Classification of Geomagnetic Micropulsations

The notation and classification of geomagnetic micropulsations have been discussed in two recent letters in this Journal [Matsushita, 1963; Jacobs et al., 1963]. At the 13th General Assembly of the International Union of Geodesy and Geophysics (IUGG) in Berkeley, California, August 1963, the question was considered in some detail by Committee 10 of the International Association of Geomagnetism and Aeronomy (IAGA). A small subcommittee, consisting of the four authors of this note, was set up to submit the recommendations which are presented below. From experimental knowledge, particularly that obtained since the IGY, it has been recognized that micropulsations can be divided into two main classes: those of a regular and mainly continuous character, and those with an irregular pattern. The first class covers the whole range of micropulsations with periods from about 0.2 to 600 sec. They can be divided into subgroups depending on their period, but it is extremely difficult to decide where the boundaries should be drawn. A purely mathematical division can be made, based perhaps on a logarithmic scale, or a division can be based on their physical and morphological properties. The second approach was adopted, and Table 1 gives the proposed classification and notation.