IMF effect on sporadic-E layers at two northern polar cap sites: Part I – Statistical study

Abstract

Abstract. In this paper we investigate the relationship between polar cap sporadic-E layers and the direction of the interplanetary magnetic field (IMF) using a 2-year database from Longyearbyen (75.2 • CGM Lat, Svalbard) and Thule (85.4 • CGM Lat, Greenland). It is found that the MLT distributions of sporadic-E occurrence are different at the two stations, but both are related to the IMF orientation. This relationship, however, changes from the centre of the polar cap to its border. Layers are more frequent during positive B y at both stations. This effect is particularly strong in the central polar cap at Thule, where a weak effect associated with B z is also observed, with positive B z correlating with a higher occurrence of Es. Close to the polar cap boundary, at Longyearbyen, the B y effect is weaker than at Thule. On the other hand, B z plays there an equally important role as B y , with negative B z correlating with the Es occurrence. Since Es layers can be created by electric fields at high latitudes, a possible explanation for the observations is that the layers are produced by the polar cap electric field controlled by the IMF. Using electric field estimates calculated by means of the statistical APL convection model from IMF observations, we find that the diurnal distributions of sporadic-E occurrence can generally be explained in terms of the electric field mechanism. However, other factors must be considered to explain why more layers occur during positive than during negative B y and why the B z dependence of layer occurrence in the central polar cap is different from that at the polar cap boundary.

Characterizing GPS radio occultation loss of lock due to ionospheric weather

“…Our results are consistent with previous ground‐based observations as summarized by Kirkwood and Nilsson []. The nighttime CS occurrence is probably due to the corresponding small‐scale electric field variation, which is assumed to be the source of E s in polar region [ Kirkwood and Nilsson , ; Mathews , ; Voiculescu et al ., ]. For comparison, we also embedded the polar electric potential contour calculated from Weimer05 model in the figure [ Weimer , ].…”

The role of electric field and neutral wind in the generation of polar cap sporadic E

“…Later, MacDougall and Jayachandran (2005) argued that Es layers observed at 77 • CGM Lat could be explained by a two-step mechanism involving horizontal convergence of ionisation followed by vertical convergence, both under the effect of electric field. Voiculescu et al (2006) and Nygrén et al (2006) investigated the statistical relation of polar cap electric field and the occurrence of sporadic E at two polar cap sites, Longyearbyen and Thule, using electric fields given by the APL model based on IMF data (Ruohoniemi and Greenwald, 1996). 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.…”

“…They form by vertical convergence of ionospheric plasma caused by appropriate structures in the vertical shear of neutral wind and/or favourable electric field directions (Nygrén et al, 1984;Whitehead, 1989;Mathews, 1998;Kirkwood and Nilsson, Correspondence to: T. Nygrén (tuomo.nygren@oulu.fi) 2000). It has been shown that Es layers are observed even inside the polar cap, despite the very high inclination of the geomagnetic field there (Wan et al, 1999;MacDougall et al, 2000a;Voiculescu et al, 2006). 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;Nygrén et al, 2006), although there are calculations showing that gravity waves might also play a role (MacDougall et al, 2000b).…”

IMF effect on sporadic-E layers at two northern polar cap sites: Part II – Electric field

“…In the first paper of this series (Voiculescu et al, 2006; hereafter referred to as Paper I), the relation of the IMF and sporadic E at two polar cap sites, Longyearbyen and Thule, were studied. In this second paper, we investigate the same data in view of the electric field mechanism of layer generation.…”

“…This paper is the second in a series on a study of the link between IMF and sporadic-E layers within the polar cap. In Paper I (Voiculescu et al, 2006), an analysis of the sporadic-E data from Thule and Longyearbyen was presented. Here we concentrate on the electric field mechanism of sporadic-E generation.…”