Proceedings with Extended Abstracts (single PDF file) - Radio ...

OBSERVATIONS OF METEOR-HEAD ECHOES USING THEJICAMARCA 50 MHZ RADAR IN INTERFEROMETER MODEJ. L. Chau, R. F. Woodman, and M. A. MillaRadio Observatorio de Jicamarca, Instituto Geofísico del Perú, Lima1. IntroductionHigh-power large-aperture radars frequently detect very fast meteor head echoes witha range-rate velocity which follows the meteoroid as it travels through the upper atmosphere.Although meteor ``head echoes'' were first observed in the late 1940s, this topic has becomean area of interest only recently as scientists have focused more intensely on the importanceand usefulness of meteors [e.g., Janches et al., 2003, and reference therein]. Head echomeasurements accurately give radial velocities (toward the radar) and altitude ranges ofdeposition. Measurements are also provided for, with varying degrees of accuracy, transversevelocities, deceleration rates, and signal strengths as a function of altitude. The powerfulnarrow-beam radars which measure head echoes detect far smaller meteors than do classicalmeteor radars [e.g., Elford, 2001]. The use of these radars allows us to study the populationof meteors which probably contributes the most material to the Earth’s upper atmosphere.One of the main drivers for the increasing interest on meteor studies has been thepresence in recent years of spectacular Leonid meteor showers. At Jicamarca that was not anexception and meteor observations, particularly of head echoes, have been carried out sinceNovember 1998.Meteor studies have been particularly difficult over Jicamarca due to the presence ofvery strong equatorial electrojet (EEJ) echoes [Farley, 1985] and non-specular trail echoes[Chapin and Kudeki, 1994]. This geophysical ``clutter'' (for meteor head echo studies) occurat similar altitudes where most head echoes are expected (between 90 and 120 kms).Nonetheless, with the recent improvements of our acquisition systems, we have started thehead echo observations around sunrise times when EEJ are expected to be weaker orsporadic.Figure 1. Range-time intensity plot of meteor echoes. The meteor-head are represented by the vertical graystriations (~1 per second). Examples of long-lived meteor trails occur around 0659 and 0706 LTIn Figure 1, we show an example where meteor head echoes are observed at the sametime when long-lived meteor trail echoes are present (around 0659 and 0706). All thestriations in light gray represent head echoes (~1 head-echo per second). Although in thiswork we discuss the head echo results, the long-lived [Chapin and Kudeki, 1994] and thenon-specular [Dyrud et al., 2002] meteor trails are being studied independently (M.Oppenheim personal communication).134