Electron Energy Flux Research Articles

Auroral Precipitation Model and its applications to ionospheric and magnetospheric studies

Based on statistical treatment of DMSP F6 and F7 spacecraft observations, an interactive Auroral Precipitation Model (APM) parameterized by magnetic activity has been created (available at http://apm.pgia.ru/). For a given level of magnetic activity the model yields a global distribution of electron precipitation and planetary patterns of both average electron energy and electron energy flux in different precipitation zones. Outputs of the model were used to determine the basic variables of the magnetosphere, such as boundary location and the area of the polar cap, magnetic flux transferred from the dayside magnetosphere into the tail, global precipitation power realized by different types of precipitation and others. The model predicts an increase in the polar cap area from about 6.3×106km2 to 2.0×107km2, in the magnetic flux from 390MWb to 1200MWb, and in the global precipitation power from 3.4GW to 188.0GW, when the magnetic activity changes from silence (null AL and Dst) to significant disturbance (AL=−1000nT, Dst=−200nT). The use of dayside auroral observations as an input for APM provides an opportunity for continuous monitoring of magnetospheric conditions. Two time intervals on Dec. 27, 2000, and Dec. 12, 2004, of dayside auroral observations with the meridian scanning photometer at Barentsburg (Spitsbergen) were selected to demonstrate derivation of magnetospheric variables with APM. It is shown that the values of the AL index derived from optical observation appear in a reasonable agreement with those published by WDC.

Hybrid pyroelectric/nanotube LiNbO3/TiO2 X-ray source

LiNbO3/TiO2 pyroelectric/nanotube system was fabricated by bonding electrochemically grown TiO2 nanotubes on −z face of pyroelectric LiNbO3 crystal and X-ray emission properties of such system were studied. The hybrid LiNbO3/TiO2 system had both higher electron energy and output X-ray flux compared to LiNbO3 without nanotubes. The endpoint energy increased from 38–45 keV to 55–74 keV, and the maximum X-ray flux increased by a factor of 3.6. The improved output energy and flux are thought to be due to the electric field amplification of nanotube tips increasing the efficiency of ionization of residual gas.

The analysis of electron fluxes at geosynchronous orbit employing a NARMAX approach

The methodology based on the Error Reduction Ratio (ERR) determines the causal relationship between the input and output for a wide class of nonlinear systems. In the present study, ERR is used to identify the most important solar wind parameters, which control the fluxes of energetic electrons at geosynchronous orbit. The results show that for lower energies, the fluxes are indeed controlled by the solar wind velocity, as was assumed before. For the lowest energy range studied here (24.1 keV), the solar wind velocity of the current day is the most important control parameter for the current day's electron flux. As the energy increases, the solar wind velocity of the previous day becomes the most important factor. For the higher energy electrons (around 1 MeV), the solar wind velocity registered 2 days in the past is the most important controlling parameter. Such a dependence can, perhaps, be explained by either local acceleration processes due to the interaction with plasma waves or by radial diffusion if lower energy electrons possess higher mobility. However, in the case of even higher energies (2.0 MeV), the solar wind density replaces the velocity as the key control parameter. Such a dependence could be a result of solar wind density influence on the dynamics of various waves and pulsations that affect acceleration and loss of relativistic electrons. The study also shows that statistically the variations of daily high energy electron fluxes show little dependence on the daily averaged Bz, daily time duration of the southward IMF, and daily integral (where Bs is the southward component of IMF).

Auroral particle precipitation characterized by the substorm cycle

Substorms release a large amount of energy, some of which is used to energize the precipitating particles in the polar region. Superposed epoch analysis was performed with 11 years of DMSP SSJ/4/5 data to characterize the substorm cycle of the diffuse, monoenergetic, and broadband/wave precipitating electrons and precipitating ions. Although substorms only increase the ion pressure by 30%, they increase the power of the diffuse, monoenergetic, and wave electron aurora by 310%, 71%, and 170%, respectively. Substorms energize the ion aurora mainly in the 21:00–05:00 magnetic local time (MLT) sector. The dynamics of the diffuse electron aurora are different from those of the other two electron aurorae. The expansion phase duration is approximately 15 min for the monoenergetic and wave electron aurorae, whereas it is 1 h for the diffuse electron aurora. The monoenergetic and wave electron aurorae appear to complete the substorm cycle within a 5 h interval, whereas the diffuse electron aurora takes more than 5 h. The diffuse electron aurora power and energy flux start increasing at 15 min before the substorm onset, whereas those for the monoenergetic and wave electron aurorae start increasing at 1 h and 15 min before the onset. The increase in the monoenergetic electron aurora power and energy flux may result from the increase in the magnetotail stretching and region‐1 field‐aligned current during the growth phase. The monoenergetic electrons may also be associated with fast flows, which have been previously observed more frequently in the dusk‐midnight sector.

