Pressure Gradients

CHAPTER TWO

AVIATION WEATHER

Figure 2-3 Typical Surface Analysis Chart

Pressure Gradients

The spacing of isobars indicates the rate of pressure change over a horizontal distance. In

Figure 2-4, the isobars are more closely spaced to the east than they are to the west, indicating

that pressure changes more rapidly on the eastern side. The rate of pressure change in a direction

perpendicular to the isobars (horizontal distance) is called the pressure gradient and this isobar

spacing represents the size of the pressure gradient force (PGF). The PGF is steep or strong,

when isobars are close together and is shallow or weak, when the isobars are far apart; the

steeper the gradient, the stronger the winds. The PGF is the initial movement of air from high

pressure to low pressure, thus it is the initiating force for wind.

2-6 Atmospheric Mechanics of Winds, Clouds and Moisture, and Atmospheric Stability