The formation of sporadic E layers by a vortical perturbation excited in a horizontal wind shear flow

G G Didebulidze,L N Lomidze

doi:10.5194/angeo-26-1741-2008

Abstract

Abstract. The formation of the mid-latitude sporadic E layers (Es layers) by an atmospheric vortical perturbation excited in a horizontal shear flow (horizontal wind with a horizontal linear shear) is investigated. A three-dimensional atmospheric vortical perturbation (atmospheric shear waves), whose velocity vector is in the horizontal plane and has a vertical wavenumber kz≠0, can provide a vertical shear of the horizontal wind. The shear waves influence the vertical transport of heavy metallic ions and their convergence into thin and dense horizontal layers. The proposed mechanism takes into account the dynamical influence of the shear wave velocity in the horizontal wind on the vertical drift velocity of the ions. It also can explain the multi-layer structure of Es layers. The pattern of the multi-layer structure depends on the value of the shear-wave vertical wavelength, the ion-neutral collision frequency and the direction of the background horizontal wind. The modelling of formation of sporadic E layers with a single and a double peak is presented. Also, the importance of shear wave coupling with short-period atmospheric gravity waves (AGWs) on the variations of sporadic E layer ion density is examined and discussed.

Highlights

The formation of the mid-latitude sporadic E layers (Es layers) and their temporal evolution results from the action of various physico-chemical processes in the mesosphere-lower thermosphere
Several observations on the vertical variability of the sporadic E layers, such as the appearance of multi-layered structures, underline the importance of their relation to the atmospheric waves and the horizontally inhomogeneous wind. These observed features of Es layers were considered by many authors as a result of an interaction of atmospheric gravity waves (AGWs) propagating through the region (Mathews et al, 1993; Yokoyama et al, 2003, 2004; Larsen et al, 2005)
In our model it is assumed that a vertical shear of the background horizontal wind is negligible and the neutral wind height variations are caused by the presence of atmospheric shear waves

Summary

Introduction

The formation of the mid-latitude sporadic E layers (Es layers) and their temporal evolution results from the action of various physico-chemical processes in the mesosphere-lower thermosphere. A vertical shear in the horizontal neutral wind is the major cause of mid-latitude Es layer formation (e.g. Several observations on the vertical variability of the sporadic E layers, such as the appearance of multi-layered structures, underline the importance of their relation to the atmospheric waves and the horizontally inhomogeneous wind (e.g. see Larsen et al, 2005). Several observations on the vertical variability of the sporadic E layers, such as the appearance of multi-layered structures, underline the importance of their relation to the atmospheric waves and the horizontally inhomogeneous wind (e.g. see Larsen et al, 2005) These observed features of Es layers were considered by many authors as a result of an interaction of AGWs propagating through the region (Mathews et al, 1993; Yokoyama et al, 2003, 2004; Larsen et al, 2005). It will be shown that the shear wave property, with regards to its transformation to shortperiod atmospheric gravity waves, can influence the variability of sporadic E layers

Ion vertical drift velocity in the horizontal shear flow

Atmospheric shear waves

Formation of sporadic E layers in the horizontal shear flow

Discussion

Conclusion