Measurement report: Significant ozone loss during winter 2020 measured from ground based microwave radiometer

Abstract. Ground-based microwave observations from MIRA2 situated in Kiruna, Sweden, were used to investigate Arctic stratospheric ozone during the winter 2019/2020. A comparison of O₃ retrievals with coincident measurements of Aura MLS between 1 October 2019 and 30 April 2020 shows good agreement across the investigated pressure levels (74, 56, 46, and 10 hPa). Remaining differences are well within the retrieval uncertainty of MIRA2. This demonstrates the capability of MIRA2 to provide robust ozone measurements for studies of stratospheric variability.

A tracer-based approach was applied to derive cumulative chemical ozone loss on isentropic surfaces. At the 475 K level, ozone depletion increased from late winter into early spring, reaching a maximum loss of 2.19±0.90 ppmv in early April 2020. The magnitude and timing of the loss are consistent with the exceptional Arctic ozone depletion stated by model simulations and satellite-based estimates during the winter 2019/2020 and agree well. Despite limited temporal sampling, the tracer-based method enables a consistent estimate of seasonal ozone loss from ground-based observations. The results highlight the ability of ground-based microwave radiometers to quantify chemical ozone depletion and its temporal evolution.

This study also demonstrates the value of ground-based measurements as an independent and complementary component of the global observing system, providing continuity and reducing reliance on satellite data for monitoring stratospheric ozone.