Europe monitors the ozone layer with the participation of BIRA-IASB
Copernicus is the EU programme for Earth observation that monitors our planet and its environment. The Copernicus Atmosphere Monitoring Service (CAMS) combines satellite observations with a chemical weather model to continuously provide data and information on atmospheric composition. BIRA-IASB provides two services to CAMS:
- validation with independent measurements including those from the Network for the Detection of Atmosphere Composition Change
- development of a stratospheric chemistry model extracted from BASCOE.
The stratospheric ozone layer is a major focus for CAMS and for BIRA-IASB because it protects life on the surface from harmful UV radiation.
Spring ozone holes every year above the Antarctic but much rarer above the Arctic
An “ozone hole” appears every year above the Antarctic, from September until November, because frigid wintertime temperatures enable Polar Stratospheric Clouds (PSC). With the return of sunlight, ozone-depleting reactions are triggered on the surfaces of those clouds by chlorine and bromine.
The industrial production of these chemicals has ended but they have a long lifetime and meteorology plays a key role: surrounded by the Southern Ocean, the Antarctic is isolated every winter by a strong and stable polar vortex which allows extremely low temperatures hence PSC. This mechanism is much rarer above the Arctic because its topography around the North Pole is much less symmetric.
Three consecutive record-breaking ozone holes monitored by CAMS in 2019 and 2020
These two years exhibited an exceptional variability of polar vortex dynamics in both hemispheres.
- In late August 2019 the Antarctic vortex weakened rapidly and stratospheric temperatures rose dramatically, leading to the weakest and shortest-lived ozone hole observed since at least 2002.
- An opposite event happened above the Antarctic one year later: the vortex was very strong and remained stable much longer than usual, still spinning around the South Pole and containing a deep ozone hole by mid-December 2020.
- Above the Arctic, in April 2020, a vortex that was exceptionally large for the Northern Hemisphere developed enabling PSC and ozone depletion. The resulting ozone hole was larger and deeper than on the two previously known occurrences, in 1997 and 2011.
The CAMS operational five day forecasting suite was able to capture these low ozone concentrations correctly. The performance of the CAMS suites are continuously monitored (Evaluation of global forecasts) and evaluated in quarterly reports (Evaluation and Quality Assurance reports) to which BIRA-IASB contributes using measurements available at international networks such as the Network for the Detection of Atmosphere Composition Change.
These extreme events do not indicate any issue with the Montreal protocol that forbids ozone-depleting chemicals. They are due to an exceptional variability of the polar meteorology, and research is ongoing to determine if this enhanced variability is a consequence of climate change.
Reference:
Inness, A., Chabrillat, S., Flemming, J., Huijnen, V., Langenrock, B., Nicolas, J., Polichtchouk, I. and Razinger M.: Exceptionally low Arctic stratospheric ozone in spring 2020 as seen in the CAMS reanalysis,J. Geophys. Res.: Atmospheres, 125, e2020JD033563, doi:10.1029/2020JD033563, 2020.
