Application of Gravity Current Model to Analysis of Squall-Line Gust Front

Abstract

An analysis of a severe gust front is made to examine its three-dimensional structure. The data used are from the storm measurement network operated by the National Severe Storms Laboratory (NSSL). The important structural features shown in the analysis include: i) intense wind and thermal gradients at the leading edge of the air mass; ii) retardation of the cold-air front near the ground; and iii) vertical protrusion of the cold air to 1700 m at the front of the cold air mass, forming a bulge called a head. Upstream of the head, the depth of the cold air was almost constant at 3350 m; iv) a well defined circulation cell with a horizontal axis was found within the head; this wind field was associated with a core of maximum horizontal wind speed of 34 m sec?1 only 175 m above the ground, upward motion of 5?10 m sec?1 within the frontal zone, and weaker downward motion on the rear side of the head. In these structural characteristics, as well as in some substructural properties, this gust frontal air mass is found to be similar to laboratory-produced gravity currents. Moreover, the horizontal displacement speed of the gust front agrees with empirical and dynamical theory of gravity currents.