We analyze the local dynamics of magnetotail reconnection onset using Magnetospheric Multiscale (MMS) data. In conjunction with MMS, the macroscopic dynamics of this event were captured by a number ...of other ground and space‐based observatories, as is reported in a companion paper. We find that the local dynamics of the onset were characterized by the rapid thinning of the cross‐tail current sheet below the ion inertial scale, accompanied by the growth of flapping waves and the subsequent onset of electron tearing. Multiple kinetic‐scale magnetic islands were detected coincident with the growth of an initially sub‐Alfvénic, demagnetized tailward ion exhaust. The onset and rapid enhancement of parallel electron inflow at the exhaust boundary was a remote signature of the intensification of reconnection Earthward of the spacecraft. Two secondary reconnection sites are found embedded within the exhaust from a primary X‐line. The primary X‐line was designated as such on the basis that (a) while multiple jet reversals were observed in the current sheet, only one reversal of the electron inflow was observed at the high‐latitude exhaust boundary, (b) the reconnection electric field was roughly five times larger at the primary X‐line than the secondary X‐lines, and (c) energetic electron fluxes increased and transitioned from anti‐field‐aligned to isotropic during the primary X‐line crossing, indicating a change in magnetic topology. The results are consistent with the idea that a primary X‐line mediates the reconnection of lobe magnetic field lines and accelerates electrons more efficiently than its secondary X‐line counterparts.
Key Points
Magnetotail reconnection onset was triggered by electron tearing during a solar wind pressure pulse
Onset was characterized by the rapid collapse of the current sheet thickness and kinetic‐scale flux rope formation
A primary X‐line was established within minutes of the onset
Turbulent and compressed sheath regions preceding interplanetary coronal mass ejections strongly impact electron dynamics in the outer radiation belt. Changes in electron flux can occur on timescales ...of tens of minutes, which are unlikely to be captured by a two‐satellite mission. The recently released Global Positioning System (GPS) data set generally has shorter revisit times (at L ∼ 4–8) owing to the large number of satellites in the constellation equipped with energetic particle detectors. Investigating electron fluxes at energies from 140 keV to 4 MeV and sheaths observed in 2012–2018, we show that the flux response to sheaths on a timescale of 6 hr, previously reported from Van Allen Probes (RBSP) data, is reproduced by GPS measurements. Furthermore, GPS data enables derivation of the response on a timescale of 30 min, which further confirms that the energy and L‐shell dependent changes in electron flux are associated with the impact of the sheath. Sheath‐driven loss is underestimated over longer timescales as the electrons recover during the ejecta. We additionally show the response of electron phase space density (PSD), which is a key quantity in identifying non‐adiabatic loss from the system and electron energization through wave‐particle interactions. The PSD response is calculated from both RBSP and GPS data for the 6 hr timescale, as well as from GPS data for the 30 min timescale. The response is divided based on the geoeffectiveness of the sheaths revealing that electrons are effectively accelerated only during geoeffective sheaths, while loss commonly occurs during all sheaths.
Key Points
Global Positioning System measurements confirm 6 hr RBSP outer belt electron flux response to interplanetary coronal mass ejection‐driven sheaths at 6 hr and 30 min timescales
Phase space density (PSD) response shows that electron energization is associated only with geoeffective sheaths but loss occurs in response to all sheaths
Impacts in electron flux and PSD presented here are related to sheaths, and the lost electrons are replenished during the early ejecta
Magnetic reconnection is a fundamental mechanism for the transport of mass and energy in planetary magnetospheres and astrospheres. While the process of reconnection is itself ubiquitous across a ...multitude of systems, the techniques used for its analysis can vary across scientific disciplines. Here we frame the latest understanding of reconnection theory by missions such as NASA’s Magnetospheric Multiscale (MMS) mission for use throughout the solar system and beyond. We discuss how reconnection can couple magnetized obstacles to both sub- and super-magnetosonic upstream flows. In addition, we address the need to model sheath plasmas and field-line draping around an obstacle to accurately parameterize the possibility for reconnection to occur. We conclude with a discussion of how reconnection energy conversion rates scale throughout the solar system. The results presented are not only applicable to within our solar system but also to astrospheres and exoplanets, such as the first recently detected exoplanet magnetosphere of HAT-11-1b.
