Climate mechanism for smallest Antarctic ozone hole

The reason for this year's small hole in the ozone layer is that the stratosphere gets warmer which has complex reasons. According to preliminary NASA's data, there were more sudden stratosphere warming (SSW) events in the southern hemisphere from July to September this year (Fig. 1). Stochastic warming in the stratosphere is a sudden change in the large-scale atmospheric circulation structure in the stratosphere.  It was first discovered by Scherhag, a German scientist. When the SSW event occurs, the stratospheric temperature in the polar region suddenly increases; meanwhile, the stratospheric circulation associated with temperature change also drastically adjusts. In addition, the zonal average wind field reverses. The polar vortex is strongly disturbed and deviates from the polar region, even completely collapsing. The yellow area in Figure 1 represents the occurrence of SSW events from July to September in 2017.

The cause of the SSW events may be the significant heat exchange in the southern hemisphere (Fig. 2) and the large amount of planetary wave flux (Fig. 3). The red line in Figure 2 shows the heat flux data in 2017. The negative value in the figure indicates that the heat flux is transmitted to the south. It can be seen that the peak heat flux to the south in 2017 occurred earlier than previous years (blue and black lines), so did the component of the planetary wave to the south, which provided momentum conditions for heat transfer.

Figure 1. Zonal Temperature Anomaly Time Series [-90, -60] of JAS in 2017 (Source: NOAA).

Figure 2. Heat Flux[-75, -45] of 100hPa (Source: NASA).

Figure 3. Heat Flux (Wave 1-3) [-75, -45] of 100hPa (Source: NASA).

It is noteworthy that the mechanism of this year's stratospheric warming is not significantly related to the global warming which however is one of the factors affecting the ozone depletion. The relationship between global warming and the ozone depletion will be covered in the next blog.