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Liu, T., Pitkänen, T., Nilsson, S., Kullen, A., Park, J.-S., Hamrin, M., . . . Yao, S. (2025). IMF By influence on fast earthward convection flows in the near-lunar magnetotail. Geoscience Letters, 12(1), Article ID 6.
Open this publication in new window or tab >>IMF By influence on fast earthward convection flows in the near-lunar magnetotail
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2025 (English)In: Geoscience Letters, E-ISSN 2196-4092, Vol. 12, no 1, article id 6Article in journal (Refereed) Published
Abstract [en]

This study investigates the effects of non-zero IMF By on the magnetotail By and fast earthward ion convection (V⊥ > 200 km/s, "⊥" indicates perpendicular to the magnetic field) in the near-lunar magnetotail plasma sheet using the plasma parameters and magnetic field detected by the ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon’s Interaction with the Sun) P1 satellite during the period 2011–2022. We find that the magnetotail By with in the same direction as IMF By dominates the entire region. The IMF By influence is hemisphere-independent, but shows a dusk-dawn asymmetry with the IMF By effect being weaker in the premidnight region than in the postmidnight region. We also find that the IMF By influence on earthward fast convection results in an interhemispheric flow asymmetry and it is highly correlated with the direction of magnetotail By. The statistical results indicate that occasionally localized dynamics can have a significant effect on magnetotail By and V⊥.

Place, publisher, year, edition, pages
Springer Nature, 2025
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-236199 (URN)10.1186/s40562-025-00379-5 (DOI)001416326700001 ()2-s2.0-85218493500 (Scopus ID)
Available from: 2025-03-17 Created: 2025-03-17 Last updated: 2025-03-17Bibliographically approved
Pitkänen, T., Kullen, A. & Chong, G. S. (2024). Importance of the dusk-dawn interplanetary magnetic field component (IMF By) to magnetospheric convection in Earth's magnetotail plasma sheet. Frontiers in Astronomy and Space Sciences, 11, Article ID 1373249.
Open this publication in new window or tab >>Importance of the dusk-dawn interplanetary magnetic field component (IMF By) to magnetospheric convection in Earth's magnetotail plasma sheet
2024 (English)In: Frontiers in Astronomy and Space Sciences, E-ISSN 2296-987X, Vol. 11, article id 1373249Article, review/survey (Refereed) Published
Abstract [en]

The solar wind and its embedded magnetic field, the interplanetary magnetic field (IMF) together with magnetic reconnection power the large-scale plasma and magnetic flux circulation in the Earth's magnetosphere-ionosphere system. This circulation is termed as convection and its strength is controlled by the north-south IMF component (IMF Bz). In recent years, an interest has arisen to investigate the lesser-known role of the dusk-dawn component (IMF By) in convection. It has been previously known though that prevailing nonzero IMF By can cause plasma flow asymmetries in the high-latitude ionosphere, but how the magnetospheric flows, for instance, in the magnetotail plasma sheet are affected, remains to be investigated. In this article, we introduce the recent progress and the latest achievements in the research of the influence of IMF By on tail plasma sheet convection. The research progress has been rapid and it has revealed that both fast and slow convection are affected in a manner that is in accordance with the asymmetries observed in the ionospheric convection. The results indicate the significance of the IMF By component on magnetospheric convection and they represent a major advance in the field of solar wind-magnetosphere coupling.

Place, publisher, year, edition, pages
Frontiers Media S.A., 2024
Keywords
interhemispheric asymmetry, interplanetary magnetic field, magnetospheric convection, magnetotail, plasma sheet, solar wind-magnetosphere coupling
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-222864 (URN)10.3389/fspas.2024.1373249 (DOI)001182354300001 ()2-s2.0-85187893856 (Scopus ID)
Available from: 2024-04-15 Created: 2024-04-15 Last updated: 2024-04-18Bibliographically approved
Wang, M., Liu, T. Z., Zhang, H., Liu, K., Shi, Q., Guo, R., . . . Liu, Y. (2024). Statistical analysis of whistler precursors upstream of foreshock transient shocks: MMS observations. Geophysical Research Letters, 51(8), Article ID e2023GL105617.
Open this publication in new window or tab >>Statistical analysis of whistler precursors upstream of foreshock transient shocks: MMS observations
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2024 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 51, no 8, article id e2023GL105617Article in journal (Refereed) Published
Abstract [en]

