Meteorology Notes Part IIAtmosphere Composition and Structure

Effect of Earth’s shape and tilt on weather and seasons

Air Mass Types and FormationGlobal Wind Systems and Ocean Currents

• About 99% of the atmosphere is composed of nitrogen and oxygen.

• 21% is oxygen• The other 1% is made

up of argon, hydrogen, carbon dioxide, water vapor, and other gases

• The amount of water vapor in the air varies from 0% to 4%. It depends on altitude of air mass, surface features beneath air, and season.

• The atmosphere also consists of tiny dust and salt particles, which are necessary in cloud formation.

• Ozone (O3) is also found in the atmosphere. It exists in small quantities in a layer will above the earths surface. It absorbs ultraviolet light from the sun. Why is this important?

• Greenhouse gases are gases near the surface that absorb radiation causing a temperature increase. Carbon Dioxide is an important one that can cause temperatures to rise.

• The atmosphere is made up of several different layers.

• Each layer has a different composition and a different temperature profile.

Troposphere-Gradual decrease in temperature from bottom to top because it is heated by the Earth’s surface

-Layer closest to the Earth’s surface

-Contains the most mass of the atmosphere

-Most weather (clouds, etc.) takes place here

-Layer where most pollution collects

-The top of the troposphere is called the Tropopause (9km – 16km); Gradual decrease in temperature stops.

Stratosphere-Located above the tropopause

-Layer primary made up of concentrated ozone with the majority near the stratopause

-Ozone absorbs ultraviolet radiation causing temperature to rise as height increases from the bottom to the top of the stratosphere.

The stratopause is located above the stratosphere where temperature stops increasing

MesosphereLocated above the stratopauseNo ozone = no gases to absorb radiation and warm the layer = gradual decrease in temperatureMesopause is the boundary between the mesosphere and the next layer, the thermosphere.

ThermosphereMinute portion of atmosphere’s massAir again increases in temperature in this layer, this time to more than 1000 degrees Celsius

Exosphere & IonosphereThe ionosphere is part of the thermosphere.The ionosphere is made up of electrically charged particles and layers of progressively lighter gases.

-Interaction of the solar wind from the sun with the ionosphere creates the Auroras

The Exosphere, above the Thermosphere, is so thin that most scientists actually consider this the beginning of space.Light gases, like helium and hydrogen, are found in this layer.There is no clear boundary between the atmosphere and outer space.

How is radiation distributed around the planet??

• Not evenly – therefore, areas with more direct radiation heat more than those with indirect radiation

• Temperature varies with the angle of the sun

Earth’s axis is tilted relative to the ecliptic at approximately 23.5 degrees

-As Earth orbits the sun this tilt angle never changes - the Earth’s axis stays fixed in space.

-Our seasons are created by this tilt and the Earth’s revolution around the Sun.

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-As the Earth moves around the sun each year, the altitude of the sun in our sky changes. At the solstices, the axis either points directly at or away from the Sun.

1.) Summer solstice- the Sun’s maximum altitude in the sky.

2.) Winter solstice- the Sun’s lowest altitude in the sky.

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-At the equinoxes, the Earth’s axis is beside the Sun, not towards or away.

1.) As a result, both hemispheres receive equal amount of light. The lengths of day and night are also equal

2.) There are two equinoxes – autumnal and vernal.

-Because of the tilt, we have some special latitudes on Earth.

a. On the equinoxes, the Sun is directly overhead on the equator.

                                                 

b. On the Summer Solstice, around June 20, the Sun is directly overhead at 23.5º N. latitude, the Tropic of Cancer.

c. On the Winter Solstice, around Dec. 20, the Sun is directly overhead at 23.5º S. latitude, the Tropic of Capricorn.

Air Mass – a large body of air that takes on the characteristics of the area over which it forms

– Source region can be either land (continental) or water (maritime), near the poles or near the equator (tropic)

• Less moisture over land, more over the ocean • Warmer near the equator, colder near the poles

TypescT – continental tropic

– warm + drymT – maritime tropic

– warm + humidcP – continental polar

– cold + drymP – maritime polar

– cold + humidA – artic – very cold and dry – associated with high

pressure

Notice: Each type tells you the source region and the temperature

Humid

Or

Dry?

Cold

Or

Warm?

Air Masses

World Heat Transfer

• Unequal distribution of radiation causes a difference in temperature between the equator and the poles.

• If the Earth did not spin, then this would cause air to move directly from the equator to the poles. However, the Earth’s turn causes a strange effect called the Coriolis effect.

Coriolis Effect• The Coriolis effect is the

APPARENT deflection of air particles due to the rotation of the Earth.– Air in the northern

hemisphere is deflected to the right.

– Air in the southern hemisphere is deflected to the left.

http://www.nasa.gov/audience/forstudents/brainbites/nonflash/bb_home_corioliseffect.html

http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/crls.rxml

Stop and Think #1

• Does the Earth Turn Two Different Ways?• Now, in your assigned group, take your globe

and turn it towards the EAST.• Look at the globe from the North Pole. Is it

turning clockwise or counter-clockwise?• Now, look at the globe from the South Pole. Is

it turning clockwise or counter-clockwise?

World Wind Belts

• The differential heating of the earth causes huge convection cells around the Earth.

http://www.atmo.arizona.edu/products/wximagery/globalir.html

Global Wind Systems• Three basic wind systems in

each hemisphere.– 1. Trade Winds

• Easterly winds between 30 degrees N and S of the equator

– 2. Prevailing Westerlies• One in Northern and Southern

hemispheres between 30 and 60 degrees latitude

– 3. Polar Easterlies• One in Northern and Southern

hemisphere between 60 degrees and the pole

Horse Latitudes – at 30 degrees N and S latitude where there are light winds and clear skiesDoldrums (ITCZ) – near the equator where there are frequent storms and heavy rains

Jet Streams• At the boundaries between the wind zones air differs

greatly in pressure and temperature.– This difference causes wind.

• Jet streams are narrow bands of high altitude, fast moving, westerly winds.– Speeds of 185 km/h– Altitudes of 10.7 – 12.2 km (located near the tropopause)

http://www.pbs.org/wgbh/nova/vanished/jetstream.html

Ocean Currents

• Ocean currents move water from place to place.

• There are two types of ocean currents: deep ocean currents (density currents) and surface currents.

Deep Ocean Currents

• Deep ocean currents are also called density currents since they are caused by differences in density.

• These currents move slowly in deep ocean waters.

• For example, Antarctic Bottom Water forms at the South pole, sinks because it is very dense (cold and salty) and moves towards the Equator.

Surface Currents

• Surface currents are caused by wind at the surface.

• They affect the upper few hundred meters of the ocean.

• They move much faster – even 100 km per day

Gyres• Surface currents are deflected by landmasses.• This causes them to form circular current

systems, called Gyres.• Gyres rotate clockwise in the northern

hemisphere and counter clockwise in the southern hemisphere.