VLF CHORUS EMISSIONS OBSERVED BY POLAR DURING THE JANUARY 10, 1997, MAGNETIC CLOUD

VLF chorus emissions occur near the dawn meridian in fast response (<6 0 s) to magnetospheric perturbations caused by sudden fluctuations in solar wind dynamic pressure and southward turnings of the interplaneta ry magnetic field (IMF) at the arrival of the Jan. 10, 1997 magnetic c loud. Raytracing analysis indicates the likely chorus source region to be near the magnetic equator with rays launched at oblique wave norma l angles, for which likely resonant electron energies are in the range E similar to 14-30 keV, consistent with observed particle data.