RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 10, ES4003, doi:10.2205/2007ES000258, 2008

Geographical Maps and Analysis of Changes of the Earth's Magnetic Field in 1995–2005

[26]  Full strength of the main field |F| altered in 1995 from 23,058 to 67,219 nT at the average in reference points of 48,833 nT, in 2000 - from 22,890 to 67,120 nT at the average in reference points of 48,725 nT, and in 2005 - from 22,740 to 67,020 nT at the average in the same points of 48,668 nT. Module of the vertical component |Z| changed in 2000 - from 0 to 66,990 nT at the average in reference points 42,113 nT, in 2005 - from 0 to 66,890 nT at the average in the same points of 42,069 nT. Value of the horizontal component |H| changed in 1995 - from 0 to 41,370 nT at the average in reference points of 16,801 nT, in 2000 - from 0 to 41,370 nT at the average in reference points of 16,801 nT, in 2005 - from 0 to 41,480 nT at the average in the same points of 16,779 nT.

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Figure 9
[27]  Shift |H| for 10 years is shown in Figure 9. Isolines |H| are drawn in 2000 nT from 2000 to 40,000 nT, the isolines of 1000 nT and 500 nT are added to them at the magnetic poles. The apparent shift of isolines |H|, up to 12o (1200 km), related to the western drift, entailing an average shift of the field in longitude 0.9o in 10 years. The adduced data provide the capability of estimating the decrease of average values for reference points in a period of 10 years (Table 1).

[28]  These values are approximately half the known [Sharma, 1989] value of decrease (0.5%) for the main magnetic dipole of the Earth over the same period (about 5% over 100 years). This is explained by the evident relative role of multipoles of higher order of the main field, not displaying any trend towards subsiding [Sharma, 1989]. Due to this reason the results obtained (Table 1) according to the data of 1995-2005 are insufficiently characterizing the specifics of alterations of the Earth's main magnetic field. On the background of the subsiding main dipole the relative role of multipoles of higher order is strengthening. It entails a considerable growth of the relative role of local deviations of the magnetic field. However, the role of multipoles in navigation is irrelevant. Let us mention that the process of decline of the main dipole against the background of multipoles, changing insignificantly, can lead to a considerably more rapid deterioration of orientation based on magnetic navigational systems (due to the growth of the relative role of local deviations of the field's strength), than in the case of the field represented only by the main dipole. For solving tasks of this kind the main magnetic dipole plays a specific part of a "signal'', and the multipoles - a part of "noise'', when a change of the ratio signal/noise is more important than a change of a signal's absolute level.

[29]  For revealing these circumstances the corresponding approximate evaluation of the main field alterations for the period of 10 years is indicative. It can be obtained by subtracting from the field's components of strength in reference points in 1995 the analogical values in the same points in 2005. It would be more correct to make the vector subtraction of the full strength of the main magnetic field, and then examine the components of the difference obtained; hence we confined ourselves to the approximate evaluation, given the preliminary character of the obtained results, applied for a rough evaluation of the value and character of change of the main field. The point is that the single use of two time series doesn't allow us to conclude, whether these alterations would grow in the course of time or reach a certain limit. It's very likely to happen that even three time series would be insufficient, as multipoles create complicated configurations, changing nonlinearly in space. At the present time the data (the Gauss coefficients) are available for evaluating 22 time series, from 1900 to 2005, i.e. in each 5 years. The results of subtracting the analogical values for 2000 in the reference points from the components of the field's strength in the same points for 1995 (the differences) are shown in Figures 10, 11, 12, and 13.

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Figure 10
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Figure 11
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Figure 12
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Figure 13
[30]  Figure 10 shows subsiding |Z| over five years in the territory of Russia by 300 nT and more, Figure 11 - oscillations |H| in the territory of Russia, Figure 12 - subsiding |F| in the territory of Russia and the increase in the territory of the USA, Figure 13 - decline of the average value |F| in the eastern hemisphere and its increase in the western hemisphere.

[31]  As it is clear from these results, the local changes of the main magnetic field over 5 years considerably exceed the average values for the whole globe, represented in Table 1. Furthermore, the average subsiding of the main field in Russia (especially of the full and vertical components) exceeds several times those for the Earth. In order to obtain the relevant evaluation for the territory of Russia we have determined the reference points, located in the territory of this country. The relevant parameters of subsiding of the main field for this region over the last 5 years for |F| were - 0.38% (that is in 3.2 times more, then on average for the entire Earth), for |H| - 0.04%, for |Z| - 0.45% (in 4.3 times more, then on average for the entire Earth).

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Figure 14
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Figure 15
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Figure 16
[32]  The corresponding approximate evaluation of the main filed alterations over 10 years is indicative. It can be obtained by subtracting from the components of the field's strength in reference points in 1995 of analogical values in the same points in 2005. The results of such calculations are shown in Figure 14, 15, 16, and 17.

[33]  The three time series (1995, 2000 and 2005) are obviously insufficient for making a reliable prediction of the prospects of change of the main magnetic field in the near future. Nevertheless these data show the relevant decrease of the field subsiding velocity over the period of 2000-2005 compared to the period 1995-2000. However, it could be not a real phenomenon, but the effect of the ten times increase of accuracy of measuring of coefficients. For a more substantial analysis of dynamics of the geomagnetic field it would be useful to apply the data available since 1900 up to the present time. If the pace of the demonstrated alterations of the main geomagnetic field increase, it might entail serious problems for the country's navigation, based on magnetometry.

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Figure 17
[34]  The comparison of results for Russia and for the whole globe shows that the present situation is inauspicious for Russia - here the main magnetic field subsides several times faster than averagely on Earth. In the United States, for example, over the same period of time the full strength of the magnetic field has increased (Figures 15, 16, and 17).


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Citation: Zhalkovsky, Ye. A. (2008), Chart-making of the Earth's main magnetic field, Russ. J. Earth Sci., 10, ES4003, doi:10.2205/2007ES000258.

Copyright 2008 by the Russian Journal of Earth Sciences

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