On the recent variations of the apparent westward drift rate

Quantitative study of the westward drift (w.d.) was initiated by Bullard et al (1950) and then followed by many others, using more or less similar methods (e.g. Yukutake, 1962; Harwood and Malin, 1976). More recently, MAGSAT results have enhanced the interest in the subject (see for example fig. 1 of Peddie, 1982). In the present paper, we compute the w.d. rate in the 1950-1980 time interval, using different methods, and we establish that the 1969-1970 secular acceleration impulse (the so-called "jerk") clearly shows up in the results.