HR: 16:35h
AN: SH54B-02    [Abstracts]
TI: Calibrating the Sunspot Number Using "the Magnetic Needle"
AU: * Svalgaard, L
EM: leif@leif.org
AF: Easy ToolKit, 6927 Lawler Ridge, Houston, TX 77055, United States
AU: Cliver, E W
EM: Edward.Cliver@hanscom.af.mil
AF: Space Vehicles Directorate, Air Force Research Laboratory, Hanscom AFB, MA , United States
AB: The 400-year long sunspot series is our primary direct record of Space Climate. Two series exist: the Zurich (now: International) series compiled by Wolf and successors, and the Group series by Hoyt and Schatten. The two series agree well back to ~1875, but before that the Group SSNs are systematically lower than the Wolf SSN. Wolf (and others) noticed that the amplitude, rD, of the daily variation of the Declination of the geomagnetic field varied with the sunspot number, R, and proposed a linear relationship: rD = a + bR. In fact, he used this relationship to calibrate the sunspot number for times before his own observations started (1849). Later researchers were less enthusiastic about this procedure. We re-examine Wolf's relationship using the range of the East component measured in force units [nT], rY, instead. This range is directly related to the intensity of the ionospheric SR currents, which in turn depends on the conductivity of the ionosphere. Solar FUV radiation creates and maintains the ionosphere, therefore the rY range (corrected for the secular decrease of the Earth's main field) is a proxy of the FUV. We show that this proxy reproduces the F10.7 radio flux and the International sunspot number with a correlation coefficient of 0.985, and recalibrate the sunspot number back to 1841 [Geomagnetic data exists that may allow such recalibration back to the 1740s]. The main conclusion is that there does not seem to be any secular increase in solar activity over the last 165 years: cycles 11 and 10 were as active as the most recent cycles 22 and 23.
DE: 1555 Time variations: diurnal to decadal
DE: 1739 Solar/planetary relationships
DE: 2439 Ionospheric irregularities
DE: 7534 Radio emissions
DE: 7536 Solar activity cycle (2162)
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2007 Joint Assembly