Precipitation Of Magnetospheric Electrons Research Articles

Impact of the transport of magnetospheric electrons on the composition of the Triton atmosphere

Due to its inclined orbit and the complex geometry of the magnetic field of Neptune, Triton experiences a highly variable magnetic environment. As precipitation of magnetospheric electrons is thought to have a large impact on the Triton atmosphere, a better understanding of the interaction between its atmosphere and the magnetosphere of Neptune is important. We aim to couple a model of the Triton atmosphere with an electron transport model to compute the impact of a varying electron precipitation on the atmospheric composition. We coupled a recent photochemical model of the Triton atmosphere with the electron transport model TRANSPlanets. The inputs of this code were determined from Voyager 2 observations and previous studies. The main inputs were the electron precipitation flux, the orbital scaling factor, and the magnetic field strength. The electron-impact ionization and electron-impact dissociation rates computed by TRANSPlanets were then used in the photochemical model. We also analyzed the model uncertainties. The coupling of the two models enabled us to find an electron density profile, as well as N$_2$ and N number densities, that are consistent with the Voyager 2 observations. We found that photoionization and electron-impact ionization are of the same order, in contrast to the results of previous photochemical models. However, we emphasize that this result depends on the hypotheses we used to determine the input variables of TRANSPlanets. Our model would greatly benefit from new measurements of the magnetic environment of Triton, as well as of the electron fluxes in the Neptune magnetosphere.

Electron Heat Fluxes Generated by Intense Whistler Waves at the Upper Ionospheric Altitudes

AbstractMagnetospheric whistler waves, chorus and hiss, can't provide the resonance heating of the core electron plasma population. However, these whistler‐mode branches, can implicitly participate in the heating processes of the core plasma thermal electron population by triggering the electron precipitation over a broad energy range from the magnetosphere and subsequent atmospheric ionization processes leading to the production of superthermal electron population. These superthermal electrons play a large role in the magnetosphere‐ionosphere‐atmosphere energy interplay with participation of both magnetically conjugate hemispheres, and their Coulomb interaction with background magnetospheric thermal electrons. Using strong hiss and chorus wave events measured by the Van Allen Probes and SuperThermal Electron Transport code, we evaluate the formation of electron heat fluxes at the upper ionospheric altitudes and discuss their consequences on the formation of electron temperature. It is found that chorus and hiss waves that initiate the precipitation of magnetospheric electrons with energies below 30 keV and the follow‐up production of secondary electrons play an important role in the energy balance of ionosphere‐magnetosphere system.

First Results of the Wave Measurements by the WHU VLF Wave Detection System at the Chinese Great Wall Station in Antarctica

AbstractA Very Low Frequency (VLF) wave detection system has been designed at Wuhan University (WHU) and recently deployed by the Polar Research Institute of China at the Chinese Great Wall station (GWS, 62.22°S, 58.96°W) in Antarctica. With a dynamic range of ∼110 dB and timing accuracy of ∼100 ns, this detection system can provide observational data with a resolution that can facilitate space physics and space weather studies. This paper presents the first results of the wave measurements by the WHU VLF wave detection system at GWS to verify the performance of the system. With the routine operation for 3 months, the system can acquire the dynamic changes of the wave amplitudes and phases of various ground‐based VLF transmitter signals emitted in both North America and Europe. A preliminary analysis indicates that the properties of the VLF transmitter signals observed at GWS during the X‐class solar flare events are consistent with previous studies. As the HWU‐GWS path crosses the South Atlantic Anomaly region, the observations also imply a good connection in space and time between the VLF wave disturbances and the lower ionosphere variation potentially caused by magnetospheric electron precipitation during the geomagnetic storm period. It is therefore well expected that the acquisition of VLF wave data at GWS, in combination with datasets from other instruments, can be beneficial for space weather studies related to the radiation belt dynamics, terrestrial lightning discharge, whistler wave propagation, and the lower ionosphere disturbance, etc., in the polar region.

