Observational evidence for 'punctuated equilibria' in the evolution of Leonid dust trail widths and implications for meteor rate predictions

Abstract

Meteor activity profiles are reported for the three Leonid storms of 1999 and 2001 and the substorm of 2000. These yield information on the evolution of the shape of cross-sections through Leonid dust trails of known age. Leonid dust trails shed 4 or more revolutions of the parent comet ago, widen rather sudden, compared to the 3 revolutions old dust trail encountered in 1999. Trails shed 4 respectively 7 revolutions ago differ little from each other in width by contrast. It is proposed that the evolution of Leonid dust trail widths is not gradual with age but progresses by a process of ‘punctuated equilibria’, parallel to a similar pattern in the orbital evolution of the parent comet 55P/Tempel–Tuttle. Trails shed 4 to 7 revolutions ago appear to represent an equilibrium phase. The current series of encounters with these trails therefore yield a unique opportunity to investigate the spatial dust density distribution for trails in this age range. Minimum and maximum rate estimates are given for the upcoming 2002 Leonids. The minimum rates possible amount to zenith hourly rates of ∼3000 for the 4-revolution trail encounter and ∼2500 for the 7-revolution trail encounter. Maximum rates possible, but unlikely to be fulfilled, are ∼6500 for the 4-revolution trail and ∼7100 for the 7-revolution trail. We can look forward with confidence to two new Leonid storms in 2002 with rates at least equal to and perhaps above those of 2001.