Turbulence and Energy Dissipation in the Interplanetary Medium: Theory, Simulations and Spacecraft Observations

NAHUEL ANDRÉS; FOUAD SAHRAOUI; MAIA BRODIANO

Simposio; 6th Asia-Pacific Conference on Plasma Physics; 2022

A long-established challenge in the solar-windcommunity is the so-called heating problem. It ismanifested by the fact that the solar wind’s protontemperature decreases slowly as a function of theradial distance from the Sun, in comparison to theprediction of the adiabatic expansion model of thesolar wind (e.g., Marsch et al. 1982). While severalscenarios have been proposed to explain thoseobservations, the main candidate is certainly localheating of the solar wind plasma via the turbulentcascade (e.g., Matthaeus & Velli 2011). In thispicture, the energy that is injected at the largestscales in the solar wind will cascade within theinertial range until it reaches the dissipation scales,where it is eventually converted into thermal heat ofthe plasma particles (see, Kiyani et al. 2015). Thisframework has led to several investigations toestimate the energy cascade rate in the solar wind atdifferent scales and different heliocentric distancesusing theoretical, numerical, and observationalstrategies.During this talk, we will discuss our recenttheoretical results using two particular compressiblemodels. Specifically, we have derived exact relationsfor fully developed homogeneous isothermal andpolytropic magnetohydrodynamic (MHD) turbulence(see, Andrés & Sahraoui, 2017; Simon & Sahraoui,2021). Using the incompressible (Politano andPouquet et al., 1998) and our compressible exactrelations, we will present our observational results atdifferent heliocentric distances using the recentNASA's mission Parker Solar Probe (Figure 1).Finally, we will summarize and discuss the mainnumerical and observational results and itsimplications in the solar wind heating problem.