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Near surface atmospheric flow over high latitude glaciers
Stockholm University, Faculty of Science, Department of Meteorology .
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis various descriptions of the near surface atmospheric flow over a high latitude glacier is used in an effort to increase our understanding of the basic flow dynamics there.

Through their contribution to sea-level change, mountain glaciers play a significant role in Earth’s climate system. Properties of the near surface atmospheric flow are important for understanding glacier response to climate change.

Here, the near surface atmospheric flow is studied from several perspectives including the effects of both rotation and slope. Rotation is an important aspect of most atmospheric flows and its significance for mesoscale flows have gained recognition over the last years. Similarly, the very stable boundary layer (VSBL) has lately gained interest. Within a VSBL over sloping terrain katabatic flow is known to be usual and persistent. For the present thesis a combination of numerical and simple analytical models as well as observations from the Vatnajökull glacier on Iceland have been used. The models have continuously been compared to available observations. Three different approaches have been used: linear wave modeling, analytic modeling of katabatic flow and of the Ekman layer, and numerical simulations of the katabatic flow using a state of the art mesoscale model. The analytic models for the katabatic flow and the Ekman layer used in this thesis both utilizes the WKB method to allow the eddy diffusivity to vary with height. This considerably improves the results of the models. Among other findings it is concluded that: a large part of the flow can be explained by linear theory, that good results can be obtained for surface energy flux using simple models, and that the very simple analytic models for the katabatic flow and the Ekman layer can perform adequately if the restraint of constant eddy diffusivity is relieved.

Place, publisher, year, edition, pages
Stockholm: Meteorologiska institutionen (MISU) , 2004. , 22 p.
Keyword [en]
Stable boundary layer, Ekman layer, Katabatic flow, gravity wave, low-level jets
National Category
Meteorology and Atmospheric Sciences
Identifiers
URN: urn:nbn:se:su:diva-197ISBN: 91-7265-913-0 (print)OAI: oai:DiVA.org:su-197DiVA: diva2:190804
Public defence
2004-06-15, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 8 C, Stockholm, 10:00
Opponent
Supervisors
Available from: 2004-05-25 Created: 2004-05-25 Last updated: 2011-02-17Bibliographically approved
List of papers
1. Linear modeling of the air flow over the Vatnajökull glacier
Open this publication in new window or tab >>Linear modeling of the air flow over the Vatnajökull glacier
2004 (English)Report (Other academic)
Place, publisher, year, edition, pages
Stockholm: Department of Meteoroly, Stockholm University, 2004. 19 p.
Series
Report / Department of Meteorology, University of Stockholm. DM, ISSN 0349-0467 ; 91
Identifiers
urn:nbn:se:su:diva-23221 (URN)
Note
Part of urn:nbn:se:su:diva-197Available from: 2004-05-25 Created: 2004-05-25 Last updated: 2010-01-29Bibliographically approved
2. Describing surface fluxes in katabatic flow on Breidamerkurjökull, Iceland
Open this publication in new window or tab >>Describing surface fluxes in katabatic flow on Breidamerkurjökull, Iceland
2004 (English)In: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, Vol. 130, no 598, 1137-1151 p.Article in journal (Refereed) Published
Abstract [en]

For very stable boundary layers there is no well-accepted theory today. In this study, an improved Prandtl model with varying diffusivity is applied to less than ideal conditions for pure katabatic flow pertaining to very stable boundary layers. We find that the improved Prandtl model adequately describes the usual and persistent katabatic glacier wind on Breidamerkurjökull. This is true even for flows with very different heights and strengths of the jet. A theoretical estimate of the katabatic jet height, based on temperature deficit and lapse rate, is verified. The calculated surface fluxes compare well with the measured turbulence parameters. A possible reason for the robustness of the katabatic jet (and other low-level jets) is given in terms of the Scorer parameter. Copyright © 2004 Royal Meteorological Society.

