Abstract
A stratospheric balloon, carrying a NaI (T1) scintillation counter for measuring 20-100keV bremsstrahlung X-ray was launched from Stamsund (L=5.6) in Norway during the recovery phase of a magnetospheric substorm. The scintillation counter recorded X-ray pulsations with periods of 20-30s when the balloon was located at L=5.4-4.8 and at 0950-1300 MLT. A rising tone type of quasi-periodic (QP) VLF emissions and Pc 3 magnetic pulsations observed at Andoya (L=6.15), located at 160km northeast of Stamsund, were closely associated with these X-ray pulsations. The one-to-one correspondence between occurrences of QP emissions and enhancements of X-ray count rate suggests that QP emissions (whistler mode waves) modulate the pitch angle diffusion rate of energetic electrons trapped in the magnetosphere through the cyclotron interaction. Further a close relation between QP emissions and Pc 3 magnetic pulsations suggests that compressional mode Pc 3 waves propagating in radial direction from the dayside magnetopause toward the earth modulate the growth rate of whistler mode waves.
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