Laboratory study of differential rotation in a convective rotating layer

The evolution of a large-scale azimuthal velocity field in a rotating cylindrical layer of fluid with meridional convective circulation was studied experimentally. Two cases were considered: direct circulation provided by a rim heater at the periphery and indirect circulation provided by a central heater. The detailed 3D structure of the mean large-scale velocity field is reconstructed using the PIV technique. Due to the action of the Coriolis force the meridional flow results in differential rotation. Differential rotation is characterized by the mean values of radial and vertical gradients of azimuthal velocity. Strong negative mean radial gradient which grows with the Grasshoff number is provided by direct circulation. In the case of indirect circulation a pronounced negative gradient arises at moderate Grashoff number. The behavior of the mean vertical gradient is quite different: a positive vertical gradient grows logarithmically with Grasshoff number under direct circulation, whereas a weak negative gradient characterizes the indirect circulation. This difference follows from the structure of the flow -- the direct circulation provides a large cyclonic area localized above the anticyclonic flow, while indirect circulation leads to a strong separation of these two areas in the radial direction (the central part is occupied by the cyclonic flow and the periphery by the anticyclonic flow). Meridional circulation leads to substantial variation of the integral angular momentum. Direct circulation results in the growth of the integral angular momentum and indirect circulation causes it to decrease. At the same heating power, the increase of angular momentum at direct circulation is much stronger than its decrease at indirect circulation.