Dayside flow bursts and high-latitude reconnection when the IMF is strongly  northward

Hu, Hongqiao; Yeoman, T. K.; Lester, M.; Liu, R.; Yang, Huigen; Grocott, Adrian

doi:10.5194/angeo-24-2227-2006

Cited by 10 publications

(17 citation statements)

References 64 publications

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“…The suggestion of throat aurora being related with reconnection is also consistent with the statistical properties of throat aurora. It has been established that the ionospheric convection driven by reconnections generally shows two‐cell or four‐cell patterns and the convection throat gate shifts from MLN toward dawn and dusk under positive and negative IMF B y conditions [ Hu et al, ; Lockwood and Moen , ; Ruohoniemi and Greenwald , ; Weimer , ]. Compared with the SuperDARN observations, we confirmed that the orientation of throat aurora is convection aligned, so the local time distribution of the S‐N throat aurora shown in Figure can be regarded as the distribution of the center of the throat gate of the ionospheric convection near MLN.…”

Section: Summary and Discussionsupporting

confidence: 72%

Observational properties of dayside throat aurora and implications on the possible generation mechanisms

et al. 2017

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Observational properties of throat aurora are investigated in detail by using 7 year continuous auroral observations obtained at Yellow River Station (magnetic latitude 76.24°N). From our inspection, throat aurora is often observed under the condition of stripy diffuse aurora contacting with the persistent discrete auroral oval, and the long‐period throat aurora observations generally consist of intermittent subsequences of throat aurora brightening followed by poleward moving auroral form and throat aurora dimming. We also noticed that the orientation of throat aurora is aligned along the ionospheric convection flow, and its local time distribution shows clear dependence on the interplanetary magnetic field (IMF) By component. These observational results indicate that factors inside the magnetosphere may play important role on occurrence of throat aurora. We thus suggest that throat aurora may present the ionospheric signature of redistribution of reconnection rate on the magnetopause by cold magnetospheric plasma flowing into the reconnection site. In addition, we also found that the occurrence rate of throat aurora clearly decreases with increase of the IMF cone angle (arccos(|Bx|/B)), which is very similar with the occurrence rate of high‐speed jet (HSJ) observed in magnetosheath depending on the IMF cone angle. This is suggested as that the HSJs occurred outside the magnetosphere may also play important role for generation of throat aurora by triggering magnetopause reconnection or by direct impacting. Although further studies are needed to clarify how the throat auroras are generated in detail, the relevant observations about throat aurora have presented important implications on a variety open questions, such as distribution and generation of cold plasma structures in the outer magnetosphere, magnetopause deformation, and possible relation between HSJ and reconnection.

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Section: Summary and Discussionsupporting

confidence: 72%

Observational properties of dayside throat aurora and implications on the possible generation mechanisms

et al. 2017

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“…Therefore, the presence of a four convection cells pattern in this event is a strong consistent evidence for the occurrence of lobe reconnection along the highlatitude magnetopause tailward of the cusp after the Fig. 9 Two-dimensional ionospheric convection pattern derived from the SuperDARN radars at 09:24-09:26 UT shock arrival (Crooker 1992;Hu et al 2006;Lu et al 2011). In other words, the intensified and equatorwardmoving discrete auroral filaments that we observe are the typical optical feature that can be attributed to lobe reconnection occurring along the high-latitude magnetopause during shock compression.…”

Section: Resultsmentioning

confidence: 62%

Simultaneous ground-based optical and SuperDARN observations of the shock aurora at MLT noon

