Polar Stratospheric Cloud and Aerosol Climatology Based on CALIOP Measurements From 2006-2017

Abstract:

Polar stratospheric particles play crucial roles in the springtime depletion of ozone at high latitudes by serving as catalytic sites for heterogeneous reactions that transform stable chlorine and bromine reservoir species into highly reactive ozone-destructive forms. These particles include background H₂SO₄/H₂O stratospheric aerosol droplets as well as polar stratospheric clouds (PSCs), whose particles can be liquid supercooled ternary solution (STS) HNO₃/H₂SO₄/H₂O droplets, solid nitric acid trihydrate (NAT), or H₂O ice. The heterogeneous reactions are most efficient on the liquid particles because of the larger total surface area density (SAD), volume density (VD), and reaction efficiencies associated with them. Furthermore, if NAT particles grow sufficiently large, they can remove gaseous odd nitrogen from the lower stratosphere through gravitational sedimentation (denitrification), which inhibits the reformation of the halogen reservoirs and prolongs ozone depletion. Thus, it is important to understand the temporal and geographic distribution of polar stratospheric particles and their composition in order to represent these processes more accurately in models used to predict the future state of stratospheric ozone.

The CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) instrument on the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite has been observing PSCs and aerosols at latitudes up to 82 degrees in both hemispheres since mid-June 2006 and has provided a rich new database for studying polar particle processes. The CALIOP particle observations over the last decade are the foundation of a recent SPARC initiative to develop a state-of-the-art reference PSC data record and climatology that will be valuable for testing existing and future global models. In this paper, we will describe the PSC climatology, highlight findings with regard to the temporal, vertical, and spatial distribution of PSCs over the last decade. We will also present a climatology of stratospheric particulate SAD and VD derived from the CALIOP measurements. Finally, we will compare the post-Pinatubo CALIOP PSC and aerosol data record with the 1979-1989 SAM II solar occultation PSC record to investigate possible long-term variability in PSC occurrence.