On a Relation between Irregular Variations of the Earth’s Rotation and Anomalous Changes of the Atmospheric Circulation

A relation between irregular variations of the rotational velocity of the earth and anomalous changes of the global zonal wind circulation is dealt with here for periods longer than 4 months. In the residuals of rotational velocity data after eliminating the mean rotational acceleration and the mean seasonal terms, determined during 20 yr from 1955 to 1975, a quasi-periodic change with about an 8-yr period from 1957 to 1964 is clearly seen as well as short-term periodic fluctuations with periods less than 2 yr. It is found, on the other hand, that the global zonal wind circulation has also anomalous changes which are quite similar to the residual velocity changes of the earth. In order to ascertain the relation between the quasi-periodic change in the earth’s rotation and that in the global zonal wind circulation, zonal wind data up to 30 km in altitude, about 10-mb level, are used for this calculation. It is shown that about 20% of the long-period term of the 8-yr period in the rotational velocity can be explained by the associated relative angular momentum of the atmosphere. As for the short-term periodic fluctuations, it is also shown to be almost ascribable to the effect of the zonal winds. Such anomalies with long- and short-periods in the angular momentum of the atmosphere may be due to the disturbances of zonal wind mainly in the tropical zone.