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Quantifying effects of latent heating on midlatitude cyclones under different climate conditions

Applicant Pfahl Stephan
Number 149140
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 01.05.2014 - 31.07.2017
Approved amount 177'026.00
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All Disciplines (2)

Discipline
Meteorology
Climatology. Atmospherical Chemistry, Aeronomy

Keywords (8)

climate change; extreme weather events; cyclone; latent heating; potential vorticity; storm; water cycle; diabatic processes

Lay Summary (German)

Lead
Die Zunahme des Wasserdampfgehaltes der Atmosphäre in einem wärmeren Klima und die damit verbundene grössere latente Wärmefreisetzung kann zu einer Intensivierung von Stürmen in den mittleren Breiten führen. In diesem Projekt wird eine Diagnostik entwickelt, die den Einfluss des latenten Heizens auf Zyklone quantifiziert. Mit Hilfe dieser Diagnostik wird dann die relative Bedeutung dieses Einflusses in verschiedenen Klimazuständen untersucht.
Lay summary

Inhalt und Ziel des Forschungsprojekts

Die Energie, die bei der Bildung von Wolken frei wird (latente Wärme), trägt zur Intensivierung von Zyklonen in den mittleren Breiten bei. Wir werden eine Diagnostik zur Quantifizierung dieses Beitrags entwickeln. Simulationen mit einem regionalen Modell, in denen die Freisetzung der latenten Wärme künstlich variiert wird, werden zum Test und zur Evaluierung der Diagnostik verwendet. Dabei werden sowohl idealisierte Simulationen als auch Fallstudien von intensiven Stürmen im Nordatlantikraum durchgeführt. Anschliessend wird die Diagnostik verwendet, um, basierend auf globalen Simulationen mit einem idealisierten Klimamodell, den Beitrag der latenten Wärmefreisetzung zur Entwicklung von Zyklonen in stark unterschiedlichen Klimazuständen zu quantifizieren.

Wissenschaftlicher und gesellschaftlicher Kontext des Forschungsprojekts

Eine mögliche Intensivierung von Zyklonen und damit verbundenen Wind- und Niederschlagsextremen in einem wärmeren Klima stellt eine grosse Herausforderung für die Gesellschaft dar. Durch die Quantifizierung des Beitrags des atmosphärischen Wasserkreislaufs zu dieser Intensivierung wird die Grundlage dafür gelegt, entsprechende Änderungen im zukünftigen Klima verstehen und besser prognostizieren zu können.

Direct link to Lay Summary Last update: 18.11.2013

Responsible applicant and co-applicants

Employees

Name Institute

Publications

Publication
Potential vorticity diagnostics to quantify effects of latent heating in extratropical cyclones. Part I: Methodology.
Büeler Dominik, Pfahl Stephan, Potential vorticity diagnostics to quantify effects of latent heating in extratropical cyclones. Part I: Methodology., in Journal of the Atmospheric Sciences.

Collaboration

Group / person Country
Types of collaboration
Prof. Paul O'Gorman, Massachusetts Institute of Technology United States of America (North America)
- in-depth/constructive exchanges on approaches, methods or results
- Publication

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
EGU General Assembly Talk given at a conference Diabatic potential vorticity anomalies in extratropical cyclones in idealized simulations of changed climates 28.04.2017 Wien, Austria Pfahl Stephan;
EMS Annual Meeting Talk given at a conference Potential vorticity diagnostic to quantify effects of latent heating in midlatitude cyclones 12.09.2016 Trieste, Italy Büeler Dominik;
International Swiss Climate Summer School Poster Potential vorticity diagnostic to quantify effects of latent heating in extratropical cyclones 28.08.2016 Grindelwald, Switzerland Büeler Dominik;
Cyclone Workshop Talk given at a conference Investigating effects of latent heating on midlatitude cyclone intensification with potential vorticity diagnostics 26.10.2015 Monterey, United States of America Pfahl Stephan; Büeler Dominik;
SPARC Storm Tracks Workshop Poster Investigating effects of latent heating on midlatitude cyclone intensification with potential vorticity diagnostics 25.08.2015 Grindelwald, Switzerland Pfahl Stephan; Büeler Dominik;
COSMO User Seminar Poster Investigating effects of latent heating on midlatitude cyclone intensification with potential vorticity diagnostics 02.03.2015 Offenbach, Germany Büeler Dominik;


Associated projects

Number Title Start Funding scheme
146834 Diabatic processes in North Atlantic weather systems: dynamics and impact on forecast errors 01.06.2013 Project funding (Div. I-III)

Abstract

A substantial part of the daily weather variability in the midlatitudes is related to extratropical cyclones. The release of latent heat during cloud formation is an important mechanism contributing to cyclone intensification. The increase in atmospheric moisture content with global warming likely affects this latent heating (LH) and may hereby induce changes in cyclone frequency and intensity, which can in turn lead to more frequent floodings, droughts, or windstorms. The quantification and proper representation of LH effects on cyclones is thus essential for reliable projections of midlatitude weather extremes in future climate. Biases in the representation of storm tracks in climate models and uncertainties in their future projections may be due to difficulties in fully capturing such LH effects, also because of the typically coarse model resolution. In this project, new diagnostic metrics will be developed for quantifying the impact of LH on midlatitude cyclones. Subsequently, the metrics will be applied to idealized GCM simulations to investigate this LH impact in different climates. The new diagnostics will be based on the cyclones’ potential vorticity (PV) budget, which will allow us to draw on the many dynamical insights that have been obtained from the PV perspective. In order to test the new metrics, simulations with a limited area model will be performed, both for real cases of severe storms and in an idealized baroclinic channel setup. Results from the new diagnostics will be compared to an existing method based on the pressure tendency equation, and sensitivity experiments with altered latent heat release will be employed for evaluating the different diagnostics. The influence of boundary conditions like baroclinicity and static stability on the effects of LH will be investigated in the channel simulations. In a second step, climate simulations with an idealized GCM in an aquaplanet setup will be performed. The newly developed LH diagnostics will be applied to midlatitude cyclones in these simulations, which will be identified with the help of an automatic cyclone tracking scheme. The influence of the GCM’s spatial resolution on the simulation of LH effects on cyclones will be evaluated in present-day simulations. Subsequently, the model will be run for colder and warmer climates, and the importance of LH will be assessed. The focus on individual systems will allow to identify changes not only in the mean storm tracks, but also in the cyclone frequency and intensity spectra. All together, this feature-based process study will yield a thorough quantification of the effects of LH on midlatitude cyclones in different climates. By applying PV-based diagnostics to climate simulations, we will facilitate the application of in-depth knowledge on storm dynamics in a climate context. The metrics that are to be developed can subsequently be used for the validation of GCM simulations and may thus help in eliminating model deficiencies. The results from this project will enhance our mechanistic understanding of variations in cyclone frequency and intensity in a changing climate and thus ultimately improve climate projections of midlatitude weather variability.
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