Using the high-time-resolution data from the Magnetospheric Multiscale mission, precursor waves upstream of foreshock transient (FT) shocks are statistically investigated using the four-spacecraft timing method. The wave frequencies and wave vectors determined in the plasma rest frame (PRF) are shown to follow the cold plasma dispersion relation for whistler waves. Combining with the feature of the right-hand polarization in the PRF, the precursors are identified as whistler-mode waves around the lower hybrid frequency. The occurrence of whistler precursors is independent of the Alfvén Mach number and the FT shock normal angle. More importantly, all the whistler precursors have group velocities pointing upstream in the shock frame, suggesting the dispersive radiation to be a possible generation mechanism. The study improves the understanding of not only the whistler precursors but also the overall FT shock dynamics.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2024
National Category
Astronomy, Astrophysics and Cosmology Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-224079 (URN)10.1029/2023GL105617 (DOI)001206327700001 ()2-s2.0-85191083510 (Scopus ID)
Available from: 2024-05-16 Created: 2024-05-16 Last updated: 2024-05-16Bibliographically approved
Park, J.-S., Shi, Q. Q., Troshichev, O. A., Kim, K.-H., Shue, J.-H., Pitkänen, T. & Zhang, H. (2024). Statistical features of polar cap North and South indices in response to interplanetary and terrestrial conditions: a revisit. Space Weather: The International Journal of Research and Application, 22(4), Article ID e2024SW003856.
Open this publication in new window or tab >>Statistical features of polar cap North and South indices in response to interplanetary and terrestrial conditions: a revisit
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2024 (English)In: Space Weather: The International Journal of Research and Application, E-ISSN 1542-7390, Vol. 22, no 4, article id e2024SW003856Article in journal (Refereed) Published
Abstract [en]

In this study, we investigate statistical features of polar cap north (PCN) and south (PCS) indices in response to various interplanetary conditions (interplanetary magnetic field [IMF] orientation in three-dimensions) and terrestrial conditions (seasonal and magnetic local time [MLT] locations of the index stations). The concurrent PCN-PCS pairs for 1998–2002 and 2004–2018 are divided based on their sign type (positive-positive, negative-negative, negative-positive, and positive-negative PCN-PCS pairs) and time coverage (the times when both index stations are in the dawn/dusk MLT sector during northern summer/winter). Analyzing the IMF orientation dependence on the occurrence probabilities of concurrent indices and on the differences between the indices in various sign types for each time coverage reveals that the statistical features in PCN-PCS pairs obtained in the dawn MLT sector can be largely explained by the effects of the three-component IMF (related to the polar cap convection patterns) combined with season (related to the hemispheric asymmetry in solar illumination-induced ionospheric conductance). However, those obtained in the dusk MLT sector are controlled dominantly by seasonal effects rather than IMF orientation effects. Our findings indicate that PCN-PCS pair data provide local views about the solar wind-magnetosphere-ionosphere (SW-M-I) coupling system with different control efficiencies of IMF orientation and season depending on the MLT location of the stations. Therefore, introducing polar cap indices recorded simultaneously at various locations in both hemispheres and analyzing them are strongly required to infer global views of the coupled SW-M-I system in the open field regions with higher confidence.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2024
Keywords
IMF orientation, ionospheric conductivity, polar cap indices, solar wind-magnetosphere-ionosphere coupling
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-223940 (URN)10.1029/2024SW003856 (DOI)001207501500001 ()2-s2.0-85191192551 (Scopus ID)
Funder
Swedish National Space Board, 118/17
Available from: 2024-05-03 Created: 2024-05-03 Last updated: 2025-04-24Bibliographically approved
Park, J.-S., Shi, Q. Q., Shue, J.-H., Degeling, A. W., Nowada, M., Tian, A. M., . . . Gjerloev, J. W. (2023). Auroral electrojet activity for long-duration radial interplanetary magnetic field events. Journal of Geophysical Research - Space Physics, 128(3), Article ID e2022JA030816.
Open this publication in new window or tab >>Auroral electrojet activity for long-duration radial interplanetary magnetic field events
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2023 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 128, no 3, article id e2022JA030816Article in journal (Refereed) Published
Abstract [en]

