childrens_illustrated_encyclopedia_template_US_layer_v1
558
Weather describes conditions, such as rain, wind, and
sunshine, that occur during a short period of time in a particular
place; climate is the overall pattern of weather in a region. From
one moment to the next the weather can change. a warm, sunny
day can be overtaken by a violent storm. dark clouds form,
high winds blow, and rain lashes the ground, yet it may be
only a few minutes before the sunny weather returns.
however, in some parts of the world, such as in parts of
the tropics, the weather barely changes for months at a
time. there it is always hot, and heavy rains fall.
Meteorologists are scientists who measure and
forecast the weather. they do this by studying clouds,
winds, and the temperature and pressure of earth’s
atmosphere. but despite the use of satellites, computers,
and other technology in weather forecasting, weather
remains a force of nature that is hard to predict.Measuring the Weather
several thousand weather stations on land, ships, and aircraft measure
weather conditions around the world. the stations contain instruments
that record temperature, rainfall, the speed and direction of wind, air
pressure, and humidity (the amount of water vapor in the air). balloons
called radiosondes carry instruments to take measurements high in the
air. Weather satellites in space send back pictures of the clouds.aneMoMeter
the sun’s heat produces winds—moving
currents of air that flow over earth’s
surface. Meteorologists use anemometers
to measure wind speed, which shows the
rate of approaching weather.The wind spins
the cups, and the
wind speed is
shown on a dial.rain gauge
droplets of water and tiny
ice crystals group together to
form clouds, and water falls
from the skies as rain and
snow. Meteorologists measure
rainfall, which is the depth of
water that would occur if the
rain did not drain away.sunshine recorder
the more direct sunshine
a region receives, the
warmer it becomes. an
instrument called a
sunshine recorder
measures daily
hours of sunshine.
the glass ball works
like a powerful lens,
focusing the sun’s
rays, which leave a line
of burn marks on a
piece of cardboard.
Barograph gives a
permanent record
of air pressure on
a chart.Rain pours through a funnel into
a container. After every 24 hours,
the collected water is poured into
a measuring cylinder that gives a
reading of the day’s total rainfall.A scale of hours on
the recorder shows
at what times the
sun was shining.Weather 558-
the sun is the driving force
for the world’s weather. the
heat of the sun’s rays produces
wind and evaporates water from the
seas, which later forms clouds and rain.
the direct heat above the equator makes
the weather hot, while the poles, which get
less of the sun’s heat, are cold and cloudy.Clouds hang over the
hot and rainy tropics
of Central Africa.Weather
barograph
a barograph measures air pressure.
this is important in weather
forecasting because high pressure
often brings settled weather; low
pressure brings wind and rain.The air over the
Sahara Desert is so
stable and dry that
rain seldom falls.Swirls of
cloud mark
patterns of
winds.Snow and ice cover the cold
Antarctic continent.US_558_Weather_1.indd 558 27/01/16 2:40 pm