Large-scale Convection Electric Field Research Articles

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.

Transport and loss of the inner plasma sheet electrons: THEMIS observations

[1] Using the electron data from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft measurements from 2007 to 2009, we derived global phase space density (PSD) distributions of plasma sheet electrons (2–100 eV/nT) to examine the transport process of the electrons to the inner magnetosphere and possible loss mechanisms of plasma sheet electrons during the convective transport. The inner boundaries of the electron plasma sheet were determined by the observed global distributions and compared with the Alfven boundaries that were calculated by the sum of the simple corotation and convection electric field models. This comparison confirms the previous results that the large-scale convection electric field controls the electron transport to the inner magnetosphere. The gradual decrease in PSD is observed from the dawn to the dayside sector, indicating the existence of some loss mechanisms in the morning sector. The loss time scales estimated from the PSD distributions were compared with the theoretical ones based on the quasi-linear diffusion theory using an empirical wave model of whistler mode chorus. We also estimated the required wave amplitudes that can explain the estimated loss time scales. It is shown that whistler mode chorus has a sufficient power to scatter the plasma sheet electrons, and the required wave amplitudes are roughly consistent with the CRRES statistical survey of the chorus wave amplitude. We suggest that the loss of plasma sheet electrons in the morning sector is mainly induced by pitch angle scattering by whistler mode chorus.

New Insights on Geomagnetic Storms from Model Simulations Using Multi-Spacecraft Data

The forecast of the terrestrial ring current as a major contributor to the stormtime Dst index and a predictor of geomagnetic storms is of central interest to ‘space weather’ programs. We thus discuss the dynamical coupling of the solar wind to the Earth's magnetosphere during several geomagnetic storms using our ring current-atmosphere interactions model and coordinated space-borne data sets. Our model calculates the temporal and spatial evolution of H+, O+, and He+ ion distribution functions considering time-dependent inflow from the magnetotail, adiabatic drifts, and outflow from the dayside magnetopause. Losses due to charge exchange, Coulomb collisions, and scattering by EMIC waves are included as well. As initial and boundary conditions we use complementary data sets from spacecraft located at key regions in the inner magnetosphere, Polar and the geosynchronous LANL satellites. We present recent model simulations of the stormtime ring current energization due to the enhanced large-scale convection electric field, which show the transition from an asymmetric to a symmetric ring current during the storm and challenge the standard theories of (a) substorm-driven, and (b) symmetric ring current. Near minimum Dst there is a factor of ∼ 10 variation in the intensity of the dominant ring current ion specie with magnetic local time, its energy density reaching maximum in the premidnight to postmidnight region. We find that the O+ content of the ring current increases after interplanetary shocks and reaches largest values near Dst minimum; ∼ 60% of the total ring current energy was carried by O+ during the main phase of the 15 July 2000 storm. The effects of magnetospheric convection and losses due to collisions and wave-particle interactions on the global ring current energy balance are calculated during different storm phases and intercompared.

Medium scale magnetospheric turbulence and quasi three-dimensional plasma sheet modeling

The role of the large- and medium-scale magnetospheric turbulence in the magnetospheric plasma dynamics is analyzed. The large scale convection electric field leads to plasma sheet compression which can be compensated by quasidiffusion flux directed against plasma pressure gradient. In the magnetostatic equilibrium regular and diffusion flux are compensated. On the basis of the developed theory the three dimensional solutions determining plasma sheet structure are modelled. The dependence of the plasma sheet structure on the interplanetary magnetic field (IMF) Bz orientation is investigated. It is shown that southward IMF orientation create the concave plasma sheet structure and northward IMF orientation can lead to the formation of convex structure in the center of plasma sheet. Possible explanation of theta-aurora formation is discussed.

Effect of the large-scale convection electric field structure on the formation of thin ionization layers at high latitudes

A three-dimensional simulation of the high-latitude ionosphere was applied to investigate the geographical distribution of E-region thin ionization layers which may be formed by the action of the convection electric field. The simulation model computes the ion densities (O +, O + 2, N +, N + 2, NO +, Fe +), and temperatures as a function of altitude, latitude, and longitude. The stationary state momentum and continuity equations are solved for each ion species, then the energy equation is solved for electrons, neutrals, and a generic ion having the mean ion mass and velocity. The various electric field patterns of the Heppner and Maynard [(1987) J. geophys. Res. 92, 4467–4489] convection electric field model were applied and the ionization density pattern was examined after a time sufficient for the formation of thin layers (≈2000 s). It was found that large areas of thin ionization layers were formed for each of the electric field patterns examined. Southward IMF B z conditions resulted in thin layers forming in the pre-midnight sector in the latitude range north of about 70° to about 80°, and after midnight between 60 and 70°. For northward B z conditions, the layers were mainly in the pre-midnight sector and covered a latitude range from about 60 to 80°.

Further observational evidence regarding the origin of plasmaspheric hiss

Explorer 45 satellite observations of medium energy electrons and ELF waves (100‐1000 hz) have been analysed during a modest isolated substorm which occurred at about 0430 UT on Feb. 13, 1972. Approximately 50 minutes before the sharp rise in AE the electron flux (E ∼ 30 ‐ 240 KeV) measured within the plasmapause near dusk at L = 5 dropped below the normal quiet time level. Simultaneously the intensity of plasmaspheric hiss emissions fell to background levels. Following the substorm activity the electron flux recovered and plasmaspheric emissions first reappeared when the electron flux (E >30 KeV) attained a value comparable to the Kennel‐Petschek stably trapped level required for cyclotron resonant instability. The substorm associated electron flux reduction is explained as a modification in the drift orbits of geomagnetically trapped electrons caused by the onset of a large scale convection electric field. The simultaneous wave and particle observations are consistent with electron cyclotron resonant generation for plasmaspheric hiss emissions. During this relatively quiet period the source location appears to be restricted to the outer plasmasphere (L ≳ 5).