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