On the Origin of High-Frequency Magnetic Fluctuations in the Interplanetary Medium: A Brownian-like Approach

Low-frequency fluctuations in the interplanetary medium have been extensively investigated and described in the framework of turbulence, and the observed universal scaling behavior represents a clear signature of the underlying energy cascade. On the contrary, the interpretation of observations of plasma fluctuations at high frequencies, where wave-wave coupling, collisionless dissipation, and anomalous plasma heating play a key role, still represents a challenge for theoretical modeling. In this paper the high frequency fluctuations occurring in the interplanetary space are described through a Brownian-like approach, where the plasma dynamics at small scales is described through a stochastic process. It is shown that a simple model based on this framework is able to successfully reproduce the main features of the spectrum of the observed magnetic fluctuations. Moreover, the Fluctuation-Dissipation Relation, derived by our model, leads to a power law between dissipation rate and temperature, which is compatible with the occurrence of Landau damping, interpreted thus as the main mechanism of dissipation in the solar wind plasma.

Automated summary

The study of low-frequency fluctuations in the interplanetary medium has revealed universal scaling behavior representing an underlying energy cascade, while the interpretation of high-frequency plasma fluctuations remains a challenge for theoretical modeling. This paper describes high frequency fluctuations in the interplanetary space using a Brownian-like approach and successfully replicates the main features of the observed magnetic fluctuations spectrum. The Fluctuation-Dissipation Relation derived in the model suggests a power law between dissipation rate and temperature, indicating Landau damping as the main mechanism of dissipation in solar wind plasma.