Distribution of the magnetic flux in elements of the magnetic field in active regions 

Valentyna Abramenko Submitted: 20041013 10:06
The unsigned magnetic flux content in flux concentrations in two active regions are calculated by using a set of 248 high resolution SOHO/MDI magnetograms for each active region. Data for flaring active region NOAA 9077 (July 14, 2000) and nonflaring active region NOAA 0061 (Aug 09, 2002) were analyzed. We present an algorithm to automatically select and quantify magnetic flux concentrations above a threshold p. Each active region is analyzed using 4 different values of the threshold, p (p=25, 50, 75 and 100 G). Probability distribution functions (PDFs) and cumulative distribution functions (CDFs) of the magnetic flux were calculated and approximated by the lognormal, exponential and power law functions in the range of flux Phi > 10^{19} Mx. The KolmogorovSmirnov test applied for each of the approximations, showed that the observed distributions are consistent with the lognormal approximation only. Neither exponential, nor power law functions can approximate satisfactory the observed distributions. The parameters of the lognormal distribution do not depend on the threshold value, however they are different for the two active regions. For flaring active region 9077, the expectation value of the magnetic flux content is mu=28.1 imes 10^{18} Mx and the standard deviation of the lognormal distribution, sigma=79.0 imes 10^{18} Mx. For
nonflaring active region NOAA 0061 these values are: mu=23.8 imes 10^{18} Mx and sigma=29.6 imes 10^{18} Mx. The lognormal character of the observed distribution functions suggests that the process of fragmentation dominates over the process of concentration in the formation of the magnetic structure in an active region.
Authors: V.I. Abramenko and D.W. Longcope
Projects: SohoMDI

Publication Status: Astrophys. J., accepted
Last Modified: 20041013 10:06


