New insights on the internal workings of the Sun. The lead researcher notes: “Solar Rossby waves are gigantic in size, with wavelengths comparable to the solar radius”. They have maximum amplitudes in the Sun’s equatorial regions.
A team of scientists led by the Max Planck Institute for Solar System Research (MPS) and the University of Göttingen has discovered new waves of vorticity on the Sun, reports Phys.org.
As described in today’s issue of Nature Astronomy, these Rossby waves propagate in the direction opposite to rotation, have lifetimes of several months, and maximum amplitudes at the Sun’s equator. For forty years scientists had speculated about the existence of such waves on the Sun, which should be present in every rotating fluid system.
Now, they have been unambiguously detected and characterized for the first time. The solar Rossby waves are close relatives of the Rossby waves known to occur in the Earth’s atmosphere and oceans.
In almost every weather map of the Earth’s northern hemisphere atmospheric Rossby waves are a prominent feature. They appear as meanders in the jet stream separating cold polar air in the north from warmer subtropical air farther to the south. Sometimes these waves reach the equatorial regions and can even affect weather in Australia.
In principle, waves of this type (often referred to as planetary waves) arise on every rotating sphere due to the Coriolis force. Saturn’s hexagon, a stable cloud pattern at the planet’s north pole, may also be an expression of these waves.
The existence of Rossby waves in stars was predicted about forty years ago. “Solar Rossby waves have very small amplitudes and periods of several months, thus they are extremely difficult to detect”, says Prof. Dr. Laurent Gizon, coordinator of the team that made the discovery and director at the MPS.
The study required high-precision observations of the Sun over many years. The scientists from MPS analyzed a six-year dataset from the Heliospheric and Magnetic Imager (HMI) onboard NASA’s Solar Dynamics Observatory (SDO), in operation since 2010.
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