scholarly journals Observing electric field and neutral wind with EISCAT 3D

2021 ◽  
Vol 39 (6) ◽  
pp. 961-974
Author(s):  
Johann Stamm ◽  
Juha Vierinen ◽  
Björn Gustavsson
Keyword(s):  
Electric Field ◽  
Three Dimensional ◽  
Momentum Equation ◽  
Neutral Wind ◽  
Worst Case ◽  
Ion Drift ◽  
F Region ◽  
Energy Flows ◽  
E Region ◽  
Radar Measurements

Abstract. Measurements of height-dependent electric field (E) and neutral wind (u) are important governing parameters of the Earth's upper atmosphere, which can be used to study, for example, how auroral currents close or how energy flows between the ionized and neutral constituents. The new EISCAT 3D (E3D) incoherent scatter radar will be able to measure a three-dimensional ion velocity vector (v) at each measurement point, which will allow less stringent prior assumptions about E and u to be made when estimating them from radar measurements. This study investigates the feasibility of estimating the three-dimensional electric field and neutral wind vectors along a magnetic field-aligned profile from E3D measurements, using the ion momentum equation and Maxwell's equations. The uncertainty of ion drift measurements is estimated for a time and height resolution of 5 s and 2 km. With the most favourable ionospheric conditions, the ion wind at E region peak can be measured with an accuracy of less than 1 m/s. In the worst case, during a geomagnetically quiet night, the uncertainty increases by a factor of around 10. The uncertainty of neutral wind and electric field estimates is found to be strongly dependent on the prior constraints imposed on them. In the lower E region, neutral wind estimates have a lower standard deviation than 10 m/s in the most favourable conditions. In such conditions, also the F region electric field can be estimated with uncertainty of about 1 mV/m. Simulated measurements of v are used to demonstrate the ability to resolve the field-aligned profile of E and u. However, they can only be determined well at the heights where they dominate the ion drift, that is above 125 km for E and below 115 km for u. At the other heights, the results are strongly dependent on the prior assumptions of smoothness.

scholarly journals Observing electric field and neutral wind with EISCAT 3D

2021 ◽  
Author(s):  
Johann Stamm ◽  
Juha Vierinen ◽  
Björn Gustavsson
Keyword(s):  
Electric Field ◽  
Three Dimensional ◽  
Momentum Equation ◽  
Neutral Wind ◽  
Worst Case ◽  
Ion Drift ◽  
F Region ◽  
Energy Flows ◽  
E Region ◽  
Radar Measurements

Abstract. Measurements of height dependent electric field (E) and neutral wind (u) are important governing parameters of the Earth's upper atmosphere, which can be used to study e.g., how auroral currents close, or how energy flows between the ionized and neutral constituents. The new EISCAT 3D (E3D) incoherent scatter radar will be able to measure a three-dimensional ion velocity vector (v) at each measurement point, which will allow less stringent prior assumptions about E and u to be made when estimating them from radar measurements. This study investigates the feasibility of estimating the three-dimensional electric field and neutral wind vectors along a magnetic field-aligned altitude profile from E3D measurements, using the ion momentum equation and Maxwell's equations. The uncertainty of ion drift measurements is estimated for a time and height resolution of 5 s and 2 km. With the most favourable ionospheric conditions, the ion wind at E region peak can be measured with an accuracy of less than 1 m/s. In the worst case, during a geomagnetically quiet night, the uncertainty increases by a factor of around ten. The uncertainty of neutral wind and electric field estimates is found to be strongly dependent on the prior constraints imposed on them. In the lower E region, neutral wind estimates have a lower standard deviation than 10 m/s in the most favourable conditions. In such conditions, also the F region electric field can be estimated with uncertainty of about 1 mV/m. Simulated measurements of v are used to demonstrate the ability to resolve the field-aligned profile of E and u. However, they can only be determined well at the heights where they significantly influence the ion drift, that is above 125 km for E and below 115 km for u. At the other heights, the results are strongly dependent on the the prior assumptions of smoothness.

scholarly journals Characteristics of very large aspect angle E-region coherent echoes at 933 MHz

1997 ◽  
Vol 15 (1) ◽  
pp. 54-62 ◽  
Author(s):  
B. J. Jackel ◽  
D. R. Moorcroft ◽  
K. Schlegel
Keyword(s):  
Phase Velocity ◽  
Scattering Layer ◽  
Aspect Angle ◽  
Ion Drift ◽  
Phase Velocities ◽  
F Region ◽  
E Region ◽  
Inversion Techniques ◽  
Coherent Backscatter ◽  
Uhf Radar

