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In this paper, we present results from an experimental study into turbulentRayleigh-Benard convection forced externally by periodically modulatedunidirectional rotation rates. We find that the azimuthal rotation velocity$\dot{\theta}$(t) and thermal amplitude $\delta$(t) of the large-scalecirculation (LSC) are modulated by the forcing, exhibiting a variety ofdynamics including increasing phase delays and a resonant peak in the amplitudeof $\dot{\theta}$(t). We also focus on the influence of modulated rotationrates on the frequency of occurrence $\eta$ of stochasticcessation/reorientation events, and on the interplay between such events andthe periodically modulated response of $\dot{\theta}$(t). Here we identify amechanism by which $\eta$ can be amplfied by the modulated response and thesenormally stochastic events can occur with high regularity. We provide amodeling framework that explains the observed amplitude and phase responses,and extend this approach to make predictions for the occurrence of cessationevents and the probability distributions of $\dot{\theta}$(t) and $\delta$(t)during different phases of a modulation cycle, based on an adiabatic approachthat treats each phase separately. Lastly, we show that such periodic forcinghas consequences beyond influencing LSC dynamics, by investigating how it canmodify the heat transport even under conditions where the Ekman pumping effectis predominant and strong enhancement of heat transport occurs. We identifyphase and amplitude responses of the heat transport, and show how increasedmodulations influence the average Nusselt number.

Dynamical and statistical phenomena of circulation and heat transfer in periodically forced rotating turbulent Rayleigh-Benard convection