Solar Wind Turbulence upstream of Mars: MAVEN Magnetometer and Solar Wind Ion Analyzer Observations

ROMANELLI, NORBERTO; ANDRÉS, NAHUEL; ET AL.

San Francisco

Congreso; AGU FALL MEETING 2023; 2023

AGU

Turbulence is a nonlinear phenomenon present in plasma flows within and around planetary magnetospheres, which is important because it enables the transfer of energy between different scales. As a result, turbulence has a key role in defining power energy spectra in the solar wind, every magnetosphere region and potentially modifying triggering conditions for other processes, such as magnetic reconnection. In the classical cascade picture, energy is transferred from large to small scales. It is only at sufficiently small scales, when dissipative processes become dominant, that kinetic bulk energy is transferred to random motions of individual particles and that plasma heating occurs. In this work, we estimate for the first time the signed incompressible energy cascade rate (direct and inverse) in the pristine solar wind at magnetohydrodynamic (MHD) scales upstream of Mars. For this, we apply third-moment theory for fully developed turbulence to more than five years of Mars Atmosphere and Volatile EvolutioN (MAVEN) magnetic field and plasma observations, when MAVEN is magnetically disconnected from the Martian bow shock. Firstly, we observe the absolute value of the incompressible energy cascade rate decreases as the Martian heliocentric distance increases, for each of the three explored Martian years. In addition, we find plasma waves associated with the extended Martian hydrogen exosphere do not have a significant effect on the nonlinear cascade of energy at the MHD scales. We also present results on the relationship between the signed energy cascade rate (and the inward and outward components) and the solar wind cross-helicity and average total energy per unit mass associated with the observed kinetic and magnetic field fluctuations. Finally, we provide a comparison with previous studies of solar wind turbulence at 1 au; where we emphasize similarities and differences in the observed trends and the phase space explored upstream of Earth and Mars.