Intital simulation of Hunga-Tonga volcanic aerosol cloud with the UM-UKCA composition-climate model

This dataset is from a series of “forward projection” interactive stratospheric aerosol simulations of the Jan 2022 Hunga-Tonga volcanic aerosol cloud with the UM-UKCA composition-climate model.   The model experiments predict how the cloud will disperse through 2022, and apply the UM-UKCA model at GA4 (Walters et al., 2014), with GLOMAP v8.2, as applied for the “MajorVolc” datasets for Agung, El Chichon and Pinatubo (Dhomse et al., 2020), those runs aligned with the Historical Eruption SO2 emissions Assessment experiment within ISA-MIP (Timmreck et al., 2018).

The “standard” Hunga-Tonga GA4 UM-UKCA experiment emits 0.4Tg of SO2 at 29-31km, within a 24-hour period, matching the detrainment duration specified for the ISA-MIP HErSEA experiment protocol.  Following the stronger than expected mid-visible backscatter ratios (BSR) measured by CALIOP satellite-borne lidar, and from ground-based lidar from Reunion Island (very high BSR values > 200), we also ran UM-UKCA simulations with “scaled-up Hunga-Tonga SO2 emission”, at 0.8, 1.2 and 1.6 Tg of SO2 emitted.

Unexpectedly strong stratospheric AOD observed from the OMPS satellite months after the eruption further strengthens the motivation for these simulations.

Several hypotheses for the high AOD from Hunga-Tonga have been suggested:
   1) an unusual amount of (or influence from) co-emitted ultra-fine ash particles
   2) “in-plume oxidised sulphate” already converted from SO2 at the time of detrainment
         (e.g. via aqueous-phase oxidation within water droplets within the eruptive plume).
   3) co-emitted marine aerosol (e.g. sea-salt aerosol) from seawater vaporized in the plume
 

There are 4 types of netcdf files, Stratospheric AOD (saod), Effective Radius (reff), Extinction (ext) and sulphate aerosol surface area density (sad).

 
For e.g.  
saod550_HT_0pt4Tg_T2Mz-20220101-20230831.nc contains
Stratospheric aerosol optical depth (sAOD) at 550nm (2D-monthly dataset vs latitude and time) with 0.4 Tg SO2 injection Jan2022 to August 2023
Whereas other files
reff_HT_0pt4Tg_T2Mz_20220101-20230831.nc,
sad_HT_0pt4Tg_T2Mz_20220101-20230831.nc
 ext550_HT_0pt4Tg_T2Mz-20220101-20230831.nc

contain particle effective radius (reff),  aerosol surface area density, aerosol extinction  as 3D-monthly fields (altitude, latitude , time) from the same simulation.
Other saod and extinction files are also available at 870 and 1020 nm.

Note that these are preliminary simulations, hence we do not expect good match with the observations.  We plan to perform additional UM-UKCA simulations, comparing to the satellite and ground-based lidar measurements, and to in-situ balloon observations from Reunion Island rapid response campaign & upcoming high-altitude balloon sampling flights in Brazil.

References :
Dhomse SS, Mann GW, Antuña Marrero JC, Shallcross SE, Chipperfield MP, Carslaw KS, Marshall L, Abraham NL, Johnson CE. 2020. Evaluating the simulated radiative forcings, aerosol properties, and stratospheric warmings from the 1963 Mt Agung, 1982 El Chichón, and 1991 Mt Pinatubo volcanic aerosol clouds. Atmospheric Chemistry and Physics. 20(21), pp. 13627-13654

Timmreck, C., Mann, G. W., Aquila, V., Hommel, R., Lee, L. A., Schmidt, A., Brühl, C., Carn, S., Chin, M., Dhomse, S. S., Diehl, T., English, J. M., Mills, M. J., Neely, R., Sheng, J., Toohey, M., and Weisenstein, D.: The Interactive Stratospheric Aerosol Model Intercomparison Project (ISA-MIP): motivation and experimental design, Geosci. Model Dev., 11, 25812608, https://doi.org/10.5194/gmd-11-2581-2018, 2018.