Ionospheric Electron Density and Conductance Changes in the Auroral Zone During Substorms

AbstractEnhanced precipitation of magnetospheric energetic electrons during substorms increases ionospheric electron density and conductance. Such enhancements, which have timescales of a few hours, are not reproduced by the existing ionospheric models. We use the linear prediction filter (LPF) method to reconstruct the substorm‐related response of electron densities and integral conductances from long‐term ionospheric observations made by the European Incoherent SCATer radar located at Tromsø. To characterize the intensity of substorm dipolarization at a 5 min time step, we use the midlatitude positive bay index. We build response functions (LP filters) as a function of substorm time between T0−1 h and T0 + 4 h (T0 is a substorm onset time) in different magnetic local time (MLT) sectors to estimate the magnitude and delays of the ionospheric density response at different altitudes. Systematic and large relative changes are mostly observed in the D‐ and E regions. The duration of the response is about 3 h. It starts and reaches maximum magnitude near midnight, propagating from there toward the east and decaying after passing into the noon‐evening sector. The reliability of LPF results is confirmed by the consistency of D‐region response with independently derived response of the auroral absorption. Whereas strong ionization increases are seen in both E‐ and D‐regions on the nightside, the D‐region response is stronger in the morning‐dayside sector. Such MLT variation corresponds to the drift motion and precipitation of the high‐energy electrons injected in the nightside magnetosphere during substorm dipolarization. The inferred ionization changes result in strong enhancements of integral Hall (and Pedersen) conductance in the nightside auroral zone, where intense auroral currents are known to occur during substorms

AIM-E: E-Region Auroral Ionosphere Model

The auroral oval is the high-latitude region of the ionosphere characterized by strong variability of its chemical composition due to precipitation of energetic particles from the magnetosphere. The complex nature of magnetospheric processes cause a wide range of dynamic variations in the auroral zone, which are difficult to forecast. Knowledge of electron concentrations in this highly turbulent region is of particular importance because it determines the propagation conditions for the radio waves. In this work we introduce the numerical model of the auroral E-region, which evaluates density variations of the 10 ionospheric species and 39 reactions initiated by both the solar extreme UV radiation and the magnetospheric electron precipitation. The chemical reaction rates differ in more than ten orders of magnitude, resulting in the high stiffness of the ordinary differential equations system considered, which was solved using the high-performance Gear method. The AIM-E model allowed us to calculate the concentration of the neutrals NO, N(4S), and N(2D), ions N+, N2+, NO+, O2+, O+(4S), O+(2D), and O+(2P), and electrons Ne, in the whole auroral zone in the 90‒150 km altitude range in real time. The model results show good agreement with observational data during both the quiet and disturbed geomagnetic conditions.

Temporal Characteristics of Energetic Magnetospheric Electron Precipitation as Observed During Long‐Term Balloon Observations

AbstractThe paper summarizes the properties of precipitation of magnetospheric electrons with energy above several hundred keV recorded by observing X‐ray bremsstrahlung in the polar stratosphere above the Murmansk region, Russia, in 1961–2019. Precipitation occurrence rate demonstrates a clear dependence on the solar activity with a maximum at the decay phase of the 11‐year solar cycle, similarly to the variability in occurrences of the high‐speed solar wind streams (HSSWS). The energetic electron precipitation (EEP) event series is often initiated by a moderate geomagnetic storm caused by a HSSWS and continues during geomagnetic storm recovery. EEP demonstrates the seasonal rate variation with the maxima in occurrence rate around the spring and the autumn solstices and correlates with fluences of relativistic electrons in the outer radiation belt. For 59 years, 589 events of precipitation were observed. Analysis of the long‐term time series revealed a growing trend in the rate of precipitation occurrence, especially in the 1990s to 2000s that is not properly explained yet.

