Stochastic fluctuations in a Babcock-Leighton model of the solar cycle

We investigate the effect of stochastic fluctuations on a flux transport mo del of the solar cycle based on the Babcock-Leighton mechanism. Specificall y, we make use of our recent flux transport model (Dikpati & Charbonneau) t o investigate the consequences of introducing large-amplitude stochastic fl uctuations in either or both the meridional flow and poloidal source term i n the model. Solar cycle-like oscillatory behavior persists even for fluctu ation amplitudes as high as 300%, thus demonstrating the inherent robustnes s of this class of solar cycle models. We also find that high-amplitude flu ctuations lead to a spread of cycle amplitude and duration showing a statis tically significant anticorrelation, comparable to that observed in sunspot data. This is a feature of the solar cycle that is notoriously difficult t o reproduce with dynamo models based on mean field electrodynamics and rely ing only on nonlinearities associated with the back-reaction of the Lorentz force to produce amplitude modulation. Another noteworthy aspect of our fl ux transport model is the fact that meridional circulation in the convectiv e envelope acts as a "clock" regulating the tempo of the solar cycle; short er-than-average cycles are typically soon followed by longer-than-average c ycles. In other words, the oscillation exhibits good phase locking, a prope rty that also characterizes the solar activity cycle. This shows up quite c learly in our model, but we argue that it is in fact a generic property of flux transport models based on the Babcock-Leighton mechanism, and relies o n meridional circulation as the primary magnetic held transport agent.