Electron Energy Flux Research Articles

Estimation of carbon dust particle lifetime in a radio-frequency thermal plasma

A carbon dust particle in a collisionless thermal plasma is studied under the assumption of the drifting Maxwellian distribution with a time varying velocity caused by the oscillatory radio-frequency (RF) field. The dust particle potential decreases while its fluctuation increases with the increasing RF field strength or the decreasing frequency even taken into account the thermionic current. As the thermionic current is increased by changing the dust particle surface temperature, the resultant increasing dust particle potential can vary from negative to positive, and the fluctuation of the dust particle potential increases first and then decreases. When the dust particle heating and mass loss processes are considered, it is found that the fluctuation of the total energy flux to the dust particle is mainly determined by the electron energy flux, which causes the stair-like increase of the dust particle surface temperature in heating process and the stair-like decrease of the dust particle radius in the mass loss process. With the increasing RF field strength or decreasing frequency, the increase of the total energy flux to the dust particle leads to the decrease of the dust particle lifetime. The results mean that the presence of the RF field can shorten the dust particle lifetime or reduce the dust particle survivability in RF plasma, by compared with in the absence of the RF field.

Solar Flare Ribbon Fronts. I. Constraining Flare Energy Deposition with IRIS Spectroscopy

Spectral lines formed at lower atmospheric layers show peculiar profiles at the “leading edge” of ribbons during solar flares. In particular, increased absorption of the BBSO/GST He i λ10830 line, as well as broad and centrally reversed profiles in the spectra of the Mg ii and C ii lines observed by the IRIS satellite, has been reported. In this work, we aim to understand the physical origin of such peculiar IRIS profiles, which seem to be common of many, if not all, flares. To achieve this, we quantify the spectral properties of the IRIS Mg ii profiles at the ribbon leading edge during four large flares and perform a detailed comparison with a grid of radiative hydrodynamic models using the RADYN+FP code. We also studied their transition region (TR) counterparts, finding that these ribbon front locations are regions where TR emission and chromospheric evaporation are considerably weaker compared to other parts of the ribbons. Based on our comparison between the IRIS observations and modeling, our interpretation is that there are different heating regimes at play in the leading edge and the main bright part of the ribbons. More specifically, we suggest that bombardment of the chromosphere by more gradual and modest nonthermal electron energy fluxes can qualitatively explain the IRIS observations at the ribbon leading front, while stronger and more impulsive energy fluxes are required to drive chromospheric evaporation and more intense TR emission in the bright ribbon. Our results provide a possible physical origin for the peculiar behavior of the IRIS chromospheric lines in the ribbon leading edge and new constraints for the flare models.

Thermal Electron Heat Fluxes Associated With Precipitated Auroral Electrons During the Saint Patrick's Days 2013 and 2015 Geomagnetic Storms

AbstractThe Rice Convection Model‐Equilibrium (RCM‐E) and SuperThermal Electron Transport (STET) are combined to investigate electron heat flux formation in the region of the diffuse aurora for the geomagnetic storms of 17 March 2013 and 17 March 2015. The primary electron precipitation into the atmosphere resulting from wave particle scattering in the magnetosphere are simulated by the magnetically and electrically RCM‐E during these two geomagnetic storms. The primary precipitating electron fluxes are modified by the STET model by taking into account atmospheric backscatter processes. The modified electron energy fluxes and their mean energies are coupled to the STET code to calculate electron thermal fluxes associated with diffuse aurora on a global scale. We use the simulated heat flux to estimate electron temperatures at the upper ionospheric altitudes and compare them with corresponding observations from the Defense Meteorological Satellite Program satellite.

