U.S. GEOLOGICAL SURVEY CIRCULAR 1039 

Magnetic Models for the 

United States for 1985 
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Magnetic Models for the 

United States for 1985 

By NORMAN W. PEDDIE and AUDRONIS K. ZUNDE 

U.S. GEOLOGICAL SURVEY CIRCULAR 1039 
DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade, product, or firm names in this publication is for descriptive 

purposes only and does not imply endorsement by the U.S. Government. 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1990 

For sale by the 

Books and Open-File Reports Section 

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Box 25425 

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Library of Congress Cataloging-in-Publication Data 

Peddie, Norman W. 

Magnetic models for the United States for 1985 I by Norman W. Peddie and 

Audronis K. Zunde. 

p. em. - (U.S. Geological Survey circular; 1039) 

Includes bibliographical references. 

Supt. of Docs. no.: I 19.4/2:1039 

1. Geomagnetism-United States-Mathematical models. 

2. Geomagnetism-Maps-Methodology. I. Zunde, Audronis K. 

II. Title Ill. Series. 

QC825.1.P39 1990 

[538'.7873'01 '5118-dc] 89-600270 

CIP 
CONTENTS 

Abstract 1 

Introduction 1 

Acknowledgment 2 

1985.0 models 2 

Secular-variation models 3 

Coefficients 4 

Charts and "GEOMAG" 4 

References cited 5 

Appendix 24 

FIGURES 

1. Graph showing magnetic declination recorded at the Tucson (Arizona) 

Magnetic Observatory since 1910 1 

2. Map showing the three regions for which 1985.0 models were derived, 

regions shown on U.S. magnetic charts, and locations of the magnetic 

observatories, repeat stations, and fill-in values used to derive the secularvariation models 3 

3-11. Maps showing locations of measurements and model values (fig. 11) used 

to derive the 1985.0 models: 

3. Land survey 8 

4. Marine-survey vector 9 

5. Marine-survey total intensity 10 

6. Pre-1975 Project MAGNET aerial-survey vector 11 

7. Aerial-survey vector (other than Project MAGNET) 12 

8. 1976-1977 Project MAGNET aerial-survey total intensity 13 

9. 1980-1983 Project MAGNET aerial-survey vector 14 

10. Canadian aerial-survey vector 15 

11. International Geomagnetic Reference Field 1985 vector values 16 

12-18. Small-scale magnetic charts for the United States, 1985: 

12. Declination 17 

13. Inclination 18 

14. Horizontal intensity 19 

15. North component 20 

16. East component 21 

17. Vertical intensity 22 

18. Total intensity 23 

TABLES 

1. Boundaries of the modeled regions 2 

2. Overall root-mean-square residual 3 

3. Spherical harmonic coefficients 4 

Contents Ill 

Magnetic Models for the United States for 1985 

By Norman W. Peddie and Audronis K. Zunde 

Abstract 

New models describing the magnetic field in the United 

States at the beginning of 1985 and the rate of change 

expected during the next few years have been developed. 

The models-which will serve as the basis for a new set of 

magnetic charts-were derived from several tens of 

thousands of original field measurements from land, marine, 

and aerial surveys; from values derived from the MAGSATbased International Geomagnetic Reference Field; and from 

. recent data from magnetic observatories and repeat stations. 

They are in the form of spherical harmonic series that 

represent the scalar magnetic potential from which all the 

field components can be derived. The models for the 

conterminous States and Alaska are of maximum degree 

and order 4 (24 coefficients each) and the models for Hawaii 

are of maximum degree and order 2 (8 coefficients each). 

INTRODUCTION 

We developed a set of five new models of the 

magnetic field in the United States that describe the 

direction and intensity of the field at 1985.0 (that is, the 

beginning of 1985) and the annual change expected 

during the next few years. They form the basis of a new 

set of magnetic charts (Peddie and Zunde, 1988a, b, c, d, 

e) that replace those of Fabiano and Jones (1976), 

Peddie and others (1976), Jones and Fabiano (1976), and 

Fabiano and Peddie (1980, 1981). Three of the models 

describe the 1985.0 field in the conterminous ( 48) States, 

Alaska, and Hawaii-the three regions shown in separate 

plates on the charts. The other two models describe 

annual change-one for the conterminous States and 

Alaska and the other for Hawaii. This report describes 

the development of the models and includes the model 

coefficients and simplified small-scale charts. 

Revision of magnetic models and charts is 

necessary because the geomagnetic field undergoes 

continual change, called secular variation, that is 

commonly irregular and not yet predictable. The 

Manuscript approved for publication June 27, 1989. 

14.5 

14.0 

13.5 

. .-..... .. · ............. .. . . . . · ·. ~ 

. . ..... 

13.0 

12.5 

12.0 

..... .. .. 

···· ... . 

. . . . . . ... 

1!.5-1--~--.---,-------,-----,---,----,------,,---------, 

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 

Year 

Figure 1. Magnetic declination recorded at the Tucson 

(Arizona) Magnetic Observatory since 1910. 

magnetic declination (D ) recorded at the Tucson 

(Arizona) Magnetic Observatory since 1910 is shown in 

figure 1 and illustrates the irregularity of the secular 

variation. New magnetic charts for the United States 

have been issued since the mid-1800's, normally at 

intervals of 5 or 10 years. Production of associated 

mathematical models began in 1965. Deel and Howe 

(1948) and Svendsen (1962) have given brief histories of 

the U.S. magnetic charts. The development of the 1975 

models was described by Fabiano and others (1979), and 

the 1980 total-intensity (F) models by Fabiano and 

others (1987). 

