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

Abstract

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 $σ$) 3.1-3.2 mHz peaks in the magnetic field power spectrum, each appearing as a large-amplitude, spherically polarized Alfvénic wave train lasting approximately 35 minutes. These results demonstrate that global solar oscillations can reach and potentially influence the solar wind.

Figures (10)

• Figure 1: 5-Minute Oscillation Event from PSP E22 (a) Parker Solar Probe (PSP) trajectory in a co-rotating frame (black). Radial lines show solar wind speed (proton bulk speed); red line shows Alfvén Mach number. Cyan bar marks the selected interval (2024-12-24 09:50–12:05). Black dots are spaced every 8 hours. (b) Trace magnetic power spectral density (PSD): FFT ($PSD_{FFT}$, blue), average wavelet ($PSD_{WL}$, orange), and frequency-rectified PSD ($PSD_{WL} \cdot f$ (L), dashed orange). Right axis: rectified PSD shown in linear-log scale ($PSD_{WL} \cdot f$ (R), black). $f_{peak}$ and $f_{mid}$ denote peak and median frequencies.
• Figure 2: Timeseries of E22 Event (a) Magnetic field time series with red shading indicating the selected interval. Carrington longitude shown above. (b) Frequency-rectified magnetic wavelet spectrogram $S(f,t)\cdot f$, with cone of influence (black dashed curve and shaded region). Horizontal dashed lines mark $1/f_{mid}$ and $1/f_{peak}$. (c) Radial bulk speeds: protons (green) and local Alfvén speed (blue). (d) Cross helicity $\sigma_c$ and plasma $\beta$. (e) Proton density from QTN. (f) PSP’s heliocentric distance and Alfvén Mach number.
• Figure 3: Oscillation Polarization (a) Frequency-dependent cross helicity $\sigma_c(f)$. (b) Magnetic field power spectral density: FFT (blue) and wavelet average (orange). Green shading marks the frequency band containing the central 50% of fluctuation energy. (c) Magnetic wavelet spectrogram with 5-minute period indicated (green dashed line). (d) Magnetic field strength $|B|$, radial component $B_r$, and 1-minute average of $B_r$. (e) Wavelet spectrogram of $B_r$. (f) $|B|$, tangential component $B_t$, and 1-minute average of $B_t$. (g) Wavelet spectrogram of $B_t$. (h) $|B|$, normal component $B_n$, and 1-minute average of $B_n$. (i) Wavelet spectrogram of $B_n$.
• Figure 4: Spherical Polarization of the Oscillations (a) Trace magnetic periodogram. 5-minute is highlighted with the green dashed line. (b) $|B|$. (c) $B_r$ and $V_r$. (d) $B_t$ and $V_r$. (e) $B_n$ and $V_n$. (f) Hodogram of $B_t-B_r$. (g) $B_n-B_r$. (h) $B_n-B_t$.
• Figure S1: Comparison between QTN and SPAN-i(a) Electron number density (ne-qtn) from Quasi-Thermal-Noise (QTN) and proton number density from SPAN-i (np-span). (b) Alpha particle number density (na-span) from SPAN-i. (c) Ratio between ne-qtn and na-span. (d) Ratio between the mass density modified with alpha particle density ($\rho^*$) and without modification ($\rho$).