In this paper, we provide statistical evidence that the level of solar wind-magnetosphere-ionosphere (SW-M-I) coupling is weaker under radial (Sun-Earth component dominant) interplanetary magnetic field (IMF) conditions than non-radial IMF conditions. This is performed by analyzing auroral electrojet activity (using SuperMAG auroral electrojet indices) in the sunlit and dark ionospheres for long-duration (at least 4 hr) radial IMF events and comparing against the same for long-duration azimuthal (dusk-dawn component dominant) IMF events. We show that the north-south IMF component (IMF Bz) plays a crucial role in controlling the level of auroral electrojet activity as a negative half-wave rectifier even for both IMF orientation categories. However, it is found that the magnitudes of the auroral electrojet indices are generally lower for radial IMF than for azimuthal IMF under similar sets of solar wind (radial bulk velocity and number density) and IMF Bz conditions, regardless of whether these indices are derived in the sunlit or dark regions. Moreover, the efficiency of coupling functions is lower for radial IMF than for azimuthal IMF, implying that increased coupling strength due to the azimuthal IMF component alone cannot well explain weaker auroral electrojets during radial IMF periods. Lastly, the contribution of the radial IMF component itself to auroral electrojet activity is also lower compared to the azimuthal IMF component. Our results suggest that the level of SW-M-I coupling characterized by auroral electrojet activity can be modulated by the radial IMF component, although the effect of this component is weaker than the other two IMF components.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2023
Keywords
auroral electrojet activity, azimuthal IMF, north-south IMF component, radial IMF, solar wind parameters, solar wind-magnetosphere-ionosphere coupling
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-206935 (URN)10.1029/2022JA030816 (DOI)000944253500001 ()2-s2.0-85152391401 (Scopus ID)
Funder
Swedish National Space Board, 118/17
Available from: 2023-04-28 Created: 2023-04-28 Last updated: 2023-04-28Bibliographically approved
Pitkänen, T., Chong, G. S., Hamrin, M., Kullen, A., Vanhamäki, H., Park, J.-S., . . . Krämer, E. (2023). Fast Earthward Convection in the Magnetotail and Nonzero IMF By: MMS Statistics. Journal of Geophysical Research - Space Physics, 128(12), Article ID e2023JA031593.
Open this publication in new window or tab >>Fast Earthward Convection in the Magnetotail and Nonzero IMF By: MMS Statistics
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2023 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 128, no 12, article id e2023JA031593Article in journal (Refereed) Published
Abstract [en]

We statistically investigate convective earthward fast flows using data measured by the Magnetospheric Multiscale mission in the tail plasma sheet during 2017–2021. We focus on “frozen in” fast flows and investigate the importance of different electric field components in the Sun-Earth (V⊥x) and dusk-dawn (V⊥y) velocity components perpendicular to the magnetic field. We find that a majority of the fast flow events (52% of 429) have the north-south electric field component (Ez) as the most relevant or dominating component whereas 26% are so-called conventional type fast flows with Ey and Ex as the relevant components. The rest of the flow events, 22%, fall into the two ’mixed’ categories, of which almost all these fast flows, 20% of 429, have Ey and Ez important for V⊥x and V⊥y, respectively. There is no Y-location preference for any type of the fast flows. The conventional fast flows are detected rather close to the neutral sheet whereas the other types can be measured farther away. Typical total speeds are highest in the mixed category. Typical perpendicular speeds are comparably high in the conventional and mixed categories. The slowest fast flows are measured in the Ez category. Most of the fast flow events are measured in the substorm recovery phase. Prevailing interplanetary magnetic field By conditions influence the V⊥y direction and the influence is most efficient for the Ez-dominated fast flows.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2023
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:umu:diva-218880 (URN)10.1029/2023JA031593 (DOI)001130317300001 ()2-s2.0-85180501515 (Scopus ID)
Funder
Swedish National Space Board, 118/17Swedish National Space Board, 271/14Swedish National Space Board, 194/19Swedish National Space Board, 81/17Swedish Research Council, 2018-03623Swedish Research Council, 2021-06683Academy of Finland, 354521
Available from: 2024-01-04 Created: 2024-01-04 Last updated: 2025-04-24Bibliographically approved
Yao, S., Li, J., Zhou, X.-Z., Shi, Q., Zong, Q.-G., Zhang, H., . . . Yang, F. (2023). Ion-Vortex Magnetic Hole With Reversed Field Direction in Earth's Magnetosheath. Journal of Geophysical Research - Space Physics, 128(7), Article ID e2023JA031749.
Open this publication in new window or tab >>Ion-Vortex Magnetic Hole With Reversed Field Direction in Earth's Magnetosheath
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2023 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 128, no 7, article id e2023JA031749Article in journal (Refereed) Published
Abstract [en]

