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Observations and Large-Eddy Simulations of Entrainment in the Sheared Sahelian Boundary Layer

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Abstract

At the top of the planetary boundary layer, the entrainment of air, which incorporates dry and warm air from the free troposphere into the boundary layer, is a key process for exchanges with the free troposphere since it controls the growth of the boundary layer. Here, we focus on the semi-arid boundary layer where the entrainment process is analyzed using aircraft observations collected during the African Monsoon Multidisciplinary Analysis experiment and large-eddy simulations. The role of the entrainment is specifically enhanced in this region where very large gradients at the planetary boundary-layer top can be found due to the presence of the moist, cold monsoon flow on which the dry, warm Harmattan flow is superimposed. A first large-eddy simulation is designed based on aircraft observations of 5 June 2006 during the transition period between dry conditions and the active monsoon phase. The simulation reproduces the boundary-layer development and dynamics observed on this day. From this specific case, sensitivity tests are carried out to cover a range of conditions observed during seven other flights made in the same transition period in order to describe the entrainment processes in detail. The combination of large-eddy simulations and observations allows us to test the parametrization of entrainment in a mixed-layer model with zero-order and first-order approximations for the entrainment zone. The latter representation of the entrainment zone gives a better fit with the conditions encountered in the Sahelian boundary layer during the transition period because large entrainment thicknesses are observed. The sensitivity study also provides an opportunity to highlight the contribution of shear stress and scalar jumps at the top of the boundary layer in the entrainment process, and to test a relevant parametrization published in the recent literature for a mixed-layer model.

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References

  • Agusti-Panareda A, Beljaars A, Ahlgrimm M, Balsamo G, Bock O, Forbes R, Ghelli F, Guichard A, Kohler M, Meynadier R, Morcrette JJ (2010) The ECMWF re-analysis for the AMMA observational campaign. Q J Roy Meteorol Soc 136: 1457–1472

    Article  Google Scholar 

  • Angevine W (2008) Transitional, entraining, cloudy, and coastal boundary layers. Acta Geophys 56: 2–20. doi:10.2478/s11600-007-0035-1

    Article  Google Scholar 

  • Angevine WM, White AB, Avery SK (1994) Boundary-layer depth and entrainment zone characterization with a boundary-layer profiler. Boundary-Layer Meteorol 68: 375–385

    Article  Google Scholar 

  • Canut G, Lothon M, Lohou F, Saïd F (2010) Observation of entrainment at the interface between monsoon flow and Saharan Air Layer. Q J Roy Meteorol Soc 136: 34–46

    Article  Google Scholar 

  • Conzemius RJ, Fedorovich E (2006a) Dynamics of sheared convective boundary layer entrainment. Part I: methodology background and large-eddy simulations. J Atmos Sci 63: 1151–1178

    Article  Google Scholar 

  • Conzemius RJ, Fedorovich E (2006b) Dynamics of sheared convective boundary layer entrainment. Part II: evaluation of bulk model predictions of entrainment flux. J Atmos Sci 63: 1179–1199

    Article  Google Scholar 

  • Conzemius RJ, Fedorovich E (2007) Bulk models of the sheared convective boundary layer: evaluation through large eddy simulations. J Atmos Sci 64: 786–807

    Article  Google Scholar 

  • Couvreux F, Guichard F, Redelsperger JL, Kiemle C, Masson V, Lafore JP, Flamant C (2005) Water-vapour variability within a convective boundary-layer assessed by large-eddy simulations and IHOP-2002 observations. Q J Roy Meteorol Soc 131: 2665–2693

    Article  Google Scholar 

  • Couvreux F, Guichard F, Redelsperger JL, Masson V (2007) Negative water vapour skewness and dry tongues in the convective boundary layer: observations and LES budget analysis. Boundary-Layer Meteorol 123: 269–294

    Article  Google Scholar 

  • Couvreux F, Guichard F, Bock O, Campistron B, Lafore J, Redelsperger JL (2010) Synoptic variability of the monsoon flux over west Africa prior to the onset. Q J Roy Meteorol Soc 136: 169–173

    Article  Google Scholar 

  • Cuxart J, Bougeault P, Redelsperger JL (2000) A turbulence scheme allowing for mesoscale and large-eddy simulations. Q J Roy Meteorol Soc 26: 1–30

