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the Creative Commons Attribution 4.0 License.
| 28 Apr 2025
Magnetospheric convection in a hybrid-Vlasov simulation
Abstract. The Dungey cycle is a fundamental process governing large-scale plasma dynamics in the near-Earth space, traditionally examined through Magnetohydrodynamic (MHD) simulations and ionospheric observations. However, MHD models often oversimplify the complexities of driving dynamics and kinetic processes, while observational data tend to lack sufficient coverage. In this study, we utilize a hybrid-Vlasov simulation to investigate the Dungey cycle, and introduce a novel method for quantifying reconnection rates in different Magnetic Local Time (MLT) sectors. This method is validated by comparing it with the ionospheric open flux change rate in the simulation. Our analysis identifies azimuthal convection channels on the dawn and dusk flanks during the simulation run, modulated by dayside reconnection events. Notably, we observe that the effective length of dayside reconnection fluctuates, even under steady solar wind conditions. Our results reveal significant deviations from MHD theory, which predicts that plasma flows within the magnetosphere should follow flux tube entropy isocontours. Instead, we demonstrate that plasma flows near reconnection sites and at the terminators exhibit more intricate patterns, deviating from earlier results. This study validates the representation of the Dungey cycle in the Vlasiator 3D simulation and enhances our understanding of global plasma convection. Future work should focus on identifying the kinetic processes that explain the deviations in the plasma convection with flux tube entropy isocontours between MHD theory and kinetic approach.
Competing interests: Some authors are members of the editorial board of Annales Geophysicae.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.- Preprint
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RC1: 'Comment on egusphere-2025-1340', Lei Dai, 01 May 2025
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Review of “Magnetospheric convection in a hybrid-Vlasov simulation” by Shi et al.
This paper presents a detailed and compelling study of magnetospheric convection using a global hybrid-Vlasov simulation. Magnetospheric convection (mainly dominated by ions) is a fundamental process in understanding large-scale magnetospheric dynamics, and this work makes a significant contribution from the global-scale ion-kinetic approach. The authors validate their method for calculating reconnection rates, and then proceed to characterize the overall convection pattern and its connection to both dayside and nightside reconnection processes. The results are solid and novel, demonstrating the capability of ion-kinetic Vlasov simulations to capture key aspects of global magnetospheric evolution. I recommend this manuscript for publication and look forward to future studies on this subject from hybrid-Vlasov simulations.
Specific comments:
1. Line 21: The phrase “between two neutral points” . I think this means between the dayside neutral lines (X-line) and nightside neutral lines (X-line). Most field lines are not reconnected at the sub-solar point.
2. Lines 33–34: The statement “The whole convection process typically lasts on a timescale of approximately one hour”. A full convection cycle usually spans 2–5 hours. The 1-hour timescale is more representative of the magnetotail’s response time (Kennel, 1996).
Reference:
Kennel, C. F. Convection and Substorms – Paradigms of Magnetospheric Phenomenology, Vol. 2, Oxford University Press, 1996.3. Lines 54–56: Suggested revision:“Dai et al (2024) presents compelling evidence of dayside-driven convection in Keogram in MHD simulations, along with ionospheric observations. This type of convection is shown to establish within 10–20 minutes across the magnetosphere. Furthermore, they argued that this type of convection is related to the equatorward and dayside-to-nightside extending of field-aligned currents (FACs), emphasizing its relation to ionospheric dynamics (Zhu et al.,2024).”
References:
Zhu, M. et al. (2024). Journal of Geophysical Research: Space Physics, 129, e2024JA032607. https://doi.org/10.1029/2024JA0326074. Line 98: If the analysis is restricted to the closed field line region, the green segment in the schematic should be drawn closer to Earth to reflect this specification.
5. Lines 112–113: The sentence could be clarified. Suggested revision:
“The radial (r) component of the electric field corresponds to clockwise convection, while the theta component of the electric field corresponds to outward convection.”6. Equation (1) and Line 115: It would be helpful to expand on why this method of estimating the reconnection rate was chosen over direct calculation along the X-line. As mentioned in Line 65, accurately determining the reconnection electric field near the diffusion region can be challenging in global simulations, which may justify the chosen approach.
7. Lines 133–134: Specify the relevant time interval more clearly. The increase in closed magnetic flux is most evident between 800 and 1200 seconds, consistent with Figure 4, which shows that nightside reconnection dominates during this interval.
8. Lines 151–152: Convection generally converges near MLT = 0 and diverges around MLT = 12. Therefore, the average convection at these location should be close to zero. In simulations, the location of the converge point and diverge point may deviate a little. This causes the fluctuation of azimuthal convection in the simulations.
9. Lines 158–160: Given the ion-kinetic nature of the simulation, it would be worthwhile for future studies to examine the Hall electric fields or ion kinetic signatures, such as off-diagonal components of the ion pressure tensor, in the magnetotail reconnection region.
10. Line 202: Consider revising “convection events” to “convection channels.” Figure 6 suggests that convection near midnight is directly triggered by nightside reconnection.
11. Lines 205–206: The sentence about minimal sunward convection is unclear. Which figure supports this? And minimal with respect to what? If the statement cannot be clarified, it may be better to remove it.
12. Line 245–246: You might reference this observational work showing that dayside reconnection is directly influenced by IMF fluctuations, as in Dai et al. (2023):
Reference:
Dai, L. et al. (2023). Geoeffectiveness of Interplanetary Alfvén waves: I. Magnetopause Magnetic Reconnection and Directly-Driven Substorms. The Astrophysical Journal, 945(1), 47. https://doi.org/10.3847/1538-4357/acb26713. Lines 255–256: The findings in Figure 6 are novel and merit stronger emphasis in the abstract. Suggested addition:
“Our analysis identifies discrete azimuthal convection channels of closed field lines, clearly initiated by dayside reconnection and propagating to the nightside. These channels are even prominent during intervals of intense nightside reconnection.”14. Line 263-265, Line 10-11. The discussion in the Line 265 are more specific and could be included for abstract. “plasma flows near reconnection sites and at the terminators deviates from isentropic behavior, suggesting the presence of non-adiabatic processes in these regions.”
15. Line 275: The 20-second cycle lacks direct support from the presented data. While potentially interesting for future research, it appears speculative in the current study.
Citation: https://doi.org/10.5194/egusphere-2025-1340-RC1
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