Zhaoming Gan Presents at Parker Solar Probe Community Workshop
The second annual Parker Solar Probe community workshop, Parker Two, took place at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, MD, and an online component using Zoom. This meeting highlights discoveries from the first eleven encounters of the Parker Solar Probe mission.
Gan’s presentation, titled The Near-Sun Turbulence Mediated by Parametric Decaying Instability of Alfvén Waves, was a joint project with colleagues Xiangrong Fu, Hui Li, Senbei Du, John Steinberg, Emma Conrad, and Jeffrey Broll.
The solar winds are gaseous material (i.e., plasma ejected by the Sun) traveling from the Sun to the Earth that are very turbulent. One of most “mysterious” and unsolved problems in modern physics is how turbulence develops. For some historical reasons, the solar wind turbulence is studied extensively in the regime assuming the flow is nearly incompressible (which is largely true at ~ 1 au, i.e., near the Earth). However, it seems that the solar winds become more and more compressible when approaching to the Sun.
Thanks to the satellite “Parker Solar Probe” (PSP), scientists are now able to measure the in-situ wind properties very near to the solar surface, where the flow becomes compressible, and the magnetic energy becomes dominant, which favors parametric decaying instability (PDI), a known instability of large-amplitude Alfvén waves.
In Gan’s research, they examined the conditions in the near-sun environment for parametric decaying instability. Such instability is important as it is capable of mediating turbulence at the “inertial” scales, helping develop turbulence, dissipating energy (thus energize particles), inducing the compressible phenomenas as we’ve observed, etc.
Gan and colleagues study the variation properties of magnetic fields, velocity, and density associated with PDI. Special attention is paid to the interplay between PDI and its turbulence background, i.e., its role in turbulence development, and vice versa the effects of turbulence background on the growth rate of PDI. Interestingly, they found that PDI is likely to occur in the near-sun environment. The authors also proposed possible observational signatures of PDI.
This work is supported by the NASA/LWS project (Grant # 80NSSC20K0377).