Abstract
Abstract. A seasonally dependent total neutral wind model obtained from experimental data is used to evaluate the diurnal variation of the vertical ion velocity in the E-region at a high-latitude location (Tromsø), for each season, in the presence of an electric field with a typical diurnal variation for quiet auroral days. The diurnal variation and spatial locations of the vertical convergence of ions are analyzed and the effect of the total wind on the occurrence of sporadic E-layers is inferred. The results show that the structure of the wind is an important factor in controlling the vertical velocities of ions, favoring or hindering the sporadic E-layer formation. The ion convergence conditions are improved when the permanent wind is removed, which suggests that sporadic E-layers occur when the mean wind has small values, thus allowing the electric field and/or the semidiurnal tide to control the ion dynamics. We conclude that for quiet days the formation of the sporadic layers is initiated by the electric field, while their evolution and dynamics is controlled by the wind. We also find that the seasonal variation of the Es layers cannot be related to the seasonally dependent wind shear. Although we focus on sporadic E-layers, our results can be used in the analysis of other processes involving the vertical dynamics of ions in the E-region at high latitudes.
Highlights
Sporadic E (Es ) layers are thin layers of plasma whose densities are several times higher than the normal density of the Eregion
The results of Brekke et al (1994) show that the total wind varies with the season, so that the results presented in this paper give us the opportunity to verify whether the seasonal distribution of Es layers could be related to the seasonal variation of the wind
An electric field having a typical quiet diurnal variation could form a layer, but its dynamics would not be consistent with the observations
Summary
Sporadic E (Es ) layers are thin layers of plasma whose densities are several times higher than the normal density of the Eregion. They form at heights between 100–125 km and have a lifetime of one to several hours. Two types of layers can be observed at high latitudes: the “auroral” type, which are thick (more than 10–15 km) and are produced by precipitating particles, and the so-called “mid-latitude” type Es , which have high densities and whose thickness is less than 5 km. In our study we will refer to the last type as Es layers
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