How can I use the output variables of iCESM to generate δ18O in atmospheric precipitation?

[ningwentao]

Respectful sir or madam，

How can I use the output variables of iCESM to generate δ18O in atmospheric precipitation?
I checked the (H218OV 、H218OL、H218OI、H216OV 、H216OL、H216OI) and (PRECSL_H218OS、PRECRL_H218OR、PRECSC_H218Os、PRECRC_H218Or、PRECSL_H216OS、PRECRL_H216OR、PRECSC_H216Os、PRECRC_H216Or) variables and found that I could not get reasonable results.
Thank you for your help.
Sincerely,
Ning

The code below is where I extracted the various parts of the water to calculate the total precipitation(H216O H218O) and then used them to calculate R18O/δ18O with NCL.


pr1_1 = f1[:]->PRECRC_H216Or ; read pr from all files
pr1_2 = f1[:]->PRECRL_H216OR
pr1_3 = f1[:]->PRECSC_H216Os
pr1_4 = f1[:]->PRECSL_H216OS
pr1 = pr1_1 + pr1_2 + pr1_3 + pr1_4

pr2_1 = f2[:]->PRECRC_H218Or ; read pr from all files
pr2_2 = f2[:]->PRECRL_H218OR
pr2_3 = f2[:]->PRECSC_H218Os
pr2_4 = f2[:]->PRECSL_H218OS
pr2 = pr2_1 + pr2_2 + pr2_3 + pr2_4

Mh2o = 18.015 ; mean molecular mass of water
Mh218o = 20.013 ; molecular mass of H218O, units = atomic mass units (1/12 mass of 12C ~ 1.66654 E -27 kg)
Mh216o = 18.009 ; molecular mass of H216O
R_VSMOW = 0.0020052 ; O18/O16 ratio in standard (here, VSMOW) = 2005.20 ± 0.45 ppm (Sharp txtbook, 2007)

R18O = (pr2/pr1)*(Mh216o/Mh218o);
R18O!0 = "time"
R18O!1 = "lat"
R18O!2 = "lon"
d18O = (R18O/R_VSMOW-1)*1000 ;

 

[nusbaume]

Hi Ning,

Apologies for the slow response! I believe the issue you are running into is that the molar masses and geochemical standard (VSMOW) is already incorporated into the isotope values in iCESM. So I believe you just need to change your final R18O and d180 calculations to the following:

R18O = pr2/pr1
d18O = (R18O - 1))*1000

Note that you might need to sanitize the H216O data (e.g. pr1) to make sure the values aren't too small (e.g. < 1e-18), as otherwise the isotope ratio can become unrealistically large.

Anyways, I hope that helps, and if you are still getting bad isotope values even after making the changes above just let me know.

Thanks, and have a great day!

Jesse

 

[ningwentao]

Hi Ning,

Apologies for the slow response! I believe the issue you are running into is that the molar masses and geochemical standard (VSMOW) is already incorporated into the isotope values in iCESM. So I believe you just need to change your final R18O and d180 calculations to the following:

R18O = pr2/pr1
d18O = (R18O - 1))*1000

Note that you might need to sanitize the H216O data (e.g. pr1) to make sure the values aren't too small (e.g. < 1e-18), as otherwise the isotope ratio can become unrealistically large.

Anyways, I hope that helps, and if you are still getting bad isotope values even after making the changes above just let me know.

Thanks, and have a great day!

Jesse

Dear Jesse,
I am very glad to receive your reply. I appreciate your help and will take your kind reminder into consideration. So everything I get makes sense.
Sincerely,
Ning