Exogenous Calcium Improves Photosynthetic Capacity of Pinus sylvestris var. mongolica under Drought

Calcium (Ca), a secondary messenger, plays an essential role in improving drought resistance. We used the Fast Chlorophyll Fluorescence Induction Dynamics technique to investigate the effects of exogenous calcium on electron transport and energy fluxes in an 8-year-old Mongolian pine to investigate the mechanism of action of Ca in regulating drought adaptation in Pinus sylvestris var. mongolica. We found water stress significantly decreased Pn and Gs, but exogenous calcium significantly improved photosynthesis under water stress. The chlorophyll a fluorescence transient (OJIP) analysis revealed that water stress increased Fo and decreased Fm, inactivating reaction centers. Water stress reduced VI and VJ while increasing Mo, destroying the electron transport chain. Exogenous calcium increased Sm while decreasing VI and Mo under water stress, enhancing electron transport from QA to QB. Furthermore, 5 mM Ca2+ increased I-P phase and ψPo, δRo, and φRo, decreasing the drought-induced reduction in electron accepters of PSⅠ. The increase in ABS/RC, TRo/RC, ETo/RC, and DIo/RC caused by 5 mM Ca2+ demonstrated that calcium can regulate photoprotection to promote photosynthetic activity. Thus, exogenous calcium alleviated drought-induced reductions in photosynthetic activity by regulating photoprotection and boosting the electron transport efficiency at the acceptor side of PSⅡ and PSⅠ.

Alternating North‐South Brightness Ratio of Ganymede's Auroral Ovals: Hubble Space Telescope Observations Around the Juno PJ34 Flyby

AbstractWe report results of Hubble Space Telescope observations from Ganymede's orbitally trailing side which were taken around the flyby of the Juno spacecraft on 7 June 2021. We find that Ganymede's northern and southern auroral ovals alternate in brightness such that the oval facing Jupiter's magnetospheric plasma sheet is brighter than the other one. This suggests that the generator that powers Ganymede's aurora is the momentum of the Jovian plasma sheet north and south of Ganymede's magnetosphere. Magnetic coupling of Ganymede to the plasma sheet above and below the moon causes asymmetric magnetic stresses and electromagnetic energy fluxes ultimately powering the auroral acceleration process. No clear statistically significant timevariability of the auroral emission on short time scales of 100s could be resolved. We show that electron energy fluxes of several tens of mW m−2 are required for its OI 1,356 Å emission making Ganymede a very poor auroral emitter.

Multi‐Scale Geomagnetic Forcing Derived From High‐Resolution Observations and Their Impacts on the Upper Atmosphere

AbstractTechniques developed in the past few years enable the derivation of high‐resolution regional ion convection and particle precipitation patterns from the Super Dual Auroral Radar Network (SuperDARN) and Time History of Events and Macroscale Interactions during Substorms All‐Sky Imager (ASI) observations, respectively. For the first time in this study, a global ionosphere‐thermosphere model (GITM) is driven by such high‐resolution patterns to simulate the I‐T response to the multi‐scale geomagnetic forcing during a real event. Specifically, GITM simulations have been conducted for the 26 March 2014 event with different ways to specify the high‐latitude forcing, including empirical models, high‐resolution SuperDARN convection patterns, and high‐resolution ASI particle precipitation maps. Multi‐scale ion convection forcing estimated from high‐resolution SuperDARN observations is found to have a very strong meso‐scale component. Multi‐scale convection forcing increases the regional Joule heating (integrated over the high‐resolution SuperDARN observation domain) by ∼30% on average, which is mostly contributed by the meso‐scale component. Meso‐scale electron precipitation derived from ASI measurements contributes on average about 30% to the total electron energy flux, and its impact on the I‐T system is comparable to the meso‐scale convection forcing estimated from SuperDARN observations. Both meso‐scale convection and precipitation forcing are found to enhance ionospheric and thermospheric disturbances with prominent structures and magnitudes of a few tens of meters per second in the horizontal neutral winds at 270 km and a few percent in the neutral density at 400 km through comparisons between simulations driven by the original and smoothed high‐resolution forcing patterns.

Operational inner magnetosphere particle transport and acceleration model (IMPTAM) for 1–300 keV electrons

Surface charging, the process of charge deposition on covering insulating surfaces of satellites is directly linked to the space environment at a time scale of a few tens of seconds. Accurate specification of the space environment at different orbits is of key importance. We introduce the model operating online in near-real time for low energy (< 200 keV) electrons in the inner magnetosphere, called Inner Magnetosphere Particle Transport and Acceleration model (IMPTAM). This model in its various versions has been operating online since March 2013 (latest version at imptam.engin.umich.edu) and it is driven by the real time solar wind (solar wind number density, dynamic pressure and velocity) and Interplanetary Magnetic Field (IMF), Y and Z components and total magnitude, parameters and by the real time Dst and Kp indices. The model provides the low energy electron (and proton) flux at all Magnetic Local Times (MLTs) and at L-shells from 3 to 10 and at all satellite orbits inside the modeling region, when necessary. IMPTAM output can serve as an input to assess surface charging levels of spacecraft immersed in severe environments and inside radiation belts models as distributions of electron seed population for further acceleration to MeV energies.

