Mesoscale <i>F</i> Region Neutral Winds Associated With Quasi‐steady and Transient Nightside Auroral Forms

Zou, Ying; Nishimura, Y.; Lyons, L. R.; Conde, M.; Varney, R. H.; Angelopoulos, V.; Mende, S. B.

doi:10.1029/2018ja025457

Cited by 20 publications

(39 citation statements)

References 46 publications

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“…In addition to the wind responses to different substorm phases, we inferred that strong meridional gradient of the zonal wind on a spatial scale of tens of kilometers may exist in the vicinity of the growth‐phase moving arc, as shown in E3. The small‐scale wind structures have been identified using scanning Doppler imagers (e.g., Anderson et al, ; Conde et al, ; Dhadly & Conde, ; Kosch et al, ; Zou et al, ). Conde et al () found a meridional wind shear associated with an auroral arc in the dusk sector moving with the arc.…”

Section: Discussionmentioning

confidence: 99%

Fabry‐Perot Interferometer Observations of Thermospheric Horizontal Winds During Magnetospheric Substorms

et al. 2019

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The high‐latitude ionosphere‐thermosphere system is strongly affected by the magnetospheric energy input during magnetospheric substorms. In this study, we investigate the response of the upper thermospheric winds to four substorm events by using the Fabry‐Perot interferometer at Tromsø, Norway, the International Monitor for Auroral Geomagnetic Effects magnetometers, the EISCAT radar, and an all‐sky camera. The upper thermospheric winds had distinct responses to substorm phases. During the growth phase, westward acceleration of the wind was observed in the premidnight sector within the eastward electrojet region. We suggest that the westward acceleration of the neutral wind is caused by the ion drag force associated with the large‐scale westward plasma convection within the eastward electrojet. During the expansion phase, the zonal wind had a prompt response to the intensification of the westward electrojet (WEJ) overhead Tromsø. The zonal wind was accelerated eastward, which is likely to be associated with the eastward plasma convection within the substorm current wedge. During the expansion and recovery phases, the meridional wind was frequently accelerated to the southward direction, when the majority of the substorm WEJ current was located on the poleward side of Tromsø. We suggest that this meridional wind acceleration is related to a pressure gradient produced by Joule heating within the substorm WEJ region. In addition, strong atmospheric gravity waves during the expansion and the recovery phases were observed.

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Section: Discussionmentioning

confidence: 99%

Fabry‐Perot Interferometer Observations of Thermospheric Horizontal Winds During Magnetospheric Substorms

et al. 2019

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“…This is understood to be due to the increased ionization brought about from particle precipitation, increasing ion-neutral collision frequencies, and thus coupling. Similar observations were also made by Zou et al (2018). Both of these studies exploited results from a Scanning Doppler Imager (SDI), a type of FPI which can measure more than one single point neutral wind measurement (Conde & Smith, 1997), setting it apart from traditional FPIs.…”

Section: Introductionmentioning

confidence: 63%

“…As studied by Conde et al (2018) and Zou et al (2018), the drastic increase in ion density introduced by precipitation will enhance the neutral-ion collision frequency, which in turn strengthens ion drag. However, the potential variability of lags with local time, and thus universal time, is not well understood and could affect the results shown here.…”

Section: 1029/2019ja026627mentioning

confidence: 99%

“…Both of these studies exploited results from a Scanning Doppler Imager (SDI), a type of FPI which can measure more than one single point neutral wind measurement (Conde & Smith, 1997) Shepherd, 2014Shepherd, , as of 2018. Thus, we would usually expect the neutral velocities observed by SCANDI to have longer lag times than those found by Conde et al (2018) and Zou et al (2018) due to less ionization from increased particle precipitation, resulting in fewer collisions between the plasma and neutrals. SCANDI allows a neutral wind delay to changes in the plasma to be resolved for each neutral wind vector determined, at a spatial resolution of approximately 100 km at 250-km altitude, thus allowing the examination of mesoscale changes in ion drag.…”

