Spatially Coherent and Intermittent Alfvénic Fluctuations in Solar Polar Spicules

Alfvénic fluctuations are a possible mechanism for transporting energy from the lower solar atmosphere into the corona, with spicules acting as dynamic conduits for this transfer. We investigate transverse and Doppler velocity fluctuations in quiet-Sun polar spicules observed in the Si IV 1394 Å line by the Interface Region Imaging Spectrograph. A Fourier analysis in both time and space is used to characterize the distribution of power in frequency and space. The temporal power spectra show broadband fluctuations, with a broad power enhancement around 3–7 mHz and maximum power near 4–6 mHz. A spatial Fourier analysis of Doppler velocity fluctuations reveals broadband behavior with a perpendicular power spectrum scaling as (Formula presented) ∼k⊥−1.43, similar to but slightly shallower than the values of −5/3 and −3/2 expected for homogeneous strong MHD turbulence, but within the range of those found in simulations of reflection-driven turbulence in the solar corona. Velocity-increment probability distribution functions exhibit non-Gaussian behavior, with the kurtosis near Gaussian at large spatial scales and increasing toward smaller scales following a power-law scaling (index ≈−0.23), consistent with the development of intermittency. A spatial coherence analysis based on cross correlation, together with spectral and kurtosis-based diagnostics, indicates an outer-scale range of about a few hundred to about a thousand kilometers, with the cross correlation method yielding smaller estimates. These results provide new observational evidence that, in addition to coherent Alfvén waves, polar spicules host multiscale Alfvénic fluctuations with characteristics consistent with intermittent MHD turbulence, highlighting their potential role in energy transport into the solar corona.