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Influence of a new turbulence regime on the global air-sea heat fluxes
Rosenstiel School of Marine and Atmospheric Science, University of Miami, Florida. (AWEP)
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
2008 (English)In: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 21, no 22, 5925-5941 p.Article in journal (Refereed) Published
Abstract [en]

Recent research has found that boundary layer turbulence changes its organization as the stratification approaches neutral from the unstable side. When the thermal forcing weakens in combination with wind speed above approximately 10 m s(-1), detached eddies are formed in the upper part of the surface layer. These eddies effectively transport drier and colder air from aloft to the surface as they move downward, thereby enhancing the surface fluxes of sensible and latent heat. This effect has been observed over both land and sea; that is, it is not dependent on the nature of the underlying surface. Here the authors perform a sensitivity study of how this reorganization of the turbulence structure influences the global air-sea heat fluxes. Using modified bulk formulations incorporating this effect, the magnitude of the enhancement in a climatic sense was estimated by the use of 40-yr ECMWF Re-Analysis (ERA-40) data in the bulk formulas. It is found that for the 1979-2001 period, the global increase of the latent and sensible heat fluxes over the ice-free oceans is 3.6 and 1.2 W m(-2), respectively. These numbers suggest that this effect is of some significance. The results also indicate that the regional and seasonal variability may be large. The largest annual increases are found over the southern oceans between 30 and 60 S where the sensible heat flux increases by 2.3 W m(-2) and the latent heat flux by 6.5 W m(-2). Ocean areas close to the equator experience almost no increase, whereas the latent heat flux from the Arabian Sea during the monsoon period is enhanced by 11.5 W m(-2).

Place, publisher, year, edition, pages
2008. Vol. 21, no 22, 5925-5941 p.
Keyword [en]
Turbulence, Fluxes, Air-sea interaction
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-96144DOI: 10.1175/2008JCLI2279.1ISI: 000261107800012OAI: oai:DiVA.org:uu-96144DiVA: diva2:170620
Available from: 2007-09-04 Created: 2007-09-04 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Fluxes of Sensible and Latent Heat and Carbon Dioxide in the Marine Atmospheric Boundary Layer
Open this publication in new window or tab >>Fluxes of Sensible and Latent Heat and Carbon Dioxide in the Marine Atmospheric Boundary Layer
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Oceans cover about 70% of the earth’s surface. They are the largest source of the atmospheric water vapour and act as enormous heat reservoirs. Thus in order to predict the future weather and climate it is of great importance to understand the processes governing the exchange of water vapour and heat between the ocean and atmosphere. This exchange is to a large extent mediated by turbulent eddies. Current numerical climate and weather forecast models are unable to resolve the turbulence, which means that the turbulent exchange needs to be simplified by using parameterizations.

Tower based measurements at the Östergarnsholm Island in the Baltic Sea have been used to study the air-sea turbulent exchange of latent and sensible heat and the heat flux parameterizations. Although the measurements are made at an island, data obtained at this site is shown to represent open ocean conditions during most situations for winds coming from the east-south sector. It is found that during conditions with small air-sea temperature differences and wind speeds above 10 m s-1, the structure of the turbulence is re-organized. Drier and colder air from aloft is transported to the surface by detached eddies, which considerably enhance the turbulent heat fluxes. The fluxes where observed to be much larger than predicted by current state-of-the-art parameterizations. The turbulence regime during these conditions is termed the Unstable Very Close to Neutral Regime, the UVCN-regime.

The global increase of the latent and sensible heat fluxes due to the UVCN-regime is calculated to 2.4 W m-2 and 0.8 W m-2 respectively. This is comparable to the current increase of the radiative forcing due to anthropogenic emissions of greenhouse gases, reported in Intergovernmental Panel on Climate Change fourth assessment report (IPCC AR4). Thus the UVCN-effect could have a significant influence when predicting the future weather and climate.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 44 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 334
Keyword
Meteorology, Sensible heat flux, Latent heat flux, Carbon dioxide, Turbulent exchange, Global heat fluxes, Marine boundary layer, Air-sea interaction, Meteorologi
Identifiers
urn:nbn:se:uu:diva-8184 (URN)978-91-554-6954-2 (ISBN)
Public defence
2007-09-28, Axel Hamergssalen, Geocentrum, Villavägen 16, Uppsala, 10:00
Opponent
Supervisors
Available from: 2007-09-04 Created: 2007-09-04Bibliographically approved

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Sahlée, ErikSmedman, Ann-SofiRutgersson, AnnaHögström, Ulf

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