A study of the abnormal cosmic ray storm that followed the solar particle ground level event (GLE) on September 23, 1978, has revealed that the protracted recovery phase is impregnated with wavelike modulations that are associated with the rotational period of the sun. The analysis of data from the global network of stations has denonstrated that these large-amplitude waves are isotropic. From an analysis of axial and longitudinal anisotropies it is concluded that the observed fluctuations did not originate from periodic changes in the cosmic ray density gradient (∇n) either in or perpendicular to the plane of the ecliptic. Although these long-duration waves cannot be ascribed to singular features on the sun, it is speculated that they may reflect changes in the topology of active regions on the visible disk. In any case, it is clear that the scope of the classical picture, in which Forbush decreases are associated with short-term anisotropic, must be expanded to include long-duration wave phenomena. These new observations provide an important clue in understanding the physical mechanism that gives rise to long-duration cosmic ray storms.