Penetration of Hydromagnetic Energy Deep Into The Magnetosphere

Magnetometer data, acquired on spacecraft and simultaneously at high and low latitudes on the ground, are compared in order to study the propagation characteristics of hydromagnetic energy deep into the magnetosphere. Single events provide evidence that wave energy at L~3 can at times be only one order of magnitude lower than at L~13. In addition, statistical analyses of the H-component ground-based data obtained during local daytime hours for July 17 to August 3, 1985 show that wave amplitudes at L~3 are generally 10 to 30 times lower than at L~13. The L-dependence of near-equator magnetic field fluctuations measured on ISEE-2 show a sharp drop in energy near the magnetopause and a more gradual fall-off of energy deeper inside the magnetosphere.