Arctic stratosphere dynamics in the winter season 2024-2025

The first half of the 2024-2025 winter season in the Arctic stratosphere was characterized by a persistent strong stratospheric polar vortex, comparable to those observed during the coldest seasons (1996-97, 2010-11, 2015-16) and 2019-2020, the season with the highest ozone depletion on record.

As a result of low temperatures in the Arctic in February 2025, polar stratospheric clouds (PSC) type I were formed, which are necessary for the start of active destruction of the ozone layer in the spring, the PSC “volume” became the maximum (~160 million km3) for all years of observations, exceeding the values ​​of February 2020 by ~30%. Such low temperatures in the polar stratosphere were due to the weakened propagation of wave activity from the troposphere, especially from late January to early February.

During this period, for about a week, the temperature in the Arctic lower stratosphere dropped below -83°C, allowing the formation of Type II PSСs (with a maximum “volume” of ~75 million km3) for several days, consisting of ice particles and usually formed only in Antarctica. The total ozone content (TOC) in the Arctic reached its minimum values.

At the end of February 2025, as a result of the increased spread of wave activity flows from the troposphere, mainly over the northeast of Eurasia, the zonal average wind began to weaken (from ~60 to ~25 m/s) and the temperature of the polar stratosphere began to increase, which corresponds to a minor sudden stratospheric warming (SSW). At the same time, an area with a reflection of wave activity from the stratosphere to the troposphere was formed over the north of Canada, from which, over the course of several days, the propagation of wave activity fluxes in the eastward direction over the North Atlantic to Europe was observed in the upper troposphere. As a result of the major SSW (which also became the early final one) in early March 2025, associated with the strengthening of the Aleutian anticyclone and the shift of the vortex to Eurasia (i.e., the strengthening of the wave with a zonal number of 1, was accompanied by an increased spread of wave activity over two regions: northeastern Eurasia and Western Europe. Minor and major / final SSWs prevented severe ozone depletion this spring that could have exceeded 2020 records.

During the major SSW, an area with low TOC and minimum values ​​according to the OMI satellite instrument on March 6, 2025, was formed over northwestern Russia and Scandinavia: 204 Dobson units (DU) over Helsinki, 221 DU over St. Petersburg, and 242 DU over Moscow.  Necessary to note that 220 DU being considered the boundary of the ozone anomaly in Antarctica. The very low TOC values ​​are confirmed by ERA5 reanalysis data, OMPS satellite measurements, and ground-based observations.

Preliminary estimates show that the formation of the low TOC region was associated with a stratospheric polar vortex with low TOC, as well as with an anticyclone in the troposphere with an elevated tropopause and the influx of air masses with a low ozone from mid-latitudes along the western periphery of the anticyclone.