Project

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The dynamics of North Atlantic warm conveyor belts and their impact on downstream wave propagation and European weather systems

Applicant Wernli Heini
Number 130079
Funding scheme Project funding (Div. I-III)
Research institution Institut für Atmosphäre und Klima ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Meteorology
Start/End 01.06.2010 - 31.05.2013
Approved amount 553'202.00
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All Disciplines (2)

Discipline
Meteorology
Climatology. Atmospherical Chemistry, Aeronomy

Keywords (12)

atmospheric dynamics; numerical modeling; Rossby wave dynamics; coherent airflows; climatology; forecast verification; extratropical cyclones; moist processes; warm conveyor belts; Rossby waves; potential vorticity; THORPEX

Lay Summary (English)

Lead
Lay summary
Warm conveyor belts (WCBs) are coherent airstreams that typically develop along cold fronts associated with extratropical cyclones. These airstreams originate in the moist subtropical marine boundary layer and ascend within 1-2 days to the upper troposphere whilst moving more than 2000 km towards the pole. They occur most frequently during winter in the western North Pacific and North Atlantic where they are responsible for the major part of precipitation. The key role of WCBs for the dynamics of the synoptic and large-scale atmospheric flow stems from their profound impact upon the tropospheric distribution of potential vorticity (PV). The coherent ascent of WCBs leads to the diabatic production of a positive PV anomaly in the lower troposphere and of a negative PV anomaly in upper-level ridges just below the tropopause. When interacting with the extratropical waveguide, these negative PV anomalies can exert a profound impact upon the downstream flow evolution. Hence a WCB can be the trigger for the amplification and breaking of an upper-level Rossby wave, which is particularly relevant in situations where Rossby wave breaking events act as precursors of high-impact weather systems (e.g., heavy precipitation in the western Mediterranean, Saharan dust storms, cold air outbreaks). Recent studies indicate that errors in medium-range numerical weather predictions might be related to the inaccurate representation of WCBs and their effect on upper-level PV. In order to advance the basic understanding of these complex, non-linear and highly important dynamical processes, this project will (i) investigate the parameters and processes that determine the intensity of a WCB, its associated PV evolution and downstream effects, (ii) assess the errors in global models' analyses and forecasts associated with the different stages of a WCB life cycle, (iii) quantify the climatological frequency of the triggering and intensification of upper-level Rossby waves by WCBs, and (iv) provide clear guidance for investigating the dynamics of WCBs within the framework of THORPEX field experiments. In three subprojects, complementary techniques will be applied in order to reach these objectives, including idealized simulations of moist baroclinic waves, real case sensitivity experiments, diagnostic investigations based upon (re-)analysis and forecast data, and a feature-based verification of WCBs in global models using independent observational datasets. In this way this project will contribute to an improved basic understanding of the dynamical effects of WCBs on the downstream evolution of upper-level Rossby waves and (high-impact) surface weather events.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Diabatic Rossby waves in the Southern Hemisphere.
Boettcher M. and H. Wernli (2015), Diabatic Rossby waves in the Southern Hemisphere., in Quart. J. Roy. Meteorol. Soc., 141, 3106-3117.
Global relationship between fronts and warm conveyor belts and the impact on extreme precipitation.
Catto J. L. E. Madonna H. Joos I. Rudeva and I. Simmonds (2015), Global relationship between fronts and warm conveyor belts and the impact on extreme precipitation., in J. Climate, 28, 8411-8429.
Verification of North Atlantic warm conveyor belt outflows in ECMWF forecasts.
Madonna E. M. Boettcher C. M. Grams H. Joos O. Martius and H. Wernli (2015), Verification of North Atlantic warm conveyor belt outflows in ECMWF forecasts., in Quart. J. Roy. Meteorol. Soc., 141, 1333-1344.
On the co-occurrence of warm conveyor belt outflows and PV-streamers.
Madonna E. S. Limbach C. Aebi H. Joos H. Wernli and O. Martius (2014), On the co-occurrence of warm conveyor belt outflows and PV-streamers., in J. Atmos. Sci., 71, 3668-3673.
Planning aircraft measurements within a warm conveyor belt.
Schäfler A. M. Boettcher C. M. Grams M. Rautenhaus H. Sodemann and H. Wernli (2014), Planning aircraft measurements within a warm conveyor belt., in Weather, 69, 161-166.
The linkage between the warm and cold conveyor belts in an idealized extratropical cyclone.
Schemm S. and H. Wernli (2014), The linkage between the warm and cold conveyor belts in an idealized extratropical cyclone., in J. Atmos. Sci., 71, 1443-1459.
Warm conveyor belts in the ERA-Interim data set (1979-2010). Part I: Climatology and potential vorticity evolution.
Madonna E. H. Wernli H. Joos and O. Martius (2014), Warm conveyor belts in the ERA-Interim data set (1979-2010). Part I: Climatology and potential vorticity evolution., in J. Climate, 27, 3-26.
Warm conveyor belts in the ERA-Interim data set (1979-2010). Part II: Moisture origin and relevance for precipitation.
Pfahl S. E. Madonna M. Boettcher H. Joos and H. Wernli (2014), Warm conveyor belts in the ERA-Interim data set (1979-2010). Part II: Moisture origin and relevance for precipitation., in J. Climate, 27, 27-40.
A 10-yr climatology of diabatic Rossby waves in the Northern Hemisphere
Boettcher M. and H. Wernli (2013), A 10-yr climatology of diabatic Rossby waves in the Northern Hemisphere, in Mon. Wea. Rev., 141, 1139-1154.
Development of an idealized downstream cyclone: Eulerian and Lagrangian perspective on the kinetic energy
Papritz L. and S. Schemm (2013), Development of an idealized downstream cyclone: Eulerian and Lagrangian perspective on the kinetic energy, in Tellus A, 65, 19539.
The role of upper-level dynamics and surface processes for the Pakistan flood of July 2010.
Martius O. H. Sodemann H. Joos S. Pfahl A. Winschall M. Croci-Maspoli M. Graf, E. Madonna B. Mueller S. Schemm J. Sedlacek M. Sprenger and H. Wernli (2013), The role of upper-level dynamics and surface processes for the Pakistan flood of July 2010., in Quart. J. Roy. Meteorol. Soc., 139, 1780-1797.
Warm conveyor belts in idealized moist baroclinic wave simulations.
Schemm S. H. Wernli and L. Papritz (2013), Warm conveyor belts in idealized moist baroclinic wave simulations., in J. Atmos. Sci., 70, 627-652.

