Sketch of different magnetic regions in M dwarf atmospheres. Starspots expand toward higher layers and have a large filling factor in the upper atmosphere. Small-scale magnetic fields (network) dominate the lower atmospheres, also with a highfilling factor. The geometrical scale given in axis on the left (km) belongs to the field lines. Atomic and molecular lines are formed at different optical depths (emphasized by different colors; the optical depth scale is given in the axis on the right) which allows us to probe changing magnetic strengths and structure size at different heights. The atmosphere parameters used for the sketch: effective temperature of 3500 K and magnetic field strength of 5 kG. Inside the magnetic spots, the temperature is about 2200 K, which is not shown here.