Results from the observations of the Leonid meteor shower in 1996-2002 by the BLM (Bologna-Lecce-Modra)

forward-scatter radio system for meteor observation carried out along two baselines, Bologna-Lecce (Italy)and 

Bologna-Modra (Slovakia), are presented and discussed. The activity curves of long-duration echoes (≥ 8 s)and their variations indicate multiple peak activity which are attributed to filamentary structure of the stream. The mass distribution exponents in the period of the shower maximum shows significant changes in individual years, with a high contribution of larger particles chiefly in 1998

Cevolani, G.

Hajduk, A.

Porubčan, V.

Pupillo, G.

English

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NOTE BREVIDOI 10.1393/ncc/i2003-10010-0IL NUOVO CIMENTO Vol. 26 C, N. 6 Novembre-Dicembre 2003The Leonid meteor shower 1996-2002:Results from forward-scatter radio observationsV. Porubcˇan(1)(2), A. Hajduk(2), G. Cevolani(3) and G. Pupillo (3)(4)(1) Astronomical Institute FMPI Comenius University - 842 48 Bratislava, Slovakia(2) Astronomical Institute of the Slovak Academy of Sciences - 845 04 Bratislava, Slovakia(3) CNR-ISAC - via Gobetti 101, 40129 Bologna, Italy(4) DET, Universita` di Firenze - 50100 FirenzeOsservatorio di Campi Salentina - 73012 Lecce, Italy(ricevuto il 17 Ottobre 2003; approvato il 7 Gennaio 2004)Summary. — Results from the observations of the Leonid meteor shower in 1996-2002 by the BLM (Bologna-Lecce-Modra) forward-scatter radio system for meteorobservation carried out along two baselines, Bologna-Lecce (Italy) and Bologna-Modra (Slovakia), are presented and discussed. The activity curves of long-durationechoes (≥ 8 s) and their variations indicate multiple peak activity which are at-tributed to filamentary structure of the stream. The mass distribution exponent sin the period of the shower maximum shows significant changes in individual years,with a high contribution of larger particles chiefly in 1998.PACS 96.50.kr – Meteors, meteoroids, and meteor streams.PACS 95.85.Bh – Radio, microwave (> 1 mm).1. – The BLM forward-scatter system for meteor observationSince September 1996, there has been operating a forward-scatter system for meteorobservations, where a radio signal is transmitted along two mutually almost rectangularbaselines. The transmitter is located at Budrio near Bologna (44.6◦N; 11.5◦E, Italy) andtwo receivers at Lecce (40.3◦N; 18.2◦E, Italy) and Modra (48.4◦N; 17.3◦E, Slovakia)—BLM. The system was built up for monitoring meteor activity, to study meteor flux fromdifferent baselines directions. The equipment utilizes a continuous wave transmittingfrequency at 42.7 MHz, a fixed modulating tone at 1 kHz and 0.25 kW mean powertransmitted in the direction of both receiving stations. The baseline distances betweenthe transmitter and receivers are: Bologna-Lecce of 700 km (azimuth 307◦) and Bologna-Modra of 590 km (azimuth 224◦). Details about the equipment can be found elsewhere [1].c© Societa` Italiana di Fisica 679680 V. PORUBCˇAN, A. HAJDUK, G. CEVOLANI and G. PUPILLO2. – Observations of the Leonid meteor shower in 1996-2002The Leonids were observed by the equipment already in 1995 (Nov. 14-21), however,along the baseline Bologna-Lecce only as a test observation. Since 1996, the transmissionhas been carried out in both directions, so the data are recorded by both receivers andthe shower was monitored each year almost regularly in the interval Nov. 10-24.From the studies of echo counts provided by the BLM forward-scatter system it isapparent that a shower activity can be clearly recognized only for echoes of longer dura-tion. In the counts of all echoes, shower echoes are almost completely covered by sporadicbackground echoes. This trend is observed also in the data from all years of the obser-vation of the Leonids. Therefore, in the present study, the Leonid activity curves werederived only for long-duration echoes of duration ≥ 8 s. Shower activity was obtained bysubtracting sporadic background counts from all echo counts (shower and sporadic) incorresponding hours. The Leonid activity curves (echoes ≥ 8 s) corrected for the radiantelevation were obtained by combining data from both stations: Lecce and Modra (fig. 1).According to the 1996 data the shower echoes exhibit a rather flat maximum onNov. 