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Publications (9 of 9) Show all publications
Juusola, L., Viljanen, A., Dimmock, A. P., Kellinsalmi, M., Schillings, A. & Weygand, J. M. (2023). Drivers of rapid geomagnetic variations at high latitudes. Annales Geophysicae, 41(1), 13-37
Open this publication in new window or tab >>Drivers of rapid geomagnetic variations at high latitudes
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2023 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 41, no 1, p. 13-37Article in journal (Refereed) Published
Abstract [en]

We have examined the most intense external (magnetospheric and ionospheric) and internal (induced) |dH/dt| (amplitude of the 10gs time derivative of the horizontal geomagnetic field) events observed by the high-latitude International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometers between 1994 and 2018. While the most intense external |dH/dt| events at adjacent stations typically occurred simultaneously, the most intense internal (and total) |dH/dt| events were more scattered in time, most likely due to the complexity of induction in the conducting ground. The most intense external |dH/dt| events occurred during geomagnetic storms, among which the Halloween storm in October 2003 featured prominently, and drove intense geomagnetically induced currents (GICs). Events in the prenoon local time sector were associated with sudden commencements (SCs) and pulsations, and the most intense |dH/dt| values were driven by abrupt changes in the eastward electrojet due to solar wind dynamic pressure increase or decrease. Events in the premidnight and dawn local time sectors were associated with substorm activity, and the most intense |dH/dt| values were driven by abrupt changes in the westward electrojet, such as weakening and poleward retreat (premidnight) or undulation (dawn). Despite being associated with various event types and occurring at different local time sectors, there were common features among the drivers of most intense external |dH/dt| values: preexisting intense ionospheric currents (SC events were an exception) that were abruptly modified by sudden changes in the magnetospheric magnetic field configuration. Our results contribute towards the ultimate goal of reliable forecasts of dH/dt and GICs.

Place, publisher, year, edition, pages
Nicolaus Copernicus University Press, 2023
National Category
Astronomy, Astrophysics and Cosmology Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-204749 (URN)10.5194/angeo-41-13-2023 (DOI)000917667200001 ()2-s2.0-85147308351 (Scopus ID)
Funder
EU, FP7, Seventh Framework Programme, 260330
Available from: 2023-02-21 Created: 2023-02-21 Last updated: 2023-10-30Bibliographically 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
Schillings, A., Palin, L., Bower, G. E., Opgenoorth, H. J., Milan, S. E., Kauristie, K., . . . Van De Kamp, M. (2023). Signatures of wedgelets over Fennoscandia during the St Patrick s Day Storm 2015. Journal of Space Weather and Space Climate, 13, Article ID 19.
Open this publication in new window or tab >>Signatures of wedgelets over Fennoscandia during the St Patrick s Day Storm 2015
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2023 (English)In: Journal of Space Weather and Space Climate, E-ISSN 2115-7251, Vol. 13, article id 19Article in journal (Refereed) Published
Abstract [en]

During the long main phase of the St Patrick's Day storm on March 17, 2015, we found three separate enhancements of the westward electrojet. These enhancements are observed in the ionospheric equivalent currents computed using geomagnetic data over Fennoscandia. Using data from the IMAGE magnetometer network, we identified localised field-aligned current (FAC) systems superimposed on the pre-existing ionospheric current system. We suggest that these localised current systems are wedgelets and that they can potentially contribute to a larger-scale structure of a substorm current wedge (SCW). Each wedgelet is associated with a negative BX spike. Each spike is recorded at a higher latitude than the former one and all three are very localised over Fennoscandia. The first spike occurred at 17:34 UT and was observed at Lycksele, R rvik and Nurmij rvi, the second spike was recorded at 17:41 UT and located at Lycksele and R rvik, whereas the last spike occurred at 17:47 UT and was observed at Kevo and Abisko. Simultaneous optical auroral data and electron injections at the geosynchronous orbit indicate that one or more substorms took place in the polar ionosphere at the time of the wedgelets. This study demonstrates the occurrence of small and short-lived structures such as wedgelets at different locations over a short time scale, 15 min in this case.

