Chaotic echoes on ionograms: Underdense scattering or total reflections?

Wright, J. W.; Argo, P.E.

doi:10.1029/93rs02126

Cited by 10 publications

(5 citation statements)

References 41 publications

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“…Interestingly, the Doppler shifts or line-of-sight velocities of so-called "chaotic" Es-echoes, recorded by Wright and Argo (1994) at Tromsø with a Dynasonde, showed similar trends for sounding frequencies from 1 to 3 MHz, although their line-of-sight velocities did not display symmetrically displaced side-peaks. They estimated that half of the decibel difference between total and backscatter echo amplitudes was due to the echo oblique paths and was specific to their own transmit and receive systems.…”

Section: Discussionmentioning

confidence: 93%

“…They estimated that half of the decibel difference between total and backscatter echo amplitudes was due to the echo oblique paths and was specific to their own transmit and receive systems. However, Wright and Argo (1994) concluded that these chaotic echoes were probably caused by near total reflections, rather than under-dense Bragg scattering.…”

Section: Discussionmentioning

confidence: 99%

“…1 and 2 provided little information about the physical phenomena responsible for the lack of F-region echoes and the simultaneous enhancement of E-region drift velocities. Following the approach of Wright and Argo (1994), a detailed The velocity components are expressed in a compass-oriented coordinate system. Azimuth angles are measured positive eastwards from compass north (∼92 • west of geographic north).…”

Section: E-and F-region Drift Velocitiesmentioning

confidence: 99%

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Southern high-latitude Digisonde observations of ionosphere E-region Bragg scatter during intense lacuna conditions

et al. 2004

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Abstract. During summer months at solar cycle minimum, F-region lacuna and slant-Es conditions (SEC) are common features of daytime ionograms recorded around local magnetic noon at Casey, Antarctica. Digisonde measurements of drift velocity height profiles show that the occurrence of lacuna prevents the determination of F-region drift velocities and also affects E-region drift velocity measurements. Unique E-region spectral features revealed as intervals of Bragg scatter superimposed on typical background Eregion reflection were observed in Digisonde Doppler spectra during intense lacuna conditions. Daytime E-region Doppler spectra recorded at carrier frequencies from 1.5 to 2.7 MHz, below the E-region critical frequency f o E, have two side-peaks corresponding to Bragg scatter at approximately ±1-2 Hz symmetrically located on each side of a centralpeak corresponding to near-zenith total reflections. Angleof-arrival information and ray-tracing simulations show that echo returns are coming from oblique directions most likely resulting from direct backscatter from just below the total reflection height for each sounding frequency. The Bragg backscatter events are shown to manifest during polar lacuna conditions, and to affect the determination of E-region background drift velocities, and as such must be considered when using standard Doppler-sorted interferometry (DSI) techniques to estimate ionospheric drift velocities. Given the Doppler and spatial separation of the echoes determined from high-resolution Doppler measurements, we are able to estimate the Bragg scatter phase velocity independently from the bulk E-region motion. The phase velocity coincides with the E×B direction derived from in situ fluxgate magnetometer records. When ionospheric refraction is considered, the phase velocity amplitudes deduced from DSI are comparable to the ion-acoustic speed expected in the E-region. We briefly consider the plausibility that these previously unreported polar cap E-region Bragg scatter Doppler spectral signatures, observed at Casey in December 1996 during SEC/lacunaCorrespondence to: R. J. Morris (ray.morris@aad.gov.au) conditions may be linked to ionosphere irregularities. These irregularities may possibly be generated by primary plasma waves triggered by current-driven instabilities, that is to say, a hybrid of the "modified two-stream" and "gradient drift" instability mechanisms.

