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Home , James Clark Ross, North magnetic pole

J. Geomag. Geoelectr., 34, 225-240, 1982

The Magnetic Poles of the Earthy

E. DAWSON and L. R. NEWITT

Division of Geomagnetism, Earth Physics Branch, Energy, Mines and Resources, Ottawa, Ontario, Canada

(Received November 26, 1981)

The motions of the Earth's magnetic dip poles and geomagnetic poles over the past 400 years are investigated. In addition, relations are sought between geomagnetic and virtual geomagnetic poles over historic times. Since 1750, the secular motion of the dip poles along their paths has been counterclock- wise. During this century this secular motion has been directed in a northwest direction with an average velocity of 11km per year for the dip pole and 10km per year for the south dip pole. In 1980, the north dip pole was located at 77.30N and 101.80W in the Canadian Archipelago, and the south dip pole at 65.60S and 139.40E just off mainland . In addition to its secular motion, each dip pole undergoes a diurnal motion caused by ionospheric current systems. This motion, which is clockwise in the north and anticlockwise in the south, may result in a displacement from the unperturbed position of 65km and 30km respectively, on an average disturbed day. The average velocity of the north during this century is N 1km per year in a northwest direction. It is about a magnitude less for the virtual geomagnetic pole. Both the geomagnetic and virtual geomagnetic pole paths display a clockwise rotation. There is a great deal of uncertainty in our attempt to use virtual geomagnetic poles to extend the geomagnetic pole path back in time to 7500 B. C. Much of this uncertainty is due to the sparse distribution of archeomagnetic measurements at a given epoch.

1. Introduction

Commander was the first to take magnetic measurements specifically to determine the position of the magnetic dip poles. It is just over 150 years since he first reached the on Cape Adelaide, on June 1, 1831. To mark the anniversary, the motions of the earth's magnetic dip poles and geomagnetic poles over the past 400 years are investigated. The predominantly dipolar geomagnetic field is approximated by an axial whose axis is coincident with the earth's rotational axis. In a spherical harmonic representation of the field, this simple model corresponds to the first term. This geocentric model, whose poles coincide with the geographic poles, is successfully used by paleomagne- ticians. A better approximation is that of a geocentric dipole inclined at 11.20 to the earth's axis of rotation. Its axis presently intersects the earth's surface at 78.80N and 70.90W, in northwest , and 78.80S and 109.10E in Antarctica. These points are called

Contribution of the Earth Physics Branch No. 1013.

225 226 E. DAWSON and L. R. NEWITT geomagnetic poles. This model is represented by the first three terms of a spherical harmonic expression of the field. The observed main field of the earth is comprised of a nondipole portion superimposed on the dipole field. The nondipole field is represented by the higher order harmonics in a spherical harmonic representation. The two magnetic poles of the observed field, the magnetic dip poles, are located where magnetic dip or inclination is +900. In 1980 the north magnetic dip pole was located at 77.30N and 101.80W in the Canadian Archipelago, and the south magnetic dip pole at 65.60S and 139.40E, just off mainland Antarctica. Archeomagnetic and paleomagnetic studies use the concept of a virtual geomagnetic pole (VGP). Geologically speaking, it is calculated for an instant in time and is related to the inclined geocentric dipole, (IRVING, 1964). By applying paleomagnetic techniques for determining (D) and magnetic inclination (I) to archeological artifacts such as pottery, bricks and kilns, VGP's have been determined for historic and pre- historic times. In addition to investigating the motions of the poles, relations will be sought between geomagnetic poles and virtual geomagnetic poles over historic times. It is hoped that a study of these past motions may lead to better predictions of future movements and assist in unravelling the complexities of the magnetic field in polar regions.

