Convection Initiative discussion Convection Initiative discussion pointspoints• What info do parametrizations & 1.5-km forecasts need?

– Initiation mechanism, time-resolved cell size & updraft velocity, entrainment rate, rain & hail rate, organization mechanisms?

• What are the priorities for an observational campaign?– What was not learned from CSIP? Chilbolton or elsewhere? Focus on

initiation or subsequent evolution? Aircraft sampling? Scan strategy?

• What are the promising new ideas in parametrization?– Why is it so difficult? Is UK a suitable place to test parametrizations?

How can we use high-res models to develop parametrizations? Can we inter-compare new approaches at University & Met Office

• What are the priorities for flood forecasting?– How well are mechanisms for quasi-stationarity captured? Relative

importance of back-building/orographic triggering/dynamical forcing?

• What new datasets should be assimilated? New DA methods?• How important is microphysics, e.g. graupel & aerosol effects?• Where do we go from here?

– Scope? Funding mechanism, e.g. consortium bid? External collaboration, e.g. Leeds? Timing? Leadership of project?

Running orderRunning order• Robin Hogan• Humphrey Lean• Ross Bannister / Stefano Migliorini• Dan Kirshbaum• Alan Grant• Bob Plant• Remi Tailleux

To leave time for discussion afterwards, please aim for 7 mins + 2 mins for questions!

1. Radar sees clear-air scattering boundary-layer top (Morcrette 2007)

2. Refractivity: moisture convergence3. Doppler lidar: BL turbulence:

Initiation, BL Initiation, BL propertiesproperties

Radar BL top

Mesoscale model BL top

                                                                                                                                                                                                                                                            

                                                           

• 1/4-degree beam provides very high resolution cloud structure compared to smaller (e.g. mobile) radars:

Congestus

Mature cells

Dissipating cell

30 dBZiso-surface (~precip)

5 dBZ iso-surface (~cloud)

Cloud Cloud structurestructure

• Derive dissipation rate from spectral width (Chapman & Browning 2001)

Vertical windVertical wind1. Track features in horizontal velocity– Typical cell

transported 5025 Mt in 50-mins

– Counter-gradient momentum flux in lower troposphere

Vertical wind cont.Vertical wind cont.2. Line convection: assume 2D

flow and integrate continuity equation (Browning et al. 1997)

MicrophysicsMicrophysics

• Polarimetric radar measurements– Variational retrieval (Hogan 2007)...

• Can also estimate ice water content.

Rain rate Hail fraction