Other
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsm51a0270h&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SM51A-0270
Other
2471 Plasma Waves And Instabilities (2772), 2483 Wave/Particle Interactions (7867), 2487 Wave Propagation (0689, 3285, 4275, 4455, 6934)
Scientific paper
Cases of Auroral Kilometric Radiation (AKR) pulsating periodically at frequencies from 1 to 3 Hz have been found in high resolution dynamic spectra obtained from Cluster Wide Band Data instrument. These frequencies are typical for Pc1 (0.2 to 5 Hz) geomagnetic field oscillations. Duration of a single chain of pulses is generally less than one minute. With the WBD bandpass filter operating nominally in the frequency range of 300 Hz to 77 kHz selected at the time of the observations, the pulsating AKR was observed in a frequency range of emission of 50 to 90 kHz, with a modulation depth of about 20 dB. We show one example at a nearly constant frequency of pulse repetition around 2 Hz, lasting for 66 s, and another at a frequency descending from 3 Hz to 1.25 Hz in a time interval of 17 s. We interpret the observed Pc1 AKR pulsations in terms of Pc1 electromagnetic ion cyclotron waves (EMIC), which are stimulated by compression of the dayside magnetosphere [Anderson and Hamilton, 1993; Anderson and Fuselier, 1993; Anderson et al., 1996; Engebretson et al., 2002]. They are produced in the equatorial magnetosphere [Erlandson and Anderson, 1996; Loto'aniu et al., 2005] at or near the ion gyro- frequencies of H+, He+ [Mursula et al., 2001] and O+ [Braysy et al., 1998], and are propagated along geomagnetic field lines [Hansen et al. 1992] to the noon sector of the high latitude ionosphere [Erlandson and Anderson, 1996], where they are observed in space and on the ground [Engebretson et al., 2002]. We propose the scenario, in which the Pc 1 waves convert to inertial Alfven waves in the auroral region and interact with the downward propagating electrons to modulate their "horseshoe" distribution function, which leads to periodic AKR growth by an electron cyclotron maser instability, in a way similar to that described by Xin and Menietti [2007] for EMIC waves.
de Feraudy Herve
Hanasz Jan
Pickett Jolene S.
Schreiber Robert
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