Convection Electric Field Research Articles

Separation and Quantification of Ionospheric Convection Sources: 1. A New Technique

AbstractThis paper describes a novel technique that allows separation and quantification of different sources of convection in the high‐latitude ionosphere. To represent the ionospheric convection electric field, we use the Spherical Elementary Convection Systems representation. We demonstrate how this technique can separate and quantify the contributions from different magnetospheric source regions to the overall ionospheric convection pattern. The technique is in particular useful for distinguishing the contributions of high‐latitude reconnection associated with lobe cells from the low‐latitude reconnection associated with Dungey two‐cell circulation. The results from the current paper are utilized in a companion paper (Reistad et al., 2019, https://doi.org/10.1029/2019JA026641) to quantify how the dipole tilt angle influences lobe convection cells. We also describe a relation bridging other representations of the ionospheric convection electric field or potential to the Spherical Elementary Convection Systems description, enabling a similar separation of convection sources from existing models.

Energetic Electrons Below the Inner Radiation Belt

AbstractEnergetic electrons have occasionally been observed with high intensity in the low‐latitude quasi‐trapping region, below the inner radiation belt, where their intensity is normally low. During magnetic storms in November 2004 and July 2006, electrons reached magnetic drift shells with L<1.1. Data from the IDP electron spectrometer on the DEMETER satellite provide high energy resolution, while multiple NOAA/POES satellites provide local time coverage. After accounting for instrumental effects caused by the high intensity, electron kinetic energy is shown to reach at least 200 keV with generally softer spectra than are normally found in the stable trapping region. Electron injection from the inner belt by an enhanced convection electric field ∼5 mV/m may explain the observations. This could provide remote testing for models of global electrodynamics.

Polarization Electric Field Inside Auroral Patches: Simultaneous Experiment of EISCAT Radars and KAIRA

AbstractThe primary focus of this study was the motion of auroral patches and the polarization electric field generated therein observed on 9 November 2015 in an experiment using the European incoherent scatter (EISCAT) radars, Kilpisjärvi Atmospheric Imaging Receiver Array (KAIRA), and an all‐sky imager simultaneously. Based on the all‐sky imager data, the drift speed of the auroral patches corresponded to a southward electric field of 14.1( ± 3.7)–17.2( ± 4.5) mV/m. The convective electric field derived from the EISCAT radars and KAIRA observation was approximately 14.6 mV/m in the southward direction. This suggest that the spatial distribution of the auroral patches reflects the distribution of the cold plasma in the magnetosphere. The electron density and the height‐integrated Hall conductance between 80 and 120 km were enhanced by a factor of 2–4 inside the auroral patches. In this situation, a polarization electric field was generated therein. Enhanced ion velocities due to the polarization electric field was observed at up to 200‐km altitude; however, the absolute values of the ion velocities were approximately 40% of what was expected from the polarization electric field. A field‐aligned current (FAC) from 5 to 10 μA/m−2 in the edges of the auroral patches could explain the weakening of the polarization electric field. Since a FAC of that order of magnitude corresponded with that observed by the Swarm satellite, it was suggested that the polarization electric field was weakened by the FAC. Furthermore, the polarization electric field propagated upward from the dynamo region to at least 200 km.

Signatures of substorm related overshielding electric field at equatorial latitudes under steady southward IMF Bz during main phase of magnetic storm

