MAY 2011
Oceanography Ch # 6
AIR SEA INTERACTION
Introduction:
An interdependent single system
Solar Radiation : Heats up earth and atm. Create winds, which drives the currents and
waves worldwide. Some radiation is reflected back into space,
6 – 1. Earth Seasons: the result of
Earth’s elliptical Orbit around the sun and a tilted Axis of rotation (23.5 Deg.) to the
plane of the path.
The seasons begin with the Vernal Equinox (March 21) when the sun is directly overhead the
Equator, followed by the Summer Solstice (Sun is then overhead the Tropic of Cancer. It is the
longest day in the Northern Hemisphere), Autumnal Equinox when the Sun is directly overhead
the Equator followed by the Winter Solstice as the Sun is directly over the Tropic of Capricon
and it is the shortest day in the Northern Hemisphere..

The Polar regions experience 6 months daylight, 24 hr/day.
6 – 2. Solar Heating
Daylight side of the earth receives solar radiation, which creates the Density – Pressure
differences which in turn is responsible for circulation and currents in the atm and the ocean.
Distribution of Solar energy – High Latitudes enjoy a broad spread, while in low
latitudes, radiation is more concentrated. The Albedo on earth materials averages 30%, and 2
to 40% over the Oceans.
Oceanic Heat flow is transferred by currents. At the Poles there is a net heat loss and at the
equator a net heat gain.
6 – 3. Physical properties of the Atmosphere.
Composition N2- 78.1%; O2 - 20.9%
Temp. 20 Deg C to 60 Deg C. Troposphere - up to 12 Km 60 Deg C at the bottom to Zero
at the top of the Stratosphere (44 Km)
1
Density – hot air rises/ Convection cells develops. The cool air is dry and more dense and
it sinks.
Water vapor – warm air holds more moisture and moves faster.
Pressure (I Atm or 14.7#/sqinch at MSL) decreases with increasing altitude.
Movement – air moves from high to low pressure.
6 – 4. Coriolis Effect on moving objects.
It influences the direction of movement not speed. In the Northern Hemisphere, objects
follow a path to the right of their intended direction. Earth spins at Zero KM/hr at the poles and
1600 Km/hr at the Equator. The Coriolis max effect is therefore at the poles.
Summary : The Coriolis effect is caused by Earth’s rotation; it influences all moving objects;
Changes only the direction of the moving object; It deflects to the right in the Northern
hemisphere, and left in ther Southern Hemisphere; It is Zero at the Equator.
6 – 5. Global Atmospheric Circulation Patterns
Circulation cells results of density. The Hadley cell –is marked by a low pressure called
the Doldrums at the Equator; Ferrel cell is the high pressure area at 30 Deg N Lat and is referred
to as the Horse latitudes and the Polar Cell extends from 60 Deg N to 90 Deg.
Pressure – Highs develop by descending air at 30 Deg N and S Latitudes and at the
Poles. Lows form where air rises at the equator and at 60 Deg N and S Latitudes
Wind belts – the lower parts of the belts are influenced by the Coriolis effect. These
winds are the Trades, Westerlies and the Polar Easterlies. At the Poles, the weather is dry and
cold – a cold desert.
Boundaries between Trades is the Doldrums also called the ITCZ (Intertropical
Convergence Zone); between Westerlies and the Trades are the Horse Latitudes and the Polar
Front lies between the westerlies and the Polar Easterlies.
Circulation Cells are real or Idealized?
Influencing factors which make it irregular (?) are:
Earth’s tilted axis ; Heat capacity differences between land and water; Uneven land
distribution. These factors cause high pressure over land in winter and low pressures in
summer.
2
6 - 6. Weather and Climate Patterns of the Oceans
The Ocean influences global weather and climate patterns. Weather – conditions at a given
time ; Climate – long term average weather.
Winds – movement from high to low pressure influenced by the Coriolis effect. In the
Northern Hemisphere, air moving from high to low pressures, curves to the right, resulting in a
counterclockwise flow around a low pressure area – Cyclonic flow.
Sea and land breezes are due to the heat capacity differences of water and of land
material. Land has 5X less capacity. At night, the land cools very quickly, resulting in a high
pressure and land breezes blow from the land to the sea.
Storms and Fronts – Disturbances (strong winds, ppt., thunder and lightening between
30 and 60 Deg N and S latitudes; Mid-day rains are common in the equatorial regions.
A warm front occurs when a mass of warm air moves into an area of cold air mass. It produces
showers over a large area, commonly influenced by the Jet Stream. A Cold front has the
opposite effect. The Jet stream is a narrow , fast moving air mass in an easterly direction.
Regardless of the front, the warmer less dense air rises above the cold dense air. Showers in a
cold front are usually heavier and shorter than those resulting from a warm front.
Tropical Cyclone (Typhoon, Hurricane) is a rotating mass of low pressure air,
characterized by strong winds and torrential precipitation. Generally there are about 100
storms / year worldwide. To initiate a hurricane, the ocean temp must exceed 77Deg F. and
there must be warm moist air. It starts with a low pressure cell, which breaks away from the
Equatorial low pressure mass. It grows as it picks up energy. When the water vapor condenses,
the stored heat is released into the surrounding atm (which warms and rises). The rising air
causes the surface pressure to drop, more water and heat are drawn into the storm as it
strengthens. As air moves across the surface toward the eye of the hurricane, the air spirals
upward. Horizontal wind speed may be less than 15 km/hr. The hurricane eye is usually calm.
The spiral arms (bands) can produce inches of rain/hr. The typical Hurricane diameter is about
200 km (max is 800 km)
The Saffir Simpson Scale is used to classify hurricanes. Based on wind speed and
damage. Max speed is 400 km/hr.
Types of Destruction. High winds and flooding. The storm surge, caused by low pressure can be
as high as 12 meters. Most damage is in the right front quadrant in coastal areas (account for
90% deaths). Historically : Galveston 1900- 6000 deaths; Bangladesh 1970 - > 1 MM deaths.
3
Ocean Climate Patterns
Equatorial Region – moderately rough seas, little ppt. which increases toward the
equator.
Sub-Tropical Regions – belts of high pressure, with very little ppt. High evaporation
rates cause high salinity
Temperate Regions – Strong Westerlies which create severe storms in winter.
Sub-Polar Regions – Extensive ppt. Temp near Zero. Sea Ice in winter.
6 -7. How Sea Ice and Ice bergs Form.
The sea ice is a mass of frozen sea water. It forms directly from sea water. 1st. slush
develops from small needle-like hexagonal xtals. Thin sheets are broken up by stress into “pan
cake ice”. Later freeze will coalesce into ice flows. Sea water salinity increases. Tends to be self
perpetuating. Survey suggests that complete melting will occur in about 2070.
Icebergs result from calving in glaciers.
Shelf ice is a thick floating ice sheet (shelf ice). Max 200 meters above the sea surface,
can cover an area up to 300,000 sqkm. The Larsen Ice Shelf has decreased by 40% since 1997.
6 – 8. Atmosphere Greenhouse Effect.
Average Temp 59 Deg F. Atm contains CO2, CH4, Water Vapor, CFCs. Without gases,
temp would be about -0.4 Deg F. The greenhouse effect – keeps earth’s surface and lower
atmosphere warm enough to sustain life.
Earth’s Heat Budget
The Visible Spectrum penetrates the atmosphere. Approx 47% is absorbed by the surface (Rock
and water), 23% is absorbed by the atmosphere itself and 30% is reflected back into space. The
absorbed radiation is partially reradiated into space as infrared radiation.
4
Gases contributing to the Greenhouse Effect

