Ultralow‐frequency waves in the magnetosphere have been observed and widely reported in the literature. One important class of such waves includes field‐line resonances, having fundamental frequencies as low as ∼1.3 mHz. Fluctuations below this frequency have been reported infrequently, although a few studies note oscillations with periods of approximately 30 min. The nature of these waves is especially interesting because the expected wavelength that would be associated with them should be larger than the scale size of the magnetosphere. In fact, the majority of these observations have been acquired using satellites located in the fairly distant magnetotail. In one of these studies, the only one which finds a discrete spectrum, data was obtained between XGSM = −8 and −18RE. In this paper, we show evidence for the existence of a discrete spectrum of oscillations within the magnetosphere that can persist for up to 2 days and perhaps longer. These observations were acquired at geosynchronous orbit and were observed at all local times simultaneously with a signature that is clearest in energetic electron data but can also be seen in the GOES magnetometer data. These facts suggest that a global‐scale magnetic fluctuation, perhaps one that originates in the magnetotail, resonates with energetic electron drift orbits via an E × B force.