During the geomagnetic storm periods, the convection electric field penetrates promptly to equatorial latitudes, causing an eastward electric field in the dayside ionosphere. Occasionally, the polarity of the dayside ionospheric electric field is inverted when the Interplanetary Magnetic Field (IMF) turns northward. In this paper, interesting observations of the strong westward electric field in the day side equatorial latitudes are presented, as evidenced by strong Counter Electrojet (CEJ) at Indian and Japanese sectors under the steady southward IMF Bz. The westward electric field perturbations are quite large with CEJ amplitude of ∼−120 nT over the Indian sector (14–15 December 2006) and ∼−220 nT for Japanese sector (7–8 November 2004). The plausible mechanisms for the observed overshielding electric fields under steady southward IMF Bz have been investigated in light of the possible role of substorm activity. The clear signatures of substorm were observed at geosynchronous particle flux measurements from LANL (Los Alamos National Laboratory) satellite and associated with sudden decrease in AL index. The observed variations of asymmetric ring current shows the enhancement of Partial Ring Current (PRC) at the dusk sector further supporting the substorm onset during that period which will probably enhance the overshielding due to increased Region 2 Field-Aligned Currents (R2 FACs). The observations of such significantly large amplitudes of CEJ associated with the substorm related overshielding events are sparse and the results bring out the important role of substorm onset and the development of PRC in accordance with the R2 FACs during intense magnetic storms which alter the day time equatorial electric field perturbations.

Response of the Geospace System to the Solar Wind Dynamic Pressure Decrease on 11 June 2017: Numerical Models and Observations

AbstractOn 11 June 2017, a sudden solar wind dynamic pressure decrease occurred at 1437 UT according to the OMNI solar wind data. The solar wind velocity did not change significantly, while the density dropped from 42 to 10 cm−3 in a minute. The interplanetary magnetic field BZ was weakly northward during the event, while the BY changed from positive to negative. Using the University of Michigan Block Adaptive Tree Solarwind Roe Upwind Scheme global magnetohydrodynamic code, the global responses to the decrease in the solar wind dynamic pressure were studied. The simulation revealed that the magnetospheric expansion consisted of two phases similar to the responses during magnetospheric compression, namely, a negative preliminary impulse and a negative main impulse phase. The simulated plasma flow and magnetic fields reasonably reproduced the Time History of Events and Macroscale Interactions during Substorms and Magnetospheric Multiscale spacecraft in situ observations. Two separate pairs of dawn‐dusk vortices formed during the expansion of the magnetosphere, leading to two separate pairs of field‐aligned current cells. The effects of the flow and auroral precipitation on the ionosphere‐thermosphere (I‐T) system were investigated using the Global Ionosphere Thermosphere Model driven by simulated ionospheric electrodynamics. The perturbations in the convection electric fields caused enhancements in the ion and electron temperatures. This study shows that, like the well‐studied sudden solar wind pressure increases, sudden pressure decreases can have large impacts in the coupled I‐T system. In addition, the responses of the I‐T system depend on the initial convection flows and field‐aligned current profiles before the solar wind pressure perturbations.

Reanalysis of Ring Current Electron Phase Space Densities Using Van Allen Probe Observations, Convection Model, and Log‐Normal Kalman Filter

AbstractModels of ring current electron dynamics unavoidably contain uncertainties in boundary conditions, electric and magnetic fields, electron scattering rates, and plasmapause location. Model errors can accumulate with time and result in significant deviations of model predictions from observations. Data assimilation offers useful tools which can combine physics‐based models and measurements to improve model predictions. In this study, we systematically analyze performance of the Kalman filter applied to a log‐transformed convection model of ring current electrons and Van Allen Probe data. We consider long‐term dynamics of μ = 2.3 MeV/G and K = 0.3 G1/2RE electrons from 1 February 2013 to 16 June 2013. By using synthetic data, we show that the Kalman filter is capable of correcting errors in model predictions associated with uncertainties in electron lifetimes, boundary conditions, and convection electric fields. We demonstrate that reanalysis retains features which cannot be fully reproduced by the convection model such as storm‐time earthward propagation of the electrons down to 2.5 RE. The Kalman filter can adjust model predictions to satellite measurements even in regions where data are not available. We show that the Kalman filter can adjust model predictions in accordance with observations for μ = 0.1, 2.3, and 9.9 MeV/G and constant K = 0.3 G1/2RE electrons. The results of this study demonstrate that data assimilation can improve performance of ring current models, better quantify model uncertainties, and help deeper understand the physics of the ring current particles.