Plasma vortices are ubiquitous in space and play important roles in the transmission of energy and mass at various scales. For small-scale plasma vortices on the order of ion gyroradius, however, their properties and characteristics remain unclear. Here, we provide unique findings of an ion-scale vortex observed in the Earth's magnetosheath. The vortex is generated by the ion diamagnetic drift associated with an isolated magnetic hole (MH). The magnetic field in the axial direction is reversed in the vortex center, which is consistent with ring-shaped currents carried by the ions. The field strength becomes very weak (<1 nT) at the field reversal region, although the ion distributions vary rather continuously across the entire structure. A kinetic equilibrium model is then applied to reconstruct the above features. These findings can help us understand the plasma vortex and MH from magnetohydrodynamics to kinetic scales.

Place, publisher, year, edition, pages
John Wiley & Sons, 2023
Keywords
electron vortex, ion vortex, kinetic scale, magnetic hole, magnetosheath
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-212504 (URN)10.1029/2023JA031749 (DOI)001040706400001 ()2-s2.0-85165598754 (Scopus ID)
Available from: 2023-08-01 Created: 2023-08-01 Last updated: 2025-04-24Bibliographically approved
Hamrin, M., Schillings, A., Opgenoorth, H. J., Nesbit-Östman, S., Krämer, E., Araújo, J. C., . . . Barnes, R. J. (2023). Space weather disturbances in non-stormy times: occurrence of dB/dt spikes during three solar cycles. Journal of Geophysical Research - Space Physics, 128(10), Article ID e2023JA031804.
Open this publication in new window or tab >>Space weather disturbances in non-stormy times: occurrence of dB/dt spikes during three solar cycles
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2023 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 128, no 10, article id e2023JA031804Article in journal (Refereed) Published
Abstract [en]

Spatio-temporal variations of ionospheric currents cause rapid magnetic field variations at ground level and Geomagnetically Induced Currents (GICs) that can be harmful for human infrastructure. The risk for large excursions in the magnetic field time derivative, “dB/dt spikes”, is known to be high during geomagnetic storms and substorms. However, less is known about the occurrence of spikes during non-stormy times. We use data from ground-based globally covering magnetometers (SuperMAG database) from the years 1985–2021. We investigate the spike occurrence (|dB/dt| > 100 nT/min) as a function of magnetic local time (MLT), magnetic latitude (Mlat), and the solar cycle phases during non-stormy times (−15 nT ≤ SYM-H < 0). We sort our data into substorm (AL < 200 nT) intervals (“SUB”) and less active intervals between consecutive substorms (“nonSUB”). We find that spikes commonly occur in both SUBs and nonSUBs during non-stormy times (3–23 spikes/day), covering 18–12 MLT and 65°–80° Mlat. This also implies a risk for infrastructure damage during non-stormy times, especially when several spikes occur nearby in space and time, possibly causing infrastructure weathering. We find that spikes are more common in the declining phase of the solar cycle, and that the occurrence of SUB spikes propagates from one midnight to one morning hotspot with ∼10 min in MLT for each minute in universal time (UTC). Finally, we discuss causes for the spikes in terms of spatio-temporal variations of ionospheric currents.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2023
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-215270 (URN)10.1029/2023ja031804 (DOI)2-s2.0-85174460250 (Scopus ID)
Funder
Swedish National Space Board, 81/17Swedish National Space Board, 108/18Swedish National Space Board, 194/19Swedish National Space Board, 118/17Swedish Research Council, 2018-03623Swedish Research Council, 2021-06683
Available from: 2023-10-15 Created: 2023-10-15 Last updated: 2023-10-30Bibliographically approved
Xiao, Y., Yao, S., Guo, R., Shi, Q., Zong, Q., Zhang, H., . . . Liu, J. (2023). Statistical properties of the distribution and generation of kinetic-scale flux ropes in the terrestrial dayside magnetosheath. Geophysical Research Letters, 50(23), Article ID e2023GL105469.
Open this publication in new window or tab >>Statistical properties of the distribution and generation of kinetic-scale flux ropes in the terrestrial dayside magnetosheath
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2023 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 50, no 23, article id e2023GL105469Article in journal (Refereed) Published
Abstract [en]

