Turbulent convection with "disconnected" top and bottom boundary layers

We have done an experimental study of turbulent thermal convection in water using a cell with a baffle placed at its mid-height, over a range of Ra th at spans from 2 x 10(8) to 2 x 10(10). It was found that in this case the l arge-scale circulation is not able to advect heat between the top and botto m plates and heat has to be carried across the baffle mainly by thermal plu mes. Furthermore, the measured Nu, still scales with Ra with an exponent co nsistent with "2/7" for Ra > 1 x 10(9). For Ra below this value, the scalin g of Nu, with Ra is more consistent with an exponent of "1/3". The measured temperature PDFs also show signatures of "soft" and "hard" turbulence belo w and above Ra similar or equal to 1 x 10(9), respectively.