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

Using numerical simulations, we investigate the onset and suppression ofparametric decay instability (PDI) in the solar wind, focusing on thesuppression effect by the wind acceleration and expansion. We also discuss therole of PDI in generating the density fluctuation in the solar wind and thecross-helicity evolution up to $1 {\rm \ au}$. Numerical simulations from thecoronal base to 1 au are conducted in a self-consistent manner; we take intoaccount the feedback of wave energy and pressure in the background.Monochromatic waves with various injection frequencies $f_0$ are injected todiscuss the suppression of PDI, while broadband waves are applied to comparethe numerical results with observation. We find, via the simulations withmonochromatic waves, that high-frequency ($f_0 \gtrsim10^{-3} {\rm \ Hz}$)Alfv\'en waves are subject to PDI. Meanwhile, the maximum growth rate of thePDI of low-frequency ($f_0 \lesssim10^{-4} {\rm \ Hz}$) Alfv\'en waves becomesnegative due to acceleration and expansion effects. Medium-frequency ($f_0\approx 10^{-3.5} {\rm \ Hz}$) Alfv\'en waves have a positive growth rate butdo not show the signature of PDI up to 1 au because the growth rate is toosmall. The medium-frequency waves experience neither PDI nor reflection so theypropagate through the solar wind most efficiently. This is called thefrequency-filtering mechanism of the solar wind. The simulations with broadbandwaves indicate that the observed trend of the density fluctuation is wellexplained by the evolution of PDI while the observed cross-helicity evolutionis in agreement with low-frequency wave propagation.

Frequency-dependent Alfv\'en-wave propagation in the solar wind: Onset and suppression of parametric decay instability