12th Conference on Middle Atmosphere

Wednesday, 6 November 2002: 4:15 PM
Convectively generated gravity waves simulated throughout the equatorial middle atmosphere
Takeshi Horinouchi, Kyoto University, Uji, Kyoto, Japan
A three-dimensional cloud-resolving mesoscale model with ice micro physics was used to simulate the gravity waves generated by tropical cumulus convection. The simulation domain extends vertically from the surface to 120 km, where the highest 20 km is a sponge layer. The grid spacing is horizontally 1.5 km and vertically 0.5 km above the mid troposphere. The initial condition and a time-dependent horizontally uniform forcing were specified based on the soundings during the TOGA-COARE Intensive Observation Period (IOP) conducted from November, 1992, through February, 1993, over the equatorial Western Pacific.

The model was able to reproduce the time sequence of overall convective activity during a week in the IOP. It was observed that cumulonimbus updrafts were accompanied with upward propagating 10-km-scale gravity waves, which spreads horizontally with concentric circular patterns, as noted in past studies. In addition, larger-scale organizations of cumulus convection such as squall lines seem responsible for gravity waves with larger horizontal scales, which dominate around the mesopause. The amplitude growth of waves with altitude created local critical levels for waves with relatively slow phase speeds, which include the circularly spreading small-scale waves mentioned above. Explicit wave breaking occurred frequently between 85 km and 100 km, creating ripples similar to those observed with airglow imaging. The impacts of simulated waves on the momentum budget and chemical constituents will be discussed in the talk.

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