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Observations of stably stratified shear-driven atmospheric turbulence at low and high Richardson numbers
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology .
2007 (English)In: Journal of the Atmospheric Sciences, ISSN 0022-4928, Vol. 64, no 2, 645-655 p.Article in journal (Refereed) Published
Abstract [en]

Stably stratified shear-driven turbulence is analyzed using the gradient Richardson number, Ri, as the stability parameter. The method overcomes the statistical problems associated with the widely used Monin–Obukhov stability parameter. The results of the Ri-based scaling confirm the presence of three regimes: the weakly and the very stable regimes and the transition in between them. In the weakly stable regime, fluxes scale in proportion with variance, while in the very stable regime, stress and scalar fluxes behave differently. At large Ri, the velocity field becomes highly anisotropic and the turbulent potential energy becomes approximately equal to half of the turbulent kinetic energy. It appears that even in the strongly stable regime, beyond what is known as the critical gradient Richardson number, turbulent motions are present.

Place, publisher, year, edition, pages
2007. Vol. 64, no 2, 645-655 p.
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
URN: urn:nbn:se:su:diva-24079DOI: 10.1175/JAS3856.1ISI: 000244276600023OAI: oai:DiVA.org:su-24079DiVA: diva2:196696
Note
Part of urn:nbn:se:su:diva-6585Available from: 2007-02-01 Created: 2007-02-01 Last updated: 2010-01-22Bibliographically approved
In thesis
1. On the Arctic Boundary Layer: From Turbulence to Climate
Open this publication in new window or tab >>On the Arctic Boundary Layer: From Turbulence to Climate
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The boundary layer is the part of the atmosphere that is in direct contact with the ground via turbulent motion. At mid-latitudes the boundary layer is usually one or a few kilometers deep, while in the Arctic it is much more shallow, typically a few hundred meters or less. The reason is that here the absolute temperature increases in the lowest kilometer, making the boundary layer semi-permanently stably stratified. The exchange of heat, momentum and tracers between the atmosphere, ocean and ground under stable stratification is discussed from an observational, modeling and climate-change point of view. A compilation of six observational datasets, ordered by the Richardson number (rather than the widely used Monin-Obukhov length) reveals new information about turbulence in the very stably stratified regime. An essentially new turbulence closure model, based on the total turbulent energy concept and these observational datasets, is developed and tested against large-eddy simulations with promising results. The role of mesoscale motion in the exchange between the atmosphere and surface is investigated both for observations and in idealized model simulations. Finally, it is found that the stably stratified boundary layer is more sensitive to external surface forcing than its neutral and convective counterparts. It is speculated that this could be part of the explanation for the observed Arctic amplification of climate change.

Place, publisher, year, edition, pages
Stockholm: Meteorologiska institutionen (MISU), 2007. 165 p.
Keyword
Atmospheric boundary layers, Turbulence, Stable stratification, Gravity waves, Mesoscale motion, Arctic climate
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences
Identifiers
urn:nbn:se:su:diva-6585 (URN)91-7155-373-8 (ISBN)
Public defence
2007-02-23, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 8 A, Stockholm, 10:00
Opponent
Supervisors
Available from: 2007-02-01 Created: 2007-02-01Bibliographically approved

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