the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 15 Jun 2026
Bursty bulk flow ionospheric impacts from triple-conjunctive observations
Abstract. Substorms are the regular reconfiguration of the Earth's geomagnetic space environment, and magnetosphere-ionosphere coupling is integral to the substorm chain. Bursty bulk flows (BBFs) are mesoscale fast plasma flows that are released from magnetic reconnection sites in the magnetotail during substorms, and they couple to the ionosphere through field aligned current (FAC) systems. BBFs may drive localised changes to the ionospheric plasma, such as velocity flows or changes to the local temperature, density and conductivity, but determining the specific ionospheric effects of a given BBF and their associated FAC is a complex undertaking. In this study we identify triple-conjugate observations of BBF detections within the magnetotail, FAC observations in low Earth orbit and ground-based radar stations that observe the local ionospheric plasma in order to evaluate the different components of the coupled BBF-FAC-ionosphere system. We evaluate over 11000 BBFs and identify only 13 events that satisfy our conjunctive criteria. We perform detailed analysis of one of these BBFs, which occurred in the recovery phase of a relatively weak substorm, to evaluate the FAC associated with this BBF and its ionospheric impacts. Multiple FAC signatures were observed that are associated with the BBF, in addition to variations in the ionospheric velocity and temperature. There is an ongoing need for coordinated observations of the coupled BBF-FAC-ionosphere system to further distinguish the ionospheric impacts of BBFs from broader substorm dynamics.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-3108', Anonymous Referee #1, 31 Jul 2026
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RC2: 'Comment on egusphere-2026-3108', Anonymous Referee #2, 06 Sep 2026
This manuscript presents a valuable multi-instrument case study combining THEMIS, Swarm, PFISR, and auroral observations to investigate the possible ionospheric signatures of a BBF. The coordinated dataset is interesting and potentially useful for improving our understanding of magnetosphere-ionosphere coupling. However, several interpretations are currently stated with greater certainty than is supported by the reported temporal and spatial correspondence, particularly regarding the association of the Swarm FAC signatures and the transient auroral feature with the specific BBF. The novelty claim should also be more carefully qualified in light of closely related studies, and several inconsistencies in the event count, plasma-density description, figures, and terminology should be corrected. I recommend publication after minor revision.
One general omission which could be considered concerns key work by Wei et al. This and some related references ought to be included and addressed in the Introduction. I mention a couple below which I am sure the authors are aware of…
Wei, D., W. Dunlop, J-Y. Yang, X-C. Dong, Y.-Q Yu, T-Y. Wang (2021), Intense dB/dt variations driven by near-Earth Bursty Bulk Flows (BBFs): A case study, Geophys. Res. Letts, doi:10.1029/2020GL091781.
Zhang, C-M., M. W. Dunlop, -Y. Yang, X. Tan, O. Marghitu, A. Blagau, C. Xiong, X-C. Dong, D. Wei, V. Constantinescu, G Kervalishvili (2026), Joint Analysis with Swarm and Ground Stations: Ionospheric Current System and Geomagnetically Induced Currents, J, Geophys. Res., http://dx.doi.org/10.1029/2025JA034698.
1. Line 347: "There is a decrease in Ne at altitude of 150 - 200 km..."Line 390-391: "An increase in electron density and velocity flow reversal was observed during and shortly after the BBF observation by THEMIS."
There is a direct contradiction of 'decrease/increase' in the interpretation of Figure 6. Please verify the data and correct the text.
2. A Bz enhancement and plasma density compression may provide useful signatures of a dipolarization front associated with a BBF. It will be good to compare these data of THEMIS-A and -E during the BBF to additionally assess whether they observe the same BBF structure.
3. . Line 310-311: "In panels b-f of Figure 5, a transient auroral brightening develops around magnetic latitude of 71°, near the north Alaskan coastline, and propagates westward before disappearing."
Line 313-315: "This auroral feature began before the THEMIS BBF detection and maps poleward of the THEMIS magnetic footpoints, so it is possible that this may be an auroral streamer that was driven by the BBF when it was located further away in the magnetotail, before it encountered the THEMIS satellites."
