English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

One proposed mechanism for heating the solar wind, from close to the sun tobeyond 10 AU, invokes low-frequency, oblique, Alfven-wave turbulence. Becausesmall-scale oblique Alfven waves (kinetic Alfven waves) are compressive, themeasured density fluctuations in the solar wind place an upper limit on theamplitude of kinetic Alfven waves and hence an upper limit on the rate at whichthe solar wind can be heated by low-frequency, Alfvenic turbulence. We evaluatethis upper limit for both coronal holes at 5 solar radii and in the near-Earthsolar wind. At both radii, the upper limit we find is consistent with models inwhich the solar wind is heated by low-frequency Alfvenic turbulence. At 1 AU,the upper limit on the turbulent heating rate derived from the measured densityfluctuations is within a factor of 2 of the measured solar wind heating rate.Thus if low-frequency Alfvenic turbulence contributes to heating the near-Earthsolar wind, kinetic Alfven waves must be one of the dominant sources of solarwind density fluctuations at frequencies of order 1 Hz. We also present asimple argument for why density fluctuation measurements do appear to rule outmodels in which the solar wind is heated by non-turbulent high-frequency waves``sweeping'' through the ion-cyclotron resonance, but are compatible withheating by low-frequency Alfvenic turbulence.

Constraining Low-Frequency Alfvenic Turbulence in the Solar Wind Using Density Fluctuation Measurements