Dynamic spectra on 13 April 2019, recorded by LOFAR (a) and BBMS in microwaves (b). The box in panel (a) with the bounds at 05:45:15 and 06:56:40 gives the spectrum region for which there is a high cross-correlation coefficient with the microwave emission at 6 GHz. The vertical dash-dotted, dashed, and dotted lines indicate the three time intervals used in Fig. 4. The vertical dash-three-dotted lines restrict the time interval for which the highest correlation coefficient was found.