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Chicone et al [Comm Math Phys (1997)] investigated existence of fast dynamosby analyzing the spectrum kinematic magnetic dynamo. In real non-degeneratebranch of the spectrum, the kinematic dynamo operator lies on a compactRiemannian 2D space of constant negative curvature. Here, generalization ofMarklund and Clarkson [MNRAS (2005)], general relativistic GR-MHD dynamoequation to include mean-field dynamos is obtained. In the absence of kinetichelicity, adiabatic constant $\gamma={1/2}$ and gravitational colapse ofnegative Riemann curvature of spatial sections enhance dynamo effect$\frac{{\delta}B}{B}=2.6\times 10^{-1}$. Critical time where linear dynamoeffects breaks down de to curvature. At recombination time, COBE temperatureanisotropies, implies that magnetic field growth rate is${\lambda}{\approx{10}^{-9}yr^{-1}}$. This places a bound on curvature till therecombination magnetic field is amplified to present value of $B_{0}=10^{-9}G$,by dynamo action. At present epoch, negative curvature becomes constant and theChicone et al result is shown to be valid in cosmology. Since negativecurvature is non-constant, Hilbert theorem which forbiddes negative constantcurvature surfaces embeddeding in $\textbf{R}^{3}$ is bypassed.

Dynamo action at recombination epoch of open Friedmann universe spatial sections