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

Abstract

Abstract. The formation of the mid-latitude sporadic E layers (E s 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 k z =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 E s 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.

Formation of sporadic-E (Es) layers under the influence of AGWs evolving in a horizontal shear flow

“…This is caused by the influence of cyclone-type background flow on the ions convergence process. In the presented work we further extend the study by Didebulidze and Lomidze (2008;. In those works it was shown that stationary atmospheric vortical perturbation (shear wave with a zero frequency), evolving in the horizontal shear flow, can be responsible for the horizontal and vertical convergence of ions and for the formation of multilayered sporadic-E.…”

“…, the function associated with AGWs is employed (Didebulidze and Lomidze, 2008;Didebulidze and Pataraya, 1999):…”

“…Lately, various observed phenomena such as multilayered structure of Es (Wakabayashi and Ono, 2005;Yokoyama et al, 2005;Brahmanandam et al, 2013) and a quasi-periodic echoes Kelley et al, 1995;Hysell et al, 2013) were associated with a possibile influence of AGWs on the formation and modulation of Es Yokoyama et al, 2004;Chen et al, 2010). Didebulidze and Lomidze (2008; proposed a sporadic-E formation by the vortical perturbations excited in the horizontal shear flows. According to them, as the transition of vortical perturbations into the short-period AGWs takes place these AGWs start to modulate Es.…”

“…Appearance of the inhomogeneous neutral wind could be related to various dynamical processes in the lower thermosphere, however the tidal motion is one of the most important one (Haldoupis et al, 2006;Pignalberi et al, 2014). Atmospheric waves, such as planetary waves (Shalimov et al, 1999;Haldoupis and Pancheva, 2002;Sauli and Bourdillon, 2008;Pignalberi et al, 2015), gravity waves, and the vortical perturbations of similar spatial scales (Didebulidze and Lomidze, 2008; could also lead to the Es formation. Shalimov et al (1999) and Shalimov and Haldoupis (2002) showed the possibility of E region plasma convergence inside a planetary wave cyclonic vortex at mid-latitudes.…”

Multilayered structures in the ionosphere F2 region and impulse‐like increase of the nightglow red 630 nm line intensity as a result of influence of shear excited atmospheric vortical perturbations

“…The shear wave velocity can change its polarization in regions with thickness of about half of its vertical wavelength λ z /2, and it can result in the increase of the upstream and downstream flows of ions along the midlatitude declined magnetic field via combined action of ion‐neutral collisional coupling and Lorentz forcing [ Didebulidze and Lomidze , 2008]. In Figure 2 for heights about λ z /2 above F 2 layer peak the northward wind decreases (or the southward one increases), and for the considered parameters of shear wave the F 2 layer peak is formed above its main peak.…”