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  • 1.
    Chong, Ghai Siung
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Pitkänen, Timo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institute of Space Sciences, Shandong University, Weihai, China.
    Hamrin, Maria
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Schillings, Audrey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Ion Convection as a Function of Distance to the Neutral Sheet in Earth's Magnetotail2021Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 126, nr 12, artikel-id e2021JA029694Artikel i tidskrift (Refereegranskat)
    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.

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  • 2. Engebretson, Mark J.
    et al.
    Kirkevold, Kathryn R.
    Steinmetz, Erik S.
    Pilipenko, Viacheslav A.
    Moldwin, Mark B.
    McCuen, Brett A.
    Clauer, C. R.
    Hartinger, Michael D.
    Coyle, Shane
    Opgenoorth, Hermann J.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Schillings, Audrey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Willer, Anna N.
    Edwards, Thom R.
    Boteler, David H.
    Gerrard, Andy J.
    Freeman, Mervyn P.
    Rose, Michael C.
    Interhemispheric Comparisons of Large Nighttime Magnetic Perturbation Events Relevant to GICs2020Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 125, nr 8, artikel-id e2020JA028128Artikel i tidskrift (Refereegranskat)
    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.

  • 3.
    Engebretson, Mark J.
    et al.
    Augsburg University, MN, Minneapolis, United States.
    Pilipenko, Viacheslav A.
    Augsburg University, MN, Minneapolis, United States; Institute of Physics of the Earth, Moscow, Russian Federation.
    Steinmetz, Erik S.
    Augsburg University, MN, Minneapolis, United States.
    Moldwin, Mark B.
    University of Michigan, MI, Ann Arbor, United States.
    Connors, Martin G.
    Athabasca University, AB, Athabasca, Canada.
    Boteler, David H.
    Natural Resources Canada, ON, Ottawa, Canada.
    Singer, Howard J.
    NOAA Space Weather Prediction Center, CO, Boulder, United States.
    Opgenoorth, Hermann J.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Schillings, Audrey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Ohtani, Shin
    JHU/APL, MD, Laurel, United States.
    Gjerloev, Jesper
    JHU/APL, MD, Laurel, United States.
    Russell, Christopher T.
    UCLA Department of Earth Planetary and Space Sciences, CA, Los Angeles, United States.
    Nighttime Magnetic Perturbation Events Observed in Arctic Canada: 3. Occurrence and Amplitude as Functions of Magnetic Latitude, Local Time, and Magnetic Disturbance Indices2021Ingår i: Space Weather: The International Journal of Research and Application, E-ISSN 1542-7390, Vol. 19, nr 3, artikel-id e2020SW002526Artikel i tidskrift (Refereegranskat)
    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.

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  • 4.
    Hamrin, Maria
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Schillings, Audrey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Opgenoorth, Hermann J.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nesbit-Östman, Sara
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Krämer, Eva
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Araújo, Juan Carlos
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för naturvetenskapernas och matematikens didaktik.
    Baddeley, Lisa
    Department of Arctic Geophysics, University Centre in Svalbard, Longyearbyen, Norway.
    Gunell, Herbert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Pitkänen, Timo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institute of Space Sciences, Shandong University, Weihai, China.
    Gjerloev, Jesper
    Johns Hopkins University, Laurel, MD, USA.
    Barnes, R. J.
    Johns Hopkins University, Laurel, MD, USA.
    Space weather disturbances in non-stormy times: occurrence of dB/dt spikes during three solar cycles2023Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 128, nr 10, artikel-id e2023JA031804Artikel i tidskrift (Refereegranskat)
    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.

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  • 5.
    Juusola, Liisa
    et al.
    Finnish Meteorological Institute, Helsinki, Finland.
    Viljanen, Ari
    Finnish Meteorological Institute, Helsinki, Finland.
    Dimmock, Andrew P.
    Swedish Institute of Space Physics, Uppsala, Sweden.
    Kellinsalmi, Mirjam
    Finnish Meteorological Institute, Helsinki, Finland.
    Schillings, Audrey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Weygand, James M.
    Department of Earth Planetary, and Space Sciences, University of California Los Angeles, CA, Los Angeles, United States.
    Drivers of rapid geomagnetic variations at high latitudes2023Ingår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 41, nr 1, s. 13-37Artikel i tidskrift (Refereegranskat)
    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.

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  • 6.
    Persson, Moa
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institutet för Rymdfysik, Kiruna, Sverige.
    Futaana, Yoshifumi
    Institutet för Rymdfysik, Kiruna, Sverige.
    Ramstad, Robin
    Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado, USA.
    Schillings, Audrey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Masunaga, Kei
    Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado, USA.
    Nilsson, Hans
    Institutet för Rymdfysik, Kiruna, Sverige.
    Fedorov, Andrei
    IRAP, CNRS, Toulouse, France.
    Barabash, Stas
    Institutet för Rymdfysik, Kiruna, Sverige.
    Global Venus-Solar wind coupling and oxygen ion escape2021Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 48, nr 4, artikel-id e2020GL091213Artikel i tidskrift (Refereegranskat)
    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.

