A comparison of radar auroral reflection data with acoustic wave theory

Leadabrand, R. L.

doi:10.6028/jres.069d.104

Cited by 8 publications

(10 citation statements)

References 9 publications

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“…Third, the position of the type 1 peak is independent of 0, whereas both components of diffuse spectra have 0-dependent mean Doppler shifts. Again, past spectral observations at frequencies below 500 MHz support our results [e.g., Leadabrand et al, 1965;Chesnut et al, 1968].…”

Section: Balsley'i[1969] Has Also Presented Evidence Indicating That supporting

confidence: 92%

“…In particular, Anchorage diffuse, spectra generally have mean Doppler shifts of less than one fifth the 3-m ion acoustic frequ, ency. Conversely, our review of past spectral observations has also indicated that diffuse spectra can have Doppler shifts that are well above the expected ion acoustic frequency [Blevis et al, 1963;Leadabrand, 1965;Ecklund et al, 1973]. Third, the position of the type 1 peak is independent of 0, whereas both components of diffuse spectra have 0-dependent mean Doppler shifts.…”

Section: Balsley'i[1969] Has Also Presented Evidence Indicating That mentioning

confidence: 84%

Section: Previous Spectral Studies Of Diffuse Radar Auroramentioning

confidence: 99%

“…The post-two-stream spectral measurements using pulsed radars were made by Leadabrand [1965 [1973,1974]. Leadabrand [1965], using 400-and 800-MHz radars located at Fraserburgh, Scotland, observed predominantly diffuse radar aurora. He found that the mean Doppler shift of the spectrum was dependent on the azimuth of the radar antenna, and he observed Doppler velocities as large as 900 m/s.…”

Section: Previous Spectral Studies Of Diffuse Radar Auroramentioning

confidence: 99%

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Diffuse radar aurora: Spectral observations of non-two-stream irregularities

Greenwald¹,

Ecklund²,

Balsley³

1975

J. Geophys. Res.

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Since the two‐stream instability was identified as the source of one type of electron density irregularity that is found in the equatorial electrojet, a number of people have suggested that this instability is also responsible for diffuse radar aurora. Consequently, there have been a number of attempts to observe two‐streamlike spectra in diffuse radar auroral backscatter. To date, these attempts have produced mixed results. In this paper we review these past spectral studies and present some recent spectral observations of 3‐m irregularities (50‐MHz radar) that were made from Anchorage and Aniak, Alaska. Our observations indicate the presence of two distinct spectral components, both of which have a number of non‐two‐stream characteristics. Namely, they have an azimuth‐dependent mean Doppler shift that approaches zero when the radar is directed perpendicular to the electrojet current. The broader spectral component, which we observe, has a typical width of 400 Hz, whereas the narrow component has a width of less than 150 Hz. The narrow component often displays a double‐peaked structure with a peak separation of 30–60 Hz. Since these spectral observations were made at angles within 30° of perpendicular to the electrojet current vector and since primary two‐stream or gradient drift irregularities are preferentially excited in the direction of the electron current vector, we conclude that our observations are of secondary irregularities generated from the primary irregularities and that these irregularities are more likely due, directly, to the gradient drift instability than to the two‐stream instability. Recent theoretical studies of small‐scale irregularity generation in the diffuse radar aurora support this contention.

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Section: Balsley'i[1969] Has Also Presented Evidence Indicating That supporting

confidence: 92%

Section: Balsley'i[1969] Has Also Presented Evidence Indicating That mentioning

confidence: 84%

Section: Previous Spectral Studies Of Diffuse Radar Auroramentioning

confidence: 99%

Section: Previous Spectral Studies Of Diffuse Radar Auroramentioning

confidence: 99%

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Diffuse radar aurora: Spectral observations of non-two-stream irregularities