The generation of kinetic-scale flux ropes (KSFRs) is closely related to magnetic reconnection. Both flux ropes and reconnection sites are detected in the magnetosheath and can impact the dynamics upstream of the magnetopause. In this study, using the Magnetospheric Multiscale satellite, 12,623 KSFRs with a scale <20 RCi are statistically studied in the Earth's dayside magnetosheath. It is found that they are mostly generated near the bow shock (BS), and propagate downstream in the magnetosheath. Their quantity significantly increases as the scale decreases, consistent with a flux rope coalescence model. Moreover, the solar wind parameters can control the occurrence rate of KSFRs. They are more easily generated at high Mach number, large proton density, and weak magnetic field strength of the solar wind, similar to the conditions that favor BS reconnection. Our study shows a close connection between KSFR generation and BS reconnection.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2023
Keywords
bow shock, flux rope, ion scale flux rope, kinetic-scale flux rope, magnetic reconnection, magnetosheath
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:umu:diva-217533 (URN)10.1029/2023GL105469 (DOI)001110552600001 ()2-s2.0-85177785004 (Scopus ID)
Funder
Swedish National Space Board, 194/19RSwedish National Space Board, 2023/00138Swedish Research Council, 2018-03623
Available from: 2023-12-14 Created: 2023-12-14 Last updated: 2023-12-14Bibliographically approved
Pitkänen, T., Chong, G. S., Hamrin, M., Kullen, A., Karlsson, T., Park, J.-S., . . . Shi, Q. (2023). Statistical survey of magnetic forces associated with earthward bursty bulk flows measured by MMS 2017–2021. Journal of Geophysical Research - Space Physics, 128(5), Article ID e2022JA031094.
Open this publication in new window or tab >>Statistical survey of magnetic forces associated with earthward bursty bulk flows measured by MMS 2017–2021
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2023 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 128, no 5, article id e2022JA031094Article in journal (Refereed) Published
Abstract [en]

We investigate the magnetic forces (the magnetic pressure gradient force, the curvature force, and their sum the j × B-force) associated with earthward bursty bulk flows (BBFs) using Magnetospheric Multiscale (MMS) data from five tail seasons (2017–2021). For the first time, the magnetic forces are inferred downtail of XGSM = −20 RE and in the GSM XY and YZ planes. The results suggest that BBFs tend to be accelerated earthward by the magnetic pressure gradient force tailward of ∼19 RE and decelerated closer to that distance in the 2017–2018 data. The force magnitudes increase with distance. This is in accordance with earlier Cluster results. In the 2019–2021 data, the pressure gradient force magnitudes are generally smaller and no clear distance for the acceleration reversal can be determined. The curvature forces for both 2017–2018 and 2019–2021 BBFs indicate earthward acceleration independent of distance, consistent with the Cluster measurements. The sum, the j × B-force, suggests for the 2017–2018 BBFs earthward acceleration tailward of XGSM ∼15 RE and deceleration within that distance, also consistent with Cluster. In contrast, the 2019–2021 BBFs show general earthward acceleration by j × B independent of distance. In the GSM XY plane, the average (j × B)xy vectors are earthward, and in the premidnight and postmidnight dawnward for the 2017–2018 BBFs. For 2019–2021, the average (× B)xy vectors have components toward the tail center. In the GSM YZ plane, the average (j × B)yz vectors are toward the neutral sheet.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2023
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:umu:diva-209169 (URN)10.1029/2022JA031094 (DOI)001000332300001 ()2-s2.0-85160392932 (Scopus ID)
Funder
Swedish Research Council, 2018‐03623Swedish National Space Board, 194/19
Available from: 2023-06-22 Created: 2023-06-22 Last updated: 2023-06-22Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-5681-0366

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