CONSTRAIN cold air outbreak

First phase of the Grey Zone Project

The study area of the first phase of the Grey Zone Project was located to the north of the British Isles. The case was based on observations and numerical weather prediction data of a cold air outbreak from January 31st, 2010. Clouds evolved from a closed stratocumulus deck to open cellular convection as the boundary layer deepened. Organised roll structures formed to some extent. The cellular patterns reached scales on the order of tens of kilometers and influenced the turbulent and convective transport. The case encompassed three parts: a large-eddy model intercomparison, a limited area model intercomparison, and a global model intercomparison. Numerical experiments were performed with convective parameterisations switched on and off, and the resolution dependence of the simulations was explored in a systematic way in the spirit of the Grey Zone Project.


The results of the first phase of the Grey Zone Project are summarized in three publications:

S. R. de Roode, Th. Frederikse, A. P. Siebesma, A. S. Ackerman, P. R. Field, A. Hill, J. Fricke, M. Grischka, R. Honnert, Ch. Lac, S. Krueger, A. T. Lasage, and L. Tomassini (2019), Turbulent transport in the grey zone: A large-eddy simulation intercomparison study of the CONSTRAIN cold air outbreak case, J. Adv. Model. Earth Syst., 11, 597-623, doi:10.1029/2018MS001443.

P. R. Field, R. Brodzkova, M. Chen, J. Dudhia, Ch. Lac, T. Hara, R. Honnert, J. Olson, P. Siebesma, S. de Roode, L. Tomassini, A. Hill, and R. McTaggart-Cowan (2017), Exploring the convective greyzone with regional simulations of a cold air outbreak, Q. J. R. Meteorol. Soc., 143, 2537-2555.

L. Tomassini, P. R. Field, R. Honnert, S. Malardel, R. McTaggart-Cowan, K. Saitou, A. T. Noda, A. Seifert (2017), The "Grey Zone" cold air outbreak global model intercomparison: a cross-evaluation using large-eddy simulations, J. Adv. Model. Earth Syst., 9, 39-64, doi:10.1002/2016MS000822.


In December 2014 the Grey Zone Project organized a workshop at the Max Planck Institute for Meteorology in Hamburg, Germany, to discuss ideas around the development of scale-aware boundary layer and convection parameterizations.

Scientific committee                                         

The Scientific Committee of the first phase of the Grey Zone Project:

Pier Siebesma, Stephan de Roode, Paul Field, Adrian Hill, Axel Seifert, Lorenzo Tomassini