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Meryl WIMMER

Post-Doctoral Researcher on Atmospheric Modelling

Master 2nd year internship

First analysis of the NAWDEX measurment campaign

Summary

Despite constant improvements in numerical weather prediction models, the predictability of extratropical cyclones is still not optimal. In fact, errors are still present and continue to affect forecasts. One source of errors concerns the representation of diabatic processes (cloud microphysics, radiation and turbulence), particularly in the Warm Conveyor Belt (WCB), a mass of warm moist air that rises in extratropical cyclones and flows towards the poles. This is why the NAWDEX project was launched in 2014, with the aim of increasing our knowledge of the impact of such processes on high altitude and improving their representation in numerical models. In this framework, a measurement campaign was carried out in autumn 2016, with 4 research aircrafts and ground instrumentation in Iceland and Western Europe.

During this internship, a first analysis of this campaign was carried out, more specifically, on the case of the extratropical cyclone of 02nd of October 2016. The aim was to study the diabatic processes within the WCB of this cyclone. For this purpose, we relied on two flights, performed by the SAFIRE team, which sampled the WCB. Numerous 24-hour WCB-type Lagrangian trajectories, initialised along the path of the two flights, were calculated from the outputs of two versions of the ARPEGE model: the 2016 operational version and the version using the PCMT deep convection scheme. In order to determine the effect of diabatic processes on upper-leel anticyclones, the study focused on potential vorticity.

WCB trajectories experienced a strong heating, mainly due to the heat latent and sensible heat of the stratiform clouds, during their ascent. Thanks to the decomposition of each source of potential vorticity, we have shown that the latent and sensible heat released within the convective and stratiform clouds is mainly responsible for a negative contribution of potential vorticity at high altitude. This contribution explains the intensification of the anticyclone over Scandinavia.

In addition, we noticed a few differences between the two versions of ARPEGE. Compared with the operational version, the forecast including PCMT seems to have a less active deep convection parameterization, letting free the resolved part of the model. This is why this version of ARPEGE generates stronger large-scale ascents responsible for greater latent and sensible heat. Finally, this version tends to produce more negative potential vorticity in the mid-troposphere while the operational version more in the upper troposphere. Despite these differences, it is currently impossible to determine which of these versions is the most realistic.

Keyword : Warm Conveyor Belt ; Lagrangian Trajectories ; Diabatic processes ; NAWDEX ;

Documents

Mid-internship slides (FR) :
Mid-internship thesis :
Slides (FR) :
Thesis (FR) :

Research Articles

Wimmer, M. , Rivière, G., Arbogast, P., Piriou, J.-M., Delanoë, J., Labadie, C., Cazenave, Q., and Pelon, J. (2022): Diabatic processes modulating the vertical structure of the jet stream above the cold front of an extratropical cyclone: sensitivity to deep convection schemes, Weather and Climate Dynamics , 3, 863–882, doi: 10.5194/wcd-3-863-2022

Supplementary:
Rivière, G., Wimmer, M. , Arbogast, P., Piriou, J.-M., Delanoë, J., Labadie, C., Cazenave, Q., and Pelon, J. (2021): The impact of deep convection representation in a global atmospheric model on the warm conveyor belt and jet stream during NAWDEX IOP6, Weather and Climate Dynamics , 2, 1011–1031, doi : 10.5194/wcd-2-1011-2021

Supplementary:

Presentations (English)

Wimmer, M. et al. : « Impact of deep convection parameterization of a global atmospheric model on the warm conveyor belts and the jet stream », Stormtracks 2022 : Midlatitude storm-tracks workshop , 29 May-3th June 2022, Oléron, France

