Strong Mixing Events Observed near the Tropopause with the MU Radar and High-Resolution Balloon Techniques

In the present paper, strong isotropic radar echo enhancements are shown that are related to the existence of nearly statically neutralized layers (40–120 m thick) observed with high-resolution (10 cm) temperature measurements performed during the Middle and Upper Atmosphere Radar, Temperature Sheets and Interferometry (MUTSI) campaign (8–26 May 2000, Japan). These events have been observed in the immediate vicinity of the tropopause, just above a jet stream maximum. They most likely result from strong turbulent mixing generated by shear instabilities and could be one of the mechanisms responsible for the generation of strong temperature gradients (temperature gradient sheets) at the mixed layer edges. Further investigations will be necessary to evaluate the occurrence of this neutralization mechanism and its contribution to the generation of strong temperature gradient sheets within the free atmosphere.