Skip to main content
SpringerLink
Log in

Impact of Boundary-Layer Processes on Near-Surface Turbulence Within the West African Monsoon

  • Article
  • Published:
Boundary-Layer Meteorology Aims and scope Submit manuscript

Abstract

High frequency measurements of near-surface meteorological data acquired in north Benin during the 2006 West African monsoon seasonal cycle, in the context of the African Monsoon Multidisciplinary Analysis (AMMA) experiment, offer insight into the characteristics of surface turbulence in relation to planetary boundary-layer (PBL) processes. A wide range of conditions is encountered at the lower and upper limits of the PBL: (i) from water-stressed to well-fed vegetation, and (ii) from small to large humidity and temperature jumps at the PBL top inversion, due to the Saharan air layer overlying the monsoonal flow. As a result, buoyant convection at the surface and entrainment at the PBL top play very different roles according to the considered scalar. We show that, when the boundary-layer height reaches the shear level between the monsoonal and Harmattan flows, the temperature source and humidity sink at the boundary-layer top are sufficient to allow the entrainment to affect the entire boundary layer down to the surface. This situation occurs mainly during the drying and moistening periods of the monsoon cycle and affects the humidity statistics in particular. In this case, the humidity turbulent characteristics at the surface are no longer driven solely by buoyant convection, but also by entrainment at the boundary-layer top. Consequently, the Monin–Obukhov similarity theory appears to fail for the parameterisation of humidity-related moments.

This is a preview of subscription content, log in via an institution to check access.

Access this article

Log in via an institution

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Institutional subscriptions

Similar content being viewed by others

References

  • Andreas EL, Hill RJ, Gosz JR, Moore DI, Otto WD, Sarma AD (1998) Statistics of surface-layer turbulence over terrain with metre-scale heterogeneity. Boundary-Layer Meteorol 86: 397–408

    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 

  • Betts AK (2000) Idealized model for equilibrium boundary layer over land. J Hydrometeorol 1: 507–523

    Article  Google Scholar 

  • Bock O, Bouin MN, Doerflinger E, Collard P, Masson F, Meynadier R, Nahmani S, Koitié M, Gaptia Lawan Balawan K, Didé F, Ouedraogo D, Pokperlaar S, Ngamini JB, Lafore JP, Janicot S, Guichard F, Nuret M (2008) West African Monsoon observed with ground-based GPS receivers during African Monsoon Multidisciplinary Analysis (AMMA). J Geophys Res 113:D21105. doi:10.1029/2008JD010,327

  • Canut G, Lothon M, Saïd F, Lohou F (2010) Observation of entrainment at the interface between monsoon flow and saharan air layer. Q J Roy Meteorol Soc. doi:10.1002/qj.471

  • Conzemius RJ, Fedorovich E (2008) A case study of convective boundary layer development during IHOP2002: numerical simulations compared to observations. Mon Weather Rev 136: 2305–2320

    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 

  • Crum TD, Stull RB (1987) Field measurements of the amount surface layer air versus height in the entrainment zone. J Atmos Sci 44: 2743–2753

    Article  Google Scholar 

  • de Arellano JVG, Gioli B, Miglietta F, Jonker HJJ, Baltink HK, Hutjes RWA, Holtslag AAM (2004) Entrainment process of carbon dioxide in the atmospheric boundary layer. J Geophys Res 109: D18110

    Article  Google Scholar 

  • De Roode SR, Duynkerke PG, Jonker HJJ (2004) Large-eddy simulation: how large is large enough?. J Atmos Sci 61: 403–421

    Article  Google Scholar 

  • Detto M, Katul G, Mancini M, Montaldo N, Albertson JD (2008) Surface heterogeneity and its signature in higher-order scalar similarity relationships. Agric For Meteorol 148: 902–916

    Article  Google Scholar 

  • Doviak RJ, Zrnic DS (1993) Doppler radar and weather observations. Academic Press, San Diego

    Google Scholar 

  • Druilhet A, Frangi J, Guedalia D, Fontan J (1983) Experimental studies of the turbulent structure parameters of the convective boundary layer. J Clim Appl Meteorol 22: 594–608

    Article  Google Scholar 

  • Durand P, Thoumieux F, Lambert D (2000) Turbulent length-scales in the marine atmospheric mixed layer. Q J Roy Meteorol Soc 126: 1889–1912

    Article  Google Scholar 

  • Jacoby-Koaly S, Campistron B, Bernard S, Bénech B, Girard-Ardhuin F, Dessens J (2002) Turbulent dissipation rate in the boundary layer via UHF wind profiler Doppler spectral width measurements. Boundary-Layer Meteorol 103: 361–389

    Article  Google Scholar 

  • Janicot S, Sultan B (2007) The large-scale context of the West African Monsoon in 2006. Exch CLIVAR Newslett 12(2): 11–17

    Google Scholar 

  • Jonker HJJ, Duynkerke PG, Cuijpers JWM (1999) Mesoscale fluctuations in scalars generated by boundary layer convection. J Atmos Sci 56: 801–808

