Diffusion Coefficients from the Rate of Decay of Meteor Trails

Abstract

SummaryThe effective diffusion coefficient for a meteor trail is calculated from the theory of ambipolar diffusion and the physical constants of the upper atmosphere. The absolute value of the diffusion coefficient so calculated, and also its gradient with height, are confirmed by measurement of the rates of decay of a large number of meteor echoes of known heights. The individual values show considerable scatter, most of which is attributed to a regular diurnal variation in the value of the diffusion coefficient. Amplitude fluctuations in persistent echoes are also briefly discussed.

Elevation, Height, and Electron Density of Echoing Points of Meteor Trails

“…Near the beginning of a trail, drxjdh is proportional to exp (-hjH), hence a small decrease in equipment sensitivity, say due to cut-off by diffusion, will shorten the detectable length of trail very much more for a bright meteor than for a faint meteor. Now the height gradient of the diffusion coefficient for the Geminid meteors is about twice as large as that for the other showers and for sporadic meteors (Weiss 1955b; this result is also confirmed by measurements on the 1953 Geminids), so that Geminids should be abnormally sensitive to cut-off by diffusion. This could well explain the lack of high Geminids, but none of the selection processes considered in Section II should operate differentially on the lower portion of the height distribution.…”

“…For reflection points close to the zenith, however, the line-of-sight wind component is always small, as the wind drift is essentially horizontal. Echo duration is related to the diffusion coefficient, which increases rapidly with height (Weiss 1955b); at 27 Mc/s height selection above 100 kID may be severe. Since the height distribution of atmospheric and meteor parameters, found either from height correlations (e.g.…”

“…The first alone suffices for measurement of the heights of the reflection points. From the rate of decay of the echo and the height of the reflection point the height-dependence of the diffusion coefficient and its absolute value can be established (Weiss 1955b). Electron densities follow from the echo amplitude and the position of the echoing point.…”

The Distribution of the Orbits of Sporadic Meteors

“…During a radio survey of meteor activity at Adelaide, extensive data on sporadic meteor activity have been accumulated. The" wind" equipment used has been fully described by Robertson, Liddy, and Elford (1953), and some preliminary work on the interpretation of the sporadic counts has appeared (Weiss 1955).…”

The 1956 Phoenicid Meteor Shower

“…Since the equipment was described by Weiss (1955a) the transmitter power has been increased considerably. At the time of the shower only one recording channel was in operation, and echoes were received only from the S. aerial, whose beam axis is directed at azimuth 14° N. of E., elevation 9°.…”