Abstract. The EISCAT UHF radar system was used to study the characteristics of E-region coherent backscatter at very large magnetic aspect angles (5–11°). Data taken using 60 μs pulses during elevation scans through horizontally uniform backscatter permitted the use of inversion techniques to determine height profiles of the scattering layer. The layer was always singly peaked, with a mean height of 104 km, and mean thickness (full width at half maximum) of 10 km, both independent of aspect angle. Aspect sensitivities were also estimated, with the Sodankylä-Tromsø link observing 5 dB/degree at aspect angles near 5°, decreasing to 3 dB/degree at 10° aspect angle. Observed coherent phase velocities from all three stations were found to be roughly consistent with LOS measurements of a common E-region phase velocity vector. The E-region phase velocity had the same orientation as the F-region ion drift velocity, but was approximately 50% smaller in magnitude. Spectra were narrow with skewness of about +1 (for negative velocities), increasing slightly with aspect angle.

scholarly journals Equatorial night-time F-region zonal electric fields

1995 ◽  
Vol 13 (8) ◽  
pp. 871-878 ◽  
Author(s):  
S. S. Hari ◽  
B. V. Krishna Murthy
Keyword(s):  
Seasonal Variation ◽  
Electric Field ◽  
Electric Fields ◽  
Night Time ◽  
Equatorial Station ◽  
F Region ◽  
Vertical Drift ◽  
Longitudinal Gradients ◽  
Cycle Maximum ◽  
E Region

Abstract. Night-time F-region vertical electrodynamic drifts at the magnetic equatorial station, Trivandrum are obtained for a period of 2 years, 1989 and 1990 (corresponding to solar cycle maximum epoch), using ionosonde h'F data. The seasonal variation of the vertical drift is found to be associated with the longitudinal gradients of the thermospheric zonal wind. Further, the seasonal variation of the prereversal enhancement of the vertical drift is associated with the time difference between the sunset times of the conjugate E-regions (magnetic field line linked to F-region) which is indicative of the longitudinal gradients of the conductivity (of the E-region). The vertical drifts and the causative zonal electric fields at Trivandrum are compared with those at Jicamarca and F-region zonal electric field models. It is seen that the night-time downward drift (as also the causative westward electric field) at Jicamarca is greater than that at Trivandrum. The prereversal enhancement of the drift is greater at Jicamarca than at Trivandrum during the summer and the equinoxes, whereas during the winter the opposite is the case.

scholarly journals Imaging and EISCAT radar measurements of an auroral prebreakup event

1996 ◽  
Vol 14 (11) ◽  
pp. 1170-1176
Author(s):  
V. Safargaleev ◽  
T. Turunen ◽  
W. Lyatsky ◽  
J. Manninen ◽  
A. Kozlovsky
Keyword(s):  
Electric Field ◽  
Ion Temperature ◽  
Auroral Breakup ◽  
E Region ◽  
Radar Measurements ◽  
Eiscat Radar ◽  
Extended Area ◽  
Auroral Arcs ◽  
Plasma Depletion

Abstract. The results of coordinated EISCAT and TV-camera observations of a prebreakup event on 15 November 1993 have been considered. The variations of the luminosity of two parallel auroral arcs, plasma depletion on the poleward edge of one of these arcs as well as electron and ion temperatures in front of a westward travelling surge were studied. It was found that a short-lived brightening of a weak zenith arc before an auroral breakup was accompanied by fading of an equatorial arc and, vice versa. A plasma depletion in the E region was detected by the EISCAT radar on the poleward edge of the zenith arc just before the auroral breakup. The plasma depletion was associated with an enhancement of ion (at the altitudes of 150–200 km) and electron (in E region) temperatures. During its occurrence, the electric field in the E-region was extremely large (~150 mV/m). A significant increase in ion temperature was also observed 1 min before the arrival of a westward travelling surge (WTS) at the radar zenith. This was interpreted as the existence of an extended area of enhanced electric field ahead of the WTS.

scholarly journals On the usefulness of <i>E</i> region electron temperatures and lower <i>F</i> region ion temperatures for the extraction of thermospheric parameters: a case study

