Stratospheric volcanic SO2 emissions and aerosol optical properties

Key contacts

The CMIP7 version of the volcanic forcing dataset has been released. Documentation on the dataset is hosted externally. This contains a detailed dive into the data. In contrast, this page provides an overview and some key, CMIP-specific information.

If you find any issues, please contribute to the discussion on GitHub.

Summary

Source IDs for CMIP7 phases

The source ID that identifies the dataset to use in CMIP7 is given below.

CMIP7

For the CMIP7 phase of CMIP7, use data with the source ID UOEXETER-CMIP-2-0-0

This data is for use in CMIP7 production simulations. All data sets for use in CMIP7 production simulations are published with a mip_era metadata value of ‘CMIP7’. This metadata value appears both in the file’s global metadata as well as its metadata on ESGF.

If you find an issue, please create an issue on GitHub so that the identification and resolution of this issue is publicly accessible.

Testing

For the testing phase of CMIP7, use data with the source ID UOEXETER-CMIP-1-3-1

This data is for testing (both of the forcing data and of modelling workflows) only. Production simulations should not be started based on any data that has a mip_era value equal to ‘CMIP6Plus’. (The mip_era metadata value appears both in each file’s global attributes as well as its metadata on ESGF.)

If you have any feedback, please add it to the relevant GitHub discussion.

Recommendation for pre-industrial control

There are dedicated pre-industrial control files for aerosol optical properties. For aerosol optical properties, these are provided as climatologies and hence have monC in their name (they also have a time axis with only twelve points, so they’re hard to miss). There is no recommendation for teams who want to run pre-industrial control with volcanic emissions as yet, that is still being developed in collaboration with early testing teams who are interested in this application.

For full details, see the external documentation.

Grids and frequencies provided

The volcanic emissions are provided with daily resolution alongside latitude, longitude and injection height information.

The aerosol optical properties are provided with monthly resolution on a latitudinal, vertical and wavelength grid. To facilitate use of our dataset in any radiative model, we provide the community with scripts (see this associated Github repository) that can be used to interpolate the files we provide on ESGF on any list of wavelength inputted by the user. These include a simple method to linearly interpolate to waveband midpoints and a weighted averaging method that is more computationally expensive but provides more representative averages, particularly for radiation schemes with broad wavebands. We therefore recommend modelling groups use the latter method where possible.

Variables provided

For the aerosol optical properties dataset, the extinction, single scattering albedo, scattering asymmetry factor, effective radius, surface area density and volume density are provided. For emissions, the volcanic SO2 injection time, latitude, longitude, height, depth and mass are provided. Further details are provided in the external documentation (section III and IV).

Uncertainty

There is considerable uncertainty in the magnitude and height of volcanic SO2 injection for the satellite era. These uncertainties are even larger in the pre-satellite era, for which there is considerable uncertainty on the occurence, timing and location of volcanic SO2 injections. These uncertainties propagate to our aerosol optical properties dataset for the pre-satellite era. Uncertainties are currently not reported in the dataset but they will be in the future.

Differences from CMIP6 or other previous versions

File formats and naming

The file formats are quite different from CMIP6 because the data is coming from a different provider. The naming may also be different. Overall, we would say that the data is more uniform now and in line with other input4MIPs data and conventions. We do not have a direct mapping/translation guide at this stage (although there is some detail in the external documentation).

Data

For a full dive into the changes from CMIP6, see the external documentation.

Revision history

UOEXETER-CMIP-1-3-1

v2.0.0 includes the following key updates: i) new H2SO4 number density variable replacing aerosol number density; ii) correction to the 1920-1978 ice-core dataset, improving consistency with pyrheliometer measurements and CMIP6. As a result of this change, the mean historical SAOD has decreased a bit, but it is still higher than CMIP6. Hence v1.3.1 is deprecated.

UOEXETER-CMIP-1-3-0

v1.3.1 does minor plus updates and adds the aerosol number density requested by some modelling groups. Hence v1.3.0 is deprecated.

UOEXETER-CMIP-1-2-0

v1.3.0 updates the handling of small eruptions in the pre-satellite era. Hence v1.2.0 is deprecated.

UOEXETER-CMIP-1-1-3

v1.2.0 includes climatology data (for piControl simulations) and updates the handling of small eruptions. Hence v1.1.3 is deprecated.