Interferometer Observations of Ion and Neutral Dynamics in the Polar Cusp

Smith, Roger W.

doi:10.1007/978-94-009-5295-9_18

Cited by 4 publications

(1 citation statement)

References 26 publications

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“…There have been many reported ground-based and satellite investigations of the thermospheric and ionospheric responses to the soft electron precipitation and ®eld-aligned current variations in the cusp region (e.g., Shepherd, 1979;Kelly and Vickrey, 1984;Kofman and Wickwar, 1984;McCormac and Smith, 1984;Oliver et al, 1984;Robinson et al, 1984;Smith, 1984;Vennerstrom et al, 1984;Wickwar, 1984;Thayer et al, 1987;Sandholt et al, 1994;Wu et al, 1996). However, there have been no reported systematic observational pictures of the seasonal behaviour of the thermospheric and ionospheric disturbances in the cusp region, partly due to the suppressive in¯uence of the solar emission on the ionization and heating processes in the summer polar upper atmosphere.…”

Section: Introductionmentioning

confidence: 99%

Seasonal effects in the ionosphere-thermosphere response to the precipitation and field-aligned current variations in the cusp region

Namgaladze¹,

Volkov²

1998

Ann. Geophys.

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Abstract. The seasonal e ects in the thermosphere and ionosphere responses to the precipitating electron¯ux and ®eld-aligned current variations, of the order of an hour in duration, in the summer and winter cusp regions have been investigated using the global numerical model of the Earth's upper atmosphere. Two variants of the calculations have been performed both for the IMF B y < 0. In the ®rst variant, the model input data for the summer and winter precipitating¯uxes and ®eld-aligned currents have been taken as geomagnetically symmetric and equal to those used earlier in the calculations for the equinoctial conditions. It has been found that both ionospheric and thermospheric disturbances are more intensive in the winter cusp region due to the lower conductivity of the winter polar cap ionosphere and correspondingly larger electric ®eld variations leading to the larger Joule heating e ects in the ion and neutral gas temperature, ion drag e ects in the thermospheric winds and ion drift e ects in the F2-region electron concentration. In the second variant, the calculations have been performed for the events of 28±29 January, 1992 when precipitations were weaker but the magnetospheric convection was stronger than in the ®rst variant. Geomagnetically asymmetric input data for the summer and winter precipitating¯uxes and ®eld-aligned currents have been taken from the patterns derived by combining data obtained from the satellite, radar and ground magnetometer observations for these events. Calculated patterns of the ionospheric convection and thermospheric circulation have been compared with observations and it has been established that calculated patterns of the ionospheric convection for both winter and summer hemispheres are in a good agreement with the observations. Calculated patterns of the thermospheric circulation are in a good agreement with the average circulation for the Southern (summer) Hemisphere obtained from DE-2 data for IMF B y < 0 but for the Northern (winter) Hemisphere there is a disagreement at high latitudes in the afternoon sector of the cusp region. At the same time, the model results for this sector agree with other DE-2 data and with the ground-based FPI data. All ionospheric and thermospheric disturbances in the second variant of the calculations are more intensive in the winter cusp region in comparison with the summer one and this seasonal di erence is larger than in the ®rst variant of the calculations, especially in the electron density and all temperature variations. The means that the seasonal e ects in the cusp region are stronger in the thermospheric and ionospheric responses to the FAC variations than to the precipitation disturbances.

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Section: Introductionmentioning

confidence: 99%

Seasonal effects in the ionosphere-thermosphere response to the precipitation and field-aligned current variations in the cusp region

Namgaladze¹,

Volkov²

1998

Ann. Geophys.

