Acta Geodaetica, Geophysica et Montanistica 6. (1971)

1–2. szám - Cz. Miletits, J.: On the latitude dependence of Pc-type pulsations

Acta Geodaet., Geophys. et Montanist. Acad. Sei. Hung., Tomus 6 (1—2), pp. 141 153 (1971) ON THE LATITUDE DEPENDENCE OF PC-TYPE PULSATIONS J. CZ. MILETITS GEOPHYSICAL RESEARCH LABORATORY OF THE HUNGARIAN ACADEMY OF SCIENCES, SOPRON [Manuscript received December 28, 1969] The paper first summarizes the investigations carried out by different authors on the latitude dependence of the period of pc-type pulsations. Using records of 30 observatories the author establishes the shortening of the period of geomagnetic pulsations with decreas­ing geomagnetic latitude from the direction of the auroral zones to the equator. Pulsations are short-period variations in the electromagnetic field of the Earth. Their periods are comprised between some seconds and some hundreds of seconds. Several authors have already dealt with the properties of simultaneous pulsations in far-off observatories. For the amplitude of the pulsations a strong increase is proved between the equator and the auroral zones. The dependence or independence of the period on the geomagnetic latitude is, however, disputed. Based on statistical data from eleven observatories between geomagnetic latitudes 28° and 67°N, Obayashi and Jacobs [1] tried to show that the periods of geomagnetic pulsations became longer with increasing geomagnetic latitude (Ф): they have found a linear relation between period and cos ~2 Ф. This statement was later withdrawn by Jacobs [2]. Jacobs and Sinno [3] have shown later for 17 stations in North America and in the Pacific (between geomagnetic latitudes 68,6°N and 77,8°S) that the period is constant for pc-s with periods longer than 30 seconds, but not for shorter periods. From simultaneous records of three Australian stations (between geo­magnetic latitudes 28°S and 51°S), Ellis [4] failed to find any appreciable variation with latitude. Duncan [5], however, established a distinct and rather great dependence on the latitude for the same three stations and for six further stations (the latter data were collected from different authors). Lock and Stevens [6] stated that pc-s appear in the same frequency domain, but not coherently, at two stations spaced about 6750 km in the Atlantic (Ф = 5l°N and 8°S). In June 1961 pc-s were recorded at three German stations with standard­ized equipments in all the three components H, D and Z. (Ф from 48,9° to 54,6°TV). Voelker [7] has found that pulsations often were different at these Acta Gcodaetica, Geophysica et Montanistica Academiae Scientiarum Hungaricae 6. 1971

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