An overview of recent results from RPI on IMAGE J. L. Green (1) and B. W. Reinisch (2) (1) NASA Goddard Space Flight Center, Greenbelt, MD (2) Center for Atmospheric Research, University of Massachusetts, Lowell, MA The Radio Plasma Imager (RPI) on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft was designed as a long-range magnetospheric radio sounder, relaxation sounder, and a passive plasma wave instrument. The RPI is a highly flexible instrument that can be programmed to perform these types of measurements at times when IMAGE is located in key regions of the magnetosphere. RPI is the first radio sounder ever flown to large radial distances into the magnetosphere. The long-range sounder echoes from RPI allow remote sensing of a variety of plasmas structures and boundaries in the magnetosphere. A profile inversion technique for RPI echo traces has been developed and provides a method for determining the density distribution of the plasma from either direct or field-aligned echoes. This technique has enabled the determination of the evolving density structure of the polar cap and the plasmasphere under a variety of geomagnetic conditions. New results from RPI show that the plasmasphere refills in slightly greater than a day at L values of 2.8 and that ion heating is probably playing a major role in the overall density distribution along the field-line. In addition, RPIÕs plasma resonance observations at large radial distances over the polar cap provided in situ measurements of the plasma density with an accuracy of a few percent. For the first time in the magnetosphere, RPI has also observed the plasma D resonances. RPI's long antennas and its very low noise receivers provide excellent observations in the passive receive-only mode when the instrument measures the thermal plasma noise as well as natural emissions such as the continuum radiation and auroral kilometric radiation (AKR). Recent passive measurements from RPI have been compared extensively with data from the Extreme Ultraviolet (EUV) imager on IMAGE, the plasma wave instrument (PWI) on Geotail, and Whisper on Cluster resulting in a number of new discoveries. For instance, these combined observations show that kilometric continuum can be generated at the plasmapause from sources in or very near the magnetic equator, within a notch region of the plasmasphere into relative narrow emission cones. This paper will also discuss new results on the distribution of plasma waves in the plasmasphere and their origin. Although the generation of plasmaspheric hiss is controversial the observations presented here point to lightning, which has a similar dayside local-time and geographic distributions, as a major contributor to the hiss emission spectrum. At frequencies from ~10 Š 50 kHz whistler mode emissions from ground-based transmitters are also observed. For these emissions the maximum intensity shifts almost exclusively to the local evening with enhancements along all L shells from 1.8 to 3. Indications are that the cyclotron resonance also operates in this frequency range. _______________ Asia-Pacific Radio Science Conference, Qingdao, China, August 24-27, 2004.