The Heights of Radar Meteors

Abstract

Previous measurements of the heights of radio meteors using VHF radars have distributions peaking at around 95km with few meteors detected above 105km. Using HF radars (frequencies 2 and 6MHz) near Adelaide, South Australia, we have now shown that there are many more meteors than previously believed ablating at above 100km, with the peak being at 110-120km, and meteors being detected to at least 140km. The gross difference from VHF measurements, as typified by our own observations at 54MHz, is because the higher frequencies are severely biased by the so-called “echo ceiling” effect. The HF height distributions have been confirmed by co-workers using the Jindalee over-the-horizon radar in central Australia, which operates at frequencies of 6-30MHz. These results have implications for a number of different areas of atmospheric research; for example the existence of metallic ions at altitudes of 140km and above, since ablation is apparently occurring much higher than was previously thought to be the case.