Plasma waves observed by the Akebono satellite in the region of ion heating/acceleration transverse to the geomagnetic field line are studied. Especially, electrostatic, broadband low-frequency noise is closely correlated with transversely accelerated ions. Simultaneous electron precipitation in the energy ranges from a few tens to hundreds eV is also usually observed. Our waveform analysis revealed that the electrostatic broadband noise is classified into two types of noise: one is continuous noise with upper cutoff around a few kilohertz, and the other is an intermittent impulsive waveform extended more than 10 kHz. A possible explanation to the dominant part of continuous broadband noise is that they are ion acoustic waves generated by precipitating electrons (approximately a few hundreds eV) and that the wave is the possible main energy source of ion heating/acceleration. The other mechanisms may, however, be sometimes important for generating the broadband noise. Using long-period observation data sets of Akebono, which is orbiting in the altitude range between 270 and 10,000 km, statistical studies on the spatial and temporal distribution of the continuous broadband noise are made. Several kinds of statistical features are clarified: (1) The occurrence region is distributed in the cusp and along the auroral oval, (2) the region is extended toward the lower latitude while the geomagnetic activity is higher, (3) the intensity is larger in the cusp than it is in the nightside, and (4) it is largest in winter and weakest in summer. ¿ 2001 American Geophysical Union