Statistical analyses of convective updraughts using radar scans and model data

Convective storms are a crucially important forecasting problem in the UK, not least because of the flooding they can cause. In the last few years many operational weather centres have begun to run at “convection permitting” resolutions, with the UK Met Office currently running a 1.5 km forecast model operationally (MetUKV). While there is evidence that precipitation forecasts at this resolution are more accurate than lower resolution forecasts, it is clear that there are still significant shortcomings in the nature of the convective clouds simulated at this resolution. Cells in the model tend to be too large and too intense, and tend not to organise into mesoscale complexes as observed, illustrating our lack of understanding of the nature of small-scale mixing and microphysical processes. The DYMECS (Dynamical and Microphysical Evolution of Convective Storms) project has obtained a large database of convective storms throughout their lifecycle by tracking them with the Chilbolton Advanced Meteorological Radar. Individual storms were tracked on a number of days using a variety of scanning techniques to extract the dynamical and microphysical properties of the storm (such as storm size, vertical velocity, maximum surface rain-rate and hail intensity). In this study we perform simulations of the DYMECS cases with the MetUKV, which allows us to apply a statistical approach to evaluate the properties and evolution of the simulated storms over a wide range of conditions. Here we present results comparing the magnitude and spatial structure of updraughts in the model and reality. Two techniques have been used to estimate vertical velocity from the radar data, which we evaluate here using the model output. Finally we investigate the sensitivity of the simulated updraughts to the turbulent mixing length and increasing horizontal resolution.