In-situ studies of equatorial spread-F over SHAR—steep gradients in the bottomside F-region and transitional wavelength results

Prakash, Satya; Pal, Sarbajit; Chandra, H.

doi:10.1016/0021-9169(91)90009-v

Cited by 29 publications

(28 citation statements)

References 33 publications

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“…The spectral index values range between 2 and 8 with a mean value of 4. This value is in close agreement with the in-situ observations from SHAR (Prakash et al, 1991). These two curves are best fit curves.…”

Section: Experimental Observationssupporting

confidence: 88%

Observations and Modelling of Nocturnal Ionospheric Irregularities in Low Latitude Region.

Singh

1997

J. geomagn. geoelec

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The analysis of VHF scintillation recorded at Varanasi shows that the ionospheric irregularities over Varanasi are mostly of small duration <30 minutes and are frequently observed during pre-midnight periods. During magnetically disturbed days there is a marked reduction in the occurrence rate of scintillations. The increase of solar activity generally-increases the depth of scintillation. Auto-correlation functions and power spectra of scintillations predict that the mean spectral index is -4, and the size of the overhead ionospheric irregularities varies from 200-500 m having drift velocity between 75 m/sec to 200 m/sec. Drift velocities and spectral indices of ionospheric irregularities derived by us agree well with the results obtained by other workers. It is shown that the thin phase screen model valid for weak scattering could explain the observed features of scintillations. The scintillation index S4, strength of turbulence CS and its dependence on various parameters are studied and it is found that the S4 index increases with increase in spectral index and decreases with increase in outer scale length L°.

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Section: Experimental Observationssupporting

confidence: 88%

Observations and Modelling of Nocturnal Ionospheric Irregularities in Low Latitude Region.

Singh

1997

J. geomagn. geoelec

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“…It is interesting to note that the earlier observations of electron density from SHAR revealed a smooth density pro®le in this region (Prakash et al, 1991). The presence of such large-scale structures in our data, point to the possibility that gravity waves might be playing a role in generating irregularities in this region.…”

Section: Large-scale Irregularitiessupporting

confidence: 56%

“…Such large increase of electron density, by a factor of 50 in a 10 km interval, has not been reported in the literature, so far. Earlier rocket¯ights from SHAR (Prakash et al, 1991) showed a number of large-scale structures in the region 100± 150 km with vertical scale sizes up to 25 km, but the electron density increase in such layers was only by a factor of 20 or less. The E-region¯ight from Thumba, reported by Prakash et al (1970), revealed the presence of layered structures with scale sizes of 5±10 km in 90± 130 km altitude region but the electron density increase in these structures was only by a factor of 10 or less.…”

Section: Large-scale Irregularitiesmentioning

confidence: 95%

“…Prakash et al (1991) studied ESF irregularities using RH-560 rockets instrumented with Langmuir probes launched from SHAR, India and found that the relationship between the spectral index, n and the mean integrated spectral power, P T , (in 20 m to 200 m scale size range) could be represented by a Gaussian function. The altitude variation of n, normalized with respect to P T , showed that the nature of spectra remains same between 230 km and the apogee of the rocket, which was 332 km.…”

Section: Introduction and Literature Reviewmentioning

confidence: 99%

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Some new features of electron density irregularities over SHAR during strong spread F

Raizada

Sinha

2000

Annales Geophysicae

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Abstract. An RH-560 rocket¯ight was conducted from Sriharikota rocket range (SHAR) (14°N, 80°E, dip latitude 5.5°N) to study electron density and electric ®eld irregularities during spread F. The rocket was launched at 2130 local time (LT) and it attained an apogee of 348 km. Results of electron density¯uctuations are presented here. Two extremely sharp layers of very high electron density were observed at 105 and 130 km. The electron density increase in these layers was by a factor of 50 in a vertical extent of 10 km. Large depletions in electron density were observed around 175 and 238 km. Both sharp layers as well as depletions were observed also during the descent. The presence of sharp layers and depletions during the ascent and the descent of the rocket as well as an order of magnitude less electron density, in 150±300 km region during the descent, indicate the presence of strong large-scale horizontal gradients in the electron density. Some of the valley region irregularities (165±178 km), in the intermediate scale size range, observed during this¯ight, show spectral peaks at 2 km and can be interpreted in terms of the image striation theory suggested by Vickrey et al. The irregularities at 176 km do not exhibit any peak at kilometer scales and appear to be of new type. The growth rate of intermediate scale size irregularities, produced through generalized Rayleigh Taylor instability, was calculated for the 200± 330 km altitude, using observed values of electron density gradients and an assumed vertically downward wind of 20 ms )1 . These growth rate calculations suggest that the observed irregularities could be produced by the gradient drift instability.

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“…Several rocket campaigns have been reported for studying the phenomenon of spread-F in the American region (Kelley et al, 1976;Morse et al, 1977;Rino et al, 1981;Szuszczewicz et al, 1981;Kelley et al, 1982;Hysell et al, 1994) and a few campaigns in the Indian zone Prakash et al, 1991;Sinha et al, 1999;. Kelley et al (1982) reported that at altitudes above about 280 km the electron density spectrum varied as k −5 while the electric field fluctuations showed a power law dependence of k −3 .…”

Section: Introductionmentioning

confidence: 99%

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

Muralikrishna¹,

Vieira²

2007

Rev. Bras. Geof.

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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 ...

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In-situ studies of equatorial spread-F over SHAR—steep gradients in the bottomside F-region and transitional wavelength results

Cited by 29 publications

References 33 publications

Observations and Modelling of Nocturnal Ionospheric Irregularities in Low Latitude Region.

Observations and Modelling of Nocturnal Ionospheric Irregularities in Low Latitude Region.

Some new features of electron density irregularities over SHAR during strong spread F

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

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