Neutrallinje

Neutrallinje, in the context of solar physics, refers to the polarity inversion line on the solar photosphere—the boundary that separates regions of opposite magnetic polarity in magnetogram data. It is the locus where the line-of-sight or vertical component of the photospheric magnetic field changes sign, commonly approximated by Bz = 0 in vector magnetograms. The neutral line is a key feature for assessing the non-potentiality of the magnetic field, as strong magnetic shear and electric currents tend to accumulate along or near this boundary.

The neutral line is closely associated with solar activity. Its geometry—length, curvature, and the degree of shear—can indicate the likelihood of energy release in flares and coronal mass ejections. Highly sheared neutral lines often accompany complex active regions and sigmoidal structures in the corona. Researchers analyze neutral-line properties, such as the distribution of magnetic field gradients and the presence of closely packed opposite polarities, to understand eruption mechanisms.

Detection and measurement rely on magnetogram data from space- and ground-based instruments, such as the Solar Dynamics Observatory’s Helioseismic and Magnetic Imager and Hinode. Challenges include noise, projection effects for regions away from the solar disk center, and the 3D nature of the field. Methods involve thresholding, smoothing, and robust tracing of the polarity boundary to map the neutral line accurately.

See also: polarity inversion line, solar magnetogram, solar activity.