2. The Field over the Two Polar Areas

MCDONALD and GUNST (1968) have shown that the geomagnetic field is asymmetric with the southern hemisphere predominating. This hemispherical asymmetry appears to be increasing as the geomagnetic moment decreases. This asymmetry is readily displayed by the main field configuration in the two polar areas. In the , the location of the total force (F) maximum, 70,000 nT, coincides almost exactly with the south magnetic dip pole. Here, as noted by NAGATA(1964), the dipole field is regionally intensified by almost 10 %. In the , the north magnetic dip pole is over 2,000km north of the total force maximum. At this dip pole, F, 58,000 nT, is about 10% less than the dipole field value. The regional field is enhanced in central Canada and where the two northern total force maxima, N 62,000 nT, are located. This nondipolar behaviour of the Arctic main field is reflected in the unique elongated pattern of the horizontal force (H) and in the restricted secular path of the north magnetic dip pole shown in Fig. 1. Although there is a general tendency for F to decrease world-wide, as represented by the north dip pole area. He interpreted this as due to a northward shift of the earth's decreasing 25 nT per year in the south dip pole area, it was increasing 50 nT per year in the north dip pole area. He interpreted this as due to a northward shift of the earth's magnetic dipole. Examination of recent secular change in F for 1980 at Resolute Bay magnetic observatory, 290 km south of the north dip pole, and at Dumont d'Urville, 120km south of the south dip pole, shows that while F is now slightly decreasing in the north, and decreasing as much as 80 nT per year at the south dip pole, the overall secular change difference between the two remains about the same. There is some evidence from plots of isoporic foci affecting the Canadian secular variation pattern (DAWSON and NEWITT, 1978a) that at least part of the change in the north is due to changes in the nondipole field. The Magnetic Poles of the Earth 227

Fig. 1. (a) The secular path of the north magnetic dip pole. (b) The secular path of the south magnetic dip pole. Numbered triangles denote observed positions listed in Table 1. Dots denote positions calculated from a least squares fit to positions listed in Table 2. Dashed lines depict periods of uncertain pole positions.

3. Motion of the Magnetic Dip Poles

3.1 Observed coordinates of the dip poles KNAPP (1969)lists 47 published positions for the Antarctic dip pole from 1642 to 1965. Many of these are re-determinations of original positions by other authors, or positions scaled from maps, or positions based on spherical harmonic models of the field. Table 1 shows a compilation of 15 positions for both dip poles based on the original observations of the observers and published by them or their immediate scientific authority.

3.2 Computed coordinates of the dip poles For the period 1550 to 1970, BARRACLOUGH (1978) lists the coefficients of 252 spherical harmonic models normalized, where necessary, to the Schmidt quasi-normalized form, expressed in nT. By adding 12 recent world magnetic models, we extended this time period to 1980. To reduce objectively the number of models to a manageable size and permit the computation of reasonably accurate pole positions, coefficients were meaned to obtain an average spherical harmonic model (ASHM) for each epoch. Only models with at least a maximum degree (NMAX) of 4 were used. In a few cases, NMAX was arbitrarily restricted to 12 on averaging. This assumes that since the field contributions of the higher terms are small, no significant change is made in a computed dip pole position by ignoring these terms. Coefficients differing from the mean value by at least 2 standard deviations were rejected and the mean re-computed. Altogether 27 spherical harmonic models were 228 E. DAWSON and L. R. NEWITT

Table 1(a). Coordinates of the north magnetic dip pole.

Table 1(b). Coordinates of the south magnetic dip pole.

rejected. The earth shape adopted for each ASHM, oblate or spherical, was based on the shape of the majority of the models determining the average. Dip pole positions were determined iteratively from an approximate pole position To minimize computing time, a search was made, not for the location of H=0 nT but for H<10 nT in the north and H<20 nT in the south. A larger allowance was made for the south owing to the larger field gradients in the area of the south dip pole. Tests show that these assumptions introduce positional errors of less than 12km in the computed pole positions. Table 2 lists the coordinates of the dip poles computed from: ASHM's, where n is the number of models used to determine the average and NMAX is the maximum degree of the ASHM. A comparison between the observed and computed dip pole coordinates shows that there is a tendency for model values to be north and west of the observed coordinates by, in general, 10, and at least double this in the south dip pole longitude.

3.3 The secular motion of the dip poles SV causes a slow drift with time in the position of the dip poles. This secular motion was determined analytically by fitting polynomials in time, from degree 1 to 3, to weighted dip pole coordinates. The observed pole positions (Table 1) were weighted as follows. Pole positions based on magnetic measurements not reduced to a daily mean value were arbitrarily assigned a weight of 1. Positions reduced to a yearly mean value were given a The Magnetic Poles of the Earth 229

Table 2. Computed coordinates of the dip poles.

weight of 40. The average weight for observed positions was 14. Computed pole positions (Table 2) were weighted as forllows:

