Radar observation of the Leonids in 1998 and 1999

Results of Ondrejov radar observations of Leonid meteor shower in 1998 and 1999 are presented. It was found that while the activity in 1998 was domina ted by the long-duration echoes resulting in a low mass distribution index averaged over an interval 23 h UT November 16 to 12 h UT November 17 as s = 1.23+/-0.02 with the peak at L-. = 234 degrees .633 +/- 0 degrees .004. Th e 1999 activity culminated at L-. = 235 degrees .285 +/- 0 degrees .002 and was mainly due to prevailing of fainter echoes yielding a mean mass distri bution index s = 1.58 +/- 0.05 between 23 h UT November 17 8 h UT November 18. The activity pattern in 1998 showed a multiple peak structure while the corresponding 1999 pattern showed only one distinct peak. The 1998 activit y rates were lower than those in 1999 by the ratio of 2.8. Our observations indicate that the main outburst of this Leonid return occurred in 1999. Th e 1998 activity is characterized by a large scatter of observed hourly echo counts while the ones in 1999 possessed only one sharp maximum. The flux c urve in 1998 shows multiple peak character while in 1999 the activity patte rns of echoes with duration in excess of 0.4 s even though their peaks do n ot coincide generally with the activity maxima. The 1998 flux reached 3.34 10(-12) m(-2) s(-1) for a limiting mass of m(0) = 10(-5) kg while for 1999 it was determined as 37.41 10(-12) m(-2) s(-1).