Low dimensional models of dynamo action in rotating magnetoconvection

Abstract

Abstract Two low-dimensional models for nonlinear dynamo action in Rayleigh-Benard convection in presence of rigid body rotation about vertical axis are constructed for metallic fluids with finite magnetic Prandtl number ( P m ) and small (or zero) thermal Prandtl number ( P r ). Dynamo effect is seen for P m ≥ 0.75 with P r = 0.025 and Taylor number, 0 T a ≤ 1000 . The value of reduced Rayleigh number at the dynamo onset ( r d ) varies with P m , P r and T a . The value of r d decreases with increase in P m and T a separately, if the other two parameters are kept fixed to some small values. However r d increases slightly if P r is increased, the value being minimum for P r = 0 . When 0.75 ≤ P m 4 , dynamo onset appears as intermittent chaotic burst. The intermittent burst changes to continuous chaos with rise in P m . The probability mass of the height of peak in average magnetic energy follows power law when P m is small. For 4 ≤ P m 6 and 600 ≤ T a 1000 dynamo effect starts at the onset of convection as finite oscillation. This effect continues in a small window of r and then disappears. The dynamo action again appears as quasi-periodic wave or chaotic wave for further increase in r .