Transcript ES-541 Class I-III

What is Carrying Capacity?
• Is the maximum
population a habitat
can support
indefinitely
• Population exceeds
it, for long periods,
degrades its
environment and
reduces future
carrying capacity
The
Biosphere
What is the Biosphere?
• Combined portions of
the planet in which all
of life exists, including
land, water and
atmosphere
• Extend from 8-km
above Earth’s surface
to 11-km below the
surface of the ocean.
The Structure of the
Earth’s Atmosphere
* Chemical Composition
* Vertical Layers
* Coriolis Force
* Hadley Cells
Current Composition
Atmospheric Composition today
The Troposphere
• The surface layer up to about 30,000 ft
• Heated from below, by ground having
absorbed solar energy
• Temperature highest near the ground, and
falls all the way up to about 30,000 ft
• It is the densest part of the atmosphere
and contains about 85% of atmosphere’s
mass.
The Stratosphere
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Heated mostly by absorbing UV light from the sun by O3 (ozone), breaking
it apart into O2 + atomic oxygen. When they recombine to make ozone, you
get energy release and heating
Ozone in the stratosphere absorbs ultraviolet radiation, warming it up in the
mid-upper parts of the layer. The reason for the increase in temperatures in
the stratosphere with height relates to the wavelength of the incoming solar
energy. At higher altitudes in the stratosphere, ozone very efficiently
absorbs UV at wavelengths between 200 and 350 nanometers. At lower
altitudes in the stratosphere, ozone absorbs UV at wavelengths between 44
and 80 nanometers but much less efficiently. This results in a rate of
warming in the lower stratosphere that is less than the rate higher in the
stratosphere, causing the temperature to increase with height.
Therefore is hottest at the highest layers, cooler down where it contacts the
cold upper troposphere
At the bottom of the stratosphere, most UV has already been absorbed
higher up, so further heating is very reduced, hence the temperature vs
height is the opposite from the Troposphere
This temperature inversion means no convection, no weather.
The Mesosphere
• Above the Stratosphere, the mass of
atmosphere is only 0.1% of the total, and the
density is too low for ozone chemistry to heat the
atmosphere
• Hence, we get the normal trend we saw in the
troposphere re-asserting itself – lower
temperature with lower pressure and lower
altitude.
• This layer is 30-50 miles above the ground.
The Ionosphere (= Thermosphere)
• Above mesosphere; density so low the
Space Shuttle and ISS orbit here, with little
drag
• Temperature can be very high; 4,000F.
But no significant heat because density is
so low.
• Heated by ionization by UV from the sun,
and the solar wind.
Hadley, Ferrel, Polar Cells
• The Coriolis deflection sets the major constraint
on how many cells the atmosphere of a planet
divides into. Coriolis force is stronger for more
rapid rotation. It is the size of the planet and
speed of rotation (and a lesser extent, the depth
of the atmosphere) which determines how many
of these. Earth’s atmosphere divides into 3 cells.
• For Jupiter, it is many more, as it is 12 times
larger in diameter and yet has a day only 12 hrs
long. Coriolis Force is very strong.
The Coriolis Effect
The Hadley Cell
• Solar heating at the equator is strongest,
causing rising convective air which is pushed
north and south at the tropopause
(troposphere/stratosphere boundary).
• At ~30deg latitude it has deflected enough by
the Coriolis force. Here, it meets air moving
down from the north (Ferrel Cell air) and both
meet and descend, warming and drying
• The return of the air, now a surface wind, to the
equator is called the “trade winds”.
Mid-latitudes - The Ferrel Cell
• Convective rising air near 60 deg latitude arrives at the tropopause,
moves (in part) to the south, deflecting by Coriolis to the west, till it
meets the northerly moving air from the tropical Hadley cell, forcing
both to descend
• These are the “Horse Latitudes” at +-30 deg (30-38) latitude.
Descending air dries. Deserts here (e.g. Sahara, Mojave/Sonora)
• Northerly moving surface winds deflected east - “the Westerlies” carrying heat from the lower latitudes to higher mid latitudes
• The primary circulation on Earth is driven by the equatorially heated
Hadley Cell, and the polar cooled Polar Cell. The Ferrel cell is a
weaker intermediate zone, in which weather systems move through
driven by the polar jet stream (boundary between Ferrel and Polar
cell, at the tropopause) and the tropical jet stream (boundary
between Ferrel and Hadley cells, at the tropopause).
The Polar Cell
• Easiest of the cells to understand – rising
air from the 60 degree latitude area in part
moves north to the pole, where it’s cold
enough to densify, converge with other
northerly winds from all longitudes, and
descends.
• This makes a “desert” at the north and
south poles.
