The near‐Earth magnetic field at 1980 determined from Magsat data

摘要: Data from the Magsat spacecraft for November 1979 through April 1980 and 91 magnetic observatories 1978 1982 are used to derive a spherical harmonic model of earth's main field its secular variation at epoch 1980.0. The is called GSFC(12/83). Constant coefficients determined degree order 13 10. first-degree external terms corresponding induced internal given as function Dst. Preliminary modeling using separate data sets dawn dusk local time showed that contain substantial contribution equatorial electrojet current. final set was therefore selected first then augmented by achieve good geographic distribution each three periods: (1) November–December 1979, (2) January–February 1980, (3) March–April 1980. A correction effects applied utilized. solution included calculation fixed biases, or anomalies, observatory data. Although similar in many respects, GSFC(12/83) differs International Geomagnetic Reference Field 3.6 nT g10 term shows slightly negative B northern polar region well other differences pattern.