arXiv subjects

Samuel T. Badman

Publications and source records attributed to Samuel T. Badman.

At least 19 recordsLinked to original sources

arXiv2026

Direct Measurement of Polar Coronal Hole-like Solar Wind in its Acceleration Phase

The early evolution of fast polar coronal hole (PCH) solar wind remains largely unconstrained by in situ measurements. In March 2025, Parker Solar Probe (Parker) at its closest approach of 9.86 Solar Radii ($R_\odot$) measured outflow from a large equatorial coronal hole (ECH) which was also measured at 1\,au and at intermediate distances by Solar Orbiter (also near its perihelion). At 1\,au the stream properties are consistent with PCH properties established by Ulysses. The stream was measured by Parker substantially below the Alfv\'en surface, with proton temperatures in excess of 2\,MK and a speed at $\sim$10\,$R_\odot$ which was only $\sim$60\% of its asymptotic value. The Solar Orbiter data indicates that the acceleration is largely complete by 60~$R_{\odot}$. Spherically-polarized fluctuations in the stream are observed to develop from near-transverse and small-angle at Parker to full reversal ``switchbacks'' at Solar Orbiter. Comparison of the implied acceleration profile to historical doppler-dimming measurements suggests that the stream's low coronal acceleration is similar to that of PCH flows. Consistent with previous work, this acceleration requires significantly more energy than can be provided by the observed thermal pressure gradients, with a significant contribution likely from the abundant Alfv\'enic fluctuation energy observed at Parker. These observations provide unique constraints on models of the radial evolution of the fastest solar wind, and indicate that these wind streams experience gradual, steady acceleration over their first few tens of solar radii of evolution.

astro-ph.SR↗

arXiv2026

Strong Prevalence of Hammerhead Velocity Distributions Close to the Heliospheric Current Sheet

The solar wind undergoes non-adiabatic heating as it travels away from the Sun. The velocity phase space distribution of non-equilibrium ions in the solar wind indicate a source of free energy that could contribute significantly to this heating. Parker Solar Probe (PSP) has observed velocity distributions containing highly anisotropic, perpendicularly diffused proton beams with a distinctly constricted gap between the core and beam populations. These distributions resemble a ``hammerhead" shape and were first reported in the fourth PSP encounter. Numerical simulations have reproduced the qualitative nature of hammerheads under certain initial conditions, but have not convincingly captured the prevalence or extreme attributes of the observed beam. This necessitates a broad study of the occurrence conditions and the associated plasma processes to better guide simulations. We statistically investigate the occurrence of these structures from 20 recent PSP encounters, and find that hammerheads dominantly occur around the Heliospheric Current Sheet (HCS). As the inclination of the HCS at PSP crossing points increases over the rising phase of the solar cycle, the occurrence of hammerheads is increasingly concentrated in narrow time periods around the HCS crossings. For comparison with previous work, we present statistical trends in the anisotropy of the proton beam and its connection to the density of proton beams as well as the drift speed of the beam to the core. Our study establishes a consistent occurrence pattern of hammerhead distributions around the HCS indicating hammerheads are diagnostics of energization processes associated with the HCS and its escaping wind.

astro-ph.SR↗

arXiv2026

Properties of Magnetic Switchbacks in the Near-Sun Solar Wind

Magnetic switchbacks are fluctuations in the solar wind in which the interplanetary magnetic field sharply deflects away from its background direction so as to create folds in magnetic field lines while remaining of roughly constant magnitude. The magnetic field and velocity fluctuations are extremely well correlated in a way corresponding to Alfvénic fluctuations propagating away from the Sun. For a background field which is nearly radial this causes an outwardly propagating jet to form. Switchbacks and their characteristic velocity jets have recently been observed to be nearly ubiquitous by Parker Solar Probe with in situ measurements in the inner heliosphere within 0.3 AU. Their prevalence, substantial energy content, and potentially fundamental role in the dynamics of the outer corona and solar wind motivate the significant research efforts into their understanding. Here we review the in situ measurements of these structures (primarily by Parker Solar Probe). We discuss how they are identified and measured, and present an overview of the primary observational properties of these structures, both in terms of individual switchbacks and their collective arrangement into ``patches''. We identify both properties for which there is a strong consensus and those that have limited or qualified support and require further investigation. We identify and collate several open questions and recommendations for future studies.

