Chapter 18: Air Pressure and Wind Flashcards
Atmospheric pressure is what?
The force exerted by the weight of the air above
Pressure decreases with what?
Increasing of altitude
What is the Millibar standard sea-level pressure?
mb
What is the standard sea-level of inches of mercury?
pressure of 29.92 inches of mercury
Two types of instruments for measuring Atmospheric Pressure?
- Barometer-
bar= pressure
metron= measuring - Mercury Barometer- Invented by Torricelli in 1643. Uses glass tube filled w/ mercury that rises when air pressure increases
What is a Aneroid Barometer?
“without liquid”
- Uses an expanding air chamber
- Created b/c there was a need for smaller instrument for measuring air pressure
What is a Barograph?
A device that continuously records the aoir pressure
The result of horizontal differences in air pressure is called what?
Wind
The three contorls of wind?
- Pressure-Gradient Force
- Coriolis Effect
- Friction (w/ surface of earth)
Pressure- Gradient Force
Force that has both magnitude and direction
*Isolabrs- lines of equal pressure shown on weather maps
*Pressure gradient-
pressure change over distance
Coriolis Effect
Modifies wind, motion, but does not produce wind
Apparent deflection of wind direction die to earth rotation.
North hem- right
South hem- left
Friction (with surface of the Earth)
Only important near the surface
Acts to slow air movement
How do upper air winds generally flow?
blow parallel to isobars called geostophic winds
One of the most prominent features of the upper-level air flow is?
A jet stream
What is a cyclone?
- center of low pressure
- pressure decreases toward center of air mass
- bring clouds and precipitation
In the Northern Hemisphere of a Cyclone the winds do what?
Go inward (convergence) Counterclockwise
In the Southern Hemisphere of a Cyclone the winds do what?
Go inward (convergence) Clockwise
What is an Anticyclone?
A center of high pressure
Pressure increase toward center
Associated w/ subsiding air
Usually brings fair weather
In the Northern Hemisphere of a Anticyclone the winds do what?
Outward (divergence)
Clockwise
In the Southern Hemisphere of a Anticyclone the winds do what?
Outward (divergence)
Counterclockwise
The cause of underlying wind circulation causes what to happen?
The wind circulation to be unequal surface heating from the sun
How many cells are their on the rotating earth?
Three pairs of atmospheric cells that redistribute the heat
What are three Idealized Global Circulations?
1) Equatorial low pressure zone: unstable air
2) Subtropical high pressure zone: stable dry air.
3) Circulation in the Mid-Latitudes: zone of westerlies.
Complex wind pasterns. Wind interrupted by cyclones.
Create cyclone& anticyclone flow
How are local winds produced?
From locally generated pressure differences that are caused bu unequal heating of earth’s surface.
Two types of small scale winds?
- Land (night) & Sea breezes (day)
2. Mountains (night) & Valley breezes (day)
What are the temperatures of Sea Breeze and Land Breeze during day and night times?
Day Time:
COOL water
WARM land
Night Time:
WARM water
COOL land
Two Wind Measurements?
1) Direction- winds are labeled from where they originate.
- direction indicated by compass direction. prevailing winds usually comes from one direction.
2) Speed- often measured using a cup anemometer
What tool gives direction and speed, but is also low-tech?
A Wind Stock!
What tool is for measuring wind direction and points into the wind?
A Wind Vane!
cup anemometer -speed
(direction -points into wind)
What tool is mechanically used for energy and is still used to pump water is what?
A Farm Windmill
