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Clouds
form when air rises and becomes saturated in response to adiabatic cooling. |
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When boundaries between air of unlike
temperatures (fronts) migrate, warmer air is pushed aloft. |
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This results in adiabatic cooling and cloud
formation. |
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Cold fronts occur when warm air is displaced by
cooler air. |
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Warm fronts occur when warm air rises over and
displaces cold air. |
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Involve
the direct addition or removal of heat energy. |
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Example: Air passing over a cool surface loses
energy through conduction. |
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If a material changes its state (pressure,
volume, or temperature) without any heat being added to it or withdrawn
from it, the change is said to be adiabatic. |
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The adiabatic process often occurs when air
rises or descends and is an important process in the atmosphere. |
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Air
pressure decreases with elevation. |
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If a
helium balloon 1 m in diameter is released at sea level, it expands as it
floats upward because of the pressure decrease. The balloon would be 6.7 m
in diameter as a height of 40 km. |
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Air
molecules in the parcel (or the balloon) have to use their kinetic energy
to expand the parcel/balloon. |
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Therefore, the molecules lost energy and slow
down their motions |
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č The
temperature of the air parcel (or balloon) decreases with elevation. The
lost energy is used to increase the potential energy of air molecular. |
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Similarly when the air parcel descends, the
potential energy of air molecular is converted back to kinetic energy. |
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č Air
temperature rises. |
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The environmental lapse rate is referred to as
the rate at which the air temperature surrounding us would be changed if we
were to climb upward into the atmosphere. |
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This rate varies from time to time and from
place to place. |
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The environmental (or ambient) lapse rate is
referred to the vertical change in temperature through still air. |
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The environmental lapse rate is not fixed. It
changes from day to day and from place to place. |
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Ge = environmental lapse rate |
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Gd = dry adiabatic lapse rate |
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Gm = moist adiabatic lapse rate |
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Absolutely Stable |
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Ge < Gm |
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Absolutely Unstable |
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Ge > Gd |
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Conditionally Unstable |
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Gm < Ge < Gd |
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During the day, surface insolation gains result
in greater heating near the surface than aloft. |
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At night, the situation reverses as terrestrial
radiation loss causes near surface chilling ŕ a temperature
inversion. |
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High clouds have low cloud temperature and low
water content and consist most of ice crystal. |
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Middle clouds are usually composite of liquid
droplets. |
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They block more sunlight to the surface than the
high clouds. |
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Low, thick, layered clouds with large horizontal
extends, which can exceed that of several states. |
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They are clouds with substantial vertical
development and occur when the air is absolute or conditionally unstable. |
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The wintertime circulation over the South Pole
is characterized by a gigantic whirlpool of cold and dense air, called the
polar vortex. |
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The cold and dense cold air in the middle of the
vortex is subsiding. |
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The sinking air carries cloud particles along
with it. |
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Remove odd nitrogen from the stratosphere. |
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Very little ozone and odd nitrogen can be
brought into the south pole. |
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The greatest production of ozone occurs in the
tropics, where the solar UV flux is the highest. |
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However, the general circulation in the
stratosphere transport ozone-rich air from the tropical upper stratosphere
to mid-to-high latitudes. |
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Ozone column depths are highest during
springtime at mid-to-high latitudes. |
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Ozone column depths are the lowest over the
equator. |
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The decrease in ozone near the South Pole is
most striking near the spring time (October). |
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During the rest of the year, ozone levels have
remained close to normal in the region. |
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Notes