|
AIR PRESSURE
Air pressure is the actual
weight or push on the Earth's surface of all the gases in the atmosphere; it
is a force per unit area. Keep in mind, that the atmosphere is dynamic and fluid;
it is a thin blanket of air that moves and ripples across the spherical earth.
Thanks to gravity, the atmosphere is held in place.
As the earth rotates on
its tilted axis, the sun can only heat one section of the atmosphere at a time.
The poles stay cold, while the equator heats up. Yet the atmosphere tries to
find a balance; the air must mix. This difference in temperature helps to keep
the air in motion by creating 3-D currents which circle the globe.
Heated air will be buoyed
up by the surrounding denser air and will rise. This rising air current reduces
the air pressure; it decreases the weight on the Earth's surface - forming an
area of Low Pressure. The surrounding denser, cooler heavy air sinks and moves
horizontally to replace the rising currents. This sinking air piles up and increases
the weight on the Earth's surface - forming an area of High Pressure.
Air flows from areas of
high pressure to low pressure, and this creates the wind. The greater the difference
in pressure, otherwise known as pressure gradient, the stronger the wind. That
is why rapidly developing winter storms with low central pressures create the
fiercest winds, while stagnant high pressure ridges in the summer barely generate
a breeze.
At weather offices, hourly weather observations are taken which include measurements
in air pressure and winds. These observations are plotted and analyzed on a
regional map. Lines of constant pressure, known as isobars, are drawn to determine
the position and strength of high and low pressure systems.
|
www.weather.gov 