    Article  Google Scholar 

  • Driedonks AGM (1982) Models and observations of the growth of the atmospheric boundary layer. Boundary-Layer Meteorol 23: 283–306

    Article  Google Scholar 

  • Faloona I, Lenschow DH, Stevens B, Campos T, Blomquist B, Thornton D, Bandy A, Gerber H, Van Zanten M (2005) Observations of entrainment in eastern Pacific marine stratocumulus using three conserved scalars. J Atmos Sci 62: 3268–3285

    Article  Google Scholar 

  • Fedorovich E, Conzemius R (2008) Effects of wind shear on the atmospheric convective boundary-layer structure and evolution. Acta Geophys 56: 114–141

    Article  Google Scholar 

  • Fedorovich E, Conzemius R, Mironov D (2004) Convective entrainment into a shear-free, linearly stratified atmosphere: bulk models reevaluated through large eddy simulations. J Atmos Sci 61: 281–295

    Article  Google Scholar 

  • Garratt JR (1992) The atmospheric boundary layer. Cambridge University Press, Cambridge, p 316

    Google Scholar 

  • Grossman RL, Nimal G (1995) Moisture flux and mixing processes in the daytime continental convective boundary layer. J Geophys Res 100: 25665–25674

    Article  Google Scholar 

  • Gryning SE, Batcharova E (1990) Analytical model for the growth of the coastal internal boundary layer during onshore flow. Q J Roy Meteorol Soc 116: 187–203

    Article  Google Scholar 

  • Kalapureddy M, Lothon M, Campistron B, Lohou F, Saïd F (2010) Wind profiler analysis of the African Easterly Jet in relation with the boundary layer and the Saharan Heat-Low. Q J Roy Meteorol Soc 136: 141–158

    Article  Google Scholar 

  • Kawa SR, Pearson J (1989) An observational study of stratocumulus entrainment and thermodynamics. J Atmos Sci 46: 2649–2661

    Article  Google Scholar 

  • Kim S, Park S, Moeng CH (2003) Entrainment processes in the convective boundary layer with varying wind shear. Boundary-Layer Meteorol 108: 221–245

    Article  Google Scholar 

  • Kim SW, Park SU, Pino D, Vilà-Gueraude Arellano J (2006) Parameterization of entrainment in a sheared convective boundary layer using a first-order jump model. Boundary-Layer Meteorol 120: 445–475

    Article  Google Scholar 

  • Lafore JP, Stein J, Asencio N, Bougeault P, Ducrocq V, Duron J, Fischer C, Héreil P, Mascart P, Redelsperger JL, Richard E, Vilà-Guerau de Arellano J (1998) The Meso-NH atmospheric simulation system. Part I: adiabatic formulation and control simulations. Ann Geophys 109: 16–90

    Google Scholar 

  • Lebel T, Parker DJ, Flamant C, Bourlès B, Marticorena B, Mougin C, Peugeot E, Diedhiou A, Haywood JM, Ngamini JB, Polcher J, Redelsperger JL, Thorncroft CD (2010) The AMMA field campaigns: multiscale and multidisciplinary observations in the West African region. Q J Roy Meteorol Soc 136: 8–33

    Article  Google Scholar 

  • Lenschow DH, Krummel PB, Siems ST (1999) Measuring entrainment, divergence and vorticity on the mesoscale from aircraft. J Atmos Ocean Technol 16: 1384–1400

    Article  Google Scholar 

  • Lilly DK (1968) Models of cloudy-topped mixed layers under a strong inversion. Q J Roy Meteorol Soc 94: 292–309

    Article  Google Scholar 

  • Lohou F, Saïd F, Lothon M, Durand P, Serça D (2010) Impact of the boundary-layer processes on surface turbulence characteristics in the frame of the west african monsoon. Boundary-Layer Meteorol 136: 1–23

    Article  Google Scholar 

  • Lothon M, Couvreux F, Donier S, Guichard F, Lacarrère P, Noilhan J, Saïd F (2007) Impact of the coherent eddies on airborne measurements of vertical turbulent fluxes. Boundary-Layer Meteorol. 124

  • Lothon M, Saïd F, Lohou F, Campistron B (2008) Observation of the diurnal cycle in the low troposphere of West Africa. Mon Weather Rev 136

  • Mahrt L. (1991) Boundary-layer moisture regimes. Q J Roy Meteorol Soc 117: 151–176

