Using laboratory water-tank experiments, detrainment from a vertical j
et rising through a density interface is explored. The experiments rev
eal that detrainment only occurs for a specific range of two governing
parameters, the Richardson number associated with the vortices and th
e normalized interface height. The shape of the detrainment domain is
explained with simple physical arguments involving velocity gradients,
baroclinic torques between the pure unmixed fluid and the environment
, and baroclinic torques between the mixed fluid and the surrounding f
luid. Detrainment is only observed when the penetrating jet consists o
f fluid with two different densities.