The Cold-Air Outbreaks in the Marine Boundary Layer Experiment model-observation intercomparison project (COMBLE-MIP) – Part 1: Model specification, observational constraints, and preliminary findings
Abstract
Models struggle to represent the coupled microphysical, turbulent and radiative processes within widespread, long-lived marine cold-air outbreak (CAO) cloud fields, contributing to forecast and climate biases. Here we combine ground-based and satellite measurements to initialize and constrain large-eddy simulations (LES) of cloud field evolution with distance downwind from the marginal ice zone during a strong, highly supercooled and convective CAO observed during the Cold-Air Outbreaks in the Marine Boundary Layer Experiment (COMBLE). LES results are compared with large-scale models run in single-column model (SCM) mode, providing an observation-constrained framework for large-scale model evaluation and future improvements. All models reproduce rapid cloud formation off the ice edge, and a monotonic ascent of downwind cloud-top heights, closely linked with time-integrated surface heat fluxes. LES generally reproduce domain-mean observational targets using a modest test domain (25×25 km 2 ), and a larger domain (125×125 km 2 ) enables better reproducing the observed growth of convective cell sizes. In realistic mixed-phase LES compared with liquid-only simulations, ice processes lead to thinner, broken cloud decks and substantially reduced cloud radiative effects on top-of-atmosphere longwave fluxes. By contrast, mixed-phase SCM simulations generally underpredict the radiative impact of ice, primarily owing to insufficient reduction of cloud cover. Results indicate that cellular cloud structure is qualitatively captured by LES, and thus LES could provide guidance to improvement of large-scale model physics schemes. Follow-on work will extend these results to larger domains, apply objective analysis of mesoscale structure, and include prognostic aerosol properties for droplet and heterogeneous ice formation.
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Authors: Timothy W. Juliano, Florian Tornow, Ann M. Fridlind, Andrew S. Ackerman, Gregory S. Elsaesser, Bart Geerts, Christian Philipp Lackner, David Painemal, Israel Silber, Mikhail Ovchinnikov, Gunilla Svensson, Michael Tjernström, Peng Wu, Alejandro Baró Pérez, Peter Bogenschutz, Dmitry Chechin, Kamal Kant Chandrakar, Jan Chylik, Andrey Debolskiy, Rostislav Yu. Fadeev, Anu Gupta, Luisa Ickes, Michail Karalis, Martin Köhler, Branko Kosović, Peter Kuma, Weiwei Li, Evgeny V. Mortikov, Hugh Morrison, Roel Neggers, Anna Possner, Tomi Raatikainen, Lea Raillard, Sami Romakkaniemi, Niklas Schnierstein, Shin‐ichiro Shima, Nikita Silin, Mikhail Tolstykh, Étienne Vignon, Lulin Xue, Meng Zhang, Xue Zheng
Institutions: Columbia University, University of Cologne, Sorbonne Université, Centre National de la Recherche Scientifique, Goethe University Frankfurt, University of Wyoming, Université Paris Sciences et Lettres, École Polytechnique Fédérale de Lausanne, NSF National Center for Atmospheric Research, Stockholm University, Chalmers University of Technology, Lomonosov Moscow State University, École Normale Supérieure - PSL, Deutscher Wetterdienst, École Polytechnique, Johns Hopkins University Applied Physics Laboratory, Langley Research Center, Bolin Centre for Climate Research, University of Hyogo, Finnish Meteorological Institute, Pacific Northwest National Laboratory, Lawrence Livermore National Laboratory, Laboratoire de Météorologie Dynamique, National Aeronautics and Space Administration, Goddard Institute for Space Studies, Swedish Meteorological and Hydrological Institute, Institute of Numerical Mathematics, A.M. Obukhov Institute of Atmospheric Physics, Institute of Mathematical Problems of Biology, Hydrometeorological Research Centre of Russian Federation