Evolution of the plasma sheet electron pitch angle distribution by whistler-mode chorus waves in non-dipole magnetic fields
We present a detailed numerical study on the effects of a non-dipole magnetic field on the Earth's plasma sheet electron distribution and its implication for diffuse auroral precipitation. Use of the modified bounce-averaged Fokker-Planck equation developed in the companion paper by Ni et a...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2012-04-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/30/751/2012/angeo-30-751-2012.pdf |
| _version_ | 1818981197848510464 |
|---|---|
| author | Q. Ma B. Ni X. Tao R. M. Thorne |
| author_facet | Q. Ma B. Ni X. Tao R. M. Thorne |
| author_sort | Q. Ma |
| collection | DOAJ |
| description | We present a detailed numerical study on the effects of a non-dipole magnetic
field on the Earth's plasma sheet electron distribution and its implication
for diffuse auroral precipitation. Use of the modified bounce-averaged
Fokker-Planck equation developed in the companion paper by
Ni et al. (2012) for 2-D non-dipole magnetic fields suggests that we
can adopt a numerical scheme similar to that used for a dipole field, but
should evaluate bounce-averaged diffusion coefficients and bounce period
related terms in non-dipole magnetic fields. Focusing on nightside
whistler-mode chorus waves at <I>L</I> = 6, and using various Dungey magnetic
models, we calculate and compare of the bounce-averaged diffusion
coefficients in each case. Using the Alternative Direction Implicit (ADI)
scheme to numerically solve the 2-D Fokker-Planck diffusion equation, we
demonstrate that chorus driven resonant scattering causes plasma sheet
electrons to be scattered much faster into loss cone in a non-dipole field
than a dipole. The electrons subject to such scattering extends to lower
energies and higher equatorial pitch angles when the southward interplanetary
magnetic field (IMF) increases in the Dungey magnetic model. Furthermore, we
find that changes in the diffusion coefficients are the dominant factor
responsible for variations in the modeled temporal evolution of plasma sheet
electron distribution. Our study demonstrates that the effects of realistic
ambient magnetic fields need to be incorporated into both the evaluation of
resonant diffusion coefficients and the calculation of Fokker-Planck
diffusion equation to understand quantitatively the evolution of plasma sheet
electron distribution and the occurrence of diffuse aurora, in particular at
<I>L</I> > 5 during geomagnetically disturbed periods when the ambient magnetic
field considerably deviates from a magnetic dipole. |
| first_indexed | 2024-12-20T17:27:30Z |
| format | Article |
| id | doaj.art-bd39de71d3a4426c8006f07278e229b3 |
| institution | Directory Open Access Journal |
| issn | 0992-7689 1432-0576 |
| language | English |
| last_indexed | 2024-12-20T17:27:30Z |
| publishDate | 2012-04-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Annales Geophysicae |
| spelling | doaj.art-bd39de71d3a4426c8006f07278e229b32022-12-21T19:31:30ZengCopernicus PublicationsAnnales Geophysicae0992-76891432-05762012-04-013075176010.5194/angeo-30-751-2012Evolution of the plasma sheet electron pitch angle distribution by whistler-mode chorus waves in non-dipole magnetic fieldsQ. Ma0B. Ni1X. Tao2R. M. Thorne3Department of Atmospheric and Oceanic Sciences, UCLA, Los Angeles, CA, USADepartment of Atmospheric and Oceanic Sciences, UCLA, Los Angeles, CA, USADepartment of Atmospheric and Oceanic Sciences, UCLA, Los Angeles, CA, USADepartment of Atmospheric and Oceanic Sciences, UCLA, Los Angeles, CA, USAWe present a detailed numerical study on the effects of a non-dipole magnetic field on the Earth's plasma sheet electron distribution and its implication for diffuse auroral precipitation. Use of the modified bounce-averaged Fokker-Planck equation developed in the companion paper by Ni et al. (2012) for 2-D non-dipole magnetic fields suggests that we can adopt a numerical scheme similar to that used for a dipole field, but should evaluate bounce-averaged diffusion coefficients and bounce period related terms in non-dipole magnetic fields. Focusing on nightside whistler-mode chorus waves at <I>L</I> = 6, and using various Dungey magnetic models, we calculate and compare of the bounce-averaged diffusion coefficients in each case. Using the Alternative Direction Implicit (ADI) scheme to numerically solve the 2-D Fokker-Planck diffusion equation, we demonstrate that chorus driven resonant scattering causes plasma sheet electrons to be scattered much faster into loss cone in a non-dipole field than a dipole. The electrons subject to such scattering extends to lower energies and higher equatorial pitch angles when the southward interplanetary magnetic field (IMF) increases in the Dungey magnetic model. Furthermore, we find that changes in the diffusion coefficients are the dominant factor responsible for variations in the modeled temporal evolution of plasma sheet electron distribution. Our study demonstrates that the effects of realistic ambient magnetic fields need to be incorporated into both the evaluation of resonant diffusion coefficients and the calculation of Fokker-Planck diffusion equation to understand quantitatively the evolution of plasma sheet electron distribution and the occurrence of diffuse aurora, in particular at <I>L</I> > 5 during geomagnetically disturbed periods when the ambient magnetic field considerably deviates from a magnetic dipole.https://www.ann-geophys.net/30/751/2012/angeo-30-751-2012.pdf |
| spellingShingle | Q. Ma B. Ni X. Tao R. M. Thorne Evolution of the plasma sheet electron pitch angle distribution by whistler-mode chorus waves in non-dipole magnetic fields Annales Geophysicae |
| title | Evolution of the plasma sheet electron pitch angle distribution by whistler-mode chorus waves in non-dipole magnetic fields |
| title_full | Evolution of the plasma sheet electron pitch angle distribution by whistler-mode chorus waves in non-dipole magnetic fields |
| title_fullStr | Evolution of the plasma sheet electron pitch angle distribution by whistler-mode chorus waves in non-dipole magnetic fields |
| title_full_unstemmed | Evolution of the plasma sheet electron pitch angle distribution by whistler-mode chorus waves in non-dipole magnetic fields |
| title_short | Evolution of the plasma sheet electron pitch angle distribution by whistler-mode chorus waves in non-dipole magnetic fields |
| title_sort | evolution of the plasma sheet electron pitch angle distribution by whistler mode chorus waves in non dipole magnetic fields |
| url | https://www.ann-geophys.net/30/751/2012/angeo-30-751-2012.pdf |
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