Place, publisher, year, edition, pages
Royal meteorological Society, 2004
Keyword
Glacier wind, Low-level jet, Very stable boundary layer, WKB method
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
urn:nbn:se:su:diva-23222 (URN)10.1256/qj.03.52 (DOI)
Note
Part of urn:nbn:se:su:diva-197Available from: 2004-05-25 Created: 2004-05-25 Last updated: 2010-01-04Bibliographically approved
3. An improved Ekman layer Approximation For Smooth Eddy Diffusity Profiles
Open this publication in new window or tab >>An improved Ekman layer Approximation For Smooth Eddy Diffusity Profiles
2005 (English)In: Boundary-Layer Meteorology, ISSN 0006-8314, Vol. 115, no 3, 399-407 p.Article in journal (Refereed) Published
Abstract [en]

The Ekman boundary-layer model is extended analytically for a gradually varying eddy diffusivity K(z) ≥ 0, z ≥ 0. A solution for the Ekman layer is provided having similar structure to the constant-K case; that is, exponentially decaying sine functions for the two horizontal wind components. The analytical asymptotic solution compares well with its numerical counterpart for various K(z). The result can be useful in theoretical studies such as Ekman pumping, for efficient estimation of the Ekman layer profiles in various analyses with near-neutral stratifications, or for a rapid initialization of mesoscale models

Place, publisher, year, edition, pages
Springer, 2005
Keyword
Boundary-layer pumping, Lambert’s W, WKB
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
urn:nbn:se:su:diva-23223 (URN)10.1007/s10546-004-5940-0 (DOI)
Note
Part of urn:nbn:se:su:diva-197Available from: 2004-05-25 Created: 2004-05-25 Last updated: 2010-01-22Bibliographically approved
4. Numerical simulations and analytical estimates of katabatic flow over a melting outflow glacier
Open this publication in new window or tab >>Numerical simulations and analytical estimates of katabatic flow over a melting outflow glacier
2006 (English)In: Boundary-layer Meteorology, ISSN 0006-8314, E-ISSN 1573-1472, Vol. 120, no 3, 509-534 p.Article in journal (Refereed) Published
Abstract [en]

A realistic simulation of katabatic flows is not a straightforward task for numerical models. One complicating factor is that katabatic flows develop within a stably stratified boundary layer, which is poorly resolved and described in many numerical models. To capture the jet-shaped shallow flow a model set-up with high vertical resolution is also required. In this study, ‘a state of the art’ mesoscale numerical model is applied in a simulation of katabatic flow over a melting glacier. A basic agreement between observations and model results is found. From scale analysis, it is concluded that the simulated flow can be classified as katabatic. Although the background flow varies in strength and direction, the simulated katabatic flow over Breidamerkurjökull is persistent. Two factors vital for this persistence are identified. First, the melting snow maintains the surface temperature close to 0 °C while the air temperature warms adiabatically as it descends the slope. This provides a ‘self enhanced’ negative buoyancy that drives the flow to a balance with local friction. Second, the jet-like shape of the resulting flow gives rise to a large ‘curvature term’ in the Scorer parameter, which becomes negative in the upper jet. This prevents vertical wave propagation and isolates the katabatic layer of the influence from the free troposphere aloft. Our results suggest that the formation of local microclimates dominated by katabatic flow is a general feature over melting glaciers. The modelled turbulence structure illustrates the importance of non-local processes. Neglecting the vertical transport of turbulence in katabatic flows is not a valid assumption. It is also found that the local friction velocity remains larger than zero through the katabatic jet, due to directional shear where the scalar wind speed approaches its maximum.

Keyword
Glacier, Katabatic flow, Non-local transport, Scorer parameter, Stable boundary layer
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:su:diva-24002 (URN)10.1007/s10546-006-9059-3 (DOI)
Available from: 2004-03-04 Created: 2004-03-04 Last updated: 2011-02-17Bibliographically approved

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