A case study of correspondence between Pc1 activity and ionospheric irregularities at polar latitudes

A possible driver of precipitation of magnetospheric energetic electrons in the high-latitude atmosphere is represented by electromagnetic ion-cyclotron (EMIC) magnetospheric waves. The precipitating particles produce variations, by collision, in the ionized component of the atmosphere, altering its chemistry and electrical conductivity, with a significant impact on the atmospheric processes. In this framework, it would be significant to find experimental evidence of a correspondence between ionospheric electron density irregularities and the occurrence of Ultra-Low-Frequency (ULF) Pc1 geomagnetic pulsations, i.e., the ground signatures of EMIC waves, at high latitudes. In this work, we face this subject by considering a specific case study occurred on 22 February 2007 during quiet magnetospheric conditions. The study is based on the analysis of simultaneous ULF geomagnetic field and Total Electron Content (TEC) measurements recorded at Mario Zucchelli Station in Antarctica. We show that Pc1 pulsations occur in correspondence to solar wind pressure increases and that, at the same time, the ionosphere is characterized by the presence of ionospheric irregularities. We suggest that a possible link between the Pc1 activity and the ionospheric irregularities may be energetic electron precipitations, driven by EMIC waves generated in the compressed magnetosphere, which produce density variations in the ionized component of the atmosphere.

Long-Term Evolution of the Occurrence Rate of Magnetospheric Electron Precipitation into the Earth’s Atmosphere

Long-Term Evolution of the Occurrence Rate of Magnetospheric Electron Precipitation into the Earth’s Atmosphere

Self‐Consistent Modeling of Electron Precipitation and Responses in the Ionosphere: Application to Low‐Altitude Energization During Substorms

AbstractWe report a new modeling capability that self‐consistently couples physics‐based magnetospheric electron precipitation with its impact on the ionosphere. Specifically, the ring current model RAM‐SCBE is two‐way coupled to an ionospheric electron transport model GLOW (GLobal airglOW), representing a significant improvement over previous models, in which the ionosphere is either treated as a 2‐D spherical boundary of the magnetosphere or is driven by empirical precipitation models that are incapable of capturing small‐scale, transient variations. The new model enables us to study the impact of substorm‐associated, spectrum‐resolved electron precipitation on the 3‐D ionosphere. We found that after each substorm injection, a high‐energy tail of precipitation is produced in the dawn sector outside the plasmapause, by energetic electrons (10 < E < 100 keV) scattered by whistler‐mode chorus waves. Consequently, an ionospheric sublayer characterized by enhanced Pedersen conductivity arises at unusually low altitude (∼85 km), with its latitudinal width of ∼5–10° in the auroral zone. The sublayer structure appears intermittently, in correlation with recurrent substorm injections. It propagates eastward from the nightside to the dayside in the same drift direction of source electrons injected from the plasma sheet, resulting in global impact within the ionosphere. This study demonstrates the model's capability of revealing complex cross‐scale interactions in the geospace environment.

Stratospheric Measurements of Magnetospheric Electron Precipitation and Interplanetary Medium Conditions in Solar Activity Cycles 22–24

High-energy electrons precipitate into the atmosphere under the influence of disturbances of the interplanetary medium on the magnetosphere. Electrons captured from interplanetary space interact in the magnetosphere with waves, resulting in both acceleration and electron energy loss. Some high-energy electrons precipitate into the atmosphere where they generate bremsstrahlung X-rays, which can penetrate deep into the atmosphere to heights of the order of 20 km. The current 11-year cycle is characterized by weak solar activity and a small number of precipitations. The paper discusses the correlation between the parameters of the interplanetary medium and the magnetosphere with the number of precipitations recorded from 1987 to the present during regular measurements of ionizing radiation in the atmosphere in the Murmansk region.

Energy deposition and ion production from thermal oxygen ion precipitation during Cassini’s T57 flyby

Cassini’s Radio Science Investigation (RSS) and Langmuir Probe observed abnormally high electron densities in Titan’s ionosphere during Cassini’s T57 flyby. We have developed a three-dimensional model to investigate how the precipitation of thermal magnetospheric O+ may have contributed to enhanced ion production in Titan’s ionosphere. The three-dimensional model builds on previous work because it calculates both the flux of oxygen through Titan’s exobase and the energy deposition and ion production rates in Titan’s atmosphere. We find that energy deposition rates and ion production rates due to thermal O+ precipitation have a similar magnitude to the rates from magnetospheric electron precipitation and that the simulated ionization rates are sufficient to explain the abnormally high electron densities observed by RSS and Cassini’s Langmuir Probe. Globally, thermal O+ deposits less energy in Titan’s atmosphere than solar EUV, suggesting it has a smaller impact on the thermal structure of Titan’s neutral atmosphere. However, our results indicate that thermal O+ precipitation can have a significant impact on Titan’s ionosphere.