1999 ◽  
Vol 17 (9) ◽  
pp. 1182-1198 ◽  
Author(s):  
J.-P. St.-Maurice ◽  
C. Cussenot ◽  
W. Kofman
Keyword(s):  
Electric Field ◽  
Electron Temperature ◽  
Plasma Temperature ◽  
Ion Temperature ◽  
Heating Rates ◽  
Neutral Winds ◽  
F Region ◽  
E Region ◽  
Effective Electric Field ◽  
Temperature Observations

Abstract. Using EISCAT data, we have studied the behavior of the E region electron temperature and of the lower F region ion temperature during a period that was particularly active geomagnetically. We have found that the E region electron temperatures responded quite predictably to the effective electric field. For this reason, the E region electron temperature correlated well with the lower F region ion temperature. However, there were several instances during the period under study when the magnitude of the E region electron temperature response was much larger than expected from the ion temperature observations at higher altitudes. We discovered that these instances were related to very strong neutral winds in the 110-175 km altitude region. In one instance that was scrutinized in detail using E region ion drift measurement in conjunction with the temperature observations, we uncovered that, as suspected, the wind was moving in a direction closely matching that of the ions, strongly suggesting that ion drag was at work. In this particular instance the wind reached a magnitude of the order of 350 m/s at 115 km and of at least 750 m/s at 160 km altitude. Curiously enough, there was no indication of strong upper F region neutral winds at the time; this might have been because the event was uncovered around noon, at a time when, in the F region, the E×B drift was strongly westward but the pressure gradients strongly northward in the F region. Our study indicates that both the lower F region ion temperatures and the E region electron temperatures can be used to extract useful geophysical parameters such as the neutral density (through a determination of ion-neutral collision frequencies) and Joule heating rates (through the direct connection that we have confirmed exists between temperatures and the effective electric field).Key words. Ionosphere (auroral ionosphere; ionosphere atmosphere interactions; plasma temperature and density)

Vertical neutral wind in the equatorial F-region deduced from electric field and ion density measurements

1995 ◽  
Vol 57 (6) ◽  
pp. 645-651 ◽  
Author(s):  
Harri Laakso ◽  
Thomas L. Aggson ◽  
F.A. Herrero ◽  
Robert F. Pfaff ◽  
William B. Hanson
Keyword(s):  
Electric Field ◽  
Neutral Wind ◽  
Ion Density ◽  
Density Measurements ◽  
F Region

scholarly journals Deriving the normalised ion-neutral collision frequency from EISCAT observations

1997 ◽  
Vol 15 (12) ◽  
pp. 1557-1569 ◽  
Author(s):  
J. A. Davies ◽  
M. Lester ◽  
T. R. Robinson
Keyword(s):  
Electric Field ◽  
Collision Frequency ◽  
Neutral Atmosphere ◽  
Ion Temperature ◽  
Neutral Winds ◽  
Velocity Magnitude ◽  
F Region ◽  
E Region ◽  
Ion Velocity ◽  
The Difference

Abstract. Common programme observations by the EISCAT UHF radar revealed an extended interval, post geomagnetic local noon on 03 April 1992, during which the F-region ion velocity orthogonal to the geomagnetic field was significantly enhanced, to values exceeding 2 km s–1 corresponding to a perpendicular electric field of some 100 mV m–1. Observations from this interval are used to illustrate a method by which estimates of the E-region ion-neutral collision frequency may be derived in the presence of enhanced electric field. From both the rotation of the ion velocity vector and the reduction in the ion velocity magnitude relative to that in the F-region, independent estimates of the normalised ion-neutral collision frequency are made at the UHF E-region tristatic altitudes; the derived values are, in general, lower than model predictions. Although initial calculations assume a stationary neutral atmosphere, first-order estimates of the E-region neutral wind are subsequently employed to calculate revised estimates of the normalised ion-neutral collision frequency; these neutral winds are derived by attributing the difference between predicted and observed enhancements in field-parallel ion temperature to thermospheric motion. The inclusion of neutral winds, which are themselves not inconsiderable, appears to have only a limited effect on the normalised collision frequencies derived.

scholarly journals Relationships between pre-sunset electrojet strength, pre-reversal enhancement and equatorial spread-F onset