Empirical relationship between electron precipitation and far‐ultraviolet auroral emissions from DMSP observations

AbstractAuroral emissions observed in the far‐ultraviolet wavelength range are compared with measurements of the coincident precipitating electrons and ions that produce the emissions in a large‐scale correlative study. The auroral emissions and particle precipitation are observed with the Special Sensor Ultraviolet Spectrographic Imager and SSJ5 detectors, respectively, both onboard the DMSP F16 satellite. Coincident observations along the same magnetic field line in the Northern Hemisphere are assembled from two consecutive winters (during 2005–2007). A numerical fit to 27,922 coincident observations provides an empirical relationship between the electron energy flux and the intensity of Lyman‐Birge‐Hopfield long emissions, JEe = 4.90 ⋅108 (eV s–1 sr–1 cm–2)/R ILBHL (valid in the absence of significant ion fluxes: JEe > 10 JEion). A fit to 1308 coincident observations provides the relationship between the average electron energy and the Lyman‐Birge‐Hopfield short to Lyman‐Birge‐Hopfield long emission ratio, <Ee > = 19.6 keV exp(–2.34 ILBHS / ILBHL) (valid from 3 to 19.6 keV). These resulting empirical relationships permit the energy flux and average energy of precipitating electrons to be inferred from far‐ultraviolet imagery, in the absence of significant ion precipitation.

Collisional effects on the generation of fast electrons in fast ignition scheme

The effects of collision on the generation and transportation of fast electrons produced by ultra-intense laser pulse in overdense plasma for densities ranging from below to 400 times critical density are investigated by collisional particle-in-cell code. It is found that a relatively stable state of fast electron energy flux exists in the simulations, where collision contributes to increasing the production of fast electrons. The unexpected increase of production is attributed to the efficient local heating of the thermal electrons, which results in higher thermal pressure and less steepened interface. Therefore, fast electrons can be effectively accelerated through 2ω oscillation from J×B force in the collisional case, while it is suppressed in the collisionless case because of the highly steepened plasma density. The collisional effects on the transportation of fast electrons in the solid target are also discussed.

Relationship between severe geomagnetic storm, energetic particle storms and thermosphere density strong disturbances

利用1997-2007年由GOES8, GOES11和GOES12星载高能粒子探测器在地球同步轨道高度上所探测到的高能质子和高能电子通量探测数据以及高度560km左右星载大气密度探测器所得的热层大气密度探测数据, 统计分析了强地磁扰动、高能粒子通量跃变和热层大气密度涨落之间的相关关系, 初步获得强地磁扰动期间, 地球同步轨道(外辐射带外环)均出现了增幅大于三个数量级的高能质子通量(尤其是<em>E</em>>1MeV)强增强现象, 随后热 层大气密度强烈上涨, 表明三者之间是正相关关系. 在时间上地球同步轨道高能质子通量强增强现象先于日均<em>Ap</em>值(地磁活动程度)上涨约一天左右, 而热层大气密度强涨落现象又明显滞后于强地磁扰动事件.

Study on high energy electron flux enhancement events and whistler chorus wave

局部加速机制是磁暴期间地球外辐射带高能电子通量增强事件发生的重要原 因. 此加速机制需要两个基本条件, 一是存在种子电子, 二是存在能与种子 电子产生共振的加速波动, 包括哨声模合声波. 通过对2004-2006年 Pi1地磁脉动持续时间与种子电子通量的相关性分析, 更明确提出Pi1地磁脉 动的持续时间可以作为种子电子通量的指示剂. 通过对三个磁暴事例地球同 步轨道的种子电子通量、高能电子通量及哨声模合声波变化情况的分析, 发 现在高能电子通量较强的事例中, 均观测到较高的种子电子通量和较强的 哨声模合声波, 这在一定程度上验证了哨声模合声波对种子电子的回旋加速 机制, 且合声波强度与高能电子通量有正的相关性.

