Simultaneous radar and spaced receiver VHF scintillation observations of ESF irregularities

Tiwari, Diwakar; Engavale, B.; Bhattacharyya, A.; Devasia, C. V.; Pant, Tarun Kumar; Sridharan, R.

doi:10.5194/angeo-24-1419-2006

Cited by 13 publications

(10 citation statements)

References 23 publications

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“…Another study by Patra et al (2005), who studied the spectral width of two radars using HF and VHF at equatorial stations, also reported that in the initial phase of the plasma bubbles the spectral width is found to be very high (300 m/s). The observations of fall in Ci index below 0.5 and high spectral width during early phase of plume observations by radar, presented by Tiwari et al (2006) and our observations are in agreement. In contrast to this, when bottomtype irregularities are seen in the radar map, the cross correlation index (Ci) does not decrease.…”

Section: Resultssupporting

confidence: 91%

“…Tiwari et al (2006) have attributed this to the large scale sinusoidal perturbations on the bottomside of the equatorial F region. Our observations presented here indicate that the bottomtype irregularities do not contain small scale irregularities of a few hundred meter scale size and also that spectral width observed during bottomtype irregularities is quite low, which is in agreement with the observations of Tiwari et al (2006). Niranjan et al (2003) have studied the post mid-night spread F over Waltair, India, using ionosonde observations.…”

Section: Resultsmentioning

confidence: 96%

“…Based on scintillation observations alone they suggested that the cross correlation index (Ci) of the spaced receivers' scintillations may be used to study the dynamics of the equatorial plasma bubbles. Tiwari et al (2006) have presented the HF radar observations at TRV made simultaneously with spaced VHF receiver scintillations at Tirunelveli. They have shown that when plume type irregularities have been observed in the radar maps during the growth period, the cross correlation index (Ci) of the spaced receiver signals is low.…”

Section: Resultsmentioning

confidence: 99%

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Simultaneous observations of ESF irregularities over Indian region using radar and GPS

et al. 2008

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Abstract. In this paper, we present simultaneous observations of temporal and spatial variability of total electron content (TEC) and GPS amplitude scintillations on L1 frequency (1.575 GHz) during the time of equatorial spread F (ESF) while the MST radar (53 MHz) located at Gadanki (13.5 • N, 79.2 • E, Dip latitude 6.3 • N), a low latitude station, made simultaneous observations. In particular, the latitudinal and longitudinal extent of TEC and L-band scintillations was studied in the Indian region for different types of ESF structures observed using the MST radar during the low solar activity period of 2004 and 2005. Simultaneous radar and GPS observations during severe ESF events in the pre-midnight hour reveal that significant GPS L band scintillations, depletions in TEC, and the double derivative of the TEC index (DROTI), which is a measure of fluctuations in TEC, obtained at low latitudes coincide with the appearance of radar echoes at Gadanki. As expected, when the irregularities reach higher altitudes as seen in the radar map during pre-midnight periods, strong scintillations on an L-band signal are observed at higher latitudes. Conversely, when radar echoes are confined to only lower altitudes, weak scintillations are found and their latitudinal extent is small. During magnetically quiet periods, we have recorded plume type radar echoes during a post-midnight period that is devoid of L-band scintillations. Using spectral slopes and crosscorrelation index of the VHF scintillation observations, we suggest that these irregularities could be "dead" or "fossil" bubbles which are just drifting in from west. This scenario is consistent with the observations where suppression of prereversal enhancement (PRE) in the eastward electric field is indicated by ionosonde observations of the height of equatorial F layer and also occurrence of low spectral width in the radar observations relative to pre-midnight period. However, absence of L-band scintillations during post-midnight Correspondence to: S. Sripathi (ssripathi@rediffmail.com) event, when radar observed plume like structures and scintillations were recorded on VHF band, raises questions about the process of evolution of the irregularities. A possible explanation is that whereas small scale (∼3 m) irregularities are generated through secondary waves that grow on the walls of km scale size irregularities, in this case evolution of the Rayleigh-Taylor instability itself did not extend to irregularities of scale sizes of a few hundred meters that produce scintillation on a L-band signal.

