Wave activity in the northern cusp, at and , in the northward IMF run. The left-hand panels show (a) the magnetic field magnitude, (b) the magnetic field components and (c) the wavelet power spectrum of between and s. Panel (d) displays a zoom-in on the northern cusp, indicating the position of the virtual spacecraft (dark-green square) at which the time series were extracted. The background colour shows the magnetic field component. Panels (e) and (f) show hodograms of the magnetic field components in the plane perpendicular to the wave vector, obtained from minimum variance analysis applied on the time intervals indicated with the black and purple bars in panel (a), respectively.