Spatial distribution of the geomagnetic spectral composition for disturbed days.

Abstract

Seven geomagnetically disturbed days were studied at a number of stations in the American Hemisphere for the purpose of determining the systematic spectral composition changes with activity level, Ap, and geomagnetic latitude. The spectral amplitudes, A, at 5, 10, 30, 60, and 120-min period, T, from a Fourier analysis of magnetograms showed a linear relationship with Ap that varied with T. There was an auroral latitude maximum of activity at all periods (which shifted poleward for lower Ap), a low latitude minimum, and a daytime equatorial enhancement of the spectra. Calling m the spectral slope from A=kTm, where k is a constant, the slopes were determined for the period ranges of 5 to 10, 10 to 60, and 60 to 240 min. Average slope values in these ranges were about 2. 4, 1. 0, and 0. 8 respectively. The 10 to 60-min slope values increased linearly with increasing Ap and decreased at auroral latitudes.

Particle diffusion in the geomagnetosphere: Comparison of estimates from measurements of magnetic and electric field fluctuations

“…It is now known that the radial diffusion coefficient for energetic particles in the earth's magnetosphere is not constant as a function of time, as was often assumed in the early days of radiation belt research [Lanzerotti et al, 1970[Lanzerotti et al, , 1978. Rather, third-invariant violation depends upon the level of geomagnetic activity, as would be expected from contemporary knowledge of geomagnetic 'noise' levels [e.g., Surkan and Lanzerotti, 1974;Campbell, 1976Campbell, , 1977. As such, the radial diffusion problem is more complicated than that envisioned a decade and a half ago.…”

Spectral characteristics of field variations during geomagnetically quiet conditions.

“…Differences in the temporal and spatial features of the spectra for three period samples are shown. On many days the high latitude activity was more evenly spread throughout the day than was found for the geomagnetically active days (CAMPBELL, 1976c). The two clear exceptions to this were on 10 November and 28 April.…”

“…Table 3 shows the linear relationship for which the data set included the 6 quiet days of Table 1 plus the 7 active day analyzed in the earlier paper (CAMPBELL, 1976c). The correlation coefficients are quite high at each period sampled.…”

“…A study of the shorter period spectral range was presented by WERTZ and CAMPBELL (1976). In the same period range as this paper the characteristics of the average day spectra (CAMPBELL 1976a) and the disturbance-time spectra (CAMPBELL, 1976c) have already been completed. Results from these last two studies will be mentioned again in this paper for comparison with quiet-time field characteristics.…”

Geoelectric power spectra over oceanic distances

“…The nature of the spectral power of geoelectric fluctuations over large distances is of intrinsic scientific interest as well as of interest for more practical concerns related to the installation and maintenance of technological systems composed of long conductors grounded to the Earth. While power spectral studies of geomagnetic field fluctuations have been investigated on a 'global' scale, using spaced magnetometers, for more than two decades [see especially Campbell, 1976aCampbell, ,b, 1977Wertz and Campbell, 1976], geoelectric measurements have generally been confined to more local and regional studies, primarily associated with magnetotelluric studies of the Earth's conductivity structure.…”