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Ann. Geophys., 22, 1575-1584, 2004
www.ann-geophys.net/22/1575/2004/
© European Geosciences Union 2004
Meteor head echo altitude distributions and the height cutoff effect studied with the EISCAT HPLA UHF and VHF radars
A. Westman1, G. Wannberg1, and A. Pellinen-Wannberg2
1EISCAT Scientific Association, Kiruna, Sweden
2Swedish Institute of Space Physics, Kiruna, Sweden
Abstract. Meteor head echo altitude distributions have been derived from data
collected with the EISCAT VHF (224MHz) and UHF (930MHz) high-power,
large-aperture (HPLA) radars. At the high-altitude end, the distributions
cut off abruptly in a manner reminiscent of the trail echo height ceiling
effect observed with classical meteor radars. The target dimensions
are shown to be much smaller than both the VHF and the UHF probing
wavelengths, but the cutoff heights for the two systems are still
clearly different, the VHF cutoff being located several km above the
UHF one. A single-collision meteor-atmosphere interaction model is used
to demonstrate that meteors in the (1.3–7.2)µg mass range will ionise
such that critical electron density at 224MHz is first reached at or
around the VHF cutoff altitude and critical density at 930MHz will be
reached at the UHF cutoff altitude. The observed seasonal variation in
the cutoff altitudes is shown to be a function of the seasonal variation
of atmospheric density with altitude. Assuming that the electron density
required for detection is in the order of the critical density, the abrupt
altitude cutoffs can be explained as a consequence of the micrometeoroid
joint size-speed distribution dropping off so fast at the large-mass,
high-velocity end that above a certain altitude the number of detectable
events becomes vanishingly small. Conversely, meteors at the low-mass end
of the distribution will be gradually retarded such that the ionisation
they generate never reaches critical density. These particles will
remain unobservable.
Key words. Radio science (instruments and techniques) –
Interplatery physics (interplanetary dust) – General or miscellaneous
(new fields)
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