Chapter 17.1Atmospheric Characteristics

What is Weather?• Weather is constantly

changing, and it refers to the state of the atmosphere at any given time and place.

• Climate, however, is based on observations of weather that have been collected over many years. Climate helps describe a place or region.

Is this map an example of weather or climate?

Composition of the Atmosphere

• Air is a mixture of different gases and particles, each with its own physical properties

• Carbon dioxide is present in very small amounts but plays a significant role in heating the atmosphere because:

• It absorbs heat given off by Earth. It also absorbs some solar energy.

What is the most abundant gas in Earth’s atmosphere?

Is this gas important meteorologically?

What is the most abundant gas in Earth’s atmosphere?

Nitrogen

Is this gas important meteorologically?NO

Minor Components of the Atmosphere

• Water Vapor• Varies from none to about

4%• It is the source of all clouds

and precipitation• It is important because it

absorbs heat given off from Earth’s surface. It also absorbs incoming solar energy

Minor Components of the Atmosphere cont.

• Latent Heat• This is the term used to

describe the heat energy that is released when water vapor changes from one state to another. (freezing, melting, condensation, etc.)

Latent heat is the energy source that drives weather, especially severe weather.

Which phase changes absorb energy?

Which phase changes release energy?

Which phase changes absorb energy?Melting and evaporation

Which phase changes release energy?

Condensation and freezing

Minor components: continued

• Particles – also known as: Aerosols

• From both man-made and natural sources

• Examples include emissions from vehicles

• These particles (aerosols) are important as they act as the surface for water vapor to condense, forming clouds

• These particles can absorb or reflect incoming solar radiation

• They also contribute to varied hues of red and orange sunrises and sunsets.

What is the importance of aerosols to weather?

The particles provide a solid surface for water vapor to condense on (condensation nuclei)

They absorb and reflect solar radiation, which can change temperatures. . .

Followed by changes in weather

Ozone• A form of oxygen that

combines Three oxygen molecules

• O3

• Not the same oxygen as we breathe (O2)

• There is very little ozone in the atmosphere, distributed unevenly, between 10 & 50 Km

• Ozone is concentrated in the stratosphere

• At this altitude oxygen molecules are split into single atoms of oxygen

The ozone layer is crucial to life on Earth. Ozone absorbs potentially harmful UV radiation from the Sun

Why is the ozone layer important to all life forms on Earth?

Ozone protects all living things by filtering our a large portion of the dangerous Ultra Violet rays

Without ozone we would not be able to stay outside exposed to the Sun for very long before it

could cause severe burns

Human influence

• Primary pollutants are emitted directly from identifiable sources

• Emissions from transportation vehicles account for nearly half of the primary pollutants by weight

Human Influence cont.

• Secondary pollutants are not emitted directly into air. The form in the atmosphere when reactions take place between primary pollutants and other substances

• This noxious mixture is called photochemical smog

Height and Structure of the Atmosphere

• As you travel away from Earth there are fewer and fewer molecules.

• Atmospheric pressure is the weight of the air above

• The average air pressure at sea level is approx. 1000 millibars (1 kg/cm2)

• As you move up in altitude air pressure drops

Why do your ears “pop” when driving up to Payson or Flagstaff?

As you move up in altitude the air becomes “thinner” less air molecules, thus less pressure

on your eardrum

You swallow to equalize the pressure on the inside of your eardrum.

Why is air cooler as you increase altitude?

As you increase in altitude the air molecules are farther away from the reflecting heat energy of the Earth’s surface, they slow

down. There are so few molecules they do not “bump” into each other, creating heat energy.

• Earth’s atmosphere becomes colder as you climb higher. But not all layers of the atmosphere show this temp. pattern.

• Layers of the Atmosphere

• The atmosphere is divided into 4 layers based on temperature.

• Troposphere• Bottom layer, closest to the

Earth.• Temp. decreases as altitude

increases.• This layer is where weather

occurs.• The rate of change in temp.

in this layer is called the environmental lapse rate

• The environmental lapse rate is not constant

• Stratosphere• The temp. decreases to

approx. 20 km, then there is a gradual increase temp. to about 50 km

• The concentration of ozone causes this increase in temp.

• Ozone absorbs ultra violet radiation from the Sun

• The result is that the atmosphere becomes heated.

• Mesosphere• Temperature decreases as

altitude increases

• Thermosphere• Temperature increases as

altitude increases• This layer contains a

fraction of the atmosphere’s mass

• The temp change is because oxygen and nitrogen absorb short wave high energy solar radiation

In which layer of the atmosphere does weather occur?

Why only in this layer?

The Troposphere is the layer of the atmosphere where weather occurs

This is the only layer where there is an abundance of gas molecules and water vapor which affect the temp. and drives

the weather