Meteoroid flaring as a possible source of intense Langmuir waves

We introduce observational evidence obtained using the co-axial 430 MHz and 46.8 MHz radars at Arecibo Observatory for meteoroid flare processes that produce radar detectable scattering 1-2 kilometers delayed from the point of the flare on the meteoroid trajectory through the atmosphere. While several such events have been observed, we concentrate on one particularly interesting event. For this ∼90 km event, the head-echo at both frequencies is indicative of multiple fragments and of flaring based on the approach described by Mathews et al. [1]. The UHF radar meteor head-echo yields evidence of two major fragments but did not show the meteoroid flare while only the much less sensitive but wider-beam VHF radar revealed the unusual "delayed-echo" feature as well as complex fragmentation and the progenitor flare. For this event the flare and the resultant delayed-echo feature were well defined in the Range-Time-Intensity results and together point to an apparent propagation speed of the process giving rise to the delayed-echo of 50-100 km/sec. This is far too fast for shock waves thus pointing to intense plasma waves generated in the presumably "explosive" termination of a meteoroid fragment that produced the intense, well-defined radar flare-echo. We assume that the plasma "waves" generated by the explosive flare propagate in the trail-plasma "waveguide" and produce strong, highly non-thermal perturbations in the distribution of the trail-plasma thus engendering the observed strong VHF radar scattering at 1-2 km delay from the flare. We note convincing recent reports [2 and references therein] of transient HF/VHF radio emissions seen from the LWA1 (Long Wavelength Array prototype) and identified as originating from along the trajectory of optical bolides observed by a network of meteor cameras. Obenberger et al. [2] attribute these emissions to mode conversion to RF of Langmuir waves in the large gradients of the trail plasma. We agree with this assessment and, based on our delayed-echo results, further suggest that the meteoroid flaring generates these waves and also that the waves are contained within the trail-plasma waveguide thus limiting dissipation. We have not seen evidence of RF emission in our observations.