The flare productivity of active regions

We have investigated the relation between the flare productivity and the magnetic complexity of active regions. We have looked at 25,006 microflares that were detected by Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) from March 2002 to February 2007. Microflares are the flares of size smaller than Geostationary Operational Environmental Satellite (GOES) C-class, which is determined by its X-ray peak flux. For each flaring event, we have obtained the information about the properties of source active regions from Solar Region Summary prepared by National Oceanic and Atmospheric Administration (NOAA)/ Space Weather Prediction Center (SWPC). Many previous studies have shown that flare size frequency distribution follows a power-law, and some studies have also shown that regions of higher magnetic complexity produce large flares. However, the relation between microflare size distribution and the magnetic complexity of the source active region was not yet studied. Therefore, we have binned the flare frequency distribution plots by magnetic complexity, and looked at how shapes/slopes of these power-law plots changed. The flare size scale we used for plotting frequency distribution was RHESSI peak count rate in 12 to 25 keV channel, background subtracted. The scales we used for the binning magnetic complexity were Mount Wilson Magnetic Classification and Zurich/McIntosh Sunspot Classification. We have also looked at the dependence of the number of flares produced per active regions to the region’s magnetic complexity. We found that for both Mount Wilson Magnetic Classification and Zurich/McIntosh Sunspot Classification the slopes of microflare size distribution plots stayed all within the range from -1.5 to -1.7, which we concluded that they were close enough to -1.8, the results from previous studies. And since the shape/slope of the plot did not change significantly among different magnetic complexity, we have also concluded that there may be “parent distribution” of flare frequency that is a fundamental property for every kinds of active region. We also found that the correlation between the number of flares produced per active region and the region’s magnetic complexity, which should show that the higher the magnetic complexity, higher the number of flares produced per active regions, was observed more clearly in Zurich/McIntosh Sunspot Classification than Mount Wilson Magnetic Classification. Knowing that regions with higher magnetic complexity are more flare productive, we have concluded that Zurich/McIntosh Classification may be more appropriate measure of magnetic complexity for microflare productive regions. Further investigation will be conducted using Michelson Doppler Imager (MDI) magnetogram data, which measures various properties of magnetic fields in the Sun’s photosphere. We will continue to look at how the flare productivity explained above would change respect to these magnetic field properties of active regions.