    Article  Google Scholar 

  • Jonker HJJ, de Arellano JVG, Duynkerke PG (2004) Characteristic length scale of reactive species in a convective boundary layer. J Atmos Sci 61: 41–56

    Article  Google Scholar 

  • Kaimal JC, Finnigan JJ (1994) Atmospheric boundary layer flows. Oxford University Press, New York, p 289

    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. doi:10.1002/qj.494

  • Lafore JP, Flamant C, Giraud F, Guichard F, Knipperts P, Mahfouf JF, Mascart P, Williams E (2010) Introduction to the AMMA special issue on: advances in understanding processes over west Africa through the AMMA field campaign. Q J Roy Meteorol Soc. doi:10.1002/qj.583

  • Lenschow DH, Stankov BB (1986) Length scales in the convective boundary layer. J Atmos Sci 43: 1198–1209

    Article  Google Scholar 

  • Lenschow DH, Wulfmeyer V, Senff C (2002) Measuring second- through fourth-order moments in noisy data. J Atmos Ocean Technol 17: 1330–1347

    Article  Google Scholar 

  • Lothon M, Couvreux F, Donier S, Guichard F, Lacarrère P, Noilhan J, Saïd F (2007) Impact of the coherent eddies on the airborne measurements of vertical turbulent fluxes. Boundary-Layer Meteorol 124: 425–447

    Article  Google Scholar 

  • 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: 3477–3500

    Article  Google Scholar 

  • Lumley JL, Panofsky HA (1964) The structure of atmospheric turbulence. Inter-Science, New York, p 239

    Google Scholar 

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

    Article  Google Scholar 

  • Moene AF, Michels BI, M HA (2006) Scaling variances of scalars in a convective boundary layer under different entrainment regimes. Boundary-Layer Meteorol 120: 257–274

    Article  Google Scholar 

  • Nicholls S, LeMone MA (1980) The fair boundary layer in gate: the relationship of subcloud fluxes and structure to the distribution and enhancement of the cumulus cloud. J Atmos Sci 37: 2051–2067

    Article  Google Scholar 

  • Parker DJ, Burton RR, Diongue-Niang A, Ellis RJ, Felton MA, Taylor CM, Thorncroft CD, Bessemoulin P, Tompkins AM (2005) The diurnal cycle of the West African Monsoon circulation. Q J Roy Meteorol Soc 131: 2839–2860

    Article  Google Scholar 

  • Ramier D, Boulain N, Cappelaere B, Timouk F, Rabanit M, Lloyd CR, Boubkraoui S, Métayer F, Descroix L, Wawrzyniak V (2009) Towards an understanding of coupled physical and biological processes in the cultivated Sahel—1. Energy and water. J Hydrol 375: 204–216

    Article  Google Scholar 

  • Redelsperger J, Thorncroft C, Diedhiou A, Lebel T, Parker DJ, Polcher J (2006) African Monsoon Multidisciplinary Analysis (AMMA): an international research project and field campaign. Bull Am Meteorol Soc 87: 1739–1746

    Article  Google Scholar 

  • Saïd F, Canut G, Durand P, Lohou F, Lothon M (2010) Seasonal evolution of the boundary-layer turbulence measured by aircraft during AMMA 2006 special observation period. Q J Roy Meteorol Soc. doi:10.1002/qj.475

  • Santanello JA, Friedl MA, Ek MB (2007) Convective planetary boundary layer interactions with the land surface at diurnal time scale: diagnostics and feedbacks. J Hydrol 8: 1082–1097

    Google Scholar 

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

    Google Scholar 

  • Sultan B, Janicot S (2003) The West African Monsoon dynamics. Part II: the ‘pre-onset’ and the ‘onset’ of the summer monsoon. J Clim 16: 3407–3427

    Article  Google Scholar 

  • Timouk F, Kergoat L, Mougin E, Lloyd CR, Cohard JM, de Rosnay P, Hiernaux P, Demarez V, Taylor CM (2009) Response of surface energy balance to water regime and vegetation development in a Sahelian landscape. J Hydrol 375: 178–189

    Article  Google Scholar 

  • Webb E, Pearman G, Leuning R (1980) Correction of flux measurements for density effects due to heat and water-vapor transfer. Q J Roy Meteorol Soc 106: 85–100

    Article  Google Scholar 

Download references

Author information

Authors and Affiliations

  1. Université de Toulouse, UPS, LA (Laboratoire d’Aérologie) CNRS, LA (Laboratoire d’Aérologie), 14 avenue Edouard Belin, 31400, Toulouse, France

    Fabienne Lohou, Frédérique Saïd, Marie Lothon, Pierre Durand & Dominique Serça

Authors
  1. Fabienne Lohou
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Frédérique Saïd
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Marie Lothon
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Pierre Durand
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Dominique Serça
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Fabienne Lohou.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Lohou, F., Saïd, F., Lothon, M. et al. Impact of Boundary-Layer Processes on Near-Surface Turbulence Within the West African Monsoon. Boundary-Layer Meteorol 136, 1–23 (2010). https://doi.org/10.1007/s10546-010-9493-0

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1007/s10546-010-9493-0

Keywords

Search

Navigation