Vertical drafts and mixing in stratified turbulence: Sharp transition with Froude numberF. Feraco, R. Marino, A. Pumir, L. Primavera, P. D. Mininni, A. Pouquet and D. RosenbergEPL, 123 4 (2018) 44002DOI: https://doi.org/10.1209/0295-5075/123/44002