The DYMECS project: A statistical approach for the evaluation of convective storms in high-resolution NWP models
Thorwald Hendrik Matthias Stein1, Robin James Hogan
2, P. Clark
2, Carol Halliwell
3, Kirsty Hanley
3, Humphrey Lean
3, John Nicol
2 and Robert Stephen Plant
1, (1)University of Reading, Meteorology, Reading, RG6, United Kingdom, (2)University of Reading, Meteorology, Reading, United Kingdom, (3)MetOffice@Reading, Reading, United Kingdom
Contact First Author: Thorwald Hendrik Matthias Stein; t.h.m.stein@reading.ac.uk
Previously Published Material: This presentation includes results from the DYMECS project, which is featured in two publications, with two further publications currently under review. The two accepted publications are:Hanley, K. E., Plant, R. S., Stein, T. H. M., Hogan, R. J., Nicol, J. C., Lean, H. W., Halliwell, C. and Clark, P. A. (2014), Mixing-length controls on high-resolution simulations of convective storms. Q.J.R. Meteorol. Soc.. doi: 10.1002/qj.2356 Stein, T. H. M., Hogan, R. J., Hanley, K. E., Nicol, J. C., Lean, H. W., Plant, R. S., Clark, P. A., and Halliwell, C. E. (2014), The three-dimensional morphology of simulated and observed convective storms over southern England. Mon. Wea. Rev., 142, 3264–3283. doi: http://dx.doi.org/10.1175/MWR-D-13-00372.1
English Abstract:
Convective storms are the frequent cause of flash floods in many mid-latitude countries and can have wide-ranging impacts on livelihoods and infrastructure, so the timing and location of these storms, as well as their evolution, are important to forecast accurately. Several forecast centers now run NWP models operationally at order 1-km resolutions, while models with sub-kilometer grid lengths are emerging to assist forecasts. Here we present results from the DYMECS project (Dynamical and Microphysical Evolution of Convective Storms), in which we observed over 1,000 storms using the Chilbolton radar in southern England and ran the Met Office Unified Model (UM) for several cases at horizontal grid lengths between 1500m and 100m. Life-cycle statistics were derived by tracking features in the rainfall from the UK radar network. We show that at 1500m grid length, the model relies on rainfall features that are too large and too long-lived compared to observations, while at 100m grid length, rainfall features are frequently too small and too intense. In comparison with the Chilbolton observations, we show that storm volumes in the 1500m simulation are a factor 1.5–2 wider than observed. At smaller grid lengths, shallow and mid-level storms have comparable widths to the observed structures, but deep storms appear slightly too narrow. Updrafts in the 1500m simulation are weaker than those derived from the radar winds but much too wide, while they are too narrow in the 100m simulation. For all diagnostics, simulations at 200m grid length perform best, but we show that results can be improved by changing the subgrid mixing length in the model's turbulence parameterization scheme. The DYMECS data form a benchmark for model evaluation at the Met Office and can be used to evaluate other models, while the statistical approach developed is applicable to radar-intensive field campaigns.
