Two intervals of whistlers detected in the cross-spectra collocated with magnetic dips (each lasting about one hour). For both panels, the first row shows the trace of the spectral matrices. The two white lines indicate 20% of the electron-cyclotron frequency f_ce and the lower hybrid frequency f_lh. The second row shows the whistler clusters detected; the assigned colors are random. The two green lines indicate 20% of the electron-cyclotron frequency f_ce and the lower hybrid frequency f_lh. The magnetic dips, detected with the method described in Sect. 2.4, are highlighted in pink.