the wind, and each layer below is moved by friction. Each succeeding layer moves at a slower speed and at an angle to the layer above. The theoretical average direction of water flow is 90° to the right in the Northern Hemisphere.
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29. t is wind stress and f is Coriolis force.
1. What drives ocean currents?
Horizontal circulation - Ekman drift
The current moves at an angle to the wind (to right in the Northern Hemisphere), turning further away from the wind direction and becoming weaker with depth. Therefore, the wind-driven component of water transport is directed perpendicular to the mean wind stress to the right in the Northern Hemisphere. The magnitude (kg m-1 s-1) is
|Me| = |t / f |, where
t is wind stress and f is Coriolis force.
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30. 2. The heat flux through the ocean surface
The heat flux is determined by the balance between four components:
- incoming solar radiation;
- outgoing back radiation;
- heat loss from evaporation;
- mechanical heat transfer between the ocean and the atmosphere.
The three last components directly depend on sea surface temperature (SST), a basic ocean property measured from satellites.
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31. 2. The heat flux through the ocean surface
Solar radiation (W m-2) received at sea level.
January 1985
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32. 2. The heat flux through the ocean surface
Solar radiation (W m-2) received at sea level.
February 1985
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

33. 2. The heat flux through the ocean surface
Solar radiation (W m-2) received at sea level.
March 1985
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

34. 2. The heat flux through the ocean surface
Solar radiation (W m-2) received at sea level.
April 1985
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

35. 2. The heat flux through the ocean surface
Solar radiation (W m-2) received at sea level.
May 1985
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

36. 2. The heat flux through the ocean surface
Solar radiation (W m-2) received at sea level.
June 1985
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

37. 2. The heat flux through the ocean surface
Solar radiation (W m-2) received at sea level.
July 1985
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

38. 2. The heat flux through the ocean surface
Solar radiation (W m-2) received at sea level.
August 1985
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

39. 2. The heat flux through the ocean surface
Solar radiation (W m-2) received at sea level.
September 1985
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

40. 2. The heat flux through the ocean surface
Solar radiation (W m-2) received at sea level.
October 1985
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

41. 2. The heat flux through the ocean surface
Solar radiation (W m-2) received at sea level.
November 1985
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

42. 2. The heat flux through the ocean surface
Solar radiation (W m-2) received at sea level.
December 1985
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43. 2. The heat flux through the ocean surface
depends on solar radiation and sea surface temperature
incoming
solar
radiation
incoming
solar
radiation
outgoing
back
radiation
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

44. 2. The heat flux through the ocean surface
January
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

45. 2. The heat flux through the ocean surface
February
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

46. 2. The heat flux through the ocean surface
March
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

47. 2. The heat flux through the ocean surface
April
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

48. 2. The heat flux through the ocean surface
May
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

49. 2. The heat flux through the ocean surface
June
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

50. 2. The heat flux through the ocean surface
July
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

51. 2. The heat flux through the ocean surface
August
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

52. 2. The heat flux through the ocean surface
September
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

53. 2. The heat flux through the ocean surface
October
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

54. 2. The heat flux through the ocean surface
November
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

55. 2. The heat flux through the ocean surface
December
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

56. 2. The heat flux through the ocean surface
200 W m-2 warm a layer of water 50 m deep by about 2.5oC per month if unopposed by heat losses from other effects.
The density of water is higher as compared with cold water. As such, warm water moves up where it accepts more solar energy. Cold water moves down, isolating the upper mixed ocean layer from cold deep waters.
This phenomenon is called stratification.
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

57. 2. The heat flux through the ocean surface
Seasonal variations in heat flux result in seasonal variations of sea surface temperature and the temperature of the upper mixed layer.
January
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58. 2. The heat flux through the ocean surface
Seasonal variations in heat flux result in seasonal variations of sea surface temperature and the temperature of the upper mixed layer.
February
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

59. 2. The heat flux through the ocean surface
Seasonal variations in heat flux result in seasonal variations of sea surface temperature and the temperature of the upper mixed layer.
March
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

