Plasma Turbulence and Turbulent Cascade Rates at High Latitudes Using MeerKAT Radio Observations

Abstract Radio observations of cosmic sources viewed through the turbulent magnetized plasma surrounding the Sun offer unique insights into the properties of plasma turbulence in the solar corona and solar wind, over a wide range of heliocentric distances and latitudes. Using new observations with the MeerKAT radio telescope (a precursor to the mid-frequency Square Kilometre Array; SKA-Mid), we investigate the amplitude of turbulent density fluctuations in the solar corona at about 10 R ⊙ , and we then use this information to evaluate the turbulent energy cascade rate and hence the level of turbulence-associated heating. The remote measurements are compared with MHD simulations of the solar corona and inner heliosphere at high heliospheric latitudes and with Parker Solar Probe equatorial measurements. In equatorial regions, the radio source broadening measurements lead to turbulent energy cascade rates ∼5 × 10 9 erg g −1 s −1 at 10 R ⊙ , somewhat consistent with global 3D MHD models and in situ observations; however, higher cascade rates are inferred at high heliospheric latitudes. Our analysis reveals significant variations in the turbulent heating rate ( σ log 10 ϵ ≃ 1.4 ) and source shapes that are more anisotropic than possible in any smooth spherically symmetric turbulence model. Both of these results highlight the influence of the large-scale structure of the solar corona and/or turbulence intermittency on the heating process closer to the Sun. The results provide new insights into the heating of the solar corona and the acceleration of the fast solar wind, especially in regions at high heliospheric latitudes that are not accessible to in situ measurements.