The Atmosphere

I. What is air?

Enlarged 10x20.94% Oxygen

78.04% Nitrogen

0.93% Argon

0.03% Carbon dioxide

0.06% Others

--A mixture of gasses

Nitrogen (78%)

•needed for growth of plants and animals

•absorbed in the form of nitrates, made by bacteria

Oxygen (21%)

• needed by animals, produced by plants

• energy released when it combines with other compounds

• breaks down some elements in rocks by oxidation

Carbon dioxide (.03%)

• needed by plants for photosynthesis

• important in greenhouse effect

Ozone (a “trace gas”)• a form of oxygen-- O3

• in stratosphere absorbs ultraviolet radiation

• at ground level is dangerous pollutant (smog)

Argon (0.9%)• inert, does not form

compounds

Water vapor (0 to 4%)

• only gas that varies much

• absorbs heat

G. Trace gases

• neon, helium, methane, krypton, xenon, hydrogen, ozone

II. What is the structure of our atmosphere?

A. troposphere-- to 11 km, zone where weather occurs

B. stratosphere-- 11-50 km, contains ozone layer, where jets fly

C. mesosphere-- 50-80 km, coldest layerD. thermosphere-- 80-85 km up,

temperatures rise, contains ionosphere and exosphere

III. What role does air pressure play in weather?

• Close to the earth atoms & molecules are pushed together because of pressure from mass above therefore greatest at sea level and decreases upward

• Differences in air’s density can cause air pressure variations

• Barometer measures air pressure, average in millibars is 1013 mb

Highs

• Cool air more dense, causes high pressure

• Highs are associated with cool dry air—clear skies

Lows

• Warmed air less dense, causes low pressure areas

• Lows are associated with warm and moist conditions—rain and storms

Air moves from areas of high pressure to areas of low pressure

IV. How does temperature affect the circulation of air in the atmosphere?

• Energy supplied by sun

• Greenhouse effect keeps heat in troposphere, makes life possible

• Heat is reflected by ice, water, snow, sand

• Heat is absorbed by vegetation and dark surfaces

Heat is transferred by radiation, conduction, and convection

• Convection currents are caused by differences in density between warm and cool fluids

• Convection causes air to rise over Equator, sink at Poles

Coriolis effect causes moving objects to be deflected to right in Northern hemisphere, left in Southern)

• Unequal heating can also cause movement, as in sea and land breezes

V. How does temperature affect the

ability of air to hold moisture?

• Warm air “holds more moisture” than cool air

• In warm air gas molecules are farther apart- more space for water vapor

• Relative humidity is the amount of water in air compared to how much it could hold at that temperature

• Air at 100 percent relative humidity is saturated, water may condense from it

May be measured with hygrometer or wet bulb / dry bulb psychrometer

• Temperature at which condensation will occur is called dew point

VI. How do clouds form

and produce precipitation?

• Condensation occurs when – 1. air is cooled below dew point and – 2. condensation nuclei (dust or salt particles)

are present

• Clouds are collections of tiny water droplets suspended in air

• At a certain size they fall as precipitation

• Snow is formed by water vapor turning directly to solid

VII. What are the names and characteristics of common cloud types?

Cloud families

• 1. cirrus-- high, white, feathery, ice clouds, also called “mare’s tails”

• 2. cumulus-- thick, puffy, “fair weather clouds”

• 3. stratus -- clouds in layers

• 4. nimbus-- produce precipitation

• Clouds also classified by height

• Stratus clouds close to ground are called “fog”

VIII. What is the significance of air masses to weather?

An “air mass” is body of air that has characteristic properties

Properties depend on where mass originated

From air mass, air flows down and spirals out clockwise, causing anticyclone (fair)

Air pushes into low pressure areas, spiraling in counterclockwise cyclone (stormy weather)

IX. How do fronts influence the weather?

• Boundary between air masses is called a front

Warm front • 1. Warm air mass meets cold air

mass• 2. Warm air slides up over cold

air in long wedge• 3. Nimbostratus clouds form and

may cause precipitation over long period

Cold front

• 1. Cold air mass meets warm air mass

• 2. Cold air forces warm air up along steep front

• 3. Showers and thunderstorms result

Stationary front causes weather to remain the same over long time

Occluded front when two cool air masses trap warm air between them, causing high winds and precipitation

X. How is weather portrayed on weather maps?

Local collecting stations contribute data in form of station models

Weather maps show

• 1. isobars, lines connecting points of equal pressure

• 2. isotherms- line connecting points of equal temperature

• 3. high and low pressure areas

4. position of fronts

El Nino and La Nina El Niño is an oscillation of the ocean-atmosphere system in

the tropical Pacific having important consequences for weather

• Information on the names El Niño and La NiñaEl Niño was originally recognized by fisherman off the coast of South America as the appearance of unusually warm water in the Pacific ocean, occurring near the beginning of the year. El Niño means The Little Boy or Christ child in Spanish. La Niña means The Little Girl. La Niña is sometimes called El Viejo, anti-El Niño, or simply "a cold event" or "a cold episode". El Niño is often called "a warm event". To provide necessary data, NOAA operates a network of buoys which measure temperature, currents and winds in the equatorial band. These buoys daily transmit data which are available to researchers and forecasters around the world in real time.

El Nino

• Warm air over warn Pacific water in red

Some years are normal and other years show strong El Nino

conditions.

The warming of the Earth’s oceans is believed to increase El Nino.

Some of the effects include droughts, floods and heat waves

(It’s safe to wake up now)

That’s all, folks!