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Mesoscale variability in the summer Arctic boundary layer
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology .
2009 (English)In: Boundary-layer Meteorology, ISSN 0006-8314, Vol. 130, no 3, 1573-1472 p.Article in journal (Refereed) Published
Abstract [en]

Observations from the summer Arctic Ocean Experiment 2001 (AOE-2001) are analysed with a focus on the interactions between mesoscale and boundary-layer dynamics. Wavelet analyses of surface-pressure variations show daylong periods with different characteristics, some featuring episodes of pronounced high-frequency surface-pressure variability, here hypothesized to be caused by trapped gravity waves. These episodes are accompanied by enhanced boundary-layer turbulence and an enhanced spectral gap, but with only minor influence on the surface stress. During these episodes, mesoscale phenomena were often encountered and usually identified as front-like features in the boundary layer, with a peak in drizzle followed by changing temperature. These phenomena resemble synoptic fronts, though they are generally shallow, shorter-lasting, have no signs of frontal clouds, and do not imply a change in air mass. Based on this analysis, we hypothesize that the root cause of the episodes with high-frequency surface-pressure variance are shallow, mesoscale fronts moving across the pack ice. They may be formed due to local-to-regional horizontal contrasts, for example, between air with different lifetimes over the Arctic or with perturbations in the cloud field causing differential cooling of the boundary layer. Thermal contrasts sharpen as the air is transported with the mean flow. The propagating mesoscale fronts excite gravity waves, which affect the boundary-layer turbulence and also seem to favour entrainment of free tropospheric air into the boundary layer.

Place, publisher, year, edition, pages
2009. Vol. 130, no 3, 1573-1472 p.
Keyword [en]
Arctic, Mesoscale
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
URN: urn:nbn:se:su:diva-24081DOI: 10.1007/s10546-009-9354-xISI: 000263418500005OAI: oai:DiVA.org:su-24081DiVA: diva2:196698
Note
Part of urn:nbn:se:su:diva-6585Available from: 2007-02-01 Created: 2007-02-01 Last updated: 2010-01-18Bibliographically 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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