arXiv subjects

O. Romeo

Publications and source records attributed to O. Romeo.

3 recordsLinked to original sources

arXiv2025

Radial dependence of ion fluences in the 2023 July 17 SEP event from Parker Solar Probe to STEREO and ACE

In the latter moments of 17 July 2023, the solar active region 13363, near the southwestern face of the Sun, was undergoing considerable evolution, which resulted in a significant solar energetic particle (SEP) event measured by Parker Solar Probe's Integrated Science Investigation of the Sun (ISOIS) and near-Earth spacecraft. Remote observations from GOES and CHASE captured two M5.0+ solar flares that peaked at 23:34 and 00:06 UT from the source region. In tandem, STEREO COR2 first recorded a small, narrow coronal mass ejection (CME) emerging at 22:54 UT and then saw a major halo CME emerge at 23:43 UT with a bright, rapidly expanding core and CME-driven magnetic shock with an estimated speed of $\sim$1400 $kms^{-1}$. Parker Solar Probe was positioned at 0.65 au, near-perfectly on the nominal Parker spiral magnetic field line which connected Earth and the active region for a 537 $kms^{-1}$ ambient solar wind speed at L1. This fortuitous alignment provided the opportunity to examine how the SEP velocity dispersion, energy spectra, elemental composition, and fluence varied from 0.65 to 1 au along a shared magnetic connection to the Sun. We find a strong radial gradient, which is best characterized for H and He as $r^{-4.0}$ and most surprisingly is stronger for O and Fe which is better described by $r^{-5.7}$.

astro-ph.SR↗

arXiv2023

Density Enhancement Streams in The Solar Wind

This letter describes a new phenomenon on the Parker Solar Probe of recurring plasma density enhancements that have $Δ$n/n ~10% and that occur at a repetition rate of ~5 Hz. They were observed sporadically for about five hours between 14 and 15 solar radii on Parker Solar Probe orbit 12 and they were also seen in the same radial range on both the inbound and outbound orbits 11. Their apparently steady-state existence suggests that their pressure gradient was balanced by the electric field. The EX electric field component produced from this requirement is in good agreement with that measured. This provides strong evidence for the measurement accuracy of the density fluctuations and the X- and Y-components of the electric field (the Z-component was not measured). The electrostatic density waves were accompanied by an electromagnetic low frequency wave which occurred with the electrostatic harmonics. The amplitudes of these electrostatic and electromagnetic waves at $\ge$ 1 Hz were greater than the amplitude of the Alfvenic turbulence in their vicinity so they can be important for the heating, scattering, and acceleration of the plasma. The existence of this pair of waves is consistent with the observed plasma distributions and is explained by a magneto-acoustic wave theory that produces a low frequency electromagnetic wave and electrostatic harmonics.

astro-ph.SR↗

arXiv2022

Density And Velocity Fluctuations of Alpha Particles in Magnetic Switchbacks

Magnetic switchbacks, or sudden reversals in the magnetic field's radial direction, are one of the more striking observations of Parker Solar Probe (PSP) thus far in its mission. While their precise production mechanisms are still unknown, the two main theories are via interchange reconnection events and in-situ generation. In this work density and abundance variations of alpha particles are studied inside and outside individual switchbacks. We find no consistent compositional differences in the alpha particle abundance ratio, $n_{αp}$, inside vs outside, nor do we observe any signature when separating the switchbacks according to $V_{αp}/V_{pw}$, the ratio of alpha-proton differential speed to the wave phase speed (speed the switchback is travelling). We argue these measurements cannot be used to rule in favour of one production mechanism over the other, due to the distance between PSP and the postulated interchange reconnection events. In addition we examine the 3D velocity fluctuations of protons and alpha particles within individual switchbacks. While switchbacks are always associated with increases in proton velocity, alpha velocities may be enhanced, unchanged, or decrease. This is due to the interplay between $V_{pw}$ and $V_{αp}$, with the Alfvénic motion of the alpha particles vanishing as the difference $|V_{pw} - V_{αp}|$ decreases. We show how the Alfvénic motion of both the alphas and the protons through switchbacks can be understood as approximately rigid arm rotation about the location of the wave frame, and illustrate that the wave frame can therefore be estimated using particle measurements alone, via sphere fitting.

astro-ph.SR↗