Ionospheric effects of the Leonid meteor shower in November 2001 as observed by rapid run ionosondes

Abstract

[1] We operated ionosondes at four stations in a rapid-run mode to obtain ionograms every minute for 102 hours during the period of the Leonid meteor shower in November 2001. Plenty of radio echoes that looked like echo traces produced by sporadic E reflection were seen in the ionograms, and this allowed statistical analysis in a single meteor shower event, including discrimination of the backscattering by meteor trails from reflection by a horizontally stratified sporadic E layer. The radio echoes seen in the ionograms were categorized into three types. The first were spontaneous echoes, which were distributed across a wide range of virtual heights; at times during the period of maximum meteor activity, there was a statistically good correlation among the echoes seen at the four stations. The echoes of this type appear to be produced by Fresnel backscattering from meteor trails. The second were also spontaneous echoes observed during the shower period but persisted for several tens of minutes at the same virtual height as the typical sporadic E layer, and the top frequency of these echoes decayed with time. Echoes of this type are thus attributed to the reflection from a meteor-induced sporadic E patch. Echoes of the last type appeared outside the period of maximum activity of the meteor shower in the same range of virtual heights as the conventional sporadic E layer, and there was no time correlation between the events observed at the four stations. These events are attributed to a periodical increase in f O E s , which is modulated by planetary-wave activity, and have no relation with the meteor shower.

Meteor‐induced transient sporadic E as inferred from rapid‐run ionosonde observations at midlatitudes

“…For the Perseids 2002 LDME, the location of the patch first created is estimated at a zenith angle of 38° or a horizontal distance of 73 km from the ionosonde. The detectable meteor ablations that generate transient sporadic E are not necessarily directly above the ionosonde, and the possibility of such events being recorded on ionograms may not be low, unlike the suggestion of Maruyama et al [2003].…”

“…The major difference between the two events was in the apparent height. In the Leonids 2001 LDME (Figure 5), the apparent height of the meteor echo was the same as that of the usual sporadic E layer at the onset of the LDME, and it was maintained throughout the event, which suggested that the meteor ablation responsible for the echo was immediately overhead and the meteor‐induced plasma was trapped by wind shear in a manner similar to the sporadic E formation [ Maruyama et al , 2003]. On the other hand, for the Perseids 2002 LDME shown in Figure 1, the apparent height was larger than the usual sporadic E layer at the onset of the LDME.…”

“…If such cases are included, we have five more LDMEs for which the duration exceeds 10 min on three nights of Perseids 2002. In the analysis of Leonids 2001, Maruyama et al [2003] have speculated that meteor events persisting for a few minutes (like some echoes as seen between 0430 and 0500 JST in Figure 5) might be returns from a metallic column. However, now, we have no reason to exclude the long‐lasting echoes for a few minutes from those of transient sporadic E events in which the sporadic E patch recedes from the ionosonde.…”

“…It was a good opportunity to investigate the possible relation between sporadic E activity and meteor showers. Maruyama et al [2003] made observations with rapid‐run ionosondes at 1‐minute intervals at four ionosonde stations in Japan and obtained approximately 1600 meteor‐related echo traces with a top frequency higher than 8 MHz, during 14 hours around the peak of the shower. They discussed the observations according to the framework of Ellyett and Goldsbrough [1976] and concluded that most of the echoes are of class 1, being well correlated with the visual observations.…”

Multi-layer structure of mid-latitude sporadic-<i>E</i> observed during the SEEK-2 campaign

“…Many observations have been carried out by using ionosondes and radars (e.g. Smith and Wright, 1972;Ogawa et al, 2002;Maruyama et al, 2003;Haldoupis et al, 2003), and rocket experiments (e.g. Dorling et al, 1969;Yamamoto et al, 1998;Roddy et al, 2004).…”