An official website of the United States government
Abstract Dipolarizing flux bundles (DFBs) have been suggested to transport energy and momentum from regions of reconnection in the magnetotail to the high latitude ionosphere, where they can generate localized ionospheric currents that can produce large nighttime geomagnetic disturbances (GMDs). In this study we identified DFBs observed in the midnight sector from ∼7 to ∼10 REby THEMIS A, D, and E during days in 2015–2017 whose northern hemisphere magnetic footpoints mapped to regions near Hudson Bay, Canada, and have compared them to isolated GMDs observed by ground magnetometers. We found 6 days during which one or more of these DFBs coincided to within ±3 min with ≥6 nT/s GMDs observed by latitudinally closely spaced ground‐based magnetometers located near those footpoints. Spherical elementary current systems (SECS) maps and all‐sky imager data provided further characterization of two events, showing short‐lived localized intense upward currents, auroral intensifications and/or streamers, and vortical perturbations of a westward electrojet. On all but one of these days the coincident DFB—GMD pairs occurred during intervals of high‐speed solar wind streams but low values of SYM/H. The observations reported here indicate that isolated DFBs generated under these conditions influence only limited spatial regions nearer Earth. In some events, in which the DFBs were observed closer to Earth and with lower Earthward velocities, the GMDs occurred slightly earlier than the DFBs, suggesting that braking had begun before the time of the DFB observation.
more »
« less
This content will become publicly available on July 28, 2026
IMAGE Satellite and Ground‐Based Magnetometer Observations of Large Geomagnetic Disturbances and Rapid Variations in Ionospheric and Vertical Currents
Abstract Ultraviolet images of Earth's polar regions obtained by high altitude spacecraft have proved to be immensely useful for documenting numerous features of the aurora and understanding the coupling between Earth's magnetosphere and ionosphere. In this study we have examined images obtained by the far ultraviolet Spectrographic Imager camera on the IMAGE satellite during the first three years of its mission (2000–2002) for comparison with observations of large geomagnetic disturbances (GMDs) by ground‐based magnetometers in eastern Arctic Canada. To our knowledge, this is the first study to investigate the use of high‐altitude imager data to identify the global context of GMDs. We found that rapid auroral motions or localized intensifications visible in these images coincide with regions of largedB/dtas well as localized and closely spaced up/down vertical currents and increased equivalent ionospheric currents, but one of the two events presented did not appear to be related to substorm processes. These magnetic perturbations and currents can appear or disappear in a few tens of seconds, thus highlighting the importance of images with a high cadence.
more »
« less
- PAR ID:
- 10646742
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 130
- Issue:
- 8
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Auroral substorms that move from auroral (<70°) to polar (>70°) magnetic latitudes (MLAT) are known to occur preferentially when a high‐speed solar wind stream passes by Earth. We report here on observations that occurred during a ∼75‐min interval with high‐speed solar wind on 28 November 2022 during which auroral arcs and very large geomagnetic disturbances (GMDs), also known as magnetic perturbation events (MPEs), with amplitude >9 nT/s = 540 nT/min moved progressively poleward at eight stations spanning a large region near and north of Hudson Bay, Canada shortly before midnight local time. Sustained GMD activity with amplitudes >3 nT/s appeared at each station for durations from 13 to 25 min. Spherical Elementary Currents Systems maps showed the poleward movement of a large‐scale westward electrojet as well as mesoscale electrojet structures and highly localized up/down pairs of vertical currents near these stations when the largest GMDs were observed. This study is consistent with other recent studies showing that very large poleward‐progressing GMDs can occur under high Vsw conditions, but is the first to document the sustained occurrence of large GMDs over such a wide high‐latitude region.more » « less
-
