RADIO-WAVE SCATTERING IN THE OUTER HELIOSPHERE - PRELIMINARY CALCULATIONS

Detailed first estimates are presented of angular broadening in the ou ter heliosphere due to scattering of radio waves by density irregulari ties. The application is to the 2-3 kHz radiation observed by Voyager. Two plausible turbulence models, which account very well for scatteri ng within 1 AU, are extrapolated beyond 10 AU. Both models predict sig nificant angular broadening in the outer heliosphere, accounting semiq uantitatively alone for the source sizes inferred from roll modulation data. Predictions are presented for radial variations in the apparent source size if scattering is important. Comparisons with available da ta argue that scattering is important (and indeed is the dominant cont ributor to the apparent source size) and that the radiation source is located in the outer heliosphere. Other evidence that scattering is im portant, such as the fluctuations in apparent source direction and int ensity, are also identified. The effects of scattering should be inclu ded in future analyses of the 2-3 kHz emissions.