Opened 2 weeks ago

Last modified 8 hours ago

#2860 new help

Spurious SST values when using ERA-Interim data

Reported by: shakka Owned by: um_support
Component: UM Model Keywords: interpolation, sea ice, SST, ancillaries
Cc: Platform: Monsoon2
UM Version: 11.1

Description

Hi helpdesk,

I'm having a bit of a nightmare trying to get ERA-Interim SST and sea ice data into the global model, and I wonder if you can help. I am attempting to use ERA-Interim data as input to force the global model at N512, before downscaling to my 4 km LAM.

The SST and SIC data are contained separately in files with ERA-Interim SSTs and SIC, interpolated onto the N512 grid (e.g. /projects/polar/elgil/hindcast/N512_SIC_SSTs/2008_SST_n512).

I have reconfigured the global model (glm_um > reconfiguration and ancillary control > configure ancils and dump fields) to use these files rather than the default climatologies usually used.

When I run the model, the job.out files show that these files are picked up successfully, and indeed, when I examine the output, I can see that the sea ice is downscaled successfully from ERA > GLM > LAM (see attached file '20080101_SIC_inheritance_glm_ERA_native.png').

However, the SSTs are completely bizarre - despite supposedly reconfiguring the SSTs from my input file, there are very artificial edge effects, where the model has set any values over sea ice to -1.7 deg. However, the sea ice fraction used is not the sea ice fraction I have supplied (see attached file '20080101_SST_inheritance_glm_ERA_native.png'). Further, the location of these areas of spurious values vary on a daily timescale.

In the areas that are *not* strangely masked, the ERA-Interim data has evidently been correctly interpolated - this is true both of the GLM and LAM. This suggests that the UM is re-writing the SST data based on incorrect (and time-varying) sea ice ancillaries.

Can you help me find out whether this is hard-wired into the code, and crucially, how to change it?

I have also plotted both SSTs and SIC with the UM's climatological ancils, and although they are more similar to each other, the area with spurious values is not exactly the same (see attached files '20080101_clim_SIC_inheritance_glm_ERA_native.png' and '20080101_clim_SST_inheritance_glm_ERA_native.png'). After discussing with colleagues, we wonder whether this is because the UM is interpolating the monthly climatologies into daily values.

This may suggest that the UM is using monthly climatologies interpolated to produce a daily sea ice field, which is then used to mask the SST data wherever sea ice is present.

Can anyone advise?

Many thanks in advance,

Ella

Attachments (4)

20080101_clim_SIC_inheritance_glm_ERA_native.png (121.4 KB) - added by shakka 2 weeks ago.
sea ice using climatological values
20080101_clim_SST_inheritance_glm_ERA_native.png (110.7 KB) - added by shakka 2 weeks ago.
SSTs using climatological values
20080101_SST_inheritance_glm_ERA_native.png (109.2 KB) - added by shakka 2 weeks ago.
SSTs using ERA-Interim
20080101_SIC_inheritance_glm_ERA_native.png (120.5 KB) - added by shakka 2 weeks ago.
sea ice using ERA-Interim

Download all attachments as: .zip

Change History (6)

Changed 2 weeks ago by shakka

sea ice using climatological values

Changed 2 weeks ago by shakka

SSTs using climatological values

Changed 2 weeks ago by shakka

SSTs using ERA-Interim

Changed 2 weeks ago by shakka

sea ice using ERA-Interim

comment:1 Changed 8 days ago by grenville

Ella
What's the suite id?
Grenville

comment:2 Changed 8 hours ago by shakka

Hi Grenville,

I thought I had replied to this, but evidently my comment didn't post. Both suites u-bh076 and u-bh069 should have the same set-up, and experience the same problem.

Thanks,
Ella

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