Observation of Terrestrial gamma-ray flashes in the RELEC space experiment on the Vernov satellite

The RELEС scientific payload of the Vernov satellite launched on July 8, 2014 includes the DRGE spectrometer of gamma-rays and electrons. This instrument comprises a set of scintillator phoswich-detectors, including four identical X-ray and gamma-ray detector with an energy range of 10 kev to 3 MeV with a total area of ~500 cm2 directed to the atmosphere, as well as an electron spectrometer containing three mutually orthogonal detector units with a geometric factor of ~2 cm2 sr. The aim of a space experiment with the DRGE instrument is the study of fast phenomena, in particular Terrestrial gamma-ray flashes (TGF) and magnetospheric electron precipitation. In this regard, the instrument provides the transmission of both monitoring data with a time resolution of 1 s, and data in the event-by-event mode, with a recording of the time of detection of each gamma quantum or electron to an accuracy of ~15 μs. This makes it possible to not only conduct a detailed analysis of the variability in the gamma-ray range, but also compare the time profiles with the results of measurements with other RELEC instruments (the detector of optical and ultraviolet flares, radio-frequency and low-frequency analyzers of electromagnetic field parameters), as well as with the data of ground-based facility for thunderstorm activity. This paper presents the first catalog of Terrestrial gamma-ray flashes. The criterion for selecting flashes required in order to detect no less than 5 hard quanta in 1 ms by at least two independent detectors. The TGFs included in the catalog have a typical duration of ~400 μs, during which 10–40 gamma-ray quanta were detected. The time profiles, spectral parameters, and geographic position, as well as a result of a comparison with the output data of other Vernov instruments, are presented for each of candidates. The candidate for Terrestrial gamma-ray flashes detected in the near-polar region over Antarctica is discussed.

Precipitation of energetic magnetospheric electrons and accompanying solar wind characteristics

From 1957 up to the present time, the Lebedev Physical Institute (LPI) has performed regular monitoring of ionizing radiation in the Earth’s atmosphere. There are cases when the X-ray radiation generated by energetic magnetospheric electrons penetrates the atmosphere and is observed at polar latitudes. The vast majority of these events occurs against the background of high-velocity solar wind streams, while magnetospheric perturbations related to interplanetary coronal mass ejections (ICMEs) are noneffective for precipitation. It is shown in the paper that ICMEs do not cause acceleration of a sufficient amount of electrons in the magnetosphere. Favorable conditions for acceleration and subsequent scattering of electrons into the loss cone are created by magnetic storms with an extended recovery phase and with sufficiently frequent periods of negative Bz component of the interplanetary magnetic field (IMF). Such geomagnetic perturbations are typical for storms associated with high-velocity solar wind streams.

The generation of Ganymede's diffuse aurora through pitch angle scattering

Abstract. Diffuse auroral intensities of neutral atomic oxygen OI λ1356 Å emission on Ganymede due to whistler mode waves are estimated. Pitch angle diffusion of magnetospheric electrons into the loss cone due to resonant wave–particle interaction of whistler mode waves is considered, and the resulting electron precipitation flux is calculated. The analytical yield spectrum approach is used for determining the energy deposition of electrons precipitating into the atmosphere of Ganymede. It is found that the intensities (4–30 R) calculated from the precipitation of magnetospheric electrons observed near Ganymede are inadequate to account for the observational intensities (≤ 100 R). This is in agreement with the conclusions reached in previous works. Some acceleration mechanism is required to energize the magnetospheric electrons. In the present work we consider the heating and acceleration of magnetospheric electrons by electrostatic waves. Two particle distribution functions (Maxwellian and kappa distribution) are used to simulate heating and acceleration of electrons. Precipitation of a Maxwellian distribution of electrons can produce about 70 R intensities of OI λ1356 Å emission for electron temperature of 150 eV. A kappa distribution can also yield a diffuse auroral intensity of similar magnitude for a characteristic energy of about 100 eV. The maximum contribution to the estimated intensity results from the dissociative excitation of O2. Contributions from the direct excitation of atomic oxygen and cascading in atomic oxygen are estimated to be only about 1 and 2 % of the total calculated intensity, respectively. The findings of this work are relevant for the present JUNO and future JUICE missions to Jupiter. These missions will provide new data on electron densities, electron temperature and whistler mode wave amplitudes in the magnetosphere of Jupiter near Ganymede.

