Transverse magnetic disturbances at 1100 kilometers in the auroral region

Transverse magnetic disturbances are regularly observed at 1100-km altitude in the auroral region with the magnetically oriented satellite 1963 38C. For the dayside period 1000–1400 LT the lower-latitude boundary of the disturbance region has an average invariant latitude Λb of 76° during magnetic quiet (Kp < 4o) and shifts southward to Λb = 68° during periods of magnetic activity (Kp ≥ 4o). For 2300–0100 LT, this latitude is 67° when Kp < 4o and is 63° when Kp ≥ 4o. The magnetic amplitudes range from about 30 γ (the minimum here detectable) to 380 γ, or about 1% of the local geomagnetic field. Such variations are absent between Λ = 31° (the minimum sampled) and the Λb appropriate to the local time and Kp. The quiet-time location and diurnal variation of the magnetic disturbance region correspond to those for the auroral oval and the trapping cutoff electrons ≥ 40 kev; all three phenomena have a nightside position comparable to the trapping cutoff for electrons ≥ 280 kev and ≥ 1.2 Mev, whose dayside displacement is also toward higher latitudes but with a small diurnal shift, ≈ 2°. The location and diurnal variation of the region containing most of these geophysical properties are reflected in the surface values of magnetic intensity recorded at the Baker Lake (Λ = 75°) and Fort Churchill (Λ = 70°) observatories; around local noon the Baker Lake values exceed those for Fort Churchill, while the reverse is true at local midnight.