AOS 100: Weather and Climate
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Transcript of AOS 100: Weather and Climate
AOS 100: Weather and Climate
Instructor: Nick BassillClass TA: Courtney Obergfell
Some Basic Info• Class website: http://www.aos.wisc.edu/~aos100nb/• Nick’s information:
- Email address: [email protected] Office: 1451 Atmospheric and Oceanic Sciences- Office hours: 4-5 W, 2:30-3:30 R*
• Courtney’s information:- Email address: [email protected] 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:
(1) RADAR(2) 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
http://www.bergenskywarn.org/Pages/BergenSkywarnUptonOpenHouse2001.htm
From:http://www.centennialofflight.gov/essay/Dictionary/radar/DI90G1.jpg
Pictures
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 ImageryVisible:
- 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