Polar Stratospheric Cloud Dynamics and Ozone Depletion

Polar stratospheric clouds (PSCs) form in the extreme cold of the polar winter stratosphere and comprise supercooled liquid droplets and crystalline phases such as nitric acid trihydrate and ice. Their seasonal appearance within the stable polar vortex provides surfaces for key heterogeneous chemical reactions that convert reservoir chlorine species into active radicals. Once sunlight returns in spring, these radicals catalyse rapid ozone destruction, giving rise to the characteristic ozone holes over Antarctica and episodic depletion events in the Arctic. The occurrence and composition of PSCs are governed by stratospheric temperatures, moisture, nitric acid concentrations and dynamical processes such as wave‐driven cooling and vortex isolation. Interannual variability in vortex strength and temperature dictates the extent and persistence of PSC formation, while sedimentation of heavy particles leads to denitrification and dehydration that modulate the availability of reactive nitrogen and water vapour. These processes feed back on ozone chemistry and radiative balance, influencing surface climate through altered ultraviolet flux and stratosphere–troposphere coupling. Understanding PSC microphysics, large‐scale circulation changes under climate forcing and the interplay of halogen and nitrogen chemistry remains critical to predicting ozone recovery and assessing future impacts of greenhouse gases and volcanic or anthropogenic perturbations.

Research from Nature Portfolio

Recent modelling investigations using high‐top atmospheric models with interactive chemistry have demonstrated that under scenarios of reduced equator‐to‐pole temperature gradients and elevated methane levels, PSC formation in the Arctic winter can increase substantially. Enhanced PSC coverage amplifies radiative forcing beyond the direct greenhouse effect of methane, illustrating non‐linear interactions between chemistry, dynamics and cloud microphysics. This work highlights the sensitivity of stratospheric cloud formation to boundary‐layer orography and greenhouse gas concentrations, and its potential influence on past and future polar climate regimes.

Polar Stratospheric Cloud Dynamics and Ozone Depletion publication trend

The graph below shows the total number of articles in polar stratospheric cloud dynamics and ozone depletion across all publications each year (not limited to Nature Index journals).

Technical terms

Polar stratospheric cloud (PSC): Cloud layers in the polar stratosphere formed at temperatures below about 195 K, composed of liquid and crystalline particles that enable heterogeneous chemistry.

Supercooled ternary solution (STS): Liquid droplets of sulphuric acid, nitric acid and water that exist at very low stratospheric temperatures prior to crystallisation.

Nitric acid trihydrate (NAT): A crystalline phase of PSC particles that contributes to denitrification by sedimentation.

Denitrification: Removal of reactive nitrogen from the stratosphere by sedimentation of PSC particles, reducing the reservoir of nitric acid and altering ozone chemistry.

Polar vortex: A circumpolar circulation in the winter stratosphere that traps cold air and facilitates PSC formation and ozone depletion.

References

1. Early Eocene low orography and high methane enhance Arctic warming via polar stratospheric clouds. Nature Geoscience (2023).
2. 14 years of lidar measurements of polar stratospheric clouds at the French Antarctic station Dumont d'Urville. Atmospheric Chemistry and Physics (2023).
3. Climatology of Polar Stratospheric Clouds Derived from CALIPSO and SLIMCAT. Remote Sensing (2024).