17 lasting for about 10-11 h (solar longitude 235.0◦-235.4◦, equinox 2000.0), withat least two peaks (235.23◦ and 235.29◦). Though not so pronounced, the peaks arewell consistent with the observations by the Ondrˇejov backscatter radar (235.20◦ and235.32◦ [2]). Visual observations yield a peak at 235.17◦ (short-lived and richer in faintermeteors).The 1997 Leonid activity curve indicates an apparent increase in the activity until09:00-09:30 UT, Nov. 17 (solar longitude 235.1◦), with some smaller enhancements inbetween. The 1997 Leonid maximum could not be observed by the BLM system due tothe shower radiant being just on the horizon at the time of the peak itself. Accordingto visual observations the maximum appeared on Nov. 17, 12:15 UT (solar longitude235.22◦) and an increased Leonid activity was observed in the interval 235.0◦-236.0◦ [3].The 1998 Leonids with a large number of bright bolides observed on Nov. 16/17were for meteor observers a very impressive observational event. The counts of echoesobserved by the BLM system show a very broad maximum, however, due to overlappinglong-duration echoes the peak itself could not be recorded. At least two secondarypeaks at 234.48◦ and 234.84◦ are apparent. These peaks were recorded also by thebackscatter radar at Ondrˇejov for echoes of duration > 10 s, showing a broad maximum(234.6◦-234.7◦) with at least three secondary peaks [4]. The event was recorded also bythe photographic all-sky cameras at Modra Observatory (receiving station of the BLMsystem) [5]. Visual observations confirmed a very broad component of the 1998 Leonidfireballs with a peak between 234.4◦-235.0◦ [6].In 1999 the BLM forward-scatter observations show a pronounced maximum at235.28◦ which is consistent with other radar and visual observations. The backscat-ter radar (Ondrejov) show the Leonid activity peak for 235.285◦ with prevailing fainterechoes [4]. The 1999 Leonids had only one distinct peak, which was at the same time themain outburst of the Leonids in this return of the parent comet to the Sun, displayinga meteor storm activity with the ZHR = 3700 on Nov. 18, 02:02 UT (solar longitude235.285◦) [7]. According to TV observations [8] the most prominent peaks appeared onNov. 18 at 01:58 and 02:11 UT.In 2000 the BLM observations show a multiple peak activity (236.10◦, 236.19◦ and236.25◦). The peaks at 236.1◦ and 236.25◦ are consistent with visual results [9] and areclose to the predicted time of the dust trail of the 1733 and 1866 perihelion passages ofthe Leonid parent comet, respectively [10].THE LEONID METEOR SHOWER 1996-2002: RESULTS ETC. 681Fig. 1. – Counts of Leonid meteor shower echoes of duration ≥ 8 s in 30 minute intervals observedby the BLM forward-scatter radio system in 1996-2002. The curves represent the mean valuesof the data from Lecce and Modra. The 1995 curve is a test observation from Lecce.The Leonids 2001 and 2002 were exceptional events for meteor observers again. In2001 the BLM observations provide a distinct peak of the shower at solar longitude236.13◦. The peak was confirmed as well as by the Ondrejov backscatter radar so byvisual observers. Visual data give two high activity peaks at 236.14◦ and 236.46◦ [11].The second peak (Nov. 18, 18:16 UT) could not be recorded by the BLM system asthe shower radiant was below horizon. The Leonids in 2002 showed two high maximaboth from visual observation displaying ZHR over 2500 at solar longitudes 236.62◦ and236.89◦ [12]. The BLM observations give the position of the peaks at 236.62◦ and236.85◦, respectively. The second peak is less pronounced due to relatively low elevationof the shower radiant at the peak.682 V. PORUBCˇAN, A. HAJDUK, G. CEVOLANI