Polar cap convection relationships with solar wind

MacDougall, J. W.; Jayachandran, P. T.

doi:10.1029/2001rs001007

Cited by 38 publications

(41 citation statements)

References 20 publications

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“…The IMF By also controls dawn-dusk motion of patches (Moen et al 2008a;Hosokawa et al 2009). Convection within the polar cap is often assumed to consist of relatively uniform anti-sunward flow with a typical speed of several hundreds of m/s (e.g., MacDougall and Jayachandran 2001).…”

Section: Introductionmentioning

confidence: 99%

Analysis of close conjunctions between dayside polar cap airglow patches and flow channels by all-sky imager and DMSP

et al. 2016

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Recent imager and radar observations in the nightside polar cap have shown evidence that polar cap patches are associated with localized flow channels. To understand how flow channels propagate from the dayside auroral oval into the polar cap, we use an all-sky imager in Antarctica and DMSP (F13, F15, F16, F17 and F18) to determine properties of density and flows associated with dayside polar cap patches. We identified 50 conjunction events during the southern winter seasons of 2007-2011. In a majority (45) of events, longitudinally narrow flow enhancements directed anti-sunward are found to be collocated with the patches, have velocities (up to a few km/s) substantially larger than the large-scale background flows (~500 m/s) and have widths comparable to patch widths (~400 km). While the patches start with poleward moving auroral forms (PMAFs) as expected, many PMAFs propagate azimuthally away from the noon over a few hours of MLT, resulting in formation of polar cap patches quite far away from the noon, as early as ~6 MLT. The MLT separation from the noon is found to be proportional to the IMF |By|. Fast polar cap flows of >~1500 m/s are predominantly seen during large IMF |By| and small |Bz|. The presence of fast, anti-sunward flow channels associated with the polar cap patches suggests that the flow channels form in the dayside auroral oval through transient reconnection and can be the source of flow channels propagating into the polar cap.

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Section: Introductionmentioning

confidence: 99%

Analysis of close conjunctions between dayside polar cap airglow patches and flow channels by all-sky imager and DMSP

et al. 2016

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“…As mentioned in previous section, most of the solar wind and IMF parameters remained steady during the interval with the exception of the By component of the IMF. The parameter that mainly controls the energy input into the magnetosphere is the IMF Bz and this component remained southward during this period indicating normal active “two cell” convection pattern [ MacDougall and Jayachandran , 2001]. What does stand out, however, is that the IMF By component was undergoing oscillations with a similar time scale to those of the undulation and the variations in the inclination.…”

Section: Discussionmentioning

confidence: 99%

“…To show that there is a systematic variation in the polar cap convection direction associated with the IMF B y variations, we have looked at the polar cap convection variation during the event. During the period of study there was a Canadian Advanced Digital Ionosonde (CADI) [ MacDougall and Jayachandran , 2001] operational at Eureka (center of the polar cap). CADI measures the convection speed and azimuth continuously.…”

Section: Discussionmentioning

confidence: 99%

“…Each solid circle represents a CADI measurement (every 30 seconds) and solid line is the two‐minute running average. Speed of the convection varied between 400 and 700 m/s (average of ∼500 m/s) and is the expected speed for the negative IMF Bz condition of ∼−4 nT [ MacDougall and Jayachandran , 2001]. The interesting feature is deviation of the convection azimuth from the expected antisunward convection direction due to the changes in the IMF By.…”

Section: Discussionmentioning

confidence: 99%

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Oscillations of the equatorward boundary of the ion auroral oval – radar observations

et al. 2008

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Three SuperDARN radars in the afternoon‐midnight sector of the auroral oval detected a boundary oscillation, originating near ∼1800 MLT sector. Analysis of the phase of the oscillations measured in three meridians indicates that the disturbance has a longitudinally (azimuthally) isolated source and away from which it propagates. The eastward and westward phase speeds are 2.6 and 3.6 km/s respectively and the period is roughly 28 minutes. An examination of the geo‐synchronous magnetic field inclination also revealed oscillations similar to the oscillations of the boundary. Solar wind and IMF conditions were steady during the period except for variations of the IMF By component. The IMF By component showed variations similar to the oscillations in the boundary and the geo‐synchronous magnetic field inclination. During reduced and negative IMF By, the boundary was moving equatorward, while during increased or positive IMF By it was moving poleward. The variations in the magnetic field inclination measured at geosynchronous orbit by the GOES satellites were consistent with these boundary motions: decreases (more stretched) and increases (more dipolar) in the inclination corresponded to equatorward and poleward moving boundaries, respectively. Polar cap convection also showed changes in the direction of the convection in response to the change in the IMF By component. Observed oscillation of the boundary can be explained by stretching of the tail field lines due to asymmetric merging associated with changes in the By component of the interplanetary magnetic field.

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“…Unfortunately, the CADI dataset from Eureka for the CME-driven event of 6 November 2000 is incomplete and thus the data from another CADI ionosonde located at Resolute (about 500 km southward of Eureka) has been used for this event. CADI ionosondes produce conventional ionograms as well as provide velocity and ionospheric drift measurements derived from the fixed frequency Doppler measurements with temporal resolution of 30 s (MacDougall & Jayachandran 2001). …”

Section: Digital Ionosonde Observationsmentioning

confidence: 99%

High-latitude ionospheric response to co-rotating interaction region- and coronal mass ejection-driven geomagnetic storms revealed by GPS tomography and ionosondes

et al. 2010

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Positive ionospheric anomalies induced in the polar cap region by co-rotating interaction region (CIR)-and coronal mass ejection (CME)-driven geomagnetic storms are analysed using four-dimensional tomographic reconstructions of the ionospheric plasma density based on measurements of the total electron content along ray paths of GPS signals. The results of GPS tomography are compared with ground-based observations of F region plasma density by digital ionosondes located in the Canadian Arctic. It is demonstrated that CIR-and CME-driven storms can produce large-scale polar cap anomalies of similar morphology in the form of the tongue of ionization (TOI) that appears on the poleward edge of the mid-latitude dayside storm-enhanced densities in positive ionospheric storms. The CIR-driven event of 14-16 October 2002 was able to produce ionospheric anomalies (TOI) comparable to those produced by the CME-driven storms of greater Dst magnitude. From the comparison of tomographic reconstructions and ionosonde data with solar wind measurements, it appears that the formation of largescale polar cap anomalies is controlled by the orientation of the interplanetary magnetic field (IMF) with the TOI forming during the periods of extended southward IMF under conditions of high solar wind velocity.

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Polar cap convection relationships with solar wind

Cited by 38 publications

References 20 publications

Analysis of close conjunctions between dayside polar cap airglow patches and flow channels by all-sky imager and DMSP

Analysis of close conjunctions between dayside polar cap airglow patches and flow channels by all-sky imager and DMSP

Oscillations of the equatorward boundary of the ion auroral oval – radar observations

High-latitude ionospheric response to co-rotating interaction region- and coronal mass ejection-driven geomagnetic storms revealed by GPS tomography and ionosondes

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