Measurement of the velocity of waves in the ionosphere: A comparison of the ray theory approach and diffraction theory

Brownlie, G.; Dryburgh, L. G.; Whitehead, J. D.

doi:10.1016/0021-9169(73)90133-5

Cited by 30 publications

(4 citation statements)

References 6 publications

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“…The tilt angles of the scatterers will ripple across the radar field of view at the phase speed of the perturbing wave. If significant backscatter is associated with a particular tilt angle (i.e., if specular reflections are important), then the mechanism is consistent with well-established interpretations of totally reflected signals from rippled isodensity contours in the E and F regions [Brownlie et al, 1973;Pfister, 1971;Bennett and D•Ison, 1993]. Specifically, a mirror reflector rippled by a gravity wave will appear to a ground-based observer to be rigidly translated at the horizontal phase speed of the gravity wave.…”

supporting

confidence: 76%

On the influence of specular reflections in MF radar wind measurements

Sürücü¹,

Franke²,

Kudeki³

1995

Radio Science

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Numerical simulations are employed to investigate possible biases in Medium Frequency (MF) wind estimates. To explain apparent biases inferred from Arecibo Initiative in Dynamics of the Atmosphere (AIDA) campaign measurements, Hines et al. (1993) have suggested that MF radar estimates of horizontal winds should be biased toward the phase speed of perturbing gravity waves if the MF scattering process is modulated by the passage of such waves through the scattering volume. One of the proposed scenarios involves modulation of the tilts of anisotropic irregularities by the perturbation winds associated with gravity waves. We use a two‐dimensional propagation model in which anisotropic scattering centers are represented by conducting line segments located at random positions inside the radar scattering volume. The scatterers are advected and tilted by the superposition of a mean wind and the perturbation winds associated with a gravity wave. Simulated complex time series, which would be recorded by a two‐receiver antenna array with a typical MF radar system parameters, are analyzed to obtain spaced antenna (SA) wind estimates for comparison with the specified wind speed at the center of the scattering volume. Numerical simulations are carried out for many different sets of gravity wave parameters. Each simulation is performed twice, once with essentially isotropic scatterers (line segments of length λ/2) and again with anisotropic (“specular”) scatterers of length 10 λ. Numerical results indicate that individual SA wind estimates are accurately predicted by the wave‐induced error model of Kudeki et al. (1993). This is true for both isotropic and specular scatterers as long as the gravity wave has a horizontal wavelength larger than the horizontal dimension of the radar range cell. The results also indicate that estimated winds averaged over one period of the perturbing gravity wave exhibit statistically significant biases when the scattering centers are highly anisotropic, but the bias is not necessarily toward the phase speed of the perturbing gravity wave and, more importantly, the magnitude of the bias exhibited in our simulations was always less than 15 m/s. Implications of the numerical results are discussed in light of observed discrepancies as large as 40 m/s in recent AIDA campaign comparisons between MF and incoherent scatter radar winds. In particular, it is argued that the simulation results support the wave‐induced fluctuations model put forth by Kudeki et al. (1993) as an explanation for the AIDA results.

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supporting

confidence: 76%

On the influence of specular reflections in MF radar wind measurements

Sürücü¹,

Franke²,

Kudeki³

1995

Radio Science

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“…Line-of-sight movements can be assessed from the phase-path changes on these traces over the recording period of 35.6s. This line-of-sight speed can be converted to a speed of horizontal movement using Pfister's Theorem (PFISTER,1971;BROWNLIE et al, 1973 4.4 The fourth event It seems quite reasonable to regard the modulated macroscale height rise between 2240 and 0000 (Fig. 9) as part of a spread-F event as the modulation consists of 4 cycles of what appears to be a TID wavetrain (periodicity 13m-see Fig.…”

Section: Resultsmentioning

confidence: 99%

Nighttime Mid-Latitude Travelling Ionospheric Disturbances Associated with Mild Spread-F Conditions.

