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Publications (10 of 57) Show all publications
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)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: 2024-01-04Bibliographically 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)2-s2.0-85165598754 (Scopus ID)
Available from: 2023-08-01 Created: 2023-08-01 Last updated: 2023-08-01Bibliographically 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
Chong, G. S., Pitkänen, T., Hamrin, M. & Kullen, A. (2022). Dawn-Dusk Ion Flow Asymmetry in the Plasma Sheet: Interplanetary Magnetic Field By Versus Distance With Respect to the Neutral Sheet. Journal of Geophysical Research - Space Physics, 127(4), Article ID e2021JA030208.
Open this publication in new window or tab >>Dawn-Dusk Ion Flow Asymmetry in the Plasma Sheet: Interplanetary Magnetic Field By Versus Distance With Respect to the Neutral Sheet
2022 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 127, no 4, article id e2021JA030208Article in journal (Refereed) Published
Abstract [en]

Previous studies have shown that the average dawn-dusk component of the perpendicular plasma flow in the plasma sheet (V⊥) can vary depending on the distance relative to the neutral sheet and the dawn-dusk component of the interplanetary magnetic field (IMF By). In this study, we combined 33 years of data from the Geotail, Time History of Events and Macroscale Interactions during Substorms, Cluster, and magnetospheric multiscale missions to study the slow (<200 km/s) ion flows perpendicular to the magnetic field. We find that IMF By has a hemispheric dependent influence on both the tail By and tail V⊥. Particularly, the influence is more prominent in the midnight sector (compared to both the pre- and post-midnight sectors) and at distances far from the neutral sheet (compared to the distances close to the neutral sheet). However, at distances close to the neutral sheet, there is an increased dominance of duskward flows which dominates over the systematic influence of IMF By on tail V⊥. Our results indicate that IMF By has a major influence on the magnetic flux transport in the magnetotail, mainly at distances far from the neutral sheet. The influence is weaker at distances close to the neutral sheet.

Place, publisher, year, edition, pages
John Wiley & Sons, 2022
Keywords
earthward and tailward flows, ion convection, magnetic flux transport, magnetotail, neutral sheet, plasma sheet
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-194471 (URN)10.1029/2021JA030208 (DOI)000777617700001 ()2-s2.0-85128720002 (Scopus ID)
Available from: 2022-05-06 Created: 2022-05-06 Last updated: 2023-09-05Bibliographically approved
Park, J.-S., Shi, Q. Q., Shi, X., Shue, J.-H., Degeling, A. W., Nowada, M., . . . Zhang, Y. (2022). Radial Interplanetary Magnetic Field-Induced North-South Asymmetry in the Solar Wind-Magnetosphere-Ionosphere Coupling: A Case Study. Journal of Geophysical Research - Space Physics, 127(2), Article ID e2021JA030020.
Open this publication in new window or tab >>Radial Interplanetary Magnetic Field-Induced North-South Asymmetry in the Solar Wind-Magnetosphere-Ionosphere Coupling: A Case Study
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2022 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 127, no 2, article id e2021JA030020Article in journal (Refereed) Published
Abstract [en]

In this paper, we present a case study of the radial interplanetary magnetic field (IMF Bx)-induced asymmetric solar wind-magnetosphere-ionosphere (SW-M-I) coupling between the northern and southern polar caps using ground-based and satellite-based data. Under prolonged conditions of strong earthward IMF on 5 March 2015, we find significant discrepancies between polar cap north (PCN) and polar cap south (PCS) magnetic indices with a negative bay-like change in the PCN and a positive bay-like change in the PCS. The difference between these indices (PCN-PCS) reaches a minimum of −1.63 mV/m, which is approximately three times higher in absolute value than the values for most of the time on this day (within ±0.5 mV/m). The high-latitude plasma convection also shows an asymmetric feature such that there exists an additional convection cell near the noon sector in the northern polar cap, but not in the southern polar cap. Meanwhile, negative bays in the north-south component of ground magnetic field perturbations (less than 50 nT) observed in the nightside auroral region of the Northern Hemisphere are accompanied with the brightening and widening of the nightside auroral oval in the Southern Hemisphere, implying a weak, but clear energy transfer to the nightside ionosphere of both hemispheres. After the hemispheric asymmetries in the polar caps disappear, a substorm onset takes place. All these observations indicate that IMF Bx-induced single lobe reconnection that occurred in the Northern Hemisphere plays an important role in hemispheric asymmetry in the energy transfer from the solar wind to the polar cap through the magnetosphere.

