Controllable outflow generator for the experiment of a non-supercell tornado

Outflows sometimes become triggers of tornado outbreak. We succeeded to experimentally simulate the generation of supercell and non-supercell tornadoes (Sassa and Takemura 2009) by using dry ice mist as the cold air of outflow. Unfortunately, the outflow simulator cannot control and maintain the characteristics of outflow even the size of dry ice and water temperature are fixed. If we control the height and speed of the gust front that is a leading edge of the outflow, we can investigate orographic effect of tornado outbreak and tornado intensity affected by environment. The present experimental study aims to develop the controllable outflow generator and demonstrate the generation of non-supercell tornado. The outflow simulator designed by us is shown in Fig. 1. We employed thermoelectric cooling modules to chill airflow. The temperature and velocity of the outflow can be changed by the control of the thermoelectric cooling modules and the fan, respectively. The outflow generated by this apparatus was found to stably hold same condition more than 2 hours. The velocity profile becomes a low-level jet type in X > 100 mm, which shows the outflow has the nature of gravity current. As shown in Fig. 2, billow pattern is clearly observed both sides of the outflow, which is induced by shear instability. The vertical vorticity concentrates in such billow. Then, non-supercell tornado can be easily reproduced by the updraft made by another fan as shown in Fig. 3. We will report the relation between the horizontal shear and tornado intensity.