scholarly journals Reconnection and energetic particles at the edge of the exterior cusp

2006 ◽  
Vol 24 (7) ◽  
pp. 1949-1956 ◽  
Author(s):  
T. Asikainen ◽  
K. Mursula
Keyword(s):  
Magnetic Field ◽  
Pitch Angle ◽  
Energetic Particles ◽  
Maximum Energy ◽  
Closed Field ◽  
Angle Distribution ◽  
Pitch Angle Distribution ◽  
Flux Transfer Events ◽  
Cusp Region ◽  
Field Lines

Abstract. In this paper we study flux transfer events (FTE) observed at the post-noon edge of the exterior cusp region by Cluster satellites. During the outbound dayside orbit on 2 February 2003, intense bursts of energetic particles were observed in close conjuction with magnetic field FTE signatures by the RAPID instrument onboard the Cluster 4. The pitch-angle distribution of the particles showed that the enhancements consist of particles flowing antiparallel to the magnetosheath field lines away from the expected reconnection site to the exterior cusp. At the same time Cluster 3 observed enhancements of energetic particles deeper in the exterior cusp with a delay of about 40 s to the Cluster 4 enhancements. The estimated maximum energy gain per particle by reconnection remains below 1 keV, thus clearly below the tens to hundreds of keV energy range observed by the RAPID instrument. These observations support the earlier statistical result of the magnetospheric origin of energetic particles in the exterior cusp. Reconnection near the exterior cusp partly releases the particles in the closed field lines of the adjacent HLPS region into the exterior cusp.

scholarly journals Comparison between CNA and energetic electron precipitation: simultaneous observation by Poker Flat Imaging Riometer and NOAA satellite

2005 ◽  
Vol 23 (5) ◽  
pp. 1555-1563 ◽  
Author(s):  
Y.-M. Tanaka ◽  
M. Ishii ◽  
Y. Murayama ◽  
M. Kubota ◽  
H. Mori ◽  
...  
Keyword(s):  
Pitch Angle ◽  
Electron Flux ◽  
Energetic Electron ◽  
Energetic Particles ◽  
Electron Precipitation ◽  
Angle Distribution ◽  
Pitch Angle Distribution ◽  
Loss Cone ◽  
Isotropic Pitch ◽  
Trapped Electron

Abstract. The cosmic noise absorption (CNA) is compared with the precipitating electron flux for 19 events observed in the morning sector, using the high-resolution data obtained during the conjugate observations with the imaging riometer at Poker Flat Research Range (PFRR; 65.11° N, 147.42° W), Alaska, and the low-altitude satellite, NOAA 12. We estimate the CNA, using the precipitating electron flux measured by NOAA 12, based on a theoretical model assuming an isotropic pitch angle distribution, and quantitatively compare them with the observed CNA. Focusing on the eight events with a range of variation larger than 0.4dB, three events show high correlation between the observed and estimated CNA (correlation coefficient (r0)>0.7) and five events show low correlation (r0<0.5). The estimated CNA is often smaller than the observed CNA (72% of all data for 19 events), which appears to be the main reason for the low-correlation events. We examine the assumption of isotropic pitch angle distribution by using the trapped electron flux measured at 80° zenith angle. It is shown that the CNA estimated from the trapped electron flux, assuming an isotropic pitch angle distribution, is highly correlated with the observed CNA and is often overestimated (87% of all data). The underestimate (overestimate) of CNA derived from the precipitating (trapped) electron flux can be interpreted in terms of the anisotropic pitch angle distribution similar to the loss cone distribution. These results indicate that the CNA observed with the riometer may be quantitatively explained with a model based on energetic electron precipitation, provided that the pitch angle distribution and the loss cone angle of the electrons are taken into account. Keywords. Energetic particles, precipitating – Energetic particles, trapped – Ionosphere-magnetosphere interactions

scholarly journals Photoelectron pitch angle distribution near Mars and implications on cross terminator magnetic field connectivity

2020 ◽  
Vol 4 (1) ◽  
pp. 1-6
Author(s):  
YuTian Cao ◽  
◽  
Jun Cui ◽  
XiaoShu Wu ◽  
JiaHao Zhong ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Pitch Angle ◽  
Angle Distribution ◽  
Pitch Angle Distribution

scholarly journals Excitation of plasma waves by unstable photoelectron and thermal electron populations on closed magnetic field lines in the Martian ionosphere

2005 ◽  
Vol 23 (4) ◽  
pp. 1249-1258
Author(s):  
N. Borisov ◽  
E. Nielsen
Keyword(s):  
Magnetic Field ◽  
Pitch Angle ◽  
Angle Distribution ◽  
Thermal Electron ◽  
Langmuir Waves ◽  
Electrostatic Waves ◽  
Martian Ionosphere ◽  
Different Populations ◽  
Field Lines ◽  
Electron Gyrofrequency

