• Appenzeller, C., , H. C. Davies, , and W. A. Norton, 1996: Fragmentation of stratospheric intrusions. J. Geophys. Res., 101 , 14351456.

  • Barriopedro, D., , R. Garcia-Herrera, , A. R. Lupo, , and E. Hernandez, 2006: A climatology of Northern Hemisphere blocking. J. Climate, 19 , 10421063.

    • Search Google Scholar
    • Export Citation
  • Borgne, J. L., 1979: Un exemple d’invasion polaire sur la région mauritano-sénégalaise. (An example of a polar intrusion into the Mauritanian-Sengalese region). Ann. Géograph., 489 , 521548.

    • Search Google Scholar
    • Export Citation
  • Bott, A., 1989: A positive definite advection scheme obtained by nonlinear renormalization of the advective fluxes. Mon. Wea. Rev., 117 , 10061016.

    • Search Google Scholar
    • Export Citation
  • Buckle, C., 1996: Weather and Climate in Africa. Addison Wesley Longman, 312 pp.

  • Cammas, J-P., , D. Keyser, , G. Lackmann, , and J. Molinari, 1994: Diabatic redistribution of potential vorticity accompanying the development of an outflow jet within a strong extratropical cyclone. Proc. Int. Symp. on the Life Cycles of Extratropical Cyclones, Vol. 2, Bergen, Norway, Geophysical Institute University of Bergen, 403–409.

  • Croci-Maspoli, M., , C. Schwierz, , and H. C. Davies, 2007: A multifaceted climatology of atmospheric blocking and its recent linear trend. J. Climate, 20 , 633649.

    • Search Google Scholar
    • Export Citation
  • Doms, G., , and U. Schättler, 2002: A description of the nonhydrostatic regional model LM. Part I: Dynamics and numerics. Documentation of the COSMO-Model, Deutscher Wetterdienst, 1–134. [Available online at http://www.cosmo-model.org.].

  • Doms, G., , J. Förstner, , E. Heise, , H. J. Herzog, , M. Raschendorer, , R. Schrodin, , T. Reinhardt, , and G. Vogel, 2005: A description of the nonhydrostatic regional model LM. Part II: Physical parameterization. Documentation of the COSMO-Model, Deutscher Wetterdienst, 1–140. [Available online at http://www.cosmo-model.org.].

  • Fall, S., , D. Niyogi, , and F. H. M. Semazzi, 2006: Analysis of mean climate conditions in Senegal (1971–98). Earth Interactions, 10. [Available online at http://EarthInteractions.org.].

  • Fall, S., , D. Niyogi, , U. C. Mohanty, , and A. Kumar, 2007: Application of weather prediction models for hazard mitigation planning: A case study of heavy off-season rains in Senegal. Nat. Hazards, 41 , 227243.

    • Search Google Scholar
    • Export Citation
  • Fehlmann, R., 1997: Dynamics of seminal PV elements. Ph.D. thesis, Diss. Naturwiss. ETH Zurich 12229, ETH Zurich, Zurich, Switzerland, 143 pp.

  • Fehlmann, R., , and H. C. Davies, 1997: Misforecasts of synoptic systems: Diagnosis via PV retrodiction. Mon. Wea. Rev., 125 , 22472264.

    • Search Google Scholar
    • Export Citation
  • Gaye, A. T., , S. Fongang, , A. Garba, , and D. Badiane, 1994: Study of Heug rainfall in Senegal using conventional data and Meteosat imagery. Vol. 49, Veille Climatique Satellitaire, Ministre de la Cooperation–ORSTOM–Meteo-France, Lannion, France, 61–71.

  • Hastenrath, S., 1985: Climate and Circulation of the Tropics. Reidel, 455 pp.

  • Hoskins, B. J., , M. E. McIntyre, , and A. W. Robertson, 1985: On the use and significance of isentropic potential vorticity maps. Quart. J. Roy. Meteor. Soc., 111 , 877946.

    • Search Google Scholar
    • Export Citation
  • Kessler, E., 1995: On the distribution and continuity of water substance in the atmospheric circulations. Atmos. Res., 38 , 109145.

  • Kiladis, G. N., 1998: Observations of Rossby waves linked to convection over the eastern tropical Pacific. J. Atmos. Sci., 55 , 321339.

    • Search Google Scholar
    • Export Citation
  • Kiladis, G. N., , and K. M. Weickmann, 1997: Horizontal structure and seasonality of large-scale circulations associated with submonthly tropical convection. Mon. Wea. Rev., 125 , 19972013.

    • Search Google Scholar
    • Export Citation
  • Knippertz, P., , and J. E. Martin, 