Single Doppler observations of boundary layer flows over heterogeneous terrain

The recent implementation of the Advanced Radar for Meteorological and Operational Research (ARMOR) has expanded boundary layer measurement capabilities within the Huntsville region and the Tennessee River valley. With a sensitivity in clear air comparable to that of the WSR-88D radar (-15 dBZ at 50 km), the ARMOR measurements are disclosing a wide variety of high-resolution ABL flows over the diverse heterogeneous surfaces within 50 km of the radar. The various surface properties within 50 km of the radar include a large reservoir on the Tennessee River, the Huntsville urban area, large expanses of both agricultural and forested regions, and topography that ranges from smooth to semi-mountainous. The paper will focus mesoscale perturbations in flow and reflectivity factor associated with these heterogeneous features. On days with weak winds, a lake breeze circulation forced by Wheeler Reservoir generates significant flow perturbations in the convective boundary layer, sometimes significant enough to produce convective initiation. On occasions, the flow perturbations appear to assume a sequence of mesoscale vortical circulations on the order of 10 km in diameter. Other recently observed flows include nocturnal drainage winds within the Tennessee River valley, and a modest Huntsville urban heat island circulation which is also apparent in the radar measurements as enhanced reflectivity factor and minor flow perturbations. This paper will quantify the mesoscale flows using the NCAR Variational Doppler Radar Analysis (VDRAS) software plus more conventional VAD techniques to examine mesoscale divergence and vertical motion.