Temporal variations in the Siple Station conjugate area.

The Siple Station conjugate intercepts in the northern hemisphere are examined for the epoch 1975-1990 according to the predictions of three internal source geomagnetic field models (IGRF-80, MAGSAT-80, Barraclough-75) and one external field model (Mead- Fairfield) under quiet and disturbed conditions. The conjugate location systematically changes in the interval studied, making it imperative that changes be made in the locations of the northern hemisphere geophysical stations during the re-activation of Siple Station in 1985-1987.