Solar radio bursts reveal hidden magnetic switchbacks near the sun, Parker Solar Probe data suggest – Image for illustrative purposes only (Image credits: Unsplash)
NASA’s Parker Solar Probe has provided new evidence of magnetic switchbacks lurking close to the Sun’s surface. Researchers analyzed data from 24 interplanetary Type III solar radio bursts captured by the spacecraft. These bursts revealed irregularities in electron beam paths that point to deflections in the Sun’s magnetic field lines.[1][2]
Type III Bursts as Probes of Solar Magnetic Fields
Type III solar radio bursts occur when beams of non-thermal electrons race along the Sun’s magnetic field lines at speeds reaching a fraction of light speed. These electrons excite plasma waves that produce radio emissions at frequencies tied to local plasma density. As the beams propagate outward, the emission frequency drifts lower because plasma density decreases with distance from the Sun.[3]
Parker Solar Probe’s FIELDS instrument recorded these bursts remotely during its close approaches. The spacecraft’s Radio Frequency Spectrometer captured spectra from about 100 kHz to 19 MHz. By tracking the frequency of peak intensity over time, scientists derived drift rates that reflect the beam’s kinematics through the heliosphere.[2]
Smooth radial propagation through uniform density would yield steadily decreasing drift rates. Yet observations showed deviations, prompting examination of magnetic field perturbations rather than density variations alone.
Drift Rate Variations Signal Field Deflections
Scientists mapped burst frequencies to emitter distances using a standard plasma density model. They fit quadratic trajectories to the distance-time profiles and computed residuals as proxies for perpendicular displacements from radial paths. Noise levels, estimated via Monte Carlo simulations, set a 2-sigma threshold at 0.57 solar radii.[2]
Of the 24 bursts studied from January 2024, when Parker Solar Probe orbited at 11 to 13 solar radii, half exhibited displacements exceeding this threshold. Average perpendicular shifts reached 1.1 solar radii over spatial scales of 1.8 to 6.4 solar radii. These occurred at heliocentric distances between 9 and 30 solar radii.[1]
Key Statistics from 12 Disturbed Events:
- Perpendicular deflections: 0.7–1.7 solar radii
- Spatial scales: 1.8–6.4 solar radii
- Equivalent density changes: 10–30%
- Equivalent field angles: 23–88°
Switchbacks Emerge as Leading Explanation
Four bursts stood out because explaining their profiles required density fluctuations exceeding 50 to 100 percent if assuming straight paths – unrealistically large. Field deflections of 69 to 87 degrees fit better, resembling magnetic switchbacks known from prior Parker observations farther out.[3]
Simulations of electron beams along kinked field lines replicated observed features: reduced drift rates, delayed emission onset and decay, intensity breaks, and striae-like fine structures. These signatures arise as beams linger at fixed densities during deflections, sustaining emission before resuming outward motion.[2]
Such switchbacks, folds spanning about one solar radius, likely originate near the Sun but evade direct in-situ detection due to Parker’s closest approaches at around nine solar radii. Radio bursts thus offer a remote sensing window into these hidden structures.
Broader Insights into Heliospheric Dynamics
The findings demonstrate that Type III burst profiles reflect both density and magnetic fluctuations. Perpendicular field perturbations between 0.7 and 1.7 solar radii account for the observed irregularities without invoking extreme plasma changes. This dual influence refines models of electron beam transport and solar wind acceleration.[1]
Multi-spacecraft validation from STEREO-A and Wind confirmed source locations for 15 events but lacked the resolution to detect similar fine-scale disturbances. Future observations with improved spectral and temporal cadence could pinpoint switchback properties more precisely.
These results position solar radio bursts as powerful tools for mapping inner heliospheric magnetic architecture at kilometric wavelengths. Parker Solar Probe continues to illuminate the Sun’s complex near-surface environment, one burst at a time.