Collaboration

Group / person Country
Types of collaboration
University of Bern Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
ECMWF Great Britain and Northern Ireland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
University of Reading Great Britain and Northern Ireland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
University of Melbourne Australia (Oceania)
- in-depth/constructive exchanges on approaches, methods or results
- Exchange of personnel

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
WGNE systematic errors workshop Talk given at a conference Forecast errors associated with mid-latitude weather systems 18.03.2013 Exeter, UK, Great Britain and Northern Ireland Wernli Heini;
WWRP/THORPEX Workshop on proposed High Impact Weather Project Talk given at a conference Predictability and dynamical processes 18.03.2013 Karlsruhe, Germany, Germany Wernli Heini;
Meeting Schweizerische Gesellschaft für Meteorologie Talk given at a conference Precipitation in extratropical cyclones: the role of warm conveyor belts 17.11.2012 Bern, Switzerland Romppainen-Martius Olivia; Madonna Erica;
2nd European Windstorm Workshop Poster Climatology and significance of diabatic Rossby-waves 04.09.2012 Leeds, United Kingdom, Great Britain and Northern Ireland Böttcher Maxi;
THORPEX PDP Working Group Meeting Talk given at a conference Warm conveyor belts 19.06.2012 Reading, UK, Great Britain and Northern Ireland Wernli Heini;
EGU General Assembly Talk given at a conference Idealized warm conveyor belts in moist baroclinic waves: PV and energy diagnostics 23.04.2012 Vienna, Austria, Austria Schemm Sebastian; Romppainen-Martius Olivia;
AGU Chapman Conference on Lagrangian Modeling Poster A Lagrangian climatology of warm conveyor belts over the past 20 years 10.10.2011 Grindelwald, Switzerland, Switzerland Wernli Heini; Madonna Erica; Schemm Sebastian;
EMS annual meeting Talk given at a conference Significance and climatology of diabatic Rossby waves 12.09.2011 Berlin, Germany, Germany Böttcher Maxi;
10th NCCR Summer School Poster Idealised warm conveyor belts in moist baroclinic wave life cycles 04.09.2011 Grindelwald, Switzerland, Switzerland Schemm Sebastian;


