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- - The atmosphere is a mixture of gases
- - upper ATM-Lower ATM
- -constant movement due to heat transfer on earth.
- -gas molecules far apart -gas molecules close
- -infrequent collision-millions of collisions
- -low pressure -high pressure
- - decreases with increasing altitude.
- -pressure= force/area
- - as temp increases, collisions increases, therefore higher pressure.
- - higher temp, higher pressure
Measuring of Pressure
- Barometer: instrument used to measure ATM pressure
- Milibar: absolute measure of pressure, consisting of 1/1000 of a bar and is equivalent to 14.7 psi
- isobar: line joining points of equal ATM pressure on a map
~~~~ Wind ~~~~
- - defined as the horizontal air movement with respect to earths surface
- - the ATM is always in motion and is omni-directional
- -Updrafts/Downdrafts: small-scale vertical motions of air
- -Ascents/subsidence: large-scale vertical motions of air
- -driving force: unequal heating of the earths surface and the different pressure of the ATM
- - wind flows generally from high pressure --> low pressure
Direction: determined by pressure gradient, Coriolis effect, and friction
- - defined as the change in atmospheric pressure measured along a line at right angels to the isobars
- - greater the PG, greater the wind speed
- - gets the wind to start moving
- - flows from high pressure to low pressure, crossing isobars at right angels
- - apparent deflection of free-moving objects to the right in the Northern hemisphere and left in the souther, in response to the rotation of the earth.
- - Strongest at poles, weaker at equator
- - proportional to speed of object
- - flows from low to high and if pg and Coriolis is equal then air will flow parallel to the isobars and is called geostrophic wind. (all wind above 5000ft is geostrophic)
- - greatest at low winds and low lat.
Anticyclones and Cyclones
- Anti: high pressure circulation, diverging air spreads at earths surface, clockwise in north
- Cyclone: low pressure, converging air, creates clouds, counterclockwise in the north
Vertical variations in pressure and wind
- - ATM pressure decreases rapidly with height
- - wind velocity is a variable with time and place an altitude
- - generally increases w/ altitude
Subtropical High Pressure (STH)
- - Every ocean basic has a STH that is centered around 30 degrees latitude.
- - They are elliptical in shape and can be up to 2,000 miles in diameter.
- - Poleward side: Westerlies
- - Equaterward side: Trade winds
- - from near the equator to about 25 degrees latitude; steady winds blowing from the east.
- - Wind system of the tropics.
Inter tropical Convergence Zone
- - centered about the equator and area where the NE and SE trade winds converge
- - this makes the winds move vertically so there are weak winds
- - weak and erratic horizontal winds - Doldrums
- - 2nd major wind system and major wind system of the middle latitudes.
- - wind goes from west --> east
- - zonal airflow- west to east
- - upper air, north-south undulations in the westerlies.
- - results in sever (short-term) weather changes that occur in the mid-lats.
- Jet streams are located high above the STH and shift position in response to the Rossby waves.
Polar High Pressure
- - High pressure cells over the polar regions
- - Antarctic High: Strong persistent feature over Antarctica.
- - Arctic High: less pronounced, more migratory
- - Major wind system of the higher latitudes, area between Polar High and 60 degrees latitude.
- - east --> west
- - cold and dry wind system.
- - very fast winds
SubPolar Low pressure
- - zone of low pressure that is situated at about 50-60 degree of latitude.
- - the low pressure means that air is rising which results in cloudiness and stormy weather.
Seasonal Variations of wind systems
- - Summer: displaced poleward
- - Winter: displaced towards equator
- - ITC- displaced between 25N+20S, greatest over the continents
- - Polar Highs- little or no displacement
Monsoons: result in a seasonal reversal of winds.
Results of Seasonal Variation
- - Middle lats are suffered the most while equator and poles are least affected
- - extension of summer-like conditions poleward
- - extension of winter-like conditions toward equator
- - most significant disturbance of general ATM circulation pattern
- - defined as a low-level winds blowing into a continent in summer and out of it in the winter.
- - controlled by ATM pressure and develop seasonally.
- created when continents heat and cool differently than oceans
- generated by the unequal heating of the earths surface
- 1) Sea Breeze: wind that blows from the sea toward land, usually during day
- 2) Land Breeze: local wind blowing from land to water, usually at night
- 3) Valley breeze: warm wind caused as heating of air near slope of a hill/mountain produces active convectional ascent of air up the topographic slope.
- 4) Mountain breeze: after dar, mountain slopes lose heat rapidly through radiation cooling, which chills adjacent air, causing it to slip down-slope.
- 5) Katabatic breeze: wind that originates in cold upland areas and cascades toward lower elevations under influence of gravity.