SABRE Goals and Objectives

The overarching goal of the SABRE mission is to significantly advance our understanding of the present day composition, chemistry, and dynamics of the stratosphere and their impacts on the climate system. SABRE measurements will greatly enhance the stratospheric observational database of the chemical, dynamical and microphysical processes that determine the formation, evolution and transport of stratospheric aerosols and their radiative properties. We seek to characterize the baseline state and variability of the stratosphere and its role in the radiative budget that determines Earth's climate.

The detailed SABRE in situ measurements are critical for

  1. Quantifying the direct radiative effects of lower stratospheric aerosols and indirect effects arising from interaction of tropopause region aerosol with cirrus clouds
  2. Evaluating and improving satellite retrievals of stratospheric aerosol properties that provide global, long-term observations of stratospheric aerosol loading, and
  3. Constraining and improving global model simulations of stratospheric aerosol sources, transport, chemistry and microphysics, which will allow improved prediction of the response of the stratosphere to future natural or anthropogenic perturbations.

SABRE measurements will ultimately enable more accurate quantification of the direct and indirect climate impacts from variations in stratospheric aerosols in the present-day atmosphere and provide a foundation for estimating changes in aerosol radiative forcing under future climate scenarios.

Specific SABRE science objectives are:

  1. Characterize stratospheric aerosol size distributions, composition, and optical properties, as well as their spatial and temporal variability. Determine the sources and chemical, dynamical, and microphysical processes that determine the observed size distributions
  2. Constrain the sulfur budget of the background stratospheric aerosol layer and evaluate the chemistry of sulfur species in the stratosphere
  3. Determine the occurrence of new particle formation in the upper troposphere / lower stratosphere and its influence on stratospheric aerosol number and size distribution
  4. Quantify the role of organic species in aerosol formation and growth in the tropical upper troposphere and lower stratosphere
  5. Characterize the evolution of stratospheric aerosol properties (microphysics, composition, and optical properties) following injection of aerosol and gas-phase aerosol precursors into the stratosphere by volcanic eruptions, wildfire pyrogenic events and anthropogenic activities such as rocket launches
  6. Quantify the impact of stratospheric aerosol variations on stratospheric ozone chemistry and stratospheric dynamics
  7. Quantify radiative forcing terms associated with anthropogenic perturbations (e.g. air traffic, rockets) to stratospheric aerosol

Individual SABRE deployments are planned to investigate in detail the various chemical and dynamical processes that influence stratospheric aerosol loading. Since tropical and monsoon regions with frequent intense deep convection represent major transport pathways for aerosol and aerosol precursors to enter the stratosphere, measurements at low latitudes will be needed to constrain the sources and processes contributing to the background stratospheric aerosol. Latitudinal transects and measurements at high latitudes will investigate stratospheric transport processes and permit an assessment of the overall stratospheric sulfur budget. Recent studies have shown that frequent moderate volcanic eruptions as well as pyrogenic injections can contribute significantly to stratospheric aerosol loading. The mature SABRE payload will allow rapid deployments in response to these events, providing a comprehensive suite of measurements for studying the chemical and physical processes following these injections. The SABRE sampling strategy is designed to address both questions related to stratospheric aerosol budgets and properties as well as the overall life cycle of stratospheric aerosol.

The detailed in situ measurements will also be used to improve satellite retrievals of stratospheric aerosol properties, and the combined satellite retrievals and in situ measurements will be used to evaluate and improve aerosol representations in global models, ultimately resulting in improved forecasts of future changes in stratospheric aerosols and their impacts on the radiation budget and climate.