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

2004 ◽  
Vol 22 (12) ◽  
pp. 4061-4069 ◽  
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)

scholarly journals Coherent backscatter radar imaging in Brazil: large-scale waves in the bottomside F-region at the onset of equatorial spread <I>F</I>

2008 ◽  
Vol 26 (11) ◽  
pp. 3355-3364 ◽  
Author(s):  
F. S. Rodrigues ◽  
D. L. Hysell ◽  
E. R. de Paula
Keyword(s):  
Large Scale ◽  
Imaging Technique ◽  
Radar Imaging ◽  
Shear Instability ◽  
Wide Field ◽  
Bottom Type ◽  
F Region ◽  
Type Layer ◽  
Spread F ◽  
Coherent Backscatter

Abstract. The 30 MHz coherent backscatter radar located at the equatorial observatory in São Luís, Brazil (2.59° S, 44.21° W, −2.35° dip lat) has been upgraded to perform coherent backscatter radar imaging. The wide field-of-view of this radar makes it well suited for radar imaging studies of ionospheric irregularities. Radar imaging observations were made in support to the spread F Experiment (SpreadFEx) campaign. This paper describes the system and imaging technique and presents results from a bottom-type layer that preceded fully-developed radar plumes on 25 October 2005. The radar imaging technique was able to resolve decakilometric structures within the bottom-type layer. These structures indicate the presence of large-scale waves (~35 km) in the bottomside F-region with phases that are alternately stable and unstable to wind-driven gradient drift instabilities. The observations suggest that these waves can also cause the initial perturbation necessary to initiate the Generalized Rayleigh-Taylor instability leading to spread F. The electrodynamic conditions and the scale length of the bottom-type layer structures suggest that the waves were generated by the collisional shear instability. These results indicate that monitoring bottom-type layers may provide helpful diagnostics for spread F forecasting.

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

2003 ◽  
Vol 21 (5) ◽  
pp. 1153-1157 ◽  
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)

scholarly journals Generation of large-scale equatorial F-region plasma depletions during lowrange spread-F season

2004 ◽  
Vol 22 (1) ◽  
pp. 15-23 ◽  
Author(s):  
Y. Sahai ◽  
P. R. Fagundes ◽  
J. R. Abalde ◽  
A. A. Pimenta ◽  
J. A. Bittencourt ◽  
...  
Keyword(s):  
Large Scale ◽  
Ionospheric Plasma ◽  
Geomagnetic Storms ◽  
Atmospheric Composition ◽  
F Region ◽  
Range Type ◽  
June Solstice ◽  
Radio Signature ◽  
Spread F ◽  
Plasma Depletions

Abstract. All-sky imaging observations of the F-region OI 630nm nightglow emission allow us to visualize large-scale equatorial plasma depletions, generally known as trans-equatorial plasma bubbles. Strong range type spread-F is the radio signature of these (magnetically) north-south aligned plasma depletions. An extensive database of the OI 630nm emission all-sky imaging observations has been obtained at Cachoeira Paulista (22.7°S, 45.0°W; dip latitude ∼16°S), Brazil, between the years 1987 and 2000. An analysis of these observations revealed that relatively few large-scale ionospheric plasma depletions occur during the months of May to August (southern winter, June solstice) in the Brazilian sector. Of the few that are observed during these months, some occur in association with geomagnetic storms and some do not. In this paper, a detailed analysis of the events when large-scale ionospheric plasma depletions were initiated and evolved during the June solstice periods are presented and discussed.Key words. Atmospheric composition and chemistry (airglow and aurora). Ionosphere (equatorial ionosphere; ionospheric irregularities)

scholarly journals Multi-instrumented observations of the equatorial F-region during June solstice: large-scale wave structures and spread-F

2018 ◽  
Vol 5 (1) ◽  
Author(s):  
Fabiano S. Rodrigues ◽  
Dustin A. Hickey ◽  
Weijia Zhan ◽  
Carlos R. Martinis ◽  
Bela G. Fejer ◽  
...  
Keyword(s):  
Large Scale ◽  
F Region ◽  
June Solstice ◽  
Spread F

scholarly journals Equatorial ionosphere bottom-type spread F observed by OI 630.0 nm airglow imaging

