The polar ionosphere

McEwen, D. J.; Guo, W.; MacDougall, J. W.; Jayachandran, P. T.

doi:10.1016/j.asr.2004.06.011

Cited by 7 publications

(5 citation statements)

References 8 publications

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“…By contrast to the regular behavior of the summer F layer, the winter heights and critical frequencies vary considerably. This is consistent with the fact that winter ionization is mainly produced by a combination of the soft particle precipitations and/or patches of enhanced ionization generated at the lower latitudes on the dayside and propagating antisunward across the polarcap with photoionization playing a secondary role [ Buchau et al , 1983; McEwen et al , 1994]. The spring and autumn data (Figure 6 (left)) reflect the transition between winter and summer conditions.…”

Section: Discussion and Interpretationsupporting

confidence: 78%

HF ground scatter from the polar cap: Ionospheric propagation and ground surface effects

et al. 2010

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[1] In addition to being scattered by the ionospheric field-aligned irregularities, HF radar signals can be reflected by the ionosphere toward the Earth and then scattered back to the radar by the rugged ground surface. These ground scatter (GS) echoes are responsible for a substantial part of the returns observed by HF radars making up the Super Dual Auroral Radar Network (SuperDARN). While a GS component is conventionally used in studying ionosphere dynamics (e.g., traveling ionospheric disturbances, ULF waves), its potential in monitoring the state of the scattering surface remains largely unexploited. To fill this gap, we investigated diurnal and seasonal variation of the ground echo occurrence and location from a poleward-looking SuperDARN radar at Rankin Inlet, Canada. Using colocated ionosonde information, we have shown that seasonal and diurnal changes in the high-latitude ionosphere periodically modulate the overall echo occurrence rate and spatial coverage. In addition, characteristics of GS from a particular geographic location are strongly affected by the state of the underlying ground surface. We have shown that (1) ice sheets rarely produce detectable backscatter, (2) mountain ranges are the major source of GS as they can produce echoes at all seasons of the year, and (3) sea surface becomes a significant source of GS once the Arctic sea ice has melted away. Finally, we discuss how the obtained results can expand SuperDARN abilities in monitoring both the ionosphere and ground surface.

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Section: Discussion and Interpretationsupporting

confidence: 78%

HF ground scatter from the polar cap: Ionospheric propagation and ground surface effects

et al. 2010

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“…During southward IMF trains of polar cap patches/solar-EUV ionized plasma drift across the polar cap from day to night (Foster 1984;, 1996McEwen et al , 2004Lorentzen et al 2004;Foster et al 2005;MacDougall & Jayachandran 2007;Moen et al 2007Moen et al , 2008aHosokawa et al 2006Hosokawa et al , 2009aHosokawa et al , 2011. While the flow channels are more localized, the polar cap patches drift across the polar cap from day to night and may be active several hours as a source for radio wave scintillations.…”

Section: Summary and Concluding Remarksmentioning

confidence: 99%

Space weather challenges of the polar cap ionosphere

Moen

Oksavik

Alfonsi

et al. 2013

J. Space Weather Space Clim.

134

184

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This paper presents research on polar cap ionosphere space weather phenomena conducted during the European Cooperation in Science and Technology (COST) action ES0803 from 2008 to 2012. The main part of the work has been directed toward the study of plasma instabilities and scintillations in association with cusp flow channels and polar cap electron density structures/patches, which is considered as critical knowledge in order to develop forecast models for scintillations in the polar cap. We have approached this problem by multi-instrument techniques that comprise the EISCAT Svalbard Radar, SuperDARN radars, in-situ rocket, and GPS scintillation measurements. The Discussion section aims to unify the bits and pieces of highly specialized information from several papers into a generalized picture. The cusp ionosphere appears as a hot region in GPS scintillation climatology maps. Our results are consistent with the existing view that scintillations in the cusp and the polar cap ionosphere are mainly due to multi-scale structures generated by instability processes associated with the cross-polar transport of polar cap patches. We have demonstrated that the SuperDARN convection model can be used to track these patches backward and forward in time. Hence, once a patch has been detected in the cusp inflow region, SuperDARN can be used to forecast its destination in the future. However, the high-density gradient of polar cap patches is not the only prerequisite for high-latitude scintillations. Unprecedented highresolution rocket measurements reveal that the cusp ionosphere is associated with filamentary precipitation giving rise to kilometer scale gradients onto which the gradient drift instability can operate very efficiently. Cusp ionosphere scintillations also occur during IMF B Z north conditions, which further substantiates that particle precipitation can play a key role to initialize plasma structuring. Furthermore, the cusp is associated with flow channels and strong flow shears, and we have demonstrated that the KelvinHelmholtz instability process may be efficiently driven by reversed flow events.

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“…The electron temperature inside a patch is often low and unstructured, indicating no precipitation of auroral electrons when it is located in the polar cap [ Rodger et al , 1994]. Patches can be observed both in winter and summer, but are most prominent during moderately disturbed conditions (Kp > 4) [ Weber et al , 1984] and near the maximum of the sunspot cycle [e.g., Dandekar , 2002; McEwen et al , 2004]. Polar cap patches tend to maximize near equinox and around magnetic noon [ Rodger and Graham , 1996] and have been observed to drift across the central polar cap [ McEwen and Harris , 1995; McEwen et al , 1995] and exit the polar cap at night [ Lorentzen et al , 2004; Pryse et al , 2006; Moen et al , 2007; Wood et al , 2009].…”

Section: Introductionmentioning

confidence: 99%

In situ measurements of plasma irregularity growth in the cusp ionosphere

et al. 2012

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The Investigation of Cusp Irregularities (ICI‐2) sounding rocket was launched on 5 December 2008 from Ny‐Ålesund, Svalbard. The high‐resolution rocket data are combined with data from an all‐sky camera, the EISCAT Svalbard Radar, and the SuperDARN Hankasalmi radar. These data sets are used to characterize the spatial structure ofFregion irregularities in the dayside cusp region. We use the data set to test two key mechanisms for irregularity growth; the Kelvin‐Helmholtz (KH) and gradient drift (GD) instabilities. Except for a promising interval of 4–6 km irregularities, the KH growth rate was found to be too slow to explain the observed plasma irregularities. The time history of the plasma gives further support that structured particle precipitation could be an important source of kilometer‐ to hectometer‐scale “seed” irregularities, which are then efficiently broken down into decameter‐scale irregularities by the GD mechanism.

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The polar ionosphere

Cited by 7 publications

References 8 publications

HF ground scatter from the polar cap: Ionospheric propagation and ground surface effects

HF ground scatter from the polar cap: Ionospheric propagation and ground surface effects

Space weather challenges of the polar cap ionosphere

In situ measurements of plasma irregularity growth in the cusp ionosphere

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