air pressure and wind

wind is the result of

horizontal differences in the atmospheric pressure

air flows from regions of

high pressure to regions of lower pressure

atmospheric air pressure

is the force exerted against a surface by continuous collision of gas molecules

mercury barometer

standard pressure measuring instrument, air pressure pushes on a pool of mercury, which forces the mercury up the tube.

air pressure commonly called

barometric pressure

fair weather corresponds with

high-pressure

rain is associated with

low-pressure

to predict weather examine

the change in air presssure over the past few hours

falling pressure is often associated with

increasing cloudiness and the possibility of precipitation

rising air pressure

generally indicates clearing conditions

station pressure are

the barometric pressure readings collected from weather stations

isobar lines

connect places of equal air pressure

anticyclones

high pressure systems, associated with dry conditions

cyclones/mid latitude cyclones

low-pressure systems at middle latitudes, associated with stormy weather

surface winds

generally blow at an angle across the isobars away from the centers of high pressure n toward the centers of low pressure

ridges

elongated high pressure areas that extend toward the poles

troughs

elongated low pressure areas that weep toward the equator

variation in air pressure cause

air movement (winds) that generate weather

horizontal pressure diff

small but important

primary factors that contribute to changes in air pressure

altitude

temp

humidity

movement of  mass of air from 1 location to another

air pressure

the force exerted against a surface by continuous collisions of gas molecules

air pressure decreases with

altitude

air pressure increases with

depth

air pressure drops more rapidly

in a column of cold (dense) air than in a column of warm (less dense) air

temp differences can be from either

unequal heating of land surfaces (local) or because of the unequal distribution of energy across the earth (global atmospheric circulation)

the amount of water vapor

reduces the density of air

cold dry air

has higher pressure

warm dry air has

higher pressure than equally warm moist air

convergence occurs

when a net airflow into a region causes pressure to rise

divergence results when

there is a net outflow of air from a region n surface pressure drops

pressure gradient force

diff in pressure that generates a force that causes the air to flow. air flows from areas of high pressure to areas to low pressure

air pressure drops

more rapidly in a column of cold (dense) air than in a column of warm (less dense) air

if isobars are close together

a steep gradient and high winds result

if isobars are far apart

low gradient with lower wind speeds

the Coriolis force

cannot generate wind it modifies airflow. deflecting force. always directed at rt angles to the direction of airflow. controls only wind direction not speed. Affected by wind speed (the stronger the wind the greater the force) strongest at poles n nonexistent at the equator.

In the northern hemisphere

a deviation to he rt is due to earths rotation

in the southern hemisphere

deviation is to the left

friction

significantly influences airflow near Earth’s surface, but its effect is negligible at higher altitudes. greater for faster winds and zero for calm conditions. dependent on the surface over which the wind is blowing. acts on slow-moving objects. reduces the Coriolis effect.

geostrophic flow

occurs when the pressure gradient force and the Coriolis force are balanced. Wind flow parallel to isobars. flow in relatively straight paths. flow with velocities proportionate to the pressure gradient force

bays ballot law

if you stand with the wind at your back, low pressure will be to your left, high pressure to ur rt.

in northern hemisphere if you stand with your back  to the wind

low pressure will be on ur left, and high pressure on ur rt. only holds for airflow aloft.

gradient winds 

winds which blow at constant speed parallel to curved isobars

curved airflow

winds around cells of high pressure or low pressure follow curved paths

low pressure

centers called cyclonic. winds flow counter clock wise in the northern hemisphere

high pressure

centers anticyclonic. winds flow clockwise in northern hemisphere.

hurricanes

tropical cyclones

tornadoes

tiny intense cyclones

friction causes

convergence around cyclone n divergence around an anti cyclone

cyclones where pressure decreases inward, friction causes

net flow toward the center

anticyclones where pressure increases outward, friction cause

a net flow away from the center

convergence can result in

cloudy weather

subsidence and divergence results in

clearing weather

vertical airflow

is associated with cyclones and anti cyclones

increased friction causes

a drop in wind speed resulting in a pileup of air upstream from the ocean to land

decreased friction causes

an increase in wind speed from the land to the ocean

wind direction is always measured from

the direction its coming from (north wind blows north to south)

wind vane

often used to show or measure wind direction

prevailing wind

consistantly blows more often than not from one direction.