Enhanced Energy Transfer Rate in Solar Wind Turbulence Observed near the Sun from Parker Solar Probe

TL;DR

This study uses Parker Solar Probe data to measure the energy transfer rate in solar wind turbulence closer to the Sun, revealing a rate nearly 100 times higher than at 1 au, indicating more intense heating near the solar corona.

Contribution

First direct estimation of fluid-scale energy transfer rate in the inner heliosphere using PSP data, showing unprecedentedly high heating rates near the Sun.

Findings

Energy transfer rate near the Sun is about 100 times higher than at 1 au.

The observed heating rates are comparable to those in terrestrial magnetosheath.

The results suggest more efficient energy cascade and heating closer to the Sun.

Abstract

Direct evidence of an inertial-range turbulent energy cascade has been provided by spacecraft observations in heliospheric plasmas. In the solar wind, the average value of the derived heating rate near 1 au is $\sim 10^{3}\, \mathrm{J\,kg^{-1}\,s^{-1}}$, an amount sufficient to account for observed departures from adiabatic expansion. Parker Solar Probe (PSP), even during its first solar encounter, offers the first opportunity to compute, in a similar fashion, a fluid-scale energy decay rate, much closer to the solar corona than any prior in-situ observations. Using the Politano-Pouquet third-order law and the von K\'arm\'an decay law, we estimate the fluid-range energy transfer rate in the inner heliosphere, at heliocentric distance $R$ ranging from $54\,R_{\odot}$ (0.25 au) to $36\,R_{\odot}$ (0.17 au). The energy transfer rate obtained near the first perihelion is about 100 times higher than the average value at 1 au. This dramatic increase in the heating rate is unprecedented in previous solar wind observations, including those from Helios, and the values are close to those obtained in the shocked plasma inside the terrestrial magnetosheath.