Otto Hahn Medal for Jan Langfellner

The Sun’s rotation leads to plasma flows that resemble gigantic hurricanes.

Gigantic “hurricanes” covering many thousands of kilometers can be found on the Sun’s visible surface. This is the main result of Dr. Jan Langfellner’s doctoral thesis which he prepared at the Max Planck Institute for Solar System Research (MPS) in Göttingen (Germany). The hurricanes arise from the interplay between hot flows of solar plasma ascending from the interior of our star, and the Sun’s rotation ? very much like hurricanes on Earth. Since some of the "wind speeds" connected to “solar hurricanes” are only slightly higher than 30 kilometers per hour, the phenomenon is difficult to detect. In recognition of his thesis work, today the Max Planck Society has awarded the Otto Hahn Medal to Jan Langfellner.  

On Earth, hurricanes occur when air flows into a low-pressure area from all sides, under particular weather conditions. The Coriolis force, which results from the Earth’s rotation around its own axis, twists these air currents: in the northern hemisphere, hurricanes rotate counterclockwise, in the southern hemisphere clockwise. "Solar hurricanes form in a process very similar to the one on Earth”, explains Jan Langfellner. However, the flows connected to solar hurricanes do not consist of air, but of hot plasma. In some places, the plasma rises up from the even hotter interior of our star, flows along its surface, cools, and sinks down again. Researchers refer to such a flow geometry as a convection cell. As on the Earth, the rotation of the star leads to a swirling of the horizontal flows.

Many thousand kilometers in diameter, the solar hurricanes are much larger than their terrestrial counterparts ? and slower. While the plasma flows into the low-pressure area with speeds up to 600 kilometers per hour, the actual vortex flow is significantly slower at about 30 kilometers per hour. "At the same time, turbulent plasma movements are superimposed on the solar hurricanes," explains Langfellner. This makes the solar vortices very hard to discover. It is necessary to examine several thousands of the huge convection cells to determine the preferred flow direction. Such analyses require an uninterrupted, high-resolution view of the Sun as provided by NASA’s Solar Dynamics Observatory (SDO) since 2010. The MPS hosts the German Data Center for SDO and thus can be seen as a kind of digital memory of the mission.

The data from SDO’s Helioseismic and Magnetic Imager (HMI) were especially valuable to Langfellner. The instrument measures the oscillations of the solar surface caused by the propagation of solar seismic waves. The plasma currents affect these waves: sound waves that propagate in the direction of the current are accelerated; those traveling in the opposite direction are slowed down. "In this way, seismic waves are used to map plasma flows in the near surface layers," says Langfellner.

Dr. Jan Langfellner studied physics with a focus on astrophysics at the University of Göttingen. In his master's thesis he focused on a class of faint stars called hot subdwarfs. In his doctoral thesis, Langfellner turned to the star in the center of our solar system. He prepared the thesis at the MPS under the supervision of Prof. Dr. Laurent Gizon, Director of the Solar and Stellar Interiors Department.

Every year the Max Planck Society honors outstanding doctoral theses with the Otto Hahn Medal. Exactly 13 students were awarded the Otto Hahn Medal from the Chemische-Physikalische-Technikalische Sektion of the Max Planck Society. (More medals were awarded for the whole society.)