Field-perpendicular and field-aligned plasma flows observed by EISCAT during a prolonged period of northward IMF

Farmer, A. D.; Lockwood, Mike; Horne, Richard B.; Bromage, B. J. I.; Freeman, K. S. C.

doi:10.1016/0021-9169(84)90066-7

Cited by 18 publications

(11 citation statements)

References 30 publications

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“…Although the declared uncertainty in the measured electron concentration is not large −10 ÷ 12% (Farmer et al, 1984;Kirkwood et al, 1986), this may result in wrong relative deviations δN e when different (quiet/disturbed) days are compared. The absence of such normalization also results in a shift between long-pulse and multi-pulse N e(h) profiles, and this shift should be taken into account before the profiles are used for analysis.…”

Section: Discussionmentioning

confidence: 99%

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Geomagnetic storm effects at F1-layer heights from incoherent scatter observations

Mikhailov

Schlegel

2003

Ann. Geophys.

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Abstract. Storm effects at F1-layer heights (160-200 km) were analyzed for the first time using Millstone Hill (midlatitudes) and EISCAT (auroral zone) incoherent scatter (IS) observations. The morphological study has shown both increases (positive effect) and decreases (negative effect) in electron concentration. Negative storm effects prevail for all seasons and show a larger magnitude than positive ones, the magnitude of the effect normally increasing with height. At Millstone Hill the summer storm effects are small compared to other seasons, but they are well detectable. At EISCAT this summer decrease takes place only with respect to the autumnal period and the autumn/spring asymmetry in the storm effects is well pronounced. Direct and significant correlation exists between deviations in electron concentration at the F1-layer heights and in the F2-layer maximum. Unlike the F2-layer the F1-region demonstrates a relatively small reaction to geomagnetic disturbances despite large perturbations in thermospheric parameters. Aeronomic parameters extracted from IS observations are used to explain the revealed morphology. A competition between atomic and molecular ion contributions to N e variations was found to be the main physical mechanism controlling the F1-layer storm effect. The revealed morphology is shown to be related with neutral composition (O, O 2 , N 2 ) seasonal and storm-time variations. The present day understanding of the F1-region formation mechanisms is sufficient to explain the observed storm effects.

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Section: Discussionmentioning

confidence: 99%

“…This allows us to consider the daytime auroral ionosphere as a midlatitude one (Farmer et al, 1984;Lathuillière and Brekke, 1985). However, EISCAT is located in the auroral zone, and particle precipitation takes place in some cases during disturbed periods.…”

Section: Model Calculationsmentioning

confidence: 99%

Geomagnetic storm effects at F1-layer heights from incoherent scatter observations

Mikhailov

Schlegel

2003

Ann. Geophys.

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“…The sunlit auroral ionospheric F-region above the EISCAT facility in geomagnetically quiet conditions when electric fields are small is controlled by local processes typical for the midlatitude ionosphere (Farmer et al, 1984;Lathuillère and Brekke, 1985). Therefore, a model which takes into account the photo-ionization of neutral atmospheric species by solar EUV, a set of main chemical processes, vertical plasma transport due to diffusion, thermospheric winds and electric fields may be used for such an analysis.…”

Section: Model Calculationsmentioning

confidence: 99%

An interpretation of ion composition diurnal variation deduced from EISCAT observations

Mikhailov

Kofman²

2001

Ann. Geophys.

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Abstract. Physical interpretation is made of the O + /Ne diurnal variations in summer, revealed by Litvine et al. (1998) from the EISCAT observations. It is shown that the observed anti-correlation between the Z 50 parameter, corresponding to the transition region between 50% of molecular and atomic ions, and the width D z of the transition, defined as the altitude width between 10% and 90% of the O + /Ne ratio, can be reproduced in model calculations and the result of different recombination laws (quadratic in the lower and linear in the upper ionosphere) as well as diurnal variations in the photoionization rates.

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“…Loclovood et al [1985b] and Loranc [1988] reported nearsimultaneous observations of large ion upfiows below 1000 km in the ionosphere on the same geomagnetic flux tube as lowenergy ion outflows in the magnetosphere. It is tempting, then, to interpret the ionospheric upflows as the diffusive response to a magnetospheric acceleration process, but typical ion upflow fluxes observed between 325 and 950 km are of the order of 108 to 10 lø cm '2 s 'l [Lockwood et al, 1982;Farmer et al, 1984; aligned current densities of at least 50 gAm'2; they modeled the subsequent expansion of the heated ions and found that large numbers of heavy ions could reach the topside ionosphere. While there is no reason to suspect that the preceding mechanisms are mutually exclusive, Loranc et al [1991 ] showed that one aspect of the statistical morphology of upward vertical ion flows in the high-latitude F region supports the hypothesis that ion-neutral frictional heating generates the observed thermal ion upflows.…”

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confidence: 99%

A time‐dependent gyro‐kinetic model of thermal ion upflows in the high‐latitude F region

Loranc¹,

Maurice²

1994

J. Geophys. Res.

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Ample evidence supports the significance of the high‐latitude ionospheric contribution to magnetospheric plasma. Assuming flux conservation along a flux tube, the upward field‐aligned ion flows observed in the magnetosphere require high‐latitude ionospheric field‐aligned ion upflows of the order of 108 to 109 cm−2 s−1. Since radar and satellite observations of high‐latitude F region flows at times exceed this flux requirement by an order of magnitude, the thermal ionospheric upflows are not simply the ionospheric response to a magnetospheric flux requirement. Several ionospheric ion upflow mechanisms have been proposed, but simulations based on fluid theory do not reproduce all the observed features of ionospheric ion upflows. Certain asymmetries in the statistical morphology of high‐latitude F region ion upflows suggest that the ion upflows may be generated by ion‐neutral frictional heating. We developed a single‐component (O+), time‐dependent gyro‐kinetic model of the high‐latitude F region response to frictional heating in which the neutral exobase is a discontinuous boundary between fully collisional and collisionless plasmas. The concept of a discontinuous neutral exobase and the assumption of a constant and uniform polarization electric field reduce the ion guiding center motion in the frame of a convecting flux tube to simple one‐dimensional ballistic trajectories. We thus are able to analytically calculate a time and height‐dependent ion velocity distribution function, from which we can compute the ion density, parallel velocity, parallel and perpendicular temperature, and parallel flux. Using our model, we simulated the response of a convecting flux tube between 500 km and 2500 km to various frictional heating inputs; the results were both qualitatively and quantitatively different from fluid model results, which may indicate an inadequacy of the fluid theory approach. The gyro‐kinetic frictional heating model responses to the various simulations were qualitatively similar: (1) initial perturbations of all the modeled parameters propagated rapidly up the flux tube, (2) transient values of the ion parallel velocity, temperature, and flux exceeded 3 km s−1, 2 × 104 K, and 109 cm−2 s−1. respectively, (3) a second transient regime developed wherein the parallel temperature drops to very low values (a few hundred Kelvins), and (4) well after heating ceased, large parallel temperatures and large downward parallel velocities and fluxes developed as the flux tube slowly returned to diffusive equilibrium. The ion velocity distributions during the simulation are often non‐Maxwellian and are sometimes composed of two distinct ion populations.

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Field-perpendicular and field-aligned plasma flows observed by EISCAT during a prolonged period of northward IMF

Cited by 18 publications

References 30 publications

Geomagnetic storm effects at F1-layer heights from incoherent scatter observations

Geomagnetic storm effects at F1-layer heights from incoherent scatter observations

An interpretation of ion composition diurnal variation deduced from EISCAT observations

A time‐dependent gyro‐kinetic model of thermal ion upflows in the high‐latitude F region

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