Giant vortices discovered on the Sun

Diagram of solar Rossby waves (Image courtesy MPS/NASA/HormesDesign)
Diagram of solar Rossby waves (Image courtesy MPS/NASA/HormesDesign)

An article published in the journal “Nature Astronomy” describes the evidence of the presence of gigantic waves called Rossby waves on the Sun’s surface. A team of scientists led by the Max Planck Institute for Solar System Research (MPS) and the University of Göttingen discovered these vortices that have sizes comparable to those of the Sun itself, confirming a hypothesis that was proposed decades ago because they exist naturally in rotating fluids.

Rossby waves are well known in connection with atmospheric physics and oceanography. In the Sun’s case, there was the suspicion that a similar phenomenon was also present in our star’s gas, the problem observing it. Laurent Gizon, director of the MPS and one of the authors of the article, explained that solar Rossby waves have very small amplitudes and periods of several months and this makes their detection difficult.

In order to obtain the observations they needed, the researchers used the data collected over six years by the Heliospheric and Magnetic Imager (HMI) one of the instruments of NASA’s Solar Dynamics Observatory (SDO), which began its scientific mission in 2010. This instrument is equipped with a spatial resolution high enough to allow to follow the movements of the photospheric granules on the Sun’s surface, convective cells with a diameter up to 1,600 kilometers (almost 1,000 miles).

A careful analysis of the Sun’s images allowed the researchers to use those granules as passive tracers to detect the underlying vortex flows that are associated with Rossby waves. Techniques related to helioseismology offered a confirmation to those discoveries allowing to trace the waves up to depths of 20,000 kilometers (12,427 miles) below the Sun’s surface.

In March 2017, an article published in the journal “Nature Astronomy” described the detection of indirect evidence of Rossby waves on the Sun based on the observation of the movements of bright spots on the solar corona. However, the authors of the new research based on data from the SDO satellite noticed no connections between those movements and Rossby waves. In short, the new evidence of the existence of those vortexes are much more conclusive.

This research can represent the beginning of new studies on the Sun to understand the influence of Rossby waves on its weather. Solar activity can have an impact that can be significant on the Earth so all the phenomena taking place on our star deserve attention.

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