Induction in arbitrarily shaped oceans VI, oceans of variable depth

We present calculations of t he electric currents induced in a model ocean by the 24 hr Sq variation. The model has realistic bathymetry and represents a further step of a consistent approach to oceanic induction in which we have introduced various complexities in order of priority. The solution obtained is compared with our previously published results for the case of an ocean of realistic shape and uniform depth. It is found that the major shelf-seas considerably modify the pattern of elect ric current circu­ lation in the oceans of the southern hemisphere. The consistent nature of the method of matched outer and inner expansions which we have used is also discussed. It seems probable that other methods, not limited to finding an outer solution and consequently more complicated, will at best only produce an outer solution since, in practice, the relatively coarse mesh necessarily used in the computation of realistic global problems precludes a fine resolution of the coastal bathymetry. Finally , the meaning of the internal and external Legendre coefficients and their relationship to Sq over the oceans is briefly discussed

Induction in arbitrarily shaped oceans. IV, sq for a simple case

World curves are presented of electric currents induced in electrically insulated oceans by Sq using a perfectly conducting sphere to simulate the underlying mantle. The curves are valid everywhere away from those coastal regions at which the sea bed rises steeply. In such cases an edge correction may be needed. The numerical computations are for periods of 6, 8, 12 and 24 hr and comparison is made with results obtained by others for a 24-hr period. Circulation conditions around the island are ignored in this note

Induction in arbitrarily shaped oceans. V, the circulation of Sq-induced currents around land masses

The model ocean used in previous papers in this series is refined to allow for five separate land masses. The ocean is taken to be of uniform depth, and insulated from the mantle which is modelled by an infinitely conducting core at uniform depth. The fast method of solution introduced in Paper IV enables the electric currents induced by Sq to be calculated on a 2° x 2° global mesh. The 'outer' solution away from the coast is calculated. The 'inner' solution will be a coastal correction different for every coastal configuration. The current is allowed to circulate round isolated land masses, giving markedly different patterns from those in Paper IV. For some harmonics it appears necessary to differentiate even between Australia and New Zealand, although the world-wide effect of the remote island of Spitz­ bergen is minimal. Current distributions are shown for periods of 6, 8, 12 and 24 hr, and a value is set on the current streaming between the various land masses for all the Legendre harmonics considered

Geomagnetic Observations for Main Field Studies:from Ground to Space

Direct measurements of the geomagnetic field have been made for more than 400 years, beginning with individual determinations of the angle between geographic and magnetic North. This was followed by the start of continuous time series of full vector measurements at geomagnetic observatories and the beginning of geomagnetic repeat stations surveys in the 19th century. In the second half of the 20th century, true global coverage with geomagnetic field measurements was accomplished by magnetometer payloads on low-Earth-orbiting satellites. This article describes the procedures and instruments for magnetic field measurements on ground and in space and covers geomagnetic observatories, repeat stations, automatic observatories, satellites and historic observations. Special emphasis is laid on the global network of geomagnetic observatories