Describe how pressure is
measured and determine how the atmosphere is affected by pressure.
OUTLINE Definition Standards of Measurement Standard Atmosphere Vertical Distribution Pascal’s Law PRESSURE Pressure is one of the most important
Standards of Measurement
Pressure is one of the most importantparameters in meteorology. A knowledge of the distribution of air and the resultant variations in air pressure over the earth is vital in understanding Earth’s fascinating weather patterns.
Learning Objective: Describe how pressureis measured and determine how the atmos-phere is affected by pressure.
Pressure is the force per unit area. Atmos-phericpressure 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 Newton’s second law. This law states that acceleration of a body is directly proportional to the force exerted on thebody and inversely proportional to the mass of that body. It may be expressed as
NOTE: Be sure to use units of mass and not
NOTE: Be sure to use units of mass and notunits of weight when applying this equation.
STANDARDS OF MEASUREMENT
Atmospheric pressure is normally measuredin 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.