Space hurricane detected for the first time above Earth
Written by Catriona Roy
A swirling storm of plasma in Earth’s upper atmosphere, named a space hurricane by its discoverers, has been observed for the first time. The researchers say that space hurricanes are probably widespread on planets with magnetic fields.
The hurricanes that are familiar to us on Earth are created and evolve in the lower atmosphere, or troposphere. Strong swirling winds and water precipitating into rain make the weather systems destructive and potentially deadly. Not just an Earth phenomenon, hurricanes have also been seen in the atmospheres of Mars, Jupiter and Saturn. On Earth, they form over bodies of water when warm air rises, leaving a low pressure area underneath which is filled by the surrounding air rushing in; the rotation of hurricanes is due to the rotation of the planet underneath, through what’s known as the Coriolis effect.
Illustration credit: Qing-He Zhang, Shandong University
A space hurricane forms differently and is composed of plasma, the same stuff that makes up the aurora. In 2014, scientists observed the phenomenon for the first time, above the North pole. It had a diameter of over 1000 km, multiple spiral arms, and lasted eight hours, depositing a large amount of energy into Earth’s ionosphere. In addition, the space hurricane had another characteristic feature similar to that of ordinary hurricanes: it ‘rained’ electrons, instead of water, causing a cyclone-shaped aurora.
Some of the features have been observed before, in auroral spots named HiLDA (high-latitude dayside auroral) spots. However, these lack the spiral shape, calm centre, and cyclone-shaped aurora that led to the 2014 instance being called a hurricane.
The spiral arms gave the impression that the system was spinning anticlockwise, however this turned out to be an illusion. The anticlockwise appearance was due to the arms marking the ‘footprints’ of reconnected magnetic field lines. The plasma actually circulated clockwise, an interesting difference to the air of tropospheric hurricanes in the northern hemisphere.
Another unique feature is that while most aurora are a result of intense magnetic activity, the aurorae connected with space hurricanes are thought to need quiet conditions in order to develop.
Qing-He Zhang of Shandong University, the lead author of the paper that published the observations earlier this year, says that this suggests “current geomagnetic activity indicators do not properly represent the dramatic activity within space hurricanes”, because the space hurricane was located further towards the Earth’s pole than the observatories used to measure activity.
The space hurricane was created by a northward interplanetary magnetic field, originating from the Sun, interacting with the Earth’s magnetic field. A funnel of electrons flowed from the North pole, accelerating and precipitating accompanied by a corkscrew magnetic field, resulting in the hurricane in the shape of a rotating disc with arms.
The research team included scientists from China, Norway, the USA and the UK, and used auroral observations taken by four satellites of the US Defense Meteorological Satellite Program.
Mike Lockwood, one of the authors of the paper, said “Until now, it was uncertain that space plasma hurricanes even existed, so to prove this with such a striking observation is incredible.”
Space hurricanes are probably universal, with the potential to appear above any planet or even moon that has its own magnetic field. The researchers say the hurricanes, like other space weather, can cause disturbances and errors in satellite communications, radar and high frequency radio communications. Possible negative effects such as these give all the more reason to study space hurricanes and improve our recognition of them.
Sources
1) Zhang, QH., Zhang, YL., Wang, C. et al. A space hurricane over the Earth’s polar ionosphere. Nat Commun 12, 1207 (2021). https://doi.org/10.1038/s41467-021-21459-y