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

• Published in: Weather and Climate Dynamics
• Main Authors: Flack, David L. A., Rivière, Gwendal, Musat, Ionela, Roehrig, Romain, Bony, Sandrine, Delanoë, Julien, Cazenave, Quitterie, Pelon, Jacques
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2021
• Subjects: [PHYS.PHYS.PHYS-AO-PH]Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph]; [SDU.STU.ME]Sciences of the Universe [physics]/Earth Sciences/Meteorology; North Atlantic
• Online Access: https://hal-insu.archives-ouvertes.fr/insu-03183467; https://hal-insu.archives-ouvertes.fr/insu-03183467/document; https://hal-insu.archives-ouvertes.fr/insu-03183467/file/wcd-2-233-2021.pdf; https://doi.org/10.5194/wcd-2-233-2021

International audience 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 observa- tion period 6, is examined using two atmospheric compo- nents (ARPEGE-Climat 6.3 and LMDZ6A) of the global cli- mate 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 ap- proximately 50 km (high resolution, HR) grid spacings, and initialised during the initiation stage of the cyclone. Cyclo- genesis 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 interac- tion with a pre-existing upper-level potential vorticity (PV) cut-off. All hindcasts produce (to some extent) a DRV. How- ever, 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 heat- ing component from the dynamical one. In contrast to some previous studies, there is no change in the relative impor- tance of diabatic heating with increased resolution. The anal- ysis shows that LMDZ6A produces stronger diabatic heat- ing compared to ARPEGE-Climat 6.3. Hindcasts initialised during the mature stage of the cyclone are compared withairborne remote-sensing measurements. There is an under- estimation of the ice water content in the model compared to the one retrieved from radar-lidar measurements. Consis- tent with the increased heating rate in LMDZ6A compared to ARPEGE-Climat 6.3, the sum of liquid and ice water con- tents is higher in LMDZ6A than ARPEGE-Climat 6.3 and, in that sense, LMDZ6A is closer to the observations. How- ever, LMDZ6A strongly overestimates the fraction of super- cooled liquid compared to the observations by a factor ...