Atmosphere

Atmosphere

AtmosphereLayer of gases that surrounds the EarthHeld in place by Earth’s gravity

Layers of the atmosphere

Five major layers TroposphereStratosphereMesosphereThermosphereExosphere

Atmosphere - compositionNitrogen – 78.08% Oxygen – 20.95%Argon – 0.9%Carbon dioxide – 0.03%Trace amounts of various other gasesWater vapor can make up – 0 to 4% of the atmosphere, depends on location

WeatherThe state of the atmosphere at a particular time and placeIncludes

PressureTemperatureHumidityClouds PrecipitationWindVisibility

TroposphereTroposphere – atmosphere layer closest to Earth’s surfaceMost of Earth’s weather occurs in this layerJet stream is a high altitude wind found at the upper level of the troposphereTemperature of air in troposphere decreases as you go further away from Earth’s surface

TroposphereAir in the troposphere is heated indirectly by the electromagnetic energy from the SunWhen the Sun’s energy is absorbed or reflected by the land and water on the surface of the Earth, it is converted to heat energy and transferred to the air directly above the land or water.Air closest to Earth is the warmest

Earth-Atmosphere Energy Balance Diagram

Temperature and VolumeWhen a gas is heated, it tends to expand

This tendencyis described ina law calledCharles’ Law

Temperature

Volume

DensityAmount of matter that is found in a particular volumeCompactness of matterDensity = mass ÷ volumeUnits g/mL or g/m3

DensityWhen air is heated, the molecules have more energy, move faster, and spread out. Mass does not change, but volume increasesWhen air is heated – density decreases

Unequal heating of EarthNot all parts of the Earth are heated equallyArea at the equator receives more direct sunlight and is warmer than the poles

Unequal heating of EarthWarm air at the equator rises and is less dense than cooler air at the polesCold air at the poles sinks and is more dense than warmer air at the equator

Air pressure and atmospheric motionQ: What makes the wind blow?

A: Air pressure differences.

Global air circulation patterns

Air pressureForce exerted by molecules in atmosphere due to gravity and temperature

PGF: Pressure gradient force – winds blow from high pressure to low

Where are winds the fastest?

Which pressure gradient would result in greater wind velocity?

Air Pressure and density

In a high pressure area, air will (rise, sink) because the air is (less, more) dense.

This is because the air is (cold, warm)

and (rises, sinks). Therefore, clouds CANNOT form.

In a low pressure area, air will (rise, sink) because the air is (less, more) dense.

This is because the air is (cold, warm)

and (rises, sinks). Therefore, clouds are

LIKELY to form.

Air PressureCan you feel it?

Air PressureAir pressure is the measure of the force with which air molecules push on a surface. Air Pressure is GREATEST at the surface of Earth because there is more of the atmosphere above you to push down on you.

As you move UP through the atmosphere, air pressure decreases.

Air Pressure is dependent on Density

Denser air will have a higher air pressure- there are more air molecules in a given space to push down on youLess dense air will have a lower air pressure- there are fewer air molecules to push down on you.More Dense= more particles to push down on you

Less Dense= fewer particles to push down on you

Air Pressure is affected by 3 factors

1- Elevation, or altitude

2- Temperature

3- Water content

Impact of Elevation on Air PressureAs you move up through the atmosphere, air pressure decreases.

There are fewer air molecules above you to push down on you, so the force of the air will be less.

Impact of Water Content (humidity) on Air Pressure

Moist air is less dense than dry air, and therefore has a lower air pressure.

A water molecule has less mass than other molecules that make up the air. If you replace some of the air molecules with water molecules, the water lowers the density (and lowers the air pressure)

Impact of Temperature on Air Pressure

Warm air is less dense than cold air. Therefore, warm air has a lower air pressure and cold air has a higher air pressure.

The molecules in warm air are moving fast and are spread farther apart. Therefore there are fewer air molecules in a given area to push down on you.

Warm Air Cold Air

BarometerThe piece of equipment used to measure air pressure is a BarometerAir Pressure is measured in millibars (mb) on a barometer.

Aneroid Barometer Mercury Barometer

Mercury (or Water) Barometer

Air Pressure Affects the WeatherAir pressure in a weather system reflects the amount of water in the air, which affects the weather.

Low air pressure usually results in Bad weather: stormy, cloudy, overcast.High air pressure usually results in Good weather: clear skies, no precipitation

Air Pressure on a Weather MapAreas of High and Low pressure on

shown on a weather map with an H or an L.

High Pressure

Low Pressure

Low vs. High

FrontsFront: boundary between air masses of two different densities

Warm frontWarm front: an area where a warm air mass is replacing a cooler air mass

Cold frontCold front: an area where a cold air mass is replacing a warmer air mass

Animation of FrontsAnimation of Fronts

low pressure

high pressure

warm or cold air warm cold

air rising or sinking rising sinking

clouds or no clouds clouds no clouds

molecules move fast or slow fast slow

molecules are packed together or far apart

far apart, less dense

packed together,

densemoist or dry moist dry