and G. PUPILLOTable I. – The mass exponent s derived for the Leonids (sh) observed in 1995-2002 and sporadic(sp) meteors (M—Modra, L—Lecce, O—Ondrˇejov).Year M-sp L-sp M-sh L-sh O-sh visual-sh1995 - 2.34 - 1.69 - 1.6 [13]1996 2.22 2.32 1.63 1.50 - 1.65 [2]1997 2.38 2.71 1.64 1.61 - 1.7 [3]1998 2.32 2.67 1.20 1.15 1.23 [4] 1.3 [6]1999 2.23 2.25 1.56 1.52 1.58 [4] 1.8 [7]2000 2.44 2.28 1.84 1.56 - 1.8 [9]2001 2.26 (2.10) 1.49 1.52 - 1.8 [11]2002 2.40 (2.21) 1.55 (1.38) - 1.9 [14]3. – Mass exponentThe FS data from the BLM system enable derive the mass distribution exponent ofthe shower and sporadic meteor echoes from the observed echo durations. The massdistribution exponent s was derived from the cumulative numbers of echo duration con-sidering diffusion for dominant process of an echo decay in the form [15]logNc =(−34)(s− 1) log TD + const,(1)where Nc is the cumulative number of echoes with the duration equal to and greaterthan TD.The values of s in individual years were obtained as the mean values from the periodof the shower maximum (approx. 12 h) and the corresponding sporadic background. Themass exponent values derived for each station separately are listed in table I (M—Modra,L—Lecce) and are compared with those obtained from other radar (O—Ondrˇejov) andvisual observations (referring mostly to the narrow peaks of the Leonid shower activity).The Lecce values for 2001 and 2002 listed in brackets could be derived only from notcomplete periods or are influenced by interferences and thus are of lower weight.4. – ConclusionsThe observations of the Leonids by the Bologna-Lecce-Modra forward-scatter systemin 1996-2002 were analysed and the activity curves of long-duration echoes (≥ 8 s) werederived. The activity curves indicate multiple peak structure especially in 1996, 1998,2000 and 2002, which is attributed to a filamentary structure of the stream. The analysisof the mass distribution s of meteoroids within the stream indicate a decrease of s withthe approaching parent comet of the stream to perihelion and an increase after its passagein 1998. The lowest value of s was observed in 1998 and the derived results are consistentwith the results obtained by other techniques.∗ ∗ ∗The authors are indebted for the support of the research to the Institute ISAO CNR,Bologna and to VEGA, the Slovak Grant Agency for Science, grant No. 1026.THE LEONID METEOR SHOWER 1996-2002: RESULTS ETC. 683REFERENCES[1] Cevolani G., Bortolotti G., Franceschi C., Grassi G., Trivellone G.,Hajduk A. and Kingsley S. P., Planet. Space Sci., 43 (1995) 765.[2] Brown P., Sˇimek M., Jones J., Arlt R., Hocking W. and Beach M., Mon. Not. R.Astron. Soc., 300 (1998) 244.[3] Arlt R. and Brown P., WGN, J. Int. Meteor Org., 26 (1998) 161.[4] Sˇimek M. and Pecina P., Astron. Astrophys., 365 (2001) 622.[5] Toth J., Kornosˇ and Porubcˇan V., Earth, Moon and Planets, 82-83 (2000) 285.[6] Brown P. and Arlt R., Mon. Not. R. Astron. Soc., 319 (2000) 419.[7] Arlt R., Rubio L. B., Brown P. and Gyssens M., WGN, J. Int. Meteor Org., 27(1999) 286.[8] Molau S., Rendtel J. and Nitschke M., WGN, J. Int. Meteor Org., 27 (1999) 296.[9] Arlt R.and Gyssens M.., WGN, J. Int. Meteor Org., 28 (2000) 195.[10] Asher D. J., Leonid Dust Trail Theories, in Proceedings of the International MeteorConference, Frasso Sabino, Italy, 23-26 Sept., 1999, edited by R. Arlt (IMO), pp. 5-21.[11] Arlt R., Krumov V., Buchman A. and Verbert J., WGN, J. Int. Meteor Org., 29(2001) 187.[12] Arlt R., Krumov V., Buchman A., Kac J. and Verbert J., WGN, J. Int. MeteorOrg., 32 (2002) 205.[13] Brown P., WGN, J. Int. Meteor Org., 24 (1996) 139.[14] Arlt R., WGN, J. Int. Meteor Org., 31 (2003) 205.[15] Kaiser T. R., Meteors (Pergamon Press, London) 1955.

The Leonid meteor shower 1996-2002: Results from 

forward-scatter radio observations

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The Leonid meteor shower 1996-2002: Results from forward-scatter radio observations

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