Dual Doppler Measurement of a Sheared, Convective Boundary Layer

The Phoenix II experiment was conducted in the spring of 1984 on the high plains of eastern Colorado, using dual Doppler radar as the primary observing tool in a study of the convective planetary boundary layer. Extensive support was provided by in situ sensors (instrumented aircraft, micrometeorological tower and surface network) for verification and extension of radar data. The two experiment days with the deepest boundary layers (which proved to be strongly sheared) were chosen for intensive study, and six 20-minute segments of continuous data from each day (about one each hour during the afternoon) have been analyzed. The time resolution of the data is approximately two minutes, and the resolution of the analysis grid (which is 9 km by 9 km by 4 km deep) is 200 m in all directions. Application of available dual Doppler synthesis and integration techniques to define the four-dimensional velocity fields produced an unacceptably high noise level in the vertical velocity and derived statistics, prompting an exploration of alternative analysis methods, and a revival of coplanar integration to reduce the error variance to an acceptable level. The success of the coplanar technique is also demonstrated in a propagation of error analysis. Pressure and buoyancy fluctuations were retrieved from the wind fields using the Gal-Chen/Hane thermodynamic recovery, although over a smaller range of physical scales. The computed momentum and buoyancy fluxes are the basis of a study of the sheared, convective boundary layer over the course of two afternoons, including turbulent kinetic energy budgets and vertical velocity variance budgets.