From: Frank Eparvier <eparvier@colorado.edu>
Date: Mon Feb 17, 2003  1:02:31 PM America/Denver
To: Frank Eparvier <eparvier@colorado.edu>
Subject: Hints for HW#2

Here are some hints for HW#2, which is due in class tomorrow!

First a correction: I made a typo in the units for all the cross
sections.  They should be cm^2, not cm^-2.  Assume the same numbers
that I give, just that I wrote the units wrong.

Second, an overall hint:  Most of the problems require simple
unit conversions.  If you don't know the conversion factors,
you can look them up in most basic physics textbooks.

Finally, here are some specific hints:

1.a. You won't be able to find final numbers for the optical
depths, since I didn't give you a distance.  Do the calculation
all the way through, carrying the distance along as a variable.

2.a. For the purpose of the calculation of optical depths, assume
that sunlight is coming in vertically from above, through the
atmosphere from infinity down to the level of interest (250 km).
The solution involves integrating over altitude.  There is a reason
that calculus is a prerequisite for this class!

2.c. The ionization rate at height z is equal to the solar flux
that remains at height z times the cross section times the number
density at height z. In equation form: J(z)=I(z)*sigma*n(z).

I hope these hints help.  Remember, I'll be in D121 today (Monday)
from 4pm-5:30pm.

Frank
------------
Dr. Frank Eparvier
Laboratory for Atmospheric & Space Physics
University of Colorado, Boulder
mailto:eparvier@colorado.edu
Office: 303-492-4546
Fax: 303-492-6444
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