WT=n-edt1T.N/12 (1) where n=the number of models determining the ASHM, dt=t-1980 where t is the epoch of the ASHM, T=430 (in years), the totallength of the period under investigation, N=NMAX, arbitrarily restricted to 12. Weights for the ASHM ranged from 0.6 to 35.9 with the average being 4.6. The standard error of these fits are listed in Table 3. Plots of the secular motion of the dip poles were derived from these polynomials. The cubic fit to the north dip pole coordinates (Fig. 1a) and the quadratic fit to the south dip pole coordinates (Fig. 1b) are representative of these plots. It should be noted that these polar motions are a consequence and not a cause of secular variation. The north dip pole appeared to reach its most southerly position after 1850. There is some independent 230 E. DAwsoN and L. R. NEWITT

Table 3. Standard error in analytic fits to dip pole coordinates (in degrees).

evidence to confirm this. MAYAUD (1953) obtained a position of 69005'N and 97005'W for 1842, south of Ross' 1831 position, from a re-examination of some early polar magnetic observations. HOPE (1957b) from examining the secular change work of BAUER (1895) concluded that the north dip pole probably reached the most southerly point of its path in the middle of the last century. Although the overall paths are strikingly different, during this century the motions along their paths have been remarkably similar. From 1900 to 1980, the average northward motion of the north dip pole was 0.080 per year and for the south dip pole 0.070 per year. During this period, both poles moved westward 0.10 per year on the average. More detail on their secular motion was obtained by determining their average velocity over 50 year periods starting at 1550, from the analytical fits to the dip pole coordinates using Eq. (2):

cosd=(cos-B1)cos(-9a)+sin1-B1sin-02cos(21-22) (2) where 0, 21 are the geographic coordinates of a pole, and 02, 22 are its coordinates 50 years later. Positions for year 2000 were extrapolated from the analytical expressions used in deriving Fig. 1. Table 4 lists the results. While there is some scepticism attached to the velocities shown for the early years, it

Table 4. Average velocity of recent pole migration (Directed along the pole paths shown in Fig. 1).

*Extrapolated The Magnetic Poles of the Earth 231 would appear that the average velocities of both poles are increasing and will continue to increase. The striking differences in the overall patterns of the north and paths (Fig. 1) are probably a manifestation of the local nondipole field. The precession of the north dip pole is counterclockwise and appears to be constrained, while that of the south dip pole appears to be clockwise and unconstrained. The precessional differences are probably due to the unreliability of the early S. H. models. One may infer that the south dip pole precession, from 1750 on, like that of the north dip pole, is also counterclockwise. Most authorities like WHITHAM et al. (1960), ALLDREDGE and VAN VOORHIS (1962) and MCDONALD and GUNST (1968) ascribe the restrictive secular motion of the north dip pole to constraints imposed by non-dipole sources within the earth's core. The present secular motion of the dip poles may be estimated from the field gradients and the secular change of the horizontal components X(north) and Y(east) in the pole areas. From the time of Amundsen's pole determination in 1904, the north dip pole has averaged 10km per year north and 3 km per year west. DAWSON and NE WITT (1978b) estimated the gradients in the dip pole area of 2.3 nT per km in X and 5.8 nT per km in Y. The annual mean values at Resolute Bay magnetic observatory indicate that, for 1980, the secular change is 36 nT per year in X and -15 nT per year in Y. These values indicate that the present motion is considerably faster than average. For 1980, the northward motion of the north dip pole is 24km per year and its westward motion is 8km per year. From the time of Webb's pole determination in 1912, the south dip pole has averaged 9km per year north and 7km per year west. From the world magnetic field model for 1975 by PEDDLE and FABIANO (1976), gradient estimates in the south dip pole area are 6.8 nT per km in X and 6.2 nT per km in Y. Annual mean values at Dumont d'Urville magnetic observatory show that for 1980 the secular change is -44 nT per year in X and -8 nT per year in Y. These values indicate that the present northward motion of the south magnetic dip pole is 8km per year which is close to its average value for this century but considerably slower than the present northward motion of the north dip pole. Its westward motion is 4km per year only. The uncertainty in the determination of the dip pole motions for 1980 is indicated by the fact that our values are, on the average, about 4 km per year larger than those determined by BARKERet al. (1981). Also, their results indicate a slight easterly motion of the south dip pole.

