Composite zonal winds in the equatorial MLT. (Left, (a)) Plots of seasonal variations of wind at 88 km for various locations between 22° N and 21° S. (Right, (b)) Zonal winds between 80 and 98 km. Note that the semi-annual oscillation is particularly strong around the March equinox. After Figure five of Venkateswara Rao et al. (2012b).