daytime.From: "Frank, John -FS" <jfrank@fs.fed.us>
Subject: RE: thanks, and a request
Date: September 16, 2015 at 3:48:21 PM MDT
To: Scott Denning <scott.denning@colostate.edu>, "Massman, William J -FS" <wmassman@fs.fed.us>
Resent-From: Scott.DENNING@colostate.edu

Scott,

Here are two data files. Hopefully they are self-explanatory with their content. This is 20Hz data. The filename refers to the end of the half-hour (i.e, year 2007, day 216, data from 2:30 to 3:00 MST). I have gone ahead and calibration corrected this data as well as time synched this data (i.e., now w and CO2 line up correctly, in the original file they were off by ~ 250 ms). FYI, the sonic is facing due west, but u and v are pointed southeast and northeast, respectively (i.e, 135o and 45o). w is straight up.

Here are some things to note:
-	The night file was time synched between sensors by -0.30 sec, the day file had to be time synched by -0.25 sec; I have already taken care of this.
-	This is not coordinate rotated. Applying the planar fit rotation will change the covariances for the night half-hour for CO2 by 1.074x and H2O by 0.992x, and for the day half-hour for CO2 by 1.096x and H2O by 1.077x.
-	This is not spectrally corrected. Applying spectral corrections for the night half-hour will increase CO2 and H2O both by 1.402x and for the day half-hour both by 1.050x.
-	Before the WPL correction the covariance for CO2 should be 0.360 mg m-2 s-1 for the night half-hour and -1.618 mg m-2 s-1 for the day half-hour. Because of the missing coordinate rotation and spectral corrections, you will only get 0.322 and -1.404 mg m-2 s-1 from these data files.
-	Before the WPL correction the covariance for H2O should be 0.0093 mg m-2 s-1 for the night half-hour and 0.1098 mg m-2 s-1 for the day half-hour. Because of the missing coordinate rotation and spectral corrections, you will only get 0.0092 and 0.0965 g m-2 s-1 from these data files.
-	After the WPL correction, the CO2 flux for night and day should be 0.286 and -1.152 mg m-2 s-1, or in more traditional units: 6.5 and -26.2 umol m-2 s-1 .
-	After the WPL correction, the H2O flux for night and day should be 0.0081 and 0.1155 g m-2 s-1, or in more traditional units: 0.45 and 6.41 mmol m-2 s-1 . As you can tell, the WPL correction doesn't cause water flux to change too much.
-	I've attached the final GLEES data that I submitted to AmeriFlux for the Water Year 2007. The values for FC and FH2O can be found for these two half-hours and are equal to the umol m-2 s-1 and mmol m-2 s-1 values listed above.
-	If you desire to have students investigate the WPL correction, most of the auxiliary data required is available in the spreadsheet I've attached. I can provide more details for the equations that we use, as well as a few other auxiliary data that are needed.

Have fun with this,
John

John Frank 
Electronics Engineer
Forest Service 
Rocky Mountain Research Station
p: 970-498-1319 
c: 970-692-4708 
jfrank@fs.fed.us
240 W. Prospect Rd. 
Fort Collins, CO 80526
www.fs.fed.us 

Caring for the land and serving people

-----Original Message-----
From: Scott Denning [mailto:scott.denning@colostate.edu] 
Sent: Tuesday, September 15, 2015 4:43 PM
To: Frank, John -FS; Massman, William J -FS
Subject: thanks, and a request

Dear John and Bill,

Thanks SO MUCH for your continuing willingness to help teach my grad students about eddy covariance, beetle kill, and ecosystem ecology. Everybody was very enthusiastic about what they learned on Friday up at GLEES, and I know that they learned more in a few hours with you than they do in weeks of lectures!

Now I'd like to assign a homework problem based on data from your site, and I could use a little help in putting this together. 

First, I’d like the students to do a flux calculation based on (nearly) raw EC data. I’m thinking we should do a simple calculation of a 30-minute CO2 flux from 10 Hz data for w and C, for one daytime case and one nighttime case. What I have in mind is simply to compute the covariance, without considering storage, coordinate rotation, WPL, or other processing. I’m not trying to teach how actual eddy covariance data are processed, but rather about how eddy covariance reveals ecosystem carbon balance. 

So could you share with me (and indirectly 15 grad students) 30 minutes of daytime and 30 minutes of nighttime vertical velocity and CO2 concentration data? 

I’m also going to have them compare annual cycles of NEE, H, and LE before and after the beetle kill, both to show the differences and (more importantly?) to familiarize the students with the Ameriflux website and some simple data analysis. 

Thanks again,
Scott