The line-of-sight velocity in a large sunspot

These are infrared observations at 1.56 micron using the GRIS instrument on the GREGOR 1.5m solar telescope. The thin curve marks the umbra-penumbra boundary while the thick curve shows the border of sunspot and quiet Sun. The data structure is four dimensional: two for spatial, one for spectra, and one for polarization states (I, Q, U, V). An inversion on the Stokes spectra yields the atmospheric parameters like temperature, velocity, magnetic field vector, etc.