American Geophysical Union Become an AGU Member
Subscribe to AGU Journals		 AGU Home AGU Publications

Read Full Article (file size: 525475 bytes)    Cited by

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, A07302, doi:10.1029/2005JA011288, 2006

Further study of flickering auroral roar emission: 2. Theory and numerical calculations

A. T. Weatherwax

Department of Physics, Siena College, Loudonville, New York, USA


P. H. Yoon

Institute for Physical Science and Technology, University of Maryland at College Park, College Park, Maryland, USA


J. M. Hughes

Space Physics Research Laboratory, Embry-Riddle Aeronautical University, Daytona Beach, Florida, USA


J. LaBelle

Department of Physics and Astronomy, Dartmouth College, Hanover, New Hampshire, USA


L. F. Ziebell

Instituto de Física, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil


Abstract

Two recent papers report ground-based observations of ∼3–30 Hz pulsations in the amplitude of 2f ce auroral roar radio emissions. These pulsations occur in groups which last for ∼1 s with adjacent pulsation groups spaced from one to several seconds. We put forth that these pulsations reflect periodic modulation of precipitating auroral electron fluxes, which could include periodic downward field-aligned bursts (FABs) and periodically modulated inverted-V electron precipitation, similar to those that could account for flickering aurora. We calculate time and frequency variations in the growth rate of Z-mode waves in the ionosphere for two different models of time-varying electron distribution functions, one corresponding to acceleration by electromagnetic ion cyclotron waves (EMIC) and the other corresponding to a simple time-varying accelerating potential (TVP). On the basis of these numerical calculations, the reported characteristics of ∼10 Hz flickering roar appear consistent with modulations induced in the electron distribution function via interaction with EMIC waves, since the modulation associated with EMIC waves results in flickering of only the lower portion of the auroral roar frequency band, as in most of the observations. The few observed cases of higher-frequency flickering roar, at ∼20–30 Hz, fall above the O+ cyclotron frequency for the altitude range on interest, and may represent a different source of electron flux modulation such as a varying electrostatic potential. The radio observations provide an additional means of probing flickering phenomenon and in particular may put constraints on the form of modulations of the electron distribution function at the auroral roar source height of a few hundred kilometers.

Received 26 June 2005; accepted 24 February 2006; published 1 July 2006.

Keywords: auroral roar; emission.

Index Terms: 2483 Ionosphere: Wave/particle interactions (7867); 2471 Ionosphere: Plasma waves and instabilities (2772); 2455 Ionosphere: Particle precipitation; 2704 Magnetospheric Physics: Auroral phenomena (2407); 2753 Magnetospheric Physics: Numerical modeling.

Read Full Article (file size: 525475 bytes)    Cited by

Citation: Weatherwax, A. T., P. H. Yoon, J. M. Hughes, J. LaBelle, and L. F. Ziebell (2006), Further study of flickering auroral roar emission: 2. Theory and numerical calculations, J. Geophys. Res., 111, A07302, doi:10.1029/2005JA011288.