Place, publisher, year, edition, pages
EDP Sciences, 2023
Keywords
Ionospheric equivalent currents, St Patrick s Day storm, Substorm, Wedgelets, Westward electrojet
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-212096 (URN)10.1051/swsc/2023018 (DOI)001010354000001 ()2-s2.0-85163322164 (Scopus ID)
Funder
Swedish National Space Board, 10077/15Swedish National Space Board, 81/17Swedish Research Council, 2018-03623
Available from: 2023-07-17 Created: 2023-07-17 Last updated: 2023-11-15Bibliographically 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
Schillings, A., Palin, L., Opgenoorth, H. J., Hamrin, M., Rosenqvist, L., Gjerloev, J., . . . Barnes, R. (2022). Distribution and Occurrence Frequency of dB/dt Spikes During Magnetic Storms 1980–2020. Space Weather: The International Journal of Research and Application, 20(5), Article ID e2021SW002953.
Open this publication in new window or tab >>Distribution and Occurrence Frequency of dB/dt Spikes During Magnetic Storms 1980–2020
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2022 (English)In: Space Weather: The International Journal of Research and Application, E-ISSN 1542-7390, Vol. 20, no 5, article id e2021SW002953Article in journal (Refereed) Published
Abstract [en]

The physical magnetospheric cause for geomagnetically induced currents (GICs) are rapid time-varying magnetic fields (dB/dt), which occur mainly during magnetic substorms and storms. When, where and why exactly such rapid dB/dt may occur is insufficiently understood. We investigated all storms since 1980 and analyzed the negative and positive dB/dt spikes (>|500| nT/min) in the north and east component using a worldwide coverage (SuperMAG). Our analysis confirmed the existence of two dB/dt spikes "hotspots" located in the pre-midnight and in the morning magnetic local time sector, independently of the geographic location of the stations. The associated physical phenomena are probably substorm current wedge onsets and westward traveling surges (WTS) in the evening sector, and wave- or vortex-like current flows in the morning sector known as Omega bands. We observed a spatiotemporal evolution of the negative northern dB/dt spikes. The spikes initially occur in the pre-midnight sector, and then develop in time toward the morning sector. This spatiotemporal sequence is correlated with bursts in the AE index, and can be repeated several times throughout a storm. Finally, we investigated the peak value of Dst and AE during the storm period in comparison with the dB/dt spike occurrence frequency, we did not find any correlation. This result implies that a moderate storm with many spikes can be as (or more) dangerous for ground-based infrastructures than a major storm with fewer dB/dt spikes. Our findings regarding the physical causes and characteristics of dB/dt spikes may help to improve the GIC forecast for the affected regions.

Place, publisher, year, edition, pages
John Wiley & Sons, 2022
Keywords
dB/dt spikes, geomagnetic storms, GICs, Omega bands, space weather, substorm current wedge
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:umu:diva-196128 (URN)10.1029/2021SW002953 (DOI)000798253500001 ()2-s2.0-85130605483 (Scopus ID)
Funder
Swedish National Space Board, 10077/15, 81/17Swedish Research Council, 2018‐03623
Available from: 2022-06-15 Created: 2022-06-15 Last updated: 2023-10-30Bibliographically approved
Persson, M., Futaana, Y., Ramstad, R., Schillings, A., Masunaga, K., Nilsson, H., . . . Barabash, S. (2021). Global Venus-Solar wind coupling and oxygen ion escape. Geophysical Research Letters, 48(4), Article ID e2020GL091213.
Open this publication in new window or tab >>Global Venus-Solar wind coupling and oxygen ion escape
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2021 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 48, no 4, article id e2020GL091213Article in journal (Refereed) Published
Abstract [en]

