Cooling of the Southern Hemisphere’s stratosphere to record levels never recorded by modern satellites could have serious consequences for the coming winter in Europe and North America. The January eruption of an underwater volcano is to blame.

The Hunga Tonga volcano in the South Pacific had a powerful eruption on January 15, spewing a plume of gas and steam 58 kilometers into the air. In addition to the shock waves felt around the planet, the eruption threw sulfides and large amounts of water vapor into the stratosphere because it occurred below sea level.

Clouds and stratosphere

All clouds (and what we call “weather”) are in the lowest layer of the atmosphere, the troposphere, up to 8 km above the poles and up to 14-16 km above the tropics.

Above is a much higher layer, the stratosphere, about 30 kilometers wide and very dry. The ozone layer is above the stratosphere. These are the layers of the atmosphere that can have a major impact on meteorological conditions in the troposphere, especially the polar vortex.

A polar vortex is basically a very large cyclone that surrounds the North Pole during the Northern Hemisphere winter. When the vortex is strong, it keeps the coldest air virtually locked in the polar zone, but when it weakens, it allows it to descend to more southerly latitudes, bringing the harshest winters.

A cloud of water vapor

The volcanic column reached very high altitudes, peaking in the mesosphere, the layer above the stratosphere. After that, the volcanic cloud remained in the middle and upper stratosphere, surrounding the entire southern hemisphere. There are many different particles in a cloud, but the most important is water vapor.

Like sulfides, water vapor has a cooling effect, but not on the surface. They actually cool the stratosphere. They transmit solar radiation, but also store heat beneath them, thus heating the surface.

It is estimated that the amount of water increased from 1,500 to more than 1,700 teragrams (1 Tg = 1 million tons) after the eruption of the Hunga Tonga volcano, that is, more than 10% of the total water vapor content in the stratosphere. A significant increase for a single event.

A cloud of water vapor still persists in the southern stratosphere today. It also crossed the equator, with peaks reaching Florida and the southern United States.

Analyzes and forecasts

A cooling effect in the southern stratosphere was observed in May, and the belt of the strongest thermal anomalies was located near 30 south latitude.

In July, the anomalies increased even more, 10 degrees below normal. And in October, cooler temperatures prevailed over much of the Southern Hemisphere, with the strongest influence of cloud water vapor between latitudes 30S and 65S.

And the cooling will continue as long as the cloud persists in the stratosphere. Not only temperatures, but also pressures are lower in areas where thermal anomalies are present.

To get an idea of ​​the impact on global weather, especially in the winter of 2022/23, the stratospheric temperature index over the mid-latitudes of the Southern Hemisphere has been tracked since 1980.

Combined with winter temperatures and pressures in the Northern Hemisphere, it provides a linear correlation and comparison of parameters, revealing a potential link.

It should be noted that correlation does not necessarily mean causation, since a hidden factor can have the same consequences for pressure anomalies. Further research is needed to confirm the meteorological result of stratospheric cooling.

But the data may support a correlation between stratospheric cooling and winter weather.

It is believed that the cooling in the stratosphere of the southern hemisphere is related to the negative pressure of the NAO. The NAO stands for North Atlantic Oscillation and describes a pressure pattern over the North Atlantic and Europe.

The negative nature of the NAO means high pressure over the North Atlantic and Greenland and lower pressure in the south. And the winter seasons after anomalous cooling in the southern stratosphere are examples of a negative NAO pattern. There are statistics that also do not indicate that colds are the cause of the patterns.

But data from the same years show that pressure in the northern hemisphere caused a weaker circulation of the polar vortex. As a result, cold polar air was able to descend over the regions of Europe and North America. And the amount of snow that fell in those regions was greater in those years.

And this year, the Hunga Tunga eruption in January threw so much water into the stratosphere that it caused a significant cooling of the stratosphere, which will continue into the next period.

Thus, the coming winter in the Northern Hemisphere will be a huge “lab test”, but in real conditions, to draw new conclusions about potential global weather changes. Photo: Dreamstime

Source: Severe Weather Europe