DETECTION OF LANGMUIR SOLITONS - IMPLICATIONS FOR TYPE-III BURST EMISSION MECHANISMS AT 2-OMEGA(PE)

We present the experimental verification of existing theoretical model s of emission mechanisms of solar type III bursts at the second harmon ic of the plasma frequency, omega(pe). This study is based on the dete ction of Langmuir and envelope solitons by the Ulysses spacecraft insi de three type III burst source regions. We show that the oscillating-t wo-stream instability, coherent radiation by Langmuir solitons and sto chastic phase mixing of the Langmuir waves in the strong turbulence re gime are the appropriate emission mechanisms at 2 omega(pe).