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Evidence of standing waves during a Pi2 pulsation event observed on Cluster
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
University of KwaZulu-Natal, Durban, South Africa.
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
2006 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 24, no 10, 2719-2733 p.Article in journal (Refereed) Published
Abstract [en]

Observations of Pi2 pulsations at middle and low latitudes have been explained in terms of cavity mode resonances, whereas transients associated with field-aligned currents appear to be responsible for the high latitude Pi2 signature. Data from Cluster are used to study a Pi2 event observed at 18:09 UTC on 21 January 2003, when three of the satellites were within the plasmasphere (L=4.7,4.5 and 4.6) while the fourth was on the plasmapause or in the plasmatrough (L=6.6). Simultaneous pulsations at ground observatories and the injection of particles at geosynchronous orbit corroborate the occurrence of a substorm. Evidence of a cavity mode resonance is established by considering the phase relationship between the orthogonal electric and magnetic field components associated with radial and field-aligned standing waves. The relative phase between satellites located on either side of the geomagnetic equator indicates that the field-aligned oscillation is an odd harmonic. Finite azimuthal Poynting flux suggests that the cavity is effectively open ended and the azimuthal wave number is estimated as m similar to 13.5.

Place, publisher, year, edition, pages
2006. Vol. 24, no 10, 2719-2733 p.
Keyword [en]
magnetospheric physics, MHD waves and instabilities, plasmasphere, storms and substorms, pi-2 pulsations, power spectra, magnetic pulsations, ulf pulsations, field-line, geomagnetic micropulsations, geosynchronous orbit, hydromagnetic-waves, inner magnetosphere, substorm onsets
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-16157ISI: 000242402000023Scopus ID: 2-s2.0-33751099046OAI: oai:DiVA.org:kth-16157DiVA: diva2:334199
Note

QC 20150727

Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically 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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