# AOS 100: Weather and Climate Instructor: Nick Bassill Class TA: Courtney Obergfell.

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AOS 100: Weather and Climate Instructor: Nick Bassill Class TA: Courtney Obergfell

Miscellaneous Class website: http://www.aos.wisc.edu/~aos100nb/ http://www.aos.wisc.edu/~aos100nb/ Extra copies of the syllabus Exam dates Class availability Willing note-takers?

Notecards I Commonly suggested topics: - Hurricanes - Tornadoes - Predicting the above - Global Warming/Climate Change - Lightning/Thunder - Earthquakes/Volcanoes/Tsunamis

Notecards II Other suggestions: - Slow down - Visuals/Models/Etc. - Post lectures before class

Review of September 3 rd : Remote Sensing Two primary types: RADAR & Satellites RADARS: - Located on the Earths surface - Send out an electromagnetic pulse; the length of time it takes to return determines the objects distance, and the intensity its size - Doppler RADAR is used to determine whether objects are coming towards or away from the RADAR site

Review Continued Two types of satellites: GOES and POES GOES Satellites: - Remain above the same location on the equator (geostationary) at a great distance - Good temporal resolution, poor spatial resolution POES Satellites - Orbit around the poles at a close distance - Very poor temporal resolution, but excellent spatial resolution

Review Continued Satellite imagery: Visible, Infrared, Water Vapor Visible relies on sunlight reflected off the Earth Infrared (IR) detects radiation emitted by the Earth, so the strength of the radiation determines how warm the object (surface, cloud, etc.) is Water Vapor detects radiation that is strongly absorbed by water, so it is a useful detector of dry/moist areas

The Ideal Gas Law Pressure = Density * Gas Constant * Temperature

The Ideal Gas Law P=ρRTP=ρRT Pressure Density Temperature Gas Constant

Density Density equals Mass divided by Volume ρ=(kg)/(m 3 ) Imagine air molecules in a box = 1 Kilogram Every side = 1 Meter

Which has the greater density? Box 1: 9 kg / (1 m * 1 m * 1 m) = 9 kg/m 3 Box 2: 3 kg / (1 m * 1 m * 1 m) = 3 kg/m 3 Box 1 is more dense

Pressure Pressure equals force per unit area Continuing the molecules in a box idea:

Which box has more pressure exerted on the inside walls? Box 1 has more molecules hitting the side, and therefore has a greater force per area is exerted on the walls

Pressure Continued In the context of the atmosphere, the surface can be thought of as the wall of the box Atmospheric pressure is most commonly reported in millibars (which are equivalent to hectoPascals) A standard pressure at sea-level is about 1013 millibars (or mb), which is equivalent to about 14.7 pounds per square inch For reference, the strongest hurricane (an area of low pressure) reached a minimum pressure of 870 mb at the sea surface The maximum sea-level pressure is 1083.8 mb

Temperature To understand temperature, we must understand Kinetic Energy (KE) Kinetic means motion, and energy measures an objects ability to do work So KE is a measure of an objects ability to do work via its motion KE=½*Mass*Velocity 2 Therefore, KE is greatly dependent on the objects velocity

Temperature Continued Temperature, then, is a measure of the average kinetic energy of the molecules in a substance (or amount of air) Therefore, faster moving molecules have a higher temperature Scales, starting with no molecule movement: Kelvin (K): begins at 0 K, Celsius (C): begins at -273.15 ºC Fahrenheit (F): begins at -459.67 ºF

Conversions: K = ºC + 273.15 ºF = 9/5 * ºC – 32 ºC = 5/9 * ºF + 32 Records: Low Temp: -128.2 ºF High Temp: 136.4 ºF

Now, for some thought experiments … Remember the Ideal Gas Law: Pressure = Density * Gas Constant * Temperature Imagine an airtight metal box, that is placed above a fire The air in the box gets warmer (T) with time This means that the molecules will move faster Which in turn means that they hit the walls of the box with more force (P) This makes sense, since P=ρ*R*T, where ρ, R stay constant

Next Thought Experiment Begin with the same situation, except this time, well let the box expand or contract as needed (i.e. like a balloon) Now, as the box is heated and the air warms, it expands, so that the pressure on the inside of the walls remains equal to the pressure on the outside of the walls This means that the density decreases (the volume goes up but the mass stays the same) Therefore, if pressure stays the same, and the temperature increases, the density must decrease Remember P=ρRT

Final Thought Experiment Again, start with a metal box. Imagine a number of molecules are suddenly added to the box at the same temperature as the original molecules If the volume is the same, the density must increase Since density increases, and we said the temperature stayed constant, the pressure must increase Remember P=ρRT

The Real Atmosphere Density is greatest near the Earths surface (due to gravity) In the part of the atmosphere closest to the Earths surface (where weather occurs), the temperature decreases with height Therefore, since density and temperature decrease with height, we must know that pressure also decreases with height, based on the ideal gas law Remember P=ρRT

Station Models These display virtually all the relevant current weather observations for a given weather station http://weather.cod.edu/notes/stnmodel.html

Meanings Wind Speeds

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