Greenwald¹,

Ecklund²,

Balsley³

1975

J. Geophys. Res.

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“…Of these, the twostream instability proposed by Buneman [1963] and Farley [1963] is generally thought to be most capable of explaining ,the diffuse radar aurora [Leadabrand, 1961;Unwin and Knox, 1968]. Despi.te the relative success of this theory in accounting for a number of auroral echo characteristics [Leadabrand, 1965;Moorcroft, 1966;Unwin and Knox, 1968], there remain a number of significant discrepancies between theory and observations. These are the following: (1) auroral echoes are often observed near perpendicular to the current flow [Ecklund and Gadsden, 1967;Tsunoda et al, 1974], (2) the associated Doppler power spectrum is more often 'broad' than 'narrow' [Hofstee and Forsyth, 1969;Greenwald et al, 1975], (3) the associated Doppler velocity is often much smaller than the ion thermal speed, and (4) auroral echoes are often observed at excessively large magnetic aspect angles [Chesnut et al, 1968;Hofstee and Forsyth, 1972].…”

Section: Introductionmentioning

confidence: 99%

on a crossed field two-stream plasma instability in the auroral plasma

Wang¹,

Tsunoda²

1975

J. Geophys. Res.

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This paper presents a detailed analysis of the Buneman‐Farley two‐stream plasma instability. We use a fluid plasma model appropriate for the E region ionosphere, including the effects of the geomagnetic field and electron and ion temperatures and their collisions with neutrals. We derive a linearized dispersion equation for the coupled electron thermal wave and ion thermal wave. The results are compared with those derived from a kinetic theory. It is shown that in the long‐wavelength limit the agreement between the above described fluid theory and kinetic theory is exact. The physical arguments for the agreement are clearly stated. From the dispersion equation we obtain closed form expressions for the phase velocities, frequencies, and growth rates describing the threshold condition and the unstable region. With these closed form results we are able to determine the physical behavior of the instability under a variety of ionospheric conditions. The closed form results show that unstable plasma waves having the maximum growth rate propagate at finite off‐perpendicular angles with respect to the geomagnetic field. This property, together with the fact that the two‐stream instability is a convective instability, is used to infer that radar auroral echoes scattered from these waves should occur at finite off‐perpendicular angles. Spatial maps of radar auroral echoes obtained with a 1210‐MHz backscatter radar at Homer, Alaska, are presented as supporting evidence. By taking data during different magnetic conditions, we were able to exclude magnetic field line distortion as a possible contributing factor.

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U.S.A. National Committee Report, Fifteenth URSI General Assembly, Munich, September 1966: Commission 3, Ionospheric Radio; Progress in Ionospheric Radio

Bowhill¹,

Bibl²,

Calvert³

et al. 1966

Radio Science

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Auroral absorption measured in the auroral zone with riometers is on the average more pronounced in the winter months for both hemispheres. Also, in winter it has a pronounced diurnal variation with a maximum a few hours before noon. The average absorption in winter is twice that in summer, but sunlight has no influence in its value [Leinbach and Basler, 1963; Basler, 1963]. Individual events at night are characterized by a quiet phase of relatively small absorption, a sharp increase of absorption associated with the breakup phase of the visible aurora, and a fast recovery with irregular fluctuation of absorption. Detailed correlation of areas of absorption and luminosity exists for such events [Ansari, 1964]. The structure is less than 200 km in the north‐south direction and 700 km in the east‐west direction [Parthasarathy and Berkey, 1965]. An event seen only after midnight consists of a relatively slow increase and recovery of extremely high absorption with no de~ailed correlation of light emission and absorption. It is associated with a harder electron spectrum [Ansari, 1964]. A peculiar type of absorption event frequently observed during midmorning usually increases very smoothly, reaches a high value of absorption, and is not accompanied by appreciable magnetic activity [Ansari, 1965]. Absorption associated either with negative bays or with breakup events shows no difference in intensity between day and night [Brown and Barcus, 1963; Brown, 1964]. There is a limited correlation between the high‐energy part of the electron spectrum, as measured by X‐rays in balloons, and the absorption [Barcus, 1965].

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A comparison of radar auroral reflection data with acoustic wave theory

Cited by 8 publications

References 9 publications

Diffuse radar aurora: Spectral observations of non-two-stream irregularities

Diffuse radar aurora: Spectral observations of non-two-stream irregularities

on a crossed field two-stream plasma instability in the auroral plasma

U.S.A. National Committee Report, Fifteenth URSI General Assembly, Munich, September 1966: Commission 3, Ionospheric Radio; Progress in Ionospheric Radio

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