GA4.0 N216 Development

As part of the GA4.0 UKCA development, in Cambridge we are developing a N216L85 GA4.0 model using the CheT(+GLOMAP) configuration. However, there is no GA4.0 N216 base model existing at MetUM version 8.4.

Create a GA4.0 N216 Base model

There are a number of steps that need to be made before a base GA4.0 N216 model is ready for UKCA to be included:

1. Assess the models available at the GA development page (password required)
   • This shows that the only existing N216 job available is xhcea (password required) on MONSooN
     • This job ran for 30 years, and the output is available on MOOSE
     • The original UKMO version of this job is ajthw.
   • There are however GA4.0 N96 jobs available at vn8.0 (aliur (password required)) and vn8.4 (amche (password required))
2. It is therefore necessary to regrid amche to N216 for use by UKCA
   • There is a guide on how change the horizontal resolution (password required) on the GA twiki.
     • The ancillary files can be taken from xhcea which already exist on MONSooN.
     • There may be other changes that have been made between aliur and xhcea which are not represented in the guide. I have therefore asked Jeremy Walton to port aliur as well as amche over to MONSooN to check the differences.
   • The new job xjgva has been created which is a GA4.0 N216L85 AMIP candidate, based on amche and using the differences from the guide (password required) and the differences between aliur and xhcea.
     • Differences between vn8.0 GA4.0 N216 (xhcea) and N96 (aliur): diff.xjgvx.xjgvz
     • Differences between vn8.4 GA4.0 N216 (xjgva) and N96 (amche): diff.xjgva.xjgvy
   • It should be noted that the settings were mainly taken from the guide rather than the differences between vn8.0 jobs. Notable differences between xjgva and xhcea, or xjgva and amche, are:
     1. In xjgva soil moisture has been initialised to $USER_ANCIL/N216/orca025/smc_snow/v1/ajthma.smc_scaled whereas amche sets this from the dump.
     2. xjgva uses the same start dump as xhcea: $USER_ANCIL/N216/start_dumps/v1/ajthma.dai1910.
     3. In the Large Scale Precipitation section, xjgva uses 7 substeps over full column, rather than 10 in xhcea.
     4. xjgva uses the standard vn8.4 spectral files, rather than the vn7.9 spectral files used by xhcea. There should be no difference in the components of the file used however.
3. xjgva compiled successfully and has been sent off for an equivalent 30-year run to xhcea.
   • xjgva runs at approximately 2400 +/- 101 seconds for each 10-day jobstep, giving a maximum throughput of 12 model months per day.
   • However, the actual throughput is quite variable, having between 3 and 12 model months per day with an average turnover of 9 model months at present.