The relationship between <i>E</i> region electron density and the power of auroral coherent echoes at 45 MHz

Williams, P. J. S.; Kustov, A. V.; Uspensky, M. V.

doi:10.1029/1998rs900039

Cited by 6 publications

(14 citation statements)

References 25 publications

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“…Such a correlation in the electron density and SNR is well known, e.g. 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: 69%

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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Section: Event Overviewmentioning

confidence: 69%

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

et al. 2003

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“…According to the EISCAT measurements, the density profiles most of the time exhibited a broad maximum near 110-120 km. One notices the correlation between the STARE echo power increases (for both radars) and the electron density enhancements, a well-known effect at VHF (Starkov et Williams et al, 1999). Figure 4b shows the electron drift (opposite to plasma convection) magnitude and direction (solid line), as observed by EISCAT (the data were smoothed with a 5-point sliding window).…”

Section: Event Overviewmentioning

confidence: 69%

Velocities of auroral coherent echoes at 12 and 144 MHz

et al. 2002

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Abstract. Two Doppler coherent radar systems are currently working at Hankasalmi, Finland, the STARE and CUTLASS radars operating at ∼ 144 MHz and ∼ 12 MHz, respectively. The STARE beam 3 is nearly co-located with the CUTLASS beam 5, providing an opportunity for echo velocity comparison along the same direction but at significantly different radar frequencies. In this study we consider an event when STARE radar echoes are detected at the same ranges as CUT-LASS radar echoes. The observations are complemented by EISCAT measurements of the ionospheric electric field and electron density behaviour at one range of 900 km. Two separate situations are studied; for the first one, CUTLASS observed F-region echoes (including the range of the EIS-CAT measurements), while for the second one CUTLASS observed E-region echoes. In both cases STARE E-region measurements were available. We show that F-region CUT-LASS velocities agree well with the convection component along the CUTLASS radar beam, while STARE velocities are typically smaller by a factor of 2-3. For the second case, STARE velocities are found to be either smaller or larger than CUTLASS velocities, depending on the range. Plasma physics of E-and F-region irregularities is discussed in attempt to explain the inferred relationship between various velocities. Special attention is paid to ionospheric refraction that is important for the detection of 12-MHz echoes.

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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 relationship between E region electron density and the power of auroral coherent echoes at 45 MHz

Abstract: Abstract. Data taken during joint observations of the European incoherent scatter (EISCAT

Cited by 6 publications

References 25 publications

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

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

Velocities of auroral coherent echoes at 12 and 144 MHz

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

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