Response Function Estimates for Sq.

Abstract

Hourly values of the earth's magnetic field recorded at world-wide magnetic observatories have traditionally been used to study Sq variations and this can lead in particular to the construction the earth's response function at the daily period and its sub-harmonics. As an alternative to least squares analyses of the Sq potential, PRICE and WILKINS (1963) proposed a method involving interpolation, line integral constraints and surface integral separation of the potential into internal and external parts. The philosophy of the first two steps of their procedure is adopted here and these steps are rendered automatic. Spherical spline interpolation is used to convert the observatory X, Y, Z values to those over a regular surface grid and the use of line integral constraints to ensure the X, Y values represent a true potential is cast as a linear inverse problem with an exact solution. With regular data now available, stable spherical harmonic analysis can be applied to separate the total field into internal and external parts and the ratio of these taken to construct the Q-response. The method is illustrated on synthetic data and is then applied to the Price-Wilkins observatory data from the 1932-3 International Polar Year. Several estimates of the Q-response at periods of 24, 12 and 8 hours are converted to Schmucker's c-response and compared to longer period data from other analyses.