斜めに貫入する冷気外出流境界における竜巻生成の実験

抄録

Non-supercell tornadoes frequently occur on the gust fronts of cold outflows intruding to environmental flow. It is quite difficult to predict the genesis of such tornadoes because the generations of parent cumulonimbi and cold outflows are not represented by ordinal environmental indices. Therefore, we need to establish new indices to represent non-supercell tornado genesis. The present laboratory experiment aims to clarify the environment of non- supercell tornadoes which are generated on gust front of cold outflow intruding environmental flow. We reproduced such flow situation by using a cold outflow simulator and an environmental flow simulator. In the present experiment, we set the cold outflow simulator at 30 deg. in attack angle. We made stereo dynamic PIV and measured 3-D velocity field on the horizontal plane. The results showed that the rotating direction of tornado-like vortices was changed with velocities of the cold outflow and the environmental flow. A counter-rotating vortex pair was observed to generated by tilting. The tornado-like vortices are also found to have the downdraft region partially.