Liu

Han

et al. 2015

Earth Planet Sp

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Using ground-based high temporal and spatial optical aurora observations, we investigated one fortuitous event to illustrate the direct responses of the fine structure auroral emission to interplanetary shock on 7 January 2005. During the shock impact to the magnetosphere, the Chinese Arctic Yellow River Station (YRS) equipped with all-sky imagers (ASIs) was situated at the magnetic local noon region (~1210 MLT) in the Northern Hemisphere, while the SuperDARN CUTLASS Finland HF radar covering the field of view (FOV) of the ASIs at YRS had fine ionospheric plasma convection measurement. We observed that an intensified red aurora manifesting as a discrete emission band at a higher latitude responds to the shock impact gradually, which results in a distinct broadening of the dayside auroral oval due to the equatorward shifting of its lower latitude boundary after the shock arrival. In contrast, the green diffuse aurora, manifesting as a relatively uniform luminosity structure, reacts immediately to the shock compression, displaying prompt appearance in the southern edge of the FOV and subsequent poleward propagation of its higher latitude boundary. Simultaneously, the CUTLASS Finland radar monitored enhanced backscatter echo power and increased echo number, which coincided with intensified discrete aurora in approximately the same latitudinal region. Doppler velocity measurement showed moving ionospheric irregularities with generally enhanced line-of-sight (LOS) speed, but with prominent sunward flow in the polar cap and antisunward flow in both the eastern and western regions. The SuperDARN global ionospheric convection pattern clearly presented a large-scale plasma flow divided in four circulation cells, with two reversed flow cells nested in the noon sector of the polar cap. These direct observations strongly suggest that the prompt shock compression intensified the wave-particle interaction in the inner magnetosphere and enhanced the lobe magnetic reconnection rate at magnetospheric high latitude.

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“…Indeed, the reversed two‐cell convection configuration is often found in the Summer Hemisphere, whereas weak, distorted, convection is typically seen in the Winter Hemisphere under northward IMF [e.g., Bythrow et al , 1985; Knipp et al , 1993; Lu et al , 1994]. Sunward plasma flows have been observed in the Northern and Southern Hemispheres under northward IMF conditions [ Reiff, 1982; Cumnock et al , 1995; Imber et al , 2006; Hu et al , 2006]. However, the reversed two‐cell convection patterns that form simultaneously in both the hemispheres have rarely been reported partly because of the fortuitous seasonal and IMF conditions that are required for such events and partly because of the inadequate global coverage of observations.…”

Section: Introductionmentioning

confidence: 99%

Reversed two-cell convection in the Northern and Southern hemispheres during northward interplanetary magnetic field

Lu¹,

Li²,

Raeder³

et al. 2011

J. Geophys. Res.

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[1] This article presents a case study of large-scale ionospheric convection in the Northern and Southern Hemispheres under strongly northward interplanetary magnetic field (IMF) conditions on 9 November 2004. Using a comprehensive data set from both ground-and space-based instruments, the study shows the formation of reversed two-cell convection in both the Northern and Southern Hemispheres that lasted for nearly 2 hours. Examination of the concurrent satellite energy-time spectrograms of precipitating particles reveals that reverse convection occurs in the region filled mostly with the boundary plasma sheet (BPS) type precipitating electrons except that the electron number flux is much smaller than that in the normal BPS. We have named this region the northward B z boundary layer (NBZBL), which we interpret as a consequence of double-lobe reconnection. This interpretation is corroborated by the global MHD simulations, which show that the NBZBL consists of mostly closed field lines, resulting from double-lobe reconnection in both the hemispheres, together with intermittent presence of overdraped open field lines, resulting from single-lobe reconnection in one of the hemispheres. In addition to reversed two-cell convection, the distribution of field-aligned currents (FACs) shows clearly the presence of a pair of the northward B z (NBZ) currents near the central polar region in both the hemispheres. Intense downward Poynting flux with a peak value around 100 mW/m 2 is also seen in the high-latitude polar region, which tends to surround the upward leg of the NBZ currents. Finally, the potential drop between the two reverse-convection cells exceeds 100 kV, which is far larger than the values reported in any previous studies of reverse convection under northward IMF conditions. The unusually large reverse potential drop in this case is attributed in part to the strong NBZ component of 35-40 nT and in part to the unusually large solar wind dynamic pressure that is about five times its nominal value.

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Dayside flow bursts and high-latitude reconnection when the IMF is strongly northward

Cited by 10 publications

References 64 publications

Observational properties of dayside throat aurora and implications on the possible generation mechanisms

Observational properties of dayside throat aurora and implications on the possible generation mechanisms

Simultaneous ground-based optical and SuperDARN observations of the shock aurora at MLT noon

Reversed two-cell convection in the Northern and Southern hemispheres during northward interplanetary magnetic field

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