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Adiabatic
lapse rate |
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= 10°C/km
or 1°C/100m |
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=
air temperature in a rising balloon drops 1°C every 100m. |
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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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Evaporation: the process whereby molecules break
free of the liquid volume. |
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Condensation: water vapor molecules randomly
collide with the water surface and bond with adjacent molecules. |
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Specific Humidity: How many grams of water vapor
in one kilogram of air (in unit of gm/kg). |
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Relative Humidity: The percentage of current
moisture content to the saturated moisture amount (in unit of %). |
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Clouds form when the relative humidity reaches
100%. |
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On
average, 1 meter of water is evaporated from oceans to the atmosphere each
year. |
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The
global averaged precipitation is also about 1 meter per year. |
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Earth’s surface lost heat to the atmosphere when
water is evaporated from oceans to the atmosphere. |
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The evaporation of the 1m of water causes
Earth’s surface to lost 83 watts
per square meter, almost half of the sunlight that reaches the surface. |
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Without the evaporation process, the global
surface temperature would be 67°C instead of the actual 15°C. |
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If a planet has a very high temperature that the
air can never reach a saturation point |
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Water vapor can be added into the atmosphere. |
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More water vapor traps more heat (a greenhouse
effect) |
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The planet’s temperature increases furthermore |
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Ever
more water evaporated into the atmosphere |
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More
greenhouse effect |
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More
warming |
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More
water vapor |
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….. |
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Two ways: |
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Increase (inject more) water vapor to the air (Aà B). |
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Reduce the temperature of the air (A à C). |
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Clouds
form when air rises and becomes saturated in response to adiabatic cooling. |
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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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Cloud effects is one of the most uncertain parts
of climate prediction. |
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Typically, clouds increase albedo è a
cooling effect |
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clouds reduce longwave radiation è a heating effect |
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The net effect of clouds on climate depends
cloud types and their optical properties, the insolation, and the
characteristics of the underlying surface. |
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In general, high clouds tend to produce a
heating (positive) feedback. Low clouds tend to produce a cooling
(negative) feedback. |
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