MAXIMUM LANGMUIR FIELDS IN PLANETARY FORESHOCKS DETERMINED FROM THE ELECTROSTATIC DECAY THRESHOLD

Maximum electric fields of Langmuir waves at planetary foreshocks are estimated from the threshold for electrostatic decay, assuming it satu rates beam-driven growth, and incorporating heliospheric variation of plasma density and temperature. Comparison with spacecraft observation s yields good quantitative agreement. Observations in type III radio s ources are also in accord with this interpretation. A single mechanism can thus account for the highest fields of beam driven waves in both contexts.