Sharp transitions in the Lagrangian acceleration statistics in rotating Rayleigh-Benard convection*

Rotation induces transitions in the heat transfer and flow structures in Rayleigh-Benard convection. While the transition in the heat transfer is definitely sharp, it is not clear whether the transition in the flow structures reveals a  similar sharpness. We investigate this transition by studying Lagrangian acceleration statistics of passive tracers. Near the top plate, the intermittency of the  acceleration statistics suddenly increases at a critical Rossby number, Ro_c = 2.25. To understand this sudden increase, we focus on the relation between the acceleration and the dynamics of plumes developing in the boundary layers, which are typically characterized by large values of vorticity. When Ro>2.25 no correlation is found between the extreme acceleration events and vertical vorticity. For Ro<Ro_c the values of (positive) vertical vorticity have increased significantly and now extreme acceleration events are correlated to large vorticity. This suggests that the sharp transition in the Lagrangian acceleration statistics is related to vortical plumes developing in the Ekman boundary layer for Ro<Ro_c.