A 2D Kaleidoscope of Electron Heat Fluxes Driven by Auroral Electron Precipitation

AbstractElectron heat flux is an important value for ionospheric space weather modeling networks. Utilizing the 2D array of Time History of Events and Macroscale Interactions during Substorms all‐sky‐imager (ASI) observations, Gabrielse et al. (2021, https://doi.org/10.3389/fphy.2021.744298) described a new method that estimates the auroral scale sizes of intense precipitating electron energy fluxes and their mean energies during two substorms on 16 February 2010. These parameters in combination with SuperThermal Electron Transport code were used to develop a new methodology to calculate electron thermal fluxes from data inputs in 2D during one of the substorms at 09:40:00 UT across Canada and Alaska. To test the effect of various precipitation lifetimes on electron heat flux values, boxcar averages ranging from 0 to 900 s were applied to the ASI data. These data are then combined with the newly developed kinetic simulation to determine the thermal fluxes associated with the observed diffuse and discrete precipitation.

Modeling the Dynamic Variability of Sub‐Relativistic Outer Radiation Belt Electron Fluxes Using Machine Learning

AbstractWe present a set of neural network models that reproduce the dynamics of electron fluxes in the range of 50 keV ∼1 MeV in the outer radiation belt. The Outer Radiation belt Electron Neural net model for Medium energy electrons uses only solar wind conditions and geomagnetic indices as input. The models are trained on electron flux data from the Magnetic Electron Ion Spectrometer instrument onboard Van Allen Probes, and they can reproduce the dynamic variations of electron fluxes in different energy channels. The model results show high coefficient of determination (R2 ∼ 0.78–0.92) on the test data set, an out‐of‐sample 30‐day period from 25 February to 25 March in 2017, when a geomagnetic storm took place, as well as an out‐of‐sample one year period after March 2018. In addition, the models are able to capture electron dynamics such as intensifications, decays, dropouts, and the Magnetic Local Time dependence of the lower energy (∼&lt;100 keV) electron fluxes during storms. The models have reliable prediction capability and can be used for a wide range of space weather applications. The general framework of building our model is not limited to radiation belt fluxes and could be used to build machine learning models for a variety of other plasma parameters in the Earth's magnetosphere.

Magnetized fluid electron model within a two-dimensional hybrid simulation code for electrodeless plasma thrusters

An axisymmetric fluid model for weakly-collisional, magnetized electrons is introduced and coupled to a particle-in-cell model for heavy species to simulate electrodeless plasma thrusters. The numerical treatment of the model is based on a semi-implicit time scheme, and specific algorithms for solving on a magnetic field aligned mesh. Simulation results of the plasma transport are obtained for a virtual electrodeless thruster. The particle and energy fluxes of electrons are discussed. A first phenomenological model is included for the anomalous cross-field electron transport, and a second one for the anomalous parallel-field electron cooling in the plume. The balances of the plasma properties reveal that wall losses are the crucial reason for the poor thrust efficiency of these thrusters. The magnetic thrust inside the source could be negative and largely depending on the location of the magnetic throat, which is found uncoupled from the location of the plasma beam sonic surface. Furthermore, a sensitivity analysis of the results against the simulated plume extension shows that finite plumes imply an incomplete electron expansion, which leads to underestimating the performances.

