Equatorial F-region irregularities generated by the Rayleigh-Taylor instability mechanism: rocket observations from Brazil

Abstract

ABSTRACT. Several sounding rockets carrying plasma diagnostic experiments were launched from the Brazilian rocket launching stations in Natal (5.9 • S, 35.2 • W Geog. Lat.) and Alcântara (2.31 • S, 44.4 • W Geog. Lat.). Langmuir Probes (LP) were used to measure the height profiles of electron density and electron temperature and High Frequency Capacitance (HFC) probes were used to measure electron density. The LP's were also used to measure the amplitude of electron density fluctuations.A detailed study of the characteristic features of electron density irregularities in the scale size range of less than a meter to a few kilometres, observed by rocket-borne electron density probes under different ionospheric conditions is presented here. The main objective of these studies is the identification of these irregularities from the point of view of the dynamic and electrodynamic processes responsible for their generation. The existing theories of the Rayleigh Taylor Instability (RTI) mechanism applicable for conditions of the geomagnetic equatorial ionosphere over Brazil are critically examined in the light of the observations. The observed characteristics of the irregularities during four rocket launches are compared with the theoretically expected characteristics. These results confirm the operation of a cascade process that is responsible for the generation of a wide spectrum of irregularities. The large-scale irregularities are first generated probably by the RTI mechanism that creates conditions favourable for the operation of the Cross-Field (CFI) or the Gradient Drift Instability (GDI) mechanism. From the k-spectra of irregularities it is possible to obtain the spectral index n corresponding to the height chosen. In most of the cases the estimated spectral indices agree well with those published in the literature for the cases of irregularities generated by the GDI mechanism.Keywords: space plasma, ionosphere, F-region, Rayleigh-Taylor instability, Cross-Field instability. RESUMO. Vários foguetes de sondagem carregando experimentos de diagnóstico de plasma foram lançados dos centros Brasileiros de lançamento de foguetesem Natal (5.9 • S, 35.2 • O Lat. Geog.) e Alcântara (2.31 • S, 44.4 • O Lat. Geog.). Sondas de Langmuir (LP) foram usadas para medir os perfis de densidade e temperatura do plasma e Sondas Capacitivas em Alta Freqüência (HFC) foram usadas para medir a densidade eletrônica. As LP's foram usadas também para medir a amplitude das flutuações de densidade eletrônica. Um estudo detalhado dos aspectos característicos das irregularidades de densidade eletrônica da escala de menos de um metro a alguns quilômetros, observadas pelas sondas de densidade eletrônica a bordo dos foguetes sob condições diferentes da ionosferaé apresentado aqui.O objetivo principal destes estudosé a identificação destas irregularidades do ponto de vista dos processos dinâmicos e eletrodinâmicos responsáveis pela geração delas. As teorias existentes do mecanismo de instabilidade de Rayleigh-Taylor aplicáveis para as condições da ...

Structural characterization of the equatorial F region plasma irregularities in the multifractal context

“…On the other hand, several plasma bubbles of mediumlarge scale were observed in the downleg profile (descent of the rocket), around the base of F region and also topside of it, but without any sharp indication of the F region base from an altitude above 240 km. The rocket traversed through regions of different altitudes separated by a few hundred kilometers during upleg and downleg, so this might elucidate the large differences observed in ascent and descent of the rocket (Muralikrishna et al, 2003;Muralikrishna and Abdu, 2006;Muralikrishna and Vieira, 2007). A detailed explanation of in situ experiment and the analysis is found in Muralikrishna et al (2003), Muralikrishna and Abdu (2006), and Muralikrishna and Vieira (2007).…”

“…Some of the key results from the aforementioned (Muralikrishna et al, 2003;Muralikrishna and Abdu, 2006;Muralikrishna and Vieira, 2007) analyses indicate (1) the initiation of a cascade process, owing to the generalized Rayleigh-Taylor instability mechanism near the base of F region that resulted in the development of plasma bubbles or large-scale irregularities, and (2) subsequently, when energy was advected to higher altitudes, smaller-scale irregularities were observed, owing to the cross-field instability mechanism.…”

“…Various different approaches had been explored to understand nonlinear characteristics and intermittency in ionospheric irregularities, like structure function analysis (Dyrud et al, 2008;Spicher et al, 2015), fractal and multifractal analysis (Wernik et al, 2003;Alimov et al, 2008;Bolzan et al, 2013;Tanna and Pathak, 2014;Miriyala et al, 2015;Chandrasekhar et al, 2016;Fornari et al, 2016;Sivavaraprasad et al, 2018;Neelakshi et al, 2019), and multispectral optical imaging (Chian et al, 2018).…”

“…A detrended fluctuation analysis (DFA;Peng et al, 1994) has been a proven successful method to find a power law correlation and monofractal scaling in noisy, nonstationary data. The DFA is a robust method as it can handle discontinuous and length-wise short data.…”

Hindcasting of Equatorial Spread F Using Seasonal Empirical Models

“…It has been established that the seeding by these waves becomes pertinent in the solstice months, when the post sunset rise (PSSR) of the F layer is weak (Tsunoda, 2010a). Muralikrishna and Vieira (2007) reported that a higher F region base is preferable for R-T instability to operate. Ossakow et al (1978) presented a numerical simulation study, showing that the injection of an artificial depletion at the bottom side of the F layer can cause ESF to occur.…”