Abstract
AbstractPolar stratospheric clouds (PSCs) play important roles in stratospheric ozone depletion during winter and spring at high latitudes (e.g., the Antarctic ozone hole). PSC particles provide sites for heterogeneous reactions that convert stable chlorine reservoir species to radicals that destroy ozone catalytically. PSCs also prolong ozone depletion by delaying chlorine deactivation through the removal of gas‐phase HNO3 and H2O by sedimentation of large nitric acid trihydrate (NAT) and ice particles. Contemporary observations by the spaceborne instruments Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), Microwave Limb Sounder (MLS), and Cloud‐Aerosol Lidar with Orthogonal Polarization (CALIOP) have provided an unprecedented polar vortex‐wide climatological view of PSC occurrence and composition in both hemispheres. These data have spurred advances in our understanding of PSC formation and related dynamical processes, especially the firm evidence of widespread heterogeneous nucleation of both NAT and ice PSC particles, perhaps on nuclei of meteoritic origin. Heterogeneous chlorine activation appears to be well understood. Reaction coefficients on/in liquid droplets have been measured accurately, and while uncertainties remain for reactions on solid NAT and ice particles, they are considered relatively unimportant since under most conditions chlorine activation occurs on/in liquid droplets. There have been notable advances in the ability of chemical transport and chemistry‐climate models to reproduce PSC temporal/spatial distributions and composition observed from space. Continued spaceborne PSC observations will facilitate further improvements in the representation of PSC processes in global models and enable more accurate projections of the evolution of polar ozone and the global ozone layer as climate changes.
Highlights
There has been a continuing stream of discoveries about polar stratospheric clouds (PSCs) from the first sightings in the late 19th century to contemporary satellite measurements during the 21st century
One possible explanation is that, on average, the size of nitric acid trihydrate (NAT) particles may be larger in the Arctic than in the Antarctic and, less likely to fall into the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) NAT class, which is limited to NAT particles with radii
Spaceborne measurements by MIPAS, Microwave Limb Sounder (MLS), and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) led to the discovery of an Antarctic circumpolar belt of NAT Polar stratospheric clouds (PSCs) triggered by localized cooling events with ice clouds in mountain waves (Höpfner, Larsen et al, 2006; Lambert et al, 2012; Section 4.2)
Summary
There has been a continuing stream of discoveries about polar stratospheric clouds (PSCs) from the first sightings in the late 19th century to contemporary satellite measurements during the 21st century The interest in PSCs changed dramatically after the surprising discovery of the Antarctic ozone hole in the 1980s, when it was hypothesized that the clouds might provide the link between anthropogenic chlorine and polar ozone destruction. It was known that they are destroyed by photolysis in the stratosphere, and that the released chlorine could deplete ozone through gas-phase reactions (Molina and Rowland, 1974). The overall depletion was expected to be 5%–10% If this were correct, how could reactions involving chlorine be responsible for the ozone hole, under conditions with little insolation, destroying a major portion of the Antarctic ozone layer?. Polar vortex-wide observations by the contemporary spaceborne instruments Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), Microwave Limb Sounder (MLS), and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), a central part of this review paper, have brought about a comprehensive and clearer understanding of PSC spatial and temporal distributions, their conditions of existence, and the processes through which they impact polar ozone
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
