Some questions on convection that could be addressed through another UK field program centered at Chilbolton Dan Kirshbaum 1

Predictability Short-term forecasting: is initial spread large enough? Synoptically forced vs. high-pressure convection – different sources of uncertainty Initial condition uncertainties well developed How to infuse uncertainty into HP case? Relationship with small/meso-scale topography Known forcings: should improve predictability but can also expose systemic errors Can back-building be predicted? Studied intensely by Schumacher et al in the States – these hypotheses can be tested over here 2

Dynamics Where is the inertial subrange? Does it depend on cloud size/environment? This is where our resolution needs to be (even if its 100 m), or models get the mixing/entrainment wrong Symptom: too many small cells, not enough mesoscale organization Role of direct mesoscale lifting/descent on the evolution of incipient storm cells Rapid intensification of shallow cumuli drifting over land and/or higher terrain Inflow into convergence zones Can strongly affect cloud growth rate 3

Answering the questions? Predictability More convective ensembles (1 km or higher resolution) in different large-scale environments Incorporate uncertainty at both large and small scales (building on results from the COPS programme) Add stochastic component to PBL/mixing schemes? Uncertainties in land-surface properties (and soil moisture)? Assimilate turbulent variability measured by lidar? Dont need a field programme for this, but observations do provide more ground-truth for verification 4

Answering the questions? Dynamics Measuring the kinetic energy spectrum of developing clouds in all stages of evolution? Can Chilbolton be used for that? LES incorporating complex terrain: capturing mesoscale forcing and the cloud-scale response At what resolution do mixing schemes break down? One possible tool: Bryan cloud model (already tried and tested for LES) No explicit PBL or radiation Terrain included Range of physics options (microphysics, turbulence) 5