Precipitation of magnetospheric electrons into the Earth’s atmosphere and the electrons of the outer radiation belt

More than 500 X-ray emission events generated by precipitating electrons from the outer radiation belt have been recorded in the Earth’s atmosphere over the many years of the Lebedev Physical Institute observing fluxes of ionized radiation. This precipitation is closely related to high-velocity solar wind streams, whose rate of occurrence, like that of precipitation events, is greatest during the decline phase of the 11-year solar activity cycle. This work considers the relationship between the high-velocity solar wind, the relativistic electron fluxes in the outer radiation belt, and the electron precipitation observed in the polar atmosphere.

DIFFUSE AURORA ON GANYMEDE DRIVEN BY ELECTROSTATIC WAVES

ABSTRACT The role of electrostatic electron cyclotron harmonic (ECH) waves in producing diffuse auroral emission O i 1356 Å on Ganymede is investigated. Electron precipitation flux entering the atmosphere of Ganymede due to pitch-angle diffusion by ECH waves into the atmospheric loss-cone is calculated. The analytical yield spectrum approach for electron energy degradation in gases is used for calculating diffuse auroral intensities. It is found that calculated O i 1356 Å intensity resulting from the precipitation of magnetospheric electrons observed near Ganymede is insufficient to account for the observed diffuse auroral intensity. This is in agreement with estimates made in earlier works. Heating and acceleration of ambient electrons by ECH wave turbulence near the magnetic equator on the field line connecting Ganymede and Jupiter are considered. Two electron distribution functions are used to simulate the heating effect by ECH waves. Use of a Maxwellian distribution with temperature 100 eV can produce about 50–70 Rayleigh O i 1356 Å intensities, and the kappa distribution with characteristic energy 50 eV also gives rise to intensities with similar magnitude. Numerical experiments are performed to study the effect of ECH wave spectral intensity profile, ECH wave amplitude, and temperature/characteristic energy of electron distribution functions on the calculated diffuse auroral intensities. The proposed missions, joint NASA/ESA Jupiter Icy Moon Explorer and the present JUNO mission to Jupiter, would provide new data to constrain the ECH wave and other physical parameters near Ganymede. These should help confirm the findings of the present study.

Ionization balance in Titan’s nightside ionosphere

Based on a multi-instrumental Cassini dataset we make model versus observation comparisons of plasma number densities, nP=(nenI)1/2 (ne and nI being the electron number density and total positive ion number density, respectively) and short-lived ion number densities (N+, CH2+, CH3+, CH4+) in the southern hemisphere of Titan’s nightside ionosphere over altitudes ranging from 1100 and 1200km and from 1100 to 1350km, respectively. The nP model assumes photochemical equilibrium, ion–electron pair production driven by magnetospheric electron precipitation and dissociative recombination as the principal plasma neutralization process. The model to derive short-lived-ion number densities assumes photochemical equilibrium for the short-lived ions, primary ion production by electron-impact ionization of N2 and CH4 and removal of the short-lived ions through reactions with CH4. It is shown that the models reasonably reproduce the observations, both with regards to nP and the number densities of the short-lived ions. This is contrasted by the difficulties in accurately reproducing ion and electron number densities in Titan’s sunlit ionosphere.

