By Hiroshi Ogawa and Hirofumi Sugimoto
Abstract: Worldwide Radio Meteor Observations recorded an Ursid outburst in 2020. The Ursid activity profile indicated the presence of two components. One was the annual activity; the other was an outburst activity. The outburst peak time occurred at λʘ = 270.45° to 270.55° with an estimated ZHR of around 40. Besides, the detailed activity structure became clear by using Japanese observed data in time bins of 10 minutes.
1. Introduction
The Ursid meteor stream is one of the major showers at the end of the year in the month of December. For 2020, there were some dust trail encounters predicted based on the calculations by J. Vaubaillon, P. Jenniskens, E. Lyytinen and M. Sato for the period of December 22 03h – 22h(UT). (Rendtel, 2019).
Worldwide radio meteor observation data were provided by the Radio Meteor Observation Bulletin (RMOB) (Steyaert, 1993) and by the radio meteor observations network in Japan (Ogawa et al., 2001). Radio meteor observations are possible even with bad weather and during daytime.
2. Method
For analyzing the worldwide radio meteor observation data, meteor activities are calculated by the “Activity Level” index (Ogawa et al., 2001). The activity profile was estimated by the Lorentz activity profile (Jenniskens, 2000). Besides of this analysis, also the Zenithal Hourly Rates were estimated (Sugimoto, 2017).
3. Results
3.1. Actitivy Level index
Figure 1 shows the result for the Ursids 2020 based on the calculations with the Activity Level Index. The line represents the average for the period for 2004–2019. The outburst was very distinct compared with past returns. The maximum activity level was estimated 0.8 ± 0.2 at λʘ = 270.54° (December 22, 5h UT). The enhanced activity began at 270.29° (December 21, 23h UT) and ended at 270.97° (December 22, 15h UT). Table 1 shows the results around the peak value.
Figure 1 Activity Level Index by radio meteor observations all over the world (the line is the average of the period for 2004–2019).
Table 1 – The Activity Level Index around the peak time.
| Date(UT) | λʘ | Activity Level |
|---|---|---|
| Dec.21 21h00m-22h00m | 270.204 | 0.1±0.2 |
| Dec.21 22h00m-23h00m | 270.246 | 0.1±0.2 |
| Dec.21 23h00m-24h00m | 270.288 | 0.4±0.2 |
| Dec.22 00h00m-01h00m | 270.331 | 0.4±0.2 |
| Dec.22 01h00m-02h00m | 270.373 | 0.6±0.2 |
| Dec.22 02h00m-03h00m | 270.416 | 0.4±0.2 |
| Dec.22 03h00m-04h00m | 270.458 | 0.8±0.3 |
| Dec.22 04h00m-05h00m | 270.501 | 0.7±0.3 |
| Dec.22 05h00m-06h00m | 270.543 | 0.8±0.2 |
| Dec.22 06h00m-07h00m | 270.586 | 0.5±0.3 |
| Dec.22 07h00m-08h00m | 270.628 | 0.5±0.2 |
| Dec.22 08h00m-09h00m | 270.670 | 0.6±0.2 |
| Dec.22 09h00m-10h00m | 270.713 | 0.4±0.2 |
| Dec.22 10h00m-11h00m | 270.755 | 0.7±0.2 |
| Dec.22 11h00m-12h00m | 270.798 | 0.4±0.2 |
| Dec.22 12h00m-13h00m | 270.840 | 0.3±0.1 |
| Dec.22 13h00m-14h00m | 270.883 | 0.2±0.2 |
| Dec.22 14h00m-15h00m | 270.925 | 0.2±0.2 |
| Dec.22 15h00m-16h00m | 270.967 | 0.1±0.2 |
| Dec.22 16h00m-17h00m | 271.010 | 0.0±0.1 |
Figure 2 shows the detailed Ursids 2020 activity structure with the two components separated using the Lorentz activity profile (Jenniskens, 2000). One component (Comp. 1) has its peak activity level as 0.5 at λʘ = 270.67° (December 22, 8h UT) with full width half maximum (FWHM) –6.0 / +4.5 hours. The other component (Comp. 2) reached 0.5 activity level at λʘ = 270.46° (December 22, 3h UT) with full width half maximum (FWHM) –2.5 / +2.0 hours (see Table 2). Comp. 1 is possibility the equivalent of the annual activity (average of the period for 2004–2019: activity level = 0.4 at λʘ = 270.60° (Ogawa and Steyaert, 2017)). Comp. 2 may be the outburst component in 2020.
