Ursids 2025 by worldwide radio meteor observations

By Hiroshi Ogawa

Abstract: Global radio meteor observations caught an unusual activity in 2025. The activity level reached AL=1.1±0.3 at λ_ʘ = 270.38° (December 22, 08^h30^m UT). This activity was possibly mixed with a traditional annual activity and a predicted encounter with a dust filament. The activity was estimated as AL=0.9 at λ_ʘ = 270.38°.

1 Introduction

The Ursids is one of the major annual meteor showers. The shower reaches a maximum with a ZHR = 10 at λ_ʘ = 270.7° in visual observations (Rendtel, 2024). Although it usually shows a weak activity level in ordinary years, some activity outburst caused by dust trails and filaments have been detected in the past.

With radio meteor observations it is possible to obtain a complete activity profile even during bad weather and daytime. Therefore, the International Project for Radio Meteor Observations (IPRMO) has been organized in 2001 to analyze a complete meteor shower activity without any radiant problem (Ogawa et al., 2001). In past research, activity profiles were derived from worldwide radio data from Radio Meteor Observation Bulletin (RMOB).

A long-term study of the Ursids by radio meteor observations has clearly established the annual activity profile. IPRMO concluded that the peak of the Ursids occurred at λ_ʘ = 270.5° with a peak Activity Level Index (AL) of 0.4 using worldwide data during the period of 2004–2024. Radio meteor observations registered also some unusual activities. For example, in recent years enhanced activity was observed twice in 2020 and 2021 (Ogawa and Sugimoto, 2021; 2022). Ogawa and Steyaert (2017) reported outburst activities in 2008, 2009 ,2014 and 2016.

In 2025, some researchers had computed some possible encounters with dust filaments (Rendtel, 2024). This paper reports the result for the Ursids 2025 using worldwide radio meteor observations.

2 Data

Data from 52 observers in 12 countries has been used in this analysis. These data were provided by the following observers who reported to RMOB and Japanese observers:

Johan Bogaerts (Belgium), Chris Steyaert (Belgium), Felix Verbelen (Belgium), Lucas Frederic (France), Philippe Rainard (France), Pierre Heinz (France), Pierre Terrier (France), SAT00 Observatoire_SAT00 (France), Bernd Wallbaum (Germany), Klaus Henning (Germany), WHS Essen (Germany), Istvan Tepliczky (Hungary), Observatory Szeged (Hungary), Vilmos Keresztesi (Hungary), GABB .IT (Italy), Licei Lunigianesi (Italy), APA Latina (Italy), Mario Bombardini (Italy), Hirofumi Sugimoto (Japan), Hironobu Shida (Japan), Hiroshi Suzuki (Japan), Kenji Fujito (Japan), Koichiro Okuno (Japan), Mai Wakita (Japan), Masahiko Matsuda (Japan), Masaki Kano (Japan), Masaki Tsuboi (Japan), Nobuo Katsura (Japan), Norihiro Nakamura (Japan), Yasufumi Yoshikawa (Japan), Jean-Claude Thibaut (Luxembourg), Aguirre Salvador (Mexico), Michal Biernacki (Poland), MAR JEN (Poland), Joan Figueras (Spain), Jochen Richert (Switzerland), Philip Norton (United Kingdom), Philip Norton Vert (United Kingdom), Philip Rourke (United Kingdom), Stephen Grimes (United Kingdom), Mike Otte (United States of America), Stanley Nelson (United States of America).

3 Method

The meteor activity is calculated by the “Activity Level Index: AL(t)” (Ogawa et al., 2001) to analyze the worldwide radio meteor observation data. The activity profile was estimated using the Lorentz activity profile (Jenniskens et al., 2000).

4 Results

Figure 1 shows the result of the Activity Level Index. A clear peak was observed at λ_ʘ = 270.38° (December 22, 8^h30^m UT) with AL = 1.1 ± 0.3. The beginning of increase was around λ_ʘ = 270.25° (December 22, 5^h00^m UT). After that, the activity level dropped back to the level of the annual activity profile (gray line in Figure 1) around λ_ʘ = 270.5° (December 22, 11^h00^m UT).

The activity level AL of the Ursids 2025 displays two estimated components using the Lorentz profile (Figure 2 and Table 1). One component corresponds to the traditional annual activity. The peak occurred at λ_ʘ = 270.47° (December 22, 10^h30^m UT). This is a similar result as in ordinary years (λ_ʘ = 270.5°).

The other component indicates an unusual activity that has AL = 0.9 at λ_ʘ = 270.38° (December 22, 08^h30^m UT). The Full Width of Half Maximum (FWHM) has a –2.0 hours and + 1.5 hours.

 

5 Discussion

Table 1 compares the estimated components by IPRMO and published information. Comp.1 in Figure 2 was the same result as the traditional annual activity by IPRMO. However, it requires discussion to explain Comp.2.

Table 1 – Comparison between the estimated components by IPRMO and the predictions.

Source	λʘ (max)	Activity	Comments
Comp.1	270.47°	AL = 0.3	–
Comp.2	270.38°	AL = 0.9	–
IPRMO	270.5°	AL = 0.4	ave.(2004–2024)
IMO	270.7°	ZHR 10	traditional activity
Jenniskens	270.26°	ZHR 25	filament
Vaubaillon	270.7°	–	densest section

Jenniskens (2006) described a possible encounter with the filament at λ_ʘ = 270.26°. However, the densest section was indicated by Vaubaillon at λ_ʘ = 270.7° (Table 1). The peak time of Comp.2 was slightly earlier than Vaubaillon, but slightly later than Jenniskens. The Activity Level was about three times higher, which was close to the ZHR given by Jenniskens. Therefore, it is possible that the encounter with the filament predicted by Jenniskens occurred later than predicted.

6 Conclusion

The worldwide radio meteor observers caught an unusual activity around λ_ʘ =270.38° for the Ursids in 2025. The Activity Level reached AL = 0.9. It is possible that this activity was caused by the encounter with a dust filament.

Acknowledgment

The worldwide data were provided by the Radio Meteor Observation Bulletin (RMOB).

We wish to thank Pierre Terrier for developing and hosting rmob.org. A very special thank you to Paul Roggemans for proofreading this article.

References

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