Airglow measurements of gravity wave and smaller-scale flow features, used together with other measurements of larger-scale winds, provide a unique ability to quantify gravity wave dynamics at mesopause altitudes. We consider here an event observed with an OH airglow imager and the meteor radar at the MU Observatory in Japan. This was a wave breaking event of unusually large amplitude and momentum flux. Our hypothesis is that such events are relatively common, and that the resulting local forcing of the mean flow represents a vigorous source of secondary gravity waves that penetrate well into the thermosphere. Our analysis suggests a gravity wave momentum flux of ~900 m2s-2, far larger than estimated by other techniques, and a mean flow acceleration of ~80 ms-1 in less than an hour. We also estimate the scales and frequencies of the secondary waves resulting from this local body forcing.