Aspect sensitivity considerations in interpreting radar meteor range-spread trail echo durations

Abstract

Initial results from June 2006 50 MHz radar campaigns at the Jicamarca Radio Observatory (JRO) reveal that full understanding of Range-Spread Trail Echoes (RSTEs) must involve knowledge of the trail viewing angle relative to kB (radar pointing direction perpendicular to the geomagnetic field) as a function of location along the meteoroid trajectory. A study of RSTEs using the JRO main array demonstrates that an overwhelming majority of long duration ([15 s) trails occur in the kB region of the radar. Short duration (5 s) trails constitute a large majority of the trails and are seen throughout the illuminated volume although with a statistically significant kB preference indicating that observed trail duration is also a function of factors such as meteoroid mass and energy. Given the apparent radar scattering aspect sensitivity of the trail plasma as it expands parallel to the geomagnetic field, we hypothesize that short duration echoes away from the kB zone might be longer duration echoes if viewed from the correct geometry. We conclude that an RSTE event viewed by two closely spaced identical radars would exhibit different properties due to the differing viewing angles. Meteoroid size, energy, and fragmentation as well as radar properties such as frequency, beam pattern, and absolute sensitivity play obvious roles as well.