Lecture 8-Atmospheric moisture, clouds, precipitation

Lecture 8-Atmospheric moisture, clouds, precipitation -...

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Atmospheric Moisture, Clouds, and Precipitation
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Ocean and Freshwater distribution on earth Oceans have 97.2% of all water. Only 2.78% of all Earth’s water is freshwater, and of that, only 0.03% exists in the atmosphere. The majority of freshwater is held as ice-but the minority is dynamic and very important to landscape processes!
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The hydrologic cycle Cycling of water (mainly surface water, in the form of lakes, rivers, & streams) as it evaporates into the atmosphere, falls as precipitation, runs off the land and flows to the ocean, and evaporates again Essentially an ocean-atmosphere-precipitation runoff cycle In the following slide, look carefully at how water moves (in various ways depending on where it is) through this cycle….we are focusing on the atmosphere for this lecture.
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Entire hydrologic cycle: ~14 days for surface water molecules to go through the entire water cycle, from evaporation-precipitation-
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Remember this for later…. .phase changes are important! Phase changes are what liquids can undergo –liquid to/from a gas, liquid to/from a solid, and (more rarely) gas to/from a solid. Knowing about phase changes is important when we discuss phase changes in precipitation… This slide has imp notes! + signs mean energy must be ‘added’/absorbed, and – signs mean energy is released in the phase
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Heat energy characteristics of water Phase changes of water absorb or release a lot of latent energy . This is the energy released or absorbed during a change of state that occurs without a change in
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Moisture in the Atmosphere- Humidity Is a General term for atmospheric moisture: = how much water vapor is in the air Other things to know for this lecture: Air temp = T a T d = Dew Point Temperature
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Factors affecting humidity 1. Availability of water is imp Advection ( horizontal transfer of heat or moisture-laden air, etc.) water bodies’ locations Evaporation rates 2. Temperature is very important : We need amounts of thermal energy to do the work of evaporation (to put moisture into the atmosphere)
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There are different measures of humidity These include: 1. Absolute humidity 2. Relative humidity *-- what you see on the weather channel! – 3. Dew point (remember T d ) Expressions of humidity (how we express humidity and relative humidity) Vapor pressure Specific humidity
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1. Absolute Humidity This is expressed as the mass of water vapor (measured in grams) per volume of air (measured in cubic meters). So, it is the quantity of water present in a particular volume of air . If we change the volume of the air mass we are looking at, but our mass of water vapor is still the same, our absolute humidity is going to change. Make sense?
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2. Relative Humidity (RH) This is a ratio - it is the ACTUAL amount of water vapor in the air divided by the maximum amount of water vapor possible at a given temperature It is expressed as a percentage RH=Actual WaterVapor / Maximum possible(WaterVapor) * 100 See notes to understand how relative humidity works throughout the day-important concept!
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Lecture 8-Atmospheric moisture, clouds, precipitation -...

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