MAGNETIC VARIATIONS ASSOCIATED WITH OCEAN WAVES AND SWELL.
PACIFIC NAVAL LAB ESQUIMALT (BRITISH COLUMBIA)
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The magnetic field induced by the motion of ocean waves across the earths magnetic field is derived by a simpler and more direct method than that used by previous authors. The solutions for the field both within and above the sea are found. They are exact expressions, reducing to those calculated in previous papers when certain approximations are made. In contrast to earlier work where only the magnetic effects of wind driven waves were considered, the importance of ocean swell in generating significant magnetic fields is stressed. In particular it is shown that even when the sea-state is slight, the presence of longperiod swell can give rise to magnetic field variations whose magnitude is as large as that produced by the shorter-period wind waves of a rough sea. For instance, an ocean swell of 20 sec period and only 10 cm amplitude induces a magnetic field of 0.2 gamma at a depth of 100 m below the surface and a field of 0.1 gamma at an altitude of 50 m above the sea. Author