Radar Observations of 8.3-m scale equatorial spread F irregularities over Trivandrum

Abstract. In this paper, we present observations of equatorial spread F (ESF) irregularities made using a newly installed 18MHz radar located at Trivandrum. We characterize the morphology and the spectral parameters of the 8.3-m ESF irregularities which are found to be remarkably different from that observed so extensively at the 3-m scale size. We also present statistical results of the irregularities in the form of percentage occurrence of the echoes and spectral parameters (SNR, Doppler velocity, Spectral width). The Doppler spectra are narrower, less structured and less variable in time as compared to those observed for 3-m scale size. We have never observed the ESF irregularity velocities to be supersonic here unlike those at Jicamarca, and the velocities are found to be within ±200ms–1. The spectral widths are found to be less than 150ms–1. Hence, the velocities and spectral width both are smaller than those reported for 3-m scale size. The velocities and spectral widths are further found to be much smaller than those of the American sector. These observations are compared with those reported elsewhere and discussed in the light of present understanding on the ESF irregularities at different wavelengths. Key words. Ionoshphere (equatorial ionosphere, plasma waves and instabilities; ionospheric irregularities)

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Collisional Rayleigh-Taylor instability and shear-flow in equatorial Spread-F plasma

Annales Geophysicae ◽

10.5194/angeo-21-1153-2003 ◽

2003 ◽

Vol 21 (5) ◽

pp. 1153-1157 ◽

Cited By ~ 6

Author(s):

N. Chakrabarti ◽

G. S. Lakhina

Keyword(s):

Shear Flow ◽

Plasma Waves ◽

Equatorial Ionosphere ◽

Stabilization Process ◽

Ionosphere Plasma ◽

F Region ◽

Spread F ◽

Bottom Side ◽

Rayleigh Taylor Instability ◽

Rt Instability

Abstract. Collisional Rayleigh-Taylor (RT) instability is considered in the bottom side of the equatorial F-region. By a novel nonmodal calculation it is shown that for an applied shear flow in equilibrium, the growth of the instability is considerably reduced. Finite but small amounts of diffusion enhances the stabilization process. The results may be relevant to the observations of long-lived irregularities at the bottom-side of the F-layer.Key words. Ionosphere (ionospheric irregularities, equatorial ionosphere, plasma waves and instabilities)

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Phase calibration approaches for radar interferometry and imaging configurations: equatorial spread F results

Annales Geophysicae ◽

10.5194/angeo-26-2333-2008 ◽

2008 ◽

Vol 26 (8) ◽

pp. 2333-2343 ◽

Cited By ~ 16

Author(s):

J. L. Chau ◽

D. L. Hysell ◽

K. M. Kuyeng ◽

F. R. Galindo

Keyword(s):

Doppler Velocity ◽

Equatorial Spread F ◽

Radar Systems ◽

Imaging Results ◽

Phase Calibration ◽

Spread F ◽

Multiple Receiver ◽

Calibration Techniques ◽

Radio Beacon ◽

Radio Stars

Abstract. In recent years, more and more radar systems with multiple-receiver antennas are being used to study the atmospheric and ionospheric irregularities with either interferometric and/or imaging configurations. In such systems, one of the major challenges is to know the phase offsets between the different receiver channels. Such phases are intrinsic to the system and are due to different cable lengths, filters, attenuators, amplifiers, antenna impedance, etc. Moreover, such phases change as function of time, on different time scales, depending on the specific installation. In this work, we present three approaches using natural targets (radio stars, meteor-head and meteor trail echoes) that allow either an absolute or relative phase calibration. In addition, we present the results of using an artificial source (radio beacon) for a continuous calibration that complements the previous approaches. These approaches are robust and good alternatives to other approaches, e.g. self-calibration techniques using known data features, or for multiple-receiver configurations constantly changing their receiving elements. In order to show the good performance of the proposed phase calibration techniques, we present new radar imaging results of equatorial spread F (ESF) irregularities. Finally we introduce a new way to represent range-time intensity (RTI) maps color coded with the Doppler information. Such modified map allows the identification and interpretation of geophysical phenomena, previously hidden in conventional RTI maps, e.g. the time and altitude of occurrence of ESF irregularities pinching off from the bottomside and their respective Doppler velocity.

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Identification of active fossil bubbles based on coordinated VHF radar and airglow measurements

Annales Geophysicae ◽

10.5194/angeo-25-2099-2007 ◽

2007 ◽

Vol 25 (10) ◽

pp. 2099-2102 ◽

Cited By ~ 19

Author(s):

R. Sekar ◽

D. Chakrabarty ◽

S. Sarkhel ◽

A. K. Patra ◽

C. V. Devasia ◽

...