3.4 Present daily motion In addition to their secular motion, the dip poles undergo more rapid daily changes of position owing to the effect of ionospheric current systems. Daily changes in position may be estimated from the diurnal field changes and the field gradients in the pole areas in a manner analogous to that used above. Figure 2(a) shows the average daily paths of the north dip pole for magnetically quiet and magnetically disturbed days in 1975. These were derived using differences between the yearly mean and hourly mean values of X and Y at Resolute Bay observatory averaged for international quiet and international disturbed days. Similar paths were determined for the south dip pole (Fig. 2b) using published diurnal inequalities for 1975 for Dumont d'Urville. There are certain similarities between the diurnal paths of the two dip poles. Both paths are crudely elliptical. Their major axes point approximately in the direction of the 232 E. DAWSON and L. R. NEWITT

Fig. 2. (a) The diurnal path of the north magnetic dip pole in 1975. (b) The diurnal path of the south magnetic dip pole in 1975. Q denotes the average quiet day path (-)D denotes the average disturbed day path (o) Hours of Universal Time are indicated.

present secular motion of their respective poles. Dissimilaritiesare due mainly to differencesin the field gradients between the two polar areas, although a part may be due to currents induced in the solid earth by ionospheric currents. The directions of the daily paths vary, being clockwise in the north and anticlockwisein the south. On an averagedisturbed day, ionosphericcurrents may displacethe north dip pole as much as 65km and the south dip pole as much as 30km from their unperturbed positions, and 2 or 3 times these distances on a severelydisturbed day.

4. Motion of Geomagnetic and Virtual GeomagneticPoles

4.1 Coordinatesof geomagneticpoles For many geophysicalstudies, the geomagneticpoles and VGP's are more significant than dip poles. Positions of the north geomagneticpole (NGP) were derived from the first three coefficientsof each ASHM using Eqs. (3) and (4)

Latitude north, oN=tan-1(-g0/(g1)2+(hi)2) (3)

Longitude west, rw=-tan-1(h1/g1). (4) The Magnetic Poles of the Earth 233

These coordinates are listed in Table 5. These results illustrate the well-known constancy of the polar angle of the geomagnetic axis during recent years. From 1750 on, the average tilt is 11.40+0.40 comparable to the 11.490 average determined by MCDONALD and GUNST (1967) for approximately the same period. This indicates that at least the first degree terms of the ASHM's are fairly reliable back to 1750, in contrast to the higher order terms which, from the dip pole results, seem only reliable back to around 1852.

4.2 Recent secular motion of the NGP To determine the smooth secular path of the NGP with time, polynomials, from degree 1 to 3, were fitted to the NGP coordinates listed in Table 4. These data were weighted using a modified version of the weighting formula (Eq. (1)) with the term N/12 deleted. The standard errors of the quadratic and cubic fits rounded off to 1 decimal were similar, being 0.20 in latitude and 1.30 in longitude. The scatter in the linear fit was more than double these values. Figure 3 shows the secular path of the NGP derived from the quadratic fit, and analytically extrapolated to year 2000. The clockwise precession of the NGP is quite distinct from the counter-clockwise rotation of the north dip pole (Fig. 1). The pole path prior to 1750 is highly questionable. Our calculations of the drift of the NGP are listed with those of other authors in Table 6. All results have been rounded off to 2 decimal places. T is the apparent rotation period of the geomagnetic pole around the geographic pole, based on its average westward drift.

4.3 Coordinates of virtual geomagnetic poles Given the angular measurements (D,I) of the magnetic field at a point, the position of a geocentric dipole pole consistent with the observed direction may be found. This pole, calculated for an instant of time geologically speaking, is called a virtual geomagnetic pole (VGP).

Table 5. Coordinates of the north geomagnetic pole. 234 E. DAWSON and L. R. NEWITT

Fig. 3. Average secular paths of the north geomagnetic pole and the virtual geomagnetic pole. Circles denote the north geomagnetic pole positions and dots the virtual geomagnetic pole positions, both derived from a quadratic least squares analysis. Dashed lines depict periods of uncertain pole positions.