60. 2. The heat flux through the ocean surface
Seasonal variations in heat flux result in seasonal variations of sea surface temperature and the temperature of the upper mixed layer.
April
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

61. 2. The heat flux through the ocean surface
Seasonal variations in heat flux result in seasonal variations of sea surface temperature and the temperature of the upper mixed layer.
May
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

62. 2. The heat flux through the ocean surface
Seasonal variations in heat flux result in seasonal variations of sea surface temperature and the temperature of the upper mixed layer.
June
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

63. 2. The heat flux through the ocean surface
Seasonal variations in heat flux result in seasonal variations of sea surface temperature and the temperature of the upper mixed layer.
July
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

64. 2. The heat flux through the ocean surface
Seasonal variations in heat flux result in seasonal variations of sea surface temperature and the temperature of the upper mixed layer.
August
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

65. 2. The heat flux through the ocean surface
Seasonal variations in heat flux result in seasonal variations of sea surface temperature and the temperature of the upper mixed layer.
September
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

66. 2. The heat flux through the ocean surface
Seasonal variations in heat flux result in seasonal variations of sea surface temperature and the temperature of the upper mixed layer.
October
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography

67. 2. The heat flux through the ocean surface
Seasonal variations in heat flux result in seasonal variations of sea surface temperature and the temperature of the upper mixed layer.
November
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68. 2. The heat flux through the ocean surface
Seasonal variations in heat flux result in seasonal variations of sea surface temperature and the temperature of the upper mixed layer.
December
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69. 2. The heat flux through the ocean surface
As a result of the release of heat from the ocean to the atmosphere local air temperature increases and the air density decreases. Light warm air moves up, twisting under the influence of the Coriolis force into a vortex structure rotating counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. This phenomena are called cyclones.
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70. 3. Vertical distribution of water properties
Pressure p (kiloPascal, 10 kPa = 1 dbar = 1 m);
Temperature T (degrees C);
Salinity S (Practical Salinity Units - psu);
correspond to promille (g salt/kg sea water);
Density r (kg m-3) represented by st = r
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71. 3. Vertical distribution of water properties
Salinity in the surface ocean layer