Abstract. It is argued that anisotropic electron pitch angle distributions in the closed magnetic field regions of the Martian ionosphere gives rise to excitation of plasma instabilities. We discuss two types of instabilities that are excited by two different populations of electrons. First, the generation of Langmuir waves by photoelectrons with energies of the order of 10eV is investigated. It is predicted that the measured anisotropy of their pitch angle distribution at the heights z≈400km causes excitation of waves with frequencies f~30kHz and wavelengths λ~30m. Near the terminators the instability of the electrostatic waves with frequencies of the order of or less than the electron gyrofrequency exited by thermal electrons is predicted. The typical frequencies of these waves depend on the local magnitude of the magnetic field and can achieve values f~3-5kHz above strong crustal magnetic fields.

scholarly journals Magnetospheric source region of discrete auroras inferred from their relationship with isotropy boundaries of energetic particles

1997 ◽  
Vol 15 (8) ◽  
pp. 943-958 ◽  
Author(s):  
A. G. Yahnin ◽  
V. A. Sergeev ◽  
B. B. Gvozdevsky ◽  
S. Vennerstrøm
Keyword(s):  
Magnetic Field ◽  
Source Region ◽  
Spatial Relationship ◽  
Auroral Oval ◽  
Energetic Particles ◽  
Closed Field ◽  
Physical Conditions ◽  
Ground Observation ◽  
Field Lines ◽  
Auroral Arcs

Abstract. According to observations, the discrete auroral arcs can sometimes be found, either deep inside the auroral oval or at the poleward border of the wide (so-called double) auroral oval, which map to very different regions of the magnetotail. To find common physical conditions for the auroral-arc generation in these magnetotail regions, we study the spatial relationship between the diffuse and discrete auroras and the isotropic boundaries (IBs) of the precipitating energetic particles which can be used to characterise locally the equatorial magnetic field in the tail. From comparison of ground observation of auroral forms with meridional profiles of particle flux measured simultaneously by the low-altitude NOAA satellites above the ground observation region, we found that (1) discrete auroral arcs are always situated polewards from (or very close to) the IB of >30-keV electrons, whereas (2) the IB of the >30-keV protons is often seen inside the diffuse aurora. These relationships hold true for both quiet and active (substorm) conditions in the premidnight-nightside (18-01-h) MLT sector considered. In some events the auroral arcs occupy a wide latitudinal range. The most equatorial of these arcs was found at the poleward edge of the diffuse auroras (but anyway in the vicinity of the electron IB), the most poleward arcs were simultaneously observed on the closed field lines near the polar-cap boundary. These observations disagree with the notion that the discrete aurora originate exclusively in the near-Earth portion of plasma sheet or exclusively on the PSBL field lines. Result (1) may imply a fundamental feature of auroral-arc formation: they originate in the current-sheet regions having very curved and tailward-stretched magnetic field lines.

scholarly journals The Influence of Spiral Arms and Bar on the Large-Scale Galactic Magnetic Field Evolution

1996 ◽  
Vol 171 ◽  
pp. 429-429
Author(s):  
K. Otmianowska-Mazur ◽  
S. von Linden ◽  
H. Lesch
Keyword(s):  
Magnetic Field ◽  
Velocity Field ◽  
Pitch Angle ◽  
Large Scale ◽  
Angle Distribution ◽  
Galactic Magnetic Field ◽  
Pitch Angle Distribution ◽  
Spiral Arms ◽  
Nearby Galaxies ◽  
The Magnetic Field

Recent observations of radio polarization from nearby galaxies show that the large-scale galactic magnetic field is aligned with spiral arms and bars and the magnetic field vectors in the interarm regions possess a spiral structure which has the same pitch angle as that in spiral arms. Our present project is going to address the following questions: What is the structure and evolution of the large-scale galactic magnetic field under the influence of spiral and bar structure in a galactic disk? To which extent could the resulting magnetic field account for the observed spiral pattern of magnetic field in nearby galaxies? The model is based on the particle-particle numerical scheme (SPH) involving two components: stars and molecular gas. The magnetic field is connected with the latter one. The magnetic field computations were performed first in two dimensions for 100 velocity fields: from 107 to 109 yrs. The resultant magnetic field is strongly affected by spiral arms, however at the given evolutionary stage its structure is different from the velocity field at the same time. The magnetic pitch angle distribution shows that the magnetic field “remembers” all the past velocity steps. The magnetic pitch angle distribution resulting after beam smoothing could quite well fit observations. The present model with fully 3D velocity field of interstellar gas should clear the problem if the magnetic field under the realistic velocity evolution of gas could explain the observed structure of large-scale magnetic field with constant pitch angle in the whole disk.

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