scholarly journals Polar observations of electron density distribution in the Earth’s magnetosphere. 2. Density profiles

2002 ◽  
Vol 20 (11) ◽  
pp. 1725-1735 ◽  
Author(s):  
H. Laakso ◽  
R. Pfaff ◽  
P. Janhunen
Keyword(s):  
Electric Field ◽  
Electron Density ◽  
Auroral Zone ◽  
Polar Cap ◽  
Geomagnetic Disturbances ◽  
Activity Data ◽  
Density Peaks ◽  
Spacecraft Potential ◽  
Order Of Magnitude ◽  
Auroral Phenomena

Abstract. Using spacecraft potential measurements of the Polar electric field experiment, we investigate electron density variations of key plasma regions within the magnetosphere, including the polar cap, cusp, trough, plasmapause, and auroral zone. The statistical results were presented in the first part of this study, and the present paper reports detailed structures revealed by individual satellite passes. The high-altitude (> 3 RE) polar cap is generally one of the most tenuous regions in the magnetosphere, but surprisingly, the polar cap boundary does not appear as a steep density decline. At low altitudes (1 RE) in summer, the polar densities are very high, several 100 cm-3 , and interestingly, the density peaks at the central polar cap. On the noonside of the polar cap, the cusp appears as a dense, 1–3° wide region. A typical cusp density above 4 RE distance is between several 10 cm-3 and a few 100 cm-3 . On some occasions the cusp is crossed multiple times in a single pass, simultaneously with the occurrence of IMF excursions, as the cusp can instantly shift its position under varying solar wind conditions, similar to the magnetopause. On the nightside, the auroral zone is not always detected as a simple density cavity. Cavities are observed but their locations, strengths, and sizes vary. Also, the electric field perturbations do not necessarily overlap with the cavities: there are cavities with no field disturbances, as well as electric field disturbances observed with no clear cavitation. In the inner magnetosphere, the density distributions clearly show that the plasmapause and trough densities are well correlated with geomagnetic activity. Data from individual orbits near noon and midnight demonstrate that at the beginning of geomagnetic disturbances, the retreat speed of the plasmapause can be one L-shell per hour, while during quiet intervals the plasmapause can expand anti-earthward at the same speed. For the trough region, it is found that the density tends to be an order of magnitude higher on the day-side (~1 cm-3) than on the nightside (~0.1–1 cm-3), particularly during low Kp.Key words. Magnetospheric physics (auroral phenomena; plasmasphere; polar cap phenomena)

scholarly journals Polar observations of electron density distribution in the Earth’s magnetosphere. 1. Statistical results

2002 ◽  
Vol 20 (11) ◽  
pp. 1711-1724 ◽  
Author(s):  
H. Laakso ◽  
R. Pfaff ◽  
P. Janhunen
Keyword(s):  
Electron Density ◽  
Individual Case ◽  
Auroral Zone ◽  
Average Density ◽  
High Time Resolution ◽  
Polar Cap ◽  
Total Electron Density ◽  
Total Electron ◽  
Magnetospheric Configuration And Dynamics ◽  
Order Of Magnitude

Abstract. Forty-five months of continuous spacecraft potential measurements from the Polar satellite are used to study the average electron density in the magnetosphere and its dependence on geomagnetic activity and season. These measurements offer a straightforward, passive method for monitoring the total electron density in the magnetosphere, with high time resolution and a density range that covers many orders of magnitude. Within its polar orbit with geocentric perigee and apogee of 1.8 and 9.0 RE, respectively, Polar encounters a number of key plasma regions of the magnetosphere, such as the polar cap, cusp, plasmapause, and auroral zone that are clearly identified in the statistical averages presented here. The polar cap density behaves quite systematically with season. At low distance (~2 RE), the density is an order of magnitude higher in summer than in winter; at high distance (>4 RE), the variation is somewhat smaller. Along a magnetic field line the density declines between these two altitudes by a factor of 10–20 in winter and by a factor of 200–1000 in summer. A likely explanation for the large gradient in the summer is a high density of heavy ions that are gravitationally bound in the low-altitude polar cap. The geomagnetic effects are also significant in the polar cap, with the average density being an order of magnitude larger for high Kp; for an individual case, the polar cap density may increase even more dramatically. The plasma density in the cusp is controlled primarily by the solar wind variables, but nevertheless, they can be characterized to some extent in terms of the Kp index. We also investigate the local time variation of the average density at the geosynchronous distance that appears to be in accordance with previous geostationary observations. The average density decreases with increasing Kp at all MLT sectors, except at 14–17 MLT, where the average density remains constant. At all MLT sectors the range of the density varies by more than 3 orders of magnitude, since the geostationary orbit may cut through different plasma regions, such as the plasma sheet, trough, and plasmasphere.Key words. Magnetospheric physics (magnetospheric configuration and dynamics; plasmasphere; polar cap phenomena)

scholarly journals A multi-satellite study of accelerated ionospheric ion beams above the polar cap

