2024/06/26 by Romanelli, Norberto, Andres, Nahuel, DiBraccio, Gina +5
#Earth and Planetary Astrophysics (astro-ph.EP) #FOS: Physical sciences #Solar and Stellar Astrophysics (astro-ph.SR) #Space Physics (physics.space-ph)
paper · doi:10.48550/arxiv.2406.18349
Solar wind turbulence is a dynamical phenomenon that evolves with heliocentric distance. Orbiting Mars since September 2014, Mars Atmosphere and Volatile EvolutioN (MAVEN) offers a unique opportunity to explore some of its main properties beyond ~1.38 au. Here, we analyze solar wind turbulence upstream of Mars's bow shock, utilizing more than five years of magnetic field and plasma measurements. This analysis is based on two complementary methodologies: 1) the computation of magnetohydrodynamic (MHD) invariants characterizing incompressible fluctuations; 2) the estimation of the incompressible energy cascade rate at MHD scales (i.e., ⟨εT⟩MHD). Our results show the solar wind incompressible fluctuations are primarily in a magnetically dominated regime, with the component travelling away from the Sun having a higher median pseudo-energy. Moreover, turbulent fluctuations have a total energy per mass of up to ~300 km2 s-2, a range smaller than reported at 1 au. For these conditions, we determine the probability distribution function of ⟨εT⟩MHD ranges mainly between ~-1x10-16 and ~1x10-16 J m-3 s-1, with a median equal to -1.8x10-18 J m-3 s-1, suggesting back-transfer of energy. Our results also suggest that |⟨εT⟩MHD| is correlated with the total energy per mass of fluctuations and that the median of ⟨εT⟩MHD does not vary significantly with the cross-helicity. We find, however, that the medians of the inward and outward pseudo-energy cascade rates vary with the solar wind cross-helicity. Finally, we discuss these results and their implications for future studies that can provide further insight into the factors affecting solar wind energy transfer rate.