Monday, December 7, 2009

Ignoring Friction

In researching my astronomy presentation on Saturn's newly discovered ring, I started relearning the concepts behind black body radiation as described in my high-school level textbook. "Ignoring friction" harps back to my high school physics textbooks that qualified most problems with "you may ignore friction in your calculations."
I have ignored reality in applying idealized black body radiation curves to understand what Bob Grumbine is saying about sea ice and earth's surface brightness in these posts:
(Subtext: any one reading me should definitely be reading Grumbine's blog; see blog roll.)

I sent Bob Grumbine an earlier draft of this illustration and I'm grateful for his answer (click to enlarge):

If I were to type to publish private correspondence from climate researchers (don't want to go there), it would be easier to explain what I learned and have yet to learn.

The illustration is both right and wrong. It is right in that it portrays idealized black body concepts; from these concepts, I was able to conclude that satellite-based measurements of ice would be nearly impossible if earth's surfaces were true black body emitters. (And now I'm reminded of someone who claimed he could disprove global warming using only high school physics.) And it is wrong in that earth's surfaces, especially ice, are way off from the ideal black body emission curve.

I'm sharing my learning process in part to thank Bob Grumbine. I don't want make more work for him, but he tries to explain science to readers at a high school level, and more impressive, took the time to review my illustration and direct my next steps in where to study.

The other reason I share is to exploit the unique learning opportunity we have with the Internet. There may be others at my level who can assist or learn from my work. For example, it appears my graph showing the attenuation of Earth's atmosphere is off. I've supplemented it with a slightly different version from wikipedia, but am still looking for a definitive reference.

I welcome comments and suggestions.


1 comment:

Alastair said...

The first thing you have got to do is ignore "friction"! Here is the specrum of the Sun:
and here is the spectrum of the earth:

Note that they hardly overlap. So radiation can be treated as incoming from the sun and outgoing from the earth.

Now adding in "friction" the high frequency radiation from the sun (UV) is absorbed in the stratosphere by O2 and O3. Terrestrial radiation is absorbed absorbed by CO2 in the middle of the terrestrial spectrum and warms the atmosphere. See Hat tip to the Buck Rabbit and


Cheers, Alastair.