The north polar vortex is usually smaller and more disturbed than the corresponding one that forms during the Antarctic winter.
In 2010/11 a generally more stable than usual Arctic vortex allowed stratospheric temperatures to drop below the PSC formation threshold for a substantial period over the northern winter. Warmings occurred in early January and early February, however parts of the Arctic ozone layer within the vortex remained cold enough for stratospheric clouds to form until early April, with temperatures substantially colder than the normal. With large amounts of clouds sunlit, ozone depletion reached its greatest towards the end of March. Ozone values at Lerwick dropped to 249 DU on 2011 March 29, when the major depletion event passed near the UK, but values across the UK returned to near normal by mid April. The major spring warming of the stratosphere occurred in early April and temperatures from then on were then too warm for PSCs to exist.
By contrast the 2012/13 vortex was very unstable with stratospheric warmings occurring in early and late December 2012. Temperatures had warmed above the PSC formation threshold in late December and were at or near record levels in 2013 January.
In 2015/16 the vortex was again very cold and stable and in early February the vortex elongated south across the UK. Spectacular displays of PSCs and nacreous clouds were seen across the UK on February 1 and 2; good views were had from Cambridge. Ozone depletion occurred, with unusually low values recorded on January 31/February 1, for example 224 DU at Reading on February 1. The vortex elongated again towards the end of the month, and further clouds were seen from parts of the UK, with 240 DU recorded at Lerwick on February 29.
Nacreous clouds were again seen over northern England and Scotland on 2017 January 27.
In 2017/18 the temperature in the ozone layer within the polar vortex, particularly over Greenland, the Russian Arctica and north of Scandinavia, was below the PSC formation threshold from mid November until early February. Polar Stratospheric Clouds formed, leading to significant ozone depletion during January and February 2018. Ozone hole levels below 220 DU appear to have been reached on February 3 in a small area between Svalbard and Scandinavia. Low values below 220 DU were also reached near the west coast of Canada on February 12, 13, 16 and 17, in what appears to be dynamic event, although PSCs were seen. A major spring warming then took place with a rapid rise in ozone amounts across the northern polar regions.