Transcript meteo_1_class_2_2012..

Overview of the Earth’s Atmosphere
• Composition
– 99% of the atmosphere is within 30km of the
Earth’s surface.
– N2 78% and O2 21%
– The percentages represent a constant amount of
gas but cycles of destruction and production are
constantly maintaining this amount.
Fig. 1-7, p. 10
Fig. 1-9, p. 11
Chapter 2
Energy: Warming the earth
and Atmosphere
Chapter 3
air temperature
Air temperature is a measure of the average speed of
the molecules (kinetic energy). In the cold volume of air
the molecules move more slowly and crowd closer
together (left). In the warm volume, they move faster
and farther apart (right).
Comparison of Kelvin,
Celsius, and
Fahrenheit scales,
along with some
world temperature
extremes.
Conversions:
°C = 5/9 x (°F – 32)
K = °C + 273
Latent Heat = the energy required to change a substance (like water) from one
phase to another (eg. Solid to liquid).
eg. Because it takes energy to evaporate water (typically taken from the water
itself), the water left behind has less energy and is cooler.
Every time a cloud forms, it warms the atmosphere.
Inside this developing thunderstorm, a vast amount
of stored heat energy (latent heat) is given up to the
air, as invisible water vapor becomes countless
billions of water droplets and ice crystals.
The transfer of heat from the
hot end of the metal pin to
the cool end by molecular
contact is called conduction.
The rising of hot air and
the sinking of cool air
sets up a convective
circulation. Normally,
the vertical part of the
circulation is called
convection, whereas
the horizontal part is
called wind. Near the
surface the wind is
advecting smoke from
one region to another.
Rising air expands and cools; sinking air is compressed and warms.
Why? As the air parcel rises, the pressure decreases, allowing the
parcel to expand. This takes energy (to expand) and the air
molecules slow down, so the parcel cools. As the parcel sinks, the
parcel volume shrinks (due to increased pressure). Because the air
molecules have less space to bounce around, their velocity
increases, causing a rise in temperature.
Radiation characterized according to wavelength. As the wavelength
decreases, the energy carried per wave increases.
The sun’s electromagnetic spectrum and some of the
descriptive names of each region. The numbers
underneath the curve approximate the percent of energy
the sun radiates in various regions.
0.4 μm = 400 nm
0.7 μm = 700 nm
The hotter sun not only radiates more energy than that of the cooler earth (the area
under the curve), but it also radiates the majority of its energy at much shorter
wavelengths. (The area under the curves is equal to the total energy emitted, and the
scales for the two curves differ by a factor of 100,000.)
Absorption of radiation by
gases in the atmosphere. The
shaded area represents the
percent of radiation absorbed
by each gas. The strongest
absorbers of infrared
radiation are water vapor and
carbon dioxide. The bottom
figure represents the percent
of radiation absorbed by all of
the atmospheric gases.
(a) Near the surface in an atmosphere with little or no greenhouse gases, the earth’s surface
would constantly emit infrared (IR) radiation upward, both during the day and at night.
Incoming energy from the sun would equal outgoing energy from the surface, but the surface
would receive virtually no IR radiation from its lower atmosphere. (No atmospheric
greenhouse effect.) The earth’s surface air temperature would be quite low, and small
amounts of water found on the planet would be in the form of ice. (b) In an atmosphere with
greenhouse gases, the earth’s surface not only receives energy from the sun but also infrared
energy from the atmosphere. Incoming energy still equals outgoing energy, but the added IR
energy from the greenhouse gases raises the earth’s average surface temperature to a more
habitable level.
Air in the lower atmosphere is heated from the ground upward.
Sunlight warms the ground, and the air above is warmed by
conduction, convection, and infrared radiation. Further warming
occurs during condensation as latent heat is given up to the air inside
the cloud.
On the average, of
all the solar energy
that reaches the
earth’s atmosphere
annually, about 30
percent (30/100) is
reflected and
scattered back to
space, giving the
earth and its
atmosphere an
albedo of 30
percent. Of the
remaining solar
energy, about 19
percent is absorbed
by the atmosphere
and clouds, and 51
percent is absorbed
at the surface.
The earth-atmosphere energy balance. Numbers represent approximations based on
surface observations and satellite data. While the actual value of each process may
vary by several percent, it is the relative size of the numbers that is important.
The average annual incoming solar radiation (yellow line) absorbed by
the earth and the atmosphere along with the average annual infrared
radiation (red line) emitted by the earth and the atmosphere.
Sunlight that strikes a surface at an angle is spread over a larger area
than sunlight that strikes the surface directly. Oblique sun rays deliver
less energy (are less intense) to a surface than direct sun rays.
The apparent path of the sun across the sky as observed at
different latitudes on the June solstice (June 21), the
December solstice (December 21), and the equinox (March
20 and September 22).
On a sunny, calm day, the air near the surface can be substantially
warmer than the air a meter or so above the surface.
The daily variation
in air temperature
is controlled by
incoming energy
(primarily from the
sun) and outgoing
energy from the
earth’s surface.
Where incoming
energy exceeds
outgoing energy
(orange shade), the
air temperature
rises. Where
outgoing energy
exceeds incoming
energy (gray
shade), the air
temperature falls.
On a clear,
calm night,
the air near
the surface
can be much
colder than
the air above.
The increase
in air
temperature
with
increasing
height above
the surface is
called a
radiation
temperature
inversion.
An idealized
distribution of air
temperature
above the
ground during a
24-hour day. The
temperature
curves represent
the variations in
average air
temperature
above a grassy
surface for a midlatitude city
during the
summer under
clear, calm
conditions.
(a) Clouds tend to keep daytime temperatures lower and nighttime
temperatures higher, producing a small daily range in temperature. (b)
In the absence of clouds, days tend to be warmer and nights cooler,
producing a larger daily range in temperature.
Monthly temperature data and annual
temperature range for (a) St. Louis,
Missouri, a city located near the middle
of a continent and (b) Ponta Delgada, a
city located in the Azores in the Atlantic
Ocean.
Monthly temperature data and annual
temperature range for (a) St. Louis,
Missouri, a city located near the middle
of a continent and (b) Ponta Delgada, a
city located in the Azores in the Atlantic
Ocean.
Temperature data for (a) San Francisco,
California (38°N) and (b) Richmond,
Virginia (38°N)—two cities with the same
mean annual temperature.
Temperature data for (a) San Francisco,
California (38°N) and (b) Richmond,
Virginia (38°N)—two cities with the same
mean annual temperature.
Mean annual total heating degree-days across the United
States (base 65°F).