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
What are the 8 components of general circulation
1) Intertropical convergence zone (ITCZ)
2) trade winds
3) subtropical highs
4) westerlies
5) jet streams (upper troposphere winds)
6) polar front (subpolar lows)
7) polar easterlies
8) polar highs
Subtropical Highs
Gigantic anticyclones off the west coast of the continents
*intensified cells of high pressure that extend about 30 latitude
Weather in Subtropical highs (STH)
weather is always clear, warm, dry, calm
- absence of wind + regions called horse latitudes
- anticyclonic
SOURCE OF TRADE WINDS + WESTERLIES
Trade winds
Cover latitudes 25 N to 25 S
prominent over oceans + interrupted over landmasses
generally easterly winds (blows from east)
winds named from direction they blow
why are trade winds called trade winds?
extremely consistent in direction + speed
used by merchants to go from Europe to Americas
hold a lot of moisture –> tremendous potential for storminess + precip.
Intertropical Convergence Zone
Zone where air from Northern hemisphere meets with southern (also called doldrums)
Weather of ITCZ
convergence + weak horizontal airflow –> feeble and irratic winds
high rainfall, instability, rising air of Hadley
Westerlies
predominant wind system of midlatitudes
btwn 30 + 60 N/S (less extensive than trades)
**Not as constant as trades bc easily interrupted by surface friction, topographic barriers, etc. SO not always blowing from west*
Jet Streams
Polar front jet stream = near poles 9-12 km above surface
Subtropical jet stream = closer to 30 degrees N/S (higher altitude than polar)
Rossby Waves
meandering curves of Jet stream
generally 3 - 7 rossby waves in jet streams
Polar Highs
High pressure cells over both polar regions (contributes to very cold temperatures in Antarctic)
typically anticyclonic
Polar easterlies
Formed by polar highs, btwn polar highs + 60 altitude
Cool + dry BUT variable
Polar Front
Meeting zone btwn polar easterlies + warmer westerlies
characterized by rising air, widespread cloudiness, precipitation
Effects on general circulation of atmosphere caused by seasons
1) during northern hemisphere summer = all components displaced northward
2) during southern hemisphere summer = all components displaced southward
displacement greatest at low latitudes + least in polar regions
shift caused bc of variations in surface warming
What are Monsoons
Monsoon winds = unusually large latitudinal migrations of trade winds
*Himalayas play large role
2 major monsoon systems + 2 minor
2 major = South + East Asia
2 minor = Australia + West Africa
Causes of monsoons
Unequal warming of continents + oceans
From Google AI answer:
Summer Monsoon: As land heats up faster than water in the summer, warm air rises, creating an area of low pressure. This area of low pressure pulls in cooler, moist air, which leads to heavy rains.
Winter Monsoon: In the winter, water off the shore of a land mass heats up and rises, creating an area of low pressure. This area of low pressure pulls in dry air from over the land mass towards the water.
Why is there an equatorial trough + polar high?
Around equator –> air is heated much more cuz more insolation SO the air rises + creates low pressure zones below
Around poles –> air is much colder, denser, so sinks down + increases pressure
