the atmosphere earth science spring 2013. characteristics of the atmosphere atmosphere- layer of...

The Atmosphere

Earth Science Spring 2013

Characteristics of the Atmosphere

• Atmosphere- layer of gases & tiny particles that surrounds the earth

• Study of the atmosphere is meteorology – Study:• Characteristics of the atmosphere• Weather- general condition of the atmosphere at a

particular time & place including temperature, air movements, & moisture content• Climate – general weather conditions over many years


• Composition– Most abundant elements in the atmosphere are

the gases: nitrogen, oxygen, & argon – Most abundant compounds are: carbon dioxide &

water vapor • Water vapor is added by evaporation & is removed by

condensation & precipitation


• Composition cont…– Ozone- oxygen molecules that has 3 oxygens • Protects the living things on earth from UV radiation of

the sun • CFCs (chlorofluorocarbons) break down ozone

– Atmospheric dust • Mineral particles lifted into the atmosphere by wind,

ash from fires, volcanic dust, & some microscopic organisms

Characteristics in the Atmosphere

• Oxygen in the Atmosphere– Animals, bacteria, & plants remove oxygen from

the atmosphere as part of their life processes – Other things that remove oxygen: forest fires,

burning of fuels, & the weathering of some rocks – Land & ocean plants produce oxygen through

photosynthesis


• Nitrogen in the Atmosphere – Amount of nitrogen in the air is maintained

through the nitrogen cycle– Nitrogen cycle• Nitrogen moves from the air to the soil, to plants and

animals, & back again to the air • Nitrogen is removed primarily by nitrogen-fixing

bacteria


• Atmospheric Pressure– Ratio of the force of the air to the area of the

surface on which it puts pressure – Atmospheric pressure is high at lower altitudes &

lower at higher altitudes • Gravity pulls of the gases of the atmosphere toward the

earth’s surface & holds them there…the closer you are to the earth’s surface the more gravitational pull there is so the more air there is


• Barometers– Barometer- instrument used to measure pressure • Mercurial barometer- well of mercury is pressed on by

the air forcing it to rise up a tube to certain height– Pressure is measured in mm of mercury– 760mm Hg = 1 atmosphere which is standard atmospheric

pressure (pressure at sea level)– Weather maps use millbars (mb)- 1 mb = 0.001 of standard

atmospheric pressure


• Barometers cont…– Aneroid barometer• Most commonly used today• No liquid in it• A sealed metal container with no air inside of it

– Sides bend inward when pressure rises – Sides return closer to original shape as pressure drops

• Can also measure altitude (altimeter)


• Layers of the Atmosphere– Altitude ↑ Air pressure ↓ rapidly – Distinct differences in temperature with ↑altitude• Due to the way solar energy is absorbed as it moves

downward though the atmosphere


• Air Pollution – Air pollutant- any substance in the atmosphere that is harmful

to people, animals, and plants • Sulfur dioxide, carbon dioxide, lead, & hydrocarbons • Main source is burning fossil fuels

– coal– Petroleum fuels

– Acid precipitation- when air pollutants becomes trapped in the atmosphere & return to the earth’s surface as precipitation

– Temperature inversion- warm air on top of cool air prevents the cool air from escaping allowing air pollutants to concentrate

Solar Energy & The Atmosphere

• Radiation – All the energy that earth receives from the sun

travels through space between the earth and the sun as radiation. • Light is a form of radiation we can see• There are many forms of radiation we cannot see

– Radiation travels through space in the form of waves at high speed


• Radiation cont...– Electromagnetic spectrum- complete range of

wavelengths of radation • Wavelengths vary....