Averages of VGP's tend to group either around the geographic pole or the geomagnetic pole depending on the time scale involved. For example, VGP's calculated from averages of paleomagnetic directions tend to group around the geographic pole. Here it is assumed that by averaging the field over thousands of years the secular variation has been averaged out. VGP's averaged over a shorter time scale tend to group around the geomagnetic pole. Any attempt to use VGP's to extend the secular motion of the NGP back in time, has, for conformity, to use the latter class of VGP's only. VGP's determined from archeomag- netic measurements fall into this category. Cox (1962) in his analysis of the present geomagnetic field, has shown that there is good agreement between the geomagnetic pole found from spherical harmonic analysis and one determined from a weighted global

Table 6. Drift of the north geomagnetic pole. The Magnetic Poles of the Earth 235 average of VGP's. Here it is assumed that the scatter of the VGP positions from the mean is a measure of the effect of the nondipole field. In using archeologically-determined VGP's, averaging positions for similar epochs should minimize this error. A list of 81 VGP positions (Table 7) was compiled from recent publications by OZIMA

Table 7. List of average virtual geomagnetic pole positions.

OA, OZIMA and AOKI (1972); B, BARBETTI (1977); K, KOVACHEVA (1980). *From a summary of all published archeomagnetic data for period 950 AD to 1450 AD (BARBETTI, 1977). 236 E. DAWSON and L. R. NEWITT

and AOKI (1972), BARBETTI (1977), and KOVACHBVA (1980). These positions were derived from samples from baked earth, ancient ovens, bricks, aboriginal fireplaces and burnt tree stumps from over 300 sites in such widely-spaced areas as Japan, southeastern Australia and southeastern Europe. The list also includes mean VGP positions from a summary of all published archeomagnetic data for the period 950 AD. to 1450 A. D. by BARBETTI (1977). Certain liberties were taken with these published results. Where the authors have expressed the date or age of a sample or samples within certain limits, generally 100 years, we have arbitrarily used the centre of the interval as the date. B. C. dates are shown with a negative sign. Where necessary, longitudes were converted to east. N is the number of samples or measurements of D and I used in determining the mean VGP positions. a95 is a measure of the group dispersion (FISHER, 1953).

4.4 Migration of virtual geomagnetic poles during historic and pre-historic times Published virtual pole position paths over archeological time scales such as by KAWAI et al. (1965), NODIA and CHELIDLE (1972) or, more recently, by KOVACHEVA (1980) and BUCHA (1980) arequite complex. The path complexity, reflecting clockwise and counter- clockwise motions, has been attributed to nondipole field contributions, a wobbling dipole field and sporadic coverage of archeological sites. Undoubtedly errors in the data also contribute to the apparent complexity of these paths. According to Cox and DOELL (1964), the westward drift of the nondipole field produces field variations with overlapping periods in the range of 150 to 1,000 years depending on the extent of the individual feature. Periods of growth and decay of maximum features of the nondipole field are estimated to have the same time range. They indicate it takes periods of the order of 104 years or more before changes in the orientation and intensity of the main inclined dipole appear to make significant contributions to the geomagnetic spectrum. This is roughly confirmed by the apparent periods of orientation of the inclined dipole shown in Table 6. It seems reasonable that using 1,000 year means of the VGP data in Table 5 should minimize at least part of the nondipole field contributions to these pole paths. Figure 4 shows the pole path plotted from running mean determinations of 1000 years. Obviously, it is quite complicated with clockwise and anticlockwise components. Despite the complexity of the pole path, a rigorous statistical F -test (IRVING, 1964) performed on the 1,000 year running means indicates that, at the 95% confidence level, these means cannot be considered identical and that a real movement has taken place. More plots (not shown) were made to try to reduce nondipole field complications by using running means of 2,000, 3,000, and 4,000 years. The pole path convolutions were reduced as the mean time span increased, with a gradual centering of the VGP pole path around the geographic pole. To determine a smooth, averaged VGP path for historic and pre-historic times consistent with the geomagnetic pole path for recent times, polynomials in time were fitted to the VGP data analogous to the approach used in determining the smooth north geomagnetic pole path in Fig. 3. Owing to the broad range of VGP longitude coordinates and to the convergence of longitude at the geographic pole, the analyses were performed using polar stereographic coordinates. Data were weighted according to the group dispersion of the pole position, WT=1/a95. Where no a95 is listed in Table 7, a weight of 1/20 was arbitrarily assigned. Although smooth plots were obtained from both quadratic and cubic polynomials, only the quadratic plot showed an apparent similarity to the The Magnetic Poles of the Earth 237

Fig. 4. Secular path of the average virtual geomagnetic pole, based on 1,000-year running means. Dates are expressed in 1,000's of years, before present.