The present‐day Venusian atmosphere is dry, yet, in its earlier history a significant amount of water evidently existed. One important water loss process comes from the energy and momentum transfer from the solar wind to the atmospheric particles. Here, we used measurements from the Ion Mass Analyzer onboard Venus Express to derive a relation between the power in the upstream solar wind and the power leaving the atmosphere through oxygen ion escape in the Venusian magnetotail. We find that on average 0.01% of the available power is transferred, and that the percentage decreases as the available energy increases. For Mars the trend is similar, but the efficiency is higher. At Earth, the ion escape does not behave similarly, as the ion escape only increases after a threshold in the available energy is reached. These results indicate that the Venusian induced magnetosphere efficiently screens the atmosphere from the solar wind.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2021
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-176001 (URN)10.1029/2020GL091213 (DOI)000620058900054 ()2-s2.0-85101128024 (Scopus ID)
Note

Originally included in thesis in manuscript form.

Available from: 2020-10-15 Created: 2020-10-15 Last updated: 2023-10-30Bibliographically approved
Chong, G. S., Pitkänen, T., Hamrin, M. & Schillings, A. (2021). Ion Convection as a Function of Distance to the Neutral Sheet in Earth's Magnetotail. Journal of Geophysical Research - Space Physics, 126(12), Article ID e2021JA029694.
Open this publication in new window or tab >>Ion Convection as a Function of Distance to the Neutral Sheet in Earth's Magnetotail
2021 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 126, no 12, article id e2021JA029694Article in journal (Refereed) Published
Abstract [en]

We utilized 33 years of data obtained by the Geotail, THEMIS, Cluster and MMS missions to investigate the slow (<200 km/s) ion flows perpendicular to the magnetic field in Earth's magnetotail plasma sheet. By using plasma β as a proxy of distance to the neutral sheet, we find that the ion flow patterns vary systematically within the plasma sheet. Particularly, in regions farther from the neutral sheet, earthward (tailward) flows exhibit a strong tendency to diverge (converge) quasi-symmetrically, with respect to the midnight meridional plane. As the distance becomes closer toward the neutral sheet, this tendency to diverge and converge gradually weakens. Moreover, duskward flows become the dominant components in both the earthward and tailward flows. These variations in ion flow patterns with distance to neutral sheet are hemispherically independent. We suggest that the spatial profiles of the electric and diamagnetic drift vary with distance to the neutral sheet and are therefore responsible for the varying ion flow patterns.

Place, publisher, year, edition, pages
John Wiley & Sons, 2021
Keywords
diamagnetic drift, earthward and tailward flows, ion convection, magnetotail, neutral sheet, plasma sheet
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:umu:diva-190970 (URN)10.1029/2021JA029694 (DOI)000735715600009 ()2-s2.0-85121832519 (Scopus ID)
Funder
Swedish National Space Board, 81/17
Available from: 2022-01-04 Created: 2022-01-04 Last updated: 2023-10-30Bibliographically approved
Engebretson, M. J., Pilipenko, V. A., Steinmetz, E. S., Moldwin, M. B., Connors, M. G., Boteler, D. H., . . . Russell, C. T. (2021). Nighttime Magnetic Perturbation Events Observed in Arctic Canada: 3. Occurrence and Amplitude as Functions of Magnetic Latitude, Local Time, and Magnetic Disturbance Indices. Space Weather: The International Journal of Research and Application, 19(3), Article ID e2020SW002526.
Open this publication in new window or tab >>Nighttime Magnetic Perturbation Events Observed in Arctic Canada: 3. Occurrence and Amplitude as Functions of Magnetic Latitude, Local Time, and Magnetic Disturbance Indices
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2021 (English)In: Space Weather: The International Journal of Research and Application, E-ISSN 1542-7390, Vol. 19, no 3, article id e2020SW002526Article in journal (Refereed) Published
Abstract [en]

