Hydromagnetic waves at 6.25 Earth radii with periods between 3 and 240 seconds

The Dodge satellite detected regular and irregular micropulsations and a variety of other temporal variations in the vector geomagnetic field at 6.25 RE. The regular micropulsations with periods between 3 and 240 sec are Alfvén waves, transverse to the ambient field, with amplitudes usually between 1 and 20 γ that increase with period. The polarization is linear or elliptical. Toroidal, poloidal, and mixed modes are observed. It is suggested that the dominant eigenmode of the outer magnetosphere has a period of about 40 sec.