Vertical drafts and mixing in stratified turbulence: Sharp transition with Froude number F. Feraco, R. Marino, A. Pumir, L. Primavera, P. D. Mininni, A. Pouquet and D. Rosenberg EPL, 123 4 (2018) 44002 Published online: 18 September 2018 DOI: 10.1209/0295-5075/123/44002