UNIT 1LESSON 3

PRESSURE

OVERVIEW 

Describe how pressure is measured and determine how the atmosphere is affected by pressure.

OUTLINE

Pressure is one of the most important parameters in meteorology. A knowledge of the distribution of air and the resultant variations in air pressure over the earth is vital in understanding Earths fascinating weather patterns.

Learning Objective: Describe how pressure is measured and determine how the atmos-phere is affected by pressure.

Pressure is the force per unit area. Atmos-pheric pressure is the force per unit area exerted by the atmosphere in any part of the atmospheric envelope. Therefore, the greater the force exerted by the air for any given area, the greater the pressure. Although the pressure varies on a horizontal plane from day to day, the greatest pressure variations are with changes in altitude. Nevertheless, horizontal variations of pressure are ultimately important in meteorology because the variations affect weather conditions.

Pressure is force, and force is related to acceleration and mass by Newtons second law. This law states that acceleration of a body is directly proportional to the force exerted on the body and inversely proportional to the mass of that body. It may be expressed as

where "a" is the acceleration, "F" is the force exerted, and "m" is the mass of the body. This is probably the most important equation in the mechanics of physics dealing with force and motion.

NOTE: Be sure to use units of mass and not units of weight when applying this equation.

Atmospheric pressure is normally measured in meteorology by the use of a mercurial or aneroid barometer. Pressure is measured in many different units. One atmosphere of pressure is 29.92 inches of mercury or 1,013.25 millibars. These measurements are made under established standard conditions.

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