Statistical maps of small‐scale electric field variability in the high‐latitude ionosphere

Cousins, E. D. P.; Shepherd, Simon

doi:10.1029/2012ja017929

Cited by 25 publications

(36 citation statements)

References 55 publications

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“…Each of the convection maps in Figures and are based on a large number of individual measurements mapped and binned into small equal area bins in the ionosphere. Note that the statistical spread of the data entering each bin mostly represents genuine variability in the ionospheric flow and has a physical meaning [cf., e.g., F07, Cousins and Shepherd , , ]. Large variability in the E field in a region can be the result of enhanced Poynting flux and heating.…”

Section: Resultsmentioning

confidence: 99%

Interhemispheric differences in ionospheric convection: Cluster EDI observations revisited

Förster

Haaland

2015

JGR Space Physics

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The interaction between the interplanetary magnetic field and the geomagnetic field sets up a large-scale circulation in the magnetosphere. This circulation is also reflected in the magnetically connected ionosphere. In this paper, we present a study of ionospheric convection based on Cluster Electron Drift Instrument (EDI) satellite measurements covering both hemispheres and obtained over a full solar cycle. The results from this study show that average flow patterns and polar cap potentials for a given orientation of the interplanetary magnetic field can be very different in the two hemispheres. In particular during southward directed interplanetary magnetic field conditions, and thus enhanced energy input from the solar wind, the measurements show that the southern polar cap has a higher cross polar cap potential. There are persistent north-south asymmetries, which cannot easily be explained by the influence of external drivers. These persistent asymmetries are primarily a result of the significant differences in the strength and configuration of the geomagnetic field between the Northern and Southern Hemispheres. Since the ionosphere is magnetically connected to the magnetosphere, this difference will also be reflected in the magnetosphere in the form of different feedback from the two hemispheres. Consequently, local ionospheric conditions and the geomagnetic field configuration are important for north-south asymmetries in large regions of geospace.

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Section: Resultsmentioning

confidence: 99%

Interhemispheric differences in ionospheric convection: Cluster EDI observations revisited

Förster

Haaland

2015

JGR Space Physics

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“…However, Codrescu et al (1995) describe the deficiencies in these models in specifying the neutral temperature and point out that variability in the plasma flow, or equivalently the electric field, will be an important additional heat source. Following this realization, several attempts to quantify the effects of structure in the plasma velocity with small and intermediate scale between 10 and 500 km have been undertaken (Codrescu et al, 2000;Cousins & Shepherd, 2012;Crowley & Hackert, 2001;Johnson & Heelis, 2005;Kivanç & Heelis, 1998;Matsuo et al, 2003) and have led to the generation of models to describe this additional energy source to the ionosphere and thermosphere (Cosgrove & Codrescu, 2009;Matsuo & Richmond, 2008), which may be accounted for in terms of an additional heating rate. (Deng & Ridley, 2007;Deng et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

Mesoscale Plasma Convection Perturbations in the High‐Latitude Ionosphere

Chen

Heelis

2018

JGR Space Physics

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An investigation of flow perturbations with spatial scale sizes between 100 and 500 km in the high‐latitude ionosphere is presented. These localized flow perturbations are deviations from the large‐scale background convection, expected to give us new insights into the magnetosphere‐ionosphere coupling process. Ion drift measurements from the Defense Meteorological Satellite Program F17 are utilized to identify these mesoscale flow perturbations. Our intent is to discover the properties of these perturbations in terms of perturbation flow speeds, location, scale size, and occurrence frequency as well as their dependence on the interplanetary magnetic field (IMF) and underlying large‐scale convection pattern. Observation suggests that flow perturbation locations strongly depend on the IMF orientation as does the occurrence frequency of the flow perturbations. For southward IMF, more flow perturbations occur in regions of sunward background flow than in regions of antisunward background flow. For flow perturbations with speeds over 300 m/s, an asymmetry in the preferred direction and scale size is seen for those embedded in sunward and antisunward background flows. Significantly less asymmetry is present for flow perturbations with speeds between 100 and 300 m/s. The flow perturbations exceeding 300 m/s are most likely closed locally with lower magnitude return flows or with adjacent flows across the convection reversal boundary and representing additional sources of frictional heating and momentum transfer to the thermosphere. The perturbation flow speed is almost independent of the scale size and underlying convection speed, but the largest speeds are preferentially seen at scale sizes between 200 and 300 km.

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“…Under these conditions the convection field is most intense, meaning stronger injections and higher flux. Strong convection can also be more variable (Cousins & Shepherd, ; Goldstein et al, ), causing ion precipitation to occur at multiple different locations, either simultaneously or at different times during the storm. The average ion spectra for strong‐ D s t are likewise consistent with strong convection—quasi‐steady or bursty—bringing earthward and precipitating dramatically increased fluxes (compared to weaker D s t conditions) at all energies, but especially at the lowest energies.…”

Section: Discussionmentioning

confidence: 99%

Empirical Characterization of Low‐Altitude Ion Flux Derived from TWINS

et al. 2018

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In this study we analyze ion differential flux from 10 events between 2008 and 2015. The ion fluxes are derived from low-altitude emissions (LAEs) in energetic neutral atom (ENA) images obtained by Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS). The data set comprises 119.44 hr of observations, including 4,284 per energy images with 128,277 values of differential ENA flux from pixels near Earth's limb. Limb pixel data are extracted and mapped to a common polar ionospheric grid and associated with values of the Dst index. Statistical analysis is restricted to pixels within 10% of the LAE emissivity peak. For weak Dst conditions we find a premidnight peak in the average ion precipitation, whose flux and location are relatively insensitive to energy. For moderate Dst, elevated flux levels appear over a wider magnetic local time (MLT) range, with a separation of peak locations by energy. Strong disturbances bring a dramatic flux increase across the entire nightside at all energies but strongest for low energies in the postmidnight sector. The arrival of low-energy ions can lower the average energy for strong Dst, even as it raises the total integral number flux. TWINS-derived ion fluxes provide a macroscale measurement of the average precipitating ion distribution and confirm that convection, either quasi-steady or bursty, is an important process controlling the spatial and spectral properties of precipitating ions. The premidnight peak (weak Dst), MLT widening and energy-versus-MLT dependence (moderate Dst), and postmidnight low-energy ion enhancement (strong Dst) are consistent with observations and models of steady or bursty convective transport.Plain Language Summary This paper performs a statistical analysis of data measured by NASA's Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) mission. The data consist of measurements of energetic neutral atoms that are emitted from the near Earth region, several hundred kilometers in altitude. We find that there is a profound change in the distributions in space and in energy that occurs for large space storms.

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Statistical maps of small‐scale electric field variability in the high‐latitude ionosphere

Cited by 25 publications

References 55 publications

Interhemispheric differences in ionospheric convection: Cluster EDI observations revisited

Interhemispheric differences in ionospheric convection: Cluster EDI observations revisited

Mesoscale Plasma Convection Perturbations in the High‐Latitude Ionosphere

Empirical Characterization of Low‐Altitude Ion Flux Derived from TWINS

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