28. Seasonal variation in the radiant distribution of meteors

Abstract

The seasonal changes in the sporadic radiant distribution are investigated on the basis of the complete data for different classes of echo duration from the Ottawa 32·7 MHz radar taken over the years 1958–62, using a more accurate response function for the Ottawa radar equipment recently determined by McIntosh (1966). A model of the radiant distribution with four point sources (i.e. apex, helion, antihelion, and toroidal) and a uniform background is assumed. The strengths of the sources have been calculated by a least-squares fit to the observed mean hourly rates in 5-day intervals. The seasonal variations have different trends for meteors with different echo duration, showing stronger shower properties for long-duration echoes (4–8 sec). Meteors with short duration echoes (≤ 1 sec) show the same properties in radiant distribution, as was found in a previous paper based on preliminary Ottawa radar records. The toroidal source is without significant activity from August till November and shows a maximum in January. The diurnal variation calculated from this model is compared with the observed hourly rates. Some recent calculations have been made by Veverka and McIntosh (unpublished) using a continuous source model, elliptical in ecliptic longitude and exponential in latitude. The agreement of their results with observed diurnal rates is not as good. This suggests that the seasonal changes in the sporadic radiant distribution have a significant influence on the diurnal and annual variations of the hourly meteor rates.