– Range from very long to very short

• Almost all of the energy reaching the earth from the sun is in the form of electromagnetic waves – Almost all of the shorter wavelengths of the electromagnetic

spectrum are absorbed in the upper layers of the atmosphere» Small amount of UV radiation reaches the Earth

– Most of the radiation that comes through the atmosphere to the earth’s surface is infrared and visible light


• Scattering– Scattering is caused by clouds, dust, and gas

molecules in the atmosphere– Scattering- when dust & water droplets trapped in

the atmosphere reflect & bend the rays • Causes rays to bend and go in all different directions

changing their wavelengths • Sends some back into space

– Makes the sky appear blue


• Reflection– Of the solar energy reaching the earth • 20% absorbed by the atmosphere• 30% scattered back into space or is reflected from the

clouds or the earth’s surface • 50% absorbed by the surface


• Absorption & Infrared Energy – Part of the absorbed radiation is made up of

infrared rays• Warmth of the sun on your skin & other surfaces on the

earth that are warm have absorbed infrared rays – Heated materials radiate their own infrared rays after they

have absorbed them» Ex: warm rocks or concrete


• The Greenhouse Effect – When the earth’s atmosphere traps infrared rays

over the earth’s surface • The visible & infrared rays of incoming sunlight pass

through the water vapor & carbon dioxide of the atmosphere. • Most of the longer infrared rays sent out by the

warmed surfaces on the earth are trapped by water vapor & carbon dioxide keeping them closer to earth• Causes the earth’s temperature to be much warmer

than it would be without an atmosphere


• Variation in Temperature– Radiation from the sun does not heat the earth

equally– Several factors affect how warm an area is:• Latitude (primary factor): the closer you are to the

equator the more direct sunlight you receive• Elevation: high elevation is warmer during the day but

becomes much cooler at night very quickly • Proximity to large bodies of water


• Conduction & Convection– Conduction• Molecules move faster as a substance is heated causing

other molecules to move faster – Makes the substance warmer

– Convection• Movement of liquids or gases when they are heated

unevenly • Causes cooler air to push warmer air up

Winds

• Pressure differences in the atmosphere at the equator and the poles create a general movement of air worldwide – Air moves from high-pressure belts toward low-

pressure belts • Air typically moves from the poles toward the equator

Winds

• Global Winds – Winds are strongly deflected by the Coriolis Effect • Winds that would blow directly from high-pressure to

low-pressure areas are deflected

– Convection cells- air flowing from the equator completes three looping patterns of air flow• Northern & Southern hemispheres each have 3

convection cells

Winds

• Global Winds– Trade Winds

• Wind flowing toward the equator from 30 degrees to 0 degrees latitude

• Named according to the direction from which they flow – Northeast trades are deflected to the right by the Coriolis effect – Southeast trades are deflected to the left by the Coriolis effect

• Doldrums- where the trade winds from the two hemispheres meet – Weak & unpredictable winds

• Horse latitudes- descending air creates a high pressure belt near 30 degrees – Weak winds

Winds

• Westerlies– Caused by air moving toward the poles being

deflected by the Coriolis Effect – Found in both hemispheres • Northern Hemisphere- southwest winds • Southern Hemisphere-northwest winds

– Located between 40 & 60 degrees latitude • Contiguous US is located within the westerlies • Hawaii is in the northeast trade winds• Parts of Alaska are in the polar easterlies

Winds

• Polar Easterlies– Above 60 degrees latitude – Caused by subpolar lows • Subpolar lows are caused by warm air moving toward

the poles & it is pushed up by the cold air moving toward the equator

– Cause storms when they meet warm air from the westerlies forming polar fronts

Winds

• Wind & Pressure Shifts– Positions of pressure belts & wind belts shift as

the sun’s vertical rays shift northward & southward during the year

– Some areas experience different wind belts during the year • Ex: Florida get westerlies in the winter & trade wind in

the summer

Winds

• Jet Streams – Upper westerly winds that are bands of high

speed winds in the upper troposphere & lower stratosphere

– Caused by large pressure differences due to the temperature differences between polar air and mid-latitude air

– Polar jet streams control the paths of storms & affect air line routes

Winds

• Local Winds – Not part of global wind belts – Breezes are light wind that extend over a distance

of less than 100km • 2 types:

– Land & sea breezes – Mountain & valley breezes

Winds

• Land & Sea Breezes – Caused by temperature differences • Land heats up much more quickly than a large body of

water creating a significant temperature different resulting in a significant pressure difference

– Sea breeze- wind moving from water to land – Land breeze- wind moving from land to water

Winds

• Mountain & Valley Breezes – Valley breeze- blows up the slopes during the

daytime• Caused by warm air moving from the valley up the

slope

– Mountain breeze- blows down the slope in to the valley• Caused by cool air moving flowing down the slope

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