MHD turbulence in space and astrophysical plasmas
by
Tsung-Dao Lee Institute/N6F-N600 - Lecture Room
Tsung-Dao Lee Institute
Host: Longqing Yi
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Abstract:
Magnetized turbulence in space plasmas is often interpreted through the Goldreich–Sridhar critical-balance paradigm, yet solar-wind observations and modern simulations consistently show major departures: the expected −5/3 velocity scaling and the predicted scale-dependent anisotropy are frequently absent, and a dominant quasi-two-dimensional (2D) component can contain most of the fluctuation energy. I will present a unified spatio-temporal MHD turbulence framework built from fully time-resolved, ultra-high-resolution simulations that treats the cascade simultaneously in wavevector and frequency space and predicts a measurable four-dimensional distribution P(k,ω). The central result (Yuen et al. 2025, ApJ, 986, 221) is that MHD turbulence naturally generates an overwhelming population of low-frequency, 2D-like fluctuations that exhibit strong nonlinear frequency broadening, couple efficiently to compressible perturbations, and dominate the long-timescale dynamics. This “low-frequency reservoir” changes how we interpret spectral slopes and anisotropy in spacecraft data and provides a concrete route to connect turbulent structure to transport: because these modes persist and interact strongly, they can regulate energetic-particle scattering and cross-field diffusion across space and astrophysical environments. I will close by noting how controlled turbulence experiments, including laser-driven platforms with high-quality field diagnostics, could test key signatures of the theory—particularly the partition of energy into near-2D, near-zero-frequency fluctuations and the scale-dependent frequency broadening—without relying on device-specific details.
Biography:
Ka Ho is an Assistant Professor at Nanjing University, specializing in computational astrophysics, turbulence, and star formation. Formerly an Oppenheimer Distinguished Postdoctoral Fellow at Los Alamos National Laboratory, he holds a Ph.D. from UW-Madison and has published over 30 papers in leading journals like Nature and ApJ. He currently leads major computational initiatives (INCITE, NERSC) and serves as a grant reviewer for top-tier agencies, including NASA and the DOE.
