scholarly journals Ionospheric response to variable electric fields in small-scale auroral structures

1998 ◽  
Vol 16 (10) ◽  
pp. 1343-1354 ◽  
Author(s):  
B. S. Lanchester ◽  
M. H. Rees ◽  
K. J. F. Sedgemore ◽  
J. R. Palmer ◽  
H. U. Frey ◽  
...  
Keyword(s):  
Electric Fields ◽  
Radar Data ◽  
Optical Measurements ◽  
Small Scale ◽  
Plasma Convection ◽  
Density Profiles ◽  
Space Resolution ◽  
E Region ◽  
Radar Measurements ◽  
Electron Density Profiles

Abstract. High time and space resolution optical and radar measurements have revealed the influence of electric fields on E-region electron density profiles in small-scale auroral structures. Large electric fields are present adjacent to auroral filaments produced by monoenergetic electron fluxes. The ionisation profiles measured within and beside the auroral filaments show the effects of plasma convection due to electric fields as well as the consequences of the response time to large and dynamic fluxes of energetic electrons. Without high-resolution optical measurements, the interpretation of the radar data is limited.Key words. Auroral ionosphere · Ionosphere-magnetosphere interactions · EISCAT

scholarly journals SEEK-2 (Sporadic-<i>E</i> Experiment over Kyushu 2) − Project Outline, and Significance

2005 ◽  
Vol 23 (7) ◽  
pp. 2295-2305 ◽  
Author(s):  
M. Yamamoto ◽  
S. Fukao ◽  
R. T. Tsunoda ◽  
R. Pfaff ◽  
H. Hayakawa
Keyword(s):  
Electric Field ◽  
Spatial Structure ◽  
Electric Fields ◽  
Density Profiles ◽  
Sounding Rockets ◽  
Optical Instruments ◽  
Observation Network ◽  
E Region ◽  
Sporadic E ◽  
Electron Density Profiles

Abstract. SEEK-2 (Sporadic-E Experiment over Kyushu 2) is an observation campaign to study the spatial structure of the field-aligned irregularity (FAI) and sporadic-E(Es)-layer by means of two sounding rockets and a ground-based observation network with radars and optical instruments. The experiment was successfully conducted on 3 August 2002, with successive launches of two sounding rockets from the Uchinoura Space Center (USC) of the Japan Aerospace Exploration Agency (JAXA). The timing of the experiment was carefully selected, while intense quasi-periodic (QP) echoes were observed with two radars in Tanegashima. The main Es-layer, with its double-layered structure, was observed at altitudes of 103–105 km, the presence of which was well accounted for by the ion accumulation due to neutral-wind shear. Several minor peaks were detected in the electron density profiles at altitudes of up to 130 km. The intensity of the electric field was 5–10 mV/m and showed intense fluctuations below 110 km. Wave-like variation of the electric field was seen above 110 km. From radar experiments, we found that QP echoes appeared around 105 km, which agreed well with the main Es-layer height. The QP echoes propagated to the west-northwest, with frontal structures elongated from north-northeast to south-southwest. Radar observations conduced throughout the SEEK-2 period, on the other hand, showed that frontal structures of the QP echoes were most frequently propagated to the southeast. This result was consistent with the direction of gravity-wave propagation observed with the OH imager during the same period. The rocket beacon experiment with the Es-layers revealed the spatial structure of the plasma densities. On the basis of these results and those from SEEK-1 in 1996, we examined the structures of the nighttime mid-latitude E-region. We concluded that the QP echoes reflect the horizontal structures of the main Es-layers. The source of the structures was not clearly determined from the experiments, but the candidates are gravity waves and the Kelvin-Helmholtz instability. The azimuth-dependent Es-instability may have contributed to enhance structures of the QP echoes, although this instability may not be a major source of the QP structure in SEEK-2. Polarization electric fields were induced from the Es-layer with QP echoes, mapped upward along the geomagnetic field, and played an important role in determining the structures of the whole ionospheric E-region. Keywords. Mid-latitude ionosphere – Ionospheric irregularities – Ionosphere-atmosphere interactions

scholarly journals Auroral E-region electron density height profile modificationby electric field driven vertical plasma transport:some evidence in EISCAT CP-1 data statistics

2004 ◽  
Vol 22 (3) ◽  
pp. 901-910 ◽  
Author(s):  
T. Bösinger ◽  
G. C. Hussey ◽  
C. Haldoupis ◽  
K. Schlegel
Keyword(s):  
Electric Field ◽  
Electron Density ◽  
Electric Fields ◽  
Plasma Transport ◽  
Plasma Convection ◽  
Ionosphere Plasma ◽  
E Region ◽  
Eiscat Radar ◽  
Electric Fields And Currents ◽  
Electron Density Profiles

