Evolution of turbulence in the expanding solar wind

The heliosphere represents the only plasma system accessible for direct measurements.

It is therefore crucial to perform experimental studies that allow understanding the fundamental processes occurring in astrophysical plasmas. Among these, turbulence, ubiquitous in the plasma universe, is of particular interest.

Space agencies recently launched spacecraft (Solar Orbiter, Parker Solar Probe, Bepi Colombo) with the specific or indirect purpose of measuring fields and paricles for turbulence studies. Older yet still operational satellites complete the fleet currently deployed in the heliosphere.

This proposal intends to take advantage of the exceptional availability of measurements on multiple points in the interplanetary space to perform accurate studies of the radial evolution of turbulence in solar wind expansion.

After identifying several favorable configurations, measurements of the same plasma at different distances from the Sun, or of plasma accelerated in the same solar source region, will be obtained.

Novel estimates of the turbulent energy transfer rate will be studied in detail, modeled, and compared with existing predictions.

The interplay of turbulence with plasma heating, waves and with kinetic processes producing non-Maxwellian features of the particle distributions will be examiend, and its radial evolution will be determined. Finally, numerical simulations will be used to interpret the results in terms of decaying turbulence.