Abstract:
Rivière, G. , Wimmer, M. et al. : « The impact of convection schemes of a global atmospheric model on the warm conveyor belt of NAWDEX IOP6: a comparison to airborne measurements », Virtual 4th Workshop NAWDEX , 8-9th Mars 2021, online
Poster:
Rivière, G. , Wimmer, M. et al. : « The impact of convection schemes of a global atmospheric model on the warm conveyor belt of NAWDEX IOP6: Lagrangian budgets », Virtual 4th Workshop NAWDEX , 8-9th March 2021, online
Rivière G. , Wimmer, M. et al. : « Microphysical and dynamical properties of warm conveyor belts near the SAFIRE Falcon flights during NAWDEX », Virtual Workshop : Warm Conveyor Belt – a challenge to forecasting , ECMWF, 10th March 2020, Reading, United Kingdom
Poster:
Rivière, G. , Wimmer, M. et al. : « Diabatic processes in the Warm Conveyor Belt of the Stalactite Cyclone - Sensitivity to two deep convection schemes of the global Météo-France model ARPEGE », Virtual Workshop : Warm Conveyor Belt – a challenge to forecasting , ECMWF, 10th March 2020, Reading, United-Kingdom
Rivière, G. , Wimmer, M. et al. : «Comparison between airborne remote sensing observations of an extratropical cyclone and short-term forecasts using a hierarchy of models », Workshop: Observational campaigns for better weather forecasts , ECMWF, 10-13th June 2019, Reading, United Kingdom

Abstract:
Rivière, G. , Wimmer, M. et al. : « Systematic comparison between RALI observations and Arpege ensemble forecasts along the flights of the SAFIRE Falcon », 2nd Workshop NAWDEX , 26-28th march 2019, Toulouse, France
Wimmer, M. et al. : « Diabatic processes in the Warm Conveyor Belt of the Stalactite Cyclone : sensitivity to the two convective parametrization schemes in ARPEGE », 2nd Workshop NAWDEX , 26-28th March 2019, Toulouse, France

Presentations (French)

Wimmer, M. et al. : « Impact des schémas de convection profonde du modèle ARPEGEsur le Jet Stream et la bande transporteuse d’air chaud du Stalactite Cyclone », Réunion DIP-NAWDEX , 11th February 2022, online
Wimmer, M. et al. : « Impact des schémas de convection profonde du modèle ARPEGE sur une bande transporteuse d'air chaud lors de la POI6 de NAWDEX », Ateliers de Modélisation de l’Atmosphère - La convection atmosphérique , CIC, 8-12th March 2021, online

Abstract:
Wimmer, M. et al. : « Impacts des schémas de convection profonde du modèle ARPEGE sur la zone d’ascendance de la bande transporteuse d’air chaud du Stalactite Cyclone », Réunion DIP-NAWDEX , 9th February 2021, online
Rivière, G. , Wimmer, M. et al.: « Effet de la paramétrisation de la convection sur la bande transporteuse d’air chaud de la dépression Stalactite et sur le courant jet d’altitude », Réunion DIP-NAWDEX , 9th February 2021, online
Rivière, G. , Wimmer, M. et al.: « Systematic comparison between RALI observations and ARPEGE ensemble forecasts along the flights of the SAFIRE Falcon », Réunion DIP-NAWDEX , 25th February 2020, Toulouse, France
Wimmer, M. et al. : « Diabatic processes in the Warm Conveyor Belt of the Stalactite Cyclone- Sensitivity to the two deep convection schemes in ARPEGE », Réunion DIP-NAWDEX , 25th February 2020, Toulouse, France
Wimmer, M. et al. : « Processus diabatiques le long de la bande transporteuse d’air chaud dans la dépression Stalactite : sensibilité à deux schémas de paramétrisation de la convection dans ARPEGE », Réunion DIP-NAWDEX , 29th January 2019, Toulouse, France
Rivière, G. , Wimmer, M. et al.: « Evaluation des prévisions ARPEGE sur la période NAWDEX et lien avec la dynamique des bandes transporteuses d’air chaud », Réunion DIP-NAWDEX , 29th January 2019, Toulouse, France