| Abstract : | In Sun and sun-like stars, there is a critical dynamo number for the operation of a large-scale dynamo, in which, the rotation rate of the object plays a critical role. It is also expected that the dynamo ceases below a critical rotation rate and this region is known as the subcritical region. In our study, we explore the possibility of the operation of the dynamo in the subcritical region using a Babcock--Leighton-type kinematic dynamo model. We find a hysteresis behavior near the transition of the large-scale dynamo. As in the Sun, both large-scale (global) and small-scale (local) dynamos are expected to operate at the same time and location, we check the hysteresis behavior in a numerical model in which both large- and small-scale dynamos are excited. For this, we use the Pencil code and set up an αΩ dynamo model with uniform shear and helically forced turbulence. We have performed a set of simulations at different relative helicity to explore the generation of large-scale oscillatory fields in the presence of small-scale dynamo. We find that in some parameter regimes, the dynamo shows hysteresis behavior, i.e., two dynamo solutions are possible depending on the initial parameters used. A decaying solution was observed when the dynamo was started with a weak field and an oscillatory strong solution was seen if the dynamo was initialized with a strong field. Thus, the hysteresis of the large-scale dynamo is also observed in presence of the small-scale dynamo, however, the regime of hysteresis is quite narrow for the case without the small-scale dynamo. |
