Abstract
Abstract. 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 simulations. That can be attributed to the more active WCB at upper levels. However, this effect is too strong and that simulation becomes less realistic than the other ones at forecast ranges beyond 1.5 d. The simulation with the PCMT scheme has an intermediate behaviour between the one with the B85 scheme and without parameterized deep convection, but its impact on the jet stream is closer to the latter one. Finally, additional numerical experiments show that main differences in the impact on the jet between PCMT and B85 largely come from the chosen closure, with the former being based on CAPE and the latter on moisture convergence.
Highlights
Despite significant and continuous improvements of numerical weather forecasts during the last decades (Simmons and Hollingsworth, 2002; Bauer et al, 2015), mid-latitude weather forecast errors still occur at synoptic and planetary scales
The effect of parameterized deep convection on warm conveyor belt (WCB) activity and jet stream was investigated by performing simulations of an explosively developing large-scale cyclone, which occurred from 29 September to 3 October 2016 during North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) and is called the Stalactite cyclone, using the Météo-France global atmospheric model ARPEGE
For two of them, parameterized deep convection was activated with distinct schemes (B85 corresponding to the Bougeault, 1985, scheme and Prognostic Condensates Microphysics and Transport (PCMT) corresponding to the Piriou et al, 2007, scheme), while for the third one, parameterized convection was turned off
Summary
Despite significant and continuous improvements of numerical weather forecasts during the last decades (Simmons and Hollingsworth, 2002; Bauer et al, 2015), mid-latitude weather forecast errors still occur at synoptic and planetary scales. One main hypothesis of the project is that the potentially misrepresented diabatic processes embedded in the so-called warm conveyor belts (WCBs) play a key role in triggering forecast errors along the North Atlantic upper-tropospheric waveguide They may significantly deteriorate the forecast of high-impact weather events more downstream. 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.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