An empirical model of radiation belt relativistic electrons (μ = 560–875 MeV G−1 and I = 0.088–0.14 RE G0.5) with average energy ∼1.3 MeV is developed. The model inputs solar wind parameters ...(velocity, density, interplanetary magnetic field (IMF) |B|, Bz, and By), magnetospheric state parameters (SYM‐H and AL), and L*. The model outputs the radiation belt electron phase space density (PSD). The model is operational from L* = 3 to 6.5. The model is constructed with neural networks assisted by information theory. Information theory is used to select the most effective and relevant solar wind and magnetospheric input parameters plus their lag times based on their information transfer to the PSD. Based on the test set, the model prediction efficiency (PE) increases with increasing L*, ranging from −0.043 at L* = 3 to 0.76 at L* = 6.5. The model PE is near 0 at L* = 3–4 because at this L* range, the solar wind and magnetospheric parameters transfer little information to the PSD. Using solar wind observations at L1 and magnetospheric index (AL and SYM‐H) models solely driven by solar wind, the radiation belt model can be used to forecast PSD 30–60 min ahead. This baseline model can potentially complement a class of empirical models that input data from low earth orbit (LEO).
Plain Language Summary
An empirical model of radiation belt relativistic electrons with an energy of 1–2 MeV is developed. The model inputs solar wind parameters, magnetospheric state parameters, and L*. L* gives a measure of radial distance from the center of the Earth with a unit of RE (radius of the Earth = 6,378 km). The model outputs the radiation belt electron phase space density (PSD). The model is operational from L* = 3 to L* 6.5. The model is constructed with an information theory informed neural networks. Information theory is used to select the relevant solar wind and magnetospheric parameters and their lag times based on the amount of information they provide to the radiation belt electrons. The model performance increases with increasing radial distance (L*) because at distances close to Earth (L* = 3–4), the solar wind and magnetospheric parameters provide little information about the radiation belt electron PSD. The model can be used to forecast radiation belt PSD 30–60 min ahead.
Key Points
An empirical model to predict state of radiation belt relativistic electrons is developed
The model prediction efficiency increases with increasing L* with a PE > 0.6 at L* > 5
The model can potentially complement a class of empirical models that input observations from low earth orbit
The Plasma Environment, Radiation, Structure, and Evolution of the Uranian System (PERSEUS) mission concept defines the feasibility and potential scope of a dedicated, standalone Heliophysics orbiter ...mission to study multiple space physics science objectives at Uranus. Uranus’s complex and dynamic magnetosphere presents a unique laboratory to study magnetospheric physics as well as its coupling to the solar wind and the planet’s atmosphere, satellites, and rings. From the planet’s tilted and offset, rapidly-rotating non-dipolar magnetic field to its seasonally-extreme interactions with the solar wind to its unexpectedly intense electron radiation belts, Uranus hosts a range of outstanding and compelling mysteries relevant to the space physics community. While the exploration of planets other than Earth has largely fallen within the purview of NASA’s Planetary Science Division, many targets, like Uranus, also hold immense scientific value and interest to NASA’s Heliophysics Division. Exploring and understanding Uranus’s magnetosphere is critical to make fundamental gains in magnetospheric physics and the understanding of potential exoplanetary systems and to test the validity of our knowledge of magnetospheric dynamics, moon-magnetosphere interactions, magnetosphere-ionosphere coupling, and solar wind-planetary coupling. The PERSEUS mission concept study, currently at Concept Maturity Level (CML) 4, comprises a feasible payload that provides closure to a range of space physics science objectives in a reliable and mature spacecraft and mission design architecture. The mission is able to close using only a single Mod-1 Next-Generation Radioisotope Thermoelectric Generator (NG-RTG) by leveraging a concept of operations that relies of a significant hibernation mode for a large portion of its 22-day orbit.
Centrioles form centrosomes that organize microtubules, assist in cell structure, and nucleate cilia that provide motility and sensation. Within the sperm, the centrosome consists of two centrioles ...(proximal and distal centriole) and a pericentriolar material known as the striated column and capitulum. The distal centriole nucleates the flagellum. Mice spermatozoa, unlike other mammal spermatozoa (e.g., human and bovine), have no ultra-structurally recognizable centrioles, but their neck has the centriolar proteins POC1B and FAM161A, suggesting mice spermatozoa have remnant centrioles. Here, we examine whether other centriolar proteins, CP110 and CEP135, found in the human and bovine spermatozoa centrioles are also found in the mouse spermatozoa neck. CP110 is a tip protein controlling ciliogenesis, and CEP135 is a centriole-specific structural protein in the centriole base of canonical centrioles found in most cell types. Here, we report that CP110 and CEP135 were both located in the mice spermatozoa neck around the proximal centriolar remnants labeled by POC1B, increasing the number of centriolar proteins found in the mice spermatozoa neck, further supporting the hypothesis that a remnant proximal centriole is present in mice.
