RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 7, ES3003, doi:10.2205/2005ES000175, 2005

Secular Variations in the Trend of the Geomagnetic Field at the Time of its Reversal

[25]  Since the early studies of transition conditions many authors emphasized the growing disturbance of the geomagnetic field or, to be more exact, of the parameters characterizing its direction, during its inversions. Using the term "disturbance'', they meant the growth of the variation magnitude and numerous outbursts and loops of large magnitude, often measuring 180o along the large circle arc.

[26]  It is possible that a change in the magnitude of the regular variations of the field direction is a seeming effect. The angular elements of the geomagnetic field vector, Dec. and Inc., are calculated using their X, Y, and Z components. It is obvious that under the conditions of the low medium field intensity, the same increments of these components lead to a greater change in the angular elements compared to the case of high field intensity.

[27]  According to the modern views, the main variation spectrum is a principally important characteristics of a dynamo mechanism. The periods of the variations included into the main spectrum (archaeomagnetic data) correspond to the periods of MAC waves in terms of their theoretical estimates [Braginskii, 1974]. MAC waves are an integral part of the generation mechanism being the manifestation of its principal instability. It is a change in the MAC wave spectrum, that is, in the periods of secular variations, that record variations in the dynamo process.

[28]  The identification of the main-spectrum variations with the MAC waves is based not only on the proximity of their theoretical and experimental periods, but also on some specific variations of the basic spectrum variations stemming from the results of arhaeomagnetic investigations. First, the main-spectrum variations have a running and a standing component, both being pertinent to MAC waves. Secondly, some variations, like, for example, the well-known variation with a period of 1200 years, show distinct global features [Burlatskaya, 1999].

[29]  The secular variations recorded during polarity reversals were studied using the Gauss-Matuyama, Matuyama-Jaramillo and Matuyama-Brunhes reversals [Petrova et al., 1980, 1992]. These authors came to the conclusion that the secular variation spectrum had not varied throughout the inversion process. Moreover, the comparison of their results with the data reported by Gurarii et al. [1994] suggested the conclusion that the basic spectrum of the geomagnetic field variation had not changed during the last 5.5 million years, that is, the dynamo mechanism operated continuously.

2005ES000175-fig04
Figure 4
[30]  However, the latest data suggest that both the above conclusion and the term "basic spectrum'' should be treated with care, where the latter implies not merely the presence of the oscillations of certain periods (characteristic time intervals), but also the persistence of these periods throughout the long time of the existence of a certain-polarity field. Gurarii et al. [2000b] proved that this view on the spectrum of these "variations'' owes its origin to the method chosen for the processing and analysis of the data available for paleomagnetic time series. The use of the wavelet analysis, as a basic technique, for the processing of the data obtained during the study of the sedimentary rocks in the Ajidere area (West Turkmenia) and characterizing the magnetic field for the period of 0.99-1.17 million years proved the high variation of the characteristic times of the recorded oscillations. This variation was observed in the data series of different durations, characterizing the field of different polarity both in the vicinity of the inversion and at a significance distance from it, this fact being proved by our new results (Figure 4).

[31]  These results do not contradict the view proposed by Braginskii [1974], yet, can be treated as another indication of the permanent instability of the generation mechanism, the extreme manifestation of which is the geomagnetic field reversal.

[32]  Therefore, the sole, most substantiated, conclusion that can be offered at the present time is that the study of this problem need be continued.


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Citation: Gurarii, G. Z. (2005), Geomagnetic field reversals: Main results and basic problems, Russ. J. Earth Sci., 7, ES3003, doi:10.2205/2005ES000175.

Copyright 2005 by the Russian Journal of Earth Sciences

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