Abstract We present a comprehensive statistical analysis of high‐frequency transient‐large‐amplitude (TLA) magnetic perturbation events that occurred at 12 high‐latitude ground magnetometer stations throughout Solar Cycle 24 from 2009 to 2019. TLA signatures are defined as one or more second‐timescale dB/dtinterval with magnitude ≥6 nT/s within an hour event window. This study characterizes high‐frequency TLA events based on their spatial and temporal behavior, relation to ring current activity, auroral substorms, and nighttime geomagnetic disturbance (GMD) events. We show that TLA events occur primarily at night, solely in the high‐latitude region above 60° geomagnetic latitude, and commonly within 30 min of substorm onsets. The largest TLA events occurred more often in the declining phase of the solar cycle when ring current activity was lower and solar wind velocity was higher, suggesting association to high‐speed streams caused by coronal holes and subsequent corotating interaction regions reaching Earth. TLA perturbations often occurred preceding or within the most extreme nighttime GMD events that have 5–10 min timescales, but the TLA intervals were often even more localized than the ∼300 km effective scale size of GMDs. We provide evidence that shows TLA‐related GMD events are associated with dipolarization fronts in the magnetotail and fast flows toward Earth and are closely temporally associated with poleward boundary intensifications (PBIs) and auroral streamers. The highly localized behavior and connection to the most extreme GMD events suggests that TLA intervals are a ground manifestation of features within rapid and complex ionospheric structures that can drive geomagnetically induced currents.more » « less
-
Abstract We present the first joint high-resolution observations of small-scale EUV jets using Solar Orbiter (SolO)’s Extreme Ultraviolet Imager and High Resolution Imager (EUI/HRIEUV) and Hαimaging from the Visible Imaging Spectrometer installed on the 1.6 m Goode Solar Telescope at the Big Bear Solar Observatory. These jets occurred on 2022 October 29 around 19:10 UT in a quiet Sun region, and their main axis aligns with the overarching magnetic structure traced by a cluster of spicules. However, they develop a helical morphology, while the Hαspicules maintain straight, linear trajectories elsewhere. Alongside the spicules, thin, elongated red- and blueshifted Hαfeatures appear to envelope the EUV jets, which we tentatively call sheath flows. The EUI jet moving upward at a speed of ∼110 km s−1is joined by a strong Hαredshift at ∼20 km s−1to form bidirectional outflows lasting ∼2 minutes. Using AI-assisted differential emission measure analysis of SolO’s Full Sun Imager, we derived total energy of the EUV jet as ∼1.9 × 1026erg with 87% in thermal energy and 13% in kinetic energy. The parameters and morphology of this small-scale EUV jet are interpreted based on a thin flux tube model that predicts Alfvénic waves driven by impulsive interchange reconnection localized as narrowly as ∼1.6 Mm with a magnetic flux of ∼5.4 × 1017Mx, belonging to the smallest magnetic features in the quiet Sun. This detection of intricate corona–chromospheric coupling highlights the power of high-resolution imaging in unraveling the mechanisms behind small-scale solar ejections across atmospheric layers.more » « less
-
Abstract Nearly all studies of impulsive geomagnetic disturbances (GMDs, also known as magnetic perturbation events MPEs) that can produce dangerous geomagnetically induced currents (GICs) have used data from the northern hemisphere. In this study, we investigated GMD occurrences during the first 6 months of 2016 at four magnetically conjugate high latitude station pairs using data from the Greenland West Coast magnetometer chain and from Antarctic stations in the conjugate AAL‐PIP magnetometer chain. Events for statistical analysis and four case studies were selected from Greenland/AAL‐PIP data by detecting the presence of >6 nT/s derivatives of any component of the magnetic field at any of the station pairs. For case studies, these chains were supplemented by data from the BAS‐LPM chain in Antarctica as well as Pangnirtung and South Pole in order to extend longitudinal coverage to the west. Amplitude comparisons between hemispheres showed (a) a seasonal dependence (larger in the winter hemisphere), and (b) a dependence on the sign of theBycomponent of the interplanetary magnetic field (IMF): GMDs were larger in the north (south) when IMFBywas >0 (<0). A majority of events occurred nearly simultaneously (to within ±3 min) independent of the sign ofByas long as |By| ≤ 2 |Bz|. As has been found in earlier studies, IMFBzwas <0 prior to most events. When IMF data from Geotail, Themis B, and/or Themis C in the near‐Earth solar wind were used to supplement the time‐shifted OMNI IMF data, the consistency of these IMF orientations was improved.more » « less
