scholarly journals Statistics of a parallel Poynting vector in the auroral zone as a function of altitude using Polar EFI and MFE data and Astrid-2 EMMA data

2005 ◽  
Vol 23 (5) ◽  
pp. 1797-1806 ◽  
Author(s):  
P. Janhunen ◽  
A. Olsson ◽  
N. A. Tsyganenko ◽  
C. T. Russell ◽  
H. Laakso ◽  
...  
Keyword(s):  
Poynting Vector ◽  
Radial Distance ◽  
Auroral Zone ◽  
Electron Precipitation ◽  
Alfven Wave ◽  
Altitude Range ◽  
Altitude Profile ◽  
Morning Sector ◽  
Field Lines ◽  
Auroral Phenomena

Abstract. We study the wave-related (AC) and static (DC) parallel Poynting vector (Poynting energy flux) as a function of altitude in auroral field lines using Polar EFI and MFE data. The study is statistical and contains 5 years of data in the altitude range 5000–30000 km. We verify the low altitude part of the results by comparison with earlier Astrid-2 EMMA Poynting vector statistics at 1000 km altitude. The EMMA data are also used to statistically compensate the Polar results for the missing zonal electric field component. We compare the Poynting vector with previous statistical DMSP satellite data concerning the electron precipitation power. We find that the AC Poynting vector (Alfvén-wave related Poynting vector) is statistically not sufficient to power auroral electron precipitation, although it may, for Kp>2, power 25–50% of it. The statistical AC Poynting vector also has a stepwise transition at R=4 RE, so that its amplitude increases with increasing altitude. We suggest that this corresponds to Alfvén waves being in Landau resonance with electrons, so that wave-induced electron acceleration takes place at this altitude range, which was earlier named the Alfvén Resonosphere (ARS). The DC Poynting vector is ~3 times larger than electron precipitation and corresponds mainly to ionospheric Joule heating. In the morning sector (02:00–06:00 MLT) we find that the DC Poynting vector has a nontrivial altitude profile such that it decreases by a factor of ~2 when moving upward from 3 to 4 RE radial distance. In other nightside MLT sectors the altitude profile is more uniform. The morning sector nontrivial altitude profile may be due to divergence of the perpendicular Poynting vector field at R=3–4 RE. Keywords. Magnetospheric physics (Auroral phenomena; Magnetosphere-ionosphere interactions) – Space plasma physics (Wave-particle interactions)

Peculiarities of electron precipitation in morning sector of auroral zone during geomagnetic storm

1986 ◽  
Vol 30 (1) ◽  
pp. 79-86
Author(s):  
Yu. V. Gotselyuk ◽  
M. S. Kazaryan ◽  
S. N. Kuznetsov ◽  
Karel Kudela ◽  
Ivan Kimák ◽  
...  
Keyword(s):  
Geomagnetic Storm ◽  
Auroral Zone ◽  
Electron Precipitation ◽  
Morning Sector

On the morphology of auroral-zone X-ray events—IV. Substorm-related electron precipitation in the local morning sector

1975 ◽  
Vol 37 (10) ◽  
pp. 1289-1303 ◽  
Author(s):  
J. Kangas ◽  
L. Lukkari ◽  
P. Tanskanen ◽  
H. Trefall ◽  
J. Stadsnes ◽  
...  
Keyword(s):  
Auroral Zone ◽  
Electron Precipitation ◽  
X Ray ◽  
Morning Sector

scholarly journals A case study of electron precipitation in the late substorm growth phase on and nearby a preonset arc

1998 ◽  
Vol 16 (12) ◽  
pp. 1567-1572 ◽  
Author(s):  
A. Olsson ◽  
P. Janhunen
Keyword(s):  
Growth Phase ◽  
Potential Drop ◽  
Electron Precipitation ◽  
Larmor Radius ◽  
Plasma Properties ◽  
Precipitation Characteristics ◽  
Coupling Parameters ◽  
Storms And Substorms ◽  
Field Lines ◽  
Auroral Phenomena

Abstract. We follow the electron precipitation characteristics on and nearby a preonset arc using the high resolution Freja TESP instrument. Our data coverage extends from about 10 min before onset up to 1 min before onset. The arc is the most equatorward one (around MLAT 62°) of a system of growth phase arcs, and it was close to the radiation belt precipitation. Within the preonset arc, inverted-V type precipitation dominates. Poleward of the arc we also find some precipitation regions, and here there is systematically a cold electron population superposed with a warm population. Using single and double Maxwellian fits to the measured electron spectra we find the ionosphere-magnetosphere coupling parameters (field-aligned conductance K and the parallel potential drop V) as well as the effective source plasma properties (density and temperature) during the event. Compared to typical expansion phase features, the preonset parallel potential drop is smaller by a factor of ten, the electron temperature is smaller by a factor of at least five, and the field-aligned conductance is about the same or larger. The fact that there are two isotropic superposed electron populations on the poleward side of the preonset arc suggests that the distance between warm trapped electrons on dipolar field lines and colder electrons on open field lines has become so small near the onset that mixing e.g. due to finite electron Larmor radius effects can take place.Key words. Ionosphere · (ionosophere-magnetosphere interactions) · Magnetospheric physics (auroral phenomena; storms and substorms).

