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Birkeland Currents

22 April 2017

Laurence also sent in the link https://watchers.news/2017/03/23/birkeland-currents-stronger-in-the-nort… … which is another discovery by ESAs Swarm Mission. It has discovered a seasonal variation of Birkeland currents – strong electrical currents in the upper atmosphere (which is not the same in the north and south polar regions).

Kristian Birkeland is famous for making a connection between auroral phenomena and electrically charged particles in the solar wind. These currents flow along Earth's magnetic lines in the polar regions – and Swarm satellites allow scientists to better understand them. Three years of measurements, together with earlier observation data, have been used to produce global climatological maps of Birkeland currents (see www.esa.int/Our_Activities/Observing_the_Earth/Swarm/Swarm_detects_asymm…

The results show differences in the currents in the northern and southern hemispheres, seasonal changes, and how they vary with the strength of the solar wind. Interaction between Earth's magnetic field and the inter-planetary magnetic field depends on how the inter-planetary field is orientated. Hardly any solar wind can enter the magnetosphere and arrive at Earth if the inter-planetary magnetic field points north, parallel to Earth's magnetic field. On the other hand, if the inter-planetary field points south the opposite is true and this allows a connection to be made with Earth's magnetic field. Part of the energy in solar wind then further energises the charged particles that are responsible for auroral displays.

The important discovery here is that Birkeland currents are weak northwards and strong southwards and this relates to asymmetry in Earth's magnetic field. In fact, the two geometric poles are not geometrically opposite each other and magnetic field activity is not the same in the north as in the south. This may account for the magnetic pole in the south being more offset than in the north, in respect of the geographic poles.

Might this account for the anomaly pointed out by Anthony Perratt in his talk to SIS at the Harlequin Theatre in Redhill (Surrey) a few years ago. He noted that rock art of plasma pinch phenomena tend to be on rock faces looking southwards, and rarely is found on north facing rock surfaces. Might it also go part of the way in explaining why some CME events do not appear to inject much energy into the earth system – but others do?

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