Height‐dependent energy exchange rates in the high‐latitude <i>E</i> region ionosphere

Cai, Lei; Aikio, Anita; Nygrén, T.

doi:10.1002/2013ja019195

Cited by 24 publications

(67 citation statements)

References 48 publications

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“…Above 125 km, the wind direction is rather constant with altitude, but the magnitude increases. Then a difference even less than 90° between the wind and plasma flow directions can produce an enhancement in Joule heating as indicated by the model calculations by Cai et al [].…”

Section: Resultsmentioning

confidence: 99%

“…Even though the Joule heating rate Q J is integrated over altitude and the wind velocities depend on altitude [see, e.g., Aikio et al , ], this figure provides some understanding for the effect of winds presented in Figure . Furthermore, Cai et al [] showed that the wind direction changes typically very slowly above this altitude.…”

Section: Resultsmentioning

confidence: 99%

“…The difference Q J − Q E is negative at 15–18 MLT for B z − / B y − and at 16–18 MLT for B z − / B y + (Figure ) indicating that neutral winds decrease Joule heating within those sectors. Cai et al [] showed that the evening decrease by winds takes place at an altitude region close to and above the Pedersen conductivity maximum at 120 km. In addition, the paper showed in the appendix that q J < q E , when u ⟂ < 2 E cos φ / B , where φ the angle between the E × B plasma drift velocity and the wind velocity u ⟂ perpendicular to B .…”

Section: Resultsmentioning

confidence: 99%

“…The measured electron density altitude profiles from the alternating code experiments are input to the calculation of Pedersen and Hall conductivity profiles as described in Cai et al []. The time resolutions are 90 s for TRO and 120 s for ESR.…”

Section: Measurements and Data Analysismentioning

confidence: 99%

“…The electric field and neutral winds are analyzed by means of stochastic inversion [ Nygrén et al , , ] as described in Cai et al []. The electric field is calculated at the altitude centered at 270 km in the F region.…”

Section: Measurements and Data Analysismentioning

confidence: 99%

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Solar wind effect on Joule heating in the high‐latitude ionosphere

2014

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The effect of solar wind on several electrodynamic parameters, measured simultaneously by the European Incoherent Scatter (EISCAT) radars in Tromsø (TRO, 66.6° cgmLat) and on Svalbard (ESR, 75.4° cgmLat), has been evaluated statistically. The main emphasis is on Joule heating rate QJ, which has been estimated by taking into account the neutral wind. In addition, a generally used proxy QE, which is the Pedersen conductance times the electric field squared, has been calculated. The most important findings are as follows. (i) The decrease in Joule heating in the afternoon‐evening sector due to winds reported by Aikio et al. (2012) requires southward interplanetary magnetic field (IMF) conditions and a sufficiently high solar wind electric field. The increase in the morning sector takes place for all IMF directions within a region where the upper E neutral wind has a large equatorward component and the F region plasma flow is directed eastward. (ii) At ESR, an afternoon hot spot of Joule heating centered typically at 14–15 magnetic local time (MLT) is observed during all IMF conditions. Enhanced Pedersen conductances within the hot spot region are observed only for the IMF Bz + /By− conditions, and the corresponding convection electric field values within the hot spot are smaller than during the other IMF conditions. Hence, the hot spot represents a region of persistent magnetospheric electromagnetic energy input, and the median value is about 3 mW/m2. (iii) For the southward IMF conditions, the MLT‐integrated QE for By− is twice the value for By+ at TRO. This can plausibly be explained by the higher average solar wind electric field values for By−.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Measurements and Data Analysismentioning

confidence: 99%

Section: Measurements and Data Analysismentioning

confidence: 99%

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Solar wind effect on Joule heating in the high‐latitude ionosphere

2014

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Lower thermospheric wind variations in auroral patches during the substorm recovery phase

et al. 2016

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Measurements of the lower thermospheric wind with a Fabry‐Perot interferometer (FPI) at Tromsø, Norway, found the largest wind variations in a night during the appearance of auroral patches at the substorm recovery phase. Taking into account magnetospheric substorm evolution of plasma energy accumulation and release, the largest wind amplitude at the recovery phase is a fascinating result. The results are the first detailed investigation of the magnetosphere‐ionosphere‐thermosphere coupled system at the substorm recovery phase using comprehensive data sets of solar wind, geomagnetic field, auroral pattern, and FPI‐derived wind. This study used three events in November 2010 and January 2012, particularly focusing on the wind signatures associated with the auroral morphology, and found three specific features: (1) wind fluctuations that were isolated at the edge and/or in the darker area of an auroral patch with the largest vertical amplitude up to about 20 m/s and with the longest oscillation period about 10 min, (2) when the convection electric field was smaller than 15 mV/m, and (3) wind fluctuations that were accompanied by pulsating aurora. This approach suggests that the energy dissipation to produce the wind fluctuations is localized in the auroral pattern. Effects of the altitudinal variation in the volume emission rate were investigated to evaluate the instrumental artifact due to vertical wind shear. The small electric field values suggest weak contributions of the Joule heating and Lorentz force processes in wind fluctuations. Other unknown mechanisms may play a principal role at the recovery phase.

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Ionospheric conductances and currents of a morning sector auroral arc from Swarm‐A electric and magnetic field measurements

Juusola

Archer

Kauristie

et al. 2016

Geophysical Research Letters

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We show the first ionospheric Hall and Pedersen conductances derived from Swarm magnetic and electric field measurements during a crossing of a morning sector auroral arc. Only Swarm‐A was used, with assumptions of negligible azimuthal gradients and vanishing eastward electric field. We find upward field‐aligned current, enhanced Hall and Pedersen conductances, and relatively weak electric field coincident with the arc. Poleward of the arc, the field‐aligned current was downward, conductances lower, and the electric field enhanced. The arc was embedded in a westward electrojet, immediately equatorward of the peak current density. The equatorward portion of the electrojet could thus be considered conductance dominant and the poleward portion electric field dominant. Although the electric field measured by Swarm was intense, resulting in conductances lower than those typically reported, comparable electric fields have been observed earlier. These results demonstrate how Swarm data can significantly contribute to our understanding of the ionospheric electrodynamics.

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Height‐dependent energy exchange rates in the high‐latitude E region ionosphere

Cited by 24 publications

References 48 publications

Solar wind effect on Joule heating in the high‐latitude ionosphere

Solar wind effect on Joule heating in the high‐latitude ionosphere

Lower thermospheric wind variations in auroral patches during the substorm recovery phase

Ionospheric conductances and currents of a morning sector auroral arc from Swarm‐A electric and magnetic field measurements

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