scholarly journals A first comparison of irregularity and ion drift velocity measurements in the E-region

2006 ◽  
Vol 24 (9) ◽  
pp. 2375-2389 ◽  
Author(s):  
R. A. Makarevich ◽  
F. Honary ◽  
V. S. C. Howells ◽  
A. V. Koustov ◽  
S. E. Milan ◽  
...  
Keyword(s):  
Drift Velocity ◽  
Hf Radar ◽  
Electron Velocity ◽  
Velocity Measurements ◽  
Vhf Radar ◽  
Positive Correlation ◽  
Ion Drift ◽  
E Region ◽  
Ion Velocity ◽  
Large Flow

Abstract. E-region irregularity velocity measurements at large flow angles with the STARE Finland coherent VHF radar are considered in context of the ion and electron velocity data provided by the EISCAT tristatic radar system, CUTLASS Finland coherent HF radar, and IMAGE fluxgate magnetometers. The data have been collected during a special experiment on 27 March 2004 during which EISCAT was scanning between several E- and one F-region altitudes along the magnetic field line. Within the E-region, the EISCAT measurements at two altitudes of 110 and 115 km are considered while the electron velocity is inferred from the EISCAT ion velocity measurements at 278 km. The line-of-sight (l-o-s) VHF velocity measured by STARE VHF los is compared to the ion and electron velocity components (Vi0 comp and Ve0 comp) along the STARE l-o-s direction. The comparison with Ve0 comp for the entire event shows that the measurements exhibit large scatter and small positive correlation. The correlation with Ve0 comp was substantial in the first half of the interval under study when Ve0 comp was larger in magnitude. The comparison with Vi0 comp at 110 and 115 km shows a considerable positive correlation, with VHF velocity being typically larger (smaller) in magnitude than Vi0 comp at 110 km (115 km) so that VVHF los appears to be bounded by the ion velocity components at two altitudes. It is also demonstrated that the difference between VVHF los and Vi0 comp at 110 km can be treated, in the first approximation, as a linear function of the effective backscatter height heff also counted from 110 km; heff varies in the range 108–114 km due to the altitude integration effects in the scattering cross-section. Our results are consistent with the notion that VHF velocity at large flow angles is directly related to the ion drift velocity component at an altitude heff.

scholarly journals Simultaneous HF measurements of E- and F-region Doppler velocities at large flow angles

2004 ◽  
Vol 22 (4) ◽  
pp. 1177-1185 ◽  
Author(s):  
R. A. Makarevitch ◽  
F. Honary ◽  
A. V. Koustov
Keyword(s):  
Hf Radar ◽  
Doppler Velocity ◽  
Plasma Convection ◽  
Aspect Angle ◽  
F Region ◽  
Significant Difference ◽  
E Region ◽  
The Difference ◽  
New Feature ◽  
Large Flow

Abstract. Data collected by the CUTLASS Finland HF radar are used to illustrate the significant difference between the cosine component of the plasma convection in the F-region and the Doppler velocity of the E-region coherent echoes observed at large flow angles. We show that the E-region velocity is ~5 times smaller in magnitude and rotated by ~30° clockwise with respect to convection in the F-region. Also, measurements at flow angles larger than 90° exhibit a completely new feature: Doppler velocity increase with the expected aspect angle and spatial anticorrelation with the backscatter power. By considering DMSP drift-meter measurements we argue that the difference between F- and E-region velocities cannot be interpreted in terms of the convection change with latitude. The observed features in the velocity of the E-region echoes can be explained by taking into account the ion drift contribution to the irregularity phase velocity as predicted by the linear fluid theory. Key words. Ionosphere (auroral ionosphere; ionospheric irregularities; plasma convection)

scholarly journals Investigation of the relationship between optical auroral forms and HF radar E region backscatter

