Development of intermediate‐scale structure at different altitudes within an equatorial plasma bubble: Implications for L‐band scintillations

Bhattacharyya, A.; Kakad, Bharati; Gurram, P.; Sripathi, S.; Sunda, Surendra

doi:10.1002/2016ja023478

Cited by 26 publications

(38 citation statements)

References 44 publications

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“…For Q‐ and D‐days, we are not only interested in the occurrence EPBs but we are also keen to know the level of degradation caused to incoming radio signal by these F‐EPBs, which is closely related to the strength and spatial scales of the ESF irregularities (Bhattacharyya et al, ). Through simulation, Keskinen et al () have demonstrated that the evolution of EPBs are considerably different during Q‐ and D‐days.…”

Section: Introductionmentioning

confidence: 99%

Evolution of Freshly Generated Equatorial Spread F (F‐ESF) Irregularities on Quiet and Disturbed Days

et al. 2018

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We examined the seasonal and solar flux dependence of the occurrence of freshly generated intermediate scale (100 m to few km) equatorial spread F (ESF) irregularities during magnetically quiet (Q) and disturbed (D) periods. We utilized long‐term (1992–2006 and 2013–2015) amplitude scintillation data on a 251 MHz signal recorded at Tirunelveli (dip lat. 1.5°N ). Also, ionosonde data (1990–2003) recorded at Trivandrum (dip lat. 0.5°N) are used. The presence of fresh ESF (F‐ESF) is identified using the maximum cross‐correlation between intensity variations recorded by two spaced receivers on a magnetic east‐west baseline. We find distinct differences in the seasonal and solar flux dependence of the usual postsunset (<22 LT) generation of F‐ESF on both Q‐ and D‐days. Interesting feature is that F‐ESF linked moderate–strong scintillations are more prevalent on D‐days as compared to Q‐days in both early (18–22 LT) and later (>22 LT) phase of evolution of the irregularities. It directly hints toward the difference in the spatial structuring (spatial scales) of F‐ESF on D‐days as compared to Q‐days. On D‐days, the occurrence of F‐ESF is more likely around midnight and early‐morning hours in all seasons. Whereas on Q‐days, the postmidnight F‐ESF is found to occur mainly during solstices of low solar activity. The possible sources for the generation of F‐ESF around midnight on Q‐days of solstices during low solar activity are examined. We also find that perturbation electric field linked with F‐ESF on D‐days sustains for longer time, which results in longer durations of the active phase of equatorial plasma bubbles.

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Section: Introductionmentioning

confidence: 99%

Evolution of Freshly Generated Equatorial Spread F (F‐ESF) Irregularities on Quiet and Disturbed Days

et al. 2018

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“…Theoretical results reported in these papers were obtained by computation of the wavefield on the ground, after the signal propagated through a one‐dimensional phase screen characterized by phase variations produced by the irregularities. In the present paper, a 2‐D model of the irregularities is used to estimate n from the S 4 indices for 251‐MHz and 1.575‐GHz signals computed under all scattering conditions, by solving the equation satisfied by the fourth moment of the complex amplitude of the wave (Bhattacharyya et al, ).…”

Section: Theoretical Results For the Frequency Exponentmentioning

confidence: 99%

“…The equation satisfied by Γ 4 in the course of the signal propagating through a thick irregularity layer followed by free space to the ground receiver (Yeh & Liu, ) is solved using the split‐step method (Bhattacharyya & Yeh, ). The irregularities are characterized by either a single‐component power‐law spectrum with slope − m as given in equation of Bhattacharyya et al () or a two‐component power‐law spectrum of the form given in equation . For the particular case of m 1 = 2 and m 2 = 4, which is considered in this paper, the constant

C_{normalΔ N} = σ_{normalΔ N}^{2} ((), q_{b}^{2} - q_{0}^{2}) / 2 π \ln ((), q_{b} / q_{0})

.…”

Section: Theoretical Results For the Frequency Exponentmentioning

confidence: 99%

“…Here, σ Δ N is the standard deviation of electron density fluctuations. It can be seen from equation that the S 4 index is a special case of Γ 4 (Bhattacharyya et al, ). In the calculation of S 4 , ambient plasma density N is assumed to be constant throughout the irregularity layer, which is effectively a region around the F layer peak, where N is a maximum.…”

