View in EDS

Comparative Dynamics of Substorms and Sawtooth Events.

Saved in:
Bibliographic Details
Title: Comparative Dynamics of Substorms and Sawtooth Events.
Authors: DiMarco, C. C.1,2 (AUTHOR) cdimarco@umich.edu, Pulkkinen, T. I.1 (AUTHOR), McPherron, R. L.3 (AUTHOR), Henderson, M. G.2 (AUTHOR), Gjerloev, J. W.4 (AUTHOR)
Source: Journal of Geophysical Research. Space Physics. Jun2026, Vol. 131 Issue 6, p1-14. 14p.
Subject Terms: *Geomagnetism, *Magnetic storms, Magnetosphere, Solar wind, Magnetospheric physics
Abstract: We present a comprehensive comparative analysis of magnetospheric substorms and sawtooth events using multi‐point observations from ground‐based magnetometers, geostationary satellites, and the Time History of Events and Macroscale Interactions during Substorms mission. Our analysis reveals that despite distinct solar wind driving conditions, with sawtooth events occurring during sustained southward interplanetary magnetic field and elevated proton densities versus more variable conditions for isolated substorms, both phenomena exhibit similar magnetic field dipolarization signatures at 8–10 RE ${R}_{E}$ in the magnetotail. This similarity is consistent with a shared near‐tail reconfiguration process, though it does not uniquely constrain the global onset mechanism or demonstrate that the entire energy release chain is identical across event types. Key differences emerge in the magnetospheric configuration: Sawtooth events maintain persistently stretched field lines at geosynchronous orbit while producing globally distributed and sustained auroral electrojet activity, compared to more dipolar geostationary configurations and clear substorm electrojet phases during isolated substorms. The locally confined midnight‐sector dipolarizations at GEO, concurrent with global particle injections, indicate that drift physics in the stretched field configuration plays a crucial role in azimuthal particle redistribution. We find evidence of a characteristic ∼3‐hr periodicity in both phenomena, whose origin may involve intrinsic magnetotail loading‐unloading timescales, solar wind persistence on comparable scales, or both. Our results imply that sawtooth events represent a storm‐time mode of repetitive substorm activity under continuously driven conditions rather than a fundamentally distinct magnetospheric process. Plain Language Summary: Earth's magnetosphere stores energy from the solar wind and periodically releases it through events called substorms. During major geomagnetic storms, a phenomenon known as a "sawtooth event" sometimes occurs, featuring repetitive bursts of energetic particles every 1–3 hr. There is debate whether sawtooth events are fundamentally different from regular substorms or simply substorms happening in rapid succession. By analyzing hundreds of events using ground‐based magnetometers and spacecraft observations, we found that substorms and sawtooth events produce similar magnetic signatures in Earth's magnetotail, consistent with a shared near‐tail reconfiguration process, and that the key difference lies in their driving conditions. Sawtooth events occur when the solar wind continuously pushes southward magnetic field and dense plasma toward Earth, preventing the magnetosphere from fully recovering between energy releases. Both phenomena exhibit a characteristic three‐hour cycle that appears to be an intrinsic timescale of how Earth's magnetic environment loads and unloads energy. Key Points: Sawtooth intervals are driven by sustained southward interplanetary magnetic field and elevated solar wind densitySawtooth and substorm events show similar dipolarization signatures at 8 to 10 Earth radiiDriving persistence not recurrence alone separates sawtooth behavior from quasi‐periodic substorms [ABSTRACT FROM AUTHOR]
Copyright of Journal of Geophysical Research. Space Physics is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
Database: GreenFILE
Description
Abstract:We present a comprehensive comparative analysis of magnetospheric substorms and sawtooth events using multi‐point observations from ground‐based magnetometers, geostationary satellites, and the Time History of Events and Macroscale Interactions during Substorms mission. Our analysis reveals that despite distinct solar wind driving conditions, with sawtooth events occurring during sustained southward interplanetary magnetic field and elevated proton densities versus more variable conditions for isolated substorms, both phenomena exhibit similar magnetic field dipolarization signatures at 8–10 RE ${R}_{E}$ in the magnetotail. This similarity is consistent with a shared near‐tail reconfiguration process, though it does not uniquely constrain the global onset mechanism or demonstrate that the entire energy release chain is identical across event types. Key differences emerge in the magnetospheric configuration: Sawtooth events maintain persistently stretched field lines at geosynchronous orbit while producing globally distributed and sustained auroral electrojet activity, compared to more dipolar geostationary configurations and clear substorm electrojet phases during isolated substorms. The locally confined midnight‐sector dipolarizations at GEO, concurrent with global particle injections, indicate that drift physics in the stretched field configuration plays a crucial role in azimuthal particle redistribution. We find evidence of a characteristic ∼3‐hr periodicity in both phenomena, whose origin may involve intrinsic magnetotail loading‐unloading timescales, solar wind persistence on comparable scales, or both. Our results imply that sawtooth events represent a storm‐time mode of repetitive substorm activity under continuously driven conditions rather than a fundamentally distinct magnetospheric process. Plain Language Summary: Earth's magnetosphere stores energy from the solar wind and periodically releases it through events called substorms. During major geomagnetic storms, a phenomenon known as a "sawtooth event" sometimes occurs, featuring repetitive bursts of energetic particles every 1–3 hr. There is debate whether sawtooth events are fundamentally different from regular substorms or simply substorms happening in rapid succession. By analyzing hundreds of events using ground‐based magnetometers and spacecraft observations, we found that substorms and sawtooth events produce similar magnetic signatures in Earth's magnetotail, consistent with a shared near‐tail reconfiguration process, and that the key difference lies in their driving conditions. Sawtooth events occur when the solar wind continuously pushes southward magnetic field and dense plasma toward Earth, preventing the magnetosphere from fully recovering between energy releases. Both phenomena exhibit a characteristic three‐hour cycle that appears to be an intrinsic timescale of how Earth's magnetic environment loads and unloads energy. Key Points: Sawtooth intervals are driven by sustained southward interplanetary magnetic field and elevated solar wind densitySawtooth and substorm events show similar dipolarization signatures at 8 to 10 Earth radiiDriving persistence not recurrence alone separates sawtooth behavior from quasi‐periodic substorms [ABSTRACT FROM AUTHOR]
ISSN:21699380
DOI:10.1029/2026JA035415