P. Brown et al., Global ground-based electro-optical and radar observations of the 1999 Leonid shower: First results, EARTH MOON, 82-3, 2000, pp. 167-190
A total of 18 image intensified CCD detectors were deployed at 6 locations
(two in Negev Desert, Israel, and one in each of the Canary Islands, Long K
ey in Florida, Haleakala in Hawaii, and the Kwajalein Atoll) to provide a r
eal-time reporting system, as well as data for subsequent detailed analysis
, for the 1999 Leonid shower. Fields of view ranged from 9 to 34 degrees, w
ith apparent limiting stellar magnitudes from about +7 to +9. In addition,
a dual frequency (29.850 and 38.15 MHz) automated meteor radar with directi
onal determination capability was located in the Canadian Arctic at Alert,
Nunavut and provided continuous monitoring of the shower from a location wh
ere the radiant was constantly above the horizon. Both the radar and electr
o-optical systems successfully recorded the activity of the shower in real
time, and typical real-time activity plots are presented. Post-event analys
is has concentrated on the Israel electro-optical wide field cameras and th
e time interval centered around the peak of the storm. About 2700 meteors h
ave been digitized, with 680 measured for this analysis. Of these 371 were
well enough determined to permit a single-station technique to yield approx
imate heights. Light curves and photometric masses were computed for these
371 Leonids which form the basis of the preliminary results reported in thi
s paper. These cameras recorded Leonid meteors with peak luminosity in the
magnitude range -3 to +5, corresponding to the photometric mass range 10(-4
) to 10(-7) kg. A regression plot of photometric mass with magnitude did no
t indicate any change in light curve shape over the interval studied here.
The peak flux as determined by the electro-optical observations was 1.6 +/-
0.1 Leonid meteors of magnitude +6.5 or brighter falling on a one square k
ilometer area (oriented perpendicular to the Leonid radiant) per hour. This
peak flux occurred at approximately 2:07 +/-: 06 UT on Nov 18 1999, corres
ponding to solar longitude lambda (o) = 235.248 (epoch 2000.0). The radar r
esults were consistent with this maximum flux rate and time. There was not
a strong change in mass distribution over the few hours around maximum, alt
hough there is some indication that the peak interval was stronger in faint
er meteors. Height histograms are provided for beginning, maximum luminosit
y and ending heights. It was found that maximum luminosity and ending heigh
ts were completely independent of mass, consistent with a dustball model in
which the meteoroids are fragmented into constituent grains prior to ablat
ion of the grains. However, the beginning height increases sharply (9.1 km
per decade of photometric mass change) with increasing mass. This is possib
ly indicative of a volatile component which ablates early in the atmospheri
c trajectory.