LUNAR SEMI-MONTHLY VARIATION IN THE PHASE DIFFERENCE OF THE GEOMAGNETIC DAILY VARIATIONS BETWEEN TWO COASTAL STATIONS
CHEN PO-FANG(Department of Geography & Geology, University of Hong Kong)
The phase relations between the daily variations of the geomagnetic field at Sheshan (佘山)amd Lunping (崙坪) Geomagnetic Observatories are described by using the concept of maximum correlation time. The data of the vertical component and the declination in 1974 were used, and the maximum entropy method (MEM) was applied to the results of the maximum correlation time series. It shows that there is a remarkable harmonic variation with a period of 14.6 days. This may be due to 'lunar ocean dynamo', as suggested by the author. When the lunar oceanic tide current flows along the East China Sea and the Taiwan Straits (a conducting channel), it will cause different magnetic fields, e.g. both in direction and in magnitude for Z, at the coastal stations located at both sides of the strait. Therefore the maximum correlation time presents the lunar semi-monthly variation.