The Capabilities and Applications of FY-3A/B SEM on Monitoring Space Weather Events

The space environment monitor (SEM), onboard the Chinese meteorological satellites FengYun-3A/B, has the abilities to measure proton flux in 3-300-MeV energy range and electron flux in 0.15-5.7-MeV energy range. SEM can also detect the heavy ion compositions, satellite surface potential, the radiation dose in sensors, and the single events. The space environment information derived from SEM can be utilized for satellite security designs, scientific studies, development of radiation belt models, and space weather monitoring and disaster warning. In this paper, the SEM's instrument characteristics are introduced, and the postlaunch calibration algorithm is presented. The applications in monitoring space weather events and the service for manned spaceflights are also demonstrated.

Effect of an MLT dependent electron loss rate on the magnetosphere‐ionosphere coupling

As plasma sheet electrons drift earthward, they get scattered into the loss cone due to wave‐particle interactions and the resulting precipitation produces auroral conductance. Realistic electron loss is thus important for modeling the magnetosphere ‐ ionosphere (M‐I) coupling and the degree of plasma sheet electron penetration into the inner magnetosphere. In order to evaluate the significance of electron loss, we used the Rice Convection Model (RCM) coupled with a force‐balanced magnetic field to simulate plasma sheet transport under different electron loss rates and under self‐consistent electric and magnetic field. We used different magnitudes of i) strong pitch angle diffusion everywhere electron loss rate (strong rate) and ii) a more realistic loss rate with its MLT dependence determined by wave activity (MLT rate). We found that electron pressure under the MLT rate is larger compared to the strong rate inside L ∼ 12 RE. The dawn‐dusk asymmetry in the precipitating electron energy flux under the MLT rate, with much higher energy flux at dawn than at dusk, agrees better with statistical DMSP observations. High‐energy electrons inside L ∼ 8 RE can remain there for many hours under the MLT rate, while those under the strong rate get lost within minutes. Under the MLT rate, the remaining electrons cause higher conductance at lower latitudes; thus after a convection enhancement, the shielding of the convection electric field is less efficient, and as a result, the ion plasma sheet penetrates further earthward into the inner magnetosphere than under the strong rate.

Structure and dynamics of the nightside poleward boundary: Sounding rocket and ground‐based observations of auroral electron precipitation in a rayed curtain

The Cascades2 auroral sounding rocket provides a case study for comparing multipoint in situ ionospheric observations of a nightside auroral poleward boundary intensification with ground‐based optical observations of the same event. Cascades2 was launched northward from Poker Flat Alaska on 20 March 2009 at 11:04 UT. The 13 min flight reached an apogee of 564 km over the northern coast of Alaska. The experiment included a five‐payload array of in situ instrumentation, ground cameras at three different points under the trajectory, multiple ground magnetometers, the Poker Flat Incoherent Scatter Radar (PFISR) radar, and the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft in the magnetotail. The rays of the poleward boundary intensification (PBI) curtain have along‐arc motions of 8.5 km/s and along‐arc spacings of 16 km. Modulated maximum energy envelopes and energy fluxes of the associated electron precipitation correspond to this spatial structure of the visible rays. The electron precipitation is additionally modulated at a higher frequency, and velocity dispersion analysis of these 8 Hz signatures implies Alfvénic wave‐particle acceleration of an ambient ionospheric electron source occurring a few hundred km above the observation point. These observations parameterize the curtain of Alfvénic activity above the PBI event, both in the dispersive ionosphere and in the magnetotail reconnection region. The along‐arc variations in brightness correspond to variations in precipitating electron energy flux interpreted as an along‐arc modulation of the maximum energy of the Alfvénic wave‐particle acceleration process; this is a new interpretation of the formation of rayed structures in auroral curtains. We consider the various possible magnetospheric and ionospheric drivers for the control of the observed along‐arc structuring and motions.

