Download Weather, Climate and Storms

Atmosphere, Weather, Climate,
and Storms
The atmosphere is a cloud of
gas and suspended solids
extending from the Earth's
surface out many thousands of
miles, becoming increasingly
thinner with distance but
always held by the Earth's
gravitational pull.
The envelope of gas
surrounding the Earth
changes from the ground
up. Five distinct layers
have been identified
using...
thermal characteristics
(temperature changes),
chemical composition,
movement, and
density.
Mesosphere
The mesosphere extends from the top of
the stratosphere to about 56 miles (90 km)
above the earth. The gases, including the
oxygen molecules, continue to become
thinner and thinner with height.
Stratosphere
The Stratosphere extends from the top of the
troposphere up to around 31 miles (50 km) above
the Earth's surface. This layer holds 19 percent of
the atmosphere's gases but very little water vapor.
Troposphere
The troposphere begins at the Earth's surface
and extends from 4 to 12 miles (6 to 20 km)
high. This is the layer of the atmosphere in
which we live.
Exosphere
The Exosphere is the outermost layer of
the atmosphere. It extends from the top of
the thermosphere to 6,200 miles (10,000
km) above the earth. In this layer, atoms
and molecules escape into space and
satellites orbit the earth.
Thermosphere
Above the mesosphere the
thermosphere extends up to near 375
miles (600 km) above the earth. This
layer is known as the upper
atmosphere.
Weather
The term "weather" refers to the momentary
conditions of the atmosphere. We usually think of the
weather in terms of the state of the atmosphere in
our own part of the world. The weather in any one
area, however, may eventually influence, or be
influenced by, the weather a great distance away.
Weather usually changes from hour to hour or from
day to day. Over many years, certain conditions are
characteristic of the weather in an area. The average
weather in an area, as well as its variations and
extremes over many years, is called climate. Like
weather, climate can change, too, but much more
slowly.
Thunderstorms
• It is estimated that there are as many as
40,000 thunderstorm occurrences each day
world-wide. This translates into an
astounding 14.6 million occurrences
annually! The United States certainly
experiences its share of thunderstorm
occurrences.
The figure
shows the
average number
of thunderstorm
days each year
throughout the
U.S. The most
frequent
occurrence is in
the
southeastern
states, with
Florida having the highest number 'thunder' days (80
to 100+ days per year).
It is in this part of the country that warm, moist air from
the Gulf of Mexico and Atlantic Ocean
• All thunderstorms require three ingredients
for their formation:
• Moisture,
• Instability, and
• a lifting mechanism.
• Water temperature also plays a large role in
how much moisture is in the atmosphere.
Recall from the Ocean Section that warm
ocean currents occur along east coasts of
continents with cool ocean currents occur
along west coasts. Evaporation is higher in
warm ocean currents and therefore put more
moisture into the atmosphere than with cold
ocean currents at the same latitude.
• Therefore, in the
southeastern U.S. the
warm water from the two
moisture sources (Atlantic
Ocean and Gulf of Mexico)
helps explain why there is
much more rain in that
region as compared to the
same latitude in Southern
California.
Instability
• Air is considered unstable if it continues to rise
when given a nudge upward (or continues to
sink if given a nudge downward). An unstable
air mass is characterized by warm moist air
near the surface and cold dry air aloft.
Sources of Lift
• Typically, for a thunderstorm to develop, there
needs to be a mechanism which initiates the
upward motion, something that will give the air a
nudge upward. This upward nudge is a direct
result of air density.
• Some of the sun's heating of the earth's surface is
transferred to the air which, in turn, creates
different air densities. The propensity for air to
rise increases with decreasing density. This is
difference in air density is the main source for lift
and is accomplished by several methods.
A cumulus cloud begins to
grow vertically, perhaps to a
height of 20,000 feet
This is the most
dangerous stage when
large hail, damaging
winds, and flash
flooding may occur
A tornado is a violently rotating
(usually counterclockwise in the
northern hemisphere) column of air
descending from a thunderstorm
and in contact with the ground.
Although tornadoes are usually
brief, lasting only a few minutes,
they can sometimes last for more
than an hour and travel several
miles causing considerable damage.
The United States experiences more
tornadoes by far than any other
country. In a typical year about 1300
tornadoes will strike the United
States. The peak of the tornado
season is April through June and
more tornadoes strike the central
United States than any other place
in the world. This area has been
nicknamed "tornado alley."
Climate
"Climate" refers to all weather conditions for a
given location over a period of time. Weather can
change from hour to hour, from day to day, from
month to month, or even from year to year. For
periods of 30 years or more, however,
meteorological records reveal that distinct weather
conditions prevail over different parts of the world.
Each set of conditions forms a climate type, and the
area covered by a particular type is called a climate
region.
• Some parts of the world are hot and rainy
nearly every day; they have a tropical wet
climate. Others are cold and snow-covered
most of the year; they have a polar climate.
Between the icy Poles and the steamy tropics
are many other climates that help make the
Earth unique.
Climate Controls
•
•
Climate Controls
Whether we have hot or cold seasons, lots of rain or very little is determined by how temperature, moisture, wind,
and air pressure mix in Earth's atmosphere. Listed below are "climate controls" and how they affect weather and
climate:
Latitude—Earth's surface and atmosphere receive varying, changing amounts of energy from the sun. Generally,
the areas around the Equator receive more while the polar areas receive less. Therefore, areas of lower latitude
tend to be warmer and polar areas tend to be colder.
Land and Water—Because land and water heat at different rates (land heats and cools more quickly than water),
areas near large bodies of water tend to have their climates moderated. That means that in general, areas along a
shoreline will have milder summer and winter temperatures. Also, bodies of water such as oceans or seas provide
lots of moisture for the atmosphere. This is especially true about warm bodies or currents of water.
Landforms—Landforms such as hills or mountains can alter wind flow. Because winds can be forced upwards by an
elevated landform, the exposed (windward) side can often have a different weather and climate than the
sheltered (leeward) side. As air travels up a mountain, moisture is "squeezed" out of the air as it cools, condenses,
and falls as precipitation. Air temperature and the amount of moisture in the air are usually decreased as it flows
down the sheltered side of the mountain.
Elevation—Generally, the higher you go in the lower portion of the atmosphere, temperature, moisture, and air
pressure decrease.
Ocean and Wind Currents—The water in Earth's oceans and the air in Earth's atmosphere are constantly moving.
The movement can be across, up, or down. This process circulates cool or warm air and water around Earth.