Hands-On, Minds-On Meteorology
Description | Programming | Operation

 Controls of Temperature Description The Controls of Temperature program is designed to allow students to gain an appreciation for how the atmosphere's properties affect the earth's global mean surface temperature. click for whole shot

Objectives

The primary objective of the Controls of Temperature application is to demonstrate how global mean surface temperature changes when parameters like amount of greenhouse gases, cloud cover, and cloud albedo are changed. The secondary objective is to have students learn to interpret graphs illustrating relationships between variables.

Programming

Theory

A three layer model problem (Ref: Wallace and Hobbs, 1977: Atmospheric Science: An Introductory Survey. Academic Press, 467pp.; Problem 6.27) shown here was solved to produce the expected global mean surface temperature given an incoming solar radiation, atmospheric absorption, global cloud cover, and global cloud albedo.

Assumptions

Any assumptions consistent with three layer atmospheric model.

All measurements are global!!

Equations

1) Cloud Albedo and Cloud Cover

Changing the cloud albedo and/or cloud cover resulted in a change of incoming solar irradiance:

New SolarE = (1-((ap * ca) + 0.17 * (1 - cc)))*342
where cc = cloud cover(%) / 100,
ap = % of greenhouse gases / 100,
ca = global cloud albedo / 100, and
342 = solar irradiance in W/m2

this new incoming solar irradiance is then fed into the surface temperature calculation

2) Surface Temperature

According to Wallace and Hobbs, 16 of 67 units, or (23.8%) of the incoming solar radiation is absorbed by atmosphere.
Also, 22 of 28 units, or (78.6%) of the outgoing longwave radiation is absorbed by atmosphere.

From the proof found above in the theory section,

E = (sigma*Temp)4 and so --> T= (E/sigma).25
so...
sfcTemp = Math.pow(([((solarE * term1) + (extraForcing*atmosPct)) /(B + 1)]/sigma),0.25);

where sigma = 5.67 x 10-8
and term1 = ((A*A) - (A*B) + A + 1) as seen in the proof for surface E
and A = 1-alpha(shortwave); B = 1-alpha(longwave)
and atmosPct = percent of normal atmosphere
and extraForcing = extra forcing due to either or both of the doubling of CO2 or water vapor in the atmosphere.

Other

N/A

Operation

Running the Program

• Click the link for Controls of Temperature.
• Changing '% of Greenhouse Gases' actually changes the absorption properties of the atmosphere (in both long and short wave). For example, if set at 40%, the absorption of long and short wave radiation by the atmosphere would be 40% of normal.
• Changing cloud cover % simply changes the global percentage of cloud cover. A nuance of this program is that you can set cloud albedo to 100% and cloud cover to 100%. If this is done, no energy reaches the Earth, and the surface temperature is 0K, regardless of the % of greenhouse gases.
• Changing cloud albedo changes the global albedo of the clouds. Visually, this is seen in the color presented on the tops of the clouds. This feature is scaled by cloud cover and would therefore have no effect if the cloud cover were set to 0%.

Extra Knowledge

Graphics

• Changing % of greenhouse gases does not cause a visual change.
• Changing cloud cover % changes the graphic to show no clouds (0%) to clouds growing in size & covering the entire sky (100%).
• Changing cloud albedo results in the clouds having a darker top (0%) to a bright white top (100%).
• Thermometers giving temperatures both in Kelvin and degrees Celsius are dynamic and correspond to the Global Mean Surface Temperature displayed to the right of the graphic.

All data can be exported, graphed, and saved using the "Graphing Tool".

 Department of Atmospheric Sciences University of Illinois at Urbana Champaign Created by Dan Bramer: Last Modified 07/27/2004 send questions/comments to bramer@atmos.uiuc.edu