Weather stations
Last updated: July 10, 2009.
Have you noticed how the weather forecast never quite seems to apply to
where you live? No wonder people talk about "hand-waving"!
Sometimes the forecasters get it right, sometimes they get it wrong,
but more often than not what they say doesn't give an accurate
picture of what's actually going to happen where you are.
One reason for this is that forecasting the weather is a very complex
scientific problem; it even leaves supercomputers scratching their
heads! Another reason is that forecasts are compiled using data
collected only from certain locations—and the nearest weather
forecasting station may be some distance from your home. One way to
get around this problem is to have a go at making your own weather
forecasts. You'll need a collection of weather-measuring
instruments—a thermometer, a barometer, an anemometer, and a
hygrometer— for starters. Or you could just buy yourself a weather
station: it's a handy little gadget that has all these instruments
built in. Let's find out more about weather stations and how they
work!
Photo: Weather forecasting is always helpful—but sometimes it's a matter of life and death.
With good forecasting, we can get advance warnings of hurricanes and other extreme weather. This satellite photo shows Hurricane Fran heading
for North Carolina and Virginia in August 1989; it went on to cause about $5 billion worth of damage. Photo by courtesy of Great Images in NASA.
What makes weather?
Weather happens because the Sun heats different places on Earth
to different temperatures. This makes air rise in some places
(creating lows, areas of low pressure, also called
depressions) and fall in others (making highs, high-pressure areas,
also called anticyclones). Lows and highs
make winds blow, and the winds endlessly shuffle different kinds of
weather round the planet's surface. Lows bring humid air (soggy with
water vapor), which usually means clouds, rain, or snow. Highs
signal hot, dry weather in summer and crisp, clear days in winter.
Storms happen where lows and highs meet up. All told, weather is
pretty complex, but you can get a reasonable idea what it's going to
do next if you measure the temperature, pressure, wind speed, and
humidity. Bring on the weather station!
Photo: Clouds play a big part in our weather, blocking out solar radiation and bringing in rain. Photo of dramatic clouds over Denver, Colorado by Warren Gretz courtesy of US DOE/NREL.
What is a weather station?
The key thing about a weather forecast is that it really applies
to just one place and, as it's based on a set of measurements,
those all have to be made in the same place, at the same time, as
well. A weather station is simply a collection of
weather-measuring instruments mounted on (or in) the same place.
Professional weather stations have very precise instruments stored in
a white, sun-proof, louvered box (called a Stevenson screen) and are
designed to be read manually. Home weather stations are now typically
electronic instruments that are read automatically by a
microprocessor (single-chip computer). Either they show their
readings on an electronic LCD display or transmit them by wireless
(radio) to a computer nearby.
Photo: A traditional weather station inside a Stevenson screen. The white, louvered panels protect the instruments from the direct heat of the Sun but allow air to circulate inside, giving more accurate measurements.
What instruments does a weather station contain?
A typical weather station contains:
- Thermometer: Measures temperature in either degrees Celsius (°C)
or Fahrenheit (°F). Home weather stations can often be made to sound an alarm if the temperature
rises or falls below a level you set (very handy if you want early
warning of a heat wave or frost).
- Barometer: Measures the maximum and minimum air pressure in
different units including Pa (Pascals) and mmHg (millimeters of
mercury). Most weather stations keep a record of how the pressure
has risen or fallen over the last 24 hours or so.
- Precipitation (rainfall) gauge: Measures how much rain (or snow) has fallen. A little plastic beaker with a scale on the side that measures the amount of rain collected in millimeters (or inches) in the last hour, day, week, or month.
- Anemometer: Measures wind speed in kilometers and miles per hour (km/h and mph). Shows both the average wind
speed and the gust speed (maximum speed). Usually there is also a vane to measure the wind direction.
- Hygrometer: Measures the humidity (the amount of water vapor in
the air, written as a percentage). A humidity of 100 percent means
completely saturated air, while 0 percent humidity means totally dry air.
Photo: The main parts of a portable, military weather station. This one can send its readings automatically
using a solar-powered transmitter. Photo by Michael Boquette courtesy of
US Air Force.
Modern weather stations often have an LCD display that
shows all the measurements automatically and updates them instantaneously,
saving the need to read the instruments one by one. Using the
measurements, a microchip inside will also figure out and display something called
the tendency (a rough forecast for the next day's weather,
summarized with a simple picture such as a sun (fine day), partly
obscured sun (dull day), or raincloud (wet day). Electronic stations
also generally have a memory so they can record hundreds of separate
measurements covering the last few months. Some stations can be
connected to a computer
with a USB cable so you can upload your data and draw proper weather
and climate charts.
Forecasting the future
Forecasting the weather means measuring things that may not happen
for days or weeks, which is always a bit tricky. Modern forecasts are
made with ultra-powerful computer models—effectively reams of
equations that computers chew through to make an accurate prediction
up to 15 days ahead. The equations describe Earth's atmosphere using
a 3D grid of points, with temperature, pressure, humidity, wind
speed, and other factors measured for each one. A modern forecast,
involving billions of calculations, needs a supercomputer to crack
it. But the first forecasts made this way, by British mathematician
Lewis Fry Richardson in the 1920s, were done entirely by hand.
Thrashing through the maths to forecast a single day's weather took
him all of six weeks!
Photo: It takes supercomputers like this to produce detailed weather forecasts.
Picture courtesy of Argonne National Laboratory published on
Flickr in 2009
under a Creative Commons Licence.
