Transcript Atmospheric Circ., Lecture 6

Atmosphere
• 78% nitrogen, 21% oxygen
Water Vapor
• up to 4% by volume
• leaves atmosphere as dew, rain or snow
Density of Air
• Warm air is less dense than cold air
• Humid air is less dense than dry air
Air Movement
• Air near sea level is packed by pressure
• As air rises - expands and cools
• As air descends- compresses and warms
Precipitation
• Warm air can hold more water vapor than
cool air
• As air rises, it cools and water vapor may
condense into clouds and eventually
precipitation
Fig 7-2a, g
Fig 7-6, g
Pressure
Figure 6.13
Figure 6.7
Uneven Solar Heating
Figure 6.1
Fig. 7-3, g
Atmospheric Circulation
• Wind = mass movement of air
• wind patterns caused by variations in solar
heating and earth’s rotation
Uneven Solar Heating &
Atmospheric Circulation
• Air is warmed in the tropics and rises
• Air is cooled near the poles and falls
Fig 7-4b, g
Earths air
Circulation if
Uneven
Solar
heating
Fig. 7-7, g
Fnft
Remember…
• …putting all of this together…the hot, humid, air
over the tropics is LESS dense (than all other air
masses); this means:
(a) Less dense air rises (like a hot air balloon);
(b) As it rises (vertical) the pressure decreases;
(c) As pressure decreases, air EXPANDS;
(d) As it expands, it COOLS
…then the reverse again…+ horizontal (wind)
movement
Fig 7-2, g
Atmos. Circ. Cont…
…When you add the horizontal (wind)
movement it pushes this (originating hot,
dry, tropical air) BOTH up and out
(North/South) for distribution throughout
the entire atmosphere. How?
Atmos. Circ. Cont…
…How?
Tropical air rises, meets density around it (more
dense than that above it but less dense than that
below it) so it can’t “move” vertically …but it
must go somewhere!
SIDEWAYS! (joins Atmospheric Circ. pattern,
moving horizontally, toward POLES) & as it rises
poleward it COOLS, gets more dense, and falls
back (toward equator) again…and again…
Water’s Thermal Properties Affect Climate:
Moderate Earth’s Climate
Fig. 6-8, p. 127
What’s with the WIND?
…Influence of the rotation of the
earth…
Fig. 7-9, p. 152
Coriolis Deflection
• “The apparent deflection of objects moving
across Earth’s surface to the right of
direction of travel in the Northern
Hemisphere and to the left in the Southern
Hemisphere.”
• Different because of difference of speed and
width of Earth @ equator vs. poles
• Increases poleward & as speed increases.
Coriolis Effect
• The eastward rotation of the earth deflects
any moving object away from its initial
course
• the deflection OF THE OBJECT is
clockwise in the Northern hemisphere
• the deflection OF THE OBJECT is
counterclockwise in the Southern
hemisphere
Figure 6.9
Figure 6.10a
Figure 6.10b
All together now…
Wind
Coriolis Effect
Atmospheric Conditions
Fig 7-12, g
Wind Patterns
• At bands between cells air is moving
vertically
• winds are weak and erratic
• doldrums or intertropical convergence zone
(ITCZ) at equator
– ascending air
• Subtropical high pressure belt at 30o
– descending air, very dry
Wind Patterns
• Within cells air moves horizontally from
high to low pressure areas
• produces strong dependable winds
– Trade winds or easterlies
– westerlies
– polar easterlies
Wind Patterns
• Within circulation cells air moves
horizontally from high to low pressure areas
(wind belt)
• produces strong dependable winds
– Trade winds (between 0 and 30o)
– Westerlies (between 30 and 60o)
– polar easterlies (between 60 and 90o)
Fnft
Global Wind Circulation
• REMEMBER:
• Movement of air across a pressure gradient parallel
to Earth’s surface is called a wind.
• Winds are designated according to the direction
from which they come.
• In contrast, ocean currents are designated according
to the direction towards which they travel.
Table 6.2
Global Wind Circulation
North
Pole
North
Pole
60°N
North
Pole
Prime
meridien
60°N
30°N
Latitude
0°
Equator
30°S
South
Pole
30°N
0°
Longitude
60°W
South
Pole
0°
60°W
30°E
30°W
0°
30°S
South
Pole
Stepped Art