Radial Evolution of Turbulent Modes near the Sun Using Parker Solar Probe and Solar Orbiter Measurements

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Abstract
We investigate the radial evolution of turbulent fluctuations in the inner heliosphere using Parker Solar Probe and Solar Orbiter observations over heliocentric distances of ∼32–90 R ⊙ . We decompose the measured fluctuations of density, velocity, and magnetic field into eight fundamental magnetohydrodynamic modes using the linear mode decomposition technique. The mode-resolved energy results show that the fluctuation energy is highly field-dependent: Velocity fluctuations are primarily Alfvénic, with both forward and backward Alfvén modes exhibiting relatively shallow radial decay, whereas magnetic fluctuations are dominated by transverse nonpropagating incompressible / magnetic island–like components. In particular, the magnetic island mode decreases approximately as δB i ∼ r −1.90 , followed closely by the forward and backward Alfvénic magnetic modes, δB A+ ∼ r −1.96 and δB A− ∼ r −2.17 . In contrast, density fluctuations are mainly governed by fast magnetosonic modes, while entropy and slow magnetosonic contributions remain comparatively weaker and decay more rapidly with heliocentric distance. We find that the variance anisotropy of the transverse incompressible magnetic island mode ( δB i ) and the Alfvén modes ( δB A± ) increases slightly with heliocentric distance. These results will help identify which magnetohydrodynamic modes are responsible for carrying turbulent energy in the inner heliosphere and how that energy evolves with distance from the Sun.
Funding Information
  • NSF EPSCoR RII Track-1 (OIA-2148653)
  • NASA Parker Solar Probe (SV4-84017)
  • GSFC and NASA Grant (80NSSC22K1011)
  • NASA Grant (80NSSC25K7672)

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