EarthCARE Stratospheric Aerosol Optical Depth and Its Impact on ICON Forecast

Stratospheric aerosols play a significant role in the Earth’s radiative balance, atmospheric chemistry and large-scale circulation. Despite their importance, vertically constrained stratospheric aerosol optical depth (AOD) fields are not routinely available for use in global climate modelling systems, which therefore continue to rely on climatological background values or total-column AOD information derived from passive remote sensing sensors. To address this limitation, we exploit observations from the EarthCARE mission to derive stratospheric AOD on a global scale following a moderate volcanic eruption and investigate the impact of the eruption induced AOD perturbation through model assimilation.

To this end, we derive the stratospheric AOD at 355 nm from measurements of the EarthCARE/ATLID high-spectral-resolution lidar (HSRL). Stratospheric aerosol layers are identified and constrained utilizing ATLID target classification products. The stratospheric AOD is calculated by vertical integration of the ATLID L2 aerosol extinction profiles and subsequently regridded to the native ICON model grid, producing monthly global fields of stratospheric AOD.

The April 2024 Ruang volcanic eruption is used as the case study to examine the temporal evolution of stratospheric aerosol loading over approximately one year. As EarthCARE was launched two months after the eruption, the early ATLID observations already capture an enhanced stratospheric aerosol load due to the presence of volcanic particles.

Independent HSRL observations at 532 nm from the DQ-1 mission launched in April 2022, are further explored as a complementary data source to bridge multi-spectral, complementary information between the two missions, and support the development of a long-term stratospheric aerosol climatology.

Finally, the impact of assimilating the EarthCARE-derived stratospheric AOD fields into the ICON forecasting system is evaluated. The experiments reveal systematic changes in radiative fluxes and coherent responses in key atmospheric variables, indicating the potential of vertically constrained stratospheric AOD observations assimilation to improve numerical model simulations.

Acknowledgements:

This work has been financially supported by the ACtIon4Cooling (Aerosol Cloud Interactions for Cooling) project, funded from the European Space Agency under Contract No. 4000147715/25/I-LR, the CERTAINTY project (Grant Agreement 101137680) funded by Horizon Europe program, the EarthCARE DISC project, funded by the European Space Agency under Contract No. 4000144997/24/I-NS and the AIRSENSE (Aerosol and aerosol cloud Interaction from Remote SENSing Enhancement) project, funded from the European Space Agency under Contract No. 4000142902/23/I-NS.