Example supersynoptic maps of V_zonal in the Earth frame computed from the MWO (top three panels), GONG (fourth panel), and HMI data (bottom panel) near cycle minima. The full data set is shown in Fig. A.2). The HL1 mode may be seen from time to time as stripes in V_zonal above 50° latitude (see regions in red ellipses). For clarity, the maps were smoothed in latitude with a Gaussian kernel of width 10°.