The Southern Hemisphere, currently in winter, will soon witness the development of significant stratospheric warming. Forecasts show strong temperature and pressure waves in the stratosphere over the South Pole. These events are in the South hemisphere, but when they occur, they are usually very strong and are known to have a global impact, potentially even affecting the upcoming northern winter.

Polar Vortex: Key Player

The main actor or driving force behind these events is polar vortex. It is the name given to a broad winter circulation over the Northern (and Southern) Hemisphere. The polar vortex behaves much like a very large cyclone, covering the entire polar region up to mid-latitudes. It is interconnected at all atmospheric levels, from the ground up, although it may take different shapes at different altitudes.

We divide it into upper (stratospheric) and lower (tropospheric) parts. The upper part is more circular and symmetrical due to fewer obstacles. Changes in the upper part can significantly affect weather anomalies in the lower atmosphere and weather at the surface. In the Southern Hemisphere, these disturbances to the stratospheric polar vortex are less pronounced due to the smaller terrain.

What is stratospheric warming?

Stratospheric warming brings rapid increase in pressure and temperature in the stratosphere. This can disrupt the circulation of the polar vortex and affect weather patterns below it for weeks. For example, in mid-March of this year, a strong sudden stratospheric warming (SSW) began over the Northern Hemisphere, splitting the polar vortex into two cores and bringing stratospheric temperatures well above normal. This high-pressure anomaly gradually moved into the lower atmosphere and affected surface weather.

Current warming over the Southern Hemisphere

Since it is winter in the Southern Hemisphere, there is an active polar vortex circulation there. The analysis shows below-average winds and the strength of the southern polar vortex, while its core is cooler but has been displaced. A strong warming wave is pushing on the cold core, raising temperatures by more than 30 °C above normalThe forecast indicates a sharp weakening of the southern polar vortex, with its strength expected to be almost halved within two weeks.

Although not all warming is officially classified as a "sudden stratospheric warming" (SSW), if it requires a change in the direction of stratospheric winds, even stronger changes in the stratosphere can have an impact on everyday weather.

Event climax and local impacts

Forecasts for the coming week show an intensification of the high pressure anomaly, which will push and shift the core of the polar vortex away from the central region. Temperature anomalies will reach early next week 25-30 °C above normalAt the peak of the event in late September, temperatures in the middle stratosphere are expected to reach almost 50 °C above normal, with the warming anomaly extending to lower stratospheric levels (19 km), indicating a strong event.

These changes can lead to negative pressure index over the South Pole, which signals a weakened polar circulation and prolonged weather disruption. An example is the widespread cold air anomaly in Australia, where disrupted pressure patterns allow cold air to escape into the mid-latitudes. Areas of high pressure take control over the polar regions, pushing out low pressure and colder air.

Global connectivity and impact on the Northern Hemisphere

Yes, stratospheric warming events over the South Pole can also affect the Northern Hemisphere. The global air circulation, known as Brewer-Dobson circulation, connects circulation from both hemispheres higher in the atmosphere, allowing "communication" between the northern and southern stratospheres.

A 2019 study showed that stratospheric warming over the South Pole led to significant changes in the electron content of the ionosphere over the United States and EuropeThere were even signs that the event was strong enough to affect weather during the following 2019/2020 winter in the Northern Hemisphere.

There is a signal between prolonged high pressure anomalies over the South Pole (August–October) and cooler temperatures in the central and eastern United States in the following months (December–February). The opposite, warmer anomalies have been observed in Europe. Stratospheric warming may significantly enhance these high-pressure anomalies, thus playing a role in the coupling between the hemispheres.

It is important to note that correlation does not imply direct causationThe signal may be lost in the complex global circulation, but a large-scale event such as stratospheric warming can produce effects in the Northern Hemisphere after a few weeks to months through the global weather system.

We will keep you updated. to inform about the weather development in the coming seasons. JRi