Penetration of Hydromagnetic Energy Deep into the Magnetosphere

Magnetometer data, acquired on spacecraft and on the ground, are analyzed to study the propagation characteristics of hydromagnetic energy deep into the magnetosphere. 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 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. Numerical calculations show that fast compressional modes generated at a thick magnetopause boundary may have their energy reduced by only one order of magnitude over a penetration depth of about 8 R sub E.