Nonspecular meteor trails from non‐field‐aligned irregularities: Can they be explained by presence of charged meteor dust?

Abstract

Nonspecular meteor echoes have been associated with field‐aligned irregularities and have been observed at low‐latitude and midlatitude sites. We present observations obtained at high latitudes with range‐time features that resemble those at lower latitudes. However, these echoes cannot come from field‐aligned irregularities, since the radar‐pointing angles are almost parallel to the magnetic field. Using interferometry, we have been able to discriminate space and time features. Our echoes could be qualitatively explained by the presence of charged dust forming from the meteoric material immersed in a turbulent flow. This can lead to a high Schmidt number plasma that can sustain meter‐scale turbulence just as it does for the polar mesospheric summer echoes. These rare events require relatively large meteoroids. The result emphasizes the importance of charged dust in understanding all long‐duration nonspecular meteor echoes. This dust will extend their diffusion times and will affect temperature estimations from specular echoes.

Derivation of turbulent energy dissipation rate with the Middle Atmosphere Alomar Radar System (MAARSY) and radiosondes at Andøya, Norway

“…The radar system is located at Andøya, Norway (69.03 • N, 16.04 • E) and designed for studying polar atmosphere, i.e. the UTLS (the upper troposphere and lower stratosphere) and MLT (the mesosphere and lower thermosphere) regions covering the ionospheric E region altitudes in polar regions Renkwitz et al, 2012Renkwitz et al, , 2013Stober et al, 2012Stober et al, , 2013Chau et al, 2014;Latteck and Strelnikova, 2015). The basic parameters of the radar system are summarized in Table 1 for convenience.…”

Observational evidence of high‐altitude meteor trail from radar interferometer

“…The echo duration threshold for classifying long versus short trails varies from 5 s to over 1 min [e.g., Malhotra et al, 2007;Sugar et al, 2010;Chau et al, 2014]. Here we choose a minimum duration of 5 s to classify long-duration trails [e.g., Sugar et al, 2010].…”

Coded continuous wave meteor radar

“…Non-specular meteor echoes could also be due to field-aligned irregularities or charged dust (Chau et al, 2014). Some of these echoes can have a large range and Doppler spread, which often makes their analysis problematic with pulsed radars with high pulse repetition rate measurements, which are designed for a point target at altitudes between 70 and 120 km.…”

“…The main categories of meteor radio scattering phenomena are known to be specular scattering from the enhanced electron density left suspended in the atmosphere behind the burning meteoroid (Pierce, 1938;Herlofson, 1947;Manning, 1948), non-specular trail echoes caused by Bragg scattering from ionospheric irregularities that form in the wake of the ablating meteoroid (Oppenheim et al, 2000;Dyrud et al, 2002;Chau et al, 2014), and finally meteor head echoes that originate from the area around the ablating meteor that has an electron density higher than the plasma frequency of the scattering radio wave (Hey et al, 1947;Evans, 1966;PellinenWannberg and Wannberg, 1994).…”