Solar Rotation Period Driven Modulations of Plasmaspheric Density and Convective Electric Field in the Inner Magnetosphere

AbstractThis paper presents the first analysis of Van Allen Probes measurements of the cold plasma density and electric field in the inner magnetosphere to show that intervals of strong modulation at the solar rotation period occur in the locations of the outer plasmasphere and plasmapause (~0.7 RE peak‐to‐peak), in the large‐scale electric field (~0.24 mV/m peak‐to‐peak), and in the cold plasma density (~250 to ~70 cm−3 peak‐to‐peak). Solar rotation modulation of the inner magnetosphere is more apparent in the declining phase of the solar cycle than near solar maximum. The periodicities in these parameters are compared to solar extreme ultraviolet irradiance, solar wind dawn‐dusk electric field, and Kp. The variations in the plasmapause location at the solar rotation period anticorrelate with solar wind electric field, magnetospheric electric field, and Kp, but not with extreme ultraviolet irradiance, indicating that convective erosion is the dominant physical process controlling the plasmapause at these timescales.

Validity Study of the Swarm Horizontal Cross‐Track Ion Drift Velocities in the High‐Latitude Ionosphere

AbstractHigh‐latitude ionospheric plasma convection plays a fundamental role in determining many processes in the terrestrial ionosphere. Electric Field Instruments on the European Space Agency's three polar‐orbiting Swarm satellites measure ionospheric ion drift velocities at about 500 km altitude using thermal ion imager energy/angle‐of‐arrival electrostatic analyzers. Recently, European Space Agency released horizontal cross‐track components of these drifts, calibrated at high latitudes. This paper concerns the validation of the Swarm horizontal cross‐track ion drift measurements. All available Swarm‐A and Swarm‐B 2 Hz data between November 2015 and July 2017 were used and the climatology of high‐latitude ion convection was constructed and examined. Results were compared to corresponding climatology obtained from the Weimer 2005 empirical convection electric field model under different interplanetary magnetic field and solar wind conditions in the northern and southern hemispheres, separately. The ion drift data sometimes exhibit large offsets at middle latitudes. However, following a recalibration of the drifts using a refinement of the offset removal, the Swarm cross‐track ion drift climatology agrees reasonably well statistically with the Weimer 2005 model, and properly responds to the changing geospace environment. The two results agree within about 200 m/s (root‐mean‐square deviation), however the correlations are higher for southward interplanetary magnetic field and in the northern hemisphere (rswarm‐A = 0.84, rswarm‐B = 0.77), for which the corresponding magnitudes of Swarm‐A and Swarm‐B drifts are ~14% and ~33% larger than the model estimates, respectively. The convection patterns seen in the revised Swarm horizontal cross‐track drift velocities are more structured than those obtained using the model, but overall no significant systematic errors are present.

Effects of booms of sounding rockets in flowing plasmas

Effects of booms of a sounding rocket on rocket charging and on the local plasma conditions are studied with numerical and analytical models accounting for flowing, ionospheric plasmas. Simulations are carried out with a first principles self-consistent Particle-In-Cell numerical code. It is shown that the booms can affect the charging of the payload and disturb the local plasma to a high degree. The boom-to-plasma potential, which varies with the position due to the convective electric field, can lead to significantly different currents, in particular electron currents, to the booms on either side of the rocket. The analytical models for the collected currents considered in this study show good agreement with the simulations. The potential difference between the plasma and the rocket can electrostatically focus the ions to create regions of enhanced ion density downstream of the rocket and can lead to an asymmetric wake. It is shown that ion focusing can be asymmetric between the booms due to the potential gradient. These effects can have implications for instrument placements and data analysis.