Line 315-317: "The THEMIS BBF observations show a significant −vy component (Fig. 2a, b) which would correspond to eastward motion of the BBFs ionospheric footpoint and associated auroral streamer for this event, rather than the more common north-south alignment of auroral streamers."
The transient auroral feature is described as propagating westward and is subsequently interpreted as a possible BBF-driven streamer. However, THEMIS observed a −vy component corresponding to eastward motion of the BBF footprint and its associated streamer. Please explain the opposite propagation directions.
4. Line 11: "Multiple FAC signatures were observed that are associated with the BBF, ..."
Line 365-366: "..., the FAC associated with that BBF in low Earth orbit, ..."
The expression 'associated with' should be substantially toned down here. The conclusions appropriately state that the FAC structures 'may be associated' with the BBF and that separating BBF-driven ionospheric variations from the broader substorm dynamics remains an open question. The degree of certainty should be consistent across the abstract, discussion, and conclusions.
5. Line 62-63: "..., the first time that the three distinct components of this coupled system have been analysed with observational data for the same event."
Line 373-374: "This analysis represents the first time that the three distinct components of the coupled BBF-FAC-ionosphere system have been analysed using observational data during the same event."
One of the BBF intervals in Lanabere et al. (2026) titled "Ionospheric currents and auroral signatures during successive earthward bursty bulk flows and dipolarization: a 7 December 2023 case study" is also a study on BBF-FAC-ionosphere system. There are other similar cases like Wei et al. (2021) titled "Intense dB/dt Variations Driven by Near-Earth Bursty Bulk Flows (BBFs): A Case Study" and Zhang et al. (2026) titled "Joint Analysis With Swarm and Ground Stations: Ionospheric Current System and Geomagnetically Induced Currents". The authors should substantially qualify the 'first time' claim and specify precisely which scientific finding is reported here for the first time.
6. The two entries on Nov 03 2023 in Table A1 share nearly identical observation intervals. Please confirm if they may represent multi-spacecraft detections of the same physical BBF. If so, they should be combined into a single item. The two Nov 11 2023 entries have the same issue. Please note that this also affects the reported count of 13 events in Line 9, 368 and 406.
7. Line 378-379: "..., although the overpass occurred slightly later than the estimated propagation time..."
The expression 'slightly later' should be substantially toned down here. The Swarm-B FAC signature was observed approximately 6-9 min after the THEMIS-A BBF detection, about one order of magnitude longer than the estimated 46 s propagation time.
8. Please add a colour bar to Figures 5 and B2 and clarify whether a common intensity scale is used across all panels. If each panel is normalized independently, this should be stated explicitly.
9. Please make the following corrections:
Line 51: 'equivilant' -> 'equivalent'
Line 96: 'phase-array' -> 'phased-array'
Line 116: 'Kenia' -> 'Kenai'
Line 331: 'PSFIR' -> 'PFISR'
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Citation: https://doi.org/10.5194/egusphere-2026-3108-RC2
Data sets
Conjunctions: BBF-radar and Swarm-radar H. George, A. P. Dimmock, V. Lanabare, H. Vanhamaki, I. Virtanen, and A. Aikio https://doi.org/10.5281/zenodo.20448703
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Bursty bulk flow ionospheric impacts from triple-conjunctive observations
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George et al.
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This study combines observations from THEMIS, Swarm, the Poker Flat incoherent scatter radar, a co-located all-sky camera, and ground magnetometer stations to study the ionospheric signatures of a bursty bulk flow. Due to the requirement to have conjunctions between so many instruments, very few suitable events were found, and only one was studied in detail. The observations show that it is difficult to determine a one-to-one correspondence between the BBF observed in the tail by THEMIS and ionospheric signatures; rather, the large-scale response of the magnetosphere/ionosphere to the substorm dominates the measurements. Despite this, the paper is a useful and interesting addition to the literature on BBFs and I recommend it for publication in Annales Geophysicae. I have only a minor comment, which is that it would be useful if the paper gave some more emphasis to the MLT of the BBF footprint. This is, I believe, in the dawn sector, so away from the typical onset region of substorms