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Finding the formation mechanisms for bipolar configurations of strong localmagnetic field under control of the relatively weak global magnetic field ofthe Sun is a key problem of the physics of solar activity. This study is aimedat discriminating whether the magnetic field or fluid motion plays a primary,active role in this process. The very origin and early development stage ofActive Region 12548 are investigated based on SDO/HMI observations of 2016 May20--25. Full-vector magnetic and velocity fields are analyzed in parallel. Theleading and trailing magnetic polarities are found to grow asymmetrically interms of their amplitude, magnetic flux, and the time variation of thesequantities. The leading-polarity magnetic element originates as a compactfeature against the background of a distributed trailing-polarity field, withan already existing trailing-polarity magnetic element. No signs of stronghorizontal magnetic fields are detected between the two magnetic poles. Nopredominant upflow between their future locations precedes the origin of thisbipolar magnetic region (BMR); instead, upflows and downflows are mixed, withsome prevalence of downflows. Any signs of a large-scale horizontal divergentflow from the area where the BMR develops are missing; in contrast, a normalsupergranulation and mesogranulation pattern is preserved. This scenario ofearly BMR evolution is in strong contradiction with the expectations based onthe model of a rising $\Omega$-shaped loop of a flux tube of strong magneticfield, and an \emph{in situ} mechanism of magnetic-field amplification andstructuring should operate in this case.

The origin and early evolution of a bipolar magnetic region in the solar photosphere