DYNAMO ACTION IN CHRISTOPHERSON HEXAGONAL FLOW

Kinematic dynamo action is investigated for the Christopherson flow co nsisting of a horizontally periodic layer of identical hexagonal cells . In each cell a conducting fluid ascends at its centre and descends a t its periphery. Boundary conditions are chosen so that the layer has a perfectly conducting base and is overlaid by a current-free atmosphe re. By numerically solving the eigenvalue problem for the induction eq uation, it is found that a dynamo operates when the magnetic Reynolds number R-m exceeds 515. According to recent theoretical results, this dynamo is expected to be slow, though our results show the growth rate is still increasing at R-m = 1000. The magnetic structure is concentr ated around stagnation points and their associated heteroclinic orbits .