physics.space-ph↗

arXiv2025

Tracing a Multi-Temperature Quiescent Prominence's Thermodynamic Evolution from Sun to Earth

Solar prominences are cool, dense stable structures routinely observed in the corona. Prominences are often ejected from the Sun via coronal mass ejections (CMEs). However, they are rarely detected in a cool, low-ionized state within CMEs measured in situ, making their evolution hard to study. We examine the thermodynamic evolution of one of these rare cases where a quiescent prominence eruption clearly preserves its low-ionized charge state as evidenced by in situ detection. We use multi-viewpoint Extreme Ultraviolet (EUV) observations to track and estimate the density, temperature and speed of the prominence as it erupts. We observe that part of the prominence remains in absorption well beyond initial liftoff, indicating the bulk of the prominence experiences minimal ionization and suggesting any strong heating is balanced by radiative losses, expansion, or conduction. From its subsequent in situ passage near 1au, charge states reveal that the prominence is composed of both cool, low-ionized ions as well as hotter plasma reflected by the presence of highly ionized iron, Fe$^{16+}$. Simulated non-equilibrium ionization and recombination results using observationally derived initial conditions match the in situ multi-thermal state for a prominence composed of 70% cool plasma with a 1.8MK peak temperature, and 30% hot plasma with a 4.3MK peak temperature. This suggests that the prominence may not be heated uniformly or that parts of it cools more rapidly. The complex, multi-thermal nature of this erupting prominence emphasizes the need for more comprehensive spectral observations of the global corona.

astro-ph.SR↗

arXiv2025

Proton specific entropy as a proxy for the $O^{7+}/O^{6+}$ charge state ratio over heliocentric distance

While the fast solar wind has well-established origins in coronal holes, the source of the slow solar wind remains uncertain. Compositional metrics, such as heavy ion charge state ratios are set in the lower corona, providing insights into solar wind source regions. However, prior to the launch of Solar Orbiter, in situ measurements of heavy ion charge state were limited to distances of 1 AU and beyond. We investigate proton specific entropy as a proxy for the oxygen charge state ratio ($O^{7+}/O^{6+}$),which generally becomes frozen-in below ~1.8 Rsun, leveraging observations from Solar Orbiter's Heavy Ion Sensor and Proton and Alphas Sensor covering 0.28 to 1 AU. Our analysis confirms a strong anti-correlation between specific entropy and the oxygen charge state ratio that persists over a broad range of distances in the inner heliosphere. We categorize observed solar wind into fast solar wind, slow Alfvenic solar wind, and slow solar wind, identifying clear distinctions in specific entropy values and charge state ratios across these types. The work demonstrates the potential to use proton specific entropy as a classifier of solar wind source regions throughout the heliosphere. By establishing the $S_p$-$O^{7+}/O^{6+}$ relationship and quantifying its radial dependence, the specific entropy can be used as a quantity to identify the solar wind source region in the absence of in-situ charge state measurements. This motivates future studies as to the applicability of this proxy to near-Sun observations (such as Parker Solar Probe) and throughout the inner heliosphere.

