arXiv subjects

H. A. Farooki

Publications and source records attributed to H. A. Farooki.

5 recordsLinked to original sources

arXiv2026

Parker Solar Probe observations of solar energetic particle (SEP) events with inverse velocity arrival (IVA) features

In SEP events, velocity dispersion (VD) is characterized by the earlier arrival of faster, higher-energy particles relative to slower ones, assuming negligible acceleration time and transport effects. The "Labor Day event" at Parker Solar Probe (PSP) on 2022 September 5 provided a unique arrival profile, in which the medium energy (~ few MeV) particles arrive earlier than both lower and higher energy particles. This created a so-called "nose" structure in the intensity spectrogram formed by measurements from the two energetic particle instruments, EPI-Lo and EPI-Hi, of the Integrated Science Investigation of the Sun (ISOIS) suite. Unlike typical VD, the delayed arrival of higher energy particles compared to medium energy particles, i.e., the "inverse velocity arrival" (IVA), could be caused by various acceleration, transport, and instrumental effects, including shock acceleration. By applying a new method based on the contour-line of the intensity, we found 14 IVA events in the ISOIS observations up to the end of 2024. Several parameters that may modify velocity dispersion characteristics are further explored including the spacecraft radial distance, the speed of corresponding CMEs and shocks, the angle between the shock normal and the upstream magnetic field, and the spacecraft magnetic footpoint longitudinal separation from the flare location. The energy of the early arriving particles, i.e., the nose energy, can be grouped into low (L, <0.5 MeV), medium(M, 0.5 - 5 MeV), and high(H, >5 MeV) categories. Most (11/14) of the IVA events have medium nose energies. This SEP list provides ingredients for examination of shock acceleration in the inner heliosphere, and the existence of IVA events sheds new light on the acceleration and propagation of SEPs.

astro-ph.SR↗

arXiv2025

Transfer of Entropy between the Magnetic Field and Solar Energetic Particles during an Interplanetary Coronal Mass Ejection

Thermodynamics of solar wind bulk plasma have been routinely measured and quantified, unlike those of solar energetic particles (SEPs), whose thermodynamic properties have remained elusive until recently. The thermodynamic kappa ($κ_{\rm EP}$) that parameterizes the statistical distribution of SEP kinetic energy contains information regarding the population's level of correlation and effective degrees of freedom (${\rm d_{eff}}$). At the same time, the intermittent kappa ($κ_{ΔB}$) that parameterizes the statistical distribution of magnetic field increments contains information about the correlation and ${\rm d_{eff}}$ involved in magnetic field fluctuations. Correlations between particles can be affected by magnetic field fluctuations, leading to a relationship between $κ_{\rm EP}$ and $κ_{ΔB}$. In this paper, we examine the relationship of ${\rm d_{eff}}$ and entropy between energetic particles and the magnetic field via the spatial variation of their corresponding parameter kappa values. We compare directly the values of $κ_{\rm EP}$ and $κ_{ΔB}$ using Parker Solar Probe IS$\odot$IS and FIELDS measurements during an SEP event associated with an interplanetary coronal mass ejection (ICME). Remarkably, we find that $κ_{\rm EP}$ and $κ_{ΔB}$ are anti-correlated via a linear relationship throughout the passing of the ICME, indicating a proportional exchange of ${\rm d_{eff}}$ from the magnetic field to energetic particles, i.e., $κ_{ΔB} \sim (-0.15 \pm 0.03)κ_{\rm EP}$, interpreted as an effective coupling ratio. This finding is crucial for improving our understanding of ICMEs and suggests that they help to produce an environment that enables the transfer of entropy from the magnetic field to energetic particles due to changes in intermittency of the magnetic field.

