Ns. Nesterov et al., THE CHROMOSPHERIC AND CORONAL MAGNETIC-FIELD OF THE SUNSPOT GROUP SGD-26825 (JUNE 1991), Soviet astronomy letters, 18(6), 1992, pp. 446-448
Using radio and optical measurements in the transition zone and corona
of the sunspot group SGD 26825, we have detected an unusually strong
magnetic field (B > 2.6 kG) with complex structure in the chromosphere
lasting approximately 3 days.