© Crown copyright Met Office Convection Permitting Modelling Humphrey Lean et al. Reading, UK Leeds April 2014

© Crown copyright Met Office mesoscale modelling questions Improve representation of convection in models with explicit convection Current 1.5km model (UKV) and higher resolution versions (both for future use and to help understanding). COPE work follows on from DYMECS.

© Crown copyright Met Office DYMECS project DYnamical and Microphysical Evolution of Convective Storms (DYMECS). Statistical analysis of convective cells with Chilbolton Radar over a number of cases. Hogan, Plant, Stein, Nicol, Clark University of Reading Lean, Halliwell, Hanley

© Crown copyright Met Office Average cell diameter (km) (over 22 convective cases). Threshold (mm/hr) RadarUKV Know that current km scale models are under-resolved for explicit convection “convection permitting”. (Hence experiments with shallow scheme..) Emilie Carter

© Crown copyright Met Office 20 April Aug m model best 500m model best 200m model best 1.5km model best 11 UTC - radar15 UTC - radar “Small”“Large” Kirsty Hanley

© Crown copyright Met Office Median storm diameter with height Thorwald Stein 3D reflectivity structure from Chilbolton. Similar message on high res models collapsing cloud diameter too much (see later talk).

© Crown copyright Met Office Visualisation of radar data Cutaway: reflectivity Surface: rainrate Shading: extent of cloud km Robin Hogan

© Crown copyright Met Office Visualisation of UKV data Cutaway: reflectivity Surface: rainrate Shading: extent of cloud km Robin Hogan

© Crown copyright Met Office Visualisation of 200m data Cutaway: reflectivity Surface: rainrate Shading: extent of cloud km Robin Hogan

© Crown copyright Met Office Width of updrafts (preliminary) John Nicol 30 most intense rain cells simulated and observed between 1200 and 1600 UTC 25 August 2012 updraftsreflectivity

© Crown copyright Met Office

Can we make the 200m model produce larger storms on 25 th Aug 2012 by changing the mixing length? Need to reduce the timestep to 3s to avoid hitting stability limit. Can produce larger storms but at the expense of the smaller storms. Increasing the mixing with height may be a solution i.e. make Smagorinsky scheme dependent on Δz. Varying the mixing length l=300m – 2491 storms l=100m – 3583 storms l=40m – 4359 storms 200m Kirsty Hanley

© Crown copyright Met Office DYMECS modelling conclusions so far….. UKV clearly under-resolves many small showers in UK High res models (~100m) improve some aspects but have problems – in particular tend to produce too narrow showers (measured by surface rain or cloud) when they should be larger. Updraft widths more correct in High res models. Above may primarily be issue with clouds. Representation very sensitive to mixing. May be able to improve high res models via mixing scheme. No satisfactory ~100m configuration..

© Crown copyright Met Office COPE work Investigate above issues on COPE cases. Well observed Different (and important) type of cases Philosophy so far has been to start on sea breeze case without rain and look at vertical velocities (see next talk). Then move on to more complex ones So far lots of evidence of problems in high res models of COPE cases (see next talk).

© Crown copyright Met Office Thank you for listening. Any questions?