Local structure of the convective boundary layer from a volume-imaging radar

The local structure and evolution of the convective boundary layer (CBL) ar e studied through measurements obtained with a volume-imaging radar, the tu rbulent eddy profiler (TEP). TEP has the unique ability to image the tempor al and spatial evolution of both the velocity field and the local refractiv e index structure-function parameter, (C) over tilde(n)(2). Volumetric imag es consisting of several thousand pixels are typically formed in as little as 1 s, Spatial resolutions are approximately 30 m by 30 m by 30 m. CBL data obtained during an August 1996 deployment at Rocks Springs, Pennsy lvania are presented. Measurements of the vertical (C) over tilde(n)(2) pro file are shown, exhibiting the well-known bright band near the capping inve rsion at z(r), as well as intermittent plumes of high (C) over tilde(n)(2). Horizontal profiles show coherent 100-m-scale (C) over tilde(n)(2) and ver tical velocity (w) structures that correspond to converging horizontal velo city vectors. To quantify the scales of structures, the vertical and stream wise horizontal correlation distances are calculated within the TEP field o f view. To study the statistics and scales of larger structures, effective volumes larger than the TEP field of view are constructed through Taylor's hypothes is. Statistics of (C) over tilde(n)(2) and w time series are compared to an appropriately scaled large eddy simulation (LES). While w time series comp arisons agree very well, the LES (C) over tilde(n)(2) predictions agree onl y with some of the measured data. Finally, the scales of (C) over tilde(n)( 2) structures in the TEP time series measurements are calculated and compar ed to the scales in the LES spatial domain. Good agreement is found only ne ar the capping inversion layer, the area of largest structures. This study highlights: the unique capabilities of the TEP instrument, and shows what a re believed to be the first statistical comparisons of measured (C) over ti lde(n)(2) data with LES derived results.