Section: Introductionmentioning

confidence: 99%

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Spatially Resolved Neutral Wind Response Times During High Geomagnetic Activity Above Svalbard

et al. 2019

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It has previously been shown that in the high‐latitude thermosphere, sudden changes in plasma velocity (such as those due to changes in interplanetary magnetic field) are not immediately propagated into the neutral gas via the ion‐drag force. This is due to the neutral particles (O, O2, and N2) constituting the bulk mass of the thermospheric altitude range and thus holding on to residual inertia from a previous level of geomagnetic forcing. This means that consistent forcing (or dragging) from the ionospheric plasma is required, over a period of time, long enough for the neutrals to reach an equilibrium with regard to ion drag. Furthermore, mesoscale variations in the plasma convection morphology, solar pressure gradients, and other forces indicate that the thermosphere‐ionosphere coupling mechanism will also vary in strength across small spatial scales. Using data from the Super Dual Auroral Radar Network and a Scanning Doppler Imager, a geomagnetically active event was identified, which showed plasma flows clearly imparting momentum to the neutrals. A cross‐correlation analysis determined that the average time for the neutral winds to accelerate fully into the direction of ion drag was 75 min, but crucially, this time varied by up to 30 min (between 67 and 97 min) within a 1,000‐km field of view at an altitude of around 250 km. It is clear from this that the mesoscale structure of both the plasma and neutrals has a significant effect on ion‐neutral coupling strength and thus energy transfer in the thermosphere.

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“…Given that the Cluster observations indicate that patches are associated with Region 1 sense FAC structures and a downward Poynting flux, this work contradicts the notion that the source of the lobe features associated with patches are generated in the ionosphere. The results of this study are therefore important for our understanding of mesoscale magnetospheric forcing on open magnetic field lines and ion-neutral coupling within patches (such as that discussed in Zou et al, 2018).…”

Section: Discussionmentioning

confidence: 95%

Mesoscale Convection Structures Associated With Airglow Patches Characterized Using Cluster‐Imager Conjunctions

et al. 2019

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Polar cap ionospheric plasma flow studies often focus on large‐scale averaged properties and neglect the mesoscale component. However, recent studies have shown that mesoscale flows are often found to be collocated with airglow patches. These mesoscale flows are typically a few hundred meters per second faster than the large‐scale background and are associated with major auroral intensifications when they reach the poleward boundary of the nightside auroral oval. Patches often also contain ionospheric signatures of enhanced field‐aligned currents and localized electron flux enhancements, indicating that patches are associated with magnetosphere‐ionosphere coupling on open field lines. However, magnetospheric measurements of this coupling are lacking, and it has not been understood what the magnetospheric signatures of patches on open field lines are. The work presented here explores the magnetospheric counterpart of patches and the role these structures have in plasma transport across the open field‐line region in the magnetosphere. Using red‐line emission measurements from the Resolute Bay Optical Mesosphere Thermosphere Imager, and magnetospheric measurements made by the Cluster spacecraft, conjugate events from 2005 to 2009 show that lobe measurements on field lines connected to patches display (1) electric field enhancements, (2) Region 1 sense field‐aligned currents, (3) field‐aligned enhancements in soft electron flux, (4) downward Poynting fluxes, and (5) in some cases enhancements in ion flux, including ion outflows. These observations indicate that patches highlight a localized fast flow channel system that is driven by the magnetosphere and propagates from the dayside to the nightside, most likely being initiated by enhanced localized dayside reconnection.

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Mesoscale F Region Neutral Winds Associated With Quasi‐steady and Transient Nightside Auroral Forms

Cited by 20 publications

References 46 publications

Fabry‐Perot Interferometer Observations of Thermospheric Horizontal Winds During Magnetospheric Substorms

Fabry‐Perot Interferometer Observations of Thermospheric Horizontal Winds During Magnetospheric Substorms

Spatially Resolved Neutral Wind Response Times During High Geomagnetic Activity Above Svalbard

Mesoscale Convection Structures Associated With Airglow Patches Characterized Using Cluster‐Imager Conjunctions

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