Nearly simultaneous measurements of radar auroral heights and doppler velocities at 398 MHz

Moorcroft, D. R.; Ruohoniemi, J. M.

doi:10.1029/ja092ia04p03333

Cited by 12 publications

(8 citation statements)

References 30 publications

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“…However, what evidence we have indicates peak densities of around 1 or 2 x 10 n el/m 3 (see, for example, Figure 1). All these values are fairly typical of coherent backscatter periods, and in particular they correspond quite well with values pertaining to the periods used in previous extensive studies of echo height using the Homer radar [Ruohoniemi and Moorcroft, 1985;Moorcroft and Ruohoniemi, 1987]. Almost all of those periods corresponded to Kp values between 2+ and 4.…”

Section: Discussionsupporting

confidence: 82%

“…Almost all of those periods corresponded to Kp values between 2+ and 4. Only one fact suggests that there might be anything special about this period; Moorcroft and Ruohoniemi [1987] found the lowest heights to occur for observations at magnetic local times between 0400 and 0600, not very different from the magnetic local times of the present experiment. However, those Homer periods also corresponded to Kp values of 5-and 6-, and it appears most likely that the unusually low heights of Moorcroft and Ruohoniemi were associated with the increased level of disturbance rather than with the magnetic local time.…”

Section: Discussioncontrasting

confidence: 76%

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Height and aspect sensitivity of large aspect angle coherent backscatter at 933 MHz

Moorcroft¹,

Schlegel²

1990

J. Geophys. Res.

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During a special experiment in May 1988, coherent echoes were obtained with the UHF EISCAT radar system while the Tromsö antenna was directed to the north at elevation angles between 10° and 13°, with corresponding magnetic aspect angles between 5.8° and 7.6°. The echoes were found to be consistent with scattering from a layer having approximately a Gaussian height profile centered on about 103 km and with an average thickness of about 6 km. This height is considerably lower than most other reports of auroral backscatter height, and the thickness is also smaller than most other reported values. These unusually low heights were confirmed with observations at the remote sites Kiruna and Sodankyla. The heights seem to be independent of aspect angle over the range of aspect angles observed. By modeling the scattering layer and comparing echo intensities at Tromsö and the remote sites, estimates of aspect sensitivity of about 6 dB/deg were obtained, with an indication that the aspect sensitivity decreases with increasing aspect angle.

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Section: Discussionsupporting

confidence: 82%

Section: Discussioncontrasting

confidence: 76%

Height and aspect sensitivity of large aspect angle coherent backscatter at 933 MHz

Moorcroft¹,

Schlegel²

1990

J. Geophys. Res.

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“…Finally, in Figure 6 we show how a double peak in the apparent backscatter height profile can arise, as has been occasionally reported in the literature [e.g., Unwin and Johnston, 1981;Moorcroft and Ruohoniemi, 1987]. At about 2052:40 UT one structure is just about to leave the beam when a second one has already entered it.…”

Section: High Range Resolution Resultssupporting

confidence: 67%

“…Ruohoniemi and Moorcroft [1985] have also reported observations with the 398-MHz Homer, Alaska, radar which yielded an average height of about 104 km. However, this was for a single postmidnight period; most periods observed with the Homer radar have significantly higher average heights [Moorcroft and Ruohoniemi, 1987]. It is likely that the large aspect angle of these observations is responsible in some way for these very low heights, but the exact mechanism is unknown.…”

Section: Discussionmentioning

confidence: 92%

Auroral radar measurements at 16‐cm wavelength with high range and time resolution

Schlegel

Turunen²,

Moorcroft³

1990

J. Geophys. Res.

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Auroral radar measurements performed with the EISCAT facility are presented. Backscatter cross sections of the irregularities produced by the two‐stream (Farley‐Buneman) or gradient drift plasma instabilities have been recorded with a range separation of 1.5 km, corresponding to a spacing of successive values in height of about 0.4 km. The apparent height profiles of the backscatter have a width of about 5–6 km and occur between 95 and 112 km altitude, with a mean at 104 km. Very often, fast motions of the backscatter layers are observed which can be explained as fast moving ionospheric structures controlled by magnetospheric convection. The maximal time resolution of the measurements is 12.5 ms. The statistics of the backscatter amplitudes at this time resolution is close to a Rice distribution with a Rice parameter a ≈ 3.7. The observed backscatter spectra do not change significantly in shape when the integration time is reduced from 5 s to 100 ms.

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“…So far, there is limited experimental verification of the F‐B instability kinetic effects at short wavelengths [ Leadabrand et al , 1965; Balsley and Farley , 1971; Moorcroft and Ruohoniemi , 1987; Schlegel et al , 1990]. The present paper provides rare observational evidence showing the existence of such effects in meter‐scale type 1 irregularities, which is in line with kinetic theory predictions.…”

Section: Introductionsupporting

confidence: 87%

Radar observation of kinetic effects at meter scales for Farley‐Buneman plasma waves

et al. 2002

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[1] Coherent backscatter Doppler measurements, made simultaneously at 144 MHz and 50 MHz from a common volume in the midlatitude E region ionosphere, were analyzed in order to study the phase velocity ratio of type 1 plasma irregularities at 1 m and 3 m wavelengths. In the analysis, high-resolution Doppler spectrograms were used first to identify the type 1 events and then to estimate the mean and spectral peak velocities from averaged power Doppler spectra. The simultaneous spectrogram signatures of type 1 echoes suggested a somewhat higher threshold for instability excitation at 144 MHz than at 50 MHz. Statistically, the measured 144 MHz to 50 MHz velocity ratios attain values above unity, mostly in the range from 1.05 to 1.14 with an overall average of 1.10. This 10% difference in the type 1 velocities at 144 MHz and 50 MHz was attributed to kinetic effects at short plasma wavelengths. For comparison, a linear kinetic model of the FarleyBuneman instability, which includes also a destabilizing plasma density gradient, was used to provide numerical estimates of type 1 phase velocities. It was found that the theoretical predictions for gradient-free Farley-Buneman waves agreed well with the observations, under the suppositions that the strongest type 1 echoes come from E region altitudes where conditions for instability are optimal and that type 1 waves have their phase velocities limited at threshold values equal to the plasma ion acoustic speed. The present study has confirmed the accuracy of the kinetic theory of the Farley-Buneman instability, which strengthens its validity and suitability for meter-scale E region irregularity studies.

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Nearly simultaneous measurements of radar auroral heights and doppler velocities at 398 MHz

Cited by 12 publications

References 30 publications

Height and aspect sensitivity of large aspect angle coherent backscatter at 933 MHz

Height and aspect sensitivity of large aspect angle coherent backscatter at 933 MHz

Auroral radar measurements at 16‐cm wavelength with high range and time resolution

Radar observation of kinetic effects at meter scales for Farley‐Buneman plasma waves

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