Characterization of Jason-3 Spacecraft Surface Charging in LEO Polar Regions From AMBER Observations

We have characterized spacecraft charging events in low Earth orbit (LEO) polar regions with the Active Monitor Box of Electrostatic Risk (AMBER) instrument onboard the Joint Altimetry Satellite Oceanography Network—3 (Jason-3) ocean topography mission for the first time for this spacecraft. AMBER data, taken at an altitude of 1336 km, over the period January 2017–March 2020, with measurements recorded close to the current solar minimum have been analyzed, using systematic filtering of ions spectrograms with selected threshold energies and time windows to detect negative spacecraft charging events; 109 spacecraft charging events were found. The events are examined visually and characterized by their spatial and temporal location, duration, and intensity (e.g., spacecraft potential). At the Jason-3 altitude (1336 km), the ion signature predominately lasts under 30 s in conjunction with auroral inverted V crossings, while intense fluxes of electrons corresponding to the encounter of the discrete auroral region last between 30 s and 1 min. Most of the detected spacecraft charging events show charging levels between −30 and −1000 V. The spacecraft charging events are located in the magnetic local time (MLT) sector 17h–05h, predominately before midnight. The distribution is equal between the northern and southern hemispheres. We found a high correlation between the charging time profile and that of the auroral electron average energy and energy flux along the satellite path. Overall statistics over three years as well as different event morphologies, electron spectra, and comparisons to worst case electron flux spectral distributions are presented and discussed.

Assimilative Mapping of Auroral Electron Energy Flux Using SSUSI Lyman‐Birge‐Hopfield (LBH) Emissions

AbstractFar ultraviolet (FUV) imaging of the aurora from space provides great insight into the dynamic coupling of the atmosphere, ionosphere, and magnetosphere on global scales. To gain a quantitative understanding of these coupling processes, the global distribution of auroral energy flux is required, but the inversion of FUV emission to derive precipitating auroral particles' energy flux is not straightforward. Furthermore, the spatial coverage of FUV imaging from Low Earth Orbit (LEO) altitudes is often insufficient to achieve global mapping of this important parameter. This study seeks to fill these gaps left by the current geospace observing system using a combination of data assimilation and machine learning techniques. Specifically, this paper presents a new data‐driven modeling approach to create instantaneous, global assimilative mappings of auroral electron total energy flux from Lyman‐Birge‐Hopfield (LBH) emission data from the Defense Meteorological System Program (DMSP) Special Sensor Ultraviolet Spectrographic Imager (SSUSI). We take a two‐step approach; the creation of assimilative maps of LBH emission using optimal interpolation, followed by the conversion to energy flux using a neural network model trained with conjunction observations of in‐situ auroral particles and LBH emission from the DMSP Special Sensor J and SSUSI instruments. The paper demonstrates the feasibility of this approach with a model prototype built with DMSP data from 17 February 2014 to 23 February 2014. This study serves as a blueprint for a future comprehensive data‐driven model of auroral energy flux that is complementary to traditional inversion techniques to take advantage of FUV imaging from LEO platforms for global assimilative mapping of auroral energy flux.

Modeling the dynamic variability of sub-relativistic outer radiation belt electron fluxes using machine learning

We present a set of neural network models that reproduce the dynamics of electron fluxes in the range of 50 keV $\sim$ 1 MeV in the outer radiation belt. The models take satellite position, a time-history of geomagnetic indices, and solar wind conditions in different length time windows as inputs. The models are then trained on electron flux data from the Magnetic Electron Ion Spectrometer (MagEIS) instrument onboard Van Allen Probes, and they can reproduce the dynamic variations of electron fluxes in different energy channels. The model results show high coefficient of determination (R-squared $\sim$ 0.78-0.92) on the test dataset, an out-of-sample 30-day period from February 25 to March 25 in 2017, when a geomagnetic storm took place, as well as an out-of-sample one-year period after March 2018. In addition, the models are able to capture electron dynamics such as intensifications, decays, dropouts, and the Magnetic Local Time (MLT) dependence of the lower energy ($\sim <$ 100 keV )electron fluxes during storms. The models have reliable prediction capability and can be used for a wide range of space weather applications. The general framework of building our model is not limited to radiation belt fluxes and could be used to build machine learning models for a variety of other plasma parameters in the Earth's magnetosphere.

Enhancing the sensitivity of water toxicity detection based on suspended Shewanella oneidensis MR-1 by reversing extracellular electron transfer direction.

