1990 年 36 巻 4 号 p. 267-276
The Antarctic Circumpolar Current (ACC) is the only tonal ocean flow around the axis of Earth's rotation. It can directly exchange the angular momentum with Earth's rotational motion. The Trans-Polar Index (TPI), variations of the pressure at the sea surface and the air temperature in the Antarctic show correlations with variations of the length of day (lod). Excitations of the Earth's rotational speed are estimated by using variations of the tonal current of the ACC, which are derived from geostrophic balance approximation of the pressure difference at the surface along the meridian. The pressure difference along the meridian is obtained by two methods; one is from the TPI and another is derived from atmospheric temperature at the surface in the Antarctic and the surface pressure at Ushuaia, in front of the Drake Passage. From the estimated excitation of the Earth's rotational speed, the ACC has proved to contribute to the exchange of the angular momentum with the solid part of the Earth. The ACC has also proved to be coupled with the increasing and/or decreasing of the El Nino.