Plasma and EM simulations of meteor head echo reflections

Dyrud, L.1, Wilson, D.1, Close, S.2, Boerve, S.3, Trulsen, J.4 and Pecseli, H.4

1 Center for Remote Sensing, USA
2 Las Alamos National Laboratory, USA
3 NDRE, Norway
4 University of Oslo, Norway

Every day billions of meteoroids impact and disintegrate in the Earth’s atmosphere. Current estimates for this global meteor flux vary from 2000-200,000 tons per year, and estimates for the average velocity range between 10 km/s to 70 km/s. The basic properties of this global meteor flux, such as the average mass, velocity, and chemical composition remain poorly constrained. We believe much of the mystery surrounding the basic parameters of the interplanetary meteor flux exists for the following reason, the unknown sampling characteristics of different radar meteor observation techniques, which are used to derive or constrain most models. We believe this arises due to poorly understood radio scattering characteristics of the meteor plasma, especially in light of recent work showing that plasma turbulence and instability greatly influences meteor trail properties at every stage of evolution. We present our results on meteor plasma simulations of head echoes using particle in cell (PIC) ions, which show that electric fields strongly influence early stage meteor plasma evolution, by accelerating ions away from the meteoroid body. We also present the results of finite difference time domain electromagnetic simulations (FDTD), which can calculate the radar cross section of the simulated meteor plasmas. These simulations have shown that the radar cross section depends in a complex manner on a number of parameters. These include a relatively weak dependence on angle between radar and meteor entry, a large dependence on radar frequency, which shows that for a given meteor plasma size and density, the reflectivity as a function of probing radar frequency varies, but typically peaks below 100 MHz. We present functional forms for the RCS of head echoes as a function of plasma parameters such as peak plasma density and size. Finally, we discuss how this parameterization of head echo RCS can be used to derive, meteoroid, ionization, and plasma properties from HPLA head echo observations.