A substorm period near 0900 UT on January 2, 1971, provided both new and confirming evidence of mid-latitude and subauroral phenomena associated with magnetospheric substorm activity. Several of the principal ground and/or balloon observations were made near L=4 at the conjugate stations Siple, Antarctica, and Roberval, Canada. Satellite data were obtained from ATS 5, positioned at synchronous orbit roughly 2 hours to the west of the Siple-Roberval meridian. A key feature of the substorm activity was the previously reported observation of correlated bursts of X rays and VLF noise. It has earlier been concluded that the VLF bursts and assoicated particle precipitation events were 'triggered' by whistlers entering the magnetosphere at L~4 outside but near the plasmapause. During the substorm period a widespread VLF phase anomaly (previously reported) was observed on subionospheric paths extending within the plasmasphere to L~2.5 and over much of North America. Conjugate ULF observations near L=4 revealed enhancements of noise power in the 8- to 128-s period range at times of individual substorm intensifications and also a large increase in noise power during the period of correlated X ray and VLF bursts activity. Conjugate VLF observations revealed a series of noise bands at frequencies below 3 kHz, with durations of the order of 30 min and center frequencies generally rising with time. The onset of each band appeared to follow within less than 10 min a substorm intensification detected from ground magnetometers or ATS 5 energetic particle detectors. Cross-L inward drifts of whistler paths were observed in the outer plasmasphere during the substorm activity. The inferred westward electric field averaged about 0.35 mV/m during the hour before the observations of correlated X ray and VLF bursts. During this hour the plasmapause appears to have been displaced to a position slightly equatorward of Siple; in terms of resonance conditions along the field lines, the X ray detectors on the balloon over Siple were then in a favorable position to observe the results of magnetospheric wave-particle interactions involving electrons of energy greater than 30 keV. The various observed phenomena show promise of providing information on (1) the relations of ULF and VLF noise activity to the magnetospheric particle population at middle latitudes, (2) the injection and subsequent drift of low and medium energy electrons during substorms, and (3) enhanced particle precipitation deep within the plasmasphere during substorms.