Rapid changes of magnetic fields associated with nighttime magnetic perturbation events (MPEs) with amplitudes |ΔB| of hundreds of nT and 5–10 min duration can induce geomagnetically induced currents (GICs) that can harm technological systems. This study compares the occurrence and amplitude of nighttime MPEs with |dB/dt| ≥ 6 nT/s observed during 2015 and 2017 at five stations in Arctic Canada ranging from 64.7° to 75.2° in corrected geomagnetic latitude (MLAT) as functions of magnetic local time (MLT), the SME (SuperMAG version of AE) and SYM/H magnetic indices, and time delay after substorm onsets. Although most MPEs occurred within 30 min after a substorm onset, ∼10% of those observed at the four lower latitude stations occurred over two hours after the most recent onset. A broad distribution in local time appeared at all five stations between 1700 and 0100 MLT, and a narrower distribution appeared at the lower latitude stations between 0200 and 0700 MLT. There was little or no correlation between MPE amplitude and the SYM/H index; most MPEs at all stations occurred for SYM/H values between −40 and 0 nT. SME index values for MPEs observed >1 h after the most recent substorm onset fell in the lower half of the range of SME values for events during substorms, and dipolarizations in synchronous orbit at GOES 13 during these events were weaker or more often nonexistent. These observations suggest that substorms are neither necessary nor sufficient to cause MPEs, and hence predictions of GICs cannot focus solely on substorms.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2021
Keywords
geomagnetically induced currents, magnetic perturbation events, magnetic storms, omega bands, substorms
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:umu:diva-182098 (URN)10.1029/2020SW002526 (DOI)000636279600009 ()2-s2.0-85103236439 (Scopus ID)
Funder
Swedish National Space Board
Available from: 2021-04-15 Created: 2021-04-15 Last updated: 2023-10-30Bibliographically approved
Engebretson, M. J., Kirkevold, K. R., Steinmetz, E. S., Pilipenko, V. A., Moldwin, M. B., McCuen, B. A., . . . Rose, M. C. (2020). Interhemispheric Comparisons of Large Nighttime Magnetic Perturbation Events Relevant to GICs. Journal of Geophysical Research - Space Physics, 125(8), Article ID e2020JA028128.
Open this publication in new window or tab >>Interhemispheric Comparisons of Large Nighttime Magnetic Perturbation Events Relevant to GICs
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2020 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 125, no 8, article id e2020JA028128Article in journal (Refereed) Published
Abstract [en]

Nearly all studies of impulsive magnetic perturbation events (MPEs) with large magnetic field variability (dB/dt) that can produce dangerous geomagnetically induced currents (GICs) have used data from the Northern Hemisphere. Here we present details of four large‐amplitude MPE events (|ΔBx| > 900 nT and |dB/dt| > 10 nT/s in at least one component) observed between 2015 and 2018 in conjugate high‐latitude regions (65–80° corrected geomagnetic latitude), using magnetometer data from (1) Pangnirtung and Iqaluit in eastern Arctic Canada and the magnetically conjugate South Pole Station in Antarctica and (2) the Greenland West Coast Chain and two magnetically conjugate chains in Antarctica, AAL‐PIP and BAS LPM. From one to three different isolated MPEs localized in corrected geomagnetic latitude were observed during three premidnight events; many were simultaneous within 3 min in both hemispheres. Their conjugate latitudinal amplitude profiles, however, matched qualitatively at best. During an extended postmidnight interval, which we associate with an interval of omega bands, multiple highly localized MPEs occurred independently in time at each station in both hemispheres. These nighttime MPEs occurred under a wide range of geomagnetic conditions, but common to each was a negative interplanetary magnetic field Bz that exhibited at least a modest increase at or near the time of the event. A comparison of perturbation amplitudes to modeled ionospheric conductances in conjugate hemispheres clearly favored a current generator model over a voltage generator model for three of the four events; neither model provided a good fit for the premidnight event that occurred near vernal equinox.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2020
Keywords
geomagnetically induced currents, magnetic perturbation events, substorms, magnetic storms, magnetic conjugacy, omega bands
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:umu:diva-176549 (URN)10.1029/2020JA028128 (DOI)000577125000035 ()2-s2.0-85089903827 (Scopus ID)
Available from: 2020-11-11 Created: 2020-11-11 Last updated: 2023-10-30Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-6968-5405

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