Accession Number : ADA332608

Title :   A Conjugate Study of ULF Waves at the Cusp

Corporate Author : ALASKA UNIV FAIRBANKS GEOPHYSICAL INST

Personal Author(s) : Olson, J. V.

PDF Url : ADA332608

Report Date : 1997

Pagination or Media Count : 13

Abstract : This report summarizes a three year study of magnetic variations measured near the footprint of the magnetospheric cusp in conjugate hemispheres. During that time data were collected from fluxgate and induction magnetometers and compared with optical data from all sky cameras and meridian scanning photometers. The spectrum of fluctuations observed near the cusp spans a frequency range from near dc to, and above, our instrument Nyquist frequency of 50 millihertz. While the spectral power is known to diminish with frequency, there are two spectral bands which carry important information concerning the physical processes taking place along cusp field lines. In the lowest frequency band, ranging from dc to approximately 10 millihertz, are a collection of signals which show the dominant spectral power. In the central cusp there occur incoherently superposed wavelets which are observed simultaneously in both hemispheres. Our analysis, and that of our colleagues, shows these to be the resonant response of the outermost portions of the geomagnetic field near the magnetopause to the impulsive pressure variations carried by the solar wind. To the morning and evening sides of the cusp are poleward traveling pulses which appear to be line currents connecting the ionosphere with the magnetopause. We conjecture that these field aligned currents are driven by reconnection events at the magnetopause. The second important frequency band ranges from 10 millihertz to our Nyquist (and above). This band contains a collection of coherent and incoherent oscillations. The coherent oscillations are short-lived packets which are believed to be generated in the upstream solar wind. The incoherent portion of the spectrum have been shown to be due to modulated electron beams impacting the ionosphere. Modulations of the beam intensity produce a quasi-periodic modification of the ionospheric c

Descriptors :   *MAGNETOSPHERE, *ULTRALOW FREQUENCY, GEOMAGNETISM, IONOSPHERE, MAGNETIC FIELDS, POWER SPECTRA, ELECTRON BEAMS, BAND SPECTRA, WAVE PACKETS, MAGNETOMETERS, SOLAR WIND, ALL SKY CAMERAS.

Subject Categories : Atmospheric Physics

Distribution Statement : APPROVED FOR PUBLIC RELEASE