Preprints
https://doi.org/10.5194/wcd-2021-38
https://doi.org/10.5194/wcd-2021-38

  15 Jun 2021

15 Jun 2021

Review status: this preprint is currently under review for the journal WCD.

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

Gwendal Rivière1, Meryl Wimmer2, Philippe Arbogast3, Jean-Marcel Piriou2, Julien Delanoë4, Carole Labadie2, Quitterie Cazenave4, and Jacques Pelon4 Gwendal Rivière et al.
  • 1Laboratoire de Météorologie Dynamique/IPSL, Ecole Normale Supérieure, PSL Research University, Sorbonne University, École Polytechnique, IP Paris, CNRS, Paris, France
  • 2CNRM, Université de Toulouse, Météo-France, CNRS, Toulouse, France
  • 3Direction des Opérations pour la prévision, Météo-France, Toulouse, France
  • 4LATMOS-IPSL, CNRS/INSU, University of Versailles, Guyancourt, France

Abstract. The effect of parameterized deep convection on warm conveyor belt (WCB) activity and 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 et al. (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 sub-grid 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 behavior. After one day of simulations, the upper-level heating rate is in average larger with B85 scheme leading to stronger potential vorticity (PV) destruction. The difference comes from the large-scale heating and not the parameterized heating.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-day 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 at longer forecast range (1.5 to 2 days) than the other ones. The simulation with PCMT scheme has an intermediate behavior between the one with 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, the former being based on CAPE and the latter on moisture convergence.

Gwendal Rivière et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on wcd-2021-38', James Booth, 14 Jul 2021
  • RC2: 'Comment on wcd-2021-38', Anonymous Referee #2, 30 Jul 2021

Gwendal Rivière et al.

Gwendal Rivière et al.

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Short summary
Inacurracies in representing processes occurring at spatial scales smaller than the grid scales of the weather forecast models are important sources of forecast errors. This is the case of deep convection representation in models with ten kilometers grid spacing. We performed simulations of a real extratropical cyclone using a model with different representations of deep convection. These forecasts lead to different behaviors in the ascending air masses of the cyclone and the jet stream aloft.