The red horizontal line on the lower panel shows the latitude displayed in the Hovmoller diagram in the upper panel. The red slanted line on the upper panel shows the phase speed of baroclinic planetary waves with zonal and meridional wavelengths of 10 degrees. The phase speed is given as a rough estimate of the actual planetary wave speed and was calculated assuming that the baroclinic gravity wave speed (determined by the ambient density stratification) is equal to a typical value of 2m/s.