We use NASA's Van Allen Probes data to build a 3‐dimensional Radiation Belt Daily Average Electron flux model (RB‐Daily‐E) covering 25 differential energies (33–7,700 keV), 17 pitch angles, and a ...variable number of L shells from 2 to 7. RB‐Daily‐E can be used to deduce the fluences observed by any satellite that flew within Van Allen Probes' 7‐year mission lifetime. We supplement Van Allen Probes fluxes with THEMIS average fluxes to cover higher L shells when applying the model to a secondary satellite. RB‐Daily‐E agrees with both the Arase high‐energy electron experiment (XEP) flux data and the GPS Combined X‐ray Dosimeter (CXD) electron flux approximately within a factor of two or better, and comparisons with AE9 are as expected. The RB‐Daily‐E Model has applications for when actual fluxes on day‐timescales are required for post‐anomaly investigations, including long‐term radiation environment effects such as solar cell and solar array degradation. We therefore applied the model to two GPS satellites to determine electron fluence inputs to the Equivalent Flux (EQFLUX) solar cell degradation model. The modeled voltage degradation well‐matched the voltage degradation trends identified in the GPS telemetry data, suggesting that the radiation environment is the primary cause of the voltage degradation. The current degradation was largely underestimated, suggesting that current degradation is influenced by other sources.
Plain Language Summary
Most industry‐standard data‐informed radiation environment models rely on statistics, which may not accurately describe the environment on a specific day. These models are used to characterize the radiation environment to determine expected degradation rates of solar array voltages and currents in space, which is important for satellite power and lifetime. A well‐known conundrum is that the expected degradation underestimates the actual degradation, raising questions about whether the radiation environment is correctly modeled or if there are other contributing factors not correctly included in degradation predictions. This paper describes a new model that estimates the electron radiation for a given day in any given orbit using data from NASA's Van Allen Probes and THEMIS missions. Comparisons to spacecraft data demonstrate the model's robustness. The new model and standard radiation models were both applied to estimate the solar array voltage and current degradation on multiple GPS satellites and compared to actual degradation. The results of the 3‐way comparison showed that the new model produces superior solar array voltage degradation estimates, demonstrating that radiation is practically the sole source of voltage degradation, and provides conclusive evidence that factors in addition to radiation need to be accounted for when estimating the solar array current.
Key Points
The Radiation Belt Daily Average Electron flux model (RB‐Daily‐E) built on Van Allen Probes and THEMIS data is consistent with GPS CXD and Arase data
RB‐Daily‐E applied to GPS orbit determined that the radiation environment is the prime contributor to GPS solar array voltage degradation
RB‐Daily‐E applied to GPS orbit determined that the radiation environment is a minor contributor to GPS solar array current degradation
Abstract
Strong shocks in collisionless plasmas, such as supernovae shocks and shocks driven by coronal mass ejections, are known to be a primary source of energetic particles. Due to their different ...mass per charge ratio, the interaction of heavy ions with the shock layer differs from that of protons, and injection of these ions into acceleration processes is a challenge. Here we show the first direct observational evidence of magnetic reflection of alpha particles from a high Mach number quasi-perpendicular shock using in situ spacecraft measurements. The intense magnetic amplification at the shock front associated with nonstationarity modulates the trajectory of alpha particles, some of which travel back upstream as they gyrate in the enhanced magnetic field and experience further acceleration in the upstream region. Our results in particular highlight the important role of high magnetic amplification in seeding heavy ions into the energization processes at nonstationary reforming shocks.
Substorms generally inject tens to hundreds of keV electrons, but intense substorm electric fields have been shown to inject MeV electrons as well. An intriguing question is whether such MeVelectron ...injections can populate the outer radiation belt. Here we present observations of a substorm injection of MeV electrons into the inner magnetosphere. In the premidnight sector at L ∼ 5.5, Van Allen Probes (Radiation Belt Storm Probes)‐A observed a large dipolarization electric field (50 mV/m) over ∼40 s and a dispersionless injection of electrons up to ∼3 MeV. Pitch angle observations indicated betatron acceleration of MeV electrons at the dipolarization front. Corresponding signals of MeV electron injection were observed at LANL‐GEO, THEMIS‐D, and GOES at geosynchronous altitude. Through a series of dipolarizations, the injections increased the MeV electron phase space density by 1 order of magnitude in less than 3 h in the outer radiation belt (L > 4.8). Our observations provide evidence that deep injections can supply significant MeV electrons.
Key Points
Unambiguous evidence of deep injections of MeV electrons from multispacecraft
Extremely large electric fields (50 mV/m) associated with the dipolarization
Strong dipolarizations may supply significant MeV electrons to radiation belts
The discovery of long-lived electrostatic coherent structures with large-amplitude electric fields ( mV/m) by the Van Allen Probes has revealed alternative routes through which planetary radiation ...belts' acceleration can take place. Following previous reports showing that small phase-space holes, with , could result from electron interaction with large-amplitude whistlers, we demonstrate one possible mechanism through which holes can grow nonlinearly (i.e., ) and subcritically as a result of momentum exchange between hot and cold electron populations. Our results provide an explanation for the common occurrence and fast growth of large-amplitude electron phase-space holes in the Earth's radiation belts.
PDF
