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Modelling and Analysis of Substorm-Related Chorus Events
KTH, Superseded Departments, Alfvén Laboratory.
2004 (English)In: Planetary Ionospheres and Atmospheres Including CIRA / [ed] Rodin A; Rees D; Gupta SP, 2004, Vol. 34, no 8, 1819-1823 p.Conference paper, Published paper (Refereed)
Abstract [en]

The substorm-related chorus event is a recognised VLF signature of the substorm expansion phase. Computer simulations support the contention that these events are generated by cyclotron resonance between whistler mode waves and energetic electrons which drift into a ground station's field of view from an injection site near midnight.

Place, publisher, year, edition, pages
2004. Vol. 34, no 8, 1819-1823 p.
Series
Advances in Space Research, ISSN 0273-1177
Keyword [en]
substorm-related chorus events, substorm expansion phase, VLF signature
National Category
Other Engineering and Technologies
Identifiers
URN: urn:nbn:se:kth:diva-5663DOI: 10.1016/j.asr.2003.07.064ISI: 000225594400028Scopus ID: 2-s2.0-8344258331OAI: oai:DiVA.org:kth-5663DiVA: diva2:10103
Conference
2nd World Space Congress/34th COSPAR Scientific Assembly
Note
QC 20100920 QC 20111101Available from: 2006-05-08 Created: 2006-05-08 Last updated: 2011-11-01Bibliographically approved
In thesis
1. VLF and ULF Waves Associated with Magnetospheric Substorms
Open this publication in new window or tab >>VLF and ULF Waves Associated with Magnetospheric Substorms
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

A magnetospheric substorm is manifested in a variety of phenomena observed both in space and on the ground. Two electromagnetic signatures are the Substorm Chorus Event (SCE) and Pi2 pulsations.

The SCE is a Very Low Frequency (VLF) radio phenomenon observed on the ground after the onset of the substorm expansion phase. It consists of a band of VLF chorus with rising upper and lower cutoff frequencies. These emissions are thought to result from Doppler-shifted cyclotron resonance between whistler mode waves and energetic electrons which drift into an observer’s field of view from an injection site around midnight. The ascending frequency of the emission envelope has been attributed to the combined effects of energy dispersion due to gradient and curvature drifts and the modification of the resonance conditions resulting from the radial component of the E × B drift. Two numerical models have been developed which simulate the production of a SCE. One accounts for both radial and azimuthal electron drifts but treats the wave-particle interaction in an approximate fashion, while the other retains only the azimuthal drift but rigorously calculates both the electron anisotropy and the wave growth rate. Results from the latter model indicate that the injected electron population should have an enhanced high-energy tail in order to produce a realistic SCE.

Pi2 are damped Ultra Low Frequency (ULF) pulsations with periods between 40 and 150 s. The impulsive metamorphosis of the nightside inner magnetosphere during the onset of the substorm expansion phase is accompanied by a broad spectrum of magnetohydrodynamic (MHD) waves. Over a limited range of local times around midnight these waves excite field line resonances (FLRs) on field lines connected with the auroral zone. Compressional waves propagate into the inner magnetosphere, where they generate cavity mode resonances. The uniform frequency of Pi2 pulsations at middle and low latitudes is a consequence of these cavity modes. A number of Pi2 events were identified at times when the Cluster constellation was located in the nightside inner magnetosphere. Electric and magnetic field data from Cluster were used to establish the existence of both cavity and field line resonances during these events. The associated Poynting flux indicated negligible radial or field-aligned energy flow but an appreciable azimuthal flux directed away from midnight.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 114 p.
Series
Trita-EE, ISSN 1653-5146 ; 2006:019
Keyword
Space physics, Subtorms, Magnetosphere, VLF waves, ULF waves
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-3939 (URN)91-7178-372-5 (ISBN)
Public defence
2006-05-23, H1, Teknikringen 33, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100920Available from: 2006-05-08 Created: 2006-05-08 Last updated: 2010-09-20Bibliographically approved

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