Sectoral power spectrum of the radial vorticity computed from 17.42 years of GONG++ RDA data starting 4 September 2001. Each m is normalized to the mean power between −500 and 100 nHz. For clarity we plot the power spectrum rebinned by a factor of three in frequency. The red line shows the theoretical dispersion relation for sectoral Rossby waves given in the text. While a m = 1 r mode seems to be present, it is likely low-frequency power leaked from m = 0.