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: 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:

(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