The Weather

Atmospheric Movement in Weather Change Atmospheric Movement in Weather Change

WeatherWeather The short-term (a few hours or days) The short-term (a few hours or days)

condition of the atmosphere at a condition of the atmosphere at a given location. given location. WaterWater and and airair move move constantly---together they create constantly---together they create WEATHER!WEATHER!– The weather of an area is due to four The weather of an area is due to four

atmospheric factorsatmospheric factors: heat energy, air pressure, winds, and moisture..

MeteorologistsMeteorologists are are scientists who study scientists who study and predict the weatherand predict the weather

Weather is the condition of Weather is the condition of Earth’s atmosphere at a Earth’s atmosphere at a particular time and place.particular time and place.

Composition of the Atmosphere

Oxygen and nitrogen = 99% of dry air. Carbon dioxide and argon make up most of the

other one percent (1%). The remaining gases are called trace gases

because only small amounts of them are present.

Composition of the Composition of the AtmosphereAtmosphere

Nitrogen is the most abundant gas in the atmosphere– Makes up a little more than three fourths of

the air we breathe– Essential to living things

Most living things cannot obtain nitrogen directly from the air

– Bacteria convert nitrogen into substances – Plants then absorb the nitrates from the soil and use

them to make proteins. – Animals must eat plants or other animals.

Getting Energy

All energy on Earth All energy on Earth comes from the Suncomes from the Sun

RadiationRadiation – is the absorption of energy.

Energy travels from the sun in electromagnetic waves.

These waves are absorbed by the things on earth.

(Ground is warmed by (Ground is warmed by radiation)radiation)

HeatHeat is is transferred to transferred to the air when the air when

the air touches the air touches the ground.the ground.

The warmer something The warmer something gets the more energy its gets the more energy its

molecules have. molecules have.

The more energy The more energy molecules have the faster molecules have the faster

they move.they move.

The faster molecules The faster molecules move the more volume move the more volume (space) they take up.(space) they take up.

The solar radiation The solar radiation heats the surface heats the surface

of the earth.of the earth.

Heat is transferred to air Heat is transferred to air molecules that come in contact molecules that come in contact

with the ground.with the ground.

As the As the

Hot Air Rises…Hot Air Rises…

Cooler air is Cooler air is pulled in pulled in

from other from other placesplaces

Do you Do you know what know what this is this is called?called?

Air PressureAir Pressure Air pressure occurs as a result Air pressure occurs as a result

of the of the weightweight of the air pressing of the air pressing down on the Earth. Caused of down on the Earth. Caused of course by Earth’s gravity.course by Earth’s gravity.

A A changechange in air pressure in air pressure usually indicates a change in usually indicates a change in weatherweather is going to occur. is going to occur.

A body of air that has A body of air that has similar similar temperature, humidity, and air temperature, humidity, and air pressure is called an air mass.pressure is called an air mass.

There is a column of air above you all the time. The weight of the air in the atmosphere causes air pressure.

Air pushes in all directions—down, up, and sidewaysAir pushes in all directions—down, up, and sideways

As the air

becomes less

dense it rises

Ground warmed by radiation

Ground warmed by radiation

Rising air spreads heat throughout the atmosphere.

Increasing AltitudeIncreasing Altitude

Altitude, or elevation, is the distance

above sea level

Air pressure decreases as altitude

increases.

As air pressure decreases, so does

density.

Why does air pressure decrease as altitude increases ?

If you are on the top of a mountain, the air If you are on the top of a mountain, the air pressure is lower because the column of air pressure is lower because the column of air above you is shorter. above you is shorter.

If you are at sea level, the column of air is If you are at sea level, the column of air is taller (pushing down on you), and that taller (pushing down on you), and that means there is more air pressure. means there is more air pressure.

Air Pressure  

An air mass with An air mass with lowlow pressure pressure

is likely to be is likely to be stormystormy. . An air mass with An air mass with highhigh pressure pressure

is likely to be is likely to be fairfair. . Air moves from areas of Air moves from areas of highhigh

pressure pressure to to areas of areas of lowlow pressure. pressure.

This movement occurs as the This movement occurs as the differences in air pressure differences in air pressure cause windcause wind. .

The Wind Winds are the result of

uneven heating of the Earth’s surface

This uneven heating causes differences in air pressure to develop.

Where Does Wind Go?

Winds always blow from areas of high pressure to areas of low pressure.– The closer wind

is to the low pressure area the faster it blows.

Pacific Ocean

Atlantic Ocean

Gulf of Mexico

Moves pressure Moves pressure systems from systems from WestWest

to to EastEast..

Air MassesAir Masses

Air massesAir masses are large are large bodies of air classified bodies of air classified by their by their temperaturetemperature (warm or cold) and (warm or cold) and

amount of amount of waterwater (wet (wet or dry). or dry).

Warm FrontWarm Front

COLD FRONTCOLD FRONT

Stationary FrontStationary Front

Occluded FrontOccluded Front