-mass of air above a given level

-it takes a shorter column of cold, more-denseair to exert the same surface pressure as a taller column of warm, less dense air

-warm air aloft is often associated with high atmospheric pressure, and cold air aloft is associated with low atmospheric pressure

-heating and cooling columns of air can establish horizontal variations in air pressure; both aloft and at the surface.... this causes winds to blow

measuring air pressure (3)

BAROMETER - detect and measure pressure changes

MERCURY BAROMETER - invented by stendent of Galileo... vaccume inside and sucks up mercury from a dish

ANEROID BAROMETER - most common type... contains no fluid (aneroid cell in vaccume contracts with air pressure)

-unit of pressure that describes force over a given area

millibar - most common unit of pressure... (equal 1/1000 of a bar)

SAP - 1013.25mb =1013.25 hPa = 29.92 inches Hg

- this is sea level pressure

Station Pressure - acquired after recorded pressure is corrected for temperature, gravity, and instrument error

Sea-level pressure - corrected for T, gravity, instrument error, and altitude

-lines connecting points of equal pressure... 1000mb is base.. drawn at interval of 4mb

******near earth's surface, atmospheric pressure decreass approximately 10mb for every 100m increase in elevation (1 inch Hg per 1000ft)

ANTI- centers of high pressure

MID LAT - centers of low pressure, also called depressions, or extratropical cyclones

-lines that connect points of equal elevation

-contour lines of low height = low pressure

-high height = high pressure

-typically decrease in value from north ot south

ISOTHERMS- lines of equal temperature... show ridges and troughs

1)any object at rest will remain at rst and any object in motion will remain in motion.. so long as no force is exerted upon it

2)force exerted on object is equal to its mass times its acceleration (F=ma)

1)pressure gradient force

2)coriolis force

3)centripital force

4)friction

pressure gradient - difference in pressure over distance...... steep pressure gradients are a rapid change in pressure over short distances.... shown with very close isobars

Pressure Gradient Force - is directed from higher to low pressure at 90 degree angles to isobars... magnitude is related to pressure gradient

-this is the force that causes wind to blow

-apparent force due to rotation of the earth

-causes wind to deflect to riht  in NH and left in SH

**the stronger the wind the greater the deflection

-coriolis effect is most strong at the poles (and none exactly over the equator

Amount of deflection depends on:

1)rotation of the earth

2)latitude

3)object's speed

**only influences wind direction, not wind speed

***coriolis effect varies with the sine of latitude (sine0=0, sine90=1)

-atmospheric layer affected by friction (usually up to 1 km)

-near surface, friction reduces wind speed, which in turn reduces the effect of the coriolis force

-coriolis no longer balances PGF and wind blows across isobars (approx 30 degrees) toward low pressure

-if convergence/divergence in pressure system are not equal, pressure will change

1)onshore wind - wind blowing from water onto land

2)offshore wind - wind blowing from land to water

3)upslope wind - wind blowing downhill from uphill

4)prevailing wind - wind direction most often observed during a given period of time

-these can greatly affect climate in a region

1)wind nose - indiates percentage of time that wind blows from a certain direction

2)wind vane - old and reliable way of determining wind direction

3)anemometer - measures wind speed... by rates of rotating cups

4)aerovane - indicates speed and direction (propellor)

5)radiosonde - can measure its angles to learn about wind.... called RAWINSONDE OBSERATION

6)wind profiler - doppler radar used to profile wind

-hierarchy of motion from tiny husts to giant storms

MICROSCALE -a few meters across or less (small turbulent eddies)

MESOSCALE - circulation within 20 km (thunderstorms, tornadoes, dust devils, hurricanes, tropical storms, land/sea breeze, mountain/valley breeeze, etc)

-when the wind envounters a solid object, it is the whirld of wind that forms on object's downward side

**Rotors are large eddies formed by mountains

clear air turbulence

-eddies formed in clear air

-sea- occurs during the day, when land warms and air rises... a PGF is established and cooled ocean air flows on land

land - occurs at night, and is basically the opposite

Sea Breeze Front - the leading edge of a sea breeze, and is followed by a rapid drop in temperature

-sometimes appears smokey or foggy

-mountain - occurs at night, cooler dense air glides down mountain.. also called gravity winds or nocturnal drainage

valley - during day, warm and gentle upslope wind up mountains

*** these both are best noticed when prevailing winds are light in clear summer weather

-one that changes direction seasonally

-winter monsoon means clear skies, with winds from land to sea

-summer monsoon yields wet and rainy weather, with winds from land to sea

Cherrapunju- gets recordrrain in summer, and almost none in winter. agerages 1080cm/yr

-downslope winds much stronger than mountain breezes

-very cold snowy air triggered to flow downhill

-can be extremely strong, usually high initial potential energy

-warm and dry wind that decends the eastern slope of the rocky mountains

-main cause is the decending compressional heating

-called foehn winds in other parts of the world

-warm dry wind that blows from east or north-east into southern california

-caused by high  pressure zone in dsert ... it pushed hot winds

-again, compressional heating as it decends

-sets stage for serious brush fires

-spectacular storm composed of dust or sand

-caused by thunderstorm downdrafts

-spinning vortica commonly seen on hot days in dry areas

-heated surface, air rises, then is spinned by wind

-can spin in either direction

1)the earth's surface is uniformly covered with water (so that differential heating between land and water does not come into play)

2)the sun is always directly over the equator (so that the winds will not shiftseasonally(

3)the easth does not rotate (so that the only force we need deal with is PGF)

-region over equatorial waters where air is warm, horizontal pressure gradients are weak, and winds are light

-weather in this area is monotonous

JULY

Bermuda High/Pacific High - ocean high pressure zones that remain constant all year

Icelandic low/Aleutian low - cyclonic low pessure zones activity represent where numerous storms tend to converge

JANUARY

Siberian High -formed by very intense cooling of land

-where upper level winds tend to concentrate into narrow bands of fast flowing air

-usually found at tropopause

subtropical jetstream- situated near 30 lat

polar front jet streatm - approx 60 lat.. over polar front

**jetstreams play a major role in global heat transfer

EL NINO

-reversla of current flow due to reversal of Hadley cells... brings warm water to Peru ratherthat the usual nutrient rich and cold antarctic water

-chokes off upwelling near Peru

-every few years, surface atmospheric pressure systems change

-strengthens the equatorial counter current that goes towards S America

SOUTHERN OSCILATION

-see saw pattern of reversing surface air pressure at opposite ends of pacific

ENSO- same thing, as El Nino and Oscillation are simultaneous

-air rises now near Peruand sinks off coast of Australia... now rains/droughts in different places

NAO/AO/PDO

NAO-North Atlantic oscilaation - pressure reversal over atlantic

AO-arctic oscillation

PDO- Pacific Decadial oscillation (every 20-30 years)