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First observations of 4 f ce auroral roar emissions
Author(s) -
Sato Y.,
Ono T.,
Sato N.,
Ogawa Y.
Publication year - 2012
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 - 10.1029/2012gl051205
Subject(s) - ionosphere , noon , physics , atmospheric sciences , altitude (triangle) , earth's magnetic field , geology , geophysics , magnetic field , geometry , mathematics , quantum mechanics
This is a report on the first observations of auroral roar emissions near 4 times the ionospheric electron cyclotron frequency ( f ce ) with a passive receiver installed in Svalbard, Norway. 4 f ce roar emissions were detected from 5.27 to 5.70 MHz during moderate geomagnetic disturbances in 22 days between May and September 2011 only from noon to evening, while no event occurred during the winter season. An analysis of a typical event shows that the electron density profile measured from EISCAT Svalbard dynasonde satisfies the condition that the upper frequency of the 4 f ce roar is nearly equal to both upper hybrid resonance frequency ( f UH ) and 4 f ce at 238‐km altitude. These observations support the idea expanded from the most commonly‐accepted generation mechanism of 2 f ce and 3 f ce roar: the origin of 4 f ce roar is upper hybrid waves favorably generated under the condition of f UH ∼ 4 f ce in the auroral F‐region ionosphere.