Evolution of Near-Sun Solar Wind Turbulence

TL;DR

This study analyzes the turbulence spectrum of near-Sun solar wind using interplanetary scintillation data, revealing how small-scale fluctuations evolve rapidly as they approach the Sun, driven by Alfvén waves.

Contribution

It provides new observational evidence of the radial evolution of small-scale solar wind turbulence within 50 solar radii.

Findings

Density irregularities of 100-500 km dominate scintillation.

Flatter spectrum observed at smaller scales near the Sun.

Rapid increase in small-scale fluctuation power closer to the Sun.

Abstract

This paper presents a preliminary analysis of the turbulence spectrum of the solar wind in the near-Sun region R < 50 Rs, obtained from interplanetary scintillation measurements with the Ooty Radio Telescope at 327 MHz. The results clearly show that the scintillation is dominated by density irregularities of size about 100 - 500 km. The scintillation at the small-scale side of the spectrum, although significantly less in magnitude, has a flatter spectrum than the larger-scale dominant part. Furthermore, the spectral power contained in the flatter portion rapidly increases closer to the Sun. These results on the turbulence spectrum for R < 50 Rs quantify the evidence for radial evolution of the small-scale fluctuations (</= 50 km) generated by Alfven waves.