How a solar switchback is formed

Solar Orbiter has made the first ever remote sensing observation of a magnetic phenomenon called a solar ‘switchback’, proving their origin in the solar surface and pointing to a mechanism that might help accelerate the solar wind.

The central image shows the Sun as seen by the ESA/NASA Solar Orbiter spacecraft’s Extreme Ultraviolet Imager (EUI) instrument on 25 March 2022. An active region on the Sun is indicated, which is thought to be the source of the observed ‘switchback’ identified in the solar corona by the Metis instrument.

An analysis of the outflow velocity in the corona shows that the switchback corresponds to very slow-moving plasma (image at right). This links it to the active region as such slow speeds would be expected above an active region that has yet to release its stored energy.

The magnetic field line sketches show the chain of events that are thought to be taking place in the magnetic field lines to generate the switchback. Active regions on the Sun can feature open and closed magnetic field lines. The closed lines arch up into the solar atmosphere before curving round back into the Sun. The open field lines connect with the interplanetary magnetic field of the Solar System. When an open magnetic region interacts with a closed region, the magnetic field lines can reconnect, creating an approximately S-shape field line and producing a burst of energy. As the field line responds to the reconnection and the release of energy, a kink is set propagating outwards. This is the switchback. A similar switchback is also sent in the opposite direction, down the field line and into the Sun.

This is the first ever remote sensing observation of a switchback, and may provide a mechanism that might help accelerate the solar wind.

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