2000 ◽  
Vol 18 (6) ◽  
pp. 608-617 ◽  
Author(s):  
S. E. Milan ◽  
M. Lester ◽  
N. Sato ◽  
H. Takizawa ◽  
J.-P. Villain
Keyword(s):  
Spectral Characteristics ◽  
Hf Radar ◽  
Vhf Radar ◽  
The Past ◽  
Optical Signature ◽  
E Region ◽  
Coherent Backscatter ◽  
First Time ◽  
The Relationship ◽  
East West

Abstract. The SuperDARN HF radars have been employed in the past to investigate the spectral characteristics of coherent backscatter from L-shell aligned features in the auroral E region. The present study employs all-sky camera observations of the aurora from Husafell, Iceland, and the two SuperDARN radars located on Iceland, Þykkvibær and Stokkseyri, to determine the optical signature of such backscatter features. It is shown that, especially during quiet geomagnetic conditions, the backscatter region is closely associated with east-west aligned diffuse auroral features, and that the two move in tandem with each other. This association between optical and radar aurora has repercussions for the instability mechanisms responsible for generating the E region irregularities from which radars scatter. This is discussed and compared with previous studies investigating the relationship between optical and VHF radar aurora. In addition, although it is known that E region backscatter is commonly observed by SuperDARN radars, the present study demonstrates for the first time that multiple radars can observe the same feature to extend over at least 3 h of magnetic local time, allowing precipitation features to be mapped over large portions of the auroral zone.Key words: Ionosphere (particle precipitation; plasma waves and instabilities)

scholarly journals Alternating-code experiment for plasma-line studies

1996 ◽  
Vol 14 (12) ◽  
pp. 1473-1479
Author(s):  
P. Guio ◽  
N. Bjørnå ◽  
W. Kofman
Keyword(s):  
Correction Term ◽  
Good Alternative ◽  
Electron Velocity ◽  
Electron Velocity Distribution ◽  
Vhf Radar ◽  
Pulse Technique ◽  
F Region ◽  
Plasma Line ◽  
E Region ◽  
Long Pulse

Abstract. We present results of the first plasma-line measurement of the incoherent spectrum using the alternating-code technique with the EISCAT VHF radar. This technique, which has earlier mostly been used to measure high-resolution E-region ion-line spectra, turned out to be a very good alternative to other techniques for plasma-line measurements. The experiment provides simultaneous measurement of the ion line and downshifted and upshifted plasma-line spectra with an altitude resolution of 3 km and a temporal resolution of 10 s. The measurements are taken around the peak of the F region, but not necessarily at the peak itself, as is the case with the long-pulse technique. The condition for success is that the scale height should be large enough such that the backscattered signal from the range extent of one gate falls inside the receiver filter. The data are analysed and the results are combined with the results of the ion-line data analysis to estimate electron mean drift velocity and thereafter electric currents along the line of sight of the radar using both the standard dispersion relation assuming a Maxwellian electron velocity distribution and the more recent model including a heat-flow correction term.

An instrument for total ion drift velocity measurements aboard the ‘Intercosmos-Bulgaria-1300’ satellite

1982 ◽  
Vol 2 (7) ◽  
pp. 71-74 ◽  
Author(s):  
L.G. Bankov ◽  
M.N. Gousheva ◽  
B.B. Kirov ◽  
N.G. Bankov ◽  
Yu. Shulchishin ◽  
...  
Keyword(s):  
Drift Velocity ◽  
Velocity Measurements ◽  
Ion Drift

scholarly journals On the relationship between the velocity of E-region HF echoes and <i>E</i>x<i>B</i> plasma drift

2005 ◽  
Vol 23 (2) ◽  
pp. 371-378 ◽  
Author(s):  
A. V. Koustov ◽  
D. W. Danskin ◽  
R. A. Makarevitch ◽  
J. D. Gorin
Keyword(s):  
Phase Velocity ◽  
Hf Radar ◽  
Line Of Sight ◽  
Plasma Drift ◽  
F Region ◽  
Plasma Drifts ◽  
E Region ◽  
Cross Track ◽  
The Relationship ◽  
Large Flow

