Upper-Level Turbulence in the North American and Asian Summer Monsoon Regions Sampled in Recent Aircraft Campaigns

Small-scale turbulence above 10 km is investigated using observations from two recent airborne field campaigns: the Asian Summer Monsoon Chemical & Climate Impact Project (ACCLIP) and the Dynamics and Chemistry of the Summer Stratosphere (DCOTSS). Turbulence is enhanced by factors of 2–24 inside clouds, within 100 km of active deep convection, above atmospheric jets, and above mountains coincident with strong low-level winds. In DCOTSS, which sampled outflow from overshooting convection over the continental United States, turbulence occurred most frequently near the tropopause, indicating enhanced troposphere-stratosphere exchange. In ACCLIP, conducted over the northwestern Pacific, turbulence was most common in the upper troposphere. We evaluate the performance of several turbulence diagnostics computed from the European Centre for Medium-Range Weather Forecasts' fifth reanalysis (ERA5) and operational forecasts, along with the clear-air turbulence flag recently introduced in the forecasts. Among the diagnostics tested, TI3 computed from operational forecast data is most skillful.