Stratospheric aerosols have a direct impact on the Earth’s climate through their albedo and their impact on ozone. Thus, they must be accounted for in all chemistry climate models. One source for such aerosol information, used by the modeling community, is the Global Space-based Stratospheric Aerosol Climatology (GloSSAC, Thomason et al., 2018; Kovilakam et al., 2020). GloSSAC’s primary product is a continuous record (currently from 1979-2022) of zonally and monthly averaged global stratospheric aerosol extinction coefficient at 525 and 1020 nm. Clearly, a continuation of the GloSSAC record with the current or improved coverage is highly desirable. However, two key instruments currently providing GloSSAC input data (Optical Spectrograph and Infrared Imaging System, OSIRIS, and Cloud-Aerosol Lidar with Orthogonal Polarization, CALIOP) are near the end of their life, leaving only the Stratospheric Aerosol and Gas Experiment (SAGE III/ISS) solar occultation observations, which will not provide the current coverage and temporal resolution. In addition, the in situ instruments, which have been used in the past for validation of the space-borne measurements, are being replaced with new improved instruments, but still need to be tied to the legacy records. Plus, the rather simple picture of stratospheric aerosol dominated by sulfate is being challenged by recent pyrocumulonimbus (pyroCb) events, by the discovery of nitrates in the lower stratosphere above the Asian monsoon, and by the incursion of organics into the lower stratosphere. 

To address these issues we propose a project divided into four tasks: 1) To review the GloSSAC climatology. Does it capture current understanding of stratospheric aerosol? Could the parameter space be improved? 2) To explore options for GloSSAC continuation and possible data record additions (i.e. what other instruments could be included?). 3) To review challenges and limitations for comparisons between in situ aerosol observations and 4) To identify key variables that represent the stratospheric aerosol layer, key existing gaps and to develop strategies to fill them. 

Project Schedule

We will start in June 2023 with an online kick-off meeting to select dates for the team meetings at ISSI, nominate additional team members (Early-Career Researchers, ECR) and assign preparatory work for Tasks 1 and 3. At the first ISSI meeting (~3 days, fall 2023), we will mainly work on Tasks 1 and 3 in parallel. Results of these tasks will be written up and preparatory work for Task 2 will be carried out before a second meeting (~3 days, fall 2024). During the second meeting Task 2 will be the main focus together with discussion on the measurement gaps and new strategies. The write up of a report and paper for Task 2 and white paper for Task 4 will be finalized during a third meeting (3 days, spring 2025). Between ISSI meetings, regular online meetings of task related sub-groups will be organized.