Movement of Pressure Systems and Large Scale Wind Patterns

AVIATION WEATHER

CHAPTER TWO

Figure 2-7 Surface Winds are Deflected Across Isobars Towards Lower Pressure

Gradient:

Surface:

Figure 2-8 Surface Winds Relates to Gradient Wind Above It

Buys Ballot's Law, A Rule Of Thumb

A rule of thumb to help remember the direction of the wind in relation to a pressure system is

Buys Ballot's Law. This law states that if the wind is at your back, the area of lower pressure

will be to your left. When standing on the Earth's surface, the low will be slightly forward or

directly left because the winds flow across the isobars.

Movement of Pressure Systems and Large Scale Wind Patterns

Weather in the Temperate Zone (which includes the U.S.) and farther north changes almost

constantly with the passage of highs and lows. These migrating systems move from west to east

with the prevailing westerly winds. They are accompanied by wind shifts, and with some

exceptions, large and rapid changes in temperature and broad areas of precipitation. These

systems furnish the most significant means of heat transfer between high and low latitudes.

The Jet Stream

Wind speeds generally increase with height through the troposphere, reaching a maximum near

the tropopause, and often culminating in the jet stream. The jet stream is a narrow band of strong

winds of 50 knots or more that meanders vertically and horizontally around the hemisphere in

wave-like patterns. The jet streams (polar and subtropical) have a profound influence on weather

patterns.

Atmospheric Mechanics of Winds, Clouds and Moisture, and Atmospheric Stability

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