The NOAA Balloon Baseline Stratospheric Aerosol Profiles (B2SAP) – In situ insight on the stratospheric aerosol layer

Stratospheric aerosols play a crucial role in the climate system, but uncertainties persist in understanding the chemical, dynamical, and microphysical processes governing their distribution and variability. The chemical and radiative impacts of stratospheric aerosols hinge on particle size distribution. However, models exhibit significant variations in how they parameterize aerosol microphysical processes and simulate size distributions, leading to divergent predictions of the time evolution of radiative impacts from stratospheric aerosol perturbation events. To refine models for assessing the effects of potential climate intervention strategies, systematic measurements are crucial. In pursuit of this understanding, the Baseline Balloon Stratospheric Aerosol Profiles (B²SAP) project utilizes compact, lightweight payloads carried by meteorological balloons. These payloads measure aerosol number density and size distributions, along with water vapor, ozone, and meteorological data from the surface to the middle stratosphere. The long-term goal of the B²SAP project is to generate climatologies of aerosol number and size distributions up to the middle stratosphere at latitudinally distributed measurement sites. Since March 2019, B²SAP payloads have been launched from Boulder, CO, USA (40°N) once to twice per month and four to six times per year from Lauder, NZ (45°S). Starting in 2022, two tropical sites were added to this evanescent network with quarterly launches: Hilo, HI, USA (20°N) and Reunion Island, FR (20°S). These measurements provide a new record of in situ observations allowing to characterize the natural stratospheric aerosol burden, its variability, and responses to perturbations, providing essential data for refining models and aiding in the validation of satellite-based estimates. In this context, we will present a subset of this growing database, emphasizing the discussion on the stratospheric aerosol layers in the North hemisphere and South hemisphere (SH) mid-latitudes. Perturbations recorded in the SH after the Australian New Year super pyroCb outbreak in 2020 will also be investigated.