Intensification of dayside diffuse auroral precipitation: contribution of dayside Whistler-mode chorus waves in realistic magnetic fields

Abstract. Compared to the recently improved understanding of nightside diffuse aurora, the mechanism(s) responsible for dayside diffuse aurora remains poorly understood. While dayside chorus has been thought as a potential major contributor to dayside diffuse auroral precipitation, quantitative analyses of the role of chorus wave scattering have not been carefully performed. In this study we investigate a dayside diffuse auroral intensification event observed by the Chinese Arctic Yellow River Station (YRS) all-sky imagers (ASI) on 7 January 2005 and capture a substantial increase in diffuse auroral intensity at the 557.7 nm wavelength that occurred over almost the entire ASI field-of-view near 09:24 UT, i.e., ~12:24 MLT. Computation of bounce-averaged resonant scattering rates by dayside chorus emissions using realistic magnetic field models demonstrates that dayside chorus scattering can produce intense precipitation losses of plasma sheet electrons on timescales of hours (even approaching the strong diffusion limit) over a broad range of both energy and pitch angle, specifically, from ~1 keV to 50 keV with equatorial pitch angles from the loss cone to up to ~85° depending on electron energy. Subsequent estimate of loss cone filling index indicates that the loss cone can be substantially filled, due to dayside chorus driven pitch angle scattering, at a rate of ≥0.8 for electrons from ~500 eV to 50 keV that exactly covers the precipitating electrons for the excitation of green-line diffuse aurora. Estimate of electron precipitation flux at different energy levels, based on loss cone filling index profile and typical dayside electron distribution observed by THEMIS spacecraft under similar conditions, gives a total precipitation electron energy flux of the order of 0.1 erg cm−2 s−1 with ~1 keV characteristic energy (especially when using T01s), which can be very likely to cause intense green-line diffuse aurora activity on the dayside. Therefore, dayside chorus scattering in the realistic magnetic field can greatly contribute to the YRS ASI observed intensification of dayside green-line aurora. Besides wave induced scattering and changes in the ambient magnetic field, variations in associated electron flux can also contribute to enhanced diffuse aurora emissions, the possibility of which we cannot exactly rule out due to lack of simultaneous observations of magnetospheric particles. Since the geomagnetic activity level was rather low during the period of interest, it is reasonable to infer that changes in the associated electron flux in the magnetosphere should be small, and consequently its contribution to the observed enhanced diffuse auroral activity should be small as well. Our results support the scenario that dayside chorus could play a major role in the production of dayside diffuse aurora, and also demonstrate that changes in magnetospheric magnetic field should be considered to reasonably interpret observations of dayside diffuse aurora.

Study of device mass production capability of the character projection based electron beam direct writing process technology toward 14 nm node and beyond

Techniques to appropriately control the key factors for a character projection (CP) based electron beam direct writing technology for mass production are shown and discussed. In order to achieve accurate CD control, the CP technique using the master CP is adopted. Another CP technique, the Packed CP, is used to obtain suitable shot count. For the alignment on the some critical layers which normally have an even surface, the process removing SiO2 material filled in the alignment marks is added and then the alignment marks can be detected using electron beam. The proximity effect correction using the simplified electron energy flux model and the hybrid exposure are used to obtain enough process margins. As a result, the sufficient CD accuracy, overlay accuracy, and yield are obtained on the 65 nm node device. Due to the proper system control, more than 10,000 production wafers have been successfully exposed so far without any major system downtime. It is shown that those techniques can be adapted to the 32 nm node production with slight modifications. It is expected that by using the Multi Column Cell exposure method, those techniques will be applicable to the rapid establishment for the 14 nm node technology.

Estimating high-energy electron fluxes by intercalibrating Reimei optical and particle measurements using an ionospheric model

This paper describes a technique for intercalibrating particle and optical measurements from the Reimei microsatellite using an ionospheric model. Reimei has three auroral cameras (“MAC”), together with electron and ion energy spectrum analysers (“ESA/ISA”). The maximum electron energy measured is 12keV, which means that during high-energy events, the particle data are often missing an important part of the energy flux. Although the total electron energy flux can be estimated from the optical measurements, the MAC data must be accurately calibrated, which is complicated by an unknown and variable background from sources such as the moon and snow reflection. Using unsaturated ESA measurements of the complete electron spectrum as input for an ionospheric model, the coincident camera observations can be calibrated, allowing estimates to be made of the total electron energy flux at other times during the same event, when the maximum energy is well above that measured by ESA.

