Creating ancils for domains over the poles

Unified Model
1

Hello, when setting up domains centred over the poles in the latest version of the nesting suite, l am getting some strange values in ancils produced by the CAP - specifically lat/lon values of the order 1x10^29. I’ve also got a large missing area over the pole.

I thought I had set up a rotated pole LAM such that the pole would be somewhere over the equator (indeed, this is what the job output shows in cylc-run/u-662/log/job/20150323T0000Z/Antarctica_10km_ancil_mask/NN/job.out) but evidently I’ve set something incorrectly. I have replicated what I did in previous versions of the nesting suite but the options have changed between those and the more recent version.

In rose-suite.conf I have set the following:

rg01_centre=-87,15
rg01_igbp_offset=0,0
rg01_name=“Antarctica”
rg01_use_centre=true
rg01_rs01_delta=0.09,0.09
rg01_rs01_npts=600,800
rg01_rot_grid=true

Are any of these likely to be explaining this output? I also need to repeat the exercise for the Arctic, which I imagine will have the same issue.

On a related note - my understanding is that ANTS isn’t configured to work with the nesting suite yet - are there plans to get this working? Ideally it would be good to use more recent datasets for ancillary production if that’s possible, which would save me making too many of my own custom ancils.

Thanks in advance!
Ella

2

Hi Ella

You appear to have chosen a grid that confounds the CAP.
I changed the horizontal grid lengths to be (0.08999, 0.09) and the CAP produced a good mask.
I left the resolution at (0.09, 0.09) and changed the domain size to (610, 800) – and that worked OK too.

Can you tweak the domain to find one that’s suitable?

Grenville

3

Interesting, thanks Grenville. Are there any particular hard-and-fast rules about what upsets the CAP or not, or is it just a matter of trial and error?

4

Hi Ella

The CAP has always been a bit difficult in polar regions and at high resolution. Are you working with someone experienced with running the UM at the poles?

Grenville

5

Hi Grenville. I suppose I might be supposed to be one of those people! I’ve never created a domain directly covering the pole though. I will ask around my colleagues who are doing similar things and see how they’ve overcome it. Eventually I’ll make my own orography/LSM ancils anyway, but need the grid itself to produce extra files that the UM will accept.
Cheers,
Ella