Identification of the weak-to-strong transition in Alfvénic turbulence from space plasma
arxiv(2023)
摘要
Plasma turbulence is a ubiquitous dynamical process that transfers energy
across many spatial and temporal scales in astrophysical and space plasma
systems. Although the theory of anisotropic magnetohydrodynamic (MHD)
turbulence has successfully described phenomena in nature, its core prediction
of an Alfvenic transition from weak to strong MHD turbulence when energy
cascades from large to small scales has not been observationally confirmed.
Here we report the first observational evidence for the Alfvenic weak-to-strong
transition in MHD turbulence in the terrestrial magnetosheath using the four
Cluster spacecraft. The observed transition indicates the universal existence
of strong turbulence regardless of the initial level of MHD fluctuations.
Moreover, the observations demonstrate that the nonlinear interactions of MHD
turbulence play a crucial role in the energy cascade, widening the directions
of the energy cascade and broadening the fluctuating frequencies. Our work
takes a critical step toward understanding the complete picture of turbulence
cascade, connecting the weak and strong MHD turbulence systems. It will have
broad implications in star formation, energetic particle transport, turbulent
dynamo, and solar corona or solar wind heating.
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