Solar flux dependence of coherence scales in scintillation patterns produced by ESF irregularities

Engavale, B.; Jeeva, K.; Nair, K. U.; Bhattacharyya, A.

doi:10.5194/angeo-23-3261-2005

Cited by 14 publications

(18 citation statements)

References 20 publications

(27 reference statements)

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“…5. Such an increase in V zonal is also in agreement with the observations of Engavale et al (2005) and Fejer et al (2005), who respectively reported pre-midnight irregularity drift and zonal drift in the equatorial F-region plasma as increasing with the solar flux. dex (R = 0.70) are quite similar and can be used to investigate solar cycle effects on the irregularity drift velocity.…”

Section: Ionospheric Irregularity Zonal Drift Velocitiessupporting

confidence: 80%

“…We have selected the period of 22:00-24:00 LT because throughout this time the scintillation-producing irregularities can be considered for practical purposes to drift at comparable velocities with the background plasma (Kil et al, 2000(Kil et al, , 2002Engavale et al, 2005). Before 22:00 LT, due to the presence of perturbation electric fields associated with the Rayleigh-Taylor instability, the irregularities are still growing and the values of V zonal may present great variability Engavale et al, 2005), whereas after 24:00 LT the scintillation-producing irregularities start to decay faster by cross-field diffusion (Basu et al, 1978). The tendency for the irregularity drift velocities to increase with increasing EUV and F10.7 cm solar fluxes can clearly be seen in the plots of Fig.…”

Section: Ionospheric Irregularity Zonal Drift Velocitiesmentioning

confidence: 99%

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Climatology and modeling of ionospheric scintillations and irregularity zonal drifts at the equatorial anomaly crest region

et al. 2017

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Abstract. In this study the climatology of ionospheric scintillations and the zonal drift velocities of scintillationproducing irregularities are depicted for a station located under the southern crest of the equatorial ionization anomaly. Then, the α−µ ionospheric fading model is used for the firstand second-order statistical characterization of amplitude scintillations. In the statistical analyzes, data are used from single-frequency GPS receivers acquired during ∼ 17 years (September 1997-November 2014 at Cachoeira Paulista (22.4 • S; 45.0 • W), Brazil. The results reveal that the nocturnal occurrence of scintillations follows the seasonal distribution of plasma bubble irregularities observed in the longitudinal sector of eastern South America. In addition to the solar cycle dependence, the results suggest that the occurrence climatology of scintillations is also modulated by the secular variation in the dip latitude of Cachoeira Paulista, since the maximum occurrence of scintillations during the peak of solar cycle 24 was ∼ 20 % lower than that observed during the maximum of solar cycle 23. The dynamics of the irregularities throughout a solar cycle, as investigated from the estimates of the mean zonal drift velocities, presented a good correlation with the EUV and F10.7 cm solar fluxes. Meanwhile, the seasonal behavior showed that the magnitude of the zonal drift velocities is larger during the December solstice months than during the equinoxes. In terms of modeling, the results for the α − µ distribution fit quite well with the experimental data and with the temporal characteristics of fading events independently of the solar activity level.

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Section: Ionospheric Irregularity Zonal Drift Velocitiessupporting

confidence: 80%

Section: Ionospheric Irregularity Zonal Drift Velocitiesmentioning

confidence: 99%

Climatology and modeling of ionospheric scintillations and irregularity zonal drifts at the equatorial anomaly crest region

et al. 2017

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“…Recorded spaced receiver scintillation observations are analyzed using full cross‐correlation technique [ Briggs , ], and parameters S 4 , V 0 , V C , and C I ( x 0 , t m ) are computed for every 3 min [ Engavale et al , ]. S 4 is a measure of strength of scintillations.…”