Key Points – Structure of Earth’s Atmosphere
• 78% Nitrogen which is fairly inert. 21% oxygen, 400ppm CO2
• Troposphere – heated from sun-warmed ground, T falls with height
• Stratosphere, heated from above by UV absorbed by ozone; T rises
with height
• Troposphere can have convection = weather; stratosphere cannot
• Mesosphere; where meteors burn up. Ionosphere, heated by solar
wind, aurorae. Top two layers almost no mass, little influence on
climate
• Hadley/Ferrel/Polar cells. Their general circulation
• Ferrel cell is weakest; having neither a strong heat source nor sink
• Coriolis force stronger with more rapid rotation and larger planet
size, making more cells
• Jet streams – tropical and polar – boundaries between the cells at
the tropopause
• Local Wind Patterns
– Due to:
• The relationship between air temperature and air
density.
• Relationship between air pressure and the movement
of air.
– Upward and downward movement of air leads to:
• The upward movement has a lifting effect on the
surface that creates areas of low pressure
• The downward movement of air has a piling up effect
resulting in areas of high pressure.
• A model of the relationships between differential
heating, the movement of air, and pressure difference
in a convective cell. Cool air pushes the less dense,
warm air upward, reducing the surface pressure. As
the uplifted air cools and becomes more dense, it
sinks, increasing the surface pressure.
• Atmospheric Pressure
– The atmosphere exerts pressure on the Earth that
decreases with increasing altitude
• This is due to the fact that with increasing altitude,
there is a decrease in the column of gases above
the Earth’s surface
– Hydrostatics considers the pressure that is exerted by
a fluid that is at rest.
• Using this as a frame of reference the atmospheric
pressure is viewed as a result of the mass of the
column of gases above the Earth.
– Using a molecular frame of reference, the
atmospheric pressure is viewed as a result of the
kinetic energy of molecules and the force with which
they strike an object.
– Atmospheric pressure is actually a result of the
• At greater
altitudes, the
same volume
contains fewer
molecules of the
gases that make
up the air. This
means that the
density of air
decreases with
increasing
altitude.
• The mercury barometer
measures the
atmospheric pressure
from the balance
between the pressure
exerted by the weight of
the mercury in a tube
and the pressure
exerted by the
atmosphere. As
atmospheric pressure
increases and
decreases, the mercury
rises and falls. This
sketch shows the
average height of the
column at sea level.
• Water and the Atmosphere
• Evaporation and Condensation
– Humidity
• The amount of water vapor in the air
• Absolute humidity is a measure of the amount
of water vapor present at a given time.
• Relative humidity is a measure of the amount of
water vapor present in the air relative to the
amount that the air could hold at that
temperature.
• The maximum
amount of water
vapor that can be
in the air at
different
temperatures. The
amount of water
vapor in the air at a
particular
temperature is
called the absolute
humidity.
– The Rate of Evaporation depends on:
• surface area of the exposed liquid.
• Air and water temperature
• Relative humidity
– The Rate of Condensation depends on:
• relative humidity
• Kinetic energy of the gas molecules in the air.
• Evaporation and condensation are occurring all the
time. If the number of molecules leaving the liquid
state exceeds the number returning, the water is
evaporating. If the number of molecules returning to
the liquid state exceeds the number leaving, the water
vapor is condensing. If both rates are equal, the air is
saturated; that is, the relative humidity is 100 percent.
– Dew point temperature
• Temperature at which the relative humidity and
the absolute humidity are the same (saturated
air)
• Dew begins to accumulate on surfaces.
• Form on C nights:
–Clear
–Calm
–Cool
Frost is the coating of ice that may form in
humid and cold condition. It forms when
temperature of a solid surface (soil) in the
open cools to below freezing point of
water.
• Fans like this one are used to mix the warmer,
upper layers of air with the cooling air in the
orchard on nights when frost is likely to form.
– Condensation nuclei
• Gives condensing moisture in the atmosphere
something to condense on.
• Necessary for the production of moisture in the
atmosphere (rain, snow).
• As condensation continues, eventually there will
be a point where enough water molecules have
condensed on the nuclei that it can no longer
remain air borne.
• It will then fall in the form of rain, snow, etc…
• This figure compares the size of the
condensation nuclei to the size of typical
condensation droplets. Note that 1 micron is
1/1,000 mm.
A
B
C
D
E
F
• (A)Cumulus clouds. (B) Stratus and stratocumulus. Note the
small stratocumulus clouds forming from increased convection
over each of the three small islands. (C) An aerial view between
the patchy cumulus clouds below and the cirrus and cirrostratus
above (the patches on the ground are clear-cut forests). (D)
Altocumulus. (E) A rain shower at the base of a cumulonimbus.
(F) Stratocumulus.