Abstract. A model developed several years ago by Huuskonen et al. (1984) predicted that vertical transport of ions in the nocturnal auroral E-region ionosphere can shift the electron density profiles in altitude during times of sufficiently large electric fields. If the vertical plasma transport effect was to operate over a sufficiently long enough time, then the real height of the E-region electron maximum should be shifted some km upwards (downwards) in the eastward (westward) auroral electrojet, respectively, when the electric field is strong, exceeding, say, 50 mV/m. Motivated by these predictions and the lack of any experimental verification so far, we made use of the large database of the European Incoherent Scatter (EISCAT) radar to investigate if the anticipated vertical plasma transport is at work in the auroral E-region ionosphere and thus to test the Huuskonen et al. (1984) model. For this purpose a new type of EISCAT data display was developed which enabled us to order a large number of electron density height profiles, collected over 16 years of EISCAT operation, according to the electric field magnitude and direction as measured at the same time at the radar's magnetic field line in the F-region. Our analysis shows some signatures in tune with a vertical plasma transport in the auroral E-region of the type predicted by the Huuskonen et al. model. The evidence brought forward is, however, not unambiguous and requires more rigorous analysis. Key words. Ionosphere (auroral ionosphere; plasma convection; electric fields and currents)

scholarly journals A statistical survey of dayside pulsed ionospheric flows as seen by the CUTLASS Finland HF radar

2000 ◽  
Vol 18 (4) ◽  
pp. 445-453 ◽  
Author(s):  
K. A. McWilliams ◽  
T. K. Yeoman ◽  
G. Provan
Keyword(s):  
Radar Data ◽  
Hf Radar ◽  
Optical Measurements ◽  
Occurrence Rate ◽  
Related Phenomenon ◽  
Plasma Convection ◽  
Flux Transfer ◽  
Statistical Survey ◽  
Spacecraft Data ◽  
Resolution Data

Abstract. Nearly two years of 2-min resolution data and 7- to 21-s resolution data from the CUTLASS Finland HF radar have undergone Fourier analysis in order to study statistically the occurrence rates and repetition frequencies of pulsed ionospheric flows in the noon-sector high-latitude ionosphere. Pulsed ionospheric flow bursts are believed to be the ionospheric footprint of newly reconnected geomagnetic field lines, which occur during episodes of magnetic flux transfer to the terrestrial magnetosphere - flux transfer events or FTEs. The distribution of pulsed ionospheric flows were found to be well grouped in the radar field of view, and to be in the vicinity of the radar signature of the cusp footprint. Two thirds of the pulsed ionospheric flow intervals included in the statistical study occurred when the interplanetary magnetic field had a southward component, supporting the hypothesis that pulsed ionospheric flows are a reconnection-related phenomenon. The occurrence rate of the pulsed ionospheric flow fluctuation period was independent of the radar scan mode. The statistical results obtained from the radar data are compared to occurrence rates and repetition frequencies of FTEs derived from spacecraft data near the magnetopause reconnection region, and to ground-based optical measurements of poleward moving auroral forms. The distributions obtained by the various instruments in different regions of the magnetosphere were remarkably similar. The radar, therefore, appears to give an unbiased sample of magnetopause activity in its routine observations of the cusp footprint.Key words: Magnetospheric physics (magnetosphere-ionosphere interactions; plasma convection; solar wind-magnetosphere interactions)

scholarly journals Meridional motions of the afternoon radar aurora, auroral electrojets, and absorption patches under variable IMF conditions

2004 ◽  
Vol 22 (5) ◽  
pp. 1649-1664
Author(s):  
R. A. Makarevitch ◽  
F. Honary ◽  
A. V. Koustov ◽  
M. V. Uspensky
Keyword(s):  
Electric Fields ◽  
Temporal Correlation ◽  
Doppler Velocity ◽  
Plasma Convection ◽  
Motion Patterns ◽  
Aspect Angle ◽  
Radar Echoes ◽  
Meridional Motion ◽  
E Region ◽  
The Imf

