Multi-instrumentation observations of a transpolar arc in the northern hemisphere

Goudarzi, Alireza; Lester, M.; Milan, S. E.; Frey, H. U.

doi:10.5194/angeo-26-201-2008

Cited by 29 publications

(39 citation statements)

References 31 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We focus on two clear dawn‐dusk motions of PCAs, at 20:23 and 23:08 UT (highlighted by the two vertical red lines) after the IMF B y polarity changes with a 69 min time delay to allow the IMF variations propagating through the magnetosphere. This clearly shows that IMF B y polarity change or strong magnitude change can trigger the existing PCA to move poleward, which confirms many previous studies (Fear & Milan, ; Goudarzi et al, ; Kullen et al, ; Milan et al, ). One point to note regarding the optical observation is that the intensity of 557.7 nm is much higher than the 630.0 nm intensity.…”

Section: Observationssupporting

confidence: 90%

“…In addition, Kullen et al () confirmed the previously reported statistical relationship between PCAs and reconnection‐induced flows in the ionosphere, implicitly indicating that an IMF B y sign change does not trigger the formation of a PCA, though it does cause a dawn‐dusk motion of an already existing PCA over the polar cap. Many other previous studies have also showed that the IMF B y polarity change (or strong magnitude change) can trigger the existing PCA to move over the polar cap (Fear & Milan, ; Goudarzi et al, ; Milan et al, ). When the IMF B y sign is positive (negative), a PCA can separate from the dusk (dawn) oval side and move across the polar cap in the Northern Hemisphere (Frank et al, ; Huang et al, ; Kullen et al, ; Milan et al, ) and the IMF B y has an opposite effect on the motion of PCAs in the Southern Hemisphere (Craven et al, ).…”

Section: Introductionmentioning

confidence: 89%

See 1 more Smart Citation

Conjugate Observations of the Evolution of Polar Cap Arcs in Both Hemispheres

et al. 2018

View full text Add to dashboard Cite

We report results from the analysis of a case of conjugate polar cap arcs (PCAs) observed on 5 February 2006 in the Northern Hemisphere by the ground‐based Yellow River Station all‐sky imager (Svalbard) and in both hemispheres by the space‐based DMSP/SSUSI and TIMED/GUVI instruments. The PCA's motion in dawn‐dusk direction shows a clear dependence on the interplanetary magnetic field (IMF) By component and presents a clear asymmetry between Southern and Northern Hemispheres, that is, formed on the duskside and moving from dusk to dawn in the Northern Hemisphere and vice versa in the other hemisphere. The already existing PCAs' motion is influenced by the changes in the IMF By with a time delay of ~70 min. We also observed strong flow shears/reversals around the PCAs in both hemispheres. The precipitating particles observed in the ionosphere associated with PCAs showed properties of boundary layer plasma. Based on these observations, we might reasonably expect that the topological changes in the magnetotail can produce a strip of closed field lines and local processes would set up conditions for the formation and evolution of PCAs.

show abstract

Section: Observationssupporting

confidence: 90%

Section: Introductionmentioning

confidence: 89%

Conjugate Observations of the Evolution of Polar Cap Arcs in Both Hemispheres

et al. 2018

View full text Add to dashboard Cite

show abstract

“…As more and more flux is closed in this magnetic local time (MLT) sector, the trapped field lines will protrude deeper into the magnetotail lobes. This mechanism has been validated by several different case studies [e.g., Goudarzi et al , ; Fear et al , ]. Furthermore, the main predictions from the mechanism, i.e., a delay in the MLT dependence on the IMF B y and an association with TRINNI flows, have been statistically verified by Fear and Milan [, ].…”

Section: Introductionmentioning

confidence: 63%

Multi‐instrument observation of simultaneous polar cap auroras on open and closed magnetic field lines

et al. 2017

Self Cite

View full text Add to dashboard Cite

This paper presents observations of polar cap auroral features on 19 January 2008, evaluated using multiple instruments with near‐simultaneous observations in both hemispheres. Analysis of the features indicates that there are at least two formation mechanisms/types of polar cap aurora occurring simultaneously on different magnetic field topologies (one on open and the other on closed magnetospheric field lines). Two high‐latitude structures were observed on opposing sides of the northern hemisphere polar cap in the same time interval. The structure on the duskside was formed on closed field lines that protruded into the polar cap and was generated by the precipitation of electrons with energies varying between 2 and 11 keV consistent with an identified mechanism for the formation of transpolar arcs. However, the structure did not extend fully across to the dayside of the auroral oval but rather stayed at ∼80° magnetic latitude for a minimum duration of 40 min. Thus, this structure is an example of a “failed” transpolar arc. The structure on the dawnside of the polar cap was associated with low‐energy electron precipitation (less than 1 keV) and no associated ion signatures, which is consistent with it being a common low‐intensity arc formed by accelerated polar rain on open field lines. The two separate types of polar cap auroras formed during the same interval, demonstrating the complexity of the solar wind‐magnetosphere coupling during the interval.

show abstract

“…Predictions from this mechanism have been verified by Fear and Milan (), who explored the relation between the position where arcs formed in the polar cap and the IMF B y component, and Fear and Milan (), who found statistical evidence for reconnection‐induced flows in the ionosphere before the formation of the TPAs. Furthermore, several recent case studies have also provided evidence in support of this mechanism (e.g., Carter et al, ; Fear et al, ; Goudarzi et al, ).…”

Section: Introductionmentioning

confidence: 92%

Interhemispheric Survey of Polar Cap Aurora

et al. 2018

Self Cite

View full text Add to dashboard Cite

This study investigates the interhemispheric nature of polar cap auroras via ultraviolet imaging, combined with particle data, to determine whether they occur on open or closed field lines. Data from the SSUSI (Special Sensor Ultraviolet Spectrographic Imager) instrument on board the DMSP (Defence Meteorological Satellite Program) spacecraft are examined. The DMSP spacecraft are in 90‐min orbits; hence, images of each hemisphere are separated by 45 min providing a good opportunity for interhemispheric study. 21 polar cap arc (PCA) events are recorded in December 2015 which have particle data from the SSJ/4 particle spectrometer associated with an arc in at least one hemisphere. Nine events are found to contain "arcs" consistent with a closed field line mechanism, that is, arcs associated with an ion signature present in both hemispheres. Six events contained arcs that were consistent with an "open field line" mechanism, that is, they were associated with electron‐only precipitation. Events containing arcs that were not consistent with either of these expectations are also explored, including an example of a "non‐conjugate" theta aurora and an interesting example of auroral morphology similar to a PCA which is associated with a geomagnetic storm. Seasonal effects are also investigated through a statistical analysis of PCAs over 4 months in 2015. It is found that PCAs are visible in the SSUSI data at least 20% of the time and that it is likely some are missed due to the spacecraft field of view and poor sensitivity in the summer hemisphere due to increased solar illumination.

show abstract

Multi-instrumentation observations of a transpolar arc in the northern hemisphere

Cited by 29 publications

References 31 publications

Conjugate Observations of the Evolution of Polar Cap Arcs in Both Hemispheres

Conjugate Observations of the Evolution of Polar Cap Arcs in Both Hemispheres

Multi‐instrument observation of simultaneous polar cap auroras on open and closed magnetic field lines

Interhemispheric Survey of Polar Cap Aurora

Contact Info

Product

Resources

About