air pressure
the weight of the atmosphere described as force per unit area
molecules that constitute air create this through their motion, size, and number, and this pressure is then exerted on all surfaces in contact with air.
average sea level
1,013.2
air pressure and density
decreases with altitude in the atmosphere
barometer
any instrument that measures air pressure created by Torricelli
mercury barometer
Torricelli developed this-- a device that measures air pressure using a column of mercury in a tube; one end of the tube is sealed, and the other end is inserted in an open vessel of mercury
760 mm of mercury
aneroid barometer
means "using no liquid"
a device that measures air pressure using partially evacuated, sealed cell.
as the air pressure outside the chamber increases, it presses inward on the chamber; as the outside pressure decreases, it relieves the pressure on the cha
aneroid barometer
imagine a small chamber, partially emptied air, that is sealed and connected to a mechanism attached to a needle on a dial. as the air pressure outside the chamber increases, it presses inward on the chamber; as the outside air pressure decreases, it reli
wind
generally horizontal motion of air across earth's surface.
two principal properties are speed and direction
differences in air pressure between one location and another produce wind
anemometer
measures wind velocity/speed
measures wind speed in kilometers per hour, miles per hour, meters per second, or knots.
wind vane
determines wind direction; the standard measurement is taken 10m (33ft) above the ground to reduce the effects of local topography on wind direction
often have roosters on them-- on top of barns
pressure gradient force
drives air from areas of higher atmospheric pressure (more dense air) to areas of lower barometric pressure (less-dense air), thereby causing winds. without this force, there would be no wind.
isobar
this is an isoline (a line along which there is a constant value) plotted on a weather map to connect points of equal **
pressure
**
the pattern of isobars provides a portrait of the pressure gradient between an area of higher pressure and one of lower pr
coriolis force
one of the forces that determines the speed and direction of winds
makes wind traveling in a straight path appear to be deflected in relation to earth's rotating surface
In a reference frame with clockwise rotation, the force acts to the left of the motio
coriolis force
force that affects the direction of moving objects.
because earth rotates eastward, such objects appear to curve to the
right
in the northern hemisphere and to the
left
in the southern hemisphere. because the speed of the earth's rotation varies with lati
friction force
one of the forces that determines the speed and direction of winds
creates drag as the wind moves across earth's surface, but this decreases with height above the surface
without this, surface winds would simply move in paths parallel to isobars and at hi
wind
result of the combination of physical forces: friction force, pressure gradient force, and coriolis force
geostrophic winds
characterized of upper tropospheric circulation
come about because pressure gradient force and Coriolis force come into balance after the air begins to move
they do not flow directly from high to low, but that flow around the pressure areas, remaining par
anticyclone
high pressure
wind flowing counter clockwise in the northern hemisphere
wind flowing clockwise in the southern hemisphere
cyclone
this is a storm or system of winds that rotates around a center of low atmospheric pressure.
Winds in this blow counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
equatorial low (intertropical convergence zone)
the other pressure areas
thermally caused low-pressure area that almost girdles earth, with air converging and ascending all along its extent; also called the intertropical convergence zone
high temp, low pressure
polar highs
the other pressure areas
weak, anticyclonic, thermally produced pressure systems positioned roughly over each pole; that over the south pole is the region of the lowest temperatures on earth.
low temp, high pressure
subtropical high
the other pressure areas
formed by mechanical factors
middle of the spectrum
one of the several dynamic high-pressure areas covering roughly the region from 20 degrees to 35 degrees north and south latitudes; responsible for the hot, dry areas of earth's
subpolar low
a region of low pressure centered approximately at 60 degrees latitude in the north
trade winds
winds converging at the equatorial low
northeast _____________ blow in the northern hemisphere and southeast ________________ blow in the southern hemisphere.
these were named during the era of sailing ships that carried merchandise for trade across the s
trade winds
these winds are the most consistent winds on earth
trade winds
flow toward the equator,
westerlies
dominant winds flowing from subtropics toward higher latitudes
stronger in the winter
less consistent than trade winds
polar front
the area of contrast between cold air from higher latitudes and warm air from lower latitudes forms this
masses of air with different characteristics meet
polar easterlies
winds, cold and dry, move away from the polar region in an anticyclonic direction. they descend and diverge clockwise in the northern hemisphere and counterclockwise in the southern hemisphere and form weak, variable winds of the _____________
antarctic high
of the two polar regions, this has the stronger and more persistent high-pressure system
azores high
a semi-permanent anticyclonic region with relatively consistent high pressure and subsiding air over the Atlantic Ocean at around 30�N latitude in winter.
this is part of a belt of subtropical anticyclones on the northern hemisphere and an important so ca
Bermuda high
A semi-permanent area of high pressure, commonly known as the Bermuda High, forms over the Atlantic Ocean during the summer and is the key weather player for most of the eastern USA. The clockwise circulation around the high brings hot, humid wind to the
pacific high
a semi-permanent, subtropical anticyclone located in the northeastern portion of the Pacific Ocean, located northeast of Hawaii and west of California
azores high
large persistent atmospheric high-pressure centre that develops over the subtropical region of the eastern North Atlantic Ocean during the winter and spring seasons in the Northern Hemisphere.
