Altitudinal dependence of meteor radio afterglows measured via optical counterparts

Abstract

Utilizing the all‐sky imaging capabilities of the first station of the Long Wavelength Array along with a host of all‐sky optical cameras, we have now observed 44 optical meteor counterparts to radio afterglows. Combining these observations, we have determined the geographic positions of all 44 afterglows. Comparing the number of radio detections as a function of altitude above sea level to the number of expected bright meteors, we find a strong altitudinal dependence characterized by a cutoff below ∼90 km, below which no radio emission occurs, despite the fact that many of the observed optical meteors penetrated well below this altitude. This cutoff suggests that wave damping from electron collisions is an important factor for the evolution of radio afterglows. This finding agrees with the hypothesis that the emission is the result of electron plasma wave emission.

Association Between Meteor Radio Afterglows and Optical Persistent Trains

“…From the observations presented in this paper, we can infer that MRAs are more related to PTs than to flares. This is consistent with previous observations from Obenberger, Homes, et al (2016) where ablation features seemed to be unrelated to MRAs. This is also consistent with the long durations of MRAs as compared to the optical flares.…”

“…From a single measurement location, we are unable to triangulate the height of the knot/MRA. However, we can assume the MRA is within the height range of 90–110 km (Obenberger, Homes, et al, 2016). Assuming a probable height of 100 km, we can project the optical measurements onto east north up (ENU) coordinates.…”

“…Therefore, it may not be surprising that not all PTs create a detectable MRA, as their chemical compositions vary. Moreover, Obenberger, Homes, et al (2016) found strong correlation between the occurrence of MRAs and altitude, and at the time this relation was interpreted to mean that the neutral collision frequency of electrons was an important factor in determining whether or not an MRA could occur. However, the results of this paper may indicate that the altitude‐dependent atmospheric abundances of O and O 2 could effect reaction rates and play a significant factor in the energy spectrum.…”

“…These meteor radio afterglows (MRAs) are characterized by a broad and smooth spectrum covering at least the 20 to 60 MHz frequency range and lasting from tens of seconds up to a few minutes (Obenberger, Taylor, Lin, et al, 2015; Obenberger, Dowell, et al, 2016). Furthermore, Obenberger, Homes, et al (2016) showed that MRAs have a strong altitude cutoff at ∼90 km, below which MRAs are not observed. The emission from MRAs has also been found to be nearly isotropic (Varghese et al, 2019).…”

Limits on radio emission from meteors using the MWA

“…Many of these transients were coincident with optical meteors, both spatially and temporally. Between April 2014 and April 2016, a total of 20,000 hours data were collected, in which 154 radio transients were detected (Obenberger et al 2016a). Optical meteor counterparts were coincident with 44 of these radio transients.…”