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

Abstract

Abstract. The data from ground based experiments conducted during the 2005 SpreadFEx campaign in Brazil are used, with the help of theoretical model calculations, to investigate the precursor conditions, and especially, the role of gravity waves, in the instability initiation leading to equatorial spread F development. Data from a digisonde and a 30 MHz coherent back-scatter radar operated at an equatorial site, Sao Luis (dip angle: 2.7 • ) and from a digisonde operated at another equatorial site (dip angle: −11.5 • ) are analyzed during selected days representative of differing precursor conditions of the evening prereversal vertical drift, F layer bottom-side density gradients and density perturbations due to gravity waves. It is found that radar irregularity plumes indicative of topside bubbles, can be generated for precursor vertical drift velocities exceeding 30 m/s even when the precursor GW induced density oscillations are marginally detectable by the digisonde. For drift velocities ≤20 m/s the presence of precursor gravity waves of detectable intensity is found to be a necessary condition for spread F instability initiation. Theoretical model calculations show that the zonal polarization electric field in an instability development, even as judged from its linear growth phase, can be significantly enhanced under the action of perturbation winds from gravity waves. Comparison of the observational results with the theoretical model calculations provides evidence for gravity wave seeding of equatorial spread F.

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

“…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.…”

Characteristics of equatorial plasma bubbles observed by TEC map based on ground-based GNSS receivers over South America

“…One is the difference in the zonal drift velocities of the EPBs due to different thermospheric zonal wind velocity from the Equator to middle latitudes and the other is the difference in the westward movement of the terminator (Huang et al, 2013). If one assumes that EPB seeding and development happen near the solar terminator passage and a successive EPB occurs soon after as the result of a periodic perturbation of the Flayer bottom side and the passage of the terminator (Tsunoda, 2006;Abdu et al, 2009;Takahashi et al, 2009;Makela et al, 2010). The distance between successive EPBs will, therefore, be determined by the velocity of the EPB and the terminator movement.…”

“…Characteristics of EPBs have been extensively studied using different techniques such as VHF radars (Tsunoda, 1981;Abdu et al, 2009), rockets Muralikrishna et al, 2007), ionosondes (Abdu et al, 1983(Abdu et al, , 2003(Abdu et al, , 2012, optical imagers (Pimenta et al, 2003;Arruda et al, 2006;Paulino et al, 2011), GNSS receivers (De Rezende et al, 2007;Takahashi et al, 2014Takahashi et al, , 2015, and satellites (Huang et al, 2002(Huang et al, , 2013McNamara et al, 2013;Park et al, 2015).…”

Rocket in situ observation of equatorial plasma irregularities in the region between E and F layers over Brazil

“…According to Abdu et al (2009) andTakahashi et al (2010), the ascension rate of the bottom-type and/or bottomside F layer is representative of the zonal electric field of F irregular structures under the modulation of wave-like disturbance. This leads to numerous studies (e.g., Alam Mukherjee and Patra, 2014;Kherani and Patra, 2015) aiming to understand the physical origin of this valleytype plasma irregularity through the possible link with the fringe field (polarization field) of F irregularities.…”