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Section: Resultssupporting

confidence: 91%

Section: Resultsmentioning

confidence: 96%

Section: Resultsmentioning

confidence: 99%

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Simultaneous observations of ESF irregularities over Indian region using radar and GPS

et al. 2008

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“…Using this technique, Kakad et al [2007] have studied the fresh generation of irregularities around midnight hours and suppression of scintillations during pre‐midnight hours during magnetically active periods. From Tiwari et al [2006], one can notice that smaller the C I , higher the maximum height reached by the irregularity layer. Sripathi et al [2008] have studied the latitudinal extent of L‐band scintillations during different ESF events.…”

Section: Discussionmentioning

confidence: 92%

Study of equinoctial asymmetry in the Equatorial Spread F (ESF) irregularities over Indian region using multi-instrument observations in the descending phase of solar cycle 23

2011

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[1] In this paper, we present the results of a morphological study of Equatorial Spread F (ESF) irregularities over Indian region based mainly on observations of (1) amplitude scintillations on GPS L-band signal and Rate of TEC Index (ROTI) obtained using a network of GPS receivers and (2) amplitude scintillations on a VHF signal using spaced receivers at Tirunelveli, an equatorial station. Occurrence of both amplitude scintillations on the GPS L1 signal and occurrence of significant ROTI recorded at several stations has been investigated. The latitudinal extent of L-band scintillations shows that their strength is weak over the dip equator but stronger over Equatorial Ionization Anomaly (EIA) region, preferentially during vernal equinox. We find an equinoctial asymmetry in both the occurrence of scintillations and ROTI wherein their occurrence is greater in the vernal equinox than in the autumn equinox. Attempts have been made to understand the asymmetry in latitudinal extent using maximum cross-correlation (C I ) of intensity fluctuations obtained from the VHF spaced receivers observations. The observations suggest that occurrence of C I less than 0.5 is more in the vernal equinox than in the autumn equinox suggesting that the maximum height of the Equatorial Plasma Bubbles (EPBs) during vernal equinox may be higher than that during autumn equinox. TIMED/GUVI retrieved peak electron density during the same period also indicates that background electron density is higher and more symmetric during vernal equinox than autumn equinox. Hence, our results suggest that background electron density may be playing a vital role in creating the equinoctial asymmetry.Citation: Sripathi, S., B. Kakad, and A. Bhattacharyya (2011), Study of equinoctial asymmetry in the Equatorial Spread F (ESF) irregularities over Indian region using multi-instrument observations in the descending phase of solar cycle 23,

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“…Eastward drifts at 300 km altitude estimated by Fukao et al . [] were found to be 140 m s −1 around 20 LT and 80 m s −1 around 24 LT. With regard to eastward drifts from Indian sector, there have been reports based on airglow imager and VHF scintillation observations [e.g., Sinha and Raizada , ; Tiwari et al ., ]. Using airglow imager observations from Sriharikota, a location ~100 km east of Gadanki, Sinha and Raizada [] estimated eastward drifts, which varied from 190 m s −1 at ~21 LT to 40 m s −1 at 01 LT. Tiwari et al .…”

Section: Resultsmentioning

confidence: 99%

First results on low‐latitude E and F region irregularities obtained using the Gadanki Ionospheric Radar Interferometer

et al. 2014

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A 30 MHz radar has recently been established at Gadanki (13.5°N, 79.2°E; 6.5°N magnetic latitude) to make unattended observations of the ionospheric field-aligned irregularities (FAI). This radar, called the Gadanki Ionospheric Radar Interferometer (GIRI), has been designed to have scanning capability of 100°in the east-west plane perpendicular to Earth's magnetic field and interferometry/imaging system to study drifts and spatial distribution of plasma irregularities at both large and small scales. In this paper, we present the first results on the E and F region FAI made using the scanning capability of the GIRI. Daytime observations of E region FAI show type 2 echoes with velocities predominantly upward northward (downward-southward) at altitudes >100 km (<100 km) and westward (eastward) in the forenoon (afternoon) with signature of tidal wind field. F region irregularities show bottom-type, bottomside and plume structures with close resemblance to those observed over the magnetic equator. Observations made with the east-west scanning capability have been used to study the origin, evolution, and drift of the FAI for the first time from Gadanki. Eastward drifts are estimated to be 90-210 m s À1 during 20-24 LT. Upward velocity as large as 500 m s À1 has been observed in the initial phase of the plume structures. Intriguingly, downward velocity as large as 60 m s À1 has also been observed in the plumes, displaying descending pattern, observed in the early evening hours. These results are presented and discussed in the light of current understanding of low-latitude plasma irregularities, and future prospects of GIRI are outlined.

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Simultaneous radar and spaced receiver VHF scintillation observations of ESF irregularities

Cited by 13 publications

References 23 publications

Simultaneous observations of ESF irregularities over Indian region using radar and GPS

Simultaneous observations of ESF irregularities over Indian region using radar and GPS

Study of equinoctial asymmetry in the Equatorial Spread F (ESF) irregularities over Indian region using multi-instrument observations in the descending phase of solar cycle 23

First results on low‐latitude E and F region irregularities obtained using the Gadanki Ionospheric Radar Interferometer

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