Abstract. The meridional motions of the CUTLASS HF and STARE VHF coherent echoes, IMAGE equivalent electrojet currents, and IRIS absorption patches during the postnoon/early-evening event of 14 February 2000 are presented. The motions were found to be synchronous, to a first approximation, for all instruments. The temporal correlation between motions in the radar and magnetometer data was exceptionally good, although spatially the areas with the E-region backscatter and most intense equivalent currents were not coincident, with the HF (VHF) echoes being shifted 100–200km (20–50km) equatorward (poleward). The meridional motions of the radar echoes and electrojet currents appeared to be controlled by the IMF Bz changes; the meridional propagation direction was equatorward (poleward) during the intervals when the IMF was southward (northward), with one exception when the poleward progression continued after the IMF southward turning. We relate the observed meridional motion patterns to the polar cap expansion/contraction during variable IMF conditions and discuss the relative importance of two types of processes: the dayside reconnection and IMF-triggered substorms. We also investigate the irregularity Doppler velocity for the STARE (144MHz) and CUTLASS (12MHz) observations at large flow angles in the context of the eastward and westward electrojet systems. We show that the 144-MHz Doppler velocity is determined by a combination of two factors: the sense of electrojet currents and the aspect angle conditions within the STARE field of view. Finally, the behavior of small dayside enhancements of the IRIS absorption (up to 0.5dB at 38.2MHz) accompanying the radar echoes and electrojet currents is examined. Since the velocity of the meridional displacements was close to that of the poleward/equatorward progressing intense currents, it is suggested that the absorption patches observed during the event were related to the heating of the E-region plasma by the unstable plasma waves in the regions of enhanced electric fields. Key words. Ionosphere (auroral ionosphere; electric fields and currents; plasma convection)

Seismo-ionospheric precursors of the 14 November 2019 M7.1 Indonesia Earthquake detected by FORMOSAT-7/COSMIC-2

2020 ◽  
Author(s):  
Jann-Yenq Liu ◽  
Chi-Yen Lin ◽  
Fu-Yuan Chang ◽  
Yuh-Ing Chen
Keyword(s):  
Electron Density ◽  
Electric Fields ◽  
Radio Occultation ◽  
Electron Content ◽  
Ion Temperature ◽  
Density Profiles ◽  
Ion Density ◽  
Total Electron ◽  
Ion Velocity ◽  
Electron Density Profiles

&lt;p&gt;FORMOSAT-7/COSMIC-2 (F7/C2), with the mission orbit of 550 km altitude, 24-deg inclination, and a period of 97 minutes, was launched on 25 June 2019.&amp;#160; Tri-GNSS Radio occultation System (TGRS), Ion Velocity Meter (IVM), and RF beacon onboard F7/C2 six small satellites allow scientists to observe the plasma structure and dynamics in the mid-latitude, low-latitude, and equatorial ionosphere in detail. &amp;#160;F7/C2 TGRS sounds ionospheric RO (radio occultation) electron density profiles, while F7/C2 IVM probes the ion density, ion temperature, and ion velocity at the satellite altitude.&amp;#160; The F7/C2 electron density profiles and the ion density, ion temperature, and ion velocity, as well as the global ionospheric map (GIM) of the total electron content (TEC) derived from global ground-based GPS receivers are used to detect seismo-ionospheric precursors (SIPs) of the 14 November 2019 M7.1 Indonesia Earthquake.&amp;#160; The GIM TEC and F7/C2 RO NmF2 significantly increase specifically over the epicenter on 25-26 October, which indicates SIPs of the 14 November 2019 M7.1 Indonesia Earthquake being detected.&amp;#160; The F7/C2 RO electron density profiles upward motions suggest that the eastward electric fields have been enhanced during the SIP days of the 2019 M7.1 Indonesia earthquake.&amp;#160; The seismo-generated electric fields of the 2019 M7.1 Indonesia earthquake are 0.34-0.64 mV/m eastward. &amp;#160;The results demonstrate that F7/C2 can be employed to detect SIPs in the ionospheric plasma, which shall shed some light on earthquake prediction/forecast.&lt;/p&gt;

scholarly journals Simultaneous imaging of aurora on small scale in OI (777.4 nm) and N<sub>2</sub>1P to estimate energy and flux of precipitation

2009 ◽  
Vol 27 (7) ◽  
pp. 2881-2891 ◽  
Author(s):  
B. S. Lanchester ◽  
M. Ashrafi ◽  
N. Ivchenko
Keyword(s):  
Temporal Resolution ◽  
Atomic Oxygen ◽  
Molecular Nitrogen ◽  
Low Energy ◽  
Optical Measurements ◽  
Small Scale ◽  
Emission Rates ◽  
Simultaneous Imaging ◽  
Radar Measurements ◽  
Multispectral Imager

