| 1. |
- Parmhed, Oskar, et al.
(författare)
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Describing surface fluxes in katabatic flow on Breidamerkurjökull, Iceland
- 2004
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Ingår i: Quarterly Journal of the Royal Meteorological Society. - : Royal meteorological Society. - 0035-9009 .- 1477-870X. ; 130:598, s. 1137-1151
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
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| 3. |
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| 4. |
- Žagar, Nedjeljka, et al.
(författare)
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Variational data assimilation in the tropics : the impact of a background error constraint
- 2004
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Ingår i: Quarterly Journal of the Royal Meteorological Society. - : Wiley. - 0035-9009 .- 1477-870X. ; 130, s. 103-125
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Tidskriftsartikel (refereegranskat)abstract
- Geostrophic adjustment theory predicts that wind information is a primary information source in the tropics. We ask whether this is true when variational data assimilation including a background-error constraint is applied. The question is investigated by carrying out three- and four-dimensional variational (4D-Var) data assimilation experiments with nonlinear shallow-water equations and idealized waves. The contribution to the analysis from mass and wind field observations is contrasted to that of spectral characteristics and multivariate relationships of equatorial waves built into a background-error covariance matrix. A background-error term for the analysis is built by using the tropical eigenmodes and the observed variability is used to determine the relative weights for different modes. Single observation sensitivity experiments illustrate an important impact of Kelvin and mixed Rossby-gravity waves in reducing the coupling between the mass and wind fields, found when only equatorial Rossby waves are utilized in the background-error constraint. The assimilation experiments demonstrate two main features. First, the wind field information is of greater value than the mass field information, in spite of the known error statistics. A second intriguing feature is that the assimilation of wind observations better resolves smaller-scale features of the height field than the assimilation of height data. When height data are used, a somewhat different analysis response is obtained for the zonal and meridional wind components, due to the strong projection onto the Kelvin wave structure for height observations. Finally, a comparison of different time windows for 4D-Var illuminates the sensitivity of height field assimilation to the length of the assimilation window.
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| 5. |
- Zilitinkevich, Sergej, et al.
(författare)
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The effect of baroclinicity on the equilibrium depth of neutral and stable planetary boundary layers
- 2003
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Ingår i: Quarterly Journal of the Royal Meteorological Society. - : Wiley. - 0035-9009 .- 1477-870X. ; 129:595, s. 3339-3356
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Tidskriftsartikel (refereegranskat)abstract
- Earlier studies of the depths of the geophysical planetary boundary layers (PBLs) basically focused on the effects of the earth's rotation and density stratification. One more inherent feature of geophysical flows, namely their baroclinicity, has not been considered in that context. The present paper makes up for this deficiency. Diagnostic equations for the depths of the equilibrium, baroclinic, neutral or stable PBLs are derived and verified against data from large-eddy simulations (LES). These latter represents the most convenient empirical-validation tool, which allows considering separately different types of PBL: barotropic and baroclinic; truly neutral and conventionally neutral; nocturnal stable and long-lived stable. The LES are performed using a new code specifically designed for modelling the neutral and stable PBL. Results from the comparison show an excellent correspondence between the proposed equations and LES data. Copyright © 2003 Royal Meteorological Society
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| 6. |
- Sundararajan, Ragothaman, et al.
(författare)
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Observations and simulations of a non-stationary coastal atmospheric boundary layer
- 2000
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Ingår i: QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY. - : ROYAL METEOROLOGICAL SOC. - 0035-9009. ; 126:563, s. 445-476
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Tidskriftsartikel (refereegranskat)abstract
- This paper studies the turbulent and mesoscale structures of a coastal marine atmospheric boundary layer in the southern Baltic Sea. Data from a field experiment are examined for a case during autumn, and this case is subsequently modelled with a mesoscal
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| 7. |
- Zilitinkevich, Sergej, et al.
(författare)
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An extended similarity theory for the stably stratified atmospheric surface layer
- 2000
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Ingår i: QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY. - : ROYAL METEOROLOGICAL SOC. - 0035-9009. ; 126:566, s. 1913-1923
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Tidskriftsartikel (refereegranskat)abstract
- An advanced similarity-theory formulation for the wind and temperature profiles in the stably stratified atmospheric surface layer (ASL) is developed with due regard to the effect of the free-flow static stability on the ASL. In the revised log-linear pro
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