We present observations of MF/HF ionospheric radio emission observed between 4--7 Re in the terrestrial magnetosphere by the Wind spacecraft. During a perigee pass, and AKR episode, two distinct radio signatures are observed: an intense, sporadic emission near f≈1.8 MHz, and a more steady and weaker emission near f≈4.4 MHz. These emissions show characteristics similar to ground observations of ionospheric 'auroral roar', although to propagate to the spacecraft they must have been generated above the ionospheric F-layer peak. We suggest that the emissions are generated on the topside ionosphere where the condition fuh≈nfce is met. These observations represent a new component of the natural terrestrial radio spectrum as viewed from space. ¿ 1999 American Geophysical Union |