Statistical Properties of Solar Active Regions Obtained from an Automatic Detection System and the Computational Biases

Details Statistical Properties of Solar Active Regions Obtained from an Automatic Detection System and the Computational Biases Statistical Properties of Solar Active Regions Obtained from an Automatic Detection System and the Computational Biases

Nov 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010apj...723.1006z&link_type=abstract

The Astrophysical Journal, Volume 723, Issue 2, pp. 1006-1018 (2010).

Astronomy and Astrophysics

Astronomy

4

Sun: General, Sun: Magnetic Topology, Sun: Surface Magnetism

Scientific paper

We have developed a computational software system to automate the process of identifying solar active regions (ARs) and quantifying their physical properties based on high-resolution synoptic magnetograms constructed from Michelson Doppler Imager (MDI; on board the SOHO spacecraft) images from 1996 to 2008. The system, based on morphological analysis and intensity thresholding, has four functional modules: (1) intensity segmentation to obtain kernel pixels, (2) a morphological opening operation to erase small kernels, which effectively remove ephemeral regions and magnetic fragments in decayed ARs, (3) region growing to extend kernels to full AR size, and (4) the morphological closing operation to merge/group regions with a small spatial gap. We calculate the basic physical parameters of the 1730 ARs identified by the auto system. The mean and maximum magnetic flux of individual ARs are 1.67 × 1022 Mx and 1.97 × 1023 Mx, while that per Carrington rotation are 1.83 × 1023 Mx and 6.96 × 1023 Mx, respectively. The frequency distributions of ARs with respect to both area size and magnetic flux follow a log-normal function. However, when we decrease the detection thresholds and thus increase the number of detected ARs, the frequency distribution largely follows a power-law function. We also find that the equatorward drifting motion of the AR bands with solar cycle can be described by a linear function superposed with intermittent reverse driftings. The average drifting speed over one solar cycle is 1.93° ± 0.04° yr^{-1} or 0.708 ± 0.015 m s-1.

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