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

We use fluctuating magnetic helicity to investigate the polarisationproperties of Alfv\'enic fluctuations at ion-kinetic scales in the solar windas a function of $\beta_p$, the ratio of proton thermal pressure to magneticpressure, and $\theta_{vB}$, the angle between the proton flow and local meanmagnetic field, $\mathbf{B}_0$. Using almost 15 years of \textit{Wind}observations, we separate the contributions to helicity from fluctuations withwave-vectors, $\textbf{k}$, quasi-parallel and oblique to $\mathbf{B}_0$,finding that the helicity of Alfv\'enic fluctuations is consistent withpredictions from linear Vlasov theory. This result suggests that the non-linearturbulent fluctuations at these scales share at least some polarisationproperties with Alfv\'en waves. We also investigate the dependence of protontemperature in the $\beta_p$-$\theta_{vB}$ plane to probe for possiblesignatures of turbulent dissipation, finding that it correlates with$\theta_{vB}$. The proton temperature parallel to $\mathbf{B}_0$ is higher inthe parameter space where we measure the helicity of right-handed Alfv\'enicfluctuations, and the temperature perpendicular to $\mathbf{B}_0$ is higherwhere we measure left-handed fluctuations. This finding is inconsistent withthe general assumption that by sampling different $\theta_{vB}$ in the solarwind we can analyse the dependence of the turbulence distribution on$\theta_{kB}$, the angle between $\textbf{k}$ and $\mathbf{B}_0$. After rulingout both instrumental and expansion effects, we conclude that our resultsprovide new evidence for the importance of local kinetic processes that dependon $\theta_{vB}$ in determining proton temperature in the solar wind.

Dependence of Solar Wind Proton Temperature on the Polarisation Properties of Alfv\'enic Fluctuations at Ion-kinetic Scales