Geog. 111 Notes 5

# Geog. 111 Notes 5 - -water and precipitation-what is...

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-water and precipitation: -what is distinct about the Earth with regard to water?: high quantity (“water planet”, hydrologic cycle), exists in three phases (vapor, liquid, ice; this helps to cycle an incredible amount of energy in environment; it exists in three phases b/c the Earth is in the perfect location from the Sun to accommodate this, not too hot and not too cold; Earth in the “habitable zone”) -what is important about water in the atmosphere?: phase change of water is important energy source (latent energy); water vapor is the source of all clouds and precipitation; the amount of water vapor determines the rate of evaporation (important to weather and plant and animal life b/c of effects during photosynthesis and regulation of body temperatures); water vapor is a principal absorber of longwave energy (a greenhouse gas) -phase changes and energy: for water to change phase, energy must be either added to or removed from the atmosphere (energy is absorbed during melting and evaporation, but is released during freezing and condensation) -jet contrails: form b/c high up the air temperature can be extremely cold (-20 to -40 degrees C), air that comes into engine is compressed (heats up, warms up) and then leaves out the back of the jet; when hot air comes out of jet it cools immediately, forming ice behind the jets -how do we measure water vapor?: “absolute” measure (vapor pressure, VP, is the pressure caused by water vapor molecules [tells how much water vapor is in the air, but tells nothing about saturation]; saturation vapor pressure, SVP, is the pressure exerted by water vapor molecules when the air is saturated [SVP increases rapidly as temperature increases, because warmer air is able to hold more water vapor molecules than colder air; this is due to evaporation and the kinetic energy of water vapor molecules), “relative” measure (relative humidity, RH, tells us how close the air is to saturation [saturation is condition in which the capacity of the air to hold water vapor is reached; RH (%)=(VP/SVP) * 100 where an RH of 0-10% is bone dry, 50% is half way to saturation, 100% is saturated air; effects on evaporation include a low RH equaling more evaporation and a high RH equaling less evaporation]), dew point temperature (the temperature to which air must be cooled to become saturated; serves as a readily available indicator of atmospheric water vapor content; to know how close the air is to saturation we need to know the dew point and the air temperature [the closer the dew point is to the air temperature the closer the air is to saturation; dew point depression, DPP, is the temperature difference b/w the air and the dew

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