 
Summary: Under consideration for publication in J. Fluid Mech. 1
The largescale flow structure in turbulent
rotating RayleighB´enard convection
Stephan Weiss and Guenter Ahlers
Department of Physics, University of California, Santa Barbara, CA 93106, USA
(Received 1 June 2011)
We report on the influence of rotation about a vertical axis on the largescale circulation
(LSC) of turbulent RayleighB´enard convection in a cylindrical vessel with aspect ratio
D/L = 0.50 (D is the diameter and L the height of the sample). The working fluid
was water at an average temperature Tav = 40 with a Prandtl number Pr = 4.38. For
rotation rates < 1 rad s1
, corresponding to inverse Rossby numbers 1/Ro between
zero and twenty, we investigated the temperature distribution at the side wall and from it
deduced properties of the LSC. The work covered the Rayleighnumber range 2.3×109 <
Ra < 7.2 × 1010
. We measured the vertical sidewall temperaturegradient, the dynamics
of the LSC, and flowmode transitions from singleroll states (SRS) to doubleroll states
(DRS). We found that modest rotation stabilizes the SRS. For modest 1/Ro < 1 we found
the unexpected result that the vertical LSC plane rotated in the prograde direction (i.e.
faster than the sample chamber), with the rotation at the horizontal midplane faster