Keyword(s):

Vhf Radar ◽

Equatorial Spread F ◽

Plasma Irregularity ◽

Scale Size ◽

Spread F ◽

Dip Equator ◽

Plasma Depletion ◽

First Time ◽

Airglow Intensity

Abstract. Plasma irregularity structures associated with an Equatorial Spread-F (ESF) event were recorded by the Indian VHF Radar on 26–27 April 2006 near midnight hours. The plasma structures were found to be isolated without having bottomside structure. They moved predominantly downward and the structures were found to be less turbulent than their post-sunset counterparts. However, the structures were characterized by meter-scale size irregularities. These structures are identified for the first time as plasma depletion structures using simultaneous, collocated measurements of OI 630.0 nm airglow intensity variations. The variation of the base height of ionospheric F layer over dip equator is also presented to buttress the result. Further, these plasma structures are shown to be "active fossil bubbles".

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Coherent backscatter radar imaging of equatorial spread F: Intermediate scale-size structures

10.1190/sbgf2011-446 ◽

2011 ◽

Author(s):

Fabiano S. Rodrigues ◽

Eurico R. de Paula ◽

Alison de O. Moraes

Keyword(s):

Radar Imaging ◽

Intermediate Scale ◽

Equatorial Spread F ◽

Scale Size ◽

Spread F ◽

Coherent Backscatter

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Simultaneous radar and spaced receiver VHF scintillation observations of ESF irregularities

Annales Geophysicae ◽

10.5194/angeo-24-1419-2006 ◽

2006 ◽

Vol 24 (5) ◽

pp. 1419-1427 ◽

Cited By ~ 9

Author(s):

D. Tiwari ◽

B. Engavale ◽

A. Bhattacharyya ◽

C. V. Devasia ◽

T. K. Pant ◽

...

Keyword(s):

Cross Correlation ◽

Spectral Width ◽

Maximum Height ◽

Plasma Bubble ◽

Equatorial Spread F ◽

Structure And Dynamics ◽

Spread F ◽

Vhf Scintillation ◽

Relationship Of ◽

The Relationship

Abstract. Simultaneous observations of equatorial spread F (ESF) irregularities made on 10 nights during March-April 1998 and 1999, using an 18-MHz radar at Trivandrum (77° E, 8.5° N, dip 0.5° N) and two spaced receivers recording scintillations on a 251-MHz signal at Tirunelveli (77.8° E, 8.7° N, dip 0.4° N), have been used to study the evolution of Equatorial Spread F (ESF) irregularities. Case studies have been carried out on the day-to-day variability in ESF structure and dynamics, as observed by 18-MHz radar, and with spaced receiver measurements of average zonal drift Vo of the 251-MHz radio wave diffraction pattern on the ground, random velocity Vc, which is a measure of random changes in the characteristics of scintillation-producing irregularities, and maximum cross-correlation CI of the spaced receivers signals. Results show that in the initial phase of plasma bubble development, the greater the maximum height of ESF irregularities responsible for the radar backscatter, the greater the decorrelation is of the spaced receiver scintillation signals, indicating greater turbulence. The relationship of the maximum spectral width derived from the radar observations and CI also supports this result.

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On the Dynamics of Equatorial Spread F

Australian Journal of Physics ◽

10.1071/ph740391 ◽

1974 ◽

Vol 27 (3) ◽

pp. 391 ◽

Cited By ~ 24

Author(s):

Tom Beer

Keyword(s):

Gravity Waves ◽

Equatorial Ionosphere ◽

Multistage Process ◽

Atmospheric Gravity Waves ◽

Equatorial Spread F ◽

Spread F ◽

Atmospheric Gravity ◽

Spatial Resonance

A theory is proposed to explain the occurrence of spread F in the equatorial ionosphere. It is envisaged as a multistage process involving: movement of ionization drift with atmospheric gravity waves that results in spatial resonance, consequent enhanceme

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Bottom-type scattering layers and equatorial spread <i>F</i>

Annales Geophysicae ◽

10.5194/angeo-22-4061-2004 ◽

2004 ◽

Vol 22 (12) ◽

pp. 4061-4069 ◽

Cited By ~ 30

Author(s):

D. L. Hysell ◽

J. Chun ◽

J. L. Chau

Keyword(s):

Large Scale ◽

Coherent Scattering ◽

Plasma Waves ◽

Equatorial Ionosphere ◽

Bottom Type ◽

Radar Images ◽

F Region ◽

Type Layer ◽

Spread F ◽

Gradient Drift

Abstract. Jicamarca radar observations of bottom-type coherent scattering layers in the post-sunset bottomside F-region ionosphere are presented and analyzed. The morphology of the primary waves seen in radar images of the layers supports the hypothesis of kudeki+bhattacharyya-1999 that wind-driven gradient drift instabilities are operating. In one layer event when topside spread F did not occur, irregularities were distributed uniformly in space throughout the layers. In another event when topside spread F did eventually occur, the irregularities within the pre-existing bottom-type layers were horizontally clustered, with clusters separated by about 30km. The same horizontal periodicity was evident in the radar plumes and large-scale irregularities that emerged later in the event. We surmise that horizontal periodicity in bottom-type layer irregularity distribution is indicative of large-scale horizontal waves in the bottomside F-region that may serve as seed waves for large-scale Rayleigh Taylor instabilities. Key words. Ionosphere (equatorial ionosphere; ionospheric irregularties; plasma waves and instabilities)

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