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Wind, Pressure, Fronts

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polar front
The stormy belt seperating the westerlies from the polar eaterlies.
monsoon
A seasonal reversal of wind direction associated with large continents (especially Asia).
aneriod barometer
An instrument used for measuring air pressure that consists of evacuated metal chambers that change shape as pressure changes.
prevailing wind
When the wind consistently blows more often from one direction than from any other.
wind vane
The instrument most commonly used to determine wind direction.
convergence
The condition that exists when the distribution of winds within a given area results in a net horizontal inflow of air into the area.
chinook
A wind blowing down the leeward side of a mountain and warming by compression (The Rockies)
sea breeze
A local wind blowing from the sea during the afternoon in costal areas.
cup anemometer
An instrument used to measure wind speed.
subpolar low
The pressure zone located at about the latitude of the Arctic and Antarctic circles.
barograph
An instrument that continuously records air pressure changes.
divergence
The condition that exists when the distribution of winds within a given area results in a net horizontal outflow of air from the region.
subtropical high
A region of several semipermanent anticyclonic centers characterized by the subsidence and divergence located roughly between latitudes 25 and 35 degrees.
westerlies
The dominant west-to-east winds that characterize the regions on the poleward sides of the subtropical highs.
trade winds
The wind belts located on the equatorward sides of the subtropical highs.
Southern Oscillation
The seesaw pattern of atmospheric pressure between the eastern and western Pacific.
El Niño
The name given to the periodic warming of the ocean that occurs in the central and eastern Pacific.
air pressure
the force exerted by the weight of a column of air above a given point
aneroid barometer
an instrument for measuring air pressure that consists of evacuated metal chambers very sensitive to variations in air pressure
anticyclone
a high pressure center characterized by a clokwise flow of air in the northern hemisphere
barometric tendency
pressure tendencey- nature of change in atmospheric pressure, useful for weather predictions
Coriolis effect
the rotation of the earth causes the wind to bend to the right in the northern hemisphere (clockwise) and to the left in the southern hemisphere (counterclockwise).
cyclone
a low pressure center characterized by a counterclockwise flow of air in the northern hemisphere
divergence
when air moves in an outward motion. also it is the net outflow around an anticyclone
equaterial low
a region marked by abundant precipitation
geostrophic balance
when wind has no friction in the upper atmosphere
high
also known as an anticyclone and is the center of high pressures. this is also where the values of the isobars increase from outside towards the inside.
isobar
the line of equal air pressure on a map
jet stream
fast moving rivers of air that range from 75-150 mph. The friction goes down. They occur most often above smooth ocean surfaces where friction is low.
land breeze
Breeze that comes off the land onto the water usually during the night.
La Niña
the opposite of El niño. Thought to be normal conditions that occurred between two El Niño events. This is triggered by surface temperatures in Eastern Pacific are cooler than average.
low
also known as a cyclone and is the center of low pressure. this is also where the values of the isobar decrease from outside toward the inside
mercury barometer
used to measure pressure. a glass tube is filled with mercury and put upside down in a dish filled with mercury. when the pressure is decreased, the mercury level is decreased.
mountain breeze
when air moves downslope. ensures that the coldest pockets of air are the lowest. this kind of breeze is dominant in the cold seasons.
polar easterlies
encountered when westerlies move polarward in the region of the subpolar low.
polar high
polar air is subsidizing and spreading equatorward
pressure gradient force (PGF)
air always wants to move from high to low.
pressure tendency
(barometric tendency) allows us to write stormy, or fair on the barometer. It is good for short range weather prediction.
Santa Ana
a strong hot dry wind that blows in winter from the deserts of southern California toward the Pacific Coast
Southern Oscillation
a reversal of airflow between normally low atmospheric pressure over the western Pacific; the cause of El Nino
wind
the movement of an air mass from areas of high pressure to areas of low pressure
standard sea level pressure in millibars? inches of mercury? pounds per square inch
1092 millibars, 29.92 inches of mercury, 14.7 pounds per square inch
isobars
lines that connect areas of equal air pressure on map
air mass
large area of air with similar/same characteristics
source region
...
front
boundary between two different air masses
cold front
fronts that are defined by heavy rains for a short period of time. also associated with cumulus or cumulonimbus clouds.
warm front
fronts that are defined by light rains that last for a long period of time. cold air is only slightly displaced. as the warm front approaches the clouds go from cirrus to strato to stratonimbus
atmospheric pressure on earth
14.7 psi (pounds per square inch)
how can you lie on a bed of nails
weight is distributed equally over higher area and so psi is less
how does an index card hold water?
pressure pushing (not pulling) on card is greater than in direction away from water because water is lighter than air
3 things affecting air pressure
humidity, temperature, altitude
contour lines are close together, high/low pressure
strong winds/ strong P.G.F. (pressure gradient force)
contour lines are far apart, high/low pressure
weak winds/ weak P.G.F (pressure gradient force)
Fropa
Front Passing