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Earth Science Weather Ch. 4


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where do most of the weather changes occur?
in the troposphere
what is the major cause of weather?
variations in insolation that cause heat energy to ve unevenly distributed in the atmosphere. this heat energy tends to move toward a condition of more uniform distribution, which results in the constant changes in the atmopshere that are the major cuase of weather
isolines that show temperature
how does the atmopshere acquire much of its heat?
directly by contant w/ earths surface
what are the other wayts in which the atmposhere is heated?
1) conduction moves heat from earth into the atmpshere as air touches earths surface
2)direct absorption of insolation from the sun by gases and aerosols moves heat into the atmosphere
3) asboprtion of long-wave infrared radiations from earths surface movie heat into the atmopshere
4) condensation releases stored heat into atmosphere
5) coriolis effect causes friction where the atmpshere and earths surface meet, which produces heat
how is heat energy transfered within the atmopshere?
by convection
what causes differences in air pressure?
differences in density
convection currents/cells
the air pressures differences in turn cause air to move in circular patterns
what do these air convectional movements do?
transfer heat energy within the atmosphere
parts of ocnvection currents that are parallel to earths surface
what source provides the most energy for atmopsheric weather changes?
radiation from the sun
as masses of air rises in the troposhere, its temperature will usually
___due to __
decrease due to expansion
what is the best variable in weather prediction?
air pressure
a combination of different variables
how does temperature effect air pressure?
1) temp increases=air expands and density and air pressure decrease
2) temp decreases=air contracts and density and air pressure increase
join areas of equal air pressure
describe high pressure
cold dry air
low pressure
its going to rain-warm moist air
high press
low press
where are the fastest winds?
where isobars are closest together
how do low press winds move?
counterclosewise and in
how do high press winds move?
clockwise and out
high pressure density
low press density
where do winds blow?
high to low pressure
15 knots=
1.15 mph
measures wind speed
winds are always named for
their origin
how does water get into the atmopshere (2 ways)
1. evaporation
2. transpiration
change from a liquid to a gas
is a cooling process-absorbs heat
water goes out of the leaves
all the ways water enters the atmospheree
speed up evaporation
1. add heat
2. wind
3. increase surface area
4. dry air-moisture content is low (slower evaporation-more wter in the air=air closer to be saturated w/ water vapor)
measures moisture in the air
dew point
the temp at which water vapor condensesinto liquidwater
when dew point and air temp. are the same...
WATER VAPOR CHANGES TO A LIQUID, realses heat into the air
what do u need for condensation
1. air must be cooled to the dew point
2. solid surface
adiabatic expansion
when warm air rises, it expands and cools to the dew point. this forms clouds. as droplets continue to grow, gravity will eventually pull them down
cp and Ca
very cold and very dry
moves south and then north east
maritime pacific
moist and cold
sttarts over north pacific brings cold moist air into western united states
maritime tropic
warm moist, forms over gulf of mexico
continental tropical
hot, dry-forms over desert southwest
air mass
huge amount of air that tkaes on the properties of the areas it formed over-area of origin
general term that refers to the water vapor content of the atmopshere
as air pressure goes up, temp goes
as air press goes down temp goes
cold front
-temp falls
air press falls
-heavy rain, short time
-air clereas out
-big slope
warm front
gentle slope
slow gentle rain
occluded front
coundary of opposing wedges of cold air masses formed when cold front overtakes warm front, lifting the warm air mass off the ground
what holds more moisture, warm or cold air?
air currents
the vertical movements of rising and sinking air
any gas that is allowed to expand bc the surrounding pressure will.....(temp_
become cooler
any gas compressed into a smaller volumme will become (temp)...
how does pressure change temp?
1. air rises, pressure decreases, air molecules spread out and collide less frequently, and temp decreases
2. air sinks, pressure increases, air molecules crowd and collide more, temp. increases
relationship of humidity and air pressure
humidity goes up, air pressure goes down
humidity goes down, air pressure goes up
explain this
lighter water vapor molecules displace heavier molecules--exert less force-less pressure
relationship between air temp and humidity
higher temp=more water in air
trade winds
winds between 30 north and south
prevailing winds
between 30 and 60 north and south
3 conditions that cause air to rise
1. air is warmed by sunlight, expands, and rises
2) warm air is forced upward by wind
3) dense, cold air mass pishes under warm air, forching it to rise
what direcidoes cold or warm air have a lower dew point?
what direction does everything move
easy to west
where do cold fronts form?
along the leading edge of a cold air mass that is advancing against a warmer air mass
explain a cold front
the ccold air mass is denser than the warmer air ahead of it, so it pushes against and under it like a wedge. this forces the warmer air up rapdily and results in terbulence, forming heavy developed clouds and heavy precipitation or thunderstorms
what happens after the cold front passes?
temp. drops sharply and pressure rises rapidly
where does a warm front form
where a warm air mass overrides the trailing edge of a cold air mass ahead of it
describe the warm front
the less dense warm air mass rides up and over the denser cold air. as the warm air mass rises above the denser cold mass, it expands and cools, causing condensation to occur over the wide, gently sloping bondery. the results are thickening, lowering clouds and widespread precipitation
where does a stationary front form?
along the boundary between warm air mass and cold air mass when neither moves in any direction
describe stationary fronts
slowly takes on the shape and characteristics of warm front as denser cold air slwly slides beneath less dense, warmer air.
result of stationary front
same widespread rain and cloudiness as warm fronts but rain and clouds may persist for longer period
why are occluded fronts important?
they are associated w/ the formation of mmidlatitude cyclones (lows)
polar front
ever-changing boundary between the colder air masses toward the poles and the warmer air masses toward the equator
what causes the unstable conditions that are characteristic of fronts and that produce much of the precipitation and stormy weather of the us
at fronts between air masses of different temps, the warm air, being less dense is forced to rise
what wayu to air masses travel?
west to east
(southwest to northeast)
have low press
during which part of the day is relative humidity usually lowest?
as air temp rises, relative humidity..
what is the underlying reaspon for movement of air in the lower part of the atmopshere?
difference in air density and differences in pressure gradient
jet streams
bands of easterly moving air at the top of the troposhere that can blow 200 mph or more

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