Spatial characteristics of midlatitude geomagnetic micropulsations

Abstract

Simultaneous recordings of geomagnetic micropulsations in the 0.001‐ to 1‐Hz frequency range across the state of California were made in late 1967. Two orthogonal horizontal components of the magnetic field were measured at sites located near Berkeley, California, Reno, Nevada, and Fresno, California. The data from the Reno and Fresno sites were telemetered by telephone to the Berkeley site, where they were reported simultaneously with the Berkeley data in analog and digital form. Digital portions of the data were analyzed, and polarization and spectral characteristics were obtained by using a method based on the theory of quasi‐monochromatic or partially polarized radiation. Depending on their spatial characteristics, micropulsations were classified into two basic types, uniform and nonuniform. Uniform micropulsations are in phase and nearly identical in amplitude and wave form at the three sites. They include Pi 1's, Pi 2's, Pc 1's, and quiet‐time Pc 2–4's. The nonuniform micropulsations, which consist primarily of daytime Pc 2–3's, exhibit substantial differences in amplitude, phase, and frequency content between the stations. A striking period increase with latitude was also observed. Examples of both uniform and nonuniform micropulsations are presented here. A reversal of the sense of rotation from counterclockwise in the morning hours to clockwise in the afternoon and evening hours with a transition occurring around noon local mean time was observed for all micropulsations. An attempt to explain the behavior of micropusations in terms of current theories of hydromagnetic wave propagation is made, and evidence for a narrow L‐shell localization of micropulsations is presented.

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“…Therefore, on a network of stations the simultaneous monitoring is conducted, i.e., the distributed system of the collection and of the processing is used. [23,24] In this case, the location of stations is the most optimal along the geomagnetic meridian and the geomagnetic parallel, which corresponds to radial and azimuthal crosssections of the magnetosphere.…”

Spectral structure of mid-latitude Pc3-4 geomagnetic pulsations.

“…Figure 1 then shows representative spectral forms of pulsation activity described by this paradigm. Some previous studies of ULF pulsations that were also based principally on the analysis of dynamic spectra have adopted such an approach too (e.g., DUNCAN, 1961;HIRASAWA et al, 1965;MAINSTONE, 1967;SAITO,1967;ZELWER and MORRISON, 1972).…”