The new models were derived by ordinary spherical 

harmonic analysis (SHA), a method commonly used for 

modeling the global field. They represent the scalar 

magnetic potential as a series of 3-dimensional spherical 

harmonics, from which the field components are derived 

by differentiation. The earlier U.S. models were derived 

by polynomial analysis and represented the field 

elements themselves as polynomial functions of latitude 

and longitude. 

The new method has some advantages over the 

older one. For example, now all the field elements are 

represented by one set of coefficients and the elements 

Introduction 
are mutually consistent. The model field now varies with 

elevation in a way that is consistent with observation and 

theory, and, like the real field, it is curl-free. The new 

models are compatible with widely available programs 

used for generating field values from global spherical 

harmonic models, such as those of the International 

Geomagnetic Reference Field (IGRF). 

Before deciding to use SHA we considered two 

other methods: magnetic dipole analysis and spherical 

cap harmonic analysis (Haines, 1985). We tested the 

former method by fitting grids of dipoles, with unconstrained magnetic moment, to the Hawaii data using a 

nonlinear least-squares technique. We found that the fit 

did not match that achievable with SHA (using a 

comparable number of coefficients) and that it improved 

as the depth of the dipoles was increased, (thus making 

the set of dipoles more like the multipoles of SHA). The 

latter method, as presently implemented, could not be 

applied iteratively and thus would not have allowed us to 

utilize the many D- and F-only measurements, and, as it 

requires removal and later addition of a global field, it 

seemed less efficient than ordinary SHA (L.R. Alldredge, oral commun., 1986). 

Acknowledgment 

We thank Susan McLean of the National Geophysical Data Center in Boulder, Colorado, for providing the 

1980-1983 Project MAGNET data and for helping us to 

update our repeat station data file. 

1985.0 MODELS 

The three models of the field at 1985.0 were 

derived from data selected from the three regions whose 

boundaries are given in table 1 and indicated by the 

heavier lines in figure 2 (the lighter lines indicate the 

regions actually shown on the charts). Data were taken 

from the following sets (figs. 3-11, which relate to these 

sets, follow "References Cited"): 

Table 1. Boundaries of the regions for which data were 

selected and 1985.0 models derived 

North latitude 

(degrees) 

South North 

Conterminous States-- 20 

Alaska--------------- 42 

Hawaii------------··- 17 

54 

74 

24 

East longitude 

(degrees) 

West East 

229 

160 

198 

299 

236 

207 

2 Magnetic Models for the United States for 1985 

Magnetic field sUJvey data (National Geophysical 

Data Center, 1984, p. 8).-This set comprises several 

hundred thousand measurements taken on land, sea, and 

in the air since 1900. We used a subset, created in 1975 

for the development of the global model A WC/75 (Peddie and Fabiano, 1976), consisting of all records dated 

1939.0 or later that include values of either D, or F, or the 

X (north), Y (east), and Z (vertical) field components. 

These measurements were already adjusted for the 

secular variation between the measurement date and 

1975.0. The measurement locations are in five classes 

(figs. 3-7): land survey, marine-survey vector, marinesurvey total intensity, pre-1975 Project MAGNETsurvey vector, and non-Project MAGNET aerial-survey 

vector. 

Field intensity measurements from the 1976-1977 

Project MAGNET aerial sUJvey of the conterminous 

United States (National Geophysical Data Center, 1984, 

p. 10).-The survey comprised 44 north-south and 7 

east -west lines flown at an altitude of 600 meters over flat 

land and 1220 meters over mountainous areas (see 

fig. 8). 

Field vector measurements from 1980-1983 Project 

MAGNET aerial sUJveys (National Geophysical Data 

Center, 1984, p. 10).-Although these were not intended 

primarily as surveys of the United States, they did 

produce some measurements in the chart regions (see 

fig. 9). 

X, Y, and Z aeromagnetic data for Canada (L.R. 

Newitt, unpub. data).-These data were especially useful 

for promoting agreement with the charts of Canada (see 

fig. 10). 

Magnetic obselVatory and repeat station values for 

1985.0.-These values were derived by linear 

extrapolation of recent observatory annual means and 

repeat station measurements (see fig. 2). 

The great number of original Project MAGNET 

measurements was reduced by retaining only every 50th 

intensity measurement and every 25th vector 

measurement. Of these we used only those taken when 

Kp (a geomagnetic disturbance index) was less than 3. To 

fill gaps in the coverage we included values computed 

from the International Geomagnetic Reference Field 

(IGRF) 1985 main-field model (International 

Association of Geomagnetism and Aeronomy, Division 

I, Working Group 1, 1986), a global model based mainly 

on data from the MAG SAT satellite survey of 1979-1980 

(Langel and others, 1982). These were computed for a 

grid of points at 500-kilometer altitude and spaced one 

degree in latitude and longitude (see fig. 11). 

