Meteoroid velocity distribution derived from head echo data collected at Arecibo during regular world day observations

[摘要] We report the observation and analysis of ionization flashes associated withthe decay of meteoroids (so-called head echos) detected by the Arecibo 430MHz radar during regular ionospheric observations in the spring and autumnequinoxes. These two periods allow pointing well-above and nearly-into theecliptic plane at dawn when the event rate maximizes. The observation of manythousands of events allows a statistical interpretation of the results, whichshow that there is a strong tendency for the observed meteoroids to come fromthe apex as has been previously reported (Chau and Woodman, 2004). The velocitydistributions agree with Janches et al. (2003a) when they are directlycomparable, but the azimuth scan used in these observations allows a newperspective. We have constructed a simple statistical model which takesmeteor velocities as input and gives radar line of sight velocities asoutput. The intent is to explain the fastest part of the velocitydistribution. Since the speeds interpreted from the measurements aredistributed fairly narrowly about nearly 60 km s^-1, double thespeed of the earth in its orbit, is consistent with the interpretation thatmany of the meteoroids seen by the Arecibo radar are moving in orbits aboutthe sun with similar parameters as the earth, but in the retrogradedirection. However, it is the directional information obtained from thebeam-swinging radar experiment and the speed that together provide theevidence for this interpretation. Some aspects of the measured velocitydistributions suggest that this is not a complete description even for thefast part of the distribution, and it certainly says nothing about the slowpart first described in Janches et al. (2003a). Furthermore, we cannot concludeanything about the entire dust population since there are probably selectioneffects that restrict the observations to a subset of the population.

[学科分类] 大气科学