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A long-standing problem is to predict the future flare productivity of anactive region (AR) when it is on the stage of early emergence. The aim of thisstudy is to probe two parameters of the photospheric magnetic field, bothderived during the emergence phase of an AR, and to compare them with the flareproductivity of the well-developed AR. The parameters are: (i) the index of themagnetic power spectrum (the slope of the spectrum) on the stage of emergence,and (ii) the flux emergence rate. Analysis of 243 emerging ARs showed that themagnetic power index increases from values typical for quiet-Sun regions to thevalues typical for mature ARs within a day while the emergence proceeds forseveral days; frequently, after the increase, the value of the power indexundulates around some mean value with fluctuations being several time less thanthe growth of the power index during the emergence onset. For a subset of 34flare-productive ARs we found no correlation between the power spectrum indexat the stage of emergence and flare index derived from the entire interval ofthe AR's presence on the disc. At the same time, the flux emergence ratecorrelates well with the flare index (the Pearson's correlation coefficient is0.74). We conclude that high flux emergence rate is a necessary condition foran AR to produce strong flares in the future, and so, the flux emergence ratecan be used to probe the future flare productivity of the AR.

On the possibility to probe the flare productivity of an active region on the early stage of emergence