Abstract
Abstract. This paper investigates the roles of electric field and neutral wind in the generation of sporadic-E layers within the polar cap. Two Es layers above Svalbard, observed by the EISCAT Svalbard Radar (ESR), were chosen for investigation. The radar experiment contains four beam directions, and this was used for determining the electric field. The neutral wind was obtained from the HWM93 model. Formation of Es layers was calculated by integrating the continuity equation under the action of driving forces due to neutral wind and electric field. A flat height profile of metal ions was assumed in the beginning. The calculation gives the time variation of the layer, which can be compared with observations. In one case the electric field was shown to be the main driving agent in layer generation. In the other case the electric field was weak and the layer was produced mainly by the neutral wind, but the electric field had influence on the height of the layer. A fairly good agreement between the variations of the observed and calculated layer altitudes was obtained and some agreement between the intensity variations was also found.
Highlights
Sporadic-E (Es) layers are thin horizontal layers with a vertical extent of 0.5–5 km and densities at least two-three times higher than the background plasma
Experimental and theoretical findings support the idea that the electric field is the main driving factor of Es layer formation within the polar cap (Parkinson et al, 1998; Wan et al, 1999; Bedey and Watkins, 2001; MacDougall and Jayachandran, 2005; Voiculescu et al, 2006; Nygren et al, 2006), there are calculations showing that gravity waves might play a role (MacDougall et al, 2000b)
Comes the calculated Fe+ ion density caused by the measured electric field only, the layer caused by model neutral wind only and after that the same due to the combined action of the measured electric field and the model neutral wind
Summary
Sporadic-E (Es) layers are thin horizontal layers with a vertical extent of 0.5–5 km and densities at least two-three times higher than the background plasma They are commonly detected at heights between 95 and 130 km. In their study of southern polar cap Es layers, Wan et al (1999) investigated the link between ionospheric electric fields, interplanetary magnetic field (IMF) and Es layers at Casey (−81◦ CGM Lat). They concluded that most of the characteristics of the relationship could be explained in terms of the convective electric field effect on ion dynamics. It was shown in these studies that the layer occurrence was in most cases in reasonable agreement with the electric field theory of sporadic E
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