Unit 3: Meteorology Part 2 Air pressure and Winds

Air Pressure REVIEW

Air Pressure Air pressure = force that is the result of the mass and weight of a column of air pushing down on an area Air in the atmosphere has pressure because air has mass. The less air there is in a given volume, the less dense the air Air at higher altitudes have less dense air, which means less pressure.

Measuring Air Pressure Barometer: device that is used to measure air pressure Two types of barometers Aneroid Measure the bulges in a thin metal disk that covers a chamber. Mercury Measures the height of mercury that is in a glass tube

Isobars and Air Pressure Air pressure is an important factor that affects weather Changes in air pressure help meteorologists predict how weather will change

Isobars and Air Pressure (cont.) Air pressure readings from barometers are shown on weather maps with lines called isobars Isobars = lines on a weather map that are drawn to connect areas that have the same air pressure

Dry Air vs. Wet Air Dry Air = 99% N and O Wet Air = 96% N and O Mass = 1,200 g/m³ Wet Air = 96% N and O Mass = 1,190 g/m³

Dry Air vs. Wet Air Dry air weighs more than humid (wet) air When drier air moves into a region, air pressure will increase Dry air has more mass (more molecules) When wet air moves into a region, air pressure will decrease Wet air has less mass (less molecules)

Low Pressure Warmer air As the warm air rises, it begins to cool atoms are more spread out Less pressure As the warm air rises, it begins to cool Capacity decreases Water begins to condense Energy is released because of the condensation Clouds develop Energy that is released powers storms

High Pressure Colder Air As the cold air sinks, it begins to warm Atoms are more “packed” together High pressure As the cold air sinks, it begins to warm Capacity increases Water evaporates and stays as water vapor (gas form) Clouds are unable to develop Clear skies!

Low Pressure vs. High Pressure

Air Movement Up and down movement of air creates cloudy or clear skies Low pressure (Rising air ) = cloudy High Pressure (Sinking air) = clear

WIND

What is wind? Wind = when air moves from high pressure to low pressure Two types of wind: Global Local

Global Winds HIGH PRESSURE Caused by differences in air pressure due to heating differences on Earth Low pressure at the equator High pressure at the poles These differences cause global wind patterns that determine climate for each region LOW PRESSURE

Global winds are named for the direction that they blow FROM.

Coriolis Effect Air moves from high pressure (poles) to low pressure (equator) So why doesn’t the wind move straight from the poles the to equator? The Earth ROTATES! Because the Earth rotates or spins, the winds seem to curve. This is called the Coriolis Effect.

Jet Streams POLAR EASTERLIES Jet Stream = boundaries between the polar easterlies and the prevailing westerlies PREVAILING WESTERLIES

Jet Streams

Local Winds Caused by a difference in air pressure at the surface of the Earth Winds are created when air shifts from high pressure to low pressure REMEMBER, global winds are caused by heating differences, not pressure differences.

Understanding Local Breezes Which heats up faster and gets hotter? Land or Water Which cools down faster and gets colder? During the day, when the sun is out, which would be warmer? During the night, when the sun is down, which would be cooler?