A tidal explanation for the sunrise/sunset anomaly in HALOE low-latitude nitric oxide observations

The difference in sunrise and sunset low-latitude nitric oxide (NO) mixing ratios in the mesosphere and lower thermosphere (MLT) is shown to be consis tent with a perturbation induced by the migrating diurnal tide. The vertica l wind of the tide can induce factor of 2 changes over 12 hours at the equa tor. The vertical, latitudinal and temporal structure of NO perturbations c losely matches the structure of vertical winds from a tidal model. In addit ion, previous observations of the seasonal and interannual variation in the tidal wind appear to correlate with NO variations.