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 The influence of Titan on Saturn kilometric radiation

2010 ◽  
Vol 28 (2) ◽  
pp. 395-406 ◽  
Author(s):  
J. D. Menietti ◽  
S.-Y. Ye ◽  
C. W. Piker ◽  
B. Cecconi
Keyword(s):  
Radio Emission ◽  
Plasma Wave ◽  
Local Time ◽  
Direction Finding ◽  
Original Study ◽  
Electron Precipitation ◽  
Occurrence Probability ◽  
Source Regions ◽  
Morning Sector ◽  
Field Lines

Abstract. Previous studies have shown that the occurrence probability of Saturn Kilometric Radiation (SKR) appears to be influenced by the local time of Titan. Using a more extensive set of data than the original study, we confirm the correlation of higher occurrence probability of SKR when Titan is located near local midnight. In addition, the direction finding capability of the Cassini Radio Plasma Wave instrument (RPWS) is used to determine if this radio emission emanates from particular source regions. We find that most source regions of SKR are located in the mid-morning sector of local time even when Titan is located near midnight. However, some emission does appear to have a source in the Saturnian nightside, consistent with electron precipitation from field lines that have recently mapped to near Titan.

scholarly journals The occurrence frequency of upward ion beams in the auroral zone as a function of altitude using Polar/TIMAS and DE-1/EICS data

2003 ◽  
Vol 21 (10) ◽  
pp. 2059-2072 ◽  
Author(s):  
P. Janhunen ◽  
A. Olsson ◽  
W. K. Peterson
Keyword(s):  
Particle Flux ◽  
Ion Beam ◽  
Radial Distance ◽  
Space Plasma ◽  
Auroral Zone ◽  
Ion Beams ◽  
Occurrence Frequency ◽  
Space Plasma Physics ◽  
Wave Heating ◽  
Auroral Phenomena

Abstract. We study the occurrence frequency of upward auroral ion beams as a function of altitude using three years of  Polar/TIMAS ion data combined with 11 years of DE-1/ EICS ion data, in order to reach a complete altitude coverage between 5000 and 30 000 km. The most interesting result is that there is a peak in ion beam occurrence frequency and invariant energy flux and invariant particle flux at ¢ 3 RE radial distance. The peak exists at about the same altitude in both the evening and midnight MLT sectors. No solar cycle effects are found. We suggest that the peak could be due to a preferred altitude of auroral potential structures at ¢ 3 RE . To substantiate the suggestion, we also present a simple Monte Carlo simulation of ion beams. Another result is that the ion beam occurrence frequency and invariant (mapped to ionospheric altitude) energy and particle fluxes increase in the radial distance range 4–6 RE , suggesting that wave heating processes may take place in this altitude range.Key words. Magnetospheric physics (auroral phenomena; magnetosphere-ionosphere interactions) – Space plasma physics (charged particle motion and acceleration)

scholarly journals The development of magnetic field line wander by plasma turbulence

2017 ◽  
Vol 83 (4) ◽  
Author(s):  
Gregory G. Howes ◽  
Sofiane Bourouaine
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Magnetic Field Line ◽  
Large Scale ◽  
Magnetic Energy ◽  
Plasma Turbulence ◽  
Alfven Wave ◽  
Astrophysical Plasmas ◽  
Field Lines ◽  
The Magnetic Field

Plasma turbulence occurs ubiquitously in space and astrophysical plasmas, mediating the nonlinear transfer of energy from large-scale electromagnetic fields and plasma flows to small scales at which the energy may be ultimately converted to plasma heat. But plasma turbulence also generically leads to a tangling of the magnetic field that threads through the plasma. The resulting wander of the magnetic field lines may significantly impact a number of important physical processes, including the propagation of cosmic rays and energetic particles, confinement in magnetic fusion devices and the fundamental processes of turbulence, magnetic reconnection and particle acceleration. The various potential impacts of magnetic field line wander are reviewed in detail, and a number of important theoretical considerations are identified that may influence the development and saturation of magnetic field line wander in astrophysical plasma turbulence. The results of nonlinear gyrokinetic simulations of kinetic Alfvén wave turbulence of sub-ion length scales are evaluated to understand the development and saturation of the turbulent magnetic energy spectrum and of the magnetic field line wander. It is found that turbulent space and astrophysical plasmas are generally expected to contain a stochastic magnetic field due to the tangling of the field by strong plasma turbulence. Future work will explore how the saturated magnetic field line wander varies as a function of the amplitude of the plasma turbulence and the ratio of the thermal to magnetic pressure, known as the plasma beta.

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