2010 ◽  
Vol 28 (2) ◽  
pp. 449-454 ◽  
Author(s):  
J. Uemoto ◽  
T. Maruyama ◽  
S. Saito ◽  
M. Ishii ◽  
R. Yoshimura
Keyword(s):  
Electric Field ◽  
Equatorial Electrojet ◽  
Layer Height ◽  
Equatorial Spread F ◽  
Magnetic Latitude ◽  
F Region ◽  
Spread F ◽  
Bottom Side ◽  
E Region ◽  
Height Increase

Abstract. The virtual height of the bottom side F-region (h'F) and equatorial spread-F (ESF) onsets at Chumphon (10.7° N, 99.4° E; 3.3° N magnetic latitude) were compared with the behaviour of equatorial electrojet (EEJ) ground strength at Phuket (8.1° N, 98.3° E; 0.1° N magnetic latitude) during the period from November 2007 to October 2008. Increase in the F-layer height and ESF onsets during the evening hours were well connected with the EEJ ground strength before sunset, namely, both the height increase and ESF onsets were suppressed when the integrated EEJ ground strength for the period from 1 to 2 h prior to sunset was negative. The finding suggests observationally that the pre-sunset E-region dynamo current and/or electric field are related to the F-region dynamics and ESF onsets around sunset.

scholarly journals VHF radar observations of the dip equatorial E-region during sunset in the Brazilian sector

2006 ◽  
Vol 24 (6) ◽  
pp. 1617-1623 ◽  
Author(s):  
C. M. Denardini ◽  
M. A. Abdu ◽  
E. R. de Paula ◽  
C. M. Wrasse ◽  
J. H. A. Sobral
Keyword(s):  
Electric Field ◽  
Equatorial Electrojet ◽  
Magnetic Activity ◽  
Maximum Intensity ◽  
Vhf Radar ◽  
F Region ◽  
Vertical Electric Field ◽  
Tentative Explanation ◽  
E Region ◽  
Activity Condition

Abstract. Using the RESCO 50 MHz backscatter radar (2.33° S, 44.2° W, DIP: –0.5), at São Luís, Brazil, we obtained Range Time Intensity (RTI) maps covering the equatorial electrojet heights during daytime and evening. These maps revealed a scattering region at an altitude of about 108 km during the sunset period. The type of 3-m irregularity region we present here has not been reported before in the literature, to our knowledge. It was mainly observed around the Southern Hemisphere summer-solstice period, under quiet magnetic activity condition. The occurrence of this echo region coincides in local time with the maximum intensity of an evening pre-reversal eastward electric field of the ionospheric F-region. A tentative explanation is proposed here in terms of the theory of the divergence of the equatorial electrojet (EEJ) current in the evening ionosphere presented by Haerendel and Eccles (1992), to explain the partial contribution of the divergence to the development of the pre-reversal electric field. The theory predicts an enhanced zonal electric field and hence a vertical electric field below 300 km as a consequence of the EEJ divergence in the evening. The experimental results of the enhanced echoes from the higher heights of the EEJ region seem to provide evidence that the divergence of the EEJ current can indeed be the driver of the observed scattering region.

scholarly journals THREE-DIMENSIONAL MAGNETOGRADIENT WAVES IN THE UPPER ATMOSPHERE

2017 ◽  
Vol 13 (4) ◽  
pp. 4881-4887
Author(s):  
George Jandieri ◽  
Anzor Gvelesiani ◽  
Zhuzhuna Diasamidze ◽  
Mzia Diasamidze ◽  
Irma Takidze
Keyword(s):  
Three Dimensional ◽  
Short Wave ◽  
Planetary Waves ◽  
Mhd Equations ◽  
One Dimension ◽  
Mhd Waves ◽  
Three Dimension ◽  
F Region ◽  
Mathematical Consequence ◽  
E Region

General dispersion equation has been obtained for three-dimensional electromagnetic planetary waves, from which follows, as particular case Khantadze results in one-dimension case. It was shown that partial magnetic field line freezing-in as in one-dimension case lead to the excitation of both “fast” and “slow” planetary waves, in two-liquid approximation (i.e. at ion drag by neutral particles) they are represent oscillations of magnetized electrons and partially magnetized ions in E region of the ionosphere. In F region of the ionosphere using one-liquid approximation only “fast” planetary wave will be generated representing oscillation of medium as a whole. Hence, it was shown that three-dimension magnetogradient planetary waves are exist in all components of the ionosphere, and as exact solutions, with well-known slow short-wave MHD waves, are simple mathematical consequence of the MHD equations for the ionosphere.

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