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Deep atmosphere inconsistencies

Posted: Mon Aug 24, 2020 9:57 am
by maxhbalsmeier

I just started with WRF. I implemented the deep atmosphere into the ICON-IAP model, so I checked wether the deep atmospehre is implemented into the ARW solver. I found that replacing the functional determinant of spherical coordinates according to

sqrt(g) = r^2*cos(latitude) -> a^2*cos(latitutde),

where a is the mean Earth radius, is sufficient to consistently derive the shallow atmosphere approximation (compare ... 6/qj.04.49 , they do not show this in detail, but go into the same direction). Otherwise you will run into inconsistencies concerning spurious divergences and/or vorticities (numerically small but aviodable). In my view the shallow atmosphere has four implications:

1.) radius and related grid properties (faces, volumes, depending on the model formulation) independant on height
2.) non-traditional Coriolis components neglected
3.) gravity independant on height
4.) metric terms ~ uw/r, vw/r neglected

I can show You detailed derivations if You like.

From a look into the documentation and the code, ARW is a deep solver in terms of aspects 2.) and 4.), but still makes approximations 1.) and 3.).

Would it be appreciated if I sat down and implemented a height-dependant gravity as well as height-dependant grid properties into the code? Since I only just begin with WRF, this would take some time.


Re: Deep atmosphere inconsistencies

Posted: Mon Aug 24, 2020 11:20 pm
by Ming Chen
Our top priority at present is MPAS development and application. The capability for deep atmosphere simulation is available in MPAS. We have no plan to add this capability to WRF. It is completely your decision whether to proceed or not on this work.

Re: Deep atmosphere inconsistencies

Posted: Tue Aug 25, 2020 8:07 am
by maxhbalsmeier
Hello Ming,
okay, thanks, good to know. I will see if I find the time.