Abstract/Summary

This thesis presents new observations of updraught pulses ascending into deep convection over time. These were obtained using an improved scanning strategy and retrieval method for retrieving vertical velocity from the Chilbolton Advanced Meteorological Radar. A vertical velocity retrieval algorithm was developed and tested on synthetic data and observations from prior campaigns. Vertical velocity is retrieved by comparing differences in Doppler velocities at a particular scale between pairs of measurements. Uncertainty was estimated to be less than 1.5 m s−1 on average with a 95th percentile of 2.4 m s−1 . Prior campaign data showed updraught structures evolving as discrete pulses or thermals noticed by studying consecutive scans. In this data multiple thermals were observed in convective cells with lifetimes mostly between 2 and 5 minutes with some up to 10 minutes. Thermals generally ascended less than 1.5 km in height and had diameters between 500 m and 2 km. To provide information in three-dimensions with high spatial and temporal resolution, a new multi-scan scanning strategy was developed that primarily bracketed reflectivity cores. New scans of a particular deep convective cloud system provided detailed observations of much of the lifetime of three individual convective cells with approximately 2 minutes resolution. Dimensions of updraught and eddy dissipation rate structures were positively correlated and coherent in along-scan, cross-scan and perpendicular to scan directions and there were more smaller ‘fragment’ type structures. Individual convective cells developed over time as multiple ascending pulses, formed plume-like structures and an overshooting top. Pulses ascended ahead of differential reflectivity columns when located near the freezing level and into the cloud top with 30 dBZ echo top height with widths similar to reflectivity towers.