ULF magnetic power spectra in the magnetosheath and magnetosphere

Magnetic power spectra parallel and perpendicular to the local magnetic field and in the frequency range 3.3 × 10−4 to 2.6 × 10−3 Hz are reported for both the magnetosheath and the magnetosphere. The measurements were mostly obtained in regions elevated ∼50° above the ecliptic plane on the night side of the earth, at geocentric distances between 11 and 35 RE. The results confirm and extend previous observations. The magnetosheath spectra are flatter than those from the magnetosphere, and in both regions the spectra parallel to the field are steeper than those perpendicular to it. The mean power level in the magnetosheath appears to rise with increasing geomagnetic activity.