Figure 6. Evolution of 1600 Leonid trail. Mean anomaly M shown as function of Aa0 (difference in semi-major axis from comet at ejection), after 6, 9, 12 and 15 revolutions of comet, which is shown by a circle.

restrict the process of scattering. Figure 6 shows some integration results, using the tangential ejection at perihelion model, for the trail generated at the 1600 return of the comet. At some values of Aao, M is quite scattered after 15 revolutions. However, particles in Figure 6 with e.g. Ado between —0.04 and 0 are in the 5:14 Jovian resonance (55P/Tempel-Tuttle is also in this resonance), and particles in the large range in Ado to the right of +0.07 are in the 1:3 resonance. The resonances cause M to be a more coherent function of Ado. Moreover, in general the dispersal of nodal positions is also greatly restricted by resonances, owing to resonant motion being near-regular rather than stochastic [10]. Since compact, resonant structures can survive for increased timescales, outbursts can occur due to Leonid meteoroids released from the comet many centuries ago, as was the case in the 1998 fireball display [11-13].

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