The data were analyzed using the method of 

iterative SHA (for example, Cain and others, 1965). The 

resulting overall root-mean-square residuals, for 

maximum degree and order (n *) ranging from 1 to 5 for 

the conterminous States and Alaska and from 1 to 3 for 
30° N ao• N go• N go• N ao• N 30° N 

o• 

. ,r.· . . : 

e Observatory 

• Repeat Station 

· • Fill-in Value 

tao• w 150° w 

Figure 2. Map showing the three regions for which 1985.0 models were derived (heavy boundary lines), and the regions 

actually shown on the 1985 U.S. magnetic charts (light boundary lines). Also shown are the locations of the magnetic 

observatories (solid circles) and repeat stations (solid squares) whose data, along with fill-in values (solid triangles), were 

used to derive the secular-variation models. 

Hawaii, are shown in table 2. For the chart compilation 

we chose the models for the conterminous States and 

Alaska of n * = 4 (24 coefficients each) and for Hawaii of 

n* = 2 (8 coefficients) because they are the simplest of 

the models that adequately represent the data. 

Table 2. Overall root-mean-square residual 

[Units, nanotesla; n*, maximum degree and order; cont., 

conterminous. Leaders(---) indicate that value was not computed] 

n* 

1 

2 

3 

4 

5 

Cont. 

States 

1582 

403 

211 

176 

174 

Alaska 

1554 

547 

281 

154 

153 

Hawaii 

277 

197 

193 

SECULAR-VARIATION MODELS 

The two secular-variation models were derived by 

the same method. The model for the conterminous States 

and Alaska was derived from estimates of the rates of 

change of the X, Y, and Z components at 30 magnetic 

observatories and 50 repeat stations and, for six locations 

far from the observatories and repeat stations, fill-in 

values computed from global secular-variation model 

USGS85S (Peddie and Zunde, 1987) (see fig. 2). The 

estimates were taken as the slopes of straight lines fitted 

by least-squares to recent data. We used the latest four or 

five observatory annual means, mostly for years from 

1981 to 1985, and the latest two or three sets of repeatstation measurements. Because observatory-based rates 

are more accurate, we gave them triple weight. The 

model for Hawaii was derived from grid values computed 

from this model along with rates estimates for the 

Honolulu observatory. The data used to derive the 

secular-variation models are given in the appendix. 

Secular-Variation Models 3 
COEFFICIENTS 

The coefficients of the five models, in the Schmidt 

quasi-normalized form (Chapman and Bartels, 1940) 

and referring to a sphere of radius 6371.2 km, are listed 

in table 3. The models are not considered valid for points 

outside the regions specified in table 1. They can be used 

with programs that synthesize field values from global 

spherical harmonic models, such as those of the IGRF. A 

suitable program can be obtained from the National 

Geophysical Data Center, NOAA, Code E/GC4/FLI, 

325 Broadway, Boulder, CO 80303. 

CHARTS AND "GEOMAG" 

The five new charts based on these models depict 

the declination, inclination (I), horizontal intensity (H), 

vertical intensity, and total intensity and their expected 

rates of change (Peddie and Zunde, 1988a, b, c, d, e). The 

Table 3. Spherical harmonic coefficients (gs and h's) of the 1985 models 

[Cont., conterminous; n, degree; m, order; nT, nanotesla; nT/yr, nanotesla per year. Leaders ( ---) indicate 

coefficients that were not determined] 

1985.0 field Annual change 

(nT) (nT/yr) 

Cont. 

Cont. States; 

n ill States Alaska Hawaii Alaska Hawaii 

.& 1 0 -28004 -27446 -36259 78.0 33.6 

,g 1 1 1186 -1853 -5785 34.5 0.7 

h 1 1 6036 1749 5497 -0.9 7.6 

,g 2 0 -6761 -5178 3784 -101.8 -17.3 

,g 2 1 118 6617 -2557 12.0 7.2 

h 2 1 -2379 5820 108 4.3 1.8 

g 2 2 3459 6134 -2086 3.4 -12.4 

h 2 2 4617 -859 97 29.0 20.6 

g 3 0 6566 1011 48.6 

,g 3 1 -3156 -8553 -38.4 

h 3 1 -1502 -6076 -30.8 

,g 3 2 -587 -6470 -4.3 

h 3 2 -4175 2073 -16.0 

g 3 3 -1335 -1667 -12.9 

h 3 3 1321 -1673 4.0 

g 4 0 -691 2080 -3.8 

g 4 1 2267 4087 13.3 

h 4 1 2034 1317 20.5 

e 4 2 771 4124 -8.7 

h 4 2 625 -1002 0.3 

,g 4 3 405 -374 -7.0 

h 4 3 -1417 505 -1.8 

g 4 4 -79 -723 -14.3 

h 4 4 -1028 -1082 -2.1 

4 Magnetic Models for the United States for 1985 
charts, which are 31 inches high and 45 inches wide, show 

the 48 conterminous States on one side at a scale of 1 to 

5 million and Alaska and Hawaii on the other at 1 to 3.5 

million. They are priced at $6.20 each, and are available 

from Distribution Branch, U.S. Geological Survey, Box 

25286, Federal Center, Building 810, Denver, Colorado 

80225. To order, please use Order Form P, if available. 

Otherwise, print your order plainly, specifying the 

reference code, title, and quantity of each chart required. 

Include your mailing address with zip code. Prepayment 

is required and must be made in U.S. funds by check or 

money order payable to Department of the Interior-USGS. For transmittal of maps outside the United 

States (except Canada and Mexico) a surcharge of 25 

percent of the net amount should be included to cover 

surface transportation. A $1.00 postage and handling 

charge is applicable on orders of less than $10.00. Please 

note that prices are subject to change. 

