Aim: Why does air move?

Do now: What type of pressure would you expect inside a hurricane?

High or Low Pressure

Notepack 35

What is Air Pressure?

• Air is made up of atoms (oxygen, carbon, nitrogen).

• Atoms have weight (extremely little weight)

• Because the atmosphere is thick, there is a lot of atoms between the ground and space.

• The weight of the air directly above the ground to the edge of space is known as air pressure.

• On average this weight is about 14.7 pounds per square inch or one ATM (atmosphere).

What is Wind? • Wind is the movement

of air from one area to another.

• Wind can be spermatic, like a breeze; or it can be uniformed and unidirectional, like the Jet Stream.

• Wind and move in a straight line or in a circular matter.

What does we use to Measure Wind? • To measure the direction

of wind we use a wind vane.

• The direction of wind is always the direction in which the wind is coming from.

• To measure wind spend, we use an anemometer.

Factors Causing Wind – Earth’s Rotation

• As the Earth rotates, the moving ground is pulling the air above it.

• This friction between the Earth and the atmosphere creates air currents that move from west to east.

• Most of the major jet stream (high altitude air currents) run west to east.

Factors Causing Wind – Earth’s Convection Currents

• Because the Earth is round and on a tilt, Earth’s surface do not heat up evenly.

• Areas where the air heats up, the air is less dense causing it to rise.

• As this air cools, it becomes more dense.

• This movement of air rising and sinking creates convection currents.

• The winds that are created are called trade winds and these winds are constant.

Factors Causing Wind – Uneven Surface Heating

• Surfaces that are hot tend to heat the air that’s above it.

• This warm air rises creating low air pressure.

• Surfaces that are cold tend to cool the air that’s above it.

• This cool air sinks creating high air pressure.

• This change in air pressure creates wind.

• Air tends to move from an area of high pressure to an area of low.

High Pressure

Low Pressure

IMPORTANT!!! PUT IN NOTES!!! I FORGOT

• When there is a high pressure area and a low pressure area in the northern hemisphere –

– The air moves out from the high pressure system (H) in a clockwise direction.

– The air moves in from the low pressure system (L) in a counter clockwise direction.

H L

Why is measuring air pressure important?

• As the air pressure rises, the better the weather will be.

• As the air pressure drops, the worse the weather will be.

Coastal Breezes • At the coast there are 2 large masses, the land and

the water.

• The land and the water have different specific heats, which means that they both absorb and radiate heat differently.

Coastal Breezes • In the daytime, both the ocean and the land are

absorbing heat from the Sun.

• Because the land has a low specific heat than the water, the land heats up faster than the water.

• This causes the air above the land to also heat up.

• Warm air rises creating low pressure.

• Because the air above the water is cooler, it is also heavier (high pressure)

• The high pressure air always moves towards the low pressure, which means that there is a breeze from the ocean to the land in the daytime.

The sand heats up fast because it has a low

specific heat

The water heats up slowly because it has a

high specific heat

The Land Breeze • In the nighttime, both the ocean and the land radiate

(giving off) heat.

• Because the land has a low specific heat than the water, the land cools faster than the water.

• This causes the air above the land too also cool down.

• But because water has a high specific heat, it takes a longer time for the water to cool.

• Because the air above the water remains warmer than the land air, the ocean air rises (low pressure)

• The high pressure air from the land moves to low pressure of the water causing a breeze from the land to the ocean in the nighttime.

The water cools down slowly because it has a

high specific heat

The sand cools down quickly because it has a

low specific heat