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

Abstract. The effect of parameterized deep convection on warm conveyor belt (WCB) activity and the jet stream is investigated by performing simulations an explosively developing large-scale cyclone that occurred during North Atlantic Waveguide Downstream Impact Experiment (NAWDEX) field campaign using Météo-France global atmospheric model ARPEGE. Three differing only from their representation are analysed. first one was performed with Bougeault (1985) scheme (B85), second Prognostic Condensates Microphysics Transport (PCMT) Piriou et al. (2007), third without any convection. In latter simulation, release convective instability at resolved scales generates localized cells marked strong heating few degrees extent in longitude latitude along fronts. runs active (B85, PCMT), rate more homogeneously distributed fronts as happens subgrid scales. This difference leads to rapid abrupt ascents WCB moderate but sustained While number trajectories does not differ much between three simulations, averaged rates over exhibits distinct behaviour. After 1 d upper-level average larger, B85 leading stronger potential vorticity (PV) destruction. comes sensible latent one. A comparison (re)analyses a large variety airborne observations NAWDEX (Doppler radar, Doppler lidar, dropsondes) made coordinated flights two aircraft outflow region shows performs better double structure lead time than other simulations. That can be attributed upper levels. However, this too simulation becomes less realistic ones forecast ranges beyond 1.5 d. PCMT has intermediate behaviour convection, its impact closer Finally, additional numerical experiments show main differences largely come chosen closure, former being based CAPE moisture convergence.