Simplified small-scale versions of the charts, along 

with charts for the X and Y components, are given in 

figures 12-18 (after "References Cited"). A dial-in 

service called "GEOMAG", by means of which field 

values from these models as well as those of the IGRF 

may be obtained directly via terminal and modem, has 

been described by Peddie (1987). For additional 

information write to Norman Peddie, U.S. Geological 

Survey, Box 25046, Mail Stop 968, Denver Federal 

Center, Denver, CO 80225. 

REFERENCES CITED 

Cain, J.C., Daniels, W.E., Hendricks, S.J., and Jensen, D.C., 

1965, An evaluation of the main geomagnetic field, 

1940-1962: Journal of Geophysical Research, v. 70, no. 

15, p. 3647-3674. 

Chapman, S., and Bartels, J., 1940, Geomagnetism, v. 2: New 

York, Oxford University Press, p. 611-612. 

Deel, S.A., and Howe, H.H., 1948, United States magnetic 

tables and magnetic charts for 1945, U.S. Coast and 

Geodetic Survey Serial 667: Washington, D.C., U.S. 

Government Printing Office, p. 10-12. 

Fabiano, E.B.,. and Jones, W.J., 1976, Magnetic horizontal 

intensity in the United States-Epoch 1975.0: U.S. 

Geological Survey Miscellaneous Investigations Series 

Map I-913. 

Fabiano, E.B., Jones, W.J., and Peddie, N.W., 1979, The 

magnetic charts of the United States for epoch 1975: U.S. 

Geological Survey Circular 810, 15 p. 

Fabiano, E.B., and Peddie, N.W., 1980, Magnetic declination in 

the United States-Epoch 1980: U.S. Geological Survey 

Miscellaneous Investigations Series Map I-1283. 

___ 1981, Magnetic total intensity in the United StatesEpoch 1980: U.S. Geological Survey Miscellaneous 

Investigations Series Map I-1370. 

Fabiano, E.B., Peddie, N.W., and Zunde, A.K., 1987, Models of 

total magnetic intensity in the United States for 1980: 

U.S. Geological Survey Open-File Report 87-619. 

Haines, G.V., 1985, Spherical cap harmonic analysis: Journal of 

Geophysical Research, v. 90, no. B3, p. 2583-2591. 

International Association of Geomagnetism and Aeronomy, 

Division I, Working Group 1, 1986, International Geomagnetic Reference Field revision 1985: EOS, v. 67, 

p. 523-524. 

Jones, W.J., and Fabiano, E.B., 1976, Magnetic vertical 

intensity in the United States-Epoch 1975.0: U.S. 

Geological Survey Miscellaneous Investigations Series 

Map I-914. 

Langel, R., Ousley, G., Berbert, J., Murphy, J., and Settle, M., 

1982, The MAGSAT mission: Geophysical Research 

Letters, v. 9, p. 243-245. 

National Geophysical Data Center, 1984, Terrestrial geophysics data services-Key to geophysical records 

documentation no. 17 (revised edition): Boulder, Colo., 

27 p. 

Peddie, N.W., 1987, GEOMAG-A geomagnetic field 

program: EOS, v. 68, no. 20, p. 530. 

Peddie, N.W., and Fabiano, E.B., 1976, A model of the 

geomagnetic field for 1975: Journal of Geophysical 

Research, v. 81, no. 14, p. 2539-2542. 

Peddie, N.W., Jones, W.J., and Fabiano, E.B., 1976, Magnetic 

inclination in the United States-Epoch 1975.0: U.S. 

Geological Survey Miscellaneous Investigations Series 

Map I-912. 

Peddie, N.W., and Zunde, A.K., 1987, A model of geomagnetic 

secular variation for 1980-1983: Physics of the Earth and 

Planetary Interiors, v. 48, p. 324-329. 

___ 1988a, The magnetic field in the United States, 1985, 

declination chart: U.S. Geological Survey Geophysical 

Investigations Map GP-986-D. 

___ 1988b, The magnetic field in the United States, 1985, 

inclination chart: U.S. Geological Survey Geophysical 

Investigations Map GP-986-I 

___ 1988c, The magnetic field in the United States, 1985, 

horizontal intensity chart: U.S. Geological Survey Geophysical Investigations Map GP-986-H. 

___ 1988d, The magnetic field in the United States, 1985, 

vertical intensity chart: U.S. Geological Survey Geophysical Investigations Map GP-986-Z. 

___ 1988e, The magnetic field in the United States, 1985, 

total intensity chart: U.S. Geological Survey Geophysical 

Investigations Map GP-986-F. 

Svendsen, K.L., 1962, United States magnetic tables for 1960: 

U.S. Coast and Geodetic Survey Publication 40-2, 91 p. 

References Cited 5 

Figures 3-18 
• 

• • 

• .. •• 

110° w too• w 

25° N 

....... ~ . 

:o 

20° N 

. .... . 

·······:········-e;------ • 

li •.. 

• 

• 

• 

160° w 155° w 

.. 

:• , . •• 

50° N 

180° w 170° w 

go• w 

• • •. 

· .. •• .. .. 

150° w 

~u 

'"' ~- . t 

ao• w ' 

.· .· ;;;·· . . . -~ .. . . . 

