Atmospheric Pressure/Wind - Chap 5 Flashcards
Atmospheric pressure
force exerted by weight of gas molecules on unit of area
exerted equally in all directions
Basically weight of all gas molecules above you, more gas molecules above you at lower altitude –> higher pressure
Ideal gas law
P = pRT
p (rho) = density
R = constant
T = temp
*increase in temp –> increase in pressure
increase in density - increase in pressure
Density of gas
changes easily with location bc gas can expand as far as pressure allows
Increase in temp
higher pressure –> more energetic collisions btwn molecules
What is air pressure influenced by
temp, density, dynamic influences
dynamic factors influencing air pressure
vertical movement of air (air goes up = low pressure, air goes down = high pressure)
dynamic high vs low, thermal high vs low
dynamic high = strongly descending air -> high pressure
dynamic low = strongly ascending air -> low pressure
thermal high = cold surface conditions cause high pressure at surface
thermal low = warm surface conditions cause low pressure at surface
Isobars
show isolines of equal pressure,
circular/oval areas = high or low pressure zones
high + low is relative to area around it
ridge
elongated area of high pressure
trough (think depression/lower)
elongated area of low pressure
pressure gradient
shown by closeness of isobars –> closer together = more abrupt pressure change
Updrafts vs downdraft, ascents vs subsidences
updraft/downdrafts = small scale vertical motion of wind
ascent/subsidence = large scale vertical motion of wind
Cause of wind
unequal warming of Earth’s surface
ideally moves from high pressure to low pressure BUT wind rarely does that bc of Coriolis effect
3 factors affecting wind direction
1) Pressure gradient force
2) Coriolis effect
3) friction
Pressure gradient force on wind direction
air moves from high to low pressure air
Coriolis effect on wind direction
1) deflects right in Northern, left in Southern
2) deflection strongest at poles, almost 0 at equator
*acts at a 90 degree angle (to right in North, to left in South)
Geostrophic wind
where pressure gradient = Coriolis effect
In upper atmosphere wind moves PARALLEL or NEARLY parallel to isobars
Friction effect on wind
mainly in lowest portions of troposphere
reduced Coriolis effect bc of drag of Earth’s surface –> causes wind to go btwn 0-90 angle of isobars
Friction layer
extends only to 1000 meters, after that winds follow geostrophic or near geostrophic course (almost parallel)
Anticyclone vs cyclone
anticyclone = high pressure center
- frictional zones = DIVERGES
cyclone = low pressure center
- frictional zones = CONVERGES
4 patterns of anticylonic circulation
1) Upper atmosphere of Northern hem = moves clockwise in geostrophic manner (parallel to isobars)
2) friction layer (low altitude) North = DIVERGENT clockwise flow, so air spirals out + away from center
3) Upper atmosphere of South = moves COUNTERCLOCKWISE in geostrophic manner
4) Friction layer south = divergent COUNTERCLOCKWISE flow, so air spirals out + away from center
4 patterns of cyclonic circulation
North - bad weather - not norm - counterclockwise
1) Upper atmosphere Northern Hem = moves COUNTERCLOCKWISE in geostrophic manner (parallel to isobars)
2) friction layer (low altitude) North = CONVERGING COUNTERCLOCKWISE flow, so air spirals out + away from center
3) Upper atmosphere of South = moves CLOCKWISE in geostrophic manner
4) Friction layer south = CONVERGENT CLOCKWISE flow, so air spirals out + away from center
Vertical movement in cyclones + anticyclones
air descends in anti-cyclones (clear weather)
–> DIVERGES from air and goes towards ground, increasing pressure on ground
air rises in cyclones (cloudy + stormy)
–> CONVERGES from ground into cyclone + continues rising, so the pressure on ground is low
What are Hadley cells
Warm air at equator rises (creates low pressure at surface)
reaches great heights + cools by the time it hits upper troposphere
air moves north/sound
descends at 30 N/S
goes back to equator as trade winds
