Atmospheric waves and their interactions in the thermospheric neutral wind as observed by the Arecibo incoherent scatter radar

Atmospheric waves and their interactions in the thermospheric neutral wind are studied based on Arecibo incoherent scatter radar observations. Our analysis suggests that the thermospheric atmosphere is usually disturbed by certain types of waves, including tides, gravity waves, and planetary waves, of which the diurnal tide is almost always the dominant disturbance. Strong interactions (defined as the coexistence of strong positive and negative correlations among the interacting waves) between the diurnal tide and gravity waves are frequently observed during the entire observation period. These strong interactions can persist for several days, although they are highly intermittent. Moreover, the sum and difference interactions between the diurnal tide and gravity waves always occur simultaneously and the energy exchange between the interacting waves is sometimes reversible. In addition to tide–gravity wave interactions, tide–planetary wave and tide–tide interactions are also found in our data. In tide–planetary wave interactions, the tidal oscillations are modulated at the interacting planetary wave periods. A combination of bispectral and correlation analyses verifies the occurrence of nonlinear interactions among different tidal components in the middle thermosphere. Moreover, during tide–tide interactions, the energy transfer trend changes very frequently, indicating that tidal energy is frequently redistributed among different tidal components. Generally, our study provides proof of strong tide–gravity wave, tide–planetary wave, and tide–tide interactions in the middle thermosphere, which has rarely been reported to date.