2006 ◽  
Vol 24 (6) ◽  
pp. 1665-1684 ◽  
Author(s):  
R. Maggiolo ◽  
J. A. Sauvaud ◽  
D. Fontaine ◽  
A. Teste ◽  
E. Grigorenko ◽  
...  
Keyword(s):  
Electric Field ◽  
Potential Drop ◽  
Auroral Zone ◽  
Ion Beams ◽  
Distribution Functions ◽  
Convection Velocity ◽  
Polar Cap ◽  
Ion Energy ◽  
Polar Cusp ◽  
Oxygen Ions

Abstract. This paper presents a study of nearly field-aligned outflowing ion beams observed on the Cluster satellites over the polar cap. Data are taken at geocentric radial distances of the order of 5–9 RE. The distinction is made between ion beams originating from the polar cusp/cleft and beams accelerated almost along the magnetic field line passing by the spacecraft. Polar cusp beams are characterized by nearly field-aligned proton and oxygen ions with an energy ratio EO+ / EH+, of the order of 3 to 4, due to the ion energy repartition inside the source and to the latitudinal extension of the source. Rapid variations in the outflowing ion energy are linked with pulses/modifications of the convection electric field. Cluster data allow one to show that these perturbations of the convection velocity and the associated ion structures propagate at the convection velocity. In contrast, polar cap local ion beams are characterized by field-aligned proton and oxygen ions with similar energies. These beams show the typical inverted V structures usually observed in the auroral zone and are associated with a quasi-static converging electric field indicative of a field-aligned electric field. The field-aligned potential drop fits well the ion energy profile. The simultaneous observation of precipitating electrons and upflowing ions of similar energies at the Cluster orbit indicates that the spacecraft are crossing the mid-altitude part of the acceleration region. In the polar cap, the parallel electric field can thus extend to altitudes higher than 5 Earth radii. A detailed analysis of the distribution functions shows that the ions are heated during their parallel acceleration and that energy is exchanged between H+ and O+. Furthermore, intense electrostatic waves are observed simultaneously. These observations could be due to an ion-ion two-stream instability.

scholarly journals Quasi-periodic precipitation with periods between 40 and 60 minutes

1996 ◽  
Vol 14 (7) ◽  
pp. 707-715 ◽  
Author(s):  
K. Rinnert
Keyword(s):  
Electric Field ◽  
Electron Density ◽  
Electron Precipitation ◽  
Statistical Characteristics ◽  
Geomagnetic Disturbances ◽  
Maximum Probability ◽  
Dst Index ◽  
Incoherent Scatter ◽  
Magnetospheric Tail ◽  
E Region

Abstract. Intervals of periodic enhancements of E-region electron density have been found in EISCAT (European Incoherent SCATter) data. The periods are typically between 40 and 60 min. The phenomenon is observed during relatively quiet times, though after geomagnetic disturbances; it may last up to 6 h. The events can occur at all times of day with a maximum probability in the MLT morning sector. Using the EISCAT database from recent years, the statistical characteristics of these events, and their relation to magnetospheric conditions defined by the Dst index and the d.c. electric field perpendicular to B\\= have been derived. The latitudinal extent is found to be several degrees, but the longitudinal extent is not known. It is concluded that these events are due to the periodically modulated flux of electron precipitation controlled by oscillations in the magnetospheric tail.

scholarly journals Algorithm for numerical simulation of electron density and stochastically convecting high latitude ionosphere

2021 ◽  
Vol 2131 (2) ◽  
pp. 022013
Author(s):  
G Vlaskov
Keyword(s):  
Numerical Simulation ◽  
Electric Field ◽  
Electron Density ◽  
Large Scale ◽  
Ionospheric Plasma ◽  
Auroral Zone ◽  
Polar Ionosphere ◽  
Magnetospheric Convection ◽  
The Monte Carlo Method ◽  
High Latitude Ionosphere

Abstract The problem of modeling the inhomogeneities of the electron density in the polar ionosphere at the level of the F - layer is considered. It is known that the distribution of ionospheric plasma changes under the action of the electric field of large-scale magnetospheric convection. Since the electric field undergoes significant fluctuations in the auroral zone, it is proposed to use the Monte Carlo method to solve this problem, simulating the process of plasma motion, like the Wiener one with deterministic drift.

scholarly journals Geomagnetic disturbances on ground associated with particle precipitation during SC

