arXiv subjects

Yuliang Ding

Publications and source records attributed to Yuliang Ding.

6 recordsLinked to original sources

arXiv2026

Spherically Polarized Alfv\'en Waves and the Gosling Boost

Alfv\'en waves are thought to play critical roles in solar wind acceleration and plasma heating in the solar corona and inner heliosphere. Parker Solar Probe (PSP) has highlighted the role of large amplitude Spherically Polarized Alfv\'en Waves (SPAWs), where the locally constant magnetic field magnitude $|\mathbf{B}|$ together with outward propagation explains the observed one sided radial velocity enhancement - the Gosling boost. Starting from the MHD equations, we derive the modified wave pressure and Poynting flux under the SPAW condition, and demonstrate both are governed solely by the transverse magnetic fluctuations. Using PSP data from Encounters 6--25, we define an unperturbed velocity baseline from the lower 10th-percentile running average and statistically characterize the radial evolution of Alfv\'enic fluctuations. The background solar wind velocity shows clear radial acceleration, while the velocity perturbation amplitude $\delta v$ decreases with heliocentric distance. This decay is anisotropic between the radial and perpendicular directions, which is a direct consequence of the growing magnetic deflection angle related to the spherical polarization. Our results demonstrate that radial velocity enhancements in the young solar wind arise naturally from SPAWs rather than from localized velocity jets, and provide direct observational evidence for the anisotropic radial evolution of SPAWs in the inner heliosphere.

astro-ph.SR↗

arXiv2026

Radial Evolution of Near-Sun Magnetic Switchbacks Alfvenicity, Occurrence Rate, and Size

Magnetic switchbacks, characterized by reversals of magnetic field direction, are widely observed in the inner heliosphere by Parker Solar Probe (PSP). With PSP reaching perihelia near 10Rs, observations from the first 24 encounters enable studies of near-Sun switchback evolution at r > 10Rs. We construct a switchback catalog within 10 < r < 55Rs by identifying magnetic field reversals with stable field magnitude and strahl-electron polarity. Statistical analysis shows that switchback Alfvenicity decreases with increasing radial distance, consistent with solar wind evolution beyond the Alfven critical point. Meanwhile, switchback occurrence rate and spatial size increase with distance, suggesting continued generation and expansion during solar wind propagation. At a given radial distance, the fraction of solar wind containing switchbacks is positively correlated with background solar wind radial velocity (VR) and Alfven Mach number (MA), while the local occurrence rate is mainly controlled by MA. These results suggest that switchback patches preferentially form in faster and higher-MA solar wind. The spatial size of switchbacks shows no clear dependence on MA or VR, implying that their size evolution is probably not determined by source conditions. Solar activity influences switchback evolution through changes in background solar wind properties, with a larger fraction of higher-MA switchbacks during solar minimum. We further identify anisotropy relative to the background magnetic field direction: the local occurrence rate and spatial size are approximately 1.5 times as large in the perpendicular direction as in the parallel direction, indicating distinct magnetic topology of switchback patches

astro-ph.SR↗

arXiv2025

What are Switchbacks?

We present a solitary Alfv\'en wave model that exhibits nontrivial three-dimensional twisting of open magnetic field lines while preserving constant $|B|$. Embedded rotational discontinuities sharply deflect the otherwise uniform field lines, producing localized, large-amplitude field reversals in one-dimensional profiles that closely resemble the ``switchbacks'' observed by the Parker Solar Probe in the inner heliosphere. This indicates that switchbacks, as seen in one-dimensional spacecraft time series, arise from traversals through strongly curved segments of open magnetic field lines.

physics.space-ph↗

arXiv2025

Solitary Alfv\'en Waves

We present the solitary Alfv\'en wave as an ideal nonlinear Alfv\'enic solution in the solitary far-field limit and construct a three-dimensional numerical model -- an \emph{Alfv\'enon}. The model is characterized by an unperturbed far field, quasi-constant $|\boldsymbol{B}|$, and open field-line topology. Direct MHD simulations of the Alfv\'enon show coherent finite-time propagation, confirming that it behaves as a nonlinear solitary Alfv\'enic solution under ideal MHD evolution.

astro-ph.SR↗

arXiv2025

In situ Evidence of 5-minute Oscillations from Parker Solar Probe

The Sun's surface vibrates in characteristic 5-minute oscillations, known as p-modes, generated by sound waves trapped within the convection zone. Although these oscillations have long been hypothesized to reach into the solar wind, direct in situ evidence has remained elusive, even during previous close encounters by Parker Solar Probe (PSP). Here, we present the first promising in situ detection of 5-minute oscillations in the upper solar corona, based on observations from PSP's three closest perihelia. In two events at 9.9 solar radii, we identify statistically significant ($\sim$ 6 $\sigma$) 3.1-3.2 mHz peaks in the magnetic field power spectrum, each appearing as a large-amplitude, spherically polarized Alfv\'enic wave train lasting approximately 35 minutes. These results demonstrate that global solar oscillations can reach and potentially influence the solar wind.

astro-ph.SR↗

arXiv2025

Two Types of $1/f$ Range in Solar Wind Turbulence

The $1/f$ noise is a ubiquitous phenomenon in natural systems. Since the advent of space exploration, the $1/f$ range has been consistently observed in \textit{in situ} solar wind measurements throughout the heliosphere, sparking decades of debate regarding its origin. Recent Parker Solar Probe (PSP) observations near the Alfv\'en surface have revealed a systematic absence of the $1/f$ range in pristine solar wind, providing a unique opportunity to investigate its origin in solar wind turbulence. Despite numerous observations of the $1/f$ range at varying frequencies, no study has systematically examined its properties across different solar wind conditions. Here, we identify two distinct types of $1/f$ ranges in solar wind turbulence: the fast/Alfv\'enic wind type and the slow/mixed wind type. The fast/Alfv\'enic type appears to be an intrinsic feature of Alfv\'enic turbulence, while the slow/mixed type resembles classical flicker noise. For the fast/Alfv\'enic type, we find a near-perfect WKB evolution of the frequency-averaged fluctuation amplitude and an intriguing migration pattern in frequency space. For the slow/mixed type, we examine the solar cycle dependence of the $1/f$ noise using the OMNI-LRO dataset spanning solar cycles 22 to 25. We also analyze the autocorrelation function of the magnetic field vectors and identify a clear relationship between the $1/f$ range and the decline in correlation, as well as unexpected resonance peaks in the autocorrelation function.

astro-ph.SR↗