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Weather and Climate Dynamics An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/wcd-2020-43
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/wcd-2020-43
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  30 Sep 2020

30 Sep 2020

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This preprint is currently under review for the journal WCD.

How Well do Models Represent the Development of Extra-Tropical Cyclones? Evaluation of Two General Circulation Models Against NAWDEX IOP 6 Observations

David L. A. Flack1, Gwendal Rivière1, Ionela Musat1, Romain Roehrig2, Sandrine Bony1, Julien Delanoë3, Quitterie Cazenave3, and Jacques Pelon3 David L. A. Flack et al.
  • 1Laboratoire de Météorologie Dynamique/IPSL, Ecole Normale Supérieure, PSL Research University, Sorbonne University, École Polytechnique, IP Paris, CNRS, Paris, France
  • 2CNRM, Université de Toulouse, Météo-France, CNRS, Toulouse, France
  • 3LATMOS-IPSL, CNRS/INSU, University of Versailles, Guyancourt, France

Abstract. The dynamical and microphysical properties of a well-observed cyclone from the North Atlantic Waveguide and Downstream impact Experiment (NAWDEX), called the Stalactite cyclone and corresponding to Intensive Observation Period 6, is examined using two atmospheric global circulation models: CNRM-CM6-1 and IPSL-CM6A. The hindcasts are performed in weather forecast mode, run at CMIP~6 resolution (LR) and c.~0.5° (HR) and initialized during the initiation stage of the cyclone. Cyclogenesis results from the merging of two relative vorticity maxima at low levels: one is associated with a Diabatic Rossby Vortex (DRV) propagating from the subtropics and the other is initiated by baroclinic development and interaction with a pre-existing upper-level PV cut-off. All hindcasts produce (to some extent) a DRV. However, the second vorticity maximum is almost absent in LR hindcasts because of an underestimated upper-level PV cut-off. The evolution of the cyclone is examined via the quasi-geostrophic ω equation, which separates the diabatic heating component from the dynamical one at each given time. In contrast with some previous studies, there is no change in the relative importance of diabatic heating with increased resolution. The analysis also shows that IPSL-CM6A produces a more active cyclone compared to the CNRM-CM6-1 due to stronger diabatism. To examine this further, hindcasts initialized during the mature stage of the cyclone are compared with airborne remote-sensing measurements. There is generally an underestimation of the ice water content in the model compared to the one retrieved from radar-lidar measurements, even when the liquid water content is added. Consistent with the increased diabatism in IPSL-CM6A compared to CNRM-CM6-1, the sum of liquid and ice water contents is higher in IPSL-CM6A than CNRM-CM6-1 and, in that sense, IPSL-CM6A is closer to the observations. However, ISPL-CM6A strongly overestimates the fraction of super-cooled liquid compared to the observations by a factor of approximately 50.

David L. A. Flack et al.

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David L. A. Flack et al.

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Latest update: 03 Dec 2020
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Short summary
The representation of an extratropical cyclone in simulations of two climate models is studied by comparing them to observations of the international field campaign NAWDEX. We show that the current resolution used to run climate model projections (more than 100 km) is not enough to represent the cyclone life cycle accurately but the use of 50 km resolution is good enough. Despite these encouraging results cloud properties (partitioning liquid/solid) are found to be far from the observations.
The representation of an extratropical cyclone in simulations of two climate models is studied...
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