Aerosol effects in OpenIFS 43r3?

Hi Joakim,
1) There is no treatment of aerosol-cloud interactions in the IFS.
2) Not in the default setup for medium range forecasts, but something like this will have been used for reanalysis, although I don't know if such settings are available in OpenIFS - perhaps Paul Berrisford would know?

I am pretty sure that there is no representation of date-dependent stratospheric aerosol in the IFS so I would think that any Pinatubo effect would be seen only via SSTs.
Note that we are currently working on a version of the aerosol climatology that can represent longer term trends in anthropogenic aerosol species, but this wouldn't be available until 49r1 at the earliest.
Regards,
Robin.

Hi Joakim,

Reanalysis started using variations in tropospheric sulphate and stratospheric, volcanic aerosol in ERA-20CM, see sections 3.2.4 and 3.2.5 in:

https://rmets.onlinelibrary.wiley.com/doi/10.1002/qj.2528

I don't know if these settings are available to use in OpenIFS, sorry.

Regards,
Paul

Hi Joakim, as part of the ongoing OpenIFS/AC project both KNMI and FMI are indeed implementing interactive aerosol processes into OpenIFS 43r3. 

The aerosol properties are however not passed to the model through external time-varying forcing files (which you seem to be referring to?) but it is done by including an interactive aerosol code in the model, together with either a minimal or a more elaborate interactive atmospheric chemistry package. 

I didn't have the impression that this is what you were looking for, but if this is of interest to you (or if you want to know more about CMIP6-type transient simulations with EC-Earth4) I would suggest to get in touch with Twan Van Noije at KNMI. 

Hi all

Thanks for the replies!

Sounds like there are some versions of IFS that have used time-varying aerosols at some point.
I also came across Chris Roberts' paper from 2018 where he says:

Tropospheric aerosol forcing is specified using version 2 of the Max Planck Institute Aerosol Climatology Simple Plume model (MACv2-SP Stevens et al., 2017), which was implemented within the IFS radiation scheme specifically for this configuration. MACv2-SP enables the prescription of the anthropogenic aerosol optical properties and associ- ated Twomey effect, and consists of nine spatial plumes re- lated to the major anthropogenic sources. The amplitudes of each plume are scaled through time to provide region- specific variations in tropospheric aerosol through the his- torical period.

Volcanic forcing is specified as a total stratospheric aerosol optical depth (SAOD) that varies with time and latitude.

That sounds like exactly what I'm looking for. And he was using 43r1 which is a lot closer to 43r3 that cy38 used for ERA-20C (I think?). Is that model version around somewhere and would it be a not-too-difficult merge?

Many thanks
Joakim

The radiation code changed in 43r3, and a new aerosol climatology was introduced. This changed the way aerosols are specfied (requiring aerosol mass per model layer, rather than optical depths), so work from earlier cycles does not carry over easily. The IFS does retain the ability to read in and use time-varying volcanic aerosol, and the optical depths at 525nm are converted to mass densities assuming the optical properties are those of tropospheric sulphate aerosols. This is how the latest cycles work, you can check for 43r3 by searching for STRAT_BG_AER_MASS_EXT in module/radiation_setup.F90 and phys_radi/radiation_scheme.F90. If you find these you can hopefully trace how it all works. Volcanic aerosol arrays are set in routine suecaec in module/yoeaerc.F90, and there are several options which are coded, including reading in data from a file. Our scripts define two files: cmip6_stratospheric_aerosol_aod.dat and CMIP5 volcanic_giss.data, but only vertically integrated amounts are used (and then re-projected to model levels using functions).

At ECMWF I am presently working (in the context of the H2020 CONFESS project) on upgrading how we handle the vertical distribution of volcanic aerosol, but plan to keep this basic mechanism for converting optical depth (which is what the observed datasets contain) to mass, so that when the radiation code calculates the optical depth, it matches the original input data.

For tropospheric aerosols, as Robin mentioned, ECMWF are working on a time-varying climatology based on simulations with the CAMS aerosol and chemistry schemes. We hope that these will become available in Cy49r1 in time for ERA6 and SEAS6 in 2024. Note that in pre-industrial times there was still a lot of atmospheric chemistry going on, and both natural and human induced aerosol emissions of many sorts. It was our inability to separate our existing aerosol climatology into "background" and "anthropogenic" that led us to ditch the MACv2-SP approach in favour of direct simulation of everything, despite the extra complexity. Our new approach also gives much more realistic spatial distributions than MACv2-SP. We are still in the middle of this work, though, and don't have a finished product yet.