Place, publisher, year, edition, pages
John Wiley & Sons, 2022
Keywords
hemispheric asymmetry, ionospheric convection, polar cap index, radial interplanetary magnetic field
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:umu:diva-192947 (URN)10.1029/2021JA030020 (DOI)000765721800026 ()2-s2.0-85125374019 (Scopus ID)
Funder
Swedish National Space Board, 118/17
Available from: 2022-03-09 Created: 2022-03-09 Last updated: 2023-09-05Bibliographically approved
Tian, A., Degeling, A. W., Park, J.-S., Shi, Q., Nowada, M., Pitkänen, T., . . . Xiao, C. (2022). Structure of Pc 5 Compressional Waves Observed in the Duskside Outer Magnetosphere: MMS Observations. Journal of Geophysical Research - Space Physics, 127(3), Article ID e2021JA029817.
Open this publication in new window or tab >>Structure of Pc 5 Compressional Waves Observed in the Duskside Outer Magnetosphere: MMS Observations
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2022 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 127, no 3, article id e2021JA029817Article in journal (Refereed) Published
Abstract [en]

The geometrical structure of the Pc 5 compressional wave is important in judging its generation mechanism and the wave-particle interaction process. In this work, 117 magnetic troughs (where magnetic field strength transiently decreases) identified from 50 Pc 5 compressional wave events in the duskside (15.5–18.5 local time) magnetosphere are studied based on the Magnetospheric Multiscale (MMS) data. We derived the three dimensional geometry of the magnetic trough by including the normal and velocity information at its boundaries from the multi-spacecraft analysis method. The magnetic trough has a magnetic bottle shape along the magnetic field line with the most probable center (with weakest magnetic field) located at θ = (Formula presented.), while the widest part of the magnetic bottle located around θ (Formula presented.) (θ denotes the angle between spacecraft position vector and the ambient magnetic field). The cross section of the magnetic trough is eccentric and has a “wedge-like” shape whose average open angle is ∼23° toward radial outward. It is found that the radial component of the current density is the dominant one at the boundaries, and the value is generally proportional to the depth of the magnetic trough. The generation of these Pc 5 compressional waves can be attributed to the drift Alfvén ballooning mirror instability. This work reveals the possible changes of magnetic field configuration caused by the Pc 5 compressional wave in the magnetosphere and may bring new ideas to the interaction way between wave field and ring current particles.

Place, publisher, year, edition, pages
John Wiley & Sons, 2022
Keywords
magnetosphere, mirror instability, multipoint data analysis, Pc5 compressional wave, ULF wave
National Category
Fusion, Plasma and Space Physics Geophysics
Identifiers
urn:nbn:se:umu:diva-193807 (URN)10.1029/2021JA029817 (DOI)000776515200037 ()2-s2.0-85127325179 (Scopus ID)
Available from: 2022-05-06 Created: 2022-05-06 Last updated: 2022-05-06Bibliographically approved
Pitkänen, T., Kullen, A., Cai, L., Park, J.-S., Vanhamäki, H., Hamrin, M., . . . Shi, Q. (2021). Asymmetry in the Earth's magnetotail neutral sheet rotation due to IMF By sign?. Geoscience Letters, 8(1), Article ID 3.
Open this publication in new window or tab >>Asymmetry in the Earth's magnetotail neutral sheet rotation due to IMF By sign?
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2021 (English)In: Geoscience Letters, ISSN 2196-4092, Vol. 8, no 1, article id 3Article in journal (Refereed) Published
Abstract [en]

Evidence suggests that a non-zero dawn-dusk interplanetary magnetic field (IMF By) can cause a rotation of the cross-tail current sheet/neutral sheet around its axis aligned with the Sun-Earth line in Earth's magnetotail. We use Geotail, THEMIS and Cluster data to statistically investigate how the rotation of the neutral sheet depends on the sign and magnitude of IMF By. In our dataset, we find that in the tail range of -30 < XGSM < -15 RE, the degree of the neutral sheet rotation is clearly smaller, there appears no significant rotation or even, the rotation is clearly to an unexpected direction for negative IMF By, compared to positive IMF By. Comparison to a model by Tsyganenko et al. (2015, doi:10.5194/angeo-33-1-2015) suggests that this asymmetry in the neutral sheet rotation between positive and negative IMF By conditions is too large to be explained only by the currently known factors. The possible cause of the asymmetry remains unclear.

Place, publisher, year, edition, pages
Springer, 2021
Keywords
Solar wind-magnetosphere interaction, Magnetosphere configuration, Magnetotail, Plasma sheet, Neutral sheet
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-180191 (URN)10.1186/s40562-020-00171-7 (DOI)000609495500002 ()2-s2.0-85099333771 (Scopus ID)
Funder
Swedish National Space Board, 118/17Swedish National Space Board, 105/14Swedish National Space Board, 81/17Swedish National Space Board, 271/14Academy of Finland, 314664
Available from: 2021-02-19 Created: 2021-02-19 Last updated: 2021-02-19Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-5681-0366

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