
pressure
The gas molecules pulled to the Earth by gravity exert a force on all surfaces they are in contact, and the amount of that force exerted per unit of surface area is pressure.

pascal (Pa)
standard unit of pressure (but in Us it is millibar[mb])

kilopascal (kPa)
Canadian standard unit of pressure

Dalton's Law
The total pressure exerted is equal to the sum of the partial pressures.

surface pressure
air pressure as it exists at the surface

sea level pressure
the pressure that would exist if the observation were at sea level.

speed
the distance traveled per unit of time.

velocity
much like speed but also incorporates direction (speed and motion of an object or substance). So, distance traveled per unit of time + direction.

acceleration
the change in velocity (not speed) with respect to time.

gravity (g)
an acceleration that is a near constant around the globe (9.8 m/sec/sec)

force (F)
the net force acting on an object.

equation of state (ideal gas law)
if the air density increases while temperature is held constant, the pressure will increase.

mercury berometer
standard instrument for measurement of pressure

barametric pressure
inconsistent because pressure is not measured by length as with a mercury berometer, which is used to measure barametric pressure to find the height of the column of mercury.

aneroid berometer
air inside is compressed by the outside air pressure. canbe quite cheap and accurate.

barographs
aneroid barometers that plot continuous pressure

isobar
isobars are lines on weather maps plotted to show continous pressure patterns

pressure gradient
rate of change n pressure

pressure gradient force
the pressure gradient gives rise to a force that sets air in motion (wind) called pressure gradient force.

hydrostatic equilibrium
the vertical gradient pressure force and gravity are of equal pressure (hydrostatic equilibrium) therefore, we can breathe easily without air being sucked to the surface.

hydrostatic equation
(formula of hydrostatic equilibrium) The rate at which pressure decreases with height equals the product of the air density and the acceleration of gravity.

Coriolis force
(one of 2 factors that effect the movement of air) The phenomenom in which the rotation of the Earth has an effect on anything that moves in a certain direction, including wind, which the rotation of the Earth deflects (turns).

friction
(one of 2 factors that effect the movement of air) air in contact with surface experiences frictional drag, which decreases wind speed. The air above this slowed air is then slowed by the slowed air below.

planetary boundary layer (boundary layer)
lowest 1.5 km (1 mile) of the atmosphere

free atmosphere
atmosphere above the lowest 1.5 km (1 mile) of atmosphere

geostrophic flow (geostrophic wind)
when the pressure gradient force is equal to the Coriolis force, the air flow becomes unaccelerated, with unchanging speed and direction.

equation of motion
states that the acceleration experienced by a mass of air is the sum of the accelerations due to the three forces of Coriolis force, pressure gradient, and frictional acceleration.

gradient flow (gradient wind)
the continual mismatch between the Coriolis forces and pressure gradient resulting in winds changing speed and direction.

supergeostrophic flow
when the Coriolis force exceeds the pressure gradient force air is forced to turn clockwise.

subgeostrophic flow
(opposite of supergeostrophic flow) Coriolis force is weaker than the pressure gradient force, causing the air to turn counterclockwise.

anticyclones
Enclosed areas of high pressure marked by roughly circular isobars or height contours where air spirals clockwise.

cyclones
Closed lowpressure systems where air spirals counterclockwise.

troughs
low pressure pressure systems

ridges
high pressure systems

azimuth
a wind's degree of angle from due north moving clockwise. used to express wind direction.

wind vane
observes wind direction

anemometers
measures wind speed

aerovane
indicates wind direction and speed

rawinsondes
radiosondes whose movement is tracked by radar

