nitrate vertical advection versus nitrate*vertical velocity

Discussion about coupled ecosystem models

Moderators: arango, robertson

Post Reply
Message
Author
fannychenillat
Posts: 5
Joined: Fri Nov 27, 2009 2:53 pm
Location: Scripps Institution of Oceanography - UCSD

nitrate vertical advection versus nitrate*vertical velocity

#1 Post by fannychenillat » Sat May 17, 2014 12:21 am

Dear all,

I am having troubles trying to understand why my nitrate_vertical_advection field (NO3_vadv) is different from my nitrate_multiplied_by_vertical_velocity field (w*NO3, w is true vertical velocity - not Omega), to within a constant.
I mean I should have similar trend, right? However, I do observe regions with complete different behavior (see figure attached). I guess I am missing something but I can't figure out what.
Any suggestion?

For information:
My NO3_vadv is computed online by ROMS, saved every 1 day.
My w*NO3 is computed offline, with w and NO3 saved every 1 day.

Thanks

Fanny
Attachments
Capture d’écran 2014-05-16 à 4.59.50 PM.png
Capture d’écran 2014-05-16 à 4.59.50 PM.png (51.18 KiB) Viewed 2519 times

cae
Posts: 29
Joined: Mon Jun 30, 2003 5:29 pm
Location: UC Santa Cruz

Re: nitrate vertical advection versus nitrate*vertical veloc

#2 Post by cae » Thu May 22, 2014 9:55 pm

Hi Fanny.

For a tracer, C, the vertical advection term in the tracer equation is wdC/dz or in flux-conservative form d(wC)/dz. It is the flux divergence that causes changes to a tracer value in a cell, not the flux across any cell boundary alone.

ROMS is written in a flux conservative form and I think it's calculating this quantity in s-space (i.e., d(omega C)/ds), but a calculation of d(wC)/dz using fields stored in the avg files should be much closer than wC.

Chris

Post Reply