the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 Oct 2025
Statistical and Temporal Characteristics of Sawtooth Events
Abstract. Magnetospheric sawtooth events are characterized by periodic particle injections and magnetic dipolarizations spread quasi-simultaneously across a wide range of magnetic local times. We present a comprehensive statistical study of magnetospheric sawtooth events (STEs) during solar cycle 24 (2008–2016), extending previous catalogs and enabling solar cycle comparisons. Our results confirm that STEs predominantly occur during the declining phase of the solar cycle and are strongly associated with geomagnetic storms. Superposed epoch analysis reveals near-simultaneous particle injections across all magnetic local time sectors but magnetic field dipolarization confined to the midnight region, supporting a scenario in which nightside tail reconnection and enhanced convection are the primary drivers. The localization of magnetic dipolarizations during STEs challenges global instability interpretations and suggest that STEs represent a stormtime substorm mode triggered under specific magnetotail conditions.
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Status: open (until 08 Dec 2025)
- RC1: 'Comment on egusphere-2025-5118', Anonymous Referee #1, 03 Nov 2025 reply
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RC2: 'Comment on egusphere-2025-5118', Anonymous Referee #2, 10 Nov 2025
reply
The study is very interesting, in particular the detailed analysis of dipolarizations associated with sawtooth oscillations. However, I find conclusions somewhat speculative, especially since the authors did not analyze solar wind and IMF properties/driving in details. There are also some styling issues. Overall, I think the article will be suitable for publication after the Introduction and the Discussion sections are revised/expanded. More specific comments are given below.
Line 20: D.-Y. Lee and his co-authors also noted that there are sawtooth events not associated with periodic solar wind driving. It is reflected, e.g., in the Conclusions section of another article D.-Y. Lee et al., 2006 https://doi.org/10.1029/2006JA011685. It should be reflected here.
The Introduction section is somewhat incomplete. A possible role of ionospheric outflow should be also mentioned, e.g., Brambles et al., https://doi.org/10.1126/science.1202869
Line 75: Looking at Figure 2, it is clear that the occurrence of sawtooth events does peak at the declining phase of Cycle 23. However, this tendency is not seen clearly in Cycle 24, we see the high occurrence also at the growing phase. The authors should clarify the statement.Line 120 - 125: It is surprising that the authors give the definition of sawtooth events in the Discussion section. For clarity, I think the definition should be already discussed in the Introduction.
Line 130-131: Again, the role of oxygen outflow (Brambles et al., 2011) and of kinetic reconnection in the magnetotail (Wang et al., 2022) should be mentioned earlier in the Introduction section.
Line 133-135: While the suggestion of a suppression threshold seems interesting, I find it also somewhat speculative, since the article does not present a detailed analysis of solar wind driving (e.g., a superposed epoch analysis of solar wind / IMF conditions). One could also propose that different types of solar wind regimes (e.g., regimes associated with high speed solar streams) could be responsible, rather than “different levels of external driving”.
Citation: https://doi.org/10.5194/egusphere-2025-5118-RC2
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- 1
Statistical and temporal characteristics of sawtooth events, by DiMarco, Pulkkinen, and Henderson
This paper uses geosynchronous particle fluxes measured by LANL spacecraft to identify sawtooth events (STEs) during solar cycle 24 and compares their occurrence and characteristics with a previous study of STEs during solar cycle 23. Sawtooth events are a poorly understood (and defined) mode of solar wind-magnetosphere coupling, and hence the publication of a new sawtooth event list will be of use to the community. However, the paper is very brief and the analysis is somewhat superficial, though the conclusions are of interest.
The Introduction, Data, and Methodology sections need to be reorganised to better introduce the reader to what a sawtooth event is. For instance, Figure 1 is not properly described, and it is not until the Data section that the nature of the sawtooth in particle fluxes is described. Theories of sawtooth formation are mentioned in the Intro before the reader really knows what a sawtooth is.
One limitation of the analysis is that the authors admit that their list “may not include all of the sawtooth events”. Can they be a bit more specific about that this means, what is the likely number of events that are not included, and how this relates to the previous event list to which theirs is compared.
It might be outside the scope of the present study, but a superposed epoch analysis of the solar wind conditions during the events may have answered some of the open questions raised in the introduction.