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Daytime aurora observed from Spitsbergen

Simmons¹,

Henriksen²

1994

Polar Record

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Daytime (or dayside cleft) aurora is almost a permanent feature of the midday skies over Spitsbergen during the continuous darkness of the polar night It was observed in one or other of its characteristic forms around geomagnetic noon on 58 of 59 clear day sduring the wintersof 1987/1988, 1990/1991, and 1992/1993. The three types of day time aurora were studied by visual, colour photographic, and interference-filter techniques to confirm the precise nature of the observed emissions. Prenoon aurora, which is characterised by diffuse, patchy, green aurora at 557.7 nm, was observed on 42 occasions. It is generated by low-energy electrons of less than 300 eV coming through the entry layer of the dayside cleft. Noontime aurora, which consists largely of pure red emissions at 630.0/636.4 nm, was observed on 50 occasions. It is generated by high-flux, very low-energy electrons of 10–50 eV flowing directly from the solar wind through the polar cusp. Postnoon aurora, which is characterised by discrete, green auroral arcs at 557.7 nm, was also observed on 42 occasions. Like prenoon aurora, it is generated by low-energy electrons of less than 300 eV derived from the entry layer of the cleft Occasionally, some background or diffuse aurora is also observed, generated by high fluxes of low-energy proton precipitation and characterised by the hydrogen lines Hα and Hβ. On the one exceptional day on which daytime aurora was not observed, magnetic activity was exceptionally low.These ground-based observations complement satellite studies of analogous auroral events. In particular, the visual characteristics of the different types of daytime aurora may be explained in terms of the flux rates and energy profiles of the electrons that have been mapped in the different regions of the dayside cleft by satellite-borne detectors.

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On the relationship between dynamics of the polar thermosphere and morphology of the aurora: Global‐scale observations from Dynamics Explorers 1 and 2

Killeen¹,

Craven²,

Frank³

et al. 1988

J. Geophys. Res.

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Simultaneous measurements of global‐scale auroral luminosity distributions and neutral winds over the northern (winter) polar cap have been obtained using instrumentation on the Dynamics Explorers 1 and 2 spacecraft. Several examples of these simultaneous measurements are presented to illustrate the relationship between the circulation of neutral air in the high‐latitude F region and the spatial distribution of the aurora. The auroral images are obtained using the Spin‐Scan Auroral Imager on the high‐altitude spacecraft (DE 1), and the neutral wind vectors are obtained along the orbit of the low‐altitude spacecraft (DE 2), using the Fabry‐Perot interferometer and the Wind and Temperature Spectrometer. These measurements make it possible to appreciate more fully the pattern of neutral winds when placed in the context of global auroral activity. Supplementary DE 2 measurements of neutral composition, ion densities, and the cross‐track component of the ion drift enable the ion drag force on the neutral gas to be correlated with the aurora. Our initial study of these data indicates (1) that a definite correlation exists between boundaries in the neutral wind field and the location of the auroral oval, with large‐scale features of the neutral circulation tracking the substorm‐dependent expansion and contraction of the auroral oval, (2) that the influence of ion drag from sunward convecting ions can extend to latitudes much lower than those normally associated with the auroral oval, (3) that the sunward neutral flow associated with the auroral oval in the dusk sector is, in general, more pronounced than that associated with the dawn sector and that this asymmetry is ascribed to the different effect of the Coriolis force in the two sectors, (4) that the flow patterns for neutrals and ions within the geomagnetic polar cap are generally asymmetric with respect to the noon‐midnight meridian, an effect considered to be controlled by the orientation of the interplanetary magnetic field, (5) that the region of the polar cusp and the apparent “midday gap,” or reduction in luminosities observed in the VUV wavelength auroral images near local noon, is closely associated with a large, antisunward surge in the neutral wind, and (6) that the morphology of the ion drag force in the polar regions is considerably more complex, even for very quiet geomagnetic conditions, than that computed by the National Center for Atmospheric Research thermospheric general circulation model for the “steady state.” This last result is considered to be a consequence of the short‐term variability in the characteristics of high‐latitude ion convection and, in particular, the motion of convection boundaries with respect to boundaries in the less responsive neutral circulation pattern.

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Interferometer Observations of Ion and Neutral Dynamics in the Polar Cusp

Cited by 4 publications

References 26 publications

Seasonal effects in the ionosphere-thermosphere response to the precipitation and field-aligned current variations in the cusp region

Seasonal effects in the ionosphere-thermosphere response to the precipitation and field-aligned current variations in the cusp region

Daytime aurora observed from Spitsbergen

On the relationship between dynamics of the polar thermosphere and morphology of the aurora: Global‐scale observations from Dynamics Explorers 1 and 2

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