An interpretation of the modulating Blazhko effect in RR Lyrae stars is presented here, in which turbulent convection inside the hydrogen and helium ionization zones becomes cyclically weakened and strengthened owing to the presence of a transient magnetic field that is generated in situ by either a turbulent or a rotational dynamo mechanism. Successful predictions, both qualitative and quantitative, are made for the small changes of the primary pulsation period, the fluctuations of light and velocity amplitudes, the slow periodicity and irregularity of the Blazhko cycles, the restricted ranges of effective temperature for the RRab and RRc Blazhko variables, and the complex correlations between the primary period change, amplitude change, and mean effective temperature. Characteristic features of the predicted light and velocity curves at high and low amplitudes, even though they are based on radiative stellar models, agree well with the observed features, for the most part. The present theory of the Blazhko effect is simple enough that it does not require any basic change in our current understanding of RRab and RRc stars as being purely fundamental-mode and first-overtone radial pulsators. It also accounts naturally for the observed fact that hotter and cooler classes of periodic variable stars do not exhibit the Blazhko effect.
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