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Section: Discussionmentioning

confidence: 93%

Section: Discussionmentioning

confidence: 99%

Section: E-and F-region Drift Velocitiesmentioning

confidence: 99%

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Southern high-latitude Digisonde observations of ionosphere E-region Bragg scatter during intense lacuna conditions

et al. 2004

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“…If the diffuse cluster 3 of Figure 4 were the result of single scattering, however obliquely, from cluster 1 or 2, the presentation of ZL versus XL in the figure would place the scattered echoes at the same ZL as the scatterer, albeit at a greater range. This is observed, for example, in oblique backscatter (Esq) from the equatorial electrojet [Wright and Argo, 1994, Figure 2]. In Figure 4, however, the chaotic echoes are at ZL values significantly greater than those of the likely scatterers.…”

Section: "Deterministic" Multiple Refractive Scatteringmentioning

confidence: 93%

On the radiophysics and geophysics of ionogram spread F

Wright¹,

Argo²,

Pitteway³

1996

Radio Science

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We consider the interpretation of "spread F" ionograms, particularly those echoes that determine most of the radio bandwidth of the phenomenon. We compare expectations based on total internal reflection with theoretical descriptions based on underdense scattering. We conclude that "Rayleigh, .... Bragg," and "diffuse multiplerefractive" radio scattering theories are not consistent with observed properties of these echoes. The total-reflection interpretation is shown to be consistent with rocket and satellite data. Evidence for multiple refractive scatter is found, but it neither greatly nor subtly extends the observed radio bandwidth. Ionograms therefore indicate comprehensively the range of plasma densities within view of the ionosonde, even in conditions of spread F. Using digital ionosonde observations, much can be learned of the spatial structures of plasma density responsible for spread F at auroral and equatorial latitudes. As an example, we suggest how contemporary theory and simulations of the equatorial "bubble" phenomenon may be reconciled with the distinctive equatorial spread F pattern.

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“…Their design process has several subtleties [?itteway and Wright, 1992], but the concept arises naturally in the dynasonde implementation of a digital ionosonde in the following way: The instrument typically transmits pulses at the rate of 100/s, of length 60 gs at-3 dB in a cosine 2 envelope, and of about 10 kW peak power, into a broadband log-periodic transmitting antenna. After ionospheric reflection or scattering (for the often uncertain distinction, see Wright and Argo [ 1994]), the analog signals from two of four or six spaced receiving dipoles [Pitteway and Wright, 1992] pass to two parallel and identical receivers. These develop quadrature dc outputs, x+iy, which are sampled and 12-bit digitized at common 5-gs or 10-gs intervals within a suitable span of range delay, usually called time of arrival, or TOA, but expressed here in kilometers, Simultaneous sampling of two spaced antennas introduces a spatial dimension as an independent variable to the complex amplitudes, identified with the antenna spatial separation (say, east, or X).…”

Section: Information Contentmentioning

confidence: 99%

A new data acquisition concept for digital ionosondes: Phase‐based echo recognition and real‐time parameter estimation

Wright¹,

Pitteway²

1999

Radio Science

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Abstract. The problem of identifying echoes in digital ionosonde observations is discussed, starting with an off-line simulation of the procedure long used in real time by the dynasonde. In that method, echoes are defined as amplitude-modulus peaks from rapid (10-1as) sampling of receiver quadrature outputs; coincidence of peak time among a small number (4-8) of repeated pulses has served well to reject impulsive noise while deciding the complex-amplitude samples to be retained for off-line analyses. This paper presents a new method of echo recognition dependent on all of the phase information contained in the same rapid sampling. No change is made in basic sounding function, but conversion to physical parameters is done first, for all 10-1as samples; the consistency of these parameters in five dimensions over four or more samples defines an echo, or at least a partial "glint." In an example recording, the new method recognizes about 60% more echoes and glints, giving better trace continuity than the earlier method. Measurement resolution among proximate echoing regions is improved. Weighted means of the physical parameters within their defining samples yields better accuracy. Almost incidentally, these results would be available immediately in a real-time implementation of the method.

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Chaotic echoes on ionograms: Underdense scattering or total reflections?

Cited by 10 publications

References 41 publications

Southern high-latitude Digisonde observations of ionosphere E-region Bragg scatter during intense lacuna conditions

Southern high-latitude Digisonde observations of ionosphere E-region Bragg scatter during intense lacuna conditions

On the radiophysics and geophysics of ionogram spread F

A new data acquisition concept for digital ionosondes: Phase‐based echo recognition and real‐time parameter estimation

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