A short ozone depletion event over Finland was observed on November

An unusual weather situation over Finland and Sweden during 3-5 November 2018 resulted in formation of an ozone-depletion event. It was predicted by the global atmospheric composition forecast of SILAM model and then registered by the OMI satellite (Figure 1).

The depth of this depletion was about 50% of the Antarctic ozone hole. The hour-by-hour evolution of the depletion event is presented here.

The event was predicted by the SILAM model global forecast five days ahead. This forecast is run every day with the global resolution of about 20km. It covers the troposphere and the stratosphere and thus creates a rare possibility to study the interaction of the low- and middle- atmosphere processes and to predict their evolution. An example of such interaction was the 4 November 2018 depletion event.

Figure 1. Total ozone column, daily average for 4 November 2018. Top: composite observed by OMI instrument (overpass ~13:30, solar time at each point), bottom: predicted by global SILAM forecast co-located in space and time with OMI observations. Dobson units.

The mechanism behind the rapid and intense but short-lived ozone depletion was totally different from the drivers of the Antarctic ozone hole. The current case was a result of deep low-pressure area (cyclone) in Atlantic south-east of Greenland at the beginning of November. It resulted in a strong updraft, which lifted the humid tropospheric air enriched with aerosols but with low ozone all the way to the stratosphere – eventually up to 20-25km. This air was transported with the stratospheric flows over Scandinavia and Finland towards Russia. By 6 November, it was mostly mixed with surrounding stratospheric air and the "ozone hole" gradually dissolved.

Further information:

Research Professor Mikhail Sofiev, Finnish Meteorological Institute, tel. +358 29 539 5433, mikhail.sofiev@fmi.fi