Self-organised

Title Date Place
THORPEX PDP Working Group Meeting 18.06.2012 Reading, UK, Great Britain and Northern Ireland

Awards

Title Year
Berufung von Olivia Martius zur Assistenzprofessorin an der Universität Bern 2011

Associated projects

Number Title Start Funding scheme
165941 Diabatic processes in North Atlantic weather systems: synoptic and mesoscale dynamics 01.06.2016 Project funding (Div. I-III)
146834 Diabatic processes in North Atlantic weather systems: dynamics and impact on forecast errors 01.06.2013 Project funding (Div. I-III)
185049 Understanding the influence of warm conveyor belts in extratropical cyclones on tropopause dynamics: analysis with observations, reanalyses and global climate simulations 01.01.2020 Project funding (Div. I-III)
156059 Atmospheric blocking - moist dynamical processes and links to flood events 01.04.2015 Project funding (Div. I-III)
148177 The mutual interaction of individual weather systems and weather regimes 01.07.2014 Ambizione

Abstract

Warm conveyor belts (WCBs) are coherent airstreams that typically develop along cold fronts associated with extratropical cyclones. These airstreams originate in the moist subtropical marine boundary layer and ascend within 1-2 days to the upper troposphere whilst moving more than 2000 km towards the pole. They occur most frequently during winter in the western North Pacific and North Atlantic where they are responsible for the major part of precipitation. WCBs are characterized by a complex interaction of physical and dynamical processes, which have not yet been investigated in full detail. The key role of WCBs for the dynamics of the synoptic and large-scale atmospheric flow stems from their profound impact upon the tropospheric distribution of potential vorticity (PV). The coherent ascent of WCBs leads to the diabatic production of a positive PV anomaly in the lower troposphere and of a negative PV anomaly in upper-level ridges just below the tropopause. When interacting with the extratropical waveguide, these negative PV anomalies can exert a profound impact upon the downstream flow evolution. Hence a WCB can be the trigger for the amplification and breaking of an upper-level Rossby wave, which is particularly relevant in situations where Rossby wave breaking events act as precursors of high-impact weather systems (e.g., heavy precipitation in the western Mediterranean, Saharan dust storms, cold air outbreaks). Recent studies indicate that errors in medium-range numerical weather predictions might be related to the inaccurate representation of WCBs and their effect on upper-level PV. In order to advance the basic understanding of these complex, non-linear and highly important dynamical processes, this project will (i) investigate the parameters and processes that determine the intensity of a WCB, its associated PV evolution and downstream effects, (ii) assess the errors in global models’ analyses and forecasts associated with the different stages of a WCB life cycle, (iii) quantify the climatological frequency of the triggering and intensification of upper-level Rossby waves by WCBs, and (iv) provide clear guidance for investigating the dynamics of WCBs during T-NAWDEX - a major international field experiment planned for autumn 2012 within the framework of THORPEX. Within three subprojects, complementary techniques will be applied in order to reach these objectives, including idealized simulations of moist baroclinic waves, real case sensitivity experiments, diagnostic investigations based upon (re-) analysis and forecast data sets, and a feature-based verification of WCBs in global models using independent observational datasets. In this way this ambitious project will contribute on the one hand to an improved basic understanding of the dynamical effects of WCBs on the downstream evolution of upper-level Rossby waves and (high-impact) surface weather events. On the other hand it will directly influence the planning and conduct of the field experiment T-NAWDEX and provide information of practical relevance for operational medium-range weather prediction.
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