Representation by two climate models of the dynamical and diabatic processes involved in the development of an explosively deepening cyclone during NAWDEX

Abstract

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 components (ARPEGE-Climat 6.3 and LMDZ6A) of the global climate models CNRM-CM6-1 and IPSL-CM6A, respectively. The hindcasts are performed in “weather forecast mode”, run at approximately 150–200 km (low resolution, LR) and approximately 50 km (high resolution, HR) grid spacings, and initialised during the initiation stage of the cyclone. Cyclogenesis results from the merging of two relative vorticity maxima at low levels: one associated with a diabatic Rossby vortex (DRV) and the other initiated by baroclinic interaction with a pre-existing upper-level potential vorticity (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. In contrast to some previous studies, there is no change in the relative importance of diabatic heating with increased resolution. The analysis shows that LMDZ6A produces stronger diabatic heating compared to ARPEGE-Climat 6.3. Hindcasts initialised during the mature stage of the cyclone are compared with airborne remote-sensing measurements. There is an underestimation of the ice water content in the model compared to the one retrieved from radar-lidar measurements. Consistent with the increased heating rate in LMDZ6A compared to ARPEGE-Climat 6.3, the sum of liquid and ice water contents is higher in LMDZ6A than ARPEGE-Climat 6.3 and, in that sense, LMDZ6A is closer to the observations. However, LMDZ6A strongly overestimates the fraction of super-cooled liquid compared to the observations by a factor of approximately 50.

The impact of deep convection representation in a global atmospheric model on the warm conveyor belt and jet stream during NAWDEX IOP6

“…Our approach is based on the case study of an extratropical cyclone that occurred during NAWDEX called the Stalactite cyclone (29 September -3 October 2016) and corresponding to Intensive Observing Period (IOP) 6. It was an explosively deepening cyclone at a rate of roughly 24 hPa in 24 hours (Flack et al, 2021) that formed off the east coast of Newfoundland and travelled over the North Atlantic toward Iceland and Greenland. This large-scale cyclone participated in the formation of a blocking over Scandinavia (Schäfler et al, 2018).…”

“…Blanchard et al (2020) and Blanchard et al (2021) studied the WCB-embedded convection by performing convection-permitting model simulations while Mazoyer et al (2021) analyzed the impact of cloud microphysics on the WCB activity of the Stalactite cyclone with similar convection-permitting simulations. Flack et al (2021) analyzed the whole life cycle of the cyclone in simulations of two climate models. Maddison et al (2020) showed that mediumrange forecast skills of the cyclone are sensitive to the choice of the deep convection schemes but none of these studies systematically investigated the role of parameterized deep convection on the WCB of the cyclone at short range.…”

The impact of deep convection representation in a global atmospheric model on the warm conveyor belt and jet stream during NAWDEX IOP6

“…Our approach is based on the case study of an extratropical cyclone that occurred during NAWDEX called the Stalactite cyclone (29 September-3 October 2016) and corresponding to Intensive Observing Period (IOP) 6. It was an explosively deepening cyclone at a rate of roughly 24 hPa in 24 h (Flack et al, 2021) that formed off the east coast of Newfoundland and travelled over the North Atlantic toward Iceland and Greenland. This large-scale cyclone participated in the formation of a block over Scandinavia (Schäfler et al, 2018).…”

“…Blanchard et al (2020) and Blanchard et al (2021) studied the WCB-embedded convection by performing convection-permitting model simulations, while Mazoyer et al (2021) analysed the impact of cloud microphysics on the WCB activity of the Stalactite cyclone with similar convection-permitting simulations. Flack et al (2021) analysed the whole life cycle of the cyclone in simulations of two climate models. Maddison et al (2020) showed that medium-range forecast skills of the cyclone are sensitive to the choice of the deep convection schemes, but none of these studies systematically investigated the role of parameterized deep convection on the WCB of the cyclone at short range.…”

Diabatic processes modulating the vertical structure of the jet stream above the cold front of an extratropical cyclone: sensitivity to deep convection schemes

“…The extratropical cyclone hereafter studied, called the "Stalactite cyclone" (1-4 October 2016), is of particular interest in a number of respects. It was formed off the Newfoundland coast and intensified over the North Atlantic with a deepening rate of 24 hPa in 24 h (Flack et al, 2021) as a classical bomb event (Sanders and Gyakum, 1980). It has been intensively observed during NAWDEX (Schäfler et al, 2018) by three flights: two flights of the French Falcon 20 from the Service des Avions Français Instrumentés pour la Recherche en Environnement (SAFIRE) and one flight from the Deutsches Zentrum für Luft-und Raumfahrt (DLR) Dassault Falcon.…”