Generation of electric fields and currents by neutral flows in weakly ionized plasmas through collisional dynamos

In weakly ionized plasmas neutral flows drag plasma across magnetic field lines generating intense electric fields and currents. An example occurs in the Earth's ionosphere near the geomagnetic equator. Similar processes take place in the Solar chromosphere and magnetohydrodynamic generators. This paper argues that not all convective neutral flows generate electric fields and currents and it introduces the corresponding universal criterion for their formation, ∇×(U×B)≠∂B/∂t, where U is the neutral flow velocity, B is the magnetic field, and t is time. This criterion does not depend on the conductivity tensor, σˆ. For many systems, the displacement current, ∂B/∂t, is negligible making the criterion even simpler. This theory also shows that the neutral-dynamo driver that generates E-fields and currents plays the same role as the DC electric current plays for the generation of the magnetic field in the Biot-Savart law.This work was supported by NSF/DOE Grant No. PHY-1500439, NASA Grant Nos. NNX11A096G and NNX14AI13G, and NSF-AGS Postdoctoral Research Fellowship Award No. 1433536. (PHY-1500439 - NSF/DOE; NNX11A096G - NASA; NNX14AI13G - NASA; 1433536 - NSF-AGS

Formation of plasma around a small meteoroid: electrostatic simulations

Obtaining meteoroid mass from head echo radar cross section depends on the assumed plasma density distribution around the meteoroid. An analytical model presented in Dimant and Oppenheim (2017a, https://doi.org/10.1002/2017JA023960; 2017b, https://doi.org/10.1002/2017JA023963) and simulation results presented in Sugar et al. (2018, https://doi.org/10.1002/2018JA025265) suggest the plasma density distribution is significantly different than the spherically symmetric Gaussian distribution used to calculate meteoroid masses in many previous studies. However, these analytical and simulation results ignored the effects of electric and magnetic fields and assumed quasi‐neutrality. This paper presents results from the first particle‐in‐cell simulations of head echo plasma that include electric and magnetic fields. The simulations show that the fields change the ion density distribution by less than ∼2% in the meteor head echo region, but the electron density distribution changes by up to tens of percent depending on the location, electron energies, and magnetic field orientation with respect to the meteoroid path.First author draf