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Weather - Level 1

OBJECTIVE

At the end of this block of study, you should be able to:

Be aware that changes in temperature bring about changes in the form
     of the moisture in the air.
Demonstrate that wind direction may be measured.
Describe that fogs and clouds are droplets of moisture which we can see in the air.
Discuss how atmospheric pressure brings about changes in the weather.
Demonstrate that air contains moisture that can be measured.
Be aware that flight safety is made possible in part by the knowledge of the
     relationships between temperature and moisture conditions of the air, so that the pilot
     can be advised where and how to avoid dangerous conditions and how to take
     advantage of favorable ones.

BACKGROUND INFORMATION

Pilots and air transportation are dependent on weather information in order to make flying safe and comfortable. There are many reasons why pilots need to know about the weather. Among them are knowing where they might encounter low visibility, where they might profit by flying above the clouds, where they might expect icing or strong winds, whether or not the terminal airport has an adequate ceiling. If weather is adverse, the pilot might need to change plans - either stay on the ground or choose another route. The pilot will need to take along more fuel if the airplane will be flying into a strong wind.

When planning a flight, the pilot contacts a flight service station for weather information. The flight service station receives weather reports from the United States Weather Bureau.

Weather forecasting is determined by the observation of such factors as temperature, winds, cloud, atmospheric pressure, humidity, dew point and frost.

TEMPERATURE

The atmosphere and the earth receive their warmth from the sun. This warmth may vary from place to place and from day to day. The degree of hotness or coldness of the air around us is called temperature. Types of precipitation depend on temperature: rain in warm weather; snow and ice in cold weather.

WIND

The horizontal movement of air relative to the surface of the earth is known as wind. The force or velocity of the wind is measured by an instrument called the anemometer. Wind vanes, weather vanes and windsocks tell the direction from which the wind is blowing.

CLOUD

Clouds are visible clusters of small water drops and/or ice particles in the atmosphere.

ATMOSPHERIC PRESSURE

The body of air which surrounds the earth is called atmosphere. Since air itself exerts pressure, the pressure of the air surrounding the earth is referred to as atmospheric pressure. At sea level, air exerts a pressure of 14.7 pounds per square inch, but a cubic yard of it weighs only about 2 pounds.

DEW

Dew is atmospheric moisture condensed as liquid upon objects cooler than air. Dew point is the temperature at which the air becomes saturated with water vapor and the relative humidity becomes 100 percent.

FROST

Frost is ice cryatals formed like dew, but at temperatures below freezing.

HUMIDITY

Humidity is the amount of moisture in the air. Relative humidity is the amount of moisture in a given body of air compared with the amount it is capable of holding at the prevailing pressure and temperature conditions.

EXPERIMENTS:

Experiment 9 - Temperature - Making An Air Thermometer

Experiment 10 - Wind - Making A Wind Anemometer

Experiment 11 - Wind - Making A Wind Vane

Experiment 12 - Wind - Making A Weather Vane

Experiment 13 - Wind - Making A Windsock

Experiment 14 - Atmospheric Pressure - Making A Barometer

Experiment 15 - Humidity - Hair Hygrometer (Detects moisture in the air)

Experiment 16 - Demonstrating Dew and Frost

Funded in part by

From
Raytheon Aviation
Educational Materials

Updated: February 23, 1999