Experimental investigation of the interaction between near-surface atmospheric boundary layer winds and downburst outflows

Abstract

This article focuses on experimental investigation of the interaction between downburst (DB) and near-surface atmospheric boundary layer (ABL) winds. The flow field of DB immersed into ABL winds (DBABL) is compared against the outflow produced by an isolated DB without ABL winds. The diameter of investigated downdrafts was 3.2 ​m. The study demonstrates that there is a profound difference between the radial velocity components in the DBABL and DB outflows in terms of peak and mean velocities, vertical profile of radial velocity, as well as the overall temporal signature of the velocity records. The asymmetry of the DBABL outflow in the along-ABL wind direction is similar to that observed in real traveling downbursts. The turbulence intensity in the near-surface DBABL winds can exceed 40% in some parts of the outflow where the downburst propagates against ABL winds. The DBABL wind profile is characterized by smaller nose-shape curvature than the DB winds in the part of the outflow where downburst and ABL winds have the same direction. The steady-state ABL wind segments and transient downburst segments in the DBABL velocity records are similar to anemometer records of real downbursts. The paper also shows that the velocity addition DBABL→≠DB→+ABL→ throughout the outflow.