Two THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft, B and C, began orbiting the Moon in 2011 and have since provided routine measurements of the plasma conditions in the lunar orbit. In this study, we systematically compare these measurements in near-Earth space with solar wind measurements obtained from the Lagrangian 1 (L1) point and propagated to the Earth, including measurements in the OMNI database and from the Wind spacecraft. A statistical comparison between THEMIS data and data from the OMNI database from September 2011 to December 2017 showed that the Y and Z components of the magnetic field and the flow speed are generally consistent between the two data sets. The ion number density and the dynamic pressure measured by THEMIS in near-Earth space are lower than those in the OMNI database, suggesting possible variation in the solar wind environment while propagating from the L1 point to near-Earth space. We further show two examples in which near-Earth solar wind measurements are applied in calculating the magnetopause location and in quantifying the magnetic field response to interplanetary shocks. Both examples suggest that using solar wind data from near-Earth space achieves better results than using solar wind data from the L1 point. These results provide validation of THEMIS-B and THEMIS-C as an alternative monitor of the near-Earth solar wind environment.
Tailward ion outflows in the Martian-induced magnetotail are known to be one of the major channels for Martian atmospheric escape. On the basis of nearly 6.5 years of observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, we investigate the statistical distribution of tailward and Marsward fluxes of heavy ions (i.e., O+ and
In this study, we investigate the generation of parametric decay instability, Langmuir turbulence formation, and electron acceleration in ionospheric heating via a two-fluid model using the Fokker–Planck equation and Vlasov–Poisson system simulations. The simulation results of both the magnetofluid model and the kinetic model demonstrate the dynamics of electron acceleration. Further, the results of the Vlasov–Poisson simulations suggest the formation of electron holes in phase space at the same spatial scale as the Langmuir wave, which are shown to be related to electron acceleration. In addition, electron acceleration is enhanced through the extension of the wavenumber spectrum caused by strong Langmuir turbulence, leading to more electron holes in phase space.
Kinetic Alfvén waves (KAWs), with a strong parallel disturbed electric field, play an important role in energy transport and particle acceleration in the magnetotail. On the basis of high-resolution observations of the Magnetospheric Multiscale (MMS) Mission, we present a detailed description of the acceleration process of electrons by KAWs in the plasma sheet boundary layer (PSBL). The MMS observed strong electromagnetic disturbances carrying a parallel disturbed electric field with an amplitude of up to 8 mV/m. The measured ratio of the electric to magnetic field perturbations was larger than the local Alfvén speed and was enhanced as the frequency increased, consistent with the theoretical predictions for KAWs. This evidence indicates that the electromagnetic disturbances should be identified as KAWs. During the KAWs, the energy flux of electrons at energies above 1 keV in the parallel and anti-parallel directions are significantly enhanced, implying occurrences of electron beams at higher energies. Additionally, the KAWs became more electrostatic-like and filled with high-frequency ion acoustic waves. The energy enhancement of electron beams is in accordance with the derived work done with the observed parallel disturbed electric field of KAWs, indicating electron acceleration caused by KAWs. Therefore, these results provide direct evidence of electron acceleration by KAWs embodying electrostatic ion acoustic waves in the PSBL.
Parametric decay instability (PDI) is an important process in ionospheric heating. This paper focuses on the frequency and wavevector matching condition in the initial PDI process, the subsequent cascade stage, and the generation of strong Langmuir turbulence. A more general numerical model is established based on Maxwell equations and plasma dynamic equations by coupling high-frequency electromagnetic waves to low-frequency waves via ponderomotive force. The primary PDI, cascade process, and strong Langmuir turbulence are excited in the simulation. The matching condition in the initial PDI stage and cascade process is verified. The result indicates that the cascade ion acoustic wave may induce or accelerate the formation of cavitons and lead to the wavenumber spectrum being more enhanced at 2kL (where kL is the primary Langmuir wavenumber). The wavenumber spectra develop from discrete to continuous spectra, which is attributed to the caviton collapse and strong Langmuir turbulence.