The local magnetic constant and its variations

L. A. Bauer
1914 Journal of Geophysical Research  
Good progress has been made by various investigators in establishing the relationship between fluctuations of the Earth's magnetism and those of the Sun's activity during the Sun-spot cycle. The magnetic quantity most frequently used for this pur.pose has been the range of the diurnal variationsgenerally of the magnetic declination. In connection with a preliminary examination of this relationship made five years ago in response to an inquiry received from Professor Hale, director of the Mount
more » ... ector of the Mount Wilson Solar Observatory, ! had occasion to employ various other magnetic quantities. One of these was what is here termed the "local magnetic constant," which, under certain assumptions, is proportional to the magnetic moment of the Earth, or to the intensity of magnetization. The desire was to use for the examination a quantity yielding results which might be more readily susceptible of a physical interpretation than those generally obtained. Since there are other investigations in which the need arises for a physical quantity, readily calculable, in terms of which the magnetic variations examined into may be appropriately expressed, and the comparison of their effects thus facilitated, I have been indu,ced to Publish some pretimi•y results. , Foaaunm. Suppose that the Earth's magnetic field arose from a uniform magnetic systerrr enclosed wholly within the surface, then its magnetic potential, V, at any point, _P, outside, will be: • • B.•,mr•, L.A. Terr. Mag. vol. 17', p. 8!, or vok 4, pp. 37-40. (The G used in (3) and subsequently, is the same constant as the c used in my previous papers.) 113 (9) (•o) CHANGES IN SOLAR ACTIVtTY •ND tN TERRESTRIAL MAGNETIS.d, 1906-1909. 1 14: L.A. BAUER [voL. XlX, No. 31 V = •T (g,0 cos u + g" sin u cos ;k + h", sin u sin X) Here R is the Earth's mean radius, r is the radius vector from the center of the Earth to/', u is the co-latitude counted continuously from north to south geographical pole, and X, the longitude counted east from Greenwich. g•0, g,•, and h n are proportional to the components of the intensity of magnetization, p, parallel, respectively, to the axis of rotation and to two rectangular axes lying in the equatorial plane, one of which is in the meridian of Greenwich and the other 90 ø East. We have thus, if u" and X" are, respectively, the co-latitude and longitude of the north end of the axis of the assumed magnetic field' 4 4 4 With the aid of (2) and (3) we then find, if _P be on the surface (r = R): 1Z• RO= H•+• . M= . (8) tf = .•/X • d-Y= being the horizontal intensity. THE LOCAL MAGNETIC CONSTANT L. A. BAUER [Vot.. XlX, No. 31 the course of a year, which, however, has been almost, if not entirely, eliminated in the quantities plotted; the curve should accordingly exhibit only a-periodic or more or less irregularly-occurring fluctuations. The broken curve is the one resulting from the Cheltenham data alone, whereas the full one is tl•e mean of Cheltenham, Porto Rico, and Honolulu; the same remark applies to the curves 3 to 8 inclusive. Curve 3. Variation in the Diurnal Range of the Magnetic Horizontal Intensity. This curve, as well as the next, was derived in a similar manner to No. 2. Curve 4. Variation in the Diurnal Range. of the Magnetic Vertical Intensity. Curves 5, 6, and 7 represent respectively the variations in the absolute magnetic elements (Declination, Horizontal Intensity, and Vertical Intensity) after elimination of the secular and seasonal variations. The declination curve (No. 5) depends only upon Cheltenham and Porto Rico, at both of which the compass points west of North; in order properly to combine the changes in declination at these two observatories, the changes were represented as percentages of the corresponding average ranges (R) multiplied by 100. Curve 8. Variation in the Earth's Magnetic Moment or, rather, in the Local Magnetic Constant. The curves, 2 to 7 inclusive, represent the magnetic data hitherto exclusively employed; in fact most of the investigations are confined to an examination of the variations in the diurnal ranges (Curve 2) of the magnetic elements with solar activity, the question as to the average effect on the absolute elements not being generally treated. Curve No. 8 is drawn for the first time; the quantities actually plotted are the changes in the local mag-
doi:10.1029/te019i003p00113 fatcat:jsruo23gerdnnhzqcpnlhtoe2m