It is a subtropical high-pressure cell that moves westward dur
pacific high
dominates the pacific in july, retreating southward in january.
aleutian low
north pacific
one of the low pressure cells that exists over the oceans around 60 degrees north latitude near their namesake islands
icelandic low
north atlantic
one of the low pressure cells that exists over the oceans around 60 degrees north latitude near their namesake islands
icelandic low and aleutian low
low pressure systems develop and strengthen
both of these cells are dominant in winter and weaken or disappear in summer with the strengthening of high pressure systems in the subtropics.
constant isobaric surface
an elevated surface in the atmosphere on which all points have the same pressure, usually 500 mb. along this constant-pressure surface, isobars mark the paths of upper-air winds.
rossby waves
within the westerly flow of geostrophic winds are great waving undulations
named for meteorologist carl g. rossby, who first described them mathematically in 1938.
these occur along the polar front, where colder air meets warmer air, and bring tongues of
rossby waves
these occur along the polar front, where colder air meets warmer air, and bring tongues of cold air southward, with warmer tropical air moving northward.
jet streams
the most prominent movement in the upper-level westerly geostrophic wind flows is this
jet streams
irregular, concentrated bands of wind occurring at several different locations that influences surface water systems
these tend to weaken during the hemisphere's summer and strengthen in it's winter as the streams shift closer to the equator.
land and sea breezes
local winds produced along most coastlines
the different heating characteristics of land and water surfaces create these breezes.
land gains heat energy and warms faster than the water offshore during the day
mountain and valley breezes
local winds resulting, respectively, when mountain air cools rapidly at night and when valley air gains heat energy rapidly during the day
mountain and valley breezes
valley slopes are heated sooner during the day than valley floors. as the slopes heat up and warm the air above, this warm, less dense air rises and crores and area of low pressures.
katabatic winds
drainage winds that are of larger regional scale and are usually stronger than local winds. they develop on elevated plateaus or highlands where layers of air at the surface cool, become denser, and flow downslope.
monsoon
an annual cycle of dryness and wetness, with seasonally shifting winds produced by changing atmospheric pressure systems; affects india, southeast asia, indonesia, northern australia, and portions of africa.
oceanic currents
the atmospheric and oceanic systems are intimately connected in that the driving force for ocean currents is the frictional drag of the winds.
stream made up of horizontal and vertical components of the circulation system of ocean waters that is produced
equatorial currents
trade winds drive the ocean surface waters westward in a concentrated channel along the equator.
these remain near the equator because of the weakness of the coriolis force, which diminishes to zero at that latitude.
thermohaline circulation (THC)
differences in temperatures and salinity produce density differences important to the flow of deep currents on earth
thermohaline circulation (THC)
to picture this, imagine a continuous channel of water beginning with the flow of the gulf stream and the north atlantic drift. when this warm, salty water mixes with the cold water of the arctic ocean, it cools, increases density, and sinks. th cold wate
el nino- southern oscillation (ENSO)
a shifting of sea-surface temperatures, air pressure, and winds across the equatorial pacific region. this shift influences marine movement.
el nino- southern oscillation (ENSO)
in the equatorial pacific, consistent trade winds drag warm surface water away from the south american coast, causing upwelling of colder, nutrient rich water from below. yet, there is a periodic warming of coastal ocean temperatures that temporarily lowe
la niana- ENSO's cool phase
when surface waters in the central and eastern pacific cool to below normal by 0.4 degrees C or more, the condition is called this. this condition is weaker and less consistent than el nino, otherwise there is no correlation in strength or weakness betwee
southern oscillation
changes in the pressure pattern and trade wind strength (direction) in the tropical pacific
enso
together el nino and the southern oscillation create this
consequences of el nino
increased rainfall in the southern US and the west coast of south america
gravitational force
one of the forces that determines the speed and direction of winds
exerts a virtually uniform pressure on the atmosphere over all of earth. this counteracts the outward centrifugal force acting on earth's spinning surface and atmosphere.
without this forc
pressure gradient force
one of the forces that determines the speed and direction of winds
drives air from areas of higher barometric pressure (more dense air) to areas of lower barometric pressure (less dense air), thereby creating winds
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air pressure differences
high and low pressure areas exist in the atmosphere principally because earth's surfaces unequally heated. for example, cold, dry, dense air at the poles exerts greater pressure than warm, humid, less-dense air along the equator
thunderstorms
turbulent weather with thunder, lightening
requires lifting mechanism-- rapid upward movement of air
turbulence, wind shear, downburst
downburst
burst of air moving downward-- rapidly moving down
hailstones
tiny ice pelts fall from the surface then hits warmer air and gets sent back up into the atmosphere-- does this over and over until the pelt grows into hail
this is a sign of an intense storm
tornados
the vortex touches the ground
often associated with thunderstorms
funnel cloud
never touches the ground
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