Statistical distribution of height‐integrated energy exchange rates in the ionosphere

Aikio, Anita; Cai, Lei; Nygrén, T.

doi:10.1029/2012ja018078

Cited by 35 publications

(112 citation statements)

References 48 publications

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“…If the neutral wind is zero, also the electromagnetic energy input Q EM into the ionosphere is equal to Q E . If the neutral wind is nonzero, one can easily see from the equations presented in Aikio et al [] that q EM = q E + σ P E·(u × B) + σ H B u·E . The last term in the equation contributes only at low altitudes, where the Hall conductance is high, but neutral wind magnitudes are low.…”

Section: Discussionmentioning

confidence: 99%

“…The middle term provides contribution, if the electric field has a component perpendicular to the neutral wind within altitudes of high Pedersen conductivity. Figure 3 in Aikio et al [] presenting the height‐integrated energy exchange rates calculated from data shows that typically Q E follows more closely Q EM than Q J , indicating that in typical situations Q E is a better proxy for the electromagnetic energy input Q EM into the ionosphere than for the Joule heating Q J . The Joule heating rate Q J describes the ion‐neutral frictional heating, which is estimated in the frame of reference of the moving neutrals.…”

Section: Discussionmentioning

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: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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

2014

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“…One of the outstanding question is how the energy dissipation disturbs thermospheric winds during substorms. The thermospheric wind is a key parameter that significantly affects mass transportation (e.g., Lilensten & Lathuillere, ; Oyama et al, ), ionospheric currents (Deng et al, ; Peymirat et al, ), and electromagnetic energy exchange (Aikio et al, ; Cai et al, ; Thayer & Semeter, ).…”

Section: Introductionmentioning

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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“…For the ion velocity to achieve a value of ∼1000 m/s (1200 m/s), an electric field of 50 mV/m (60 mV/m) is required. Such electric field magnitudes are relatively high; nevertheless, they commonly occur in the dusk sector under disturbed conditions [ Aikio et al , ]. Also, Figure reveals an enhancement in the eastward electrojet in the dusk sector after the zero epoch.…”

Section: Discussionmentioning

confidence: 99%

Effects of solar wind high‐speed streams on the high‐latitude ionosphere: Superposed epoch study

et al. 2015

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Solar wind high‐speed streams (HSSs) are the most important source of geomagnetic disturbances during the declining phase of the solar cycle. Their ionospheric response, especially at high latitudes, is not fully understood yet. We carried out a phase‐locked superposed epoch analysis to study the effects of HSSs on the high‐latitude ionospheric F region, using data from the Sodankylä ionosonde (L = 5.25) during 2006–2008. We found that the F layer critical frequency foF2 decreases between 12 and 23 magnetic local time (MLT) in summer and around equinoxes for several days. Our interpretation, supported by numerical estimations, is that increased electric fields in the evening sector of the auroral and subauroral regions create ion‐neutral frictional heating. Frictional heating will increase the loss rate of O+ due to two reasons. The first one is neutral heating producing thermal expansion of the atmosphere and enhancing N2 and O2 contents at the F region peak. The second one is ion heating which may occur under strong enough electric fields (about 50–60 mV/m), leading to enhancement of the reaction coefficients. An increase in foF2 is observed in two different MLT sectors. First, a short‐lived foF2 increase is visible during all seasons near noon on the first day after the arrival of the HSS, possibly triggered by the compressed solar wind plasma pressure pulse, which may produce particle precipitation from the dayside central plasma sheet. Second, foF2 is enhanced for several days in the morning sector during equinoxes and in winter. We suggest that this is caused by the low‐energy tail of particle precipitation.

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Statistical distribution of height‐integrated energy exchange rates in the ionosphere

Cited by 35 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

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

Effects of solar wind high‐speed streams on the high‐latitude ionosphere: Superposed epoch study

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