Acta Geodaetica et Geophysica Hungarica 29. (1994)

1-2. szám - MILETITS J. CZ. - HOLLÓ L. - VERŐ J. - ZIEGER B.: Interplanetary magnetic field-dependent and geomagnetic latitude dependent periods of pulsations (A re-evaluation)

Acta Geod. Geoph. Hung., Vol. 29(1-Z),pp. 179-195 (1994) INTERPLANETARY MAGNETIC FIELD-DEPENDENT AND GEOMAGNETIC LATITUDE DEPENDENT PERIODS OF PULSATIONS — A RE-EVALUATION J Cz Miletits1, L Holló1, J Verő1, В Zieger1 [Manuscript received March 13, 1994] Some twenty years ago a detailed comparison was made based on data of the Nagycenk Observatory (L — 2.0) between periods of geomagnetic pulsations and interplanetary conditions. According to it, periods were clearly dependent on the scalar magnitude of the interplanetary magnetic field, (IMF), |fl|, and even the form of the connection, T = 160/|B| could be confirmed. Since then, the same problem has been several times attacked. The (geomagnetic) latitude dependence of the periods may veil this connection. Nevertheless, field line resonances are also influenced by interplanetary conditions, as e.g. the occurrence frequency of the resonance depends on IMF. Anyway, following types of the pulsation periods can be separated: 1. IMF dependent periods (upstream waves with slightly transformed spectra) everywhere in the zone studied (L 1.7 to 3 or more) 2. Latitude dependent periods, i.e. field line resonances, often simultaneously with upstream waves 3. Long period events with similar periods everywhere (from the tail?) mainly at higher latitudes 4. Short periods during geomagnetically active intervals (storms). It is not exclu­ded that the IMF dependence of periods may be different at different L-values, even within the mid-latitude region, due to interference of the field line reso­nances. Keywords: field line resonance; geomagnetic pulsations; Nagycenk geomagnetic observatory; upstream waves 1. Introduction Based on data of the Nagycenk (NCK, L =. 2.0) observatory, the connections between (Pc2-4) pulsation activity and several interplanetary-magnetospheric pa­rameters have been studied since the International Geophysical Year, IGY, in 1957. Thus data and results for more than three complete solar cycles are available. Quite recently questions have been raised about the validity of the previously found connections. That is why we should like to summarize experience and results in this field, together with results concerning meridional changes of the pulsation acti­vity (periods) based on results of several pulsation arrays in Central and Northern Europe. 'Geodetic and Geophysical Research Institute of the Hungarian Academy of Sciences, H-9401 Sopron, РОВ 5, Hungary 1217-8977/94/$ 4-00 ©1994 Akadémiai Kiadó, Budapest

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