Atmospheric Pressure and Wind Chapter 15 Section 3

Why Air Moves Wind is created by differences in air pressure Warm air is less dense and creates areas of low pressure Warm air rises Cold air is more dense and creates areas of high pressure Cold air sinks Surface winds blow from polar high-pressure areas to equatorial low-pressure areas

Why Air Moves The uneven heating of the Earth produces pressure belt, this happens in increments of 30 degrees latitude Air doesn’t move in one large circular pattern from the poles to the equator At 30 degrees N & S the warm air from the equator cools and sinks At the poles the cold air sinks and starts to warm and become less dense at 60 degrees N & S and rise The curving of moving objects, such as wind, by the Earth’s rotation is called the Coriolis effect

Types of Winds There are two types of winds; local & global winds Global winds are part of a pattern of air circulation that moves across the Earth These winds travel longer distances The winds that blow from 30 degrees latitude to the equator in the north & south hemisphere is called trade winds The area of low pressure at the equator is known as the Doldrums

Types of Winds The Westerlies are wind belts found in both the Northern and Southern Hemispheres between 30 and 60 degrees latitude The polar easterlies are wind belts that extend from the poles to 60 degrees latitude in both hemispheres The jet streams are narrow belts of high-speed winds that blow in the upper troposphere & lower stratosphere

Types of Winds Local winds are influenced by the geography of an area As air warms and becomes less dense it rises and produces lower pressure Colder air becomes more dense and sinks producing areas of high pressure A land breeze is produced by an area of low pressure over the water The water hold stays warmer than the land does at night causing the air to warm and rise pulling the cooler land air out to the sea

Types of Winds A sea breeze occurs when a land mass heats the air above it, the warmer less dense air rises and is replace by cooler more dense from the sea A mountain breeze occurs when the mountains cool quicker than the valley below, the cool mountain air is more dense and sinks into the valley A valley breeze occurs when the valley air heats up during the day, the warmer less dense air moves up the mountains face