Characterizing the limitations to the coupling between Saturn's ionosphere and middle magnetosphere

Observations of Saturn's ultraviolet and infrared aurora show structures that, when traced along the planetary magnetic field, map to the inner, middle, and outer magnetosphere. From low to high latitudes the structures seen in the UV are the Enceladus footprint, which maps to an equatorial radius of 4 RS (Saturn radii); a diffuse emission that maps to a broad equatorial region from 4–11 RS on the nightside; and a bright ring of emission that maps to ∼15 RS. With the exception of the Enceladus spot, the magnetospheric drivers for these auroral emissions are not yet fully understood. We apply a 1D spatial, 2D velocity space Vlasov solver to flux tubes mapping from equatorial radii of 4, 6, 9, and 13 RS to Saturn's southern atmosphere. The aim is to globally characterize the field‐aligned potential structure and plasma density profiles. The ionospheric properties ‐ the field‐aligned current densities at the ionospheric boundary, energy intensity profiles and fluxes of the electrons precipitating into the ionosphere ‐ are also determined. We then couple our results to an ionospheric model to calculate the Pedersen conductances at the foot of the relevant flux tubes. We find that for a zero net potential drop between the ionosphere and magnetosphere, there exists a sharp potential drop at ∼1.5 RS along the magnetic field line as measured from the planetary center. The strength of this potential drop is approximately equal to that of the ambipolar potential resulting from the centrifugal confinement of the heavy, cold magnetospheric ion population. We also find that the ionospheric properties respond to changes in the magnetospheric plasma population, which are reflected in the nature of the precipitating electron population. For the flux tube mapping to 9 RS (−70°), the incident electron energy flux into the ionosphere resulting from a magnetospheric plasma population with a small fraction of hot electrons is an order of magnitude less than that inferred from observations, implying that significant high‐latitude field‐aligned potentials (up to 1.5 keV) may exist in the saturnian magnetosphere. Calculated ionospheric Pedersen conductances range from 3.0–18.9 mho, and are thus not expected to limit the currents flowing between the ionosphere and magnetosphere.

Exogenic controls on sulfuric acid hydrate production at the surface of Europa

External agents have heavily weathered the visible surface of Europa. Internal and external drivers competing to produce the surface we see include, but are not limited to: aqueous alteration of materials within the icy shell, initial emplacement of endogenic material by geologic activity, implantation of exogenic ions and neutrals from Jupiter's magnetosphere, alteration of surface chemistry by radiolysis and photolysis, impact gardening of upper surface layers, and redeposition of sputtered volatiles. Separating the influences of these processes is critical to understanding the surface and subsurface compositions at Europa. Recent investigations have applied cryogenic reflectance spectroscopy to Galileo Near-Infrared Mapping Spectrometer (NIMS) observations to derive abundances of surface materials including water ice, hydrated sulfuric acid, and hydrated sulfate salts. Here we compare derived sulfuric acid hydrate (H2SO4·nH2O) abundance with weathering patterns and intensities associated with charged particles from Jupiter's magnetosphere. We present models of electron energy, ion energy, and sulfur ion number flux as well as the total combined electron and ion energy flux at the surface to estimate the influence of these processes on surface concentrations, as a function of location. We found that correlations exist linking both electron energy flux (r∼0.75) and sulfur ion flux (r=0.93) with the observed abundance of sulfuric acid hydrate on Europa. Sulfuric acid hydrate production on Europa appears to be limited in some regions by a reduced availability of sulfur ions, and in others by insufficient levels of electron energy. The energy delivered by sulfur and other ions has a much less significant role. Surface deposits in regions of limited exogenic processing are likely to bear closest resemblance to oceanic composition. These results will assist future efforts to separate the relative influence of endogenic and exogenic sources in establishing the surface composition.