Abstract. In this study, velocities of E-region HF echoes observed by the Stokkseyri HF radar are compared with ExB plasma drifts in the F-region measured by the DMSP satellites. Events were selected for which the DMSP track projected to the height of 110km was almost perpendicular to the central beams of the radar, resulting in a direct comparison of the cross-track component of the ExB drift and the line-of-sight HF velocity. We found that the typical ratio of HF velocity to the DMSP drift is ~0.35 in a range of DMSP drifts of 0-1700m/s. It is suggested that E-region HF velocities, observed both along the electrojet and at large flow angles, are significantly affected by scatter from the bottom of the electrojet layer where the irregularity phase velocity is expected to be strongly depressed with respect to the ExB flow.

scholarly journals A classification of spectral populations observed in HF radar backscatter from the E region auroral electrojets

2001 ◽  
Vol 19 (2) ◽  
pp. 189-204 ◽  
Author(s):  
S. E. Milan ◽  
M. Lester
Keyword(s):  
Spectral Width ◽  
Hf Radar ◽  
Type I ◽  
Radar Backscatter ◽  
Vhf Radar ◽  
Flow Angle ◽  
E Region ◽  
Gradient Drift ◽  
Limiting Velocity

Abstract. Observations of HF radar backscatter from the auroral electrojet E region indicate the presence of five major spectral populations, as opposed to the two predominant spectral populations, types I and II, observed in the VHF regime. The Doppler shift, spectral width, backscatter power, and flow angle dependencies of these five populations are investigated and described. Two of these populations are identified with type I and type II spectral classes, and hence, are thought to be generated by the two-stream and gradient drift instabilities, respectively. The remaining three populations occur over a range of velocities which can greatly exceed the ion acoustic speed, the usual limiting velocity in VHF radar observations of the E region. The generation of these spectral populations is discussed in terms of electron density gradients in the electrojet region and recent non-linear theories of E region irregularity generation.Key words. Ionosphere (ionospheric irregularities)

scholarly journals Effects of solar eclipse on the electrodynamical processes of the equatorial ionosphere: a case study during 11 August 1999 dusk time total solar eclipse over India

2002 ◽  
Vol 20 (12) ◽  
pp. 1977-1985 ◽  
Author(s):  
R. Sridharan ◽  
C. V. Devasia ◽  
N. Jyoti ◽  
Diwakar Tiwari ◽  
K. S. Viswanathan ◽  
...  
Keyword(s):  
Electric Fields ◽  
Solar Eclipse ◽  
Equatorial Ionosphere ◽  
Hf Radar ◽  
F Region ◽  
Large Enhancement ◽  
Temporal Structures ◽  
E Region ◽  
Field Lines ◽  
Electric Fields And Currents

Abstract. The effects on the electrodynamics of the equatorial E- and F-regions of the ionosphere, due to the occurrence of the solar eclipse during sunset hours on 11 August 1999, were investigated in a unique observational campaign involving ground based ionosondes, VHF and HF radars from the equatorial location of Trivandrum (8.5° N; 77° E; dip lat. 0.5° N), India. The study revealed the nature of changes brought about by the eclipse in the evening time E- and F-regions in terms of (i) the sudden intensification of a weak blanketing ES-layer and the associated large enhancement of the VHF backscattered returns, (ii) significant increase in h' F immediately following the eclipse and (iii) distinctly different spatial and temporal structures in the spread-F irregularity drift velocities as observed by the HF radar. The significantly large enhancement of the backscattered returns from the E-region coincident with the onset of the eclipse is attributed to the generation of steep electron density gradients associated with the blanketing ES , possibly triggered by the eclipse phenomena. The increase in F-region base height immediately after the eclipse is explained as due to the reduction in the conductivity of the conjugate E-region in the path of totality connected to the F-region over the equator along the magnetic field lines, and this, with the peculiar local and regional conditions, seems to have reduced the E-region loading of the F-region dynamo, resulting in a larger post sunset F-region height (h' F) rise. These aspects of E-and F-region behaviour on the eclipse day are discussed in relation to those observed on the control day.Key words. Ionosphere (electric fields and currents; equatorial ionosphere; ionospheric irregularities)

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