The global precipitation of magnetospheric electrons into Titan’s upper atmosphere

We couple a two-stream electron transport model to a three-dimensional model of Titan’s plasma interaction to calculate the global precipitation of magnetospheric electrons into Titan’s atmosphere. We describe energy deposition rates from eleven simulations that vary the following parameters: relative orientation of the solar and magnetospheric ram directions, initial electron distribution, electron bounce times in Saturn’s magnetosphere, and whether we account for magnetic mirroring. Most of the energy from auroral electrons is deposited on the magnetospheric wake-side of Titan’s thermosphere, with peak rates between 25 and 35eVcm−3s−1, and the least amount of energy is deposited on the magnetospheric ram-side. We calculate globally averaged peak energy deposition rates of ∼13eVcm−3s−1 near 1200km altitude, ∼1eVcm−3s−1 near 1200km altitude, and ∼10eVcm−3s−1 near 1350km altitude for electron distributions characteristic of Saturn’s plasma sheet, lobe, and magnetosheath, respectively. Globally averaged energy deposition rates are decreased by ∼70% when we assume that the electron bounce times are a factor of 10 shorter because the thermalization of magnetospheric electrons in Titan’s atmosphere erodes Saturn’s flux tubes over time scales comparable to the time it takes for electrons to bounce in Saturn’s magnetosphere. Magnetic mirroring further reduces the globally averaged energy deposition rates by ∼30% to 70%. The total power deposited in Titan’s thermosphere by magnetospheric electrons varies between 0.13 and 1.5×108W for the eleven simulations analyzed, which is about an order of magnitude smaller than the power deposited by solar EUV (∼109W for λ<800Å) during the 2007 to 2009 solar minimum.

Magnetosphere–atmosphere coupling at Saturn: 1 – Response of thermosphere and ionosphere to steady state polar forcing

We present comprehensive calculations of the steady state response of Saturn’s coupled thermosphere–ionosphere to forcing by solar radiation, magnetospheric energetic electron precipitation and high latitude electric fields caused by sub-corotation of magnetospheric plasma. Significant additions to the physical processes calculated in our Saturn Thermosphere Ionosphere General Circulation Model (STIM–GCM) include the comprehensive and self-consistent treatment of neutral–ion dynamical coupling and the use of self-consistently calculated rates of plasma production from incident energetic electrons. Our simulations successfully reproduce the observed high latitude temperatures as well as the latitudinal variations of ionospheric peak electron densities that have been observed by the Cassini Radio Science Subsystem experiment (RSS). We find magnetospheric energy deposition to strongly control the flow of mass and energy in the high and mid-latitude thermosphere and thermospheric dynamics to play a crucial role in driving this flow, highlighting the importance of including dynamics in any high latitude energy balance studies on Saturn and other Gas Giants. By relating observed H3+ column emissions and temperatures to the same quantities inferred from simulated atmosphere profiles we identify a potential method of better constraining the still unknown abundance of vibrationally excited H2 which strongly affects the H3+ densities. Our calculations also suggest that local time variability in H3+ column emission flux may be largely driven by local time changes of H3+ densities rather than temperatures. By exploring the parameter space of possible high latitude electric field strengths and incident energetic electron fluxes, we determine the response of thermospheric polar temperatures to a range of these magnetospheric forcing parameters, illustrating that 10keV electron fluxes of 0.1–1.2mWm−2 in combination with electric field strengths of 80–100mVm−1 produce H3+ emissions consistent with observations. Our calculations highlight the importance of considering thermospheric temperatures as one of the constraints when examining the state of Saturn’s magnetosphere and its coupling to the upper atmosphere.

Unusual electron density profiles observed by Cassini radio occultations in Titan's ionosphere: Effects of enhanced magnetospheric electron precipitation?

[1] The Cassini radio science facility provided 13 occultation electron density profiles of Titan during the period of 2006 and 2009. This paper presents the results of all of these occultation observations. It shows that ten of the observed electron density profiles are similar, but three are significantly different. The number of observations is relatively small for meaningful statistical conclusions, but it is shown, using the corresponding measured electron spectra, that the three anomalous profiles in the ionospheric peak regions are likely to be the result of unusually intense electron precipitation events.