The impact of gravity waves rising from convection in the lower atmosphere on the generation and nonlinear evolution of equatorial bubble

Abstract

Abstract. The nonlinear evolution of equatorial F-region plasma bubbles under varying ambient ionospheric conditions and gravity wave seeding perturbations in the bottomside F-layer is studied. To do so, the gravity wave propagation from the convective source region in the lower atmosphere to the thermosphere is simulated using a model of gravity wave propagation in a compressible atmosphere. The wind perturbation associated with this gravity wave is taken as a seeding perturbation in the bottomside F-region to excite collisional-interchange instability. A nonlinear model of collisional-interchange instability (CII) is implemented to study the influences of gravity wave seeding on plasma bubble formation and development. Based on observations during the SpreadFEx campaign, two events are selected for detailed studies. Results of these simulations suggest that gravity waves can play a key role in plasma bubble seeding, but that they are also neither necessary nor certain to do so. Large gravity wave perturbations can result in deep plasma bubbles when ionospheric conditions are not conducive by themselves; conversely weaker gravity wave perturbations can trigger significant bubble events when ionospheric conditions are more favorable. But weak gravity wave perturbations in less favorable environments cannot, by themselves, lead to strong plasma bubble responses.

Radar and satellite investigations of equatorial evening vertical drifts and spread <i>F</i>

“…Finally, the occurrence of topside ESF structures despite weak PRE peaks could also be associated with strong initial perturbations provided by atmospheric gravity waves as suggested by theoretical studies (e.g. Kherani et al, 2009). …”

“…Previous studies have also suggested that initial density perturbations (seed waves) could play a significant role in the development of ESF (e.g. Abdu et al, 2009;Kherani et al, 2009;Tsunoda, 2010). The low ESF occurrence despite a significant PRE could be attributed to the absence of triggering perturbations.…”

A numerical simulation study of the collisional‐interchange instability seeded by the pre‐reversal vertical drift

“…To infer the development of EPB under the action of CII for simplified cases, we monitor the time history of the maximum vertical velocity (v max , the vertical component of ıE u ) inside the density depletion. The linear, exponential, and multiexponential growth of this velocity with time represent, respectively, the steady state, linear growth, and nonlinear growth (or the development of the EPB) of CII [Kherani et al, 2009].…”

“…These studies revealed the generation of the EPB initiated by a seed perturbation at the bottomside of the rising F layer. The seed perturbation used is either in the form of plasma density perturbation [Kherani et al, 2004;Huba and Joyce, 2007] or of wind perturbation [Huang and Kelley, 1996a;Kherani et al, 2009;Keskinen, 2010]. The seed perturbation may also arise from the shear instability as shown by Aveiro et al [2011].…”

Gravity wave initiation of equatorial spread F/plasma bubble irregularities based on observational data from the SpreadFEx campaign

“…The requirements on the PRE/evening vertical drift and the height of the F layer for the spread F "on" and "off" conditions and its varying growth rates and intensities have been widely discussed in the literature (e.g., Farley et al, 1970;Abdu et al, 1983Abdu et al, , 2006Fejer et al, 1999;Sultan, 1996;Sastri et al, 1997). Models have been developed to investigate the effects of the evening zonal electric fields, F layer bottom-side density gradients, and zonal, meridional and vertical winds on the ESF instability development conditions (e.g., Zalesak et al, 1982;Sekar et al, 1994;Maruyama, 1988;Keskinen et al, 2003;Kudeki et al, 2007;Kherani et al, 2009a). An important prerequisite concerns the nature and the intensity of the density perturbation needed to initiate the instability growth, which appears to be the least understood aspect of the ESF processes.…”