ATMS 120 1st Edition Lecture 4 Outline of Last Lecture I General temperature variations II Seasonal variations in temperatures III Seasons the effects of latitude IV Proximity to large bodies of water V Vertical temperature variations Outline of Current Lecture I Phase change for water A Energy associated with phase changes II Measuring moisture vapor pressure B Crushed can example III Saturation vapor pressure Current Lecture I Water is the only element that naturally exists in all three phases solid liquid gas It is most dense in the liquid phase In the gas phase it is called water vapor In the liquid phase it exists as clouds and raindrops As a solid ice it exists as ice clouds snow ice pellets soft hail graupel and hail You cannot see water vapor Steam is not the same thing was water vapor Latent heat heat associated with phase change Sublimation is the process of a solid going to a gas and skipping the liquid phase in the process Deposition is the process of a gas going to a solid and skipping the liquid phase in the process A Going from solid liquid gas heat is required energy must be supplied to the system Going from gas liquid solid heat is released The energy required to boil a gallon of water is equivalent to 5 sticks of dynamite The energy released in a phase change of water example Hurricane Katrina s clouds is enormous is as much as 6x the energy of the bomb dropped on Nagasaki II Total air pressure is the sum of the pressures from individual gases Dalton s Law On Earth the primary contributors to the dry air pressure are oxygen nitrogen and argon Since water vapor is a highly variable gas in space and time it can contribute a significant These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute amount to the total air pressure Vapor pressure force per unit area applied ONLY by the water vapor molecules the weight of the water vapor measured in mb The combination of dry air and moist air equal total vapor pressure Hot air has the ability to retain more water than cold air When water condenses a lot of energy is released B In class the professor showed an example of how energy is released when water condenses He put a small amount of water in an aluminum can and put it on a hot plate Once the water in the can started boiling he turned it over into a container of cool water The can immediately collapsed A pressure gradient was created which made the can collapse This is how the gradient was created When the can was on the hot plate with the water boiling most of the air in the can was water vapor When the can was put into the container of cool water the water vapor quickly condensed Since the can was sealed the top of the can was submerged into the water no air could rush in The rapid drop in density and pressure caused the can to collapse III Saturation vapor pressure the vapor pressure when the atmosphere can no longer hold any more water vapor without condensing out as a liquid It is the saturation point of the air with respect to water When the saturation vapor pressure equals vapor pressure meaning the amount of water in the atmosphere matches the amount that it can hold the relative humidity is 100 and the air is saturated When the saturation vapor pressure is greater than the vapor pressure the relative humidity is less than 100 and the air is not saturated Air has a finite holding capacity for water vapor that depends on temperature