Figure 2 – Estimated components using the Lorentz profile. (the curve with triangles means Comp. 1, the curve with the circles is Comp. 2. The black line represents Comp. 1 and Comp. 2 combined. The circles with error margins are the Ursids observed in 2020).
Table 2 – The estimated components of the Ursids 2020.
| Component | maximum time | λʘ | Activity Level | FWHM (hours) |
|---|---|---|---|---|
| Comp. 1 | Dec. 22nd 8h UT | 270.67° | 0.5 | -6.0 / +4.5 |
| Comp. 2 | Dec. 22nd 3h UT | 270.46° | 0.5 | -6.0 / +4.5 |
3.2. Estimated ZHR_r
Besides the activity level index analysis, also the Zential Hourly Rate (ZHRr) was estimated by using the Radio Meteor Observations (Figure 3). Peak times occurred at December 22, 3h (λʘ = 270.46°), 5h (λʘ = 270.54°) and 7h to 8h (λʘ = 270.63° to 270.67°) similar to the Activity Level Index results. The estimated ZHRr were 37 ± 2, 39 ± 3 and 23 ± 3.
Figure 3 – The estimated ZHRr obtained from the Woldwide radio meteor observations.
In order to visualize the detailed activity structure, we calculated the values in 10 minutes time bins by using the radio meteor observations from Japan only (Figure 4). This is because the Japanese observers record their data counted in 10 minutes time bins. The double outbursts were detected at λʘ = 270.476° (December 22, 03h50m to 04h00m UT) and λʘ = 270.561° (December 22, 05h50m to 06h00m UT). The ZHRr values were estimated as 66 ± 15 and 66 ± 10.
Figure 4 – Estimated ZHRr every 10 minutes (using only Japanese observational data).
Acknowledgment
The Ursids 2020 data were provided by the following observers:
The Ursids 2020 data were provided by the following observers: AAV Planetario_di_Venezia (Italy), Balogh Laszlo (Hungary), Bill Ward (UK), Chris Steyaert (Belgium), Daniel D SAT01_DD (France), Fabio Moschini _IN3GOO (Italy), Felix Verbelen (Belgium), GAML Osservatorio_Astronomico_Gorga (Italy), Hirofumi Sugimoto (Japan), Hironobu Shida (Japan), Hirotaka Otsuka (Japan), Ian Evans (UK), Istvan Tepliczky (Hungary), Jean Marie F5CMQ (France), Jochen Richert (Switzerland), Jose Carballada (Spain), Juan Zapata (Mexico), Karlovsky Hlohovec_Observatory (Slovakia), Kees Meteor (Netherlands), Kenji Fujito (Japan), Mario Bombardini (Italy), Masaki Kano (Japan), Masaki Tsuboi (Japan), Maurizio Morini _IU2JWG (Italy), Mike Otte (USA), Nobuo Katsura (Japan), Per DL0SHF (Germany), Philip Norton (UK), Philip Rourke (UK), Rafael Martinez (Puerto Rico), Rainer Ehlert (Mexico), Ronda Ronda (Spain), Salvador Aguirre (Mexico), Stan Nelson (USA), Tomohiro Nakamura (Japan), Tracey Snelus (UK), WHS Essen (Germany).
The worldwide data were provided by the Radio Meteor Observation Bulletin (RMOB) (http://www.rmob.org/).
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