Testing gyrokinetic simulations of electron turbulence

An extensive set of tests comparing gyrokinetic predictions of temperature-gradient driven electron turbulence to power balance transport analyses and fluctuation measurements are presented. These tests use data from an L-mode validation study on the DIII-D tokamak (Luxon 2002 Nucl. Fusion 42 614) in which the local value of is varied by modulated electron cyclotron heating; the GYRO code (Candy and Waltz 2003 J. Comput. Phys. 186 545) is used to make the gyrokinetic predictions. Using a variety of novel measures, both local and global nonlinear simulations are shown to predict key characteristics of the electron energy flux Qe and long-wavelength (low-k) Te fluctuations, but systematically underpredict (by roughly a factor of two) the ion energy flux Qi. A new synthetic diagnostic for comparison to intermediate wavelength Doppler backscattering measurements is presented, and used to compare simulation predictions against experiment. In contrast to the agreement observed in the low-k Te fluctuation comparisons, little agreement is found between the predicted and measured intermediate-k density fluctuation responses. The results presented in this paper significantly expand upon those previously reported in DeBoo et al (2010 Phys. Plasmas 17 056105), comparing transport and multiple turbulence predictions from numerically converged local and global simulations for all four experimental heating configurations (instead of only fluxes and low-k Te fluctuations for one condition) to measurements and power balance analyses.

Use of the Auroral Boundary Index for potential forecasting of ionospheric scintillation

The Hardy‐Gussenhoven Auroral Dosing Model (HGADM) was developed to compute electron characteristic energy and energy flux values onto the global grid and is often used to generate the inputs for other phenomenological models. Forecasting auroral conditions is limited by rapid changes in the ionosphere due to variable solar conditions. However, through a statistical analysis of Auroral Boundary Index data we have developed a technique which allows us to forecast/predict the appropriate inputs to the HGADM, thereby providing a means of forecasting the characteristic energy and energy flux values. This paper will initially discuss the statistical analysis and the development of the forecast mode for the HGADM. We then discuss the possibility that aurora‐based indices along with other environmental indicators can be correlated to ionospheric disturbances.

On the influence of solar wind conditions on the outer‐electron radiation belt

The dependence of outer‐radiation belt electron fluxes upon solar wind velocity and density is investigated using the OMNI solar wind database and LANL‐GEO geosynchronous satellites for a period spanning over 20 years. Two dimensional probability distribution functions (PDF) of the flux‐solar wind velocity (Vsw) and flux‐solar wind density are calculated for electron energies in the 10's of keV to MeV range. The PDF's are normalized by Vsw and density and reveal new distinct relationships. Triangle‐shaped flux‐Vsw distributions become non‐linear PDF's, and the most probable flux increases with Vsw. The only significant saturation of fluxes observed with an increase in Vsw occurs for the lower energy electron fluxes (31.7 keV). The low energy fluxes exhibit a positive correlation with solar wind density, while mid‐to‐high energy electron fluxes are anti‐correlated with density. The maximum probability in the PDF's depends upon both velocity and density, the probability is higher for larger Vsw, and the maximum probability is larger for a given Vsw than for density. The results indicate that Vsw may be more important for determination of fluxes than density, especially for periods of high Vsw if suitable mixed delay times are applied to each solar wind parameter. It is shown that the source population of relativistic electrons of tens of keV exhibit a 2‐D normalized flux‐Vsw PDF, which is strikingly similar to that of the relativistic electrons. The findings support a model whereby solar wind velocity drives convective transport of source and seed electrons, to the inner magnetosphere, where local acceleration and subsequent radial diffusion is responsible for the enhanced fluxes. The results of this study also indicate that, statistically, ULF waves driven by dynamic pressure variations may act as a significant cause of loss for electrons in the 100's of keV to MeV range.

Fluid-model analysis of electron swarms in a space-varying field: Nonlocality and resonance phenomena

The physically based, benchmarked fluid model developed by Robson et al. [R. E. Robson, R. D. White, and Z. Lj. Petrovic, Rev. Mod. Phys. 77, 1303 (2005)] and extended to analyze electron swarms in a spatially homogeneous electric field under conditions corresponding to the Franck-Hertz experiment [P. Nicoletopoulos and R. E. Robson, Phys. Rev. Lett. 100, 124502 (2008)] is generalized to investigate the nonlocal response and resonance phenomena associated with electrons subject to an externally prescribed, spatially varying electrostatic field. Analytic expressions are first derived for the mean velocity, energy, and heat flux of electrons in a harmonically varying field, and expressions are then given for fields with more general spatial dependences. Numerical examples are given for both benchmark model cross sections and a real gas.