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 $σ$) 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.

astro-ph.SR↗

arXiv2025

Bayesian and Deterministic Neural Network approaches to Faraday Cup calibration and plasma parameter estimation

We describe a novel scheme for analyzing particle detector measurements when a well-calibrated, similarly instrumented spacecraft is present in a similar orbit. To prepare ground truth from measurements provided by a reference spacecraft, the method uses dynamic time warping (DTW)--a technique often used for pattern-matching in time series data. An artificial neural network (ANN) is created and trained to reproduce this ground truth from measurements at the target spacecraft. Unlike previous approaches, this procedure is insensitive to calibration errors in the target data stream, as the neural network may be trained from poorly calibrated particle spectra or even directly from low-level data in engineering units. We demonstrate a proof-of-concept by training an ANN to estimate solar wind proton densities, temperatures, and speeds from the DSCOVR PlasMag Faraday Cup, using the \textit{Wind} Solar Wind Experiment as a reference. We present both deterministic and Bayesian neural network approaches. Applications for Parker Solar Probe, HelioSwarm, and other missions are discussed.

astro-ph.SR↗

arXiv2025

Multi-spacecraft Measurements of the Evolving Geometry of the Solar Alfvén Surface Over Half a Solar Cycle

The geometry of a star's Alfvén surface determines stellar angular momentum loss, separates a causally distinct 'corona' and stellar wind, and potentially affects exoplanetary habitability. The solar Alfvén surface is the only such structure that is directly measurable and since 2021, has been routinely measured in situ by NASA's Parker Solar Probe (Parker). We use these unique measurements in concert with Solar Orbiter and L1 in situ data spanning the first half of the Solar Cycle 25 in time and from 0.045 - 1 au in heliocentric distance to develop a radial scaling technique to estimate the morphology of the Alfvén surface from measurements of the solar wind speed and local Alfvén speed. We show that accounting for solar wind acceleration and mass flux is necessary to achieve reasonable agreement between the scaled location of the Alfvén surface and the locations of direct crossings measured by Parker. We produce continuous 2D equatorial cuts of the Alfvén surface over half a Solar Cycle (ascending phase and maximum). Parker's earliest crossings clipped outward extrusions, many of which are likely transient related, while more recently Parker has unambiguously sampled deep sub-Alfvénic flows. We analyze the average altitude, departure from spherical symmetry, and surface roughness, finding that all are positively correlated to solar activity. For the current modest Solar Cycle, the height varies up to 30\% which corresponds to a near-doubling in angular momentum loss per unit mass loss.

astro-ph.SR↗

arXiv2025

Observational Constraints on the Radial Evolution of O$^{6+}$ Temperature and Differential Flow in the Inner Heliosphere

Over decades of solar wind observations, heavy ions have been observed to have a higher temperature and flow faster than protons in the solar corona and heliosphere. Remote observations have largely been limited to the low corona ($< 4R_{\odot}$), while in situ observations for heavy ions ($Z>2$) have only been sampled at 1 au and beyond. As a result, theories that address heavy ion heating and acceleration remain largely unconstrained. With the launch of Solar Orbiter, heavy ion kinetics can be probed closer to the Sun, as close as the orbit of Mercury ($65R_{\odot}$), to examine their radial behavior. Through a statistical analysis of O$^{6+}$, this work provides a comprehensive analysis of the velocity and temperature of O$^{6+}$ from 0.3 au to 1 au. The study finds that the O$^{6+}$ relative drift, normalized to the local Alfvén speed, and its temperature compared to protons, both decrease with distance from the Sun and show some speed dependence. The O$^{6+}$ temperature is well fit by a single temperature adiabatic profile across all wind speeds, suggesting there is no significant heating at these heliocentric distances. This is in contrast to what is observed for protons and He$^{2+}$. Alfvénic fluctuations, with full 180$^{\circ}$ field rotation, create momentary negative differential streaming where the speed of O$^{6+}$ trails the protons. The amount of negative differential streaming gradually increases at larger distances. These results provide critical constraints to the proposed mechanisms seeking to describe ion heating and acceleration in the solar wind.

astro-ph.SR↗

arXiv2025

Compression and Reconnection Investigations of the MagnetoPause (CRIMP): A Mission Concept to Uncover the Impact of Mesoscale Reconnection and Plasma Outflow Processes at the Dayside Magnetopause

The Compression and Reconnection Investigations of the Magnetopause (CRIMP) mission is a hypothesis-driven, Heliophysics Medium-Class Explorer (MIDEX) Announcement of Opportunity (AO) mission concept designed to study mesoscale structures and particle outflow along Earth's magnetopause using two identical spacecraft. CRIMP is designed to uncover the impact of magnetosheath mesoscale drivers, dayside magnetopause mesoscale phenomenological processes and structures, and localized plasma outflows on magnetic reconnection and the energy transfer process in the dayside magnetosphere. CRIMP accomplishes this through uniquely phased spacecraft configurations that allow multipoint, contemporaneous measurements at the magnetopause. This enables an unparalleled look at mesoscale spatial differences along the dayside magnetopause on the scale of 1-3 Earth Radii (Re). Through these measurements, CRIMP will uncover how local mass density enhancements affect global reconnection, how mesoscale structures drive magnetopause dynamics, and if the magnetopause acts as a perfectly absorbing boundary for radiation belt electrons. This allows CRIMP to determine the spatial scale size, extent, and temporal evolution of energy and mass transfer processes at the magnetopause - crucial measurements to determine how the solar wind energy input to the magnetosphere is transmitted between regions and across scales.

physics.space-ph↗

arXiv2025

An assessment of observational coverage and gaps for robust Sun to heliosphere integrated science

Understanding the generation and development of the continuous outflow from the Sun requires tracing the physical conditions from deep in the corona to the heliosphere. Detailed global observations of plasma state variables and the magnetic field are needed to provide critical constraints to the underlying physics driving models of the corona and solar wind. Key diagnostics of the solar wind require measurements at its formation site and during its outflow to continuously track it across rapidly changing regions of space. A unified view of the solar wind is only possible through coordinated remote and in situ observations that probe these different regions. Here, we discuss current observational coverage and gaps of different plasma properties and review recent coordinated studies. We highlight how these efforts may become more routine with the launch of upcoming and planned missions.

astro-ph.SR↗

arXiv2025

Formation of Magnetic Switchbacks via expanding Alfvén Waves

Context. Large-amplitude inversions of the solar wind's interplanetary magnetic field have long been documented; however, observations from the Parker Solar Probe (PSP) mission have renewed interest in this phenomenon as such features, often termed switchbacks, may constrain both the sources of the solar wind as well as in-situ nonlinear dynamics and turbulent heating. Aims. We aim to show that magnetic field fluctuations in the solar wind are consistent with Alfvénic fluctuations that naturally form switchback inversions in the magnetic field through expansion effects. Methods. We examine PSP observations of the evolution of a single stream of solar wind in a radial scan from PSP's tenth perihelion encounter from approximately 15-50 solar radii. We study the growth and radial scaling of normalized fluctuation amplitudes in the magnetic field, $δB/B$, within the framework of spherical polarization. We compare heating rates computed via outer-scale decay from consideration of wave-action to proton heating rates empirically observed through considering adiabatic expansion. Results. We find that the magnetic field fluctuations are largely spherically polarized and that the normalized amplitudes of the magnetic field, $δB/B$, increases with amplitude. The growth of the magnetic field amplitude leads to switchback inversions in the magnetic field. While the amplitudes do not grow as fast as predicted by the conservation of wave action, the deviation from the expected scaling yields an effective heating rate, which is close to the empirically observed proton heating rate. Conclusions. The observed scaling of fluctuation amplitudes is largely consistent with a picture of expanding Alfvén waves that seed turbulence leading to dissipation. The expansion of the waves leads to the growth of wave-amplitudes, resulting in the formation of switchbacks.

astro-ph.SR↗

arXiv2025

Helium Abundance Periods Observed by the Solar Probe Cup on Parker Solar Probe: Encounters 1-14

Parker Solar Probe is a mission designed to explore properties of the solar wind closer than ever before. Detailed particle observations from the Solar Probe Cup (SPC) have primarily focused on examining the proton population in the solar wind. However, several periods throughout the Parker mission have indicated that SPC has observed a pronounced and distinctive population of fully ionized helium, He$^{2+}$. Minor ions are imprinted with properties of the solar wind's source region, as well as mechanisms active during outflow, making them sensitive markers of its origin and formation at the Sun. Through a detailed analysis of the He$^{2+}$ velocity distributions functions, this work examines periods where significant and persistent He$^{2+}$ peaks are observed with SPC. We compute the helium abundance and examine the stream's bulk speed, density, temperature, magnetic field topology, and electron strahl properties to identify distinctive solar wind features that can provide insight to their solar source. We find that nearly all periods exhibit an elevated mean helium composition ($8.34\%$) compared to typical solar wind and a majority ($\sim87\%$) of these periods are connected to coronal mass ejections, with the highest abundance reaching $23.1\%$. The helium abundance and number of events increases as the solar cycle approaches maximum with a weak dependence on speed. Additionally, the events not associated with a CME are clustered near the heliospheric current sheet suggesting they are connected to streamer belt outflows. However, there are currently no theoretical explanations that fully describe the range of depleted and elevated helium abundances observed.

astro-ph.SR↗

arXiv2025

Differentiating the acceleration mechanisms in the slow and Alfvénic slow solar wind

In the corona, plasma is accelerated to hundreds of kilometers per second, and heated to temperatures hundreds of times hotter than the Sun's surface, before it escapes to form the solar wind. Decades of space-based experiments have shown that the energization process does not stop after it escapes. Instead, the solar wind continues to accelerate and it cools far more slowly than a freely-expanding adiabatic gas. Recent work suggests that fast solar wind requires additional momentum beyond what can be provided by the observed thermal pressure gradients alone whereas it is sufficient for the slowest wind. The additional acceleration for fast wind can be provided through an Alfvén wave pressure gradient. Beyond this fast-slow categorization, however, a subset of slow solar wind exhibits high Alfvénicity that suggest Alfvén waves could play a larger role in its acceleration compared to conventional slow wind outflows. Through a well-timed conjunction between Solar Orbiter and Parker Solar Probe, we trace the energetics of slow wind to compare with a neighboring Alfvénic slow solar wind stream. An analysis that integrates remote and heliospheric properties and modeling of the two distinct solar wind streams finds Alfvénic slow solar wind behaves like fast wind, where a wave pressure gradient is required to reconcile its full acceleration, while non-Alfvénic slow wind can be driven by its non-adiabatic electron and proton thermal pressure gradients. Derived coronal conditions of the source region indicate good model compatibility but extended coronal observations are required to effectively trace solar wind energetics below Parker's orbit.

astro-ph.SR↗

arXiv2024

Characteristics and Source Regions of Slow Alfvenic Solar Wind Observed by Parker Solar Probe

Using a classification scheme for solar wind type based on the heliocentric distance of the observation, we look at near perihelion observations from Parker Solar Probe Encounters Four to Fourteen to study the sources of the slow Alfv$é$nic solar wind (SASW). Through Potential Field Source Surface (PFSS) modeling and ballistic mapping, we connect streams to their solar source and find that a primary population of SASW comes from low magnetic field strength regions (low-$B_0$), likely small coronal holes (CHs) and their over-expanded boundaries, while a second population of high field strength (high-$B_0$) seems to emerge from non-CH structures potentially through interchange reconnection with nearby open field lines. This low-$B_0$ SASW shows larger expansion than the fast solar wind (FSW) but similar mass flux, potentially indicating additional heating below the critical point, and emergence from a cooler structure, which could lead to slower wind emerging from CH-like structures. We show that this low-$B_0$ SASW shows stronger preferential acceleration of alpha particles (similar to the FSW) than the high-$B_0$ SASW, and that this is a velocity dependent phenomenon as found in previous studies. To have additional confidence in our mapping results, we quantify the error on both the PFSS model and ballistic mapping and discuss how additional multi-point observations of plasma parameters and composition would allow us to better constrain our models and connect the solar wind to its source.

astro-ph.SR↗

arXiv2024

Mixed Source Region Signatures Inside Magnetic Switchback Patches Inferred by Heavy Ion Diagnostics

Since Parker Solar Probe's (Parker's) first perihelion pass at the Sun, large amplitude Alfvén waves grouped in patches have been observed near the Sun throughout the mission. Several formation processes for these magnetic switchback patches have been suggested with no definitive consensus. To provide insight to their formation, we examine the heavy ion properties of several adjacent magnetic switchback patches around Parker's 11th perihelion pass capitalizing on a spacecraft lineup with Solar Orbiter where each samples the same solar wind streams over a large range of longitudes. Heavy ion properties (Fe/O, C$^{6+}$/C$^{5+}$, O$^{7+}$/O$^{6+}$) related to the wind's coronal origin, measured with Solar Orbiter can be linked to switchback patch structures identified near the Sun with Parker. We find that switchback patches do not contain distinctive ion and elemental compositional signatures different than the surrounding non-switchback solar wind. Both the patches and ambient wind exhibit a range of fast and slow wind qualities, indicating coronal sources with open and closed field lines in close proximity. These observations and modeling indicate switchback patches form in coronal hole boundary wind and with a range of source region magnetic and thermal properties. Furthermore, the heavy ion signatures suggest interchange reconnection and/or shear driven processes may play a role in their creation.

astro-ph.SR↗

arXiv2024

In situ observations of large amplitude Alfvén waves heating and accelerating the solar wind

After leaving the Sun's corona, the solar wind continues to accelerate and cools, but more slowly than expected for a freely expanding adiabatic gas. We use in situ measurements from the Parker Solar Probe and Solar Orbiter spacecrafts to investigate a stream of solar wind as it traverses the inner heliosphere. The observations show heating and acceleration of the the plasma between the outer edge of the corona and near the orbit of Venus, in connection to the presence of large amplitude Alfvén waves. Alfvén waves are perturbations in the interplanetary magnetic field that transport energy. Our calculations show the damping and mechanical work performed by the Alfvén waves is sufficient to power the heating and acceleration of the fast solar wind in the inner heliosphere.

astro-ph.SR↗

arXiv2024

Near subsonic solar wind outflow from an active region

During Parker Solar Probe (Parker) Encounter 15 (E15), we observe an 18-hour period of near subsonic ($\mathrm{M_S \sim}$ 1) and sub-Alfvénic (SA), $\mathrm{M_A}$ <<< 1, slow speed solar wind from 22 to 15.6 R$_\odot$. As the most extreme SA interval measured to date and skirting the solar wind sonic point, it is the deepest Parker has probed into the formation and acceleration region of the solar wind in the corona. The stream is also measured by Wind and MMS near 1AU at times consistent with ballistic propagation of this slow stream. We investigate the stream source, properties and potential coronal heating consequences via combining these observations with coronal modeling and turbulence analysis. Through source mapping, in situ evidence and multi-point arrival time considerations of a candidate CME, we determine the stream is a steady (non-transient), long-lived and approximately Parker spiral aligned and arises from overexpanded field lines mapping back to an active region. Turbulence analysis of the Elsässer variables shows the inertial range scaling of the $\mathrm{\mathbf{z}^{+}}$ mode ($\mathrm{f \sim ^{-3/2}}$) to be dominated by the slab component. We discuss the spectral flattening and difficulties associated with measuring the $\mathrm{\mathbf{z}^{-}}$ spectra, cautioning against making definitive conclusions from the $\mathrm{\mathbf{z}^{-}}$ mode. Despite being more extreme than prior sub-Alfvénic intervals, its turbulent nature does not appear to be qualitatively different from previously observed streams. We conclude that this extreme low dynamic pressure solar wind interval (which has the potential for extreme space weather conditions) is a large, steady structure spanning at least to 1AU.

astro-ph.SR↗