.. ··.. . . . ... ·.... . ·. 

• • • • • • •• 

• • 

• 

· .. 

.. 

. 

. .. . • 

• . . · .. . •. 

• ••• 

• 

140° w 

• 

Figure 3. Locations (solid squares) of land-survey measurements used to derive the 1985.0 models. 

8 Magnetic Models for the United States for 1985 

40° N 

30° N 

60° N 
25° N 

• • : . . .. • : Q • • ••. 

. • • ~U• 

.: 

:. 

• • ~"\:> 

20· N _______ ~ _ -.~·"- _. --~-v:- _____ _ . . . . . . • : . • .. . • 

160° w 155° w 

so• N ~ 

. ---

tao• w 170° w 

• - . 160° w 150° w 140° w 

Figure 4. Locations (solid squares) of marine-survey vector measurements used to deriv.e the 1985.0 models. 

Figures 3-18 9 
··~·-: :-~~~. 

0 

--~ o"\) zo• N ....... i ......... . \); ..... . 

\ 

.. 

• • . ·1!1 

160° w 

.. •• .. 

155° w 

• • ._ I 

... ·'I>~: 

• 

I 

I 

• 

..... . ..... 180° w 

• 

I 

• 

170° w 

•• • ••••••• . -,. .. .•. . ....... 

,. 

•••••••••••••• 

160° w 

. ... ... --

150° w 

. . ' . ........ . · •.. , ... . ., 

• • 

• _•!1- 30° N 

• • 

so• N 

· .. •. 50° N -····-·· ~--,~ . ...... ..... 

. . . •..... 

1401 w 

Figure 5. Locations (solid squares, thinned out for clarity) of marine-suNey total-intensity measurements used to 

derive the 1985.0 models. 

10 Magnetic Models for the United States for 1985 
.• • • .. •• • J' 

25° N 

20° N 

50° N 

.. 110° w 100° w 

. . . r!e . 

.. .... 

·~ • 

:· .. 

• 

160° w 155° w 

• 

• 

.... • • 

;. 

. . 

... 

• ···:··~· 

• • • • -~ .. ~ .. ..... . ... .. ;/1 .... ... .... •• • • • • • .. 

y :- • • ...... ·=-

. .... • • .... . . --· -~·· 

• • 

. · . ....,. . . . . . . . .. ...,.. : . : .. ·~" ... •• • ' - _._.. ... ,. • ~0 • • • • • •• • =-·~l .: • • • r~ . . . . .... ~... •·. .. ·' .. .... ... ~ .. ·.: .. .:\ . =········ . ~·. : . .. .. ... ~... . : 

180° w 170° w 

• : . I 

• • • • 

90° w so• w 

• 

• • JtJ. 

• • • • • • • • ·• 

• .. . 

• • • 

so• N 

. ... ·.-

• • ' ·' • • • t'·.· • 

• •. .. • 

••• --= •••••• ·. • ••• • •·• • • .,. 50° N . -. -..... . . .... . .... .. . .. .. • ~ .... 140° w 

Figure 6. Locations (solid squares, thinned out for clarity) of pre-1975 Project MAGNET aerial-survey vector 

measurements used to derive the 1985.0 models. 

Figures3-18 11 
,. 

,.• : 

. 7~ . ·······;·····}-·'\),······ 

I 

• 

: ... ·--· .. -· -~ ... ... • 

• 

~· • 

• • • 

• •• 

• 

• • • • • • 

150° w 

• 

• • • •• • 

•• • • • • • • • • • • • • • 

1401 w 

Figure 7. Locations (solid squares, thinned out for clarity) of non-Project MAGNET aerial-survey vector measurements 

used to derive the 1985.0 models. 

12 Magnetic Models for the United States for 1985 
30° N 30° N 

• 

• Q" 

• • • !::)" ~" . ~ 

110° w 100° w 90° w ao• w ' 

Figure 8. Locations (solid squares, thinned out for clarity) of Project MAGNET aerial survey total-intensity measurements 

taken during 1976-1977 used to derive the 1985.0 models. 

Figures 3-18 13 
•· I I 

• 

• • • • 

• • 

. ~~ . 20° N · · · · · ·.: ......... 0. · · · · · 

170° w 

. . ............... :.: ................ -~-

•. ·• 

• • 

. •• ;.. 

Figure 9. Locations (solid squares, thinned out for clarity) of Project MAGNET aerial-survey vector measurements taken 

during 1980-1983 used to derive the 1985.0 models. 

14 Magnetic Models for the United States for 1985 
•. • ·;;). ... 

. • . •. . . .. . . . . • 

• .. • • 

• • • 

• • • ----·-·:··-------{)·----- ~ • 

• • 

• • • 

• • . • 60° N • • • 

• • ~- . • •. • 

• .·• ~-- .. • .. • .. • 

• • • • ~ • . . • • • • . ·.· • .. • • • • .. • • • 

• • • • 

• • • 

• • • • 

• • • • • • • 

• • • 50' N ... • -- . 

• .• -- . 

• 

150° w 140° w 

Figure 10. Locations (solid squares) of Canadian aerial-survey vector measurements used to derive the 1985.0 models. 

Figures 3-18 15 
• • 1!1 1!1 • 

• • • • • 

~o· • • 

• . 