    Article  Google Scholar 

  • Pino D, Vilà-Guerau de Arellano J (2008) Effects of shear in the convective boundary layer: analysis of the turbulent kinetic energy budget. Acta Geophys 56: 167–193

    Article  Google Scholar 

  • Pino D, Vilà-Guerau de Arellano J, Duynkerke PG (2003) The contribution of shear to the evolution of a convective boundary layer. J Atmos Sci 60: 1913–1926

    Article  Google Scholar 

  • Pino D, Vilà-Gueraude Arellano J, Kim S-W (2006) Representing sheared convective boundary layer zero- and first-order-jump mixed-layer models: Large-eddy simulation verification. J Appl Meterol Clim 45: 1224–1243

    Article  Google Scholar 

  • Redelsperger JL, Sommeria G (1982) Method of representing the turbulence at scales inferior to the grid in a three-dimensional model of cloud convecion. Boundary-Layer Meteorol 21: 509–530

    Article  Google Scholar 

  • Saïd F, Canut G, Durand M, Lothon P, Lohou F (2010) Seasonal evolution of boundary-layer turbulence measured by aircraft during the AMMA 2006 special observation period. Q J Roy Meteorol Soc 136: 47–65

    Article  Google Scholar 

  • Sorbjan Z (1996) Effects caused by varying the strength of the capping inversion based on a large eddy simulation model of the shear-free convective boundary layer. J Atmos Sci 53: 2015–2024

    Article  Google Scholar 

  • Sorbjan Z (2004) Large-eddy simulations of the baroclinic mixed layer. Boundary-Layer Meteorol 112: 57–80

    Article  Google Scholar 

  • Stull RB (1976) The energetics of entrainment across a density interface. J Atmos Sci 33: 1260–1267

    Google Scholar 

  • Stull RB (1988) An introduction to boundary layer meteorology, new edition, 1999. Kluwer, Dordrecht, p 666

    Google Scholar 

  • Sullivan PP, Moeng C-H, Stevens B, Lenschow DH, Mayor SD (1998) Structure of the entrainment zone capping the convective atmospheric boundary layer. Q J Roy Meteorol Soc 55: 3042–3064

    Google Scholar 

  • Sun J, Xu Q (2009) Parameterization of sheared convective entrainment in the first-order jump model: evaluation through large-eddy simulation. Boundary-Layer Meteorol 132: 279–288

    Article  Google Scholar 

  • Sun J, Yuan W (2008) Effect of the entrainment flux ratio on the relationship between entrainment rate and convective Richardson number. Boundary-Layer Meteorol 126: 237–247

    Article  Google Scholar 

  • Tennekes H (1973) A model for the dynamics of the inversion above a convective boundary layer. J Atmos Sci 30: 538–567

    Google Scholar 

  • Tennekes H, Driedonks AGM (1981) Basic entrainment equations for the atmospheric boundary layer. Boundary-Layer Meteorol 20: 515–531. doi:10.1007/BF00122299

    Article  Google Scholar 

  • Turner D, Wagner E, Wulfmeyer V, Pal S, Larry K (2010) Raman lidar observations of water vapor mixing ratio turbulence profiles in the convective boundary layer. Oral presentation, International symposium for the advanced of boundary layer remote sensing, 28–30 June 2010, Paris

  • Van Zanten MC, Duynkerke P, Cuijpers J (1999) Entrainment parameterization in convective boundary layers. J Atmos Sci 56: 813–828

    Article  Google Scholar 

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Authors and Affiliations

  1. Laboratoire d’Aérologie, Université de Toulouse, CNRS UMR 5560, Toulouse, France

    Guylaine Canut, Marie Lothon & Frédérique Saïd

  2. CNRM-GAME, Météo-France and CNRS, Toulouse, France

    Fleur Couvreux

  3. Applied Physics Department, BarceloneTech (UPC) and Institute for Space Studies of Catalonia (IEEC-UPC), Barcelona, Spain

    David Pino

Authors
  1. Guylaine Canut
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  2. Fleur Couvreux
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  3. Marie Lothon
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  4. David Pino
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  5. Frédérique Saïd
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Correspondence to Guylaine Canut.

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Canut, G., Couvreux, F., Lothon, M. et al. Observations and Large-Eddy Simulations of Entrainment in the Sheared Sahelian Boundary Layer. Boundary-Layer Meteorol 142, 79–101 (2012). https://doi.org/10.1007/s10546-011-9661-x

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