On the possibility of probing the flare productivity of an active region in the early stage of emergence

Abstract

Prediction of the future flare productivity of an active region (AR) when it is in the early-emergence stage is a longstanding problem. The aim of this study is to probe two parameters of the photospheric magnetic field, both derived during the emergence phase of an AR, and to compare them with the flare productivity of a well developed AR. The parameters are: (i) the index of the magnetic power spectrum (the slope of the spectrum) at the stage of emergence, and (ii) the flux emergence rate. Analysis of 243 emerging ARs showed that the magnetic power index increases from values typical of quiet-Sun regions to those typical of mature ARs within a day, while the emergence proceeds for several days; frequently, after the increase, the value of the power index oscillates around some mean value with the fluctuations being several times smaller than the growth of the power index during the emergence onset. For a subset of 34 flare-productive ARs we found no correlation between the power spectrum index at the stage of emergence and the flare index derived from the entire interval of the AR’s presence on the disc. At the same time, the flux emergence rate correlates well with the flare index (Pearson’s correlation coefficient is 0.74). We conclude that a high flux emergence rate is a necessary condition for an AR to produce strong flares in the future; thus the flux emergence rate can be used to probe the future flare productivity of an AR.

A statistical study of magnetic flux emergence in solar active regions prior to strongest flares

“…In this work we confirmed our previous findings (Kutsenko, Abramenko, & Kutsenko 2021) regarding the flare productivity and flux emergence rate of ARs: ARs emerging at a higher rate tend to produce stronger flares. Although flare-productive ARs exhibit higher flux emergence rate, its consistent difference from of flare-quiet ARs is not well pronounced.…”

“…For instance, NOAA AR 09087 exhibited relatively high peak magnetic flux of about 5.5×10 The relationship between flare index and the flux emergence rate shown in the right panel of Fig. 8 supports our results reported in Kutsenko, Abramenko, & Kutsenko (2021): fast-emerging ARs exhibit, in general, higher flare productivity, the correlation coefficient from the combined data set (N=84) is 0.61 +0.12 −0.15 . The similar relationship (with less inclined slope) seems to be valid for the separate subset of type II ARs (blue circles).…”

“…In the present study, we aim to re-examine the statement that prior to a strong flare there is always a large emergence of new magnetic flux. Note that in our previous paper (Kutsenko, Abramenko, & Kutsenko 2021), we moved from emergence to flaring. Namely, we detected all ARs emerged on the solar disc between 2010 and 2017.…”

“…First, to treat SOHO/MDI and SDO/HMI data by the same procedures to ensure the homogeneity of the derived magnetic flux values. Second, to ensure the consistency of the data reduction techniques applied in this work and in our previous works on AR emergence (Kutsenko, Abramenko, & Pevtsov 2019;Kutsenko, Abramenko, & Kutsenko 2021) in order to perform the comparison of the results. The SDO/HMI algorithm for the lineof-sight magnetic field calculations is similar to that for SOHO/MDI data.…”

“…8 shows the relationship between flare index and peak magnetic flux of all ARs in our sample (left panel) and the relationship between flare index and flux emergence rate of ARs of types I and II (right panel). In both panels we also overplotted data points on ARs (black circles) analysed in Kutsenko, Abramenko, & Kutsenko (2021). These data points are 34 emerging ARs with the flare index exceeding unity.…”