English

The signatures of the geoeffectiveness solar disturbed events on the Magnetosphere Convection Electric Field (MCEF) universal time variation from 1964 to 2009 are investigated. Here, attention is focused our on the periods concerned by the whole shock activity and by the different types of the geoeffectiveness Coronal Mass Ejections (CMEs) which are one-day-shock, two-days-shock and three-days-shock. The investigation is made with respect to the orientation of the Interplanetary Magnetic Field (IMF). The MCEF time profiles show three different trends except for one-day-shock activity and for three-days-shock activity where we have four trends and one trend, respectively. The MCEF time profiles of the whole disturbed activity, the all shock activity and the one-day-shock activity present the initial phase where the Interplanetary Magnetic Field (IMF) is southward. During the two-days-shock activity, the initial phase of the MCEF shows a non-sensitive trend to the change of the direction of the IMF z-component while for the three-days-shock activity, the MCEF always exhibits the signature of the northward IMF. The last trend of the MCEF time profile shows the southward IMF signature except for the one-day-shock and the three-days-shock activities where that of the northward IMF was seen. Key words: Magnetosphere convection electric field, interplanetary magnetic field, shock activity, coronal mass ejections (CMEs). &nbsp

Assessing Ionospheric Convection Estimates From Coherent Scatter From the Radio Aurora

AbstractCoherent radar backscatter spectra from auroral E region plasma irregularities can be measured with great precision and accuracy. The Doppler spectra obtained from those measurements can be used to estimate auroral convection patterns using an empirical model. These estimates are consistent with rocket, optical, and incoherent scatter radar data, but direct comparison between the different data sets is not straightforward. In order to establish the quality of the empirical model, alternative approaches are then needed. In this work, we use the electrostatic nature of the convection electric field to assess the physical consistency of the empirical model: The model will be satisfactory to the extent that the convection patterns derived from them are incompressible. The incompressibility criteria were assessed for the estimated convection patterns obtained from the substorm of 20 December 2015. Two different approaches were used for this assessment. First, an electrostatic potential was fitted to the convection pattern produced by the empirical model. A good fit implies that there exists an incompressible convection pattern consistent with the Doppler spectra measurements. Second, the uncertainties on the Doppler spectral estimates where propagated through the empirical model to calculate the expected uncertainties on the divergence of the convection field obtained directly from the empirical model. The convection field will be incompressible if its divergence lies within the uncertainty estimates. Both approaches indicate that the evaluated convection patterns are consistently incompressible.

Measurements of convection electric field in the inner magnetosphere

In this paper, we study the characteristic of large-scale convection electric field in the inner magnetosphere, using magnetospheric multiscale (MMS) observations between L =5 and L =8 over the period from September 1, 2015 to October 31, 2016, covering almost all magnetic local time (MLT). Observations show that the DC convection electric field generally has small variations in this region. We investigate whether the convection electric field is correlated with geomagnetic indices and solar wind parameters. It is found that, among the studied parameters, solar wind electric field, z component of interplanetary magnetic field, AE and Kp indices show good correlations with the averaged convection electric field. The results in this paper provide valuable information for understanding the role of electric field on the dynamics of the inner magnetosphere.

Precipitation of Hydrogen Energetic Neutral Atoms at the Upper Atmosphere of Mars

AbstractWe study the properties of neutral hydrogen atoms precipitating onto the upper atmosphere of Mars. Energetic neutral atoms (ENAs) are produced by the charge exchange process between protons of solar wind (both upstream and shocked) as well as planetary origins and the Martian exospheric neutrals. Using a global hybrid plasma model for Mars‐solar wind interaction combined with an up‐to‐date exosphere model of Mars, we calculate the fluxes, spatial distributions, energy spectra, and direction distributions of hydrogen ENAs (H‐ENAs) at the Martian exobase for each source proton population. H‐ENAs originating from the upstream solar wind region and the magnetosheath dominate the precipitation. Two percent of the solar wind flux penetrates through the magnetic barrier as H‐ENAs under solar minimum conditions. The precipitating solar wind H‐ENA flux is axially symmetric about Sun‐Mars line, while the magnetosheath and planetary H‐ENAs have higher fluxes and a more‐extended precipitation area in the hemisphere where the convection electric field is pointing away from the planet, causing a significant precipitation beyond the terminator. The observed asymmetry is consistently explained by an asymmetric plasma flow in the dayside magnetosheath. The solar wind dynamic pressure increases the solar wind H‐ENA precipitation normalized by the upstream proton flux, due to a closer bow shock position and thus a higher exospheric column density for charge exchange. The spatial distribution of the magnetosheath solar wind and planetary H‐ENAs becomes more axially symmetric with increased dynamic pressure. The solar wind interaction with Mars exhibits more gas‐dynamic‐like signatures for higher dynamic pressure.

