Abstract
Abstract. The decay of underdense meteor trails in the polar mesopause region is thought to be predominantly due to ambipolar diffusion, a process governed by the ambient temperature and pressure. Hence, observations of meteor decay times have been used to indirectly measure the temperature of the mesopause region. Using meteor observations from a SKiYMET radar in northern Sweden during 2005, this study found that weaker meteor trails have shorter decay times (on average) than relatively stronger trails. This suggests that processes other than ambipolar diffusion can play a significant role in trail diffusion. One particular mechanism, namely electron-ion recombination, is explored. This process is dependent on the initial electron density within the meteor trail, and can lead to a disproportionate reduction in decay time, depending on the strength of the meteor.
Highlights
Introduction and backgroundAt any location during any given day, many thousands of meteors enter our Earth’s upper atmosphere
Defining a “decay time”, τ1/2, as the time taken for the power to drop to half the peak, the ambipolar diffusion coefficient can be estimated from the meteor echo decay time by λ2 ln 2
Meteor radars are routinely used around the world to measure upper atmospheric parameters such as the magnitude and direction of the wind and the temperature
Summary
At any location during any given day, many thousands of meteors enter our Earth’s upper atmosphere. Defining a “decay time”, τ1/2, as the time taken for the power to drop to half the peak, the ambipolar diffusion coefficient can be estimated from the meteor echo decay time by λ2 ln 2. Hocking et al, 1997), that do not require observed (or modeled) pressure, but instead use the vertical profile of meteor decay times. Ballinger et al.: Ambipolar diffusion in the polar mesopause region were observed over Esrange, averaging over 10 000 per day Over half of these were rejected in order to ensure that only the most reliable meteor signals, and corresponding decay times, were retained (see Ballinger, 2007, for further details of the filtering process). Method of temperature estimation that uses ablating meteors requires the assumption that ambipolar diffusion alone governs the decay of the underdense meteor echoes. Alternative mechanisms exist, which can affect the decay rate (Dyrud et al, 2001; Havnes and Sigernes, 2005; Dimant and Oppenheim, 2006a,b; Holdsworth et al, 2006)
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