Water vapor

CO2 from Human activity. Over the last 200 years, CO2 in the atm has increased 30%
(?). Currently, it is 380 ppm. Ice investigations indicate that CO2 is 27% above the
highest level in the last 650,000 years (?).

Methane CH4; NOx; Tropospheric Ozone and CFCs
If there is Global Warming, possible consequences are:

Rise in MSL from melting Glaciers

Species distribution shift and possible extinctions

Longer and more intense heat waves. Severe droughts and increase ppt locally

Water contamination leading to more medical challenges

Increase frequency and intensity of tropical cyclones.

Increase acidity of sea water, affecting organisms which build hard parts .

Higher than normal sea surface temp., which may affect deep water circulation.
On the other hand, global warming may cause

Early spring- longer growing seasons

Increase Ice cap.

Increase cloud cover?
Role of the Ocean
Acts as a carbon sink
Thermal sponge
5
Other Possibilities

Stimulate productivity using Iron filings to fertilize the ocean – The Iron Hypothesis.
Concerns : Depletion of O2; increase ocean acidity, Release CO2 and N2O

Capture emissions and pump into the deep ocean or deep reservoirs

Decrease consumption

Increase research into understanding how the earth systems work.
6- 9. Can wind power be harnessed
Denmark generates 18% of its needs
Wind turbines planned for offshore Cape Cod.
What can be done to reduce GHG?
There is a discernable human influence on global climate (Deforestation and fossil fuel
use). Natural causes may not be the only causing factor. Inter-Governmental Panel on Climate
Change 1st. Report 1990.
Kyoto Accord 1997. Reduce emissions by 5% of 1990 levels
6