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Cluster observations of whistler mode ducts and banded chorus
Author(s) -
Haque N.,
Inan U. S.,
Bell T. F.,
Pickett J. S.,
Trotig J. G.,
Facskó G.
Publication year - 2011
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2011gl049112
Subject(s) - chorus , equator , physics , astrophysics , geology , astronomy , geophysics , latitude , art , literature
Bell et al. (2009) proposed that the source region for banded chorus consists of whistler mode ducts of depleted electron density ( N e ) for upper band (UB) chorus for all wave normal angles (θ) and ducts of either enhanced or depleted N e for lower band (LB) chorus for small θ and θ near or greater than the Gendrin angle, respectively. This paper provides support for this model using new high resolution (17 km) N e observations from the Cluster WHISPER and EFW instruments. Data is examined from January 20, 2004, when strong banded chorus was observed over 3000 km of the Cluster 2 orbit, ending at the magnetic equator. Previous analysis of LB chorus on this day indicated the wave normal angles were larger than the Gendrin angle. Using the N e data, we show that the LB chorus is generated within depletion ducts in the source region and that the half‐width of these ducts (∼70 km) is comparable to the transverse scale (∼100 km) of the chorus source region. Making use of the fact that the group velocity of the LB chorus waves has a significant cross‐ L component, we show that the source region extends over 500 km near the magnetic equator.