A North-South Asymmetry in Location of Solar Sources of Great Geomagnetic Storms.

At the 106th meeting of the Society, the author presented evidence that, in the years 1937-1959, a major flare in the northern solar hemisphere had about four times greater probability than a similar southern flare of being followed within three days by a great magnetic storm. This concentration of great-storm sources in the solar north occurred about equally in each of the three sunspot cycles, No. 17, 18, and 19. Evidence for a preferred hemisphere for great- storm sources in earlier cycles has now been examined. Most of the data for this study were taken from the Royal Greenwich Observatory's "Sunspot and Geomagnetic-Storm Data, 187#1954." The Greenwich data reveal that over 50% of the total observed spotted area, and over 50% of the great spots (A>~500), occurred in the solar north in cycles 1418, and in the south in cycles 12 and 13. Earlier data, in part from published records of Spoerer, in part generously made available by A. S. Milsom from his work with unpublished drawings of Schwabe, indicate that the solar north was the more spotted in cycles 8 and 9, and south in cycles 10 and 11. Regarding geomagnetic activity, a substantial majority of the great storms apparently came from northern active centers in cycles 16-19, and from southern centers in cycles 10, 13 and 14; the two hemispheres contributed about equally in cycle 15; cycles 11 and 12 are probably, but less clearly, south- dominant. In most of the earlier cycles, as in 17-19, the degree of asymmetry in location of storm sources is increased when the lower limit for what shall be called a "great storm" is raised. Usually, the hemisphere that is more spotted in a given cycle produced more of the great storms; but not always, for the two curves are not perfectly in phase. The asymmetry in location of great-storm sources does not appear proportional to, and far exceeds in magnitude, the asymmetry in spottedness. This work was supported by the Air Force Cambridge Research Center, through a contract with Harvard University. % of the total observed spotted area, and over 50% of the great spots (A>~500), occurred in the solar north in cycles 1418, and in the south in cycles 12 and 13. Earlier data, in part from published records of Spoerer, in part generously made available by A. S. Milsom from his work with unpublished drawings of Schwabe, indicate that the solar north was the more spotted in cycles 8 and 9, and south in cycles 10 and 11. Regarding geomagnetic activity, a substantial majority of the great storms apparently came from northern active centers in cycles 16-19, and from southern centers in cycles 10, 13 and 14; the two hemispheres contributed about equally in cycle 15; cycles 11 and 12 are probably, but less clearly, south- dominant. In most of the earlier cycles, as in 17-19, the degree of asymmetry in location of storm sources is increased when the lower limit for what shall be called a "great storm" is raised. Usually, the hemisphere that is more spotted in a given cycle produced more of the great storms; but not always, for the two curves are not perfectly in phase. The asymmetry in location of great-storm sources does not appear proportional to, and far exceeds in magnitude, the asymmetry in spottedness. This work was supported by the Air Force Cambridge Research Center, through a contract with Harvard University. % of the total observed spotted area, and over 50% of the great spots (A>~500), occurred in the solar north in cycles 1418, and in the south in cycles 12 and 13. Earlier data, in part from published records of Spoerer, in part generously made available by A. S. Milsom from his work with unpublished drawings of Schwabe, indicate that the solar north was the more spotted in cycles 8 and 9, and south in cycles 10 and 11. Regarding geomagnetic activity, a substantial majority of the great storms apparently came from northern active centers in cycles 16-19, and from southern centers in cycles 10, 13 and 14; the two hemispheres contributed about equally in cycle 15; cycles 11 and 12 are probably, but less clearly, south- dominant. In most of the earlier cycles, as in 17-19, the degree of asymmetry in location of storm sources is increased when the lower limit for what shall be called a "great storm" is raised. Usually, the hemisphere that is more spotted in a given cycle produced more of the great storms; but not always, for the two curves are not perfectly in phase. The asymmetry in location of great-storm sources does not appear proportional to, and far exceeds in magnitude, the asymmetry in spottedness. This work was supported by the Air Force Cambridge Research Center, through a contract with Harvard University. % of the total observed spotted area, and over 50% of the great spots (A>~500), occurred in the solar north in cycles 1418, and in the south in cycles 12 and 13. Earlier data, in part from published records of Spoerer, in part generously made available by A. S. Milsom from his work with unpublished drawings of Schwabe, indicate that the solar north was the more spotted in cycles 8 and 9, and south in cycles 10 and 11. Regarding geomagnetic activity, a substantial majority of the great storms apparently came from northern active centers in cycles 16-19, and from southern centers in cycles 10, 13 and 14; the two hemispheres contributed about equally in cycle 15; cycles 11 and 12 are probably, but less clearly, south- dominant. In most of the earlier cycles, as in 17-19, the degree of asymmetry in location of storm sources is increased when the lower limit for what shall be called a "great storm" is raised. Usually, the hemisphere that is more spotted in a given cycle produced more of the great storms; but not always, for the two curves are not perfectly in phase. The asymmetry in location of great-storm sources does not appear proportional to, and far exceeds in magnitude, the asymmetry in spottedness. This work was supported by the Air Force Cambridge Research Center, through a contract with Harvard University. % of the total observed spotted area, and over 50% of the great spots (A>~500), occurred in the solar north in cycles 1418, and in the south in cycles 12 and 13. Earlier data, in part from published records of Spoerer, in part generously made available by A. S. Milsom from his work with unpublished drawings of Schwabe, indicate that the solar north was the more spotted in cycles 8 and 9, and south in cycles 10 and 11. Regarding geomagnetic activity, a substantial majority of the great storms apparently came from northern active centers in cycles 16-19, and from southern centers in cycles 10, 13 and 14; the two hemispheres contributed about equally in cycle 15; cycles 11 and 12 are probably, but less clearly, south- dominant. In most of the earlier cycles, as in 17-19, the degree of asymmetry in location of storm sources is increased when the lower limit for what shall be called a "great storm" is raised. Usually, the hemisphere that is more spotted in a given cycle produced more of the great storms; but not always, for the two curves are not perfectly in phase. The asymmetry in location of great-storm sources does not appear proportional to, and far exceeds in magnitude, the asymmetry in spottedness. This work was supported by the Air Force Cambridge Research Center, through a contract with Harvard University.