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

• Published in: Weather and Climate Dynamics
• Main Authors: G. Rivière, M. Wimmer, P. Arbogast, J.-M. Piriou, J. Delanoë, C. Labadie, Q. Cazenave, J. Pelon
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2021
• Subjects: Meteorology. Climatology; QC851-999; North Atlantic
• Online Access: https://doi.org/10.5194/wcd-2-1011-2021; https://doaj.org/article/3ce4574bc3dd47fe9e9f23edcf058366

The effect of parameterized deep convection on warm conveyor belt (WCB) activity and the jet stream is investigated by performing simulations of an explosively developing large-scale cyclone that occurred during the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) field campaign using the Météo-France global atmospheric model ARPEGE. Three simulations differing only from their deep convection representation are analysed. The first one was performed with the Bougeault ( 1985 ) scheme (B85), the second one with the Prognostic Condensates Microphysics and Transport (PCMT) scheme of Piriou et al. ( 2007 ) , and the third one without any parameterized deep convection. In the latter simulation, the release of convective instability at the resolved scales of the model generates localized cells marked by strong heating with few degrees extent in longitude and latitude along the fronts. In runs with active parameterized deep convection (B85, PCMT), the heating rate is more homogeneously distributed along fronts as the instability release happens at subgrid scales. This difference leads to more rapid and abrupt ascents in the WCB without parameterized deep convection and more moderate but more sustained ascents with parameterized deep convection. While the number of WCB trajectories does not differ much between the three simulations, the averaged heating rates over the WCB trajectories exhibits distinct behaviour. After 1 d of simulations, the upper-level heating rate is on average larger, with the B85 scheme leading to stronger potential vorticity (PV) destruction. The difference comes from the resolved sensible and latent heating and not the parameterized one. A comparison with (re)analyses and a large variety of airborne observations from the NAWDEX field campaign (Doppler radar, Doppler lidar, dropsondes) made during the coordinated flights of two aircraft in the WCB outflow region shows that B85 performs better in the representation of the double jet structure at 1 d lead time than the other two ...