Atmospheric boundary layer height measurements with wind profilers: successes and cautions

Abstract

Wind profiling radars have previously been deployed at a number of fixed and temporary sites to measure boundary layer structure and behavior. One of the most useful parameters produced by these instruments is the height of the convective boundary layer (CBL), also known as the mixing height. This is usually determined from the location of the peak of reflectivity caused by turbulence acting on a gradient of humidity at the CBL top. Various practitioners use techniques that differ only in subtle detail to find the CBL top. These measurements have proved quite useful in basic and applied boundary layer research. However, a number of phenomena can complicate or even completely frustrate CBL height measurements. These include hydrometeors, residual layers, clouds, birds, and insects. The addition of other measurements, such as cloud base from a ceilometer, and the use of other variables measured by the radar, such as the turbulence profile, can help to distinguish these phenomena from the true CBL in some cases. The present authors shows a variety of examples ranging from simple through problematic to impossible, and discusses how the uncertainty in some cases can be reduced. Some remarks on the possibilities of automated recognition of CBL height in profiler signals is also included.