Stuck in someone else's frames? break free!
|| WIND, HUMIDITY, AND AIR PRESSURE
Many factors such as temperature, wind, air pressure, and
moisture make up what is called weather.
The following are a few very general suggestions for
obtaining information and making predictions about weather
Use a wind vane to find patterns of wind direction and sub-
sequent changes in weather. For example, consider the west
coast of the United States. Winds from the south, southwest,
west, and northwest usually bring rain because they blow from
Winds from the northwest, north, northeast, and east usually
bring fair and cooler weather because they come from cooler
On the east coast of the United States, winds coming from the west, northwest, or north usually bring fair and cooler weather because they come from cooler land farther north or from drier land farther west. Winds from the northeast, east, southeast, and south usually bring rain because they blow from the ocean.
You might also use an anemometer ("ann-e-MOM-et-ter": an
instrument for measuring wind direction and speed), or the
Beaufort Scale to determine how long it takes for certain
types of weather to move into your locale. The ("BO-fort")
Scale is a scale of wind velocity (speed). The U.S. National
Weather Service uses an adaptation of this scale. It employs
numbers from 0 to 12, representing calm, light air, light
breeze, gentle breeze, moderate breeze, fresh breeze, strong
breeze, moderate gale, fresh gale, strong gale, whole gale,
storm, and hurricane. Zero (calm) is a wind velocity of less
than 1 mile per hour and 12 (hurricane) represents a velocity
of over 75 miles per hour (Concise Columbia Encyclopedia).
We'll have to find out if velocity is (or is not) a factor in
tornadoes. Are cyclones and tornadoes the same things?
Cyclones, according to Concise Columbia Encyclopedia, are
masses of rotating winds, spinning clockwise in the southern
hemisphere and counter-clockwise in the northern hemisphere.
Tornadoes, are dark, funnel-shaped clouds containing
violently rotating air that develops below a heavy cumulo-
nimbus** cloud mass and extends toward the earth. The
diameter of a tornado varies from a few feet to a mile; the
rotating winds reach velocities of 200 to 300 miles per hour,
and the updraft at the center may reach 200 miles per hour.
In comparison with a cyclone, a tornado covers a much smaller
area but is much more violent and destructive. The atmo-
spheric conditions required for the formation of a tornado
include great thermal instability, high humidity, and the
convergence of warm, moist air at low levers with cooler,
drier air above. Tornadoes occurring over water are called
"waterspouts." (C.C. Encyclopedia)
** ("CEUM-you-low-NIM-bus"; an extremely dense, vertically
developed cumulus cloud with a relatively hazy outline and a
glaciated top, usually producing heavy rain, thunderstorm, or
hailstorm. American Heritage Dictionary.)
We can make some kinds of predictions about weather from air
Until weather satellite photos became available, the
barometer was the major instrument used to forecast long term
changes in the weather. You can use a barometer to identify
patterns between readings and subsequent weather changes.
You will find that a rising barometer usually means the
approach of a high pressure air mass that generally brings
increasingly cool, heavy air and better weather.
A falling barometer usually means the approach of a low
pressure air mass that generally brings increasingly warm,
light air and stormy weather.
A barometer is an instrument for measuring atmospheric
pressure. The mercurial barometer consists of a mercury-
filled glass tube, that is sealed at one end and inverted in
a cup of mercury. Pressure on the surface of the mercury in
the cup supports the mercury in the tube, which varies in
height depending on variations in atmospheric pressure. At
32o F, standard sea-level pressure (1 standard atmosphere) is
14.7 lb/in.2 (14.7 pounds per square inch, which is
equivalent to a column of mercury 29.92 inches in height.
The aneroid barometer contains a sealed, partially evacuated
metallic box. As the air pressure on it varies, one of its
surfaces expands or contracts; this motion is transmitted by
a train of levers to a pointer, which shows the pressure on a
graduated scale. (C.C. Encyclopedia)
Will Rogers said something like "everybody talks about the
weather, but nobody does anything about it." We can't do
anything about it, but storm warnings are helpful, in that
they give us a chance to survive.
Here's what Mark Twain had to say about barometers and
weather forecasting in general, in his speech to the New
England Society on December 22, 1987: "Probable nor'east to
sou'west winds, varying to the southard and westard and
eastard and points between; high and low barometer, sweeping
round from place to place; probable areas of rain, snow,
hail, and drought, succeeded or preceded by earthquakes with
thunder and lightning."
Frequently, people complain that changes in barometric
pressure has made their bones ache. They also complain that
wind makes people irritable, because it puts electricity into
the air. Then there are the hair-dressers who excuse their
poor work by saying the weather caused hair to be unmanageable
or frizzy, or something. We don't know whether or not this
stuff is true, but when one person says it, the other person
nods and makes knowing, agreeing comments.
Weather predictions are often made from moisture information.
An hygrometer ("hi-GROMM-itter") can be used to measure the
amount of water (humidity) found in the air.
The most common type of hygrometer is the dry- and wet-bulb
psychrometer ("sigh-CHROMM-itter") It consists of two mercury
thermometers, one of which has a wet wick around its bulb.
The sling type of psychrometer is swung around in the air.
Water evaporating from the wick absorbs heat from the bulb,
causing the thermometer reading to drop. The observer, after
reading the dry-bulb temperature and the drop in the wet-bulb
temperature, can determine the relative humidity from
appropriate tables. Among other kinds of hygrometers are
ones that use human hair or electrical resistance, rather
than thermometers, to determine moisture content. (CC Encyc)
In general, you will find that the humidity of the air
increases before a rain and decreases afterwards. In terms
of approaching weather fronts, the humidity will usually
change as shown.
We have seen advertisements for a glass swan, cut in half and
mounted on a well-finished and highly polished board. One
puts colored water into the swan until it is a little more
than half full, and hangs this arrangement on the living room
wall, and calls it a "barometer." It is said that when the
pressure rises, the colored water goes up into the swan's
neck; when the pressure falls, the water goes back down into
the body of the swan. We don't know if it really works.
Folk "instruments," just like folk remedies, often function
very well. You could buy one for your mom, and find out if
it works or not. (Moms really hate things like that, but
they love their kids, and treasure the kids' gifts.)
Any problems with this page? Send URL to webmaster. Thank you!
We publish two newsletters a couple of times a month. To subscribe, send a blank email to the appropriate email address. Topica will send you a message asking if you really intended to subscribe - just click reply - that's it!
Free Recipe Collection Newsletter:
Jewish Recipe Collection Newsletter:
Tired of Geek Speak when