17.1 Atmospheric

Characteristics

3/12/2015

p. 476 - 482

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Weather vs. Climate

Weather is the state of the atmosphere at

any given time and place.

– (Is constantly changing.)

Climate is based on observations of weather

collected over many years.

– (Helps describe a place or region.)

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Composition of Atmosphere

(The make-up of air can and has changed

through time.)

– (Gases from volcanoes)

– (Oxygen did not start till about 2.5 BYA.)

Major components today:

– Nitrogen (most) and Oxygen make up 99%

– Argon just less than 1% (0.93%)

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Variable (means changing)

Components of Air

Water vapor makes up clouds and precipitation

– Varies from 0 to 4%.

Ozone – a form of Oxygen that forms in the air.

– (Located 10 to 50 km.)

– (UV light splits O2 into O, O3)

– Ozone absorbs UV light Too much UV would lead death for many organisms.

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Human Influence

Primary Pollutants - toxic substances

released directly into the air.

Secondary Pollutants - toxic substances that

form when reactions take place among

primary pollutants.

– (Reactions that are triggered by strong sunlight

are called photochemical reactions.)

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Height and Structure of the

Atmosphere

The atmosphere thins as you go up.

– (Less air above to push down creating pressure.)

– (½ of the atmosphere is 5.6 km or below.)

Temperature changes as you go up.

– Is divided vertically into four layers based on

temperatures changes.

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Thermal Structure of Atmosphere

1. Troposphere – bottom thermal layer

• All weather occurs here.

• Temperature decreases with elevation.

• (Varies but on average is 0-12km.)

• Upper boundary called the tropopause.

2. Stratosphere

• Temperature increase

• Maximum ozone layer.

• Upper boundary called the stratopause.

• (20 – 50 km.)

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(Cont.)3. Mesosphere

• Temperatures again decrease

• Temperatures can reach -90°C.

• Upper boundary the Mesopause.

• (Elevation from 50 – 80km.)

4. Thermosphere – uppermost layer.

• A layer that contains only a tiny fraction of the atmosphere’s mass.

• Oxygen and Nitrogen absorb radiation causing heating of this layer.

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Earth – Sun Relationships

(Earth’s Motions)

– (Rotation – the spinning of Earth on its axis)

– (Revolution – the Earth orbiting around the sun.)

Earth’s Orientation causes seasonal

changes as Earth’s position relative to the

sun continually changes as it orbits.

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(cont. Earth’s orientation)

Earth’s axis is tilted 23 1/2° from

perpendicular.

If the axis was not tilted we would not have

seasons.

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Solstices and Equinoxes

Summer solstice – first day of summer.

– Most daylight in northern hemisphere.

Winter solstice – first day of winter.

– Least daylight in northern hemisphere.

Spring and Autumnal Equinoxes are the

two times when the Sun’s rays strike Earth

at the equator.

– Equal daylight in both hemispheres (12 hours)