Airflows over steep complex terrain with characteristic length scales of the order of kilometers contain the flow impingement, separation and reattachment. In order to develop an accurate model of simulating the above-mentioned topographic effects, we have been examining the large-eddy simulation (LES) technique using a finite-difference method (FDM). These LES codes are referred to as the RIAM-COMPACT (Research Institute for Applied Mechanics, Kyushu University, Computational Prediction of Airflow over Complex Terrain).
First, using the RIAM-COMPACT, we performed the calculations of stably stratified airflows over Miyake-jima. The characteristic phenomena of stably stratified airflows with various Froude numbers were successfully simulated. Next, in the airflow patterns obtained, the passive particles were released from the top of Miyake-jima. Based on their results by using the passive particles tracking method, behaviors of volcanic smokes were discussed. It was found that a variety of smoke patterns were induced, corresponding to the difference in the flow pattern around Miyake-jima.

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