~ 

2oo N • . ~~ . • • 

- -. - ... -: - ... -. - ... -~ -. - ... -

• • 1!1 • • • -~ • • 

• • • • • • • 

• • • • • • • • 

160° w 155° w 

. • . • 

•• • • 

• • • 

• 

• • 

50° N 

tao• w t70° w 

too• w go• w 

tao• w 

• • • 

. . . 

. . • • .. - ... • • • • • •••••• 

• . . • 

• • • 

• • • • 

t50° w 

ao• w 

... ::::·:::·: .. j0 

I! 

······ •••• .... · ·••• .. ~·. •• . 

. ... . .... · ... ·· .. . . .. . .. . ... .. . . ·. . . . . . . . ~. . .. .. . . . . . . . . .. ·..... . ... ·. . . . . ·. . . . . . . •. . .... -· .. ... .~· .. . . . ..-· . . . . ... . . . ... -· •. . .. . . -·.. . . . . . 

t40° w 

ao• N 

50° N 

Figure 11. Locations (solid squares) for which International Geomagnetic Reference Field 1985 vector values were 

produced for use in deriving the 1985.0 models. 

16 Magnetic Models for the United States for 1985 
-~ 

--- CHANGE IN MINUTES OF ARC PER YEA~ \ 

110° w 

,' I 

·I 

·I 

~10.5°E-------.~ I 

·~-----~- ~I ro,·l 

/;II 1/.1 

It) ~ I . I . 

50' N-

-DECLINATION IN DEGREES · 0 

. p:'cP' 

--- CHANGE IN MINUTES OF ARC PER YEAR 

180° w 170° w 160° w 

Figure 12. Magnetic declination in the United States, 1985. 

90° w ao• w 

150' w 1401 w 

' ' ' . "·. ":-

.. · 30° N 

Figures 3-18 17 
25° N 

/,' 

/.' 

- INCLINATION IN DEGREES 

50° N . .' tfPfl / 

--- CHANGE IN MINUTES OF ARC PER YEAR 

180° w 170° w 160° w 

Figure 13. Magnetic inclination in the United States, 1985. 

18 Magnetic Models for the United States for 1985 

•/ 

/, / . / / 

150° w 

~ 

.. I 

' :· ..... I 40° N 

\ 

\ 

·./ #'·. I·. 82oN I , . 

I ·. I •. 

I I 

~ 

~ 

/ 

I 

I 

'.I 

1401 w 

I 

50' N 
2S' N · · · · · ......... : ....... "\, 

'61 

: Q ", . 

. ~ " . - • - 2aooo-:- ~AI~"\>,': 

20 N·······:·····':Y.il/~~~··· 

"· : v. ............. .... ,<? : 

'· ~-----·--~~--29000~ .......... - ............... 

160' w 1SS' w 

<?<?o 

Oo / ' . . / . - HORIZONTAL INTENSITY IN NANOTESLAS 

so• N. 

--- CHANGE IN NANOTESLAS PER YEAR / 

/ 

1801 w 1701 w 1601 w 

Figure 14. Magnetic horizontal intensity in the United States, 1985. 

/ 

1401 w 

/ /(,;) so• N 

Figures 3-18 19 
401 N 

--- CHANGE IN NANOTESLAS PER YEAR 

uo• w too• w 

1601 1f 155° w 

·~o 

~. • . 

. . / / 

: .,/ / C:J1 - NORTH COMPONENT IN NANOTESLAS • 

50' N 

--- CHANGE IN NANOTESLAS PER YEAR 

180° 1f 170° w 1601 w 

Figure 15. Magnetic north component in the United States, 1985. 

20 Magnetic Models for the United States for 1985 

90° w 

/ 

/ 

1501 1f 

8,01 1f 

I 

1401 w 

401 N 

.... 

, \ 601 N 

501 N 
30' N ·. 

--- CHANGE IN NANOTESLAS PER YEAR 

1001 w 

25' N · · · · · · ·: · · · · · · · · · · · .:~. · · · · · I 

-

'\ 

\ 

~ 

:O -ssoo- · \ 

' <:::. ' \ 

-----...:..._ ~ ~~ : 

201 N · · · · · · · ~ · "·· -~~ ·r-\_ · · · · · · 

: 'UI~ \r. 

