Weather

Earth’s Changing Atmosphere

I. What is Weather?

A. AtmosphereWeather = day to day

changes in the atmosphere – layer of gases surrounding Earth

- composed of 5 layers which are separated by differences in temperature

What is Weather?

1. Troposphere- where all weather occurs- where life is found- layer closest to Earth’s

surface- as altitude increase in the

troposphere, air temperature decreases

What is Weather?

2. Stratosphere- where jet airplanes fly –

clear skies- where the ozone layer is

found- ozone layer blocks harmful

ultraviolet rays- ozone layer was depleted

by the production and use of CFC’s (chlorofluorocarbons)

What is Weather?

- CFC’s were used as propellants in hair spray, spray paint, etc. and as refrigerants

- CFC’s in the atmosphere inhibited the formation of new ozone

- holes in the ozone layer formed over the south and north poles

What is Weather?

- since CFC’s were banned in the mid 1980s. new ozone formation has increased and the holes are beginning to close

- as altitude in the stratosphere increases, temperature increases due to heating from the absorption of ultraviolet radiation by the ozone layer

What is Weather?

3. Mesosphereas altitude increases,

temperature decreases- where the ionosphere is

found – layer of charged particles (ions) that influence how radio waves travel above Earth’s surface

What is Weather?

d. Thermosphere- as altitude increases,

temperature increases- temperature increase is

caused by the absorption of harmful gamma radiation

- atmosphere is very thin in the thermosphere (few molecules are floating around)

- those few molecules have a lot of energy, but they are few and far between

What is Weather?

5. Exosphere- boundary between Earth’s

atmosphere and outer space6. Composition of the

Atmosphere- composed of a mixture of gases

(air)- 78 % Nitrogen (N2)- 21 % Oxygen (O2)- 1 % Carbon dioxide (CO2), Argon

(Ar) and other gases

What is Weather?

B. The Water Cycle- weather is most effected by

the amount of water in the air

- describes the movement of water from the hydrosphere (all the water on Earth) to the geosphere ( the solid part of Earth) and the atmosphere (all of the gases surrounding Earth)

What is Weather?

- uses the processes of1. precipitation - water

falling out of the atmosphere

2. evaporation - change of liquid water to gaseous water vapor

3. transpiration - loss of water from the leaves of plants (evapotranspiration)

What is Weather?

4. runoff - liquid water flowing over the solid surface of Earth

5. infiltration - movement of water into the ground

What is Weather?

C. Humidity, Relative Humidity, Holding Capacity, and Dewpoint

1. Humidity - how much water is in the air

2. Holding capacity - how much water air at a specific temperature can hold

What is Weather?

- holding capacity increases as air temperature increases

- holding capacity decreases as air temperature decreases

What is Weather?

3. Relative Humidity - value determined by comparing humidity to holding capacity

- expressed as a percentage (%)

- determined using a sling psychrometer

What is Weather?a. Calculating Relative Humidity1. Take the difference between the

wet and dry bulb temperatures 2. Find the dry bulb temperature

on the left hand side of the chart.

3. Read across to the column with the same value as the difference between the wet and dry bulb temperatures

4. The value found in the corresponding box is the relative humidity

What is Weather?

4. Dewpoint - temperature at which water in air condenses into a liquid

- varies depending upon air temperature

- expressed as a temperature in °C or °F

- when air temperature reaches the dewpoint, precipitation may occur if there is enough water in the air

What is Weather?

- depends upon holding capacity

- precipitation can occur when the air temperature is warmer than the dewpoint because there is so much water in the air

What is Weather?

D. Clouds and Precipitation1. Clouds - when water in the

air begins to condense, it may form clouds

- clouds are defined by their altitude (height), shape, and formation

What is Weather?

a. Stratiform Clouds - formed by horizontally blowing winds

- thick layers of clouds

What is Weather?

b. Cumuliform Clouds - formed by vertically rising air

- big and puffy clouds- cumulus clouds - big,

puffy, fair weather clouds - usually formed under high pressure

What is Weather?

- cumulonimbus – thunderheads- massive, anvil-shaped clouds

- stratus clouds - close to ground, make thick layers

- nimbostratus - thick, low-lying, precipitation causing clouds

- cirrus - high, thin, wispy clouds

- made of ice crystals

What is Weather?

2. Precipitation - water falling out of the atmosphere

- may be either solid or liquida. rain - liquid waterb. snow - 6 sided ice crystal,

no 2 are alikec. sleet - ice pellets

What is Weather?

d. freezing rain - supercooled water - water cooled to lower than 0º C

- water has no surface to freeze on

- water comes out of the atmosphere - freezes to make a layer of ice upon contact with a surface with a temperature = or < 0C

What is Weather?e. hail - similar to sleet in its

structure- only occurs during summer

months during thunderstorms and other severe weather

- form by updrafts of air- can be as small as a grain of sand

or as large as a grapefruit (and possibly larger)

- water needs a condensation nucleus to form - substance for water to freeze on

ex.: volcanic ash, salt crystals, dust