Convection Electric Field and Plasma Convection in a Twisted Magnetotail: A THEMIS Case Study 1–2 January 2009

AbstractWe investigate THEMIS satellite measurements made in a tail‐aligned constellation during a time interval on 1–2 January 2009, which has previously been attributed to an interval of an interplanetary magnetic field By‐driven magnetotail twisting. We find evidence for that the orientation of the convection electric field in the tail is twist‐mode dependent. For earthward flow and a negative twist (induced tail By< 0), the electric field is found to have northward Ez and tailward Ex components. During a positive twist (induced tail By> 0), the directions of Ez and Ex are reversed. The Ey component shows the expected dawn‐to‐dusk direction for earthward flow. The electric field components preserve their orientation across the neutral sheet, and a quasi‐collinear field is observed irrespective to the tail distance. The electric field associated with the tailward flow has an opposite direction compared to the earthward flow for the negative twist. For the positive twist, the results are less clear. The corresponding plasma convection and thus the magnetic flux transport have an opposite dawn‐dusk direction above and below the neutral sheet. The directions depend on the tail twist mode. The hemispherically asymmetric earthward plasma flows are suggested to be a manifestation of an asymmetric Dungey cycle in a twisted magnetotail. The role of tailward flows deserve further investigation.

Temporal and spatial variations of the equatorial electrojet during storm times from CHAMP observations

In this study, we examined the characteristics of temporal and spatial variations of the equatorial electrojet (EEJ) as extracted from the scalar magnetic field data from the CHAMP satellite during magnetic storms on 15 May and 24 August 2005. The main physical mechanisms of EEJ disturbances were analyzed using CHAMP data for the field-aligned currents (FACs), atmospheric mass density, thermospheric zonal winds, and ionospheric electron density. We found that the EEJ had eastward and westward enhancements in the main phase and recovery phase, respectively. The region 1 FACs were significantly strengthened after the storm onset and were much stronger than those in region 2, and they also moved to middle and low latitudes, which indicates that the dawn-to-dusk convection electric field in the auroral zone can penetrate from high latitudes to middle and low latitudes. Therefore, we believed that the prompt penetration electric field was mainly responsible for the eastward enhancement of the EEJ during the main phase. Interestingly, the westward peak of the EEJ coincided in time and space with the propagation of the atmospheric mass density disturbance from high latitudes to middle and low latitudes, whereas the zonal wind weakened and even turned eastward during the recovery phase. In this study, the enhanced equatorward wind at middle and low latitudes can be the main reason for the westward enhancement in the EEJ, whereas previous studies suggested that the enhanced westward zonal wind was responsible for the westward enhancement in the EEJ.

Reproducible Aspects of the Climate of Space Weather Over the Last Five Solar Cycles

AbstractEach solar maximum interval has a different duration and peak activity level, which is reflected in the behavior of key physical variables that characterize solar and solar wind driving and magnetospheric response. The variation in the statistical distributions of the F10.7 index of solar coronal radio emissions, the dynamic pressure PDyn and effective convection electric field Ey in the solar wind observed in situ upstream of Earth, the ring current index DST, and the high‐latitude auroral activity index AE are tracked across the last five solar maxima. For each physical variable we find that the distribution tail (the exceedences above a threshold) can be rescaled onto a single master distribution using the mean and variance specific to each solar maximum interval. We provide generalized Pareto distribution fits to the different master distributions for each of the variables. If the mean and variance of the large‐to‐extreme observations can be predicted for a given solar maximum, then their full distribution is known.

