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The atmospheric boundary layer over melting glaciers

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It's hard to determine the dept of the surface layer because of unevenly melt. ... In times of continues melt fluxes can be calculated by using radiation balance. ... – PowerPoint PPT presentation

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Title: The atmospheric boundary layer over melting glaciers


1
The atmospheric boundary layer over melting
glaciers
  • By J. Oerlemans
  • Presentation by Jasper Donker

2
Outline
  • Introduction
  • Measurments on katabatic flow
  • Modelling katabatic flow

3
Introduction
  • Melting is sensitive to air temperature
    variations
  • Downward sensible heat flux increases with
    increasing temperatures
  • The surface stays at melting point for long
    periods of time
  • Causing a katabatic flow down the glaciers

4
Experiment on the kathabatic winds above glaciers
  • Done at 3 different locations
  • Pasterze (Austria)
  • West of greenland
  • Vatnajökull(ice land)
  • Weatherstations at the surface measure wind
    direction and speed
  • Vertical structure is determined with the help of
    zeppelins caring sensors

5
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6
Greenland measurments on katabatic wind
7
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8
The Prandl model
  • The prandl model was used to make a model for the
    vertical structure of the katabatic glacial wind
  • This model couldn't describe the decrease in eddy
    diffusivity when approaching the surface
  • The steep velocity gradient close to the surface
    could not be produced
  • Katebatic jet is more pronounced
  • With increasing strength the height of the
    katebatic jet is increased this is not reproduced

9
Problems with applying flux theory
  • The top of the boundary layer is hard to identify
  • Its hard to determine the dept of the surface
    layer because of unevenly melt.

10
Determine surface fluxes
  • In times of continues melt fluxes can be
    calculated by using radiation balance.
  • Profiling method doesnt work
  • Microtopograpic method has much better results

11
Modified model for the surface layer a constant
flux layer
12
Flow dependent eddy diffusivity
  • Values for the eddy diffusivity were taken
    constant in previous model
  • Due to dependence of turbulent mixing on the
    strength of the katabatic flow this is not
    realistic
  • This modification gives better estimates.

13
Conclusions
  • Katabatic flow is present over melting glaciers
  • Its difficult to apply existing stable
    boundary-layer theory to glacier wind.
  • Micrographic method is best method to determine
    roughness of the surface
  • Modified model should be tested.

14
The End
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