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  • 7.
    Pitkänen, Timo
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, China.
    Chong, Ghai Siung
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hamrin, Maria
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Kullen, A.
    Space and Plasma Physics, School of Electrical Engineering and Computer Science, Royal Institute of Technology, Stockholm, Sweden.
    Vanhamäki, H.
    Space Physics and Astronomy Research Unit, University of Oulu, Oulu, Finland.
    Park, J.-S.
    Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, China.
    Nowada, M.
    Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, China.
    Schillings, Audrey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Krämer, Eva
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Fast Earthward Convection in the Magnetotail and Nonzero IMF By: MMS Statistics2023Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 128, nr 12, artikel-id e2023JA031593Artikel i tidskrift (Refereegranskat)
    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.

  • 8. Schillings, Audrey
    et al.
    Gunell, Herbert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Belgian Institute for Space Aeronomy, Brussels, Belgium.
    Nilsson, Hans
    De Spiegeleer, Alexandre
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Ebihara, Yusuke
    Westerberg, Lars G.
    Yamauchi, Masatoshi
    Slapak, Rikard
    The fate of O+ ions observed in the plasma mantle: particle tracing modelling and cluster observations2020Ingår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 38, nr 3, s. 645-656Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ion escape is of particular interest for studying the evolution of the atmosphere on geological timescales. Previously, using Cluster-CODIF data, we investigated the oxygen ion outflow from the plasma mantle for different solar wind conditions and geomagnetic activity. We found significant correlations between solar wind parameters, geomagnetic activity (K-p index), and the O+ outflow. From these studies, we suggested that O+ ions observed in the plasma mantle and cusp have enough energy and velocity to escape the magnetosphere and be lost into the solar wind or in the distant magnetotail. Thus, this study aims to investigate where the ions observed in the plasma mantle end up. In order to answer this question, we numerically calculate the trajectories of O+ ions using a tracing code to further test this assumption and determine the fate of the observed ions. Our code consists of a magnetic field model (Tsyganenko T96) and an ionospheric potential model (Weimer 2001) in which particles initiated in the plasma mantle region are launched and traced forward in time. We analysed 131 observations of plasma mantle events in Cluster data between 2001 and 2007, and for each event 200 O+ particles were launched with an initial thermal and parallel bulk velocity corresponding to the velocities observed by Cluster. After the tracing, we found that 98% of the particles are lost into the solar wind or in the distant tail. Out of these 98 %, 20% escape via the dayside magnetosphere.

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  • 9.
    Schillings, Audrey
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. School of Physics and Astronomy, University of Leicester, Leicester, United Kingdom.
    Palin, L.
    Toulouse, France.
    Opgenoorth, Hermann J.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. School of Physics and Astronomy, University of Leicester, Leicester, United Kingdom.
    Hamrin, Maria
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Rosenqvist, L.
    Swedish Defence Research Agency, Stockholm, Sweden.
    Gjerloev, J.W.
    JHU/APL, MD, Laurel, United States; Department of Physics and Technology, University of Bergen, Bergen, Norway.
    Juusola, L.
    Finnish Meteorological Institute, Helsinki, Finland.
    Barnes, R.
    JHU/APL, MD, Laurel, United States.
    Distribution and Occurrence Frequency of dB/dt Spikes During Magnetic Storms 1980–20202022Ingår i: Space Weather: The International Journal of Research and Application, E-ISSN 1542-7390, Vol. 20, nr 5, artikel-id e2021SW002953Artikel i tidskrift (Refereegranskat)
    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.

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  • 10.
    Schillings, Audrey
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. School of Physics and Astronomy, University of Leicester, United Kingdom.
    Palin, Laurianne
    Thales Alenia Space, Toulouse, France.
    Bower, Gemma E.
    School of Physics and Astronomy, University of Leicester, United Kingdom.
    Opgenoorth, Hermann J.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. School of Physics and Astronomy, University of Leicester, United Kingdom.
    Milan, Steve E.
    School of Physics and Astronomy, University of Leicester, United Kingdom.
    Kauristie, Kirsti
    Finnish Meteorological Institute, Dynamicum Erik Palménin aukio 1, Helsinki, Finland.
    Juusola, Liisa
    Finnish Meteorological Institute, Dynamicum Erik Palménin aukio 1, Helsinki, Finland.
    Reeves, Geoff D.
    Space Science and Applications Group, Los Alamos National Laboratory, NM, Los Alamos, United States.
    Henderson, Mike G.
    Space Science and Applications Group, Los Alamos National Laboratory, NM, Los Alamos, United States.
    Paxton, Larry J.
    Johns Hopkins University Applied Physics Laboratory, Laurel, United States.
    Lester, Mark
    School of Physics and Astronomy, University of Leicester, United Kingdom.
    Hamrin, Maria
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Van De Kamp, Max
    Finnish Meteorological Institute, Dynamicum Erik Palménin aukio 1, Helsinki, Finland.
    Signatures of wedgelets over Fennoscandia during the St Patrick s Day Storm 20152023Ingår i: Journal of Space Weather and Space Climate, E-ISSN 2115-7251, Vol. 13, artikel-id 19Artikel i tidskrift (Refereegranskat)
    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.

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