Cold Dense Ion Outflow Observed in the Martian‐Induced Magnetotail by MAVEN

AbstractCold ion outflow is one of the candidate processes to cause significant atmospheric escape from Mars. We here report on the cold dense heavy ion outflow event observed in Martian‐induced magnetotail by Mars Atmosphere and Volatile EvolutioN (MAVEN) on 4 December 2014. In the outflow event, the cold dense heavy ion outflow was observed only in south dusk downward convection electric field (E) lobe. During the event, the strong crustal magnetic field was located on dayside of Mars. It suggests that combination of minimagnetosphere and downward E facilitates the cold dense heavy ion outflow. In order to estimate the CO2+ density, we adopted a fitting method of log‐normal distribution to the O2+ time of flight distributions to eliminate O2+ contamination in the CO2+ time of flight data. Contribution of O2+, O+, and CO2+ to the total heavy ions (~134 cm−3) is about 71%, 26%, and 3%, respectively. Average heavy ion flux was ~5.4 × 107 cm−2s−1, assuming the escape velocity at 2,000‐km altitude.

Rapid Enhancements of the Seed Populations in the Heart of the Earth's Outer Radiation Belt: A Multicase Study

AbstractTo better understand rapid enhancements of the seed populations (hundreds of keV electrons) in the heart of the Earth's outer radiation belt (L* ~ 3.5–5.0) during different geomagnetic activities, we investigate three enhancement events measured by Van Allen Probes in detail. Observations of the fluxes and the pitch angle distributions of energetic electrons are analyzed to determine rapid enhancements of the seed populations. Our study shows that three specified processes associated with substorm electron injections can lead to rapid enhancements of the seed populations, and the electron energy increases up to 342 keV. In the first process, substorm electron injections accompanied by the transient and intense substorm electric fields can directly lead to rapid enhancements of the seed populations in the heart of the outer radiation belt. In the second process, the substorm injected electrons are first trapped in the outer radiation belt and subsequently transported into L* < 4.5 by the convection electric field. In the third process, the lower energy electrons are first injected at L* ~ 5.3 and then undergo drift resonance with ultralow‐frequency waves. These accelerated electrons by ultralow‐frequency waves are further transported into L* < 4.5 due to the convection electric field. This process is consistent with the radial diffusion. Our results suggest that these specified processes are important for understanding the dynamics of the seed populations in the heart of the outer radiation belt.

Energetic Electron Injections Deep Into the Inner Magnetosphere: A Result of the Subauroral Polarization Stream (SAPS) Potential Drop

AbstractIt has been reported that the dynamics of energetic (tens to hundreds of keV) electrons and ions is inconsistent with the theoretical picture in which the large‐scale electric field is a superposition of corotation and convection electric fields. Combining one year of measurements by the Super Dual Auroral Radar Network, DMSP F‐18, and the Van Allen Probes, we show that subauroral polarization streams (SAPSs) are observed when energetic electrons have penetrated below L = 4. Outside the plasmasphere in the premidnight region, potential energy is subtracted from the total energy of ions and added to the total energy of electrons during SAPS onset. This potential energy is converted into radial motion as the energetic particles drift around Earth and leave the SAPS azimuthal sector. As a result, energetic electrons are injected deeper than energetic ions when SAPSs are included in the large‐scale electric field picture, in line with observations.

Space Weather Influence on Electromagnetic Geosynchronous Debris Perturbations Using Statistical Fluxes

AbstractDue to the space plasma and the Sun, spacecraft at geosynchronous Earth orbit can charge naturally negative tens of kV. This charging can cause arcing which can damage spacecraft electronics and solar panels. A charged spacecraft will also experience a perturbative force and torque due to Earth's electric and magnetic fields. These electromagnetic perturbations have recently been postulated to cause significant orbital changes for lightweight debris objects. This paper investigates the effects of electromagnetic perturbations by using a charging model that uses measured flux distributions to better simulate natural charging and includes the convection electric field. This is done for a calm space weather case of KP = 2−, a stormy case where KP = 8, and a worst possible case where the voltage is held at −30 kV the entire time. It is found that neglecting electromagnetic effects on lightweight Mylar debris can lead to 100 km displacements after only a one orbit, and the covariance associated with such objects must be increased during periods of high charging.