12th Conference on Middle Atmosphere

Monday, 4 November 2002: 12:59 PM
Effects of Parameterizing Convectively Forced Gravity Wave Drag in NCAR CCM3
Hye-Yeong Chun, Yonsei University, Seoul, Korea; and I. -. S. Song, J. -. J. Baik, and Y. -. J. Kim
The parameterization of gravity wave drag induced by subgrid-scale cumulus convection (GWDC) proposed by Chun and Baik (1998, JAS) is implemented in the NCAR CCM3, and its effects on perpetual January and July circulations are investigated. The cloud-top wave stress is found to be concentrated in the tropical region where major convective activity occurs. The GWDC parameterization can alleviate systematic model biases in the zonal-mean zonal wind and temperature fields in most regions. In particular, excessive easterlies in the tropical stratosphere can be alleviated by the GWDC process about 50% in both January and July. The zonal-mean temperature and horizontal divergence in the tropical lower stratosphere are also significantly improved by including the GWDC process. The maximum westerly acceleration due to the GWDC process averaged over 15oS-15oN latitudes is about the half of momentum forcing required for driving a QBO westerly phase. This suggests that including the GWDC parameterization can provide a better chance for realistic QBO simulations, which is not properly simulated in most current GCMs.

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