Abstract. The high-power Defford radar has been upgraded to provide Doppler information regarding the motion of echoes from weak refractive index inhomogeneities within the optically clear atmosphere. A case study is presented in which data from the radar are used to derive the detailed velocity structure in and above the planetary boundary layer. These data are analysed to show how convective circulations in the boundary layer can perturb the height of a shallow inversion overlying it, thereby producing local enhancements of wind shear and a decrease in dynamic stability within the inversion. The measurements were obtained as part of a Boundary-Layer Project in which simultaneous measurements were made using fast-response instruments suspended from a tethered balloon within the region scanned by the radar. The balloon-borne probes showed that the most intense turbulence and fluctuations of temperature and refractivity were encountered when radar-detected hummocks in the height of the inversion were advected through the probes. The fine-scale turbulence measurements within the perturbed inversion are consistent with the existence of Kelvin-Helmholtz billows.
Two Doppler radars have been used to measure simultaneously the vertical and horizontal velocity components within an isolated air mass shower. Precipitation growth was found to be restricted to a small region of gently rising air within which the vertical and horizontal air velocities relative to the shower rarely exceeded 1 m sec−1. Ice crystals within the updraught were balanced by it; graupel particles developed during descent through it. The growth rate of the graupel was consistent with a cloud liquid water content about half the adiabatic value. As in many showers studied using Doppler radar, the updraught was restricted to the upper parts of the shower. The descent of the graupel beneath the updraught was associated with weak downdraughts and a local increase in the horizontal winds relative to the shower.
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