Nocturnal planetary boundary layer structure and turbulence episodes during the Project STABLE field program

Abstract

Sulfur hexafluoride (SF6) tracer was released continuously during the experiments and measured 10-20 km downwind by a mobile continuous analyzer. The tracer transport was shown to be consistent with low-level winds on the 304-m tower, except on the third night. It was hypothesized that on the third night the spatial variability of the wind field was much more extreme than on the other nights and, hence, the winds from the 304-m tower did not reflect the true plume movement. A spatially averaged mean wind was more successful in explaining the observed horizontal plume movement. The wider-than-expected across-arc concentration distribution on the third night was attributed to continuously varying shear; whereas the occasional secondary maxima in the tracer pattern were due to discontinuities in the vertical wind shear. -from Authors