72. 3. Vertical distribution of water properties
The water density is a function of temperature, salinity, and pressure.
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73. 3. Vertical distribution of water properties
The pressure field
The pressure in the water column increases with depth and depends on the vertical distribution of water density.
We can calculate the differences between pressures at different depths or depth differences between two surfaces of constant pressure. For the latter purpose a quantity called steric height is introduced.
Its meaning is the height by which the water column between depths z1 and z2 with standard temperature T = 0oC and salinity S = 35.0 expands if its temperature and salinity are changed to the observed values.
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74. 3. Vertical distribution of water properties
Typically h is a few tens of centimeters. Oceanographers map the shape of the sea surface by showing contours of equal steric height relative to a depth of no motion, where pressure is assumed to be constant (usually 1500 or 2000 m).
Dynamic height D (m2 s-2), typically used in calculations, is equal to g h, i. e., the product of gravity and steric height.
From steric height or dynamic height we can estimate the horizontal pressure gradient resulting in geostrophic water circulation.
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75. 4.1. Horizontal circulation Geostrophic flow
4. Water circulation
4.1. Horizontal circulation
Geostrophic flow
Mean dynamic height (m2 s-2), or steric height multiplied by gravity, for the World Ocean at 0 m relative to 2000 m. Arrows indicate the direction of the implied geostrophic movement of water.
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76. 4.1. Horizontal circulation
4. Water circulation
4.1. Horizontal circulation
The variations of sea surface height can be measured from satellites by radar-altimeters.
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77. 4.1. Horizontal circulation Geostrophic flow
4. Water circulation
4.1. Horizontal circulation
Geostrophic flow
Water at station A is denser than water at station B. As the weight of the water above z = z0 is the same, the water column must be longer at B than at A.
In geostrophic flow, water moves along isobars, with the higher pressure on its right in the Northern Hemisphere (away from the equator).
Distribution of isobars and isopycnals at any depth level above z = z0.
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78. g is acceleration of gravity (g = 9.8 m s-2),
4. Water circulation
4.1. Horizontal circulation
Geostrophic flow
The magnitude (mass transport per unit depth) of geostrophic flow:
where r0 is an average water density,
g is acceleration of gravity (g = 9.8 m s-2),
Td is the length of a day (86,400 s),
f is the latitude,
Dh is the difference in steric height between two adjacent isobars.
f = (Td / 4 p sin f)-1 is known as Coriolis parameter.
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79. 4.1. Horizontal circulation Geostrophic flow
4. Water circulation
4.1. Horizontal circulation
Geostrophic flow
Illustration of the relationship between a map of steric height (dynamic topography), geostrophic flow, and the evaluation of the geostrophic mass transport per unit depth M' between two streamlines (contours of constant steric height) in the Southern Hemisphere.
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80. 4.1. Horizontal circulation Geostrophic flow
4. Water circulation
4.1. Horizontal circulation
Geostrophic flow
For both station pairs, A and B and A' and B', Dh in Equation is given by h2 - h1.
The geostrophic velocity is inversely proportional to the distance between streamlines, or equal to M' divided by density and by the distance between points A and B, because the section AB is perpendicular to the streamlines.
If station pair A' and B' is used for the calculation, similar Equation still produces the correct geostrophic mass transport M' between streamlines h1 and h2, but the velocity derived from M' and distance A'B' is only the velocity component vn perpendicular to the section A'B'.
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81. 4.1. Horizontal circulation - 1½-layer model
4. Water circulation
4.1. Horizontal circulation - 1½-layer model
It is is an approximation to the ocean's density structure. The ocean is divided into a deep layer of constant density r2 and much shallower layer above it, again of constant density r1 = r2 - Dr. The lower layer is considered motionless. The thickness of the upper layer z = H(x, y, t) is allowed to vary.
h(x,y) = - Dr / r0 H(x,y).
The factor  Dr / r0  is of the order 0.01 or less. Hence, in a 11/2 layer ocean the sea surface is a scaled mirror of the depth of the pycnocline ( times larger).
Side view of a 1½-layer ocean
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82. Rossby wave in the Southern Hemisphere
4. Water circulation
4.1. Horizontal circulation – Rossby waves
Total poleward flow in greater in magnitude between A and B than between C and D because the Coriolis parameter f is smaller in magnitude at A and B than at C and D; the thermocline deepens in ABCD. By the same argument, the thermocline shallows in A'B'C'D'; the eddy moves west.
Rossby wave in the Southern Hemisphere
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83. 4.1. Horizontal circulation – Rossby waves
4. Water circulation
4.1. Horizontal circulation – Rossby waves
As a result of Rossby waves propagating to the west, warm water in the upper mixed layer is concentrated in the western parts of the oceans.
Sea surface temperature in degrees Celsius during Northern Hemisphere winter
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84. 4.1. Horizontal circulation
4. Water circulation
4.1. Horizontal circulation
The combination of geostrophic flow and wind forcing results in the general pattern of ocean currents
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85. 4.1. Horizontal circulation
4. Water circulation
4.1. Horizontal circulation
The general circulation in all oceans is anticyclonic, i.e., clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.
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86. 4.2. Vertical circulation Upwelling In the eastern parts of the
oceans permanent
equatorward winds generate
offshore Ekman drift and
coastal upwelling of
rich in nutrients waters
resulting in high primary
production.
A prolonged poleward wind along a west coast can result in downwelling.
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87. 5. The role of stratification in phytoplankton growth
Phytoplankton growth in the deep ocean layers is limited by the lack of sunlight, necessary for photosynthesis.
In the upper mixed layer phytoplankton growth is typically limited by the lack of nutrients, because stratification isolates the upper layer from rich in nutrients deep waters.
As such, the parameters regulating stratification and vertical circulation are extremely important for understanding of phytoplankton growth - the process called primary production.
IoE The Basics of Satellite Oceanography. 1. The Basic Concepts of Oceanography