Automatic detection of solar active regions from SOHO/MDI and SDO/HMI synoptic magnetograms.

We develop an adaptive method to automatically identify ARs from radial synoptic maps observed by SOHO/MDI and SDO/HMI, calibrate the detections between HMI and MDI data based on identified ARs flux and area and further derive a homogeneous dataset including ARs' area and flux over the last two solar cycles. The data are compared with sunspot number, USAF/NOAA sunspot area, SMARPs and SHARPs and BARD area and flux, which show reasonable agreement. The identified ARs during the overlap period of MDI and HMI have the same areas as a whole while the AR flux based on MDI maps is about 1.36 times as large as that of HMI maps. Based on our dataset, we find strong ARs (| flux | > 1022Mx) contribute most to the difference between cycles 23 and 24 while other ARs (| flux | < 1022Mx) are similar in the two cycles in both area and flux. [ABSTRACT FROM AUTHOR]