Low frequency geomagnetic fluctuations (0.025 to 20 Hz) on the floor of Monterey Bay

Abstract

Two coil antennas consisting of 5460 turns of copper wire were utilized to measure the vertical component and a horizontal component of the fluctuations of the geomagnetic field on the floor of Monterey Bay at a depth of approximately seventy meters. The results indicate that the power spectral density of the fluctuations varies from 1.6 x 10 nT /Hz at 0.01 Hz to 8 x lO" 8 nT2 /Hz at 20 Hz for the horizontal component and from 3.2 x 10 2 nT2 /Hz at 0.01 Hz to 6.3 x 10' s nT2 /Hz at 20 Hz for the vertical. Both components exhibit a monotonic decrease of about 20 dB/decade as the frequency increases, except in the 8-20 Hz region in which the Schumann resonances occur. Measurements of the power spectral density for the vertical component show relatively small excursions from average measurements as a function of wave action, while the horizontal power spectral density varies greatly throughout the day and as a function of seawater motions.