What is pressure? Pressure is accumulative force of gas particles High Energy gas (HOT) has lots of movement, therefore.

What is pressure?

Pressure is accumulative force of gas particles

http://www.falstad.com/gas/

High Energy gas (HOT) has lots of movement, therefore high pressure

Low Energy (COLD) has less pressure

How do we measure pressure?Using a Barometer

The height of the Mercury Column is equal to the pressure acting on the surface of the mercury

P = gh

P = (density)(gravity)(height)

Two Types of Pressure Systems Occur in Nature

Low Pressure Systems - “Cyclones”

High Pressure Systems - “Anti-Cyclones”

Each type has specific characteristics related to the behavior of the gases that make up the system and how they interact with each other

High Pressure Systems - “Anti-Cyclones”

Winds blow outward and clockwise at surface

Associated with converging winds higher in the atmosphere

Weather: clear and “fair”

Low Pressure Systems

Winds blow inward and counterclockwise at surface

Associated with diverging winds higher in the atmosphere

Weather: cloudy with precipitation (rising air)

What is Wind?

Wind is the movement of Air

Wind forms as a result of three factors:

Pressure Gradient Force

Coriolis Effect

Friction with the Earth’s Surface:

Pressure Gradients

Air wants to move from high to low pressure (greater pressure difference = higher speed)

Isobars = lines of equal pressure

Coriolis Effect: Same effect as for ocean currents

Moving air (wind) is deflected to the right of intended path

Creates rotational movement

Friction with the Earth’s Surface

As air moves across the Earth’s surface, it is slowed by contact with features of the Earth’s surface

This slows down surface level winds, but also creates mixing because higher level winds continue at higher velocities

Wind is measured using two devices

SPEED is measured using an ANEMOMETER

DIRECTION is measured using a WEATHER VANE

• Local Winds are caused by temperature differences.

• Two common types include :Sea and Land Breezes: Occur in coastal areas

• Sea Breeze

• During the day, the land warms up because of the sun. Air rises over the land.

• To replace this air, cooler air from the sea flows towards the land (sea breeze)

• Land Breeze

• c. During the night, the ocean is warmer than the land. Air rises over the ocean.

• d. To replace this air, cooler air from the land flows towards the sea (land breeze)

• II. Mountain and Valley Breezes

• a. Valley Breeze: During the DAY air on the slopes of mountains heats up and moves up the mountain slope

• b. Mountain Breeze: At NIGHT air near the mountain top cools more quickly than air lower down, so it flows down slope towards the valley

Sea and Land Breezes (cont’d)

• Land Breeze

• During the night, the ocean is warmer than the land. Air rises over the ocean.

• To replace this air, cooler air from the land flows towards the sea (land breeze)

Day = Sea Breeze

Night = Land Breeze

• Mountain and Valley Breezes

• Valley Breeze: During the DAY air on the slopes of mountains heats up and moves up the mountain slope

• Mountain Breeze: At NIGHT air near the mountain top cools more quickly than air lower down, so it flows down slope towards the valley

Valley Breezes

Mountain Breezes