Water toxicity detection is of great significance to ensure the safety of water supply. With suspended electrochemically active bacteria (EAB) as the sensing element, a novel microbial electrochemical sensor (MES) has recently been reported for the real-time detection of water toxicity, but its practical applications need to further improve the sensitivity. Extracellular electron transfer (EET) is an important factor affecting MES performance. In the study, the EET of suspended EAB-based MES was optimized to further enhance the sensitivity. Firstly, by using a model EAB stain Shewanella oneidensis MR-1, it was revealed that the sensitivity was increased at most 2.7 times with inward EET (i.e., cathodic polarization). Then, a novel conjecture based on electron transfer and energy fluxes was proposed and testified to explain this phenomenon. Finally, three key operating parameters of inward EET were orthogonally optimized. The optimized parameters of inward EET included a potential of - 0.5V, a cell density of 1.8 × 108CFU/mL, and an electron acceptor concentration of 15mM.

Observations of kinetic Alfvén waves and associated electron acceleration in the plasma sheet boundary layer

Kinetic Alfvén waves (KAWs), with a strong parallel disturbed electric field, play an important role in the energy transport and particle acceleration in the magnetotail. Based on the high-resolution observations of the Magnetospheric Multiscale (MMS) mission, we present the detailed acceleration process of electrons by KAWs in the plasma sheet boundary layer (PSBL). MMS observed strong electromagnetic disturbances carrying parallel disturbed electric field with an amplitude up to 8 mV/m. The measured ratio of the electric to magnetic field perturbations is larger than the local Alfvén speed and enhances as the frequency increases, in consistent with the theoretical predictions for KAWs. These evidences indicate that the electromagnetic disturbances should be identified as KAWs. During the KAWs, the energy flux of electrons at energies above 1 keV in the parallel and anti-parallel direction significantly enhance, implying occurrences of electron beams at higher energies. Meanwhile, the KAWs become more electrostatic-like and filled with high frequency ion acoustic waves. The energy enhancement of electron beams accords to the derived work done by the observed parallel disturbed electric field of KAWs, indicating electron acceleration caused by KAWs. Therefore, the paper provides a direct evidence of electron acceleration by KAWs embodying electrostatic ion acoustic waves in the PSBL.

Relation of Jupiter's Dawnside Main Emission Intensity to Magnetospheric Currents During the Juno Mission

AbstractWe compare Jupiter's dawn‐side main auroral emission intensity observed by the Hubble Space Telescope with the simultaneous magnitude of the dawn‐side magnetospheric equatorial radial current as observed by Juno during Orbits 3–7. We show that the peak auroral intensity and the square of the radial current per radian of azimuth are strongly correlated with R ≈ 0.9, and that the chance that the two phenomena are unrelated is negligible. We also fit empirical profiles of the total radial current flowing per radian of azimuth to the observed values and estimate the precipitating electron energy flux during each observation, and show this exhibits a similar correlation to the current. We find 1 mW m−2 of precipitating energy flux is associated with ∼5–11 kR of auroral emission, consistent with modeling studies. This is the first demonstration of a statistical relationship between the intensity of Jupiter's auroras and the strength of the magnetospheric currents, specifically the radial current, the j × B force of which accelerates plasma in the sense of planetary rotation. This result provides compelling evidence that the magnetosphere‐ionosphere coupling current system at Jupiter plays a key role in powering the planet's dawn side main auroral emission. We further show that there is no association between the auroral intensity and the rate of change of the magnetic energy density outside the current sheet.

Validation of SSUSI-derived auroral electron densities: comparisons to EISCAT data

