A Numerical Experiment on the Occurrence of Atmospheric Hydraulic Jump at the Taebaek Mountains Downwind

Abstract

Large-eddy simulation of the lee-side hydraulic jump at the downwind side of the Taebaek Mountains demonstrates the advection of a warm anomaly and the atmospheric reverse roller of negative vorticity. The lee-side hydraulic jump entrains the upper-level atmospheric air into the lower-level atmosphere. The simulated lee-side hydraulic jump occurs under the following conditions on the effective height <i>ĥ</i> and width <i>â</i> of an obstacle: <i>ĥ</i> ≥ 0.74 for â > 10, which are equivalent to <i>Fr_h</i> ≤ 1.35 for <i>Fr_a</i> < 0 .1, where <i>Fr_h</i> and <i>Fr_a</i> are the Froude numbers defined in terms of the height and width of the obstacle, respectively. In detail, the hydraulic jump occurs when the upwind-side mean wind (<i>U</i>) ≤ 12 ms^{- 1} for the buoyancy frequency (<i>N</i>) = 0.009 s^{- 1}. The wind speed dramatically increases within the 30-minute period when the hydraulic jump occurs. The stronger upwind causes a warmer anomaly and stronger downslope wind gust. This study situates the atmospheric hydraulic jump phenomenon with regard ro wildfire occurrence, and describes it using the Froude number for the width and height of the obstacle. It is shown that a more vulnerable atmospheric environment can be formed when the hydraulic jump occurs, and the wave-breaking of mountain waves related to the hydraulic jump can be predicted by the Froude number.