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The Atmospheric General Circulation in Thermodynamical Coordinates
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology .
2014 (English)In: Journal of Atmospheric Sciences, ISSN 0022-4928, E-ISSN 1520-0469, Vol. 71, no 3, 916-928 p.Article in journal (Refereed) Published
Abstract [en]

The zonal and meridional components of the atmospheric general circulation are used to define a global thermodynamic stream function in dry static energy versus latent heat coordinates. Diabatic motions in the tropical circulations and fluxes driven by midlatitude eddies are found to form a single, global thermodynamic cycle. Calculations based on the ERA-Interim reanalysis dataset indicate that the cycle has a peak transport of 428 Sv (Sv = 109 kg s−1). The thermodynamic cycle encapsulates a globally interconnected heat and water cycle comprising ascent of moist air where latent heat is converted into dry static energy, radiative cooling where dry air loses dry static energy, and a moistening branch where air is warmed and moistened. It approximately follows a tropical moist adiabat and is bounded by the Clausius-Clapeyron relationship for near-surface air. The variability of the atmospheric general circulation is related to ENSO events using reanalysis data from recent years (1979-2009) and historical simulations from the EC-Earth coupled climate model (1850-2005). The thermodynamic cycle in both EC-Earth and ERA-Interim widens and weakens with positive ENSO phases and narrows and strengthens during negative ENSO phases with a high correlation coefficient. Weakening in amplitude suggests a reduction in moist convection in the tropics, while widening suggests an increase in mean tropical near-surface moist static energy.

Place, publisher, year, edition, pages
2014. Vol. 71, no 3, 916-928 p.
Keyword [en]
Climate, Atmosphere, Mass transport, Stream function, Thermodynamic, Hydrothermal
National Category
Climate Research
Research subject
Meteorology; Oceanography
URN: urn:nbn:se:su:diva-96549DOI: 10.1175/JAS-D-13-0173.1ISI: 000331927800004OAI: diva2:677063
Available from: 2013-12-09 Created: 2013-11-22 Last updated: 2014-05-15Bibliographically approved
In thesis
1. Atmospheric & Oceanic Applications of Eulerian and Lagrangian Transport Modelling
Open this publication in new window or tab >>Atmospheric & Oceanic Applications of Eulerian and Lagrangian Transport Modelling
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents several ways to understand transports of air and water masses in the atmosphere and ocean, and the transports of energy that they imply. It presents work using various kinds of observations as well as computer simulations of the atmosphere and oceans. One of the main focuses is to identify similarities and differences between models and observations, as well as between different models.

The first half of the thesis applies Lagrangian methods to study flows in the atmosphere and oceans. Part of the work focuses on understanding how particles follow the currents in the Baltic Sea and how they disperse. It is suggested that the commonly used regional ocean model for the Baltic Sea, RCO, underestimates the transport and the dispersion of the particles, which can have consequences for studies of e.g. biogeochemistry as well as for operational use. A similar methodology is used to study how particles are transported between the tropics and mid-latitudes by the large-scale atmospheric circulation. It is found that the mass transport associated with northbound and southbound particles can cancel in the zonally averaged circulation, and we propose that the degree of cancellation depends on the method of averaging.

The latter half of the thesis focuses on Eulerian stream functions and specifically a thermodynamic stream function that combines the zonal and meridional circulations of the atmosphere into a single circulation. The results are used to study the inter-annual variability of the intensity and thermodynamic properties of the global atmospheric circulation. A significant correlation to ENSO variability is found both in reanalysis and the EC-Earth coupled climate model. It is also shown that a set of models from the CMIP5 project show a slowdown of the atmospheric circulation as a result of global warming and associated changes in near-surface moisture content and upper-level radiative cooling.

Abstract [sv]

Denna avhandling presenterar olika metoder för att studera datormodeller av atmosfä- ren, haven, och klimatsystemet. Metoderna använder såväl Lagrangeska synsätt dvs att betrakta atmosfären eller haven som individuella partiklar i rörelse, som Eulerska synsätt där atmosfären och haven ses som gas eller vätska i rörelse. I artikel 1 sjö- sätts ett antal “surface drifters” i Östersjön som driver fritt med havsströmmarna och vars hastighet mäts av satelliter. Genom att modellera Lagrangeska partiklars rörelser i Östersjön och jämföra med dessa “surface drifters” kan det visas att datormodeller kan underskatta både medelhastigheten av partiklarna samt deras utbredning. I ar- tikel 2 simuleras luftmassornas rörelser mellan tropikerna och mellanbreddgraderna (∼ 45◦N/S). Ett medelvärde över all longituder tenderar att ignorera betydande mass- och energitransporter mellan tropikerna och mellanbredderna, och dessa kvantifieras i detalj i artikel 2.

Artiklarna 3 och 4 presenterar en metod för att studera atmosfärens storskaliga rörelser utifrån ett termodynamiskt perspektiv där luftmassornas värme och fukt studeras. Det visas att variationer ytvattentemperatur vid ekvatorn i Stilla havet kan få atmosfären att, i ett globalt medelvärde, bli fuktigare och varmare samtidigt som masstransporter- na saktar ner. På samma sätt visas att en global uppvärmning till följd av ökade utsläpp av växthusgaser kan få atmosfären att bli varmare, fuktigare och att masstransporterna kan sakta ner. 

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University, 2014. 46 p.
Eulerian, Lagrangian, trajectory, climate, atmosphere, ocean, modelling, drifter, thermodynamic, climate change
National Category
Climate Research
Research subject
Atmospheric Sciences and Oceanography
urn:nbn:se:su:diva-97348 (URN)978-91-7447-823-5 (ISBN)
Public defence
2014-02-07, Ahlmannsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
EU, FP7, Seventh Framework Programme, 217246

At the time of the doctoral defence the following papers were unpublished and had a status as follows: Paper 3: In press; Paper 4: Manuscript.

Available from: 2014-01-16 Created: 2013-12-09 Last updated: 2014-01-08Bibliographically approved

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