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Title: The magnetospheric lobe at geosynchronous orbit

Abstract

On rare occasions, satellites at geosynchronous altitude enter the magnetospheric lobe, characterized by extremely low ion fluxes between 1 eV and 40 keV and electron fluxes above a few hundred eV. One year of plasma observations from two simultaneously operating spacecraft at synchronous orbit is surveyed for lobe encounters. A total of 34 full encounters and 56 apparent near encounters are identified, corresponding to {approximately}0.06% of the total observation time. Unlike energetic particle (E>40 keV) dropouts studied earlier, there is a strong tendency for the lobe encounters to occur postmidnight, as late as 07 local time. The two spacecraft encounter the lobe with different rates and in different seasons. These occurrence properties are not simply explicable in terms of the orbital geometry in either the solar magnetic or the geocentric solar magnetospheric coordinate system. A composite coordinate system which previously organized more energetic particle dropouts is somewhat more successful in organizing the lobe encounters, suggesting that solar wind distortion of the magnetic equatorial plane away from the dipole location and toward the antisolar direction may be largely responsible for these dropouts. The authors results further suggest that this distortion persists even sunward of the dawn-dusk terminator. However, a simple dawn-duskmore » symmetric distortion does not fully account for all the seasonal and local time asymmetries in the occurrence of the lobe encounters; thus there is probably an additional dawn-dusk asymmetry in the distorted field. The lobe encounters are strongly associated with magnetospheric activity and tend to occur in association with rare magnetosheath encounters at synchronous orbit. It thus appears that the presence of the lobe at geosynchronous orbit is the result of major, probably asymmetric modifications of the magnetospheric field geometry in times of strong disturbance. 19 refs., 7 figs., 1 tab.« less

Authors:
; ;  [1]
  1. Los Alamos National Lab., Los Alamos, NM (United States) [and others
Publication Date:
OSTI Identifier:
166258
Resource Type:
Journal Article
Journal Name:
Journal of Geophysical Research
Additional Journal Information:
Journal Volume: 99; Journal Issue: A9; Other Information: PBD: 1 Sep 1994
Country of Publication:
United States
Language:
English
Subject:
66 PHYSICS; EARTH MAGNETOSPHERE; OPEN CONFIGURATIONS; DISTURBANCES; REMOTE SENSING; SATELLITES; ORBITS

Citation Formats

Thomsen, M.F., Bame, S.J., and McComas, D.J. The magnetospheric lobe at geosynchronous orbit. United States: N. p., 1994. Web. doi:10.1029/94JA00423.
Thomsen, M.F., Bame, S.J., & McComas, D.J. The magnetospheric lobe at geosynchronous orbit. United States. doi:10.1029/94JA00423.
Thomsen, M.F., Bame, S.J., and McComas, D.J. Thu . "The magnetospheric lobe at geosynchronous orbit". United States. doi:10.1029/94JA00423.
@article{osti_166258,
title = {The magnetospheric lobe at geosynchronous orbit},
author = {Thomsen, M.F. and Bame, S.J. and McComas, D.J.},
abstractNote = {On rare occasions, satellites at geosynchronous altitude enter the magnetospheric lobe, characterized by extremely low ion fluxes between 1 eV and 40 keV and electron fluxes above a few hundred eV. One year of plasma observations from two simultaneously operating spacecraft at synchronous orbit is surveyed for lobe encounters. A total of 34 full encounters and 56 apparent near encounters are identified, corresponding to {approximately}0.06% of the total observation time. Unlike energetic particle (E>40 keV) dropouts studied earlier, there is a strong tendency for the lobe encounters to occur postmidnight, as late as 07 local time. The two spacecraft encounter the lobe with different rates and in different seasons. These occurrence properties are not simply explicable in terms of the orbital geometry in either the solar magnetic or the geocentric solar magnetospheric coordinate system. A composite coordinate system which previously organized more energetic particle dropouts is somewhat more successful in organizing the lobe encounters, suggesting that solar wind distortion of the magnetic equatorial plane away from the dipole location and toward the antisolar direction may be largely responsible for these dropouts. The authors results further suggest that this distortion persists even sunward of the dawn-dusk terminator. However, a simple dawn-dusk symmetric distortion does not fully account for all the seasonal and local time asymmetries in the occurrence of the lobe encounters; thus there is probably an additional dawn-dusk asymmetry in the distorted field. The lobe encounters are strongly associated with magnetospheric activity and tend to occur in association with rare magnetosheath encounters at synchronous orbit. It thus appears that the presence of the lobe at geosynchronous orbit is the result of major, probably asymmetric modifications of the magnetospheric field geometry in times of strong disturbance. 19 refs., 7 figs., 1 tab.},
doi = {10.1029/94JA00423},
journal = {Journal of Geophysical Research},
number = A9,
volume = 99,
place = {United States},
year = {1994},
month = {9}
}