Transcript Layer closest to the Earth`s surface

Meteorology Notes Part II
Atmosphere Composition and Structure
Effect of Earth’s shape and tilt on weather
and seasons
Air Mass Types and Formation
Global Wind Systems and Ocean Currents
• About 99% of the
atmosphere is
composed of nitrogen
and oxygen.
• 21% is oxygen
• The other 1% is made
up of argon, hydrogen,
carbon dioxide, water
vapor, and other gases
• The amount of water vapor in the
air varies from 0% to 4%. It depends
on altitude of air mass, surface
features beneath air, and season.
• The atmosphere also consists of
tiny dust and salt particles, which
are necessary in cloud formation.
• Ozone (O3) is also found in the
atmosphere. It exists in small
quantities in a layer will above the
earths surface. It absorbs ultraviolet
light from the sun. Why is this
important?
• Greenhouse gases are gases near
the surface that absorb radiation
causing a temperature increase.
Carbon Dioxide is an important one
that can cause temperatures to rise.
• The
atmosphere is
made up of
several
different layers.
• Each layer has a
different
composition
and a different
temperature
profile.
Troposphere
-Gradual decrease in temperature from bottom
to top because it is heated by the Earth’s surface
-Layer closest to the Earth’s surface
-Contains the most mass of the atmosphere
-Most weather (clouds, etc.) takes place here
-Layer where most pollution collects
-The top of the troposphere is called the
Tropopause (9km – 16km); Gradual decrease in
temperature stops.
Stratosphere
-Located above the tropopause
-Layer primary made up of concentrated
ozone with the majority near the
stratopause
-Ozone absorbs ultraviolet radiation causing
temperature to rise as height increases from
the bottom to the top of the stratosphere.
The stratopause is located above the
stratosphere where temperature stops
increasing
Mesosphere
Located above the stratopause
No ozone = no gases to absorb
radiation and warm the layer = gradual
decrease in temperature
Mesopause is the boundary between
the mesosphere and the next layer, the
thermosphere.
Thermosphere
Minute portion of atmosphere’s mass
Air again increases in temperature in
this layer, this time to more than 1000
degrees Celsius
Exosphere & Ionosphere
The ionosphere is part of the thermosphere.
The ionosphere is made up of electrically
charged particles and layers of progressively
lighter gases.
-Interaction of the solar wind from the sun
with the ionosphere creates the Auroras
The Exosphere, above the Thermosphere, is
so thin that most scientists actually consider
this the beginning of space.
Light gases, like helium and hydrogen, are
found in this layer.
There is no clear boundary between the
atmosphere and outer space.
How is radiation distributed around the planet??
• Not evenly – therefore, areas with more direct
radiation heat more than those with indirect
radiation
• Temperature varies with the angle of the sun
Earth’s axis is tilted
relative to the ecliptic at
approximately 23.5
degrees
-As Earth orbits the sun
this tilt angle never
changes - the Earth’s
axis stays fixed in space.
-Our seasons are
created by this tilt and the
Earth’s revolution around
the Sun.
-As the Earth moves
around the sun each year,
the altitude of the sun in
our sky changes. At the
solstices, the axis either
points directly at or away
from the Sun.
1.) Summer solsticethe Sun’s maximum
altitude in the sky.
4
3
1
2.) Winter solsticethe Sun’s lowest altitude
in the sky.
2
2
3
-At the equinoxes, the
Earth’s axis is beside
the Sun, not towards or
away.
1.) As a result, both
hemispheres receive
equal amount of light.
The lengths of day and
night are also equal
1
2.) There are two
equinoxes – autumnal
and vernal.
4
-Because of the tilt, we have
some special latitudes on
Earth.
a. On the equinoxes, the
Sun is directly overhead on
the equator.
b. On the Summer Solstice, around June
20, the Sun is directly overhead at 23.5º N.
latitude, the Tropic of Cancer.
c. On the Winter Solstice, around Dec. 20,
the Sun is directly overhead at 23.5º S.
latitude, the Tropic of Capricorn.
Air Mass – a large body of air that takes on the characteristics of
the area over which it forms
– Source region can be either land (continental)
or water (maritime), near the poles or near the Humid
equator (tropic)
• Less moisture over land, more over the ocean
• Warmer near the equator, colder near the poles
Types
cT – continental tropic
– warm + dry
mT – maritime tropic
– warm + humid
cP – continental polar
– cold + dry
mP – maritime polar
– cold + humid
A – artic – very cold and dry – associated with high
pressure
Notice: Each type tells you the source region and the
temperature
Or
Dry?
Cold
Or
Warm?
Air Masses
World Heat Transfer
• Unequal distribution of radiation causes a difference in
temperature between the equator and the poles.
• If the Earth did not spin, then this would cause air to move
directly from the equator to the poles. However, the Earth’s
turn causes a strange effect called the Coriolis effect.
Coriolis Effect
• The Coriolis effect is the
APPARENT deflection of air
particles due to the
rotation of the Earth.
– Air in the northern
hemisphere is deflected to
the right.
– Air in the southern
hemisphere is deflected to
the left.
http://www.nasa.gov/audience/forstudents/brainbites/nonflash/bb_home_coriolisef
fect.html
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/crls.rxml
Stop and Think #1
• Does the Earth Turn Two Different Ways?
• Now, in your assigned group, take your globe
and turn it towards the EAST.
• Look at the globe from the North Pole. Is it
turning clockwise or counter-clockwise?
• Now, look at the globe from the South Pole. Is
it turning clockwise or counter-clockwise?
World Wind Belts
• The differential
heating of the
earth causes
huge convection
cells around the
Earth.
http://www.atmo.arizona.edu/products/wximagery/globalir.html
Global Wind Systems
• Three basic wind systems in
each hemisphere.
– 1. Trade Winds
• Easterly winds between 30 degrees
N and S of the equator
– 2. Prevailing Westerlies
• One in Northern and Southern
hemispheres between 30 and 60
degrees latitude
– 3. Polar Easterlies
• One in Northern and Southern
hemisphere between 60 degrees
and the pole
Horse Latitudes – at 30
degrees N and S latitude where
there are light winds and clear
skies
Doldrums (ITCZ) – near the
equator where there are
frequent storms and heavy
rains
Jet Streams
• At the boundaries between the wind zones air differs
greatly in pressure and temperature.
– This difference causes wind.
• Jet streams are narrow bands of high altitude, fast
moving, westerly winds.
– Speeds of 185 km/h
– Altitudes of 10.7 – 12.2 km (located near the tropopause)
http://www.pbs.org/wgbh/nova/vanished/jetstrea
m.html
Ocean Currents
• Ocean currents move water from place to
place.
• There are two types of ocean currents: deep
ocean currents (density currents) and surface
currents.
Deep Ocean Currents
• Deep ocean currents are also called density
currents since they are caused by differences
in density.
• These currents move slowly in deep ocean
waters.
• For example, Antarctic Bottom Water forms at
the South pole, sinks because it is very dense
(cold and salty) and moves towards the
Equator.
Surface Currents
• Surface currents are caused by wind at the
surface.
• They affect the upper few hundred meters of
the ocean.
• They move much faster – even 100 km per day
Gyres
• Surface currents are deflected by landmasses.
• This causes them to form circular current
systems, called Gyres.
• Gyres rotate clockwise in the northern
hemisphere and counter clockwise in the
southern hemisphere.