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The Grey Zone Project aims to systematically explore convective transport and cloud processes in weather and climate models at various resolutions, ranging from high resolution turbulent resolving scales all the way to coarse resolutions that require full parameterized descriptions of these processes. By exploring the behaviour of these models with and without convective parameterizations through the so-called grey zone the project aims to answer
- Which are the relative contributions of the parameterized versus the resolved contributions to the convective transport?
- How well do models operate in the grey zone without an explicit convection parameterization?
- How well do models operate in the grey zone with a convection parameterization?
- How should scale-aware convection parameterizations behave in the grey zone?
The Grey Zone project aims to apply this methodology on a number of different types of moist convective systems. The type of moist convection considered here is a cold air outbreak.
Cold air outbreaks are a common feature in the winter time to the north of the British where cold air from the polar cap sweeps off the ice edge over open water. The convection begins as organised rolls near to the ice edge but eventually changes into open cellular convection as the boundary layer evolves (see Brummer and Pohlmann (2000) and references therein). These cloud morphological changes can have important impacts on the transport of heat and moisture as well as radiative effects such as high latitude Short Wave errors that are one of the largest biases in climate models (Karlsson and Svensson, 2010, Trenberth and Fasullo, 2010, Bodas-Salcedo et al. 2012). Accurate forecasts of such events are also important for civil aviation safety (e.g. Wilkinson et al. 2012).
The proposed intercomparison case is based on observations taken during the Met Office CONSTRAIN campaign and associated NWP simulations. Constrain took place over the North Atlantic, with flights carried out from Prestwick airport from January 12 to 31 2010. The aim of CONSTRAIN was to better determine the various ice and mixed-phase cloud microphysical parameters used in the Met Office Unified Model (UM) and cloud resolving models.
The proposed case is based in observations and NWP data from January 31st 2010 (see synoptic chart below). Observations show that this day was characterised by northerly flow and stratocumulus clouds at 66N -11W. As air advects over warmer seas the Sc transitions to mixed-phase cumulus clouds at around 60N, prior to reaching land.
The domain of interest is of the order of 1500 km by 750 km which will be The domain of interest is of the order of 1500 km by 750 km which will be explored with various resolutions by both global Numerical Weather Prediction (NWP) models and Limited Area Models (LAMs). Since it will be unfeasible to fully resolve the relevant moist convective processes for these two model types, we also have set up the case for idealised LAM and Large Eddy Simulation (LES) models that can run in a Langrangian setting on a smaller domain of around 100 km. For this set up it will be feasible for a number of models to run at a turbulent resolved (~100m) resolution.
- Global Case - Global Models will run this case at their highest spatial resolution (3~10km). The main research questions here are i) how well is the parameterized convection capable of representing realistically the transport of heat, moisture and momentum, thereby obtaining the correct vertical thermodynamical structure and cloud properties and ii) are global models already entering the grey zone at their highest spatial resolution and how does this affect their behaviour
- LAM case - LAMs will be executed at various resolutions in the range of 1 to 10 km. Here the main research questions are how convective transport and cloud processes are changing at these various resolutions with and without convection parameterizations
- LES case - LES codes and LAM’s will be run in a more idealized Lagrangian setting at a smaller domain of 100 km at turbulent resolving scales of 200 m ( and coarser) that will be advected with the mean flow. These runs will serve as a reference and the realism of the interaction between the parameterised cloud microphysics and the resolved turbulence will be explored: to what extent are the observed mesoscale structures (cloud streets and closed cells) realistically reproduced and how do these structures degrade with decreasing resolutions in the range of 100 m to a few kilometres.
Bodas-Salcedo A. , K. D. Williams, P. R. Field, and A. P. Lock, 2012:Contribution of midlatitude cyclone clouds to the short-wave deficit in the Southern Ocean . Submitted J. Clim.
Brummer, B and Pohlmann, S, 2000: Wintertime roll and cell convection over Greenland and Barents Sea regions: A climatology. Journal of Geophysical Research-Atmospheres. 105, D12, 15559-15566, 10.1029/1999JD900841
Karlsson, J., and G. Svensson, 2010: The simulation of Arctic clouds and their influence on the winter surface temperature in present-day climate in the CMIP3 multi-model dataset. Clim. Dyn., DOI 10.1007/s00382-00010-00758-00386.
Trenberth, K. E., and J. T. Fasullo, 2010: Simulation of Present-Day and Twenty-First-Century Energy Budgets of the Southern Oceans. Journal of Climate, 23, 44 0-454.
Wilkinson, J.M, Helen Wells, Paul R. Field and Paul Agnew, 2012: Investigation and Prediction of Helicopter Triggered Lightning over the North Sea. Submitted t o Met. Apps.