Section: Theoretical Results For the Frequency Exponentmentioning

confidence: 99%

“…The reason ambient plasma density has been introduced in Figure a, where the x axis shows the fractional density fluctuation, is because traditionally, it has been argued that for a given percentage density fluctuation associated with the irregularities that map down from the equatorial region to the EIA region, stronger L‐band scintillations are observed in the EIA region only because the ambient density is higher. This is only partially correct (Bhattacharyya et al, ). Two different ambient plasma frequencies are considered so that for a given percentage density fluctuation, the case with higher N represents larger density fluctuations.…”

Section: Theoretical Results For the Frequency Exponentmentioning

confidence: 99%

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Signal Frequency Dependence of Ionospheric Scintillations: An Indicator of Irregularity Spectrum Characteristics

et al. 2019

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Multifrequency scintillation observations show that strong amplitude scintillations on very high frequency (VHF) signals are accompanied by weak L‐band scintillations near the dip equator and strong L‐band scintillations in equatorial ionization anomaly (EIA) region. For several decades this has been attributed to higher ambient plasma density in the EIA region. Recent work suggests that occurrence of stronger L‐band scintillations in the EIA region requires that the intermediate‐scale (~100 m to few km) ionospheric irregularity spectrum in this region be significantly shallower than that in the equatorial region. However, this has not been established so far. Signal frequency dependence of amplitude scintillations is characterized by the frequency exponent that determines the dependence on signal frequency of the S4 index: the standard deviation of normalized intensity fluctuations. In this paper, theoretical calculations of the frequency exponent for VHF and L‐band signals are carried out using different irregularity spectra and compared with observations in order to characterize power‐law irregularity spectra in different latitude zones. Intermediate‐scale irregularities in the equatorial and low‐latitude region, which are aligned with the geomagnetic field, are described by a two‐dimensional model. Model simulations show that the frequency exponent derived from S4 indices for VHF and L‐band signals is determined only by the characteristics of the irregularity spectrum and hence can be utilized to identify the nature of the power‐law irregularity spectrum. Frequency exponents computed using VHF and L‐band observations near the dip equator and EIA regions show distinct patterns, which clearly indicate steep and shallow irregularity spectra, respectively, in these regions.

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Disturbance dynamo effects over low‐latitude F region: A study by network of VHF spaced receivers

et al. 2017

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Generation of equatorial spread F (ESF) irregularities resulting from magnetic disturbance is known for past few decades. However, better prediction models for this phenomenon are still lacking. Magnetic storms also affects the F region plasma drifts. In this work we examined variability in (i) occurrence of such freshly generated ESF and (ii) low‐latitude F region zonal plasma drifts over Indian longitude. For this purpose simultaneous observations of amplitude scintillations on 251 MHz signal, recorded by a network of spaced receivers located at low‐latitude stations, are utilized. Observational stations are situated such that it longitudinally (latitudinally) covers an area of 5.6° (13°). Here effect of disturbance dynamo (DD) electric field at low‐latitude F region and its variability are studied for three magnetic storms occurring in 2011. These magnetic storms are having nearly similar type characteristics except their start time. We find that as time difference (i.e., ΔT) between local sunset and start of magnetic activity decreases, the DD effects seen at low‐latitude F region zonal irregularity drift around midnight becomes stronger. For a given magnetic storm the DD effect on F region zonal irregularity drifts is found to be only marginally stronger at dip equator in comparison to off‐equatorial stations. Although effect of DD on F region zonal irregularity drifts are felt simultaneously, generation of fresh ESF is variable within a smaller longitudinal belt of 5.6°. It is attributed to the presence of LSWS at the bottomside of F region, as initiation of ESF is highly likely (unlikely) in the vicinity of crest (trough) of such LSWS.

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Development of intermediate‐scale structure at different altitudes within an equatorial plasma bubble: Implications for L‐band scintillations

Cited by 26 publications

References 44 publications

Evolution of Freshly Generated Equatorial Spread F (F‐ESF) Irregularities on Quiet and Disturbed Days

Evolution of Freshly Generated Equatorial Spread F (F‐ESF) Irregularities on Quiet and Disturbed Days

Signal Frequency Dependence of Ionospheric Scintillations: An Indicator of Irregularity Spectrum Characteristics

Disturbance dynamo effects over low‐latitude F region: A study by network of VHF spaced receivers

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