Request to add ERA5 re-analysis files on ARCHER-2 for Jan 2019 to Mar 2022 (post-ERA-interim period)

Dear NCAS-CMS Helpdesk,

I have run a series of interactive stratospheric aerosol simulations of the Hunga-Tonga volcanic aerosol cloud, with GA4 UM-UKCA CheST+GLOMAP on ARCHER-2 (UM experiments xphy and xphr)

These have already shown some very interesting results, the main one being there is more AOD in the stratosphere right now than can be explained by 0.4Tg of SO2 measured from TROPOMI (and also IR sensors).

I have run a sequence of simulations scaling up the 0.4Tg of SO2 by a factor of 2, of 3 and of 4, and the finding we have suggests a factor of 3 increase in SO2 is consistent with the AOD currently being measured from satellite (e.g. from the OMPS instrument).

These simulations are free-running experiments based on re-starting the model from a state where the QBO was in a similar phase as the current situation, and capture the dispersion of the cloud in quite good agreement with the observations.

But the match of the winds etc. is only approximate.

In discussion with the group at Univ. Colorado, there is a MIP for interactive stratospheric aerosol models, which involves each model running with “specified dynamics” — i.e. to run nudged to meteorological re-analysis files.

The UM-UKCA has this functionality, and we have run nudged simulations of several eruption-clouds, but currently the ARCHER-2 directory has only the ERA-interim re-analysis fields, with data-files only up to June 2019.

The ERA5 re-analysis essentially replaces ERA-interim, and for running the currently meteorological setting, we will need to run with ERA5 re-analysis meteorology.

With the Hunga-Tonga aerosol cloud at this unexpectedly high strat-AOD (given the relative modest SO2 emission of 0.4Tg), and several groups working to understand potential reasons for this – which include already-oxidised-within-volume-plume-sulphate, sea-spray from the detraining vaporised seawater, and/or ultra-fine ash particles.

Each of these is a plausible mechanism for how there can be more strat-AOD than expected from the 0.4Tg emission of SO2.

And then this is quite a priority to get equivalent ERA-5 re-analysis files produced so that the UK community model can run these simulations, both for the MIP, and for UK science.

I think it was Luke Abraham (NCAS-CMS, Univ. Cambridge) and/or Mohit Dalvi (JWCRP Met Office) who originally co-produced this archive of the ERA-interim re-analysis netCDF files currently stored on ARCHER-2 at:


Please can someone in the NCAS-CMS team (Luke?) explore how we can plan to get the ERA5 re-analysis files into equivalent netCDF files on ARCHER so that users can run simulations with the nudged UM-UKCA model.

I guess it will require the ERA5 files to be extracted and the scripts used to generate the ERA-interim re-analysis archive be adjusted to produce the ERA5 equivalents.

And I realise it’s not a simple request – and happy to discuss to help with any required communications and planning to achieve this.

Thanks a lot for your help,

Best regards,


Dr. Graham Mann
Lecturer in Atmospheric Science, Univ. Leeds.

Hi Graham,

These files are available on Monsoon2 here


However, they haven’t been copied back to ARCHER2 yet. We can copy these across, but there are also necessary code changes that have to be made to be able to read these files correctly.

The code changes are documented in UM ticket #5336. They are for Rose versions of the UM and you will need to back-port these to vn8.4.

Best wishes,

Hi Luke

Thanks for explaining this.

OK, that would be great, yes pls can you (or someone in the NCAS-CMS team) copy the ERA5 directory & files over to ARCHER-2

I will look into the code-change that needs to be back-ported to the v8.4 branch, and if it is a fairly straightforward change I am happy to back-port that to the v8.4 nudging FCM branch.

I will be able to look into this tomorrow or Wed and send an update to this later this week.

Likewise please can you post an update to this helpdesk ticket once the ERA5 files are copied over to ARCHER-2

Thanks again, much appreciated

Best regards


The era5 files are on ARCHER here: