Ian James Cohen

The ion foreshock is the region upstream of Earth's bow shock where magnetic field lines connect to the quasi‐parallel shock surface. Within this region, there exist a variety of backstreaming ion populations from the shock ramp that can generate ultra‐low frequency (ULF) waves through wave‐particle interactions. In this work, we use data from the Magnetospheric Multiscale (MMS) mission to study such ULF waves and backstreaming ions during a prolonged interval of above‐average solar wind helium abundance, embedded in a multi‐day period of strong solar activity driven by a coronal mass ejection. When interplanetary magnetic field orientations positioned MMS within the ion foreshock, the spacecraft captured the complete evolutionary sequence of the backstreaming ion velocity distributions: the initial formation of a reflected ion beam, followed by phase bunching and generation of coherent ULF waves, and eventual thermalization and randomization in velocity space to form diffuse ions. Intervals with elevated energetic He++ flux exhibited broadened and frequency‐downshifted wave spectra, consistent with heavy‐ion cyclotron resonance effects. The unusually rapid beam‐to‐diffuse transitions observed near the foreshock boundary likely result from the combined effects of multi‐species wave‐particle interactions and higher backstreaming ion densities during this active interval. These findings underscore the need for simulations and modeling that incorporate multi‐species effects.

Bursty bulk flows, injections, and related flows are a key component of plasma energy and flux transport during substorms. Mixed observational features require researchers to carefully define their quantitative criteria in studies of such events, a process that requires presuming some quantity of the output events. In this work we present a novel supervised random forest classification model for identifying substorm related flows in the plasma sheet. Our model allows a more complete view of event variety, and avoids the presumptive nature of data‐derived quantitative classification. We observe no correlation between event velocities and geomagnetic activity, however an uneven formation of large‐scale dipolarization in the tail region during strong substorms is statistically present in our data. A bi‐modality also appears in the event occurrence location during strong substorms. Some model limitations and future work is discussed.

Bursty bulk flows (BBFs) are fast flows of plasma in the tail and are responsible for much of the energy flux transport earthward from the tail into the inner magnetosphere despite being relatively short‐lived. BBFs are often accompanied by injections in which particles that have been accelerated to 10–100s of keV are transported earthward. We quantify kinetic energy transport by both the thermal plasma of the BBF and the energetic particles of the injections to see how significantly injections contribute. We studied three different cases. In the first, a BBF with no observed injections, we found that the thermal ion population was responsible for almost all the kinetic energy transport. In the second, a BBF with only an electron injection, the thermal ions were again dominant, suggesting that neither electron population is a major contributor to energy transport. Finally, the third event contained an ion injection. This time, the energetic ions transported a comparable amount of energy as the thermal ions. The energy transport from the thermal ions alone is similar to the other events and the total energy transport is higher, suggesting that the ion injection is adding extra energy transport to the process. Global magnetospheric modeling shows that this is a straightforward reconnection event, so unique conditions are not necessary for energetic ions to be a significant contributor to earthward kinetic energy transport during a BBF. Therefore, an energy transport calculation assuming a solely thermal flow can lead to an underestimate if there is a concurrent ion injection.

Origins, Worlds, and Life: Planetary Science and Astrobiology in the Next Decade identified a Uranus Orbiter and Probe as the highest-priority strategic mission for the decade 2023–2032, as it enables broad cross-disciplinary science in the largely unexplored Uranian system. The mission architecture evaluated by the Decadal Survey was a singular proof of concept demonstrating that a moderately instrumented mission could deliver Decadal-priority science with a reduced cost and risk posture by leveraging existing technologies to the maximum extent possible. With revised assumptions since the Decadal, we have explored a large trade space including launch vehicles, propulsion options, cruise trajectories, available power sources, viable concept of operations, and science data return for later launch dates without a Jupiter gravity assist. The most repeatable trajectory solutions employ either a commercially derived solar electric propulsion (SEP) transfer stage or the availability of a more capable launch vehicle under development, such as the SpaceX Starship. Orbit insertion has been moved farther from Uranus to acknowledge the remaining uncertainty in Uranian ring structure. A streamlined, SEP-adaptable, orbiter design was developed using two Next Gen Radioisotope Thermoelectric Generators, and the probe design was matured, reducing the entry gravitational acceleration, and assuming the largest Decadal-recommended payload to provide margin for future instrument selections. With this updated design, we also constructed a detailed concept of operations for three representative science cases, returning 13–15 Gbit of science data and spacecraft telemetry per ∼34 day orbit.

The ion foreshock is the region upstream of Earth’s bow shock where magnetic field lines connect to the quasi-parallel shock surface. Within this region, there exist a variety of backstreaming ion populations from the shock ramp that can generate ultra-low frequency (ULF) waves through wave-particle interactions. In this work, we use data from the Magnetospheric Multiscale (MMS) mission to study such ULF waves and backstreaming ions during a prolonged interval of above-average solar wind helium abundance, embedded in a multi-day period of strong solar activity driven by a CME. When interplanetary magnetic field (IMF) orientations positioned MMS within the ion foreshock, the spacecraft captured the complete evolutionary sequence of the backstreaming ion velocity distributions: the initial formation of a reflected ion beam, followed by phase bunching and generation of coherent ULF waves, and eventual thermalization and randomization in velocity space to form diffuse ions. Intervals with elevated energetic He++ flux exhibited broadened and frequency-downshifted wave spectra, consistent with heavy-ion cyclotron resonance effects. The unusually rapid beam-to-diffuse transitions observed near the foreshock boundary likely result from the combined effects of multi-species wave-particle interactions and higher backstreaming ion densities during this active interval. These findings underscore the need for simulations and modeling that incorporate multi-species effects.

Shocks in collisionless astrophysical plasmas redistribute some of the incident flow energy into both thermal and non‐thermal energy. Quantifying the partition of that energy amongst various particle species or their sub‐populations, and electromagnetic energy, represents a fundamental goal of shock physics. It embodies the role of the equation of state for the system. Here we apply a framework to assess all the incident and downstream energy fluxes at a crossing of Earth's bow shock for which the upstream magnetic field was roughly aligned with the shock normal direction. Such quasi‐parallel shocks are known to be non‐steady and to produce significant populations of suprathermal particles. We quantify the evolution of all the important carriers of energy flux through the shock region. We sub‐divide the proton population into thermal, suprathermal, and energetic components in order to investigate the shock's efficiency in energizing the nonthermal particles. While the largest energy fluxes are found in the incident proton ram energy and downstream proton thermal enthalpy fluxes, a significant suprathermal population pervades the regions both up‐ and downstream. We also evaluate the energy fluxes attributable to fluctuations in the fluid and field parameters.

This study investigates energy dissipation in small‐scale solar wind turbulence using a novel approach to autocorrelation function analysis leveraging high‐resolution data from the Magnetospheric Multiscale Mission (MMS). We analyze magnetic field fluctuations at ion dissipation scales, focusing on short 20‐s intervals to isolate dissipation‐scale dynamics. Using MMS's fluxgate magnetometer, fast plasma investigation, and energetic particle detector, we compute normalized correlation functions as functions of the interplanetary magnetic field cone angle. Our results show that turbulence is correlated over short spatial scales (100–1,000 km), with shorter correlation lengths in the compressional component compared to the transverse components. We find that the transverse correlation lengths differ most when the interplanetary magnetic field is nearly perpendicular to the solar wind flow (cone angle ), and that they vary approximately as the inverse sine of the cone angle. The characteristics of the correlation length suggest that the turbulence observed is primarily two‐dimensional. These findings highlight the anisotropic nature of dissipation‐scale turbulence and its dependence on solar wind conditions, providing insights into energy transfer in space plasmas.

This study investigates energy dissipation in small-scale solar wind turbulence using a novel approach to autocorrelation function analysis leveraging high-resolution data from the Magnetospheric Multiscale Mission (MMS). We analyze magnetic field fluctuations at ion dissipation scales, focusing on short 20-second intervals to isolate dissipation-scale dynamics. Using MMS’s fluxgate magnetometer, fast plasma investigation, and energetic particle detector, we compute normalized correlation functions as functions of solar wind parameters, including interplanetary magnetic field cone angle and solar wind speed. Our results show that turbulence decorrelates over short spatial scales ($\sim$ 100-1000 km), with faster decorrelation in the compressional component compared to the transverse components. We find that the transverse correlation lengths differ most when the interplanetary magnetic field is nearly perpendicular to the solar wind flow (cone angle $\sim 90^{\circ}$), and that they vary approximately as the inverse sine of the cone angle. The characteristics of the correlation length suggest that the turbulence observed is primarily two-dimensional. These findings highlight the anisotropic nature of dissipation-scale turbulence and its dependence on solar wind conditions, providing insights into energy transfer in space plasmas.

The outflow of low‐energy ions into inner magnetosphere is a key contributor to the warm plasma cloak, and O ⁺ torus, which can also contribute to storm time ring current particularly after local acceleration. Although outflows are well observed, their source and transport in the inner magnetosphere remain unclear. Using Helium Oxygen Proton and Electron mass spectrometer data from the Van Allen Probes, we systematically examine outflows during geomagnetic storms. We developed an automated event identification method to detect outflows, estimate onset times, and record occurrence details. With this event set, we performed a statistical analysis of occurrence characteristics and storm phase dependence, separately for outflows parallel and anti‐parallel to the magnetic field. Our findings show: (a) outflows are mostly detected off the magnetic equator; (b) with the understanding that the parallel outflows are from the Southern Hemisphere, while anti‐parallel from the Northern Hemisphere, we observed more events in the hemisphere within which the source of O ⁺ outflow lies; (c) the peak of the occurrence rate in MLT is derived at mid‐night with skewing toward dawn; (d) during the main phase of the storms, outflows events are concentrated at post‐midnight and dawn. Decrease in the occurrence rate is observed in the recovery phase. Hemispheric and dawn‐dusk asymmetries are evident in the event distribution patterns; (e) a preference for outflows from the summer hemisphere. These results offer new insights into nightside, low‐energy outflows. Our large event data set enables us to explore the sources of energization and their transport better.