2010 ◽  
Vol 28 (1) ◽  
pp. 247-265 ◽  
Author(s):  
V. Safargaleev ◽  
A. Kozlovsky ◽  
F. Honary ◽  
A. Voronin ◽  
T. Turunen
Keyword(s):  
Solar Wind ◽  
Electric Field ◽  
Current System ◽  
Auroral Zone ◽  
Ionospheric Irregularity ◽  
Wind Pressure ◽  
Geomagnetic Disturbances ◽  
Equatorial Station ◽  
Ionospheric Conductivity ◽  
The Impact

Abstract. We have examined several cases of magnetosphere compression by solar wind pressure pulses using a set of instruments located in the noon sector of auroral zone. We have found that the increase in riometric absorption (sudden commencement absorption, SCA) occurred simultaneously with the beginning of negative or positive magnetic variations and broadband enhancement of magnetic activity in the frequency range above 0.1 Hz. Since magnetic variations were observed before the step-like increase of magnetic field at equatorial station (main impulse, MI), the negative declinations resembled the so-called preliminary impulse, PI. In this paper a mechanism for the generation of PI is introduced whereby PI's generation is linked to SCA – associated precipitation and the local enhancement of ionospheric conductivity leading to the reconstruction of the ionospheric current system prior to MI. Calculation showed that PI polarity depends on orientation of the background electric field and location of the observation point relative to ionospheric irregularity. For one case of direct measurements of electric field in the place where the ionospheric irregularity was present, the sign of calculated disturbance corresponded to the observed one. High-resolution measurements on IRIS facility and meridional chain of the induction magnetometers are utilized for the accurate timing of the impact of solar wind irregularity on the magnetopause.

scholarly journals Altitude dependence of plasma density in the auroral zone

2002 ◽  
Vol 20 (11) ◽  
pp. 1743-1750 ◽  
Author(s):  
P. Janhunen ◽  
A. Olsson ◽  
H. Laakso
Keyword(s):  
Plasma Density ◽  
Radial Distance ◽  
Auroral Zone ◽  
Auroral Region ◽  
The Earth ◽  
Spacecraft Potential ◽  
Evening Sector ◽  
Altitude Dependence ◽  
Plasma Depletions ◽  
Auroral Phenomena

Abstract. We study the altitude dependence of plasma depletions above the auroral region in the 5000–30 000 km altitude range using five years of Polar spacecraft potential data. We find that besides a general decrease of plasma density with altitude, there frequently exist additional density depletions at 2–4 RE radial distance, where RE is the Earth radius. The position of the depletions tends to move to higher altitude when the ionospheric footpoint is sunlit as compared to darkness. Apart from these cavities at 2–4 RE radial distance, separate cavities above 4 RE occur in the midnight sector for all Kp and also in the morning sector for high Kp. In the evening sector our data remain inconclusive in this respect. This holds for the ILAT range 68–74. These additional depletions may be substorm-related. Our study shows that auroral phenomena modify the plasma density in the auroral region in such a way that a nontrivial and interesting altitude variation results, which reflects the nature of the auroral acceleration processes.Key words. Magnetospheric physics (auroral phenomena; magnetosphere–ionosphere interactions)

scholarly journals Multi-layer structure of mid-latitude sporadic-<i>E</i> observed during the SEEK-2 campaign

2005 ◽  
Vol 23 (7) ◽  
pp. 2347-2355 ◽  
Author(s):  
M. Wakabayashi ◽  
T. Ono
Keyword(s):  
Electric Field ◽  
Electron Density ◽  
Electric Fields ◽  
Wind Shear ◽  
Lower Layer ◽  
Layer Structure ◽  
Electron Density Profile ◽  
Neutral Wind ◽  
Density Peaks ◽  
Dc Electric Field

Abstract. In the mid-latitude ionospheric region, sporadic-E layers (Es layers) have often been observed, revealing multiple layers. The Es layers observed during the SEEK-2 rocket campaign showed double electron density peaks; namely, there are stable lower peaks and relatively unstable upper peaks. We examined the effects of wind shear and the electric fields on the generation of the multiple layer structure, in comparison with the electron density profile, the neutral wind, and the DC electric field observed by the S310 rocket experiments. The results showed that the neutral wind shear is mainly responsible for the generation of the lower layer, while the DC electric field makes a significant contribution to the formation of the upper layer. The difference between the lower and upper layers was also explained by the enhanced AC electric field observed at about 103–105 km altitude. The external DC electric field intensity is expected to be ~5 mV/m, which is enough to contribute to generate the Es layers in the ionosphere. Keywords. Ionosphere (Electric fields; Ionospheric irregularities, Mid-latitude ionosphere)

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