Bowman

1991

J. geomagn. geoelec

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Several diverging duplicate traces and one converging duplicate trace for mild mid-latitude spread-F events (on one particular night) have been used to investigate medium-scale travelling ionospheric disturbances (TIDs) during night hours. Sweptfrequency and fixed-frequency sonograms (which have phase information added) show spread-F characteristics similar to those recorded for more intense spread-F events. These include modulated height rises in the isoionic contours and electron-density depletions. The phase-path information on the fixed-frequency recordings allowed the detection of the TID wavetrains responsible for the modulation. Usually for these mild events one tilt in the isoionic contours produced by one cycle of a wavetrain is sufficiently large to allow significant off-vertical reflections which in turn are responsible for a diverging trace. Speeds of travel have been determined by considering both the rate of change of group-range for the duplicate traces as well as the rate of change of phase-path indicated on each fixed-frequency recording. The speeds of travel of these nighttime TIDs are compared with the speeds of daytime TIDs.

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“…Fading of the received echoes because of many scales of propagating gravity waves is sometimes referred to as “interference fading,” which is not a real fading but looks like fast fading and hence it cannot be utilized to determine the drift velocities. [ Hines and Raghava Rao , 1968; Brownlie et al , 1973; Hocking , 1983a].…”

Section: Potential Problems Regarding the Mf Spaced Antenna And Hf Domentioning

confidence: 99%

A comparison study of zonal drift velocities measurements as seen by MF spaced antenna and HF Doppler radar in the Indian dip equatorial mesospheric and lower thermospheric (80–100 km) region

Ramkumar

Gurubaran²,

Rajaram

et al. 2010

J. Geophys. Res.

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[1] The simultaneous measurements of zonal drift velocities, observed in the heights of 84-98 km in the Indian geomagnetic dip equatorial region by an medium frequency (MF, 1.98 MHz) spaced antenna and a high-frequency (HF, 18 MHz) Doppler radars, are compared on selected few days in the solar maximum years of 1998, 1999, and 2000. The agreement between the two radar measurements is found to be good below about 88 km, where the neutral turbulence induced ionospheric irregularities are more predominant. Above 90 km, however, the agreement becomes poor and at the highest height of 98 km it becomes the least. At this height, more often the HF Doppler radar shows a westward drift of about 200 m/s whereas the MF spaced antenna radar values lie within ±10 m/s and sometimes attain maximum values of ±50 m/s. Detailed discussions are made on the possible sources of underestimation of the drift velocities measured by the MF radar and the nature of scattering irregularities that are produced because of large neutral turbulences and plasma instabilities. It is suggested that these neutral and plasma turbulences (particularly type II plasma irregularities) contribute in a different manner to different radar frequencies and techniques and hence very different drift velocities in the heights of 90-100 km particularly in the geomagnetic dip equatorial region. Discussions are also made on (1) the real atmospheric and ionospheric physical process prevailing in the 90-100 km region and (2) the technical aspects of the radars that limits them to measure only particular types of motion in this region.Citation: Ramkumar, T. K., S. Gurubaran, R. Rajaram, D. Tiwari, and K. S. Viswanathan (2010), A comparison study of zonal drift velocities measurements as seen by MF spaced antenna and HF Doppler radar in the Indian dip equatorial mesospheric and lower thermospheric (80-100 km) region,

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Measurement of the velocity of waves in the ionosphere: A comparison of the ray theory approach and diffraction theory

Cited by 30 publications

References 6 publications

On the influence of specular reflections in MF radar wind measurements

On the influence of specular reflections in MF radar wind measurements

Nighttime Mid-Latitude Travelling Ionospheric Disturbances Associated with Mild Spread-F Conditions.

A comparison study of zonal drift velocities measurements as seen by MF spaced antenna and HF Doppler radar in the Indian dip equatorial mesospheric and lower thermospheric (80–100 km) region

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