AOS 100: Weather and Climate

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

Some Basic Info • Class website: http://www.aos.wisc.edu/~aos100nb/ • Nick’s information: - Email address: npbassill@wisc.edu - Office: 1451 Atmospheric and Oceanic Sciences - Office hours: 4-5 W, 2:30-3:30 R* • Courtney’s information: - Email address: obergfell@wisc.edu - Office: 1311 Atmospheric & Oceanic Sciences - Office hours: 11-12:15 M, 2:40-3:40 T* * And by appointment

Class Overview • Every class will have a rather intensive weather discussion that will focus on anything interesting going on weather-wise, as well as the forecast for Madison • Hopefully this class itself will focus as much as possible on real weather! (Think thunderstorms, hurricanes, snowstorms, along with climate and climate change, etc.) • However, to get to this point, we must first cover a little background (Think how the atmosphere works, the diurnal cycle, how we observe weather, etc.)

Now Let’s Get Our Learn On …

What does “Remote Sensing” Mean? • “Remote sensing is the small or large-scale acquisition of information of an object or phenomenon, by the use of either recording or real-time sensing device(s) that are not in physical or intimate contact with the object” • From: http://en.wikipedia.org/wiki/Remote_sensing

Primary Types • For meteorological considerations, there are two primary types of remotely sensed observations: • RADAR • Satellite

RADAR • RADAR is an acronym for “RAdio Detection And Ranging” • RADAR uses radiowaves or microwaves to detect objects • RADAR dishes send out a pulse of electromagnetic radiation, which can be reflected back by objects • The length of time it takes for the pulse to return, as well as the strength of the return pulse indicate how near/far and how big the object(s) are - From: http://en.wikipedia.org/wiki/Radar

RADAR Continued • RADAR was largely developed before and during World War II as a method of detecting enemy ships and airplanes • However, it was noticed that this was less effective when it was raining or snowing • This eventually led to the widespread use of RADAR for detecting weather phenomena

More RADAR • The RADAR beam is directed at a slight angle above the horizon (~0.5º) • This ensures that the beam is not immediately blocked by nearby trees, buildings, etc. • The intensity of return is measured in “decibels” (DBZ), which uses a logarithmic scale

Pictures From:http://www.centennialofflight.gov/essay/Dictionary/radar/DI90G1.jpg http://www.bergenskywarn.org/Pages/BergenSkywarnUptonOpenHouse2001.htm

http://www.tropicalstorms.us/current/radar.gif

Thunderstorms over Michigan

Doppler RADAR • Doppler RADAR makes use of the “Doppler Effect” to determine whether objects are traveling towards or away from the radar site • Doppler RADAR measures the change in wavelength of the incoming signal (compared with the signal that was sent out) http://www.grc.nasa.gov/WWW/K-12/airplane/Images/doppler.gif

Velocity (from the Doppler RADAR) This feature is extremely useful for detecting tornadoes – many tornadoes are first “detected” using this method

Satellites • Unlike RADAR, satellites observe the weather exclusively from space • The widespread use of satellites for meteorological purposes are a by-product of the “space race” which began in the 1950s • There are two primary types of satellite (orbits): Polar Operational Environmental Satellite (POES) and Geostationary Operational Environmental Satellite (GOES)

POES vs. GOES • POES(s) orbit around the poles fairly close to the Earth (~850 km above) • GOES(s) orbit much further above the surface (~36,000 km), and always remain above the same location on the equator

GOES • Since they remain over the same location, they constantly transmit images of the same location at a rate of about 15 minutes • Because they are high above the Earth’s surface, they capture a large portion of the Earth with each image • However, the spatial resolution is lower as a result

POES • POES(s) rotate around the Earth, so the point on the Earth’s surface that they are above constantly changes • POES(s) are very close to the Earth, so the images have very high spatial resolution • However, the temporal resolution is very poor (about two images a day for any one location)

Examples GOES POES

Types of Imagery Visible: - This imagery can only measure visible light (~0.6 µm wavelength) - Therefore, it can only be used during the daytime Infrared (IR): - This imagery uses infrared radiation (~10-12 µm wavelength), and therefore can operate at any time of day - Here, colors (or shades of gray) depend on the color of the emitting object Water Vapor: - This imagery uses a wavelength (~6.6 µm) that is strongly absorbed by water vapor, and can be used any time of day - Bright white areas indicate lots of water vapor (often clouds), while dark areas indicate a much drier atmosphere

AOS 100: Weather and Climate