The evolution of compressible solar wind turbulence in the inner heliosphere: PSP, THEMIS and MAVEN observations

TL;DR

This study computes the compressible energy transfer rate in solar wind turbulence from 0.2 to 1.7 AU using spacecraft data, revealing how compressibility influences energy cascade and relates to solar wind heating.

Contribution

First observational computation of the compressible energy cascade rate in the inner heliosphere across multiple spacecraft and distances.

Findings

Moderate increase of compressible cascade rate with distance.

Compressibility up to 25% affects cascade dynamics.

Connections made between cascade rate and ion temperature.

Abstract

The first computation of the compressible energy transfer rate from $\sim$ 0.2 AU up to $\sim$ 1.7 AU is obtained using PSP, THEMIS and MAVEN observations. The compressible energy cascade rate $\varepsilon_C$ is computed for hundred of events at different heliocentric distances, for time intervals when the spacecraft were in the pristine solar wind. The observational results show moderate increases of $\varepsilon_C$ with respect to the incompressible cascade rate $\varepsilon_I$. Depending on the level of compressibility in the plasma, which reach up to 25 $\%$ in the PSP perihelion, the different terms in the compressible exact relation are shown to have different impact in the total cascade rate $\varepsilon_C$. Finally, the observational results are connected with the local ion temperature and the solar wind heating problem.