Posted by **Krysten** on Friday, March 5, 2010 at 6:06am.

On a sunny day in an estuary, the surface irradiance is 1.6*10^17 photons cm^-2 s^-1. What is k if the irradiance is 7.3*10^13 photons cm^-1 s^-1 at 16 m depth?

At a spot in the ocean, the surface irradiance is 7.8*10^16 photons and k=.14 m^-1. At what depth does the euphotic zone end?

Your airplane leaves 20 degrees N(linear velocity= 845 nm/h) heading to a point due north at 25 degrees north (linear velocity = 815 nm/h). You set the autopilot dor due north and go to sleep. If your flight time is 30 minutes, how far off and in what direction are you if you take no corrective action?

What is the instantaneous acceleration (both magnitude and direction) due to the coriolis force on an object moving at 160 m s^-1 to the west located at 17 degrees south, 86 degrees west?

In a fit of pique, the Canadians fire a cannonball due south from vancouver (lat 49.2 degrees N) at a randomly picked city (39.4 degrees N). Assuming the cannonball takes 48 minutes to get there, by how far and in what direction will the cannonball miss?

- Oceanography (Help please Damon!) -
**drwls**, Friday, March 5, 2010 at 8:17am
If you had posted these questions separately, an answer might have been obtained sooner. I can only help with some of your questions. Oceanography is not my field.

(a) For the first one, solve this "Beer's law" equation for k:

exp(-kL) = 7.3*10^13/1.6*10^17 = 4.56*10^-4

kL = 7.7

k = 7.7/16 = 0.48 m^-1

This assumes the sun is overhead. It usually isn't.

(b) Use the same equation, but the lower value of k. Use the definition of the the "euphotic zone" (whatever that is) to solve for L

At extreme depths, Beer's law may not apply because scattering becomes important. You also need to know the elevation angle of the sun.

- Oceanography -
**Damon**, Friday, March 5, 2010 at 1:28pm
I can only guess that we are talking about the decay constant in I = Io e^-kx

Where for example :

Io = 1.6 * 10^17 *10^4 photons/m^2s

and

i at 16 m = 7.3 * 10^13 * 10^4 = 1.6 * 10^17 * 10^4 * e^-k(16)

4.56 *10^-4 = e^-16k

ln 4.56 -4 ln10 = -16 k

1.517 - 9.210 = -7.693 =16 k

k = 0.481/m

For the second part I do not know how dark it is when we say the euphotic zone ends. I am sure the irradiance for that is defined in whatever text the student is using.

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