Simulations from our venusian general circulation model (GCM) forcing the presence of planetary-scale waves and mesoscale gravity waves were compared with infrared (IR) heterodyne observations of Doppler wind velocities in the venusian mesospheric altitude region (110. km). Observations confirmed the strong short-term variations in the venusian mesospheric wind velocity in a time scale of hours and days during March 16-22 and April 2-6 in 2009 at the morning/evening terminator. The variability in our GCM wind velocity produced by Kelvin wave was, in general, of the order of ±3-4. m/s with a period of 4. days for each latitude region. Comparing simulations with observations, the periodicity of the Kelvin-type disturbance was not seen in the observational data. The amplitude of the GCM wind velocity variation was only comparable to observed variability for the mid-latitude in March 2009. In most cases, the observations showed much higher variability than that produced by Kelvin wave. Our simulation also investigated the impact of upward propagating gravity waves on mesospheric and thermospheric wind variations. The results indicated that gravity waves could cause a wind variation with a ±15. m/s RMS amplitude at an altitude of about 110. km. The apparent randomness of the observed temporal variations and most of the variability can be potentially explained by the gravity wave breaking, although there remains unexplained sudden wind enhancement with 58. m/s with a time scale of 1-2. days in the observations.
- Infrared observations