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 largescale 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
Pictures
From:http://www.centennialofflight.gov/ess
ay/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