A note on the altitude profiles of the electron production in the atmosphere by micrometeoroids entering it at different initial speeds

Abstract

We have extended our earlier model (Mendis et al., 2005) for the study of the dynamical, thermal and charging history of micrometeoroids entering the earth's atmosphere, by taking into account the role of sputtering, which is important for high‐speed ones. As before we confine ourselves to motion in the night side of the earth. In this short note we will not discuss these, but will confine our attention to the limited, yet important, effect of electron production in the atmosphere, by three different classes of micrometeoroids (fast—“cometary,” average—“cometary,” and slow—“asteroidal”). It is seen that the altitude profiles of the electron production, which lead to the radar signatures of these bodies, are different, not just quantitatively but also qualitatively. This is due to the different relative importance of the three processes responsible for electron production, namely the ones associated with ablation and sputtering of the infalling micrometeoroid and thermionic electron emission from it. It is seen that sputtering‐associated electron production is the dominant process, particularly at higher altitudes, for the fast micrometeoroid (initial entry speed 60 km/s), ablation‐associated electron production is the dominant process for the average one (initial entry speed 30 km/s), while thermionic electron emission is the dominant process for the slow one (initial entry speed 12.5 km/s).

The electrical effects of micrometeoroids entering the terrestrial atmosphere at different speeds

“…Once again, in the interest of brevity we will restrict ourselves to vertical entry as in Mendis and Maravilla (2009), and we will consider three 'stony' micrometeoroids each of initial radius 40 μm, entering the 'top' of the atmosphere with initial speeds of 60, 30 and 15 km s −1 , representing respectively fast and average (speed) cometary micrometeoroids and a slow asteroidal one.…”

“…They found that sputtering-associated electron production was by far the dominant one at higher altitudes, and in the process also extended the range of atmospheric ionization to significantly higher altitudes. Very recently, we (Mendis and Maravilla 2009) added sputtering to our earlier model (Mendis et al 2005), taking into account the velocity dependence of the yield, as opposed to a constant one as assumed by Brosch et al (2001), and ran it for an initial speed of entry of 60 km s −1 . Continuing to use the 'free-molecular domain' approach, we used a much smaller initial size (40 μm, corresponding to a small micrometeoroid, instead of the large value of 20 cm, used by previous authors).…”

“…The main goal of this recent paper (Mendis and Maravilla 2009) was to compare the altitude profile of the electron production rate by this fast (60 km s −1 ) 'cometary' micrometeoroid with those of an 'average' (30 m s −1 ) cometary micrometeoroid as well as a slow-moving (12.5 km s −1 ) 'asteroidal' one, and show that they differ not just quantitatively, but also qualitatively.…”

“…The model equations (excluding the role of sputtering, valid for higher velocities) are given in Mendis et al (2005) and the additional terms resulting from physical sputtering are included in Mendis and Maravilla (2009). So in the interest of conserving space in this brief note these will not be written out at length.…”

Observational evidence of high‐altitude meteor trail from radar interferometer

“…The sputtering process can result in nonnegligible meteoroid mass loss and the production of ionization at much higher altitudes than those associated with thermal ablation only [Rogers et al, 2005]. Furthermore, a recent numerical simulation study on the electron production by Mendis and Maravilla [2009] highlighted the importance of physical sputtering as a dominant process for large and fast meteoroid at high altitudes. Our own numerical simulations of meteoroid ablation for a speed of 60 km s À1 with diameters of 1 mm and 1 cm indicate that sputtering can produce significant amounts of plasma up to 10 12 electrons m À1 and 10 14 electrons m À1 , respectively (J.…”