' observed' path of the north geomagnetic pole. This comparison is shown in Fig. 3. Despite the apparent similarity in these paths, a comparison of velocities along them reveals a basic uncertainty in this picture. Average velocities were computed at 500 year intervals for the VGP path and 50 year intervals for the NGP path using Eq. (2) in the manner outlined earlier. Over the past 500 years, the average velocity of the NGP along its path is 2.8km per year. Over the same period, the average velocity of the VGP is about one magnitude less. In fact, its velocity over the entire historic and pre-historic period, as represented by the quadratic time model, is remarkably constant. For comparison, over the past 500 years the north dip pole has averaged 6km per year and the south dip pole 4.8km per year along their respective paths. The apparent period of the smooth VGP path is around 14,000 years compared to 3,000 years for the geomagnetic pole period based on data with a much shorter time base.

5. The Earth's Magnetic Poles During a Period of Geomagnetic Instability

It is well-known that changes are occurring in the distribution of the earth's magnetic energy. MCDONALD and GUNST (1967) and VEROSUB and Cox (1971) have shown that most of the energy lost by the dipole field is gained by the nondipole field. It is interesting to speculate on the displacement of the Earth's magnetic poles during the next period of geomagnetic instability if the enhancement of the nondipole field strength continues at the expense of a declining dipole field. 238 E. DAWSON and L. R. NEWITT

A coarse estimate of the next period of geomagnetic instability was made following the method of VEROSUB and Cox (1971). Dipole (UD) and nondipole (UND) energyvalues were computed from 33 ASHM's with an NMAX>6 for the period 1550 to 1980. Linear polynomials in time, fitted to weighted values of UD and UND,were used to reject energy values which differed from the polynomial value by at least two standard deviations. The weighting followed the procedure outlined earlier using Eq. (1). The final fits were made to 25 ASHM covering the period 1780 to 1980. The results, expressed in Eqs. (5) and (6), are in units of 1017joules. The standard error of the dipole and nondipole models are 0.452 and 0.653 units respectively. T is the year.

Dipole UD=150.364-.051T (5)

Nondipole UND=-64.935+.040T (6)

These results, covering the past 200 years, are very similar to those of VEROSUBand Cox (1971) for a 120 year period, with the dipole energy decreasing at a rate of 5.1x1015 joules per year and -78% of it appearing in the nondipole field. From Eqs. (5) and (6), UD =UND in 2370 A. D., and UD=0 in 2950 AD. It appears that a period of magnetic instability could occur between years 2370 and 2950 A. D. if the present trend continues. During the period of geomagnetic instability, the dominant imprint of the dipole field will vanish and the definition of a dipole pole at the earth's surface will become meaningless. Noting that at the dip poles the dipole and nondipole values of H cancel out, it is highly probable that during this period of instability more than one area will occur where these conditions for defining a dip pole will be met.

6. Conclusions

The motions of the dip poles and geomagnetic poles over the past 400 years have been investigated. Since at least 1850, the predominant secular motion of both dip poles has been northward. This runs counter to motions generally associated with secular variation, namely the westward drift of gross features of the field. Since 1750, the precession of the dip poles is counterclockwise. The geomagnetic and virtual geomagnetic pole paths display a clockwise rotation. During this period there is a considerable velocity contrast among these poles. The velocities of the dip poles along their paths average 7km per year, more than double that shown by the north geomagnetic pole and at least a magnitude greater than that displayed by the VGP. There is a great deal of uncertainty in our attempt to use VGP to extend the geomagnetic pole path back in time. Some of this uncertainty is probably due to errors in the archeomagnetic measurements and errors in dating the magnetizations. However the biggest uncertainty is undoubtedly due to the sparse distribution of archeomagnetic measurements at a given epoch. Although Cox (1962) showed that the mean position of a worldwide uniform distribution of VGP is close to the geomagnetic pole position, this was derived from weighted model values for one epoch. To at least partially solve the question of the fundamental periods associated with dipole field variations, an enlarged compilation of VGP positions, with subsets from a wider range of countries, is necessary. Finally regarding the future movements of poles, if they continue on their present The Magnetic Poles of the Earth 239 paths, their projected positions for the year 2000 are (1) north dip pole 80.80N, 109.50W, in the (2) south dip pole 64.10S, 137.90E, in the Indian Ocean (3) north geomagnetic pole 78.90N, 70.00W, in Kane Basin.

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