\ 

\ 

Q ~ / Q 

~~~,'~/ / o' . / Q' 

/ Q' 

' ... ' 

/. : ... / /// ... I;/ /~ - EAST COMPONENT IN NANOTESLAS " 

50' N. 

--- CHANGE IN NANOTESLAS PER YEAR 

180 1 w 1701 w 160' w 

Figure 16. Magnetic east component in the United States, 1985. 

901 w so• w 

\ 

50' N 

150° w 1401 w 

Figures 3-18 21 
/ ....... '/.( ...... ··:. ·,,/ 

--- CHANGE IN NANOTESLAS PER YEAR : '-..· 

uo• w too• w 90° w ao• w 

25° N 

\ )0. \c:f1fil·. 

I . 

I 

. 601 N 

'~'~ooo . 

\ ~ \. 

- VERTICAL INTENSITY IN NANOTESLAS 

50° N 

--- CHANGE IN NANOTESLAS PER YEAR 

501 N 

tao• w t70° w t60° w t50° w t401 w 

Figure 17. Magnetic vertical intensity in the United States, 1985. 

22 Magnetic Models for the United States for 1985 
--- CHANGE IN NANOTESLAS PER YEAR 

90° w ao• w 

25' N ----/-: 

J!J.. 'lr-

:v 

-...... .... .... 1' . 

20' N 

. , 

' \ · .. '\ 

·. \ \ .t~ ALASKA \ 60' N ooo ·. --~--

I 

160° w 155° w I 

so ooo . 

-

's, 

TOTAL 

..... . 

INTENSITY IN 

~ NANOTESLAS 0 

50° N- 50' N 

--- CHANGE IN NANOTESLAS PER YEAR 

180° w 170° w 160° w 150° w 140° w 

Figure 18. Magnetic total intensity in the United States, 1985. 

Figures 3-18 23 
APPENDIX: Secular-variation data 

[Lat, latitude; Lon, Longitude (east if positive, west if negative); Elev, elevation above mean sea level; X, Y, and t estimated rates of 

change of the X, Y, and Z field components; m, meters; St, State postal zip code abbreviation. Parenthetical part of repeat-station name 

serves to distinguish that station from others nearby] 

• • • Lat Lon Elev X y z 

Name St (degrees) (m) (nanotesla per year) 

Magnetic observatories 

B_aker Lake , Canada ----------- 64.333 ,-96.033 45 23.6 -14.5 -39.4 

Barrow -·---------------- AK 71.323 -156.620 0 -22.1 -21.7 -25.5 

Boulder ----------------- co 40.138 -105.?38 1650 -1.1 -30.8 -63.4 

Cambridge Bay, Canada -------- 69.200 -105.000 20 17.5 -25.5 -25.0 

Cape Wellen, USSR ------------ 66.163 -169.835 10 -16.1 -13.5 -0.2 

College ----------------- AK 64.860 -147.837 90 -3.8 -29.7 -18.0 

Del Rio ----------------- TX 29.300 -100.800 357 -16.7 -31.0 -52.0 

Fort Churchill, Canada ------- 58.767 -94.100 40 26.5 -26.3 -51.2 

Fredericksburg ---------- VA 38.205 -77.373 69 22.4 -42.1 -115.6 

Fresno ------------------ CA 37.092 -119.718 336 3.4 -22.8 -59.4 

Godhavn, Greenland ----------- 69.252 -53.533 24 30.5 25.0 -21.0 

Great Whale River, Canada ---- 55.267 -77.783 23 50.6 -18.5 -58.9 

Guam, u.s. ------------------- 13.583 144.870 150 11.9 -4.3 1.3 

Honolulu ---------------- HI 21.320 -158.002 3 1.4 -27.2 -32.7 

Kakioka, Japan --------------- 36.230 140.190 26 -5.2 -12.2 25.9 

Magadan, USSR ---------------- 60.117 151.017 0 -35.7 -5.3 -5.6 

Meanook, Canada -------------- 54.617 -113.333 678 8.9 -39.4 -46.1 

Mould Bay, Canada ------------ 76.200 -119.400 150 -0.3 -19.5 -19.1 

Narssarssuaq, Greenland ------ 61.100 -45.200 4 46.3 33.5 -24.4 

Newport ----------------- WA 48.263 -117.120 780 8.2 -34.0 -37.5 

Ottawa, Canada --------------- 45.400 -75.550 760 45.3 -27.6 -103.6 

Petropavlovsk, USSR ---------- 52.900 158.433 110 ·25.7 -9.9 10.8 

Resolute Bay, Canada --------- 74.700 -94.900 30 14.2 -8.7 -29.0 

San Juan, Puerto Rico -------- 18.113 -66.150 400 -17.9 -63.9 -144.9 

Sitka ------------------- AK 57.058 -135.325 22 13.7 -34.0 -29.5 

Saint John's, Canada --------- 47.600 -52.683 0 57.6 19.0 -83.6 

Thule (II), Greenland -------- 77.483 -69.167 60 21.2 8.4 -22.2 

Tucson ------------------ AZ 32.247 -110.833 770 -16.1 -18.3 -53.8 

Victoria, Canada ------------- 48.517 -123.417 197 13.2 -30.7 -41.6 

Yellowknife, Canada ---------- 62.400 -114.500 183 11.0 -32.3 -35.8 

24 Magnetic Models for the United States for 1985 
APPENDIX: Secular -variation data-Continued 

• • • Lat Lon Elev X y z 

Name St (degrees) (rn) (nanotes1a per year) 

Repeat stations 

Majuro (new airport) --------- 7.067 171.280 0 -16.9 -7.7 -40.3 

