Speaker
Description
Solar Wind is a plasma medium radially accelerated from the lower layers of the Heliosphere (at about 2000 km from the Sun surface) that embeds all the solar system.
Like Earth’s atmosphere, Solar Wind is also a turbulent fluid. However, the interaction of the charged particles of solar wind plasma with the electromagnetic fields makes plasma turbulence different from that of any non-conducting fluid.
Solar wind turbulence presents spectra of kinetic and magnetic field fluctuations with multiple slopes (in contrast to the single slope of non-conducting fluids). A change in slope at certain scales is the reflection of a change of the mechanism that drives turbulence. At large scales (inertial range), turbulence is mainly driven by the non-linear interaction of Alfvén Waves. Conversely, between the gyro-radius of protons and electrons (dispersive range), non-linear interaction of Kinetic Alfvén Waves (KAW) is generally considered to be the mechanism that drives turbulence at these scales.
The spectrum of density fluctuations is similar to the magnetic and kinetic fluctuations spectra, in spite of one important difference: a flatter spectral slope appears before the transition to the dispersion scales. It has been proposed that this transition might be caused by KAW interactions at inertial range scales (“active density cascade”), although it is yet unclear.
Via Hall-MHD numerical simulations that can take into account the radial expansion of the Solar Wind, we have reproduced, for the first time, the flat end of the inertial-range density spectra, as well as the dispersion range slope for plasma conditions close to solar wind ones. We are currently working on the generation of the steeper large scale part of the density spectrum and the identification of the mechanism responsible for the generation of the flat density spectrum.
