Resolution of the Azimuthal Ambiguity in Photospheric Vector Magnetograms of Solar Active Regions

We describe a simple technique to resolve the inherent azimuthal ambiguity of 180^o in vector magnetic field measurements of solar active regions. The desired azimuth solution is the one that minimizes an introduced function. This function includes a weighted combination of the height derivative of the magnetic field strength, calculated under conditions of minimum electric current density, and the vertical component of a current density vector purely perpendicular to the magnetic field lines. The above function reduces the number of ambiguity states to two for each location on the heliographic plane. The process is initially local, i.e., independent for each location on the heliographic plane. Then, the initial azimuth solution is subjected to a numerical analysis which yields the global azimuth solution and ensures maximum continuity of the photospheric magnetic field vector. This tactic reduces dramatically the required computing time to only a small fraction of the time required by existing techniques. The construction of the above-mentioned function is such that the method works equally well for active regions located either near or far from the center of the solar disk. The speed and simplicity of this novel technique may lead to a near real-time processing of acquired photospheric vector magnetograms. A reliable azimuth solution is a prerequisite for further analysis of solar magnetic fields. Reaching such a solution fast, is paramount for challenging modern problems, such as space weather forecasting, for example.