Upload
raymond-snow
View
218
Download
0
Tags:
Embed Size (px)
Citation preview
Energy in = energy out
Half of solar radiationreaches Earth
The atmosphere is transparent to shortwave but
absorbs longwave radiation
(greenhouse effect)
The atmosphere is heated from the
bottom by longwave radiation and convection
I. Uneven heating of Earth’s surface causes predictable latitudinal variation in climate. Why? - Angle of incidence… equator vs. poles
Climatic Variation & Seasons on Earth
Thus, radiation is more intense near the equator compared to the poles. For this reason, it’s warmer near the equator than at the poles.
North Pole
Earth
Equator
South Pole
Uneven heating of Earth’s surface causes atmospheric circulation
Greater heating at equator than poles 1. sun’s rays hit more directly 2. less atmosphere to penetrate
Therefore 1. Net gain of energy at equator 2. Net loss of energy at poles
II. What about seasons? Why do we have them?
Tilt!Because of the tilt of Earth’s axis, the amount of radiation received
by Northern and Southern Hemispheres varies seasonally
A. Northern Hemisphere has summer when it tilts toward the sun, winter when it tilts away
B. Southern Hemisphere has summer when it tilts toward the sun, winter when it tilts away
Earth’s distance from the sun varies throughout the year – doesn’t that cause the seasons?
I. Tilt of the Earth’s axis towards or away from the sun creates the seasons
Earth’s Seasons
North Pole
Earth
When the north pole tilts toward thesun, it gets more radiation – more warmth
during the summer
SUMMER (Northern Hemisphere)
South Pole
WINTER (Southern Hemisphere)
When the north pole tilts toward thesun, the south pole tilts away
So when it’s summer in the north, it’s winter in the south
Equator
I. Tilt of the Earth’s axis towards or away from the sun creates the seasons
Earth’s Seasons
When the north pole tilts away from the sun, it gets less radiation –
So it’s colder during the winter
North Pole
Earth
WINTER (Northern Hemisphere)
South Pole
SUMMER (Southern Hemisphere)
When the north pole tilts away from thesun, the south pole tilts toward it…
When it’s winter in the north, it’s summer in the south
Equator
Air rises and falls in Hadley, Ferrel, and
Polar cells(vertical circulation)
Circulation cells explain global distribution of
rainfall
Earth’s rotation determines
wind direction (horizontal circulation,
Coriolis force)
High heat capacity of water and ocean currents buffer ocean temperatures
Land temperatures fluctuate more, especially in higher latitudes
These differences in surface energy balance influence air movements, and create prevailing winds
• Salinity – The difference in the salinity of hot and cold water drives the currents. The higher the salinity of the water, the more dense the water is.
• Density - the state or quality of compactness; closely set or crowded condition.
• Water Mass – Area of different salinity density in the ocean.
At 30º N & S, air descends more strongly over cold ocean than over land
In January…
These pressure gradients create geographic variation in prevailing windsAt 60 º N & S, air descends more strongly over cold land than over ocean
In summer at 60 º N & S, air descends over cold ocean (high pressure) and rises over warm land (low pressure)
Cool equator-ward flow of air on W coast of continents Warm poleward flow of air on E coasts of continents
Ocean currents are similar to wind patterns: 1. Driven by Coriolis forces 2. Driven by winds
Ocean currents move 40% of “excess heat” from equator to poles
Driven by circulation of deep ocean waters Deepwater formation occurs near Greenland and in Antarctic
60% of heat transport is carried by atmosphere through storms that move along pressure gradients
The Pacific Ocean strongly influences the climate system becauseIt is the largest ocean basinNormal ocean current and wind direction in central Pacific is easterly
Winds and surface water
• Wind blowing over the ocean can move it due to frictional drag.
• Waves create necessary roughness for wind to couple with water.
• One “rule of thumb” holds that wind blowing for 12 hrs at 100 cm per sec will produce a 2 cm per sec current (about 2% of the wind speed)
Top-down drag
• Wind acts only on the surface water layer.• This layer will also drag the underlying water,
but with less force.• Consequently, there is a diminution of speed
downward.• Direction of movement is also influenced by
the Coriolis Effect and Ekman Spiral
Geostrophic Flow Surface currents generally mirror average planetary
atmospheric circulation patterns