Abstract. The coupling of the atmosphere to the space environment has become recognized as an important driver of atmospheric chemistry and dynamics. In order to quantify the effects of particle precipitation on the atmosphere, reliable global energy inputs on spatial scales commensurate with particle precipitation variations are required. To that end, we have validated auroral electron densities derived from the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) data products for average electron energy and electron energy flux by comparing them to EISCAT (European Incoherent Scatter Scientific Association) electron density profiles. This comparison shows that SSUSI far-ultraviolet (FUV) observations can be used to provide ionization rate and electron density profiles throughout the auroral region. The SSUSI on board the Defense Meteorological Satellite Program (DMSP) Block 5D3 satellites provide nearly hourly, 3000 km wide high-resolution (10 km×10 km) UV snapshots of auroral emissions. These UV data have been converted to average energies and energy fluxes of precipitating electrons. Here we use those SSUSI-derived energies and fluxes as input to standard parametrizations in order to obtain ionization-rate and electron-density profiles in the E region (90–150 km). These profiles are then compared to EISCAT ground-based electron density measurements. We compare the data from two satellites, DMSP F17 and F18, to the Tromsø UHF radar profiles. We find that differentiating between the magnetic local time (MLT) “morning” (03:00–11:00 MLT) and “evening” (15:00–23:00 MLT) provides the best fit to the ground-based data. The data agree well in the MLT morning sector using a Maxwellian electron spectrum, while in the evening sector using a Gaussian spectrum and accounting for backscattered electrons achieved optimum agreement with EISCAT. Depending on the satellite and MLT period, the median of the differences varies between 0 % and 20 % above 105 km (F17) and ±15 % above 100 km (F18). Because of the large density gradient below those altitudes, the relative differences get larger, albeit without a substantially increasing absolute difference, with virtually no statistically significant differences at the 1σ level.

Shape evolution and growth mechanisms of 3D-printed nanowires

3D printing of nanowires using Focused Electron Beam Induced Deposition (FEBID) enables the direct-write fabrication of complex 3D objects on almost any substrate surface. The physical properties of such freestanding structures are determined by the dimensions of constituent nanowires. However, little knowledge is available about the exact shape of the nanowires, which is indispensable for calculations and simulations as well as for optimization in applications. In this study, we evaluate the thicknesses and widths of freestanding segments as a function of the inclination angles, primary electron energy, beam currents, and precursor flux. Furthermore, the cross-sectional shape, the cross-sectional area, and the evolution along the length of the wire are investigated. Basing on detailed scanning electron microscopy measurements and Monte Carlo/Finite Differences simulations, the effects that the growth parameters have on the segment growth are elucidated. The results shed light on the growth evolution of the structures and form the basis for future studies on the fabrication of high-precision, arbitrarily shaped nanowires.

Verification of a quasi-linear model for gyrokinetic turbulent transport

The verification and calibration of a new quasi-linear transport model with a large database of gyrokinetic turbulence simulations is presented in this paper. In a previous paper (Staebler et al 2020 Plasma Phys. Control. Fusion 63 015013), a model for the saturated spectrum of electric potential fluctuations was developed based on the properties of the non-linear 3D spectrum. In this paper, a modification to the overall multiplicative factor in this model is found to be necessary to improve the fit to scans of the temperature and density gradients. The error in the fit of the quasi-linear fluxes of electron and ion energy fluxes is significantly better than for previous saturation models. The spectral shift model for the impact of equilibrium E × B velocity shear (Staebler et al 2013 Phys. Rev. Lett. 110 055003) and the zonal flow mixing model for electron-scale turbulence (Staebler et al 2016 Phys. Plasmas 23 062518) are both revised to be compatible with this new model. The models for the loss of bounce averaging and electron collisions in the TGLF reduced linear equations (Staebler et al 2005 Phys. Plasmas 12 102508) are also changed to improve the linear eigenmodes.

Estimation of electron fluxes in the Earth's geostationary orbit with Tikhonov regularization during a magnetically quiet period

Electron energy fluxes in the Earth's outer radiation belt are estimated using an inverse theory of the Tikhonov regularization based upon observations in geostationary orbits. Particle Detector (PD) experiment aboard a geostationary satellite GEO-KOMPSAT-2A (GK2A) at a geographic longitude of 128.2°E provided observations of electrons within a 150–2,400 keV energy range with an unprecedented energy resolution of ΔE/E in the range of 5–25%. Instrument response functions, calculated with Monte-Carlo simulations, are deconvoluted with electron observations. Using regularization parameters determined from Generalized Cross Validation (GCV), the Tikhonov method was applied to observations made during a geomagnetically quiet period. This Tikhonov regularization method, now possible for observations in the Earth's radiation belt for the first time, allows direct inference of electron fluxes without resorting to predetermined functional forms. Comparisons of our results with those from conventional methods indicate differences among the results as large as ∼200%.