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The paper by Popova et al. presents an oversimplified mathematical model ofsolar activity with a claim of predicting/postdicting it for several millenniaahead/backwards. The work contains several flaws devaluating the results: (1)the method is unreliable from the point of view of signal processing (it isimpossible to make harmonic predictions for thousands of years based on only 35years of data) and lacks quality control, (2) the result of post-dictionapparently contradicts the observational data. (3) theoretical speculationsmake little sense, To summarize, a multi-harmonic mathematical model, hardlyrelated to full solar dynamo theory, is presented, which is not applicable torealistic solar conditions because of the significant chaotic/stochasticintrinsic component and strong non-stationarity of solar activity. The obtainedresult is apparently inconsistent with the data in the past and thus cannot betrusted for the future predictions.

Comment on the paper by Popova et al. "On a role of quadruple component of magnetic field in defining solar activity in grand cycles"