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arXiv2025

Comparing Methods for Calculating Solar Energetic Particle Intensities: Re-binning versus Spectral Binning

Solar energetic particle (SEP) events have been observed for decades in the interplanetary medium by spacecraft measuring the intensity of energetic ions and electrons. These intensities provide valuable information about particle acceleration, the effects of bulk plasma dynamics on particle transport, and the anisotropy of particle distributions. Since measured intensities are typically reported in narrow energy bins, it is common to re-bin intensities over a wider energy range to improve counting statistics. We investigate two methods for calculating intensities across multiple energy bins: a) \textit{re-binned intensity} ($\overline{j}_{\rm linlin}$), which is calculated by integrating the intensity over energy space and corresponds to the intensity at an effective energy that depends on the time-varying spectral index, and b) \textit{spectral binned intensity} ($\overline{j}_{\rm loglog}$), calculated by integrating the log-intensity in log-energy space, yielding the intensity at the log-centered energy that is independent of the spectral index and remains constant over time. We compare these methods using Parker Solar Probe (PSP) IS$\odot$IS measurements of energetic protons, and we prescribe criteria for selecting the appropriate method for different scenarios. Our results show that the re-binned intensity is consistently larger (up to a factor of 5) than the spectral binned intensity for two SEP events observed by PSP, although the time series of the two methods are strongly correlated. Overall, both measures are important for SEP spectral analysis, and the selection of the appropriate measure depends on whether a physical (spectral binned intensity) or a statistical (re-binned intensity) representation is needed for a given analysis.

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arXiv2024

Observations of Kappa Distributions in Solar Energetic Protons and Derived Thermodynamic Properties

In this paper we model the high-energy tail of observed solar energetic proton energy distributions with a kappa distribution function. We employ a technique for deriving the thermodynamic parameters of solar energetic proton populations measured by the Parker Solar Probe (PSP) Integrated Science Investigation of the Sun (IS$\odot$IS) EPI-Hi high energy telescope (HET), over energies from 10 - 60 MeV. With this technique we explore, for the first time, the characteristic thermodynamic properties of the solar energetic protons associated with an interplanetary coronal mass ejection (ICME) and its driven shock. We find that (1) the spectral index, or equivalently, the thermodynamic parameter kappa of solar energetic protons ($κ_{\rm EP}$) gradually increases starting from the pre-ICME region (upstream of the CME-driven shock), reaching a maximum in the CME ejecta ($κ_{\rm EP} \approx 3.5$), followed by a gradual decrease throughout the trailing portion of the CME; (2) solar energetic proton temperature and density ($T_{\rm EP}$ and $n_{\rm EP}$) appear anti-correlated, a behavior consistent to sub-isothermal polytropic processes; and (3) values of $T_{\rm EP}$ and $κ_{\rm EP}$ appear are positively correlated, indicating an increasing entropy with time. Therefore, these proton populations are characterized by a complex and evolving thermodynamic behavior, consisting of multiple sub-isothermal polytropic processes, and a large-scale trend of increasing temperature, kappa, and entropy. This study and its companion study by Livadiotis et al. (2024) open a new set of procedures for investigating the thermodynamic behavior of energetic particles and their shared thermal properties.

astro-ph.SR↗

arXiv2024

Kappa-tail technique: Modeling and application to Solar Energetic Particles observed by Parker Solar Probe

We develop the kappa-tail fitting technique, which analyzes observations of power-law tails of distributions and energy-flux spectra and connects them to theoretical modeling of kappa distributions, to determine the thermodynamics of the examined space plasma. In particular, we (i) construct the associated mathematical formulation, (ii) prove its decisive lead for determining whether the observed power-law is associated with kappa distributions; and (iii) provide a validation of the technique using pseudo-observations of typical input plasma parameters. Then, we apply this technique to a case-study by determining the thermodynamics of solar energetic particle (SEP) protons, for a SEP event observed on April 17, 2021, by the PSP/ISOIS instrument suite onboard PSP. The results show SEP temperatures and densities of the order of $\sim 1$ MeV and $ \sim 5 \cdot 10^{-7} $ cm$^{-3}$, respectively.

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