Abstract. Simultaneous images of the aurora in three emissions, N21P (673.0 nm), OII (732.0 nm) and OI (777.4 nm), have been analysed; the ratio of atomic oxygen to molecular nitrogen has been used to provide estimates of the changes in energy and flux of precipitation within scale sizes of 100 m, and with temporal resolution of 32 frames per second. The choice of filters for the imagers is discussed, with particular emphasis on the choice of the atomic oxygen line at 777.4 nm as one of the three emissions measured. The optical measurements have been combined with radar measurements and compared with the results of an auroral model, hence showing that the ratio of emission rates OI/N2 can be used to estimate the energy within the smallest auroral structures. In the event chosen, measurements were made from mainland Norway, near Troms\\o, (69.6 N, 19.2 E). The peak energies of precipitation were between 1–15 keV. In a narrow curling arc, it was found that the arc filaments resulted from energies in excess of 10 keV and fluxes of approximately 7 mW/m2. These filaments of the order of 100 m in width were embedded in a region of lower energies (about 5–10 keV) and fluxes of about 3 mW/m2. The modelling results show that the method promises to be most powerful for detecting low energy precipitation, more prevalent at the higher latitudes of Svalbard where the multispectral imager, known as ASK, is now installed.

scholarly journals D- and E-region effects in the auroral zone during a moderately active 24-h period in July 2005

2007 ◽  
Vol 25 (8) ◽  
pp. 1837-1849 ◽  
Author(s):  
J. K. Hargreaves ◽  
M. J. Birch ◽  
B. J. I. Bromage
Keyword(s):  
Energetic Electron ◽  
Radar Data ◽  
Early Morning ◽  
Auroral Zone ◽  
Small Scale ◽  
Absorption Region ◽  
Horizontal Structure ◽  
D Region ◽  
E Region ◽  
Eiscat Radar

Abstract. The effects of energetic electron precipitation into the auroral region at a time of enhanced solar wind have been investigated during a continuous period of 24 h, using the European Incoherent Scatter (EISCAT) radar, an imaging riometer, and particle measurements on an orbiting satellite. The relative effects in the E region (120 km) and D region (90 km) are found to vary during the day, consistent with a gradual hardening of the incoming electron spectrum from pre-midnight to morning. Whereas the night spectra are single peaked, the daytime spectra are found to be double peaked, suggesting the presence of two distinct populations. A comparison between the radiowave absorption observed with the riometer and values estimated from the radar data shows generally good agreement, but with some discrepancies suggesting the occurrence of some small-scale features. The height and thickness of the absorbing region are estimated. Two periods of enhanced precipitation and the related radio absorption, one near magnetic midnight and one in the early morning, are studied in detail, including their horizontal structure and movement of the absorption patches. A sharp reduction of electron flux recorded on a POES satellite is related to the edge of an absorption region delineated by the imaging riometer. The observed particle flux is compared with a value deduced from the radar data during the overpass, and found to be in general agreement.

scholarly journals Estimating along-track plasma drift speed from electron density measurements by the three Swarm satellites

2015 ◽  
Vol 33 (7) ◽  
pp. 829-835 ◽  
Author(s):  
J. Park ◽  
H. Lühr ◽  
C. Stolle ◽  
G. Malhotra ◽  
J. B. H. Baker ◽  
...  
Keyword(s):  
Electron Density ◽  
Plasma Convection ◽  
Polar Cap ◽  
Satellite Constellations ◽  
Density Profiles ◽  
Radar Network ◽  
Swarm Satellites ◽  
High Latitude Ionosphere ◽  
Electron Density Profiles ◽  
Along Track

Abstract. Plasma convection in the high-latitude ionosphere provides important information about magnetosphere–ionosphere–thermosphere coupling. In this study we estimate the along-track component of plasma convection within and around the polar cap, using electron density profiles measured by the three Swarm satellites. The velocity values estimated from the two different satellite pairs agree with each other. In both hemispheres the estimated velocity is generally anti-sunward, especially for higher speeds. The obtained velocity is in qualitative agreement with Super Dual Auroral Radar Network data. Our method can supplement currently available instruments for ionospheric plasma velocity measurements, especially in cases where these traditional instruments suffer from their inherent limitations. Also, the method can be generalized to other satellite constellations carrying electron density probes.

scholarly journals Global sounding of <i>F</i> region irregularities by COSMIC during a geomagnetic storm

2018 ◽  
Author(s):  
Klemens Hocke ◽  
Huixin Liu ◽  
Nicholas Pedatella ◽  
Guanyi Ma
Keyword(s):  
Spatial Scales ◽  
Low Earth Orbit ◽  
Small Scale ◽  
Electron Content ◽  
Polar Regions ◽  
Tangent Point ◽  
Density Profiles ◽  
Total Electron ◽  
Electron Density Profiles ◽  
Ray Path

Abstract. We analyze reprocessed electron density profiles and TEC profiles of the ionosphere in September 2008 (around solar minimum) and September 2013 (around solar maximum) obtained by the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC). The TEC profiles describe the total electron content along the ray path from the GPS satellite to the low Earth orbit as function of the tangent point of the ray. Some of the profiles in the magnetic polar regions show small-scale fluctuations with spatial scales

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