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April 28th is Final Warming day, the last stratospheric warming of the spring marking the dissipation of the stratospheric polar vortex.
The stratosphere is that portion of the atmosphere on average above 12 km above sea level; during the winter semester the polar stratosphere is subject to heating which is defined as STRATWARMING. In the case of intense events called ‘Majors’, these can determine a division of the polar vortex or split and affect the weather of the middle latitudes by intensifying thermal and precipitation anomalies. The reason for these stratospheric warmings, characterized by sudden temperature increases of up to 50°C or more within a week, are not fully known although it is more likely that they are due to a transfer of heat and momentum by the tropospheric waves.
Stratospheric warming can also occur during spring; LThe last warm-up of the season is called FINAL WARMING. This is an irreversible process that always occurs during spring. The formation is a little different from stratwarming and is due to an increase in solar radiation affecting the Pole between April and June. Due to photochemical effects the stratospheric polar vortex disappears and is replaced by a stratospheric polar anticyclone.
The stratospheric polar vortex will then tend to reform in autumn when stratospheric temperatures begin to drop. On average it occurs around mid-April, the month with the greatest frequency. When they happen earlier they are defined as early, after April 12th they are considered late. On the other hand, the tropospheric polar vortex becomes smaller during the summer as the polar front rises in latitude and becomes less unstable.
The effects of Final Warming vary over time of the middle latitudes and not exactly obvious but those that can have the greatest repercussions on the circulation are the dynamic ones, i.e. those that are helped by the waves arriving from the troposphere, which does not always happen. It is possible that the final warming this year could continue the effects of the stratwarming of March 4th
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