Cloud-scale modelling at Manchester during VOCALS

1. P. Connolly, G. Vaughan, J. Crosier etc Cloud-scale modelling at Manchester during VOCALS

2. Plans for LES / microphysical modelling • Appoint new cloud physics PDRA who will be working with the LEM, supervised by me. • NCAS cloud physics post (Jonny Crosier) to begin to use the LES model and develop it. Working closely with the Cloud Physics PDRA and doing data analysis to aid this. This is to have the modelling expertise within NCAS. • Main points of interest during VOCALS: • Validating the LEM against aircraft, and hyperspectral imager observations at differing degrees of complexity (e.g. Bulk schemes, including aerosol measurements, etc). • Quantifying the uncertainties associated with (1) changing surface sensible and latent heat fluxes; (2) Changing the magnitude and locations of lids and dry layers; (3) including the effects of aerosols as CCN. • Investigating the effects of the above on 3-D cloud structure (comparison with Do-228) • The importance of the entrainment zone humidity at the top of the boundary layer • One-way nesting the LEM within WRF simulations (from WP4?). Linking to above – e.g. Effects on cloud structure further away from shore – are POCS initiated by aerosol or dynamical/thermodynamical effects?

3. Tools to use • Use version 2.4 of the Met Office LEM as the principal tool at a range of resolutions. • Use developments made through APPRAISE, interface with LEM for modelling aerosol properties from aircraft measurements – the LEM with mostly be run with a 2-moment bulk scheme and validated against a bin model... • The modelling validation strategy will involve performing both simple 1-D `column' model simulations with. • The met office LEM • The APPRAISE (manchester) core model; thus evaluating the performance of the microphysics part of the code. • We will then extrapolate this to 3-D simulations, testing both non- and precipitating cases.

4. What have we been doing? • Looking at a cloud topped marine bl case study from FIRE – off California coast, simulated in 3-D with interactive radiation (30m resolution) to understand how absorption of short-wave radiation at cloud top can reduce the thickness of the Sc and de-couple the cloud layer from the mixed layer. • Developing microphysical model with best numerics/schemes etc – not shown today. • Take a quick look at the FIRE case

5. FIRE test case

6. FIRE test case

7. Almost Adiabatic LWC Inversion at top Short-wave warming at cloud-top FIRE test case

8. To re-iterate • We will be performing LES simulations (validated with an explicit bin microphysics model) at a range of resolutions <50m down to 5m resolution to investigate cloud-scale processes and their effects on things like albedo and drizzle rate, accumulation etc. • Aim is to understand the uncertainties in modelling 3-D cloud structure for both non-precipitating and drizzling (if observed) strato-cumulus clouds during VOCALS. • By uncertainties we mean quantifying those associated with sensible/latent heat surface fluxes, slight changes in the magnitude and location of dry layers and those associated with using the aerosol data.

9. Some possible questions/pit-falls • How do we know that the bin microphysical scheme is doing as it should? • There will be on-going validation exercises between this model and cloud chamber studies as part of (1) APPRAISE-ICE and (2) SIMPLEX – Manchester chamber. • The closure studies (between aircraft and CCN data) will be performed with the same aerosol model, thus adding to the validity. • Is the approach of validating against a 1-D scheme and then applying in a 3-D scheme valid? • We are aiming to test the bulk scheme through as wide range of the phase space as possible.