The occurrence of wave-breaking was associated with a mean state characterized by vertical wind (speed and directional) shear and a critical level with a southerly (cross-mountain) wind component that decreased to zero and a Richardson number less than unity just above the NCAR Electra flight level of 5500m, as diagnosed by a nearby radiosonde. The turbulence induced by wave breaking was reported by flight scientists. The high frequency (25Hz) data recorded a maximum vertical motion of 10m/s, a maximum turbulence kinetic energy of 10m2s-2 , a maximum horizontal vorticity of 0.2s-1.
During the first transverse, the convective region was convectively unstable as indicated by the positive explicit heat flux. The spectra of velocity components indicated energy-containing peaks approximately at scales of 85km, 25km, and 10km corresponding to three maxima approximately of the same length scales in the terrain spectrum along the cross-section. The second transverse illustrated the evolution of turbulence and fluxes 30 minutes after the first transverse. The flight level data for the second transverse indicated that the the turbulence was much stronger and the TKE maximum advected downstream. The GPS dropsonde data was used to diagnose a hydraulic jump that was located just below the flight level and was associated with strong down slope winds, a sudden transition to turbulence with a local wind reversal, and convective instability.
The strong down slope wind and hydraulic jump are captured by a real data 1-km COAMPS simulation. Some theoretical aspects of the wave breaking are examined based on the real data simulation and idealized 2-D simulations with multi-scale terrain. Shorter waves excited by smaller scale terrain superposed on the leading edge of the longer waves corresponding to large scale terrain promote wave breaking and significantly modify the horizontal and vertical distribution of TKE.
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