Exciting phenomenon: Space hurricanes occur above both polar caps of the Earth – gigantic cyclones made of charged particles in the ionosphere, as shown by satellite data. Researchers have detected 256 of these space hurricanes in ten years in the southern polar region alone; such ionospheric cyclones also occur about twelve times a year in the northern hemisphere. The strange thing is that they do not occur during solar storms, but rather during calm space weather.
The one that starts at about 80 kilometers above sea level ionosphere is a place as important as it is mysterious. On the one hand, the charged particles circulating there form an important protective shield against aggressive radiation and facilitate terrestrial radio communications. On the other hand, this layer, which extends far into space, always has new surprises in store. Researchers have made enormous discoveries there in recent years Plasma bubbles, X-shaped structures and huge curves Plasma tubes discovered.
Plasma vortex between heaven and earth
Since 2021, another phenomenon has been added: space hurricanes. These are hundreds of kilometers of plasma vortices in which charged particles rotate around a silent central eye – like tropical storms in the lower atmosphere. There is also a shower of electrons and strong updrafts in these ionospheric hurricanes. These plasma flows, which usually occur in the summer and in the afternoon, can trigger hurricane-like auroras, but they are usually not visible in the sun.
What’s strange, however, is that unlike normal aurora borealis, space hurricanes that last for several hours don’t occur during solar storms. Instead, plasma cyclones occur when the Irish magnetosphere is actually completely calm and no particularly strong bursts of solar wind are penetrating near-Earth space. “Despite extremely calm conditions, the space hurricane carries large amounts of energy and momentum into the ionosphere,” report Qing-He Zhang of Shangdong University in China and colleagues.
Are there space hurricanes at both poles?
However, so far, such space hurricanes have only been observed in the polar region of the northern hemisphere. Here, they occur on average about twelve times a year, mainly on summer afternoons, as the researchers report. However, it remains to be determined whether this phenomenon also occurs in the southern polar region and in what form.
That’s why Zhang and his team looked for such ionospheric vortices in the Southern Hemisphere for the first time. To do so, they evaluated data from 2005 to 2016 from American weather satellites in Earth-synchronous orbit at an altitude of about 813 kilometers. These DSMP satellites carry special plasma-measuring devices, which means they can also detect the signatures of auroras, space hurricanes, and other ionospheric phenomena.
256 events at the South Pole
And indeed: Analysis of satellite data showed that ionospheric cyclones also exist over the southern polar region. “We identified 256 such events, which, excluding possible double observations, correspond to at least 111 different space hurricanes,” Zhang and his colleagues report. “They exhibit the typical characteristics of space hurricanes, including a strong horizontal and annular plasma flow, a quiescent center, and intense electron precipitation with updrafts.”
Similar to their northern counterparts, southern space hurricanes also occur above the 80th parallel and thus toward the poles of the normal auroral oval. A single hurricane lasts from a few tens of minutes to several hours before dying down again and disappearing as suddenly as it appeared. Space hurricanes also occur more frequently in the south polar region during the polar summer and appear to occur independently of solar storms in mostly calm space weather conditions, the team determined.
Many unanswered questions
It is still unclear what impact space hurricanes will have on the ionosphere beyond their duration. “A normal hurricane is associated with the transport of large amounts of energy and air masses,” Zhang and his colleagues explain. “A hurricane in the Earth’s upper atmosphere must therefore also be violent and transfer a lot of energy and momentum to the ionosphere. Measurements show that charged particles orbit the eye of the space hurricane at an average speed of 3,600 kilometers per hour.” ten times faster than normal plasma circulates in the polar ionosphere.
How and why ionospheric cyclones appear seemingly out of the blue is not yet fully understood. However, measurement data and satellite images suggest that the field lines of the Earth’s magnetic field could play a decisive role. If reconnections occur between them – a kind of short circuit – this could accelerate the charged particles and create vortices. The team hopes that further observations and measurements will shed more light on the mechanisms. (Journal of Geophysical Research: Space Physics, 2024, is that i: 10.1029/2024JA032753; Natural Communications, 2021, is that i: 10.1038/s41467-021-21459-y)
Source: Journal of Geophysical Research: Space physics, EOS
August 12, 2024 – Nadja Podbregar