Section: Vhf Scintillation Observations and Data Analysis Techniquementioning

confidence: 99%

Structuring of intermediate scale equatorial spread F irregularities during intense geomagnetic storm of solar cycle 24

et al. 2016

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Here we examine the structuring of equatorial plasma bubble (EPB) during intense geomagnetic storm of solar cycle (SC) 24 that occurred on 17 March 2015 using spaced receiver scintillation observations on a 251 MHz radio signal, recorded by a network of stations in Indian region. As yet, this is the strongest geomagnetic storm (Dstmin∼−223nT) that occurred in present SC. Present study reveals that the structuring of equatorial spread F (ESF) irregularities was significantly different on 17 March as compared to quiet days of corresponding month. ESF irregularities of intermediate scale (100 m to few kilometers) are observed at unusually higher altitudes (≥ 800 km) covering wider longitudinal‐latitudinal belt over Indian region. A presence of large‐scale irregularity structures with stronger ΔN at raised F peak with small‐scale irregularities at even higher altitudes is observed. It caused strong focusing effect (S4>1) that prevails throughout premidnight hours at dip equatorial station Tirunelveli. Other observational aspect is that zonal irregularity drifts over low‐latitude station Kolhapur exhibited a large deviation of ∼230 m/s from their average quiet time pattern. During this geomagnetic storm, two southward turnings of significant strength (BZ≤−15 nT) occurred at 11.4 IST (Indian standard time) and 17.9 IST. The later southward turning of interplanetary magnetic field (IMF)BZ resulted in a large eastward prompt penetration electric field (PPEF) close to sunset hours in Indian longitude. Estimates of PPEF obtained from real‐time ionospheric model are too low to explain the observed large upliftment of F region in the post sunset hours. Possible reason for observed enhanced PPEF‐linked effects is discussed.

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“…The effect of magnetic disturbances on equatorial F region plasma drifts is seen as well, over and above the day‐to‐day variability in the quiet time eastward drift of the ground scintillation pattern, for which a monthly pattern of local time variation is estimated using the spaced receiver data [ Bhattacharyya et al , 2002; Engavale et al , 2005]. In the absence of magnetic disturbances, when perturbation electric fields associated with the R‐T instability dies down after 2200 LT, irregularities tend to drift with the background plasma as shown in a computer simulation of the evolution of the R‐T instability in the presence of a realistic background plasma motion [ Retterer , 1999].…”

Section: Introductionmentioning

confidence: 99%

Magnetic activity linked generation of nighttime equatorial spread F irregularities

et al. 2007

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Results derived from a statistical study of the generation of equatorial spread F (ESF) irregularities as a result of magnetic activity based on spaced receiver ionospheric scintillation data recorded at a dip equatorial station is reported here. For a study of this nature it is essential to establish whether the observed scintillations are caused by freshly generated irregularities or by irregularities generated earlier, which later drift onto the signal path. It has been observed in the past that the maximum cross‐correlation between the spaced receiver signals is significantly less than 1 during the initial phase of development of ESF irregularities due to the presence of perturbation electric fields associated with the Rayleigh‐Taylor (R‐T) instability that produces equatorial plasma bubbles (EPBs), whereas in the later phase, when these perturbation electric fields die down, the correlation between the two signals increases rapidly. This feature is used in the present study to identify freshly generated ESF irregularities associated with EPBs using spaced receiver scintillation data. Magnetically disturbed days are chosen by using three hourly geomagnetic activity index ap, daily index Ap, and also AE index to study the cases of prompt penetration of high‐latitude electric field to the equatorial ionosphere. Disturbed time statistical occurrence pattern of freshly generated irregularities shows seasonal variation for all three types of magnetic disturbances: disturbance dynamo, prompt penetration, combination of disturbance dynamo and prompt penetration. However, it is found that fresh generation of the irregularities due to magnetic activity is most likely to occur around midnight hours in all seasons. Suppression of generation of irregularities immediately after sunset due to inhibition of the growth of the R‐T instability on the bottomside of the equatorial F region is clearly seen in vernal equinox (March and April) and solstice months but is not observed for autumnal equinox (September and October).

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Solar flux dependence of coherence scales in scintillation patterns produced by ESF irregularities

Cited by 14 publications

References 20 publications

Climatology and modeling of ionospheric scintillations and irregularity zonal drifts at the equatorial anomaly crest region

Climatology and modeling of ionospheric scintillations and irregularity zonal drifts at the equatorial anomaly crest region

Structuring of intermediate scale equatorial spread F irregularities during intense geomagnetic storm of solar cycle 24

Magnetic activity linked generation of nighttime equatorial spread F irregularities

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