The lunar atmospheric tide at twenty-seven stations widely distributed over the globe

Abstract

Determinations of the lunar atmospheric tide at twenty-seven stations, in America, Africa and other parts of the world, have been made by the Chapman-Miller method from bi-hourly values of the barometric pressure extending, in the aggregate for the twenty-seven stations, over about 500 years. Examination of the results thus obtained reveals the following: (1) The amplitude c₂ decreases with increasing latitude, though the decrease is not quite regular. (2) The phase angles θ₂ are in the usual quadrant, betokening a lag of high tide after the moon’s transit, though the lag itself differs from station to station. (3) At almost all the stations the lunar air-tide undergoes a very appreciable annual change; a reduction in the values of both θ₂ and c₂ occurs in both hemispheres near the December solstice. (4) No very appreciable variation of the air-tide with height has been found up to about 3350 m. (5) In the U. S. A. the tide has a notable reduction of c₂ on the western coast, but no striking contrast in the case of θ₂ can be noted. (6) Several stations in East Africa, together with Singapore and Batavia, show results which indicate a specially interesting region where the tide has the biggest amplitude found anywhere on the surface of the earth, and where the phase lag is normal. (7) An asymmetrical distribution of c₂ about the equator in the same continent (Africa) is also very surprising and requires proper interpretation.