Midway (1980) ---------------- 28.210 -177.380 0 -12.3 -27.8 5.1 

Wake ------------------------- 19.312 166.623 0 -21~3 -6.5 19.9 

Anchorage (NBS) --------- AK 61.235 -149.868 40 -2.7 -30.9 -14.5 

Bethel (airport 2) ------ AK 60.783 -161.833 30 -9.1 -23.4 5.7 

Fort Yukon (IGY) ----·--· AK 66.563 -145.260 130 5.9 -15.8 4.2 

Homer (1) --------------- AK 59.640 -151.493 10 1.0 -16.7 4.6 

Kodiak (1975) ----------- AK. 57.800 -152.365 0 -0.6 -22.9 4.9 

Kotzebue (1975) --------- AK 66.877 -162.637 0 -8.9 -9.2 0.4 

Nome (airport 3) -------- AK 64.515 -165.383 20 -23.7 -8.0 -5.1 

Northway (IGY) ---------- AK 63.018 -141.797 580 1.3 -24.5 0.6 

Unalakleet (1975) ------- AK 63.890 -160.797 0 -8.5 -10.4 1.2 

Marion (forest) --------- AL 32.657 -87.278 0 -9.9 -52.7 -88.6 

Castle Rock ------------- CA 37.240 -122.130 490 -16.7 -28.4 -39.5 

Lompoc ------------------ CA 34.637 -120.532 80 -4.2 -18.8 -44.5 

Fort Myers -------------- FL 26.610 -81.883 0 -41.2 -66.0 -102.7 

Key West (golf aux 2) --- FL 24.573 -81.743 0 -35.0 -85.8 -95.3 

Spruce Creek (1958) ----- FL 29.077 -81.032 10 -14.6 -72.7 -105.2 

Bainbridge (1958) _,.. _____ GA 30.907 -84.600 30 -16.2 -58.5 -96.8 

Milledgeville (golf) ---- GA 33.095 -83.283 0 -6.4 -50.8 -98.4 

Waycross (airport) ------ GA 31.255 -82.400 40 -9.3 -56.0 -105.0 

Bangor (Broadway) ------- ME 44.828 -68.788 60 57.4 -19.1 -111.3 

Bangor (Griffin) -------- ME 44.825 -68.808 40 50.2 -17.7 -115.0 

Fort Kent (hosp. B) ----- ME 47.268 -68.595 190 58.2 -15.3 -105.9 

Fort Kent (pasture) ----- ME 47.247 -68.587 190 69.9 -8.1 -104.6 

Detroit (River Rouge) --- MI 42.343 -83.253 190 23.9 -50.6 -106.3 

Detroit (park) -··-----·- MI 42.355 -83.262 190 23.9 -50.2 -106.0 

Marquette (golf 1947) --- MI 46.538 -87.423 270 19.1 -45.6 -79.7 

Marquette (golf 2) ------ MI 46.538 -87.422 240 23.4 -43.9 -79.7 

Brooklyn ---------------- MS 31.030 -89.170 120 -14.9 -52.3 -82.8 

Grenada (1971) ---------· MS 33.750 -89.797 60 -14.3 -44.7 -81.1 

Lamar (B 1981) ---------- MS 30.925 -89.387 0 -17.3 -51.4 -81.9 

Goldsboro (airport) ----- NC 35.385 -77.983 40 -6.5 -54.7 -123.5 

Bowbells ---------------- ND 48.800 -102.242 590 40.3 -48.4 -55.4 

Syracuse (Drumlins B) --- NY 43.017 -76.105 210 31.5 -36.0 -114.9 

Syracuse (Drumlins) ----- NY 43.017 -76.103 220 33.6 -35.7 -114.8 

Indiantow-n Gap (airf) --- PA 40.453 -76.545 160 35.1 -44.0 -122.1 

Indiantown Gap (lake) --- PA 40.417 -76.597 130 35.1 -46.5 -121.8 

Kingston (campus) ------- RI 41.480 -71.518 70 42.7 -30.6 -126.6 

Kingston (turf) --------- RI 41.488 -71.545 30 37.5 -29.5 -128.7 

Appendix 25 
APPENDIX: Secular-variation data-Continued 

Name St 

Lat Lon 

(degrees) 

Elev 

(m) 

Repeat stations--Continued 

Fort Jackson ------------ sc 34.017 -80.915 150 

Fort Jackson (2) -------- sc 34.018 -80.910 150 

Brownsville (golf 2) ---- TX 2~.883 -97.497 10 

Dallas (observatory) ---- TX 32.982 -96.750 210 

Orange· (C) -----·-------- TX 30.063 -93.802 0 

Van Horn (airport) ------ TX 31.062 -104.787 1200 

Salt Lake City (hill) --- UT 40.782 -111.855 0 

Burlington (LP) --------- VT 44.457 -73.155 120 

Burlington (RS) --------- VT 44.470 -73.197 120 

Eau Claire -------------- WI 44.833 -91.532 300 

Model fill-in values 

10.000 -90.000 0 

10.000 -105.000 0 

10.000 -120.000 0 

10.000 -135.000 0 

75.000 150.000 0 

0.000 180.000 0 

26 Magnetic Models for the United States for 1985 

•U.S. GOVERNMENT PRINTING OFFICE: 1989-0-773·047/06018 

• • • X y z 

(nanotesla per year) 

9.1 -53.6 -107.4 

11.2 -53.8 -108.8 

-48.3 -39.5 -48.5 

-29.1 -51.9 -77.2 

-27.6 -47.7 -68.3 

-31.4 -33.0 -54.0 

-32.9 -31.3 -36.4 

45.1 -28.9 -110.6 

40.1 -34.8 -124.2 

11.0 -55.3 -84.9 

-49.9 -41.4 -16.1 

-34.9 1.9 -25.9 

-20.6 0.6 -58.5 

-14.1 -19.3 -53.1 

-22.5 -6.6 -34.2 

-8.8 -9.3 7.6 


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t'eaa1e ana Lunae-MAL.NI:IIL MODELS FOR THE UNITEO STATES FOR 1985-U.S. Geological Survey Circular 1039