The mean fractional electron density fluctuation amplitude derived from auroral backscatter data

Oksman, J.; Uspensky, M. V.; Starkov, G. V.; Stepanov, G. S.; Vallinkoski, M.

doi:10.1016/0021-9169(86)90075-9

Cited by 25 publications

(27 citation statements)

References 18 publications

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“…A similar correlation of echo power and effective density was described in paper 1 for the morning case. The correlation is not a surprise; it is expected for very fast plasma flows (Oksman et al, 1986;Nielsen et al, 1988) which certainly was the case.…”

Section: February 1999 Eventmentioning

confidence: 72%

STARE velocities: 2. Evening westward electron flow

et al. 2004

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Abstract. Four evening events and one morning event of joint EISCAT/STARE observations during ∼22 h are considered and the differences between observed STARE line-ofsight (l-o-s) velocities and EISCAT electron drift velocities projected onto the STARE beams are studied. We demonstrate that the double-pulse technique, which is currently in use in the STARE routine data handling, typically underestimates the true phase velocity as inferred from the multi-pulse STARE data. We show that the STARE velocities are persistently smaller (1.5-2 times) than the EISCAT velocities, even for the multi-pulse data. The effect seems to be more pronounced in the evening sector when the Finland radar observes at large flow angles. We evaluate the performance of the ion-acoustic approach (IAA, Nielsen and Schlegel, 1985) and the off-orthogonal fluid approach (OOFA, Uspensky et al., 2003) techniques to predict the true electron drift velocity for the base event of 12 February 1999. The IAA technique predicts the convection reasonably well for enhanced flows of >∼1000 m/s, but not so well for slower ones. By considering the EISCAT N (h) profiles, we derive the effective aspect angle and effective altitude of backscatter, and use this information for application of the OOFA technique. We demonstrate that the OOFA predictions for the base event are superior over the IAA predictions and thus, we confirm that OOFA predicts the electron velocities reasonably well in the evening sector, in addition to the morning sector, as concluded by Uspensky et al. (2003). To check how "robust" the OOFA model is and how successful it is for convection estimates without the EISCAT support, we analysed three additional evening events and one additional morning event for which information on N (h) profiles was intentionally ignored. By accepting the mean STARE/EISCAT velocity ratio of 0.55 and the mean azimuth rotation of 9 • (derived for the basic event), we show that the OOFA performs reasonably well for these additional events.

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Section: February 1999 Eventmentioning

confidence: 72%

STARE velocities: 2. Evening westward electron flow

et al. 2004

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“…Williams et al (1999). It can be clearly seen under the condition of strong plasma flow (Oksman et al, 1986;Nielsen et al, 1988), which is the case for the considered event.…”

Section: Event Overviewmentioning

confidence: 88%

“…In these formulas P (h) ∝ (δN/N) 2 (N(h)/N max ) 2 exp −a 2 tan 2 ψ(h) is the relative backscatter power (or the relative volume cross section) at a specific height, where the (Oksman et al, 1986), which, for simplicity, is assumed to be height independent (as in the measurements, for example, by Pfaff et al, 1984). Power also depends on the E-layer electron density N (h).…”

Section: Oofa Modellingmentioning

confidence: 99%

STARE velocities: the importance of off-orthogonality and ion motions

et al. 2003

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Abstract. A 3.5-h morning event of joint EISCAT/STARE observations is considered and the differences between the observed STARE velocities and the electron drift components (EISCAT) are studied. We find that the STAREFinland radar velocity was larger than the EISCAT convection component for a prolonged period of time. In addition, a moderate 5-20 • offset between the EISCAT convection azimuth and the corresponding STARE estimate was observed. We show that both the STARE-Finland radar velocity "overspeed" and the offset in the azimuth can be explained by fluid plasma theory, if the ion drift contribution to the irregularity phase velocity is taken into account under the condition of a moderate backscatter off-orthogonality. We call such an explanation the off-orthogonal fluid approach (OOFA).In general terms, we found that the azimuth of the maximum irregularity phase velocity V ph is not collinear with the V E×B electron flow direction, but differs by 5-15 • . Such an azimuth offset is the key factor, not only for the explanation of the Finland velocity overspeed, but also for the revisions of the velocity cosine rule, traditionally accepted in the STARE method at large flow angles. We argue that such a rule is only a rough approximation. The application of the OOFA to the STARE l-o-s velocities gives a reasonable agreement with the EISCAT convection data, implying that ion motions and the non-orthogonality of backscatter are important to consider for VHF auroral echoes. The data set discussed had the STARE velocity magnitudes, which were 1.5-2 times smaller than the electron V E×B velocities, as was found earlier by Nielsen and Schlegel (1983).

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“…This model assumes that echoes are received from a range of electrojet heights and that the power of the signal from each height is determined by the local electron density, the true aspect angle (with the refraction taken into account), and the amplitude of the ionospheric irregularities (Oksman et al, 1986;Kustov et al, 1990;Williams et al, 1999). For strong electric fields of more than 30-40 mVm −1 , it is assumed that the irregularity amplitude is electric-field-independent, so that irregularity amplitude flow and aspect angle variations need only to be taken into account.…”

Section: Discussionmentioning

confidence: 99%

CUTLASS HF radar observations of high-velocity E-region echoes

et al. 2001

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Abstract.A short event of high-velocity E-region echo observations by the Pykkvibaer HF radar is analysed to study echo parameters and the echo relation to the Farley-Buneman plasma instability. The echoes were detected in several beams aligned closely to the magnetic L-shell direction. Two echo groups were identified: one group corresponded to the classical type 1 echoes with velocities close to the nominal ionacoustic speed of 400 ms −1 , while the other group had significantly larger velocities, of the order of 700 ms −1 . The mutual relationship between the echo power, Doppler velocity, spectral width and elevation angles for these two groups was studied. Plotting of echo parameters versus slant range showed that all ∼700 ms −1 echoes originated from larger heights and distances of 500-700 km, while all ∼400 ms −1 echoes came from lower heights and from farther distances; 700-1000 km. We argue that both observed groups of echoes occurred due to the Farley-Buneman plasma instability excited by strong (∼70 mVm −1 ) and uniformly distributed electric fields. We show that the echo velocities for the two groups were different because the echoes were received from different heights. Such a separation of echo heights occurred due to the differing amounts of ionospheric refraction at short and large ranges. Thus, the ionospheric refraction and related altitude modulation of ionospheric parameters are the most important factors to consider, when various characteristics of E-region decametre irregularities are derived from HF radar measurements.

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The mean fractional electron density fluctuation amplitude derived from auroral backscatter data

Cited by 25 publications

References 18 publications

STARE velocities: 2. Evening westward electron flow

STARE velocities: 2. Evening westward electron flow

STARE velocities: the importance of off-orthogonality and ion motions

CUTLASS HF radar observations of high-velocity E-region echoes

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