Modeling the Altitude Distribution of Meteor Head Echoes Observed with HPLA Radars: Implications for the Radar Detectability of Meteoroid Populations

Abstract

The altitude distribution of meteors detected by a radar is sensitive to the instrument's response function and can thus provide insight into the physical processes involved in radar measurements. This, in turn, can be used to determine the rate of ablation and ionization of the meteoroids and ultimately the input flux on Earth. In this work, we model the radar meteor head echo altitude distribution for three High Power and Large Aperture radar systems, by considering meteoroid populations from the main cometary family sources. In this simulation, we first use the results of a dynamical model of small meteoroids impacting Earth's upper atmosphere to model the incoming mass, velocity, and entry angular distributions. We then combine these with the Chemical Ablation Model and establish the meteoroid ionization rates as a function of mass, velocity, and entry angle in order to determine the altitude at which these radars should detect the produced meteors and the portion of produced meteors from each population that are detected by these radars. We explore different sizes of head plasma as well as the possible effects on radar scattering of the head echo aspect sensitivity. We find that the modeled altitude distributions are generally in good agreement with measurements, particularly for ultra-high-frequency radars. In addition, our results indicate that the number of particles from Jupiter Family Comets (JFCs) required to fit the observations is lower than predicted by astronomical models. It is not clear yet if this discrepancy is due to the overprediction of JFC meteoroids by dynamical models or due to unaccounted physical processes in the treatment of ablation, ionization, and detections of meteoroids as they pass through Earth's atmosphere.

Differential Ablation of Organic Coatings From Micrometeoroids Simulated in the Laboratory

“…Such an increase in SNR would make the PPy ablation easier to detect than the Fe core ablation although the PPy ablates over a relatively narrow range of altitudes, whereas the Fe ablation has a much broader profile. This could potentially explain the existence of a high‐altitude tail on the altitude distribution of meteors present in Arecibo observations (Swarnalingam et al., 2019).…”

“…(based on Mathews et al, 1997) where r e is the electron radius. F is a factor defined by F = 1 when 𝐴𝐴 𝓁𝓁 < 𝜆𝜆∕4 and by (Janches et al, 2017;Swarnalingam et al, 2019). Here, we use the wavelength of the Arecibo 430 MHz radar.…”

Ablation Rates of Organic Compounds in Cosmic Dust and Resulting Changes in Mechanical Properties During Atmospheric Entry

“…In fact, organic pyrolysis might explain the discrepancy between the observed height distributions of meteor head echoes made by three HPLA radars, and the modeled distributions assuming only metal silicate ablation, where a significant population of higher altitude meteors were observed than were predicted (Figure 10 in Swarnalingam et al. [2019]). Finally, if organic pyrolysis leads to fragmentation before the dust particle melts, and the resulting silicate subunits are too small to continue heating to above their melting point, this might be observable as a high altitude trail which suddenly terminated.…”

Modeling Meteoroid Impacts on the Juno spacecraft

“…The basic summary of all four meteoroid population models used here and their free parameters are shown in Table 1. Models used in this article were constrained by numerous inner solar system observations such as Infrared Astronomical Satellite (IRAS) observations of the Zodiacal Cloud (Low et al 1984;Hauser et al 1984;Nesvorný et al 2010), orbital distributions of radar meteors at Earth (Campbell-Brown 2008;Galligan & Baggaley 2004), meteoroid mass flux at Earth (Love & Brownlee 1993;Carrillo-Sánchez et al 2016or meteor size-frequency distribution at Earth (Grun et al 1985) and used to explain or reproduce various meteoroid related phenomena on Mercury (Pokorný et al 2017(Pokorný et al , 2018, Venus (Janches et al 2020), Earth (Swarnalingam et al 2019), Moon (Janches et al 2018;Pokorný et al 2019), Mars (Carrillo-Sánchez et al 2020, or Ceres (Pokorný et al 2021)…”