2010 ◽  
Vol 37 (3) ◽  
pp. n/a-n/a ◽  
Author(s):  
H. Takahashi ◽  
M. A. Abdu ◽  
M. J. Taylor ◽  
P.-D. Pautet ◽  
E. de Paula ◽  
...  
Keyword(s):  
Equatorial Ionosphere ◽  
Bottom Type ◽  
Spread F

scholarly journals Rocket and radar investigation of background electrodynamics and bottom-type scattering layers at the onset of equatorial spread <i>F</i>

2006 ◽  
Vol 24 (5) ◽  
pp. 1387-1400 ◽  
Author(s):  
D. L. Hysell ◽  
M. F. Larsen ◽  
C. M. Swenson ◽  
A. Barjatya ◽  
T. F. Wheeler ◽  
...  
Keyword(s):  
Electric Fields ◽  
Large Scale ◽  
Layer Structure ◽  
Horizontal Structure ◽  
Bottom Type ◽  
Chemical Release ◽  
Spread F ◽  
Density Vector ◽  
Plasma Depletions ◽  
Electron Density Profiles

Abstract. Sounding rocket experiments were conducted during the NASA EQUIS II campaign on Kwajalein Atoll designed to elucidate the electrodynamics and layer structure of the postsunset equatorial F region ionosphere prior to the onset of equatorial spread F (ESF). Experiments took place on 7 and 15 August 2004, each comprised of the launch of an instrumented and two chemical release sounding rockets. The instrumented rockets measured plasma number density, vector electric fields, and other parameters to an apogee of about 450 km. The chemical release rockets deployed trails of trimethyl aluminum (TMA) which yielded wind profile measurements. The Altair radar was used to monitor coherent and incoherent scatter in UHF and VHF bands. Electron density profiles were also measured with rocket beacons and an ionosonde. Strong plasma shear flow was evident in both experiments. Bottom-type scattering layers were observed mainly in the valley region, below the shear nodes, in westward-drifting plasma strata. The layers were likely produced by wind-driven interchange instabilities as proposed by Kudeki and Bhattacharyya (1999). In both experiments, the layers were patchy and distributed periodically in space. Their horizontal structure was similar to that of the large-scale plasma depletions that formed later at higher altitude during ESF conditions. We argue that the bottom-type layers were modulated by the same large-scale waves that seeded the ESF. A scenario where the large-scale waves were themselves produced by collisional shear instabilities is described.

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

2004 ◽  
Vol 22 (3) ◽  
pp. 911-922 ◽  
Author(s):  
D. Tiwari ◽  
A. K. Patra ◽  
C. V. Devasia ◽  
R. Sridharan ◽  
N. Jyoti ◽  
...  
Keyword(s):  
Spectral Width ◽  
Plasma Waves ◽  
Equatorial Ionosphere ◽  
Doppler Velocity ◽  
Spectral Parameters ◽  
Equatorial Spread F ◽  
Ionosphere Plasma ◽  
Scale Size ◽  
Spread F ◽  
Present Understanding

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)

scholarly journals High-resolution coherent backscatter interferometric radar images of equatorial spread F using Capon's method

2017 ◽  
Vol 35 (3) ◽  
pp. 393-402 ◽  
Author(s):  
Fabiano S. Rodrigues ◽  
Eurico R. de Paula ◽  
Gebreab K. Zewdie
Keyword(s):  
High Resolution ◽  
Low Power ◽  
Numerical Simulations ◽  
Fourier Method ◽  
Equatorial Spread F ◽  
Radar Images ◽  
F Region ◽  
Spread F ◽  
Short Baselines ◽  
Coherent Backscatter

Abstract. We present results of Capon's method for estimation of in-beam images of ionospheric scattering structures observed by a small, low-power coherent backscatter interferometer. The radar interferometer operated in the equatorial site of São Luís, Brazil (2.59° S, 44.21° W, −2.35° dip latitude). We show numerical simulations that evaluate the performance of the Capon method for typical F region measurement conditions. Numerical simulations show that, despite the short baselines of the São Luís radar, the Capon technique is capable of distinguishing localized features with kilometric scale sizes (in the zonal direction) at F region heights. Following the simulations, we applied the Capon algorithm to actual measurements made by the São Luís interferometer during a typical equatorial spread F (ESF) event. As indicated by the simulations, the Capon method produced images that were better resolved than those produced by the Fourier method. The Capon images show narrow (a few kilometers wide) scattering channels associated with ESF plumes and scattering regions spaced by only a few tens of kilometers in the zonal direction. The images are also capable of resolving bifurcations and the C shape of scattering structures.

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