| 11. |
- Cabrit, B, et al.
(author)
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Comparison between EISCAT UHF and VHF backscattering cross section
- 1996
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In: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS. - : AMER GEOPHYSICAL UNION. ; 101:A2, s. 2369-2376
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Journal article (other academic/artistic)abstract
- We present a comparison between the backscattering cross sections at 224 and 933 MHz measured with European Incoherent Scatter (EISCAT) radars during the passage of a discrete are. It shows a difference of 2 orders of magnitude which cannot simply be expl
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| 12. |
- Engebretson, Mark J., et al.
(author)
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Interhemispheric Comparisons of Large Nighttime Magnetic Perturbation Events Relevant to GICs
- 2020
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In: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 125:8
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Journal article (peer-reviewed)abstract
- 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.
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| 13. |
- Engebretson, Mark J., et al.
(author)
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Nighttime Magnetic Perturbation Events Observed in Arctic Canada: 3. Occurrence and Amplitude as Functions of Magnetic Latitude, Local Time, and Magnetic Disturbance Indices
- 2021
-
In: Space Weather. - : American Geophysical Union (AGU). - 1542-7390. ; 19:3
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Journal article (peer-reviewed)abstract
- 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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| 14. |
- Jackel, B., Eglitis, P., Donovan, E., Viljanen, A., Wallis, D., Cogger, L. and Opgenoorth, H.
(author)
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Observations of highly correlated near-simultaneous magnetic field perturbations at contraposed ground stations.
- 2001
-
In: Journal of Geophysical Research. ; 106, s. 25857-
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Journal article (peer-reviewed)abstract
- A merged data set from Canadian Auroral Network for the OPEN Program Unified Study (CANOPUS) and Magnetometers-Ionospheric Radars-All-Sky Cameras Large Experiment (MIRACLE) magnetometer stations is used to study variations observed at widely separated loc
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| 15. |
- Kaurisitie, K., Syrjsuo, M., Amm, O., Viljanen, A., Pulkkinen, T.I. and Opgenoorth, H.J.
(author)
-
A statistical study of evening sectorarcs and electrojets.
- 2001
-
In: Advances in Space Research. ; 28, s. 16045-1610
-
Journal article (peer-reviewed)abstract
- We present results of a statistical study of evening sector auroral arcs associated with electrojets. The study (including similar to 1000 all-sky camera (ASC) frames) is based on data of the MIRACLE instrument network. An automatic search engine is used
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| 16. |
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| 17. |
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| 18. |
- Lockwood, M., Fazakerley, A., Opgenoorth, H., Moen, J., van Eyken, A.P., Dunlop, M., Bosqued, J.M., Lu, G., Cully, C., Eglitis, P., McCrea, I., Hapgood, M. A., Wild, M.N., Stamper, R., Denig, W., Taylor, M., . Wild, J.A., Provan, G., Amm, O., Kauristie
(author)
-
Coordinated Cluster, ground-based instrumentation and low-altitude satellite observations of transient poleward-moving events in the ionosphere and in the tail lobe
- 2001
-
In: Annales Geophysicae. ; 19:10, s. 1589-1612
-
Journal article (peer-reviewed)abstract
- During the interval between 8:00–9:30 on 14 January 2001, the four Cluster spacecraft were moving from the central magnetospheric lobe, through the dusk sector mantle, on their way towards intersecting the magnetopause near 15:00 MLT and 15:00 UT. Throug
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| 19. |
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| 20. |
- Marklund, Göran, et al.
(author)
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On the electrodynamic state of the auroral ionosphere during northward interplanetary magnetic field - a transpolar arc case study
- 1991
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In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 96:A6, s. 9567-9578
-
Journal article (peer-reviewed)abstract
- The ionospheric electrodynamical state has been reconstructed for a transpolar arc event during northward interplanetary magnetic field conditions. An extensive set of observations by Viking and other satellites and by ground-based radars has been used to provide realistic model input data or to verify the modeling results. The resulting convection pattern is found to be consistent with the Viking electric field and intimately linked to the prevalent auroral distribution. It is characterized by a large evening cell, well extended across noon and split up by two separated potential minima, and a minor crescent-shaped morning cell. The convection signatures are found to vary a lot along the transpolar arc depending on the relative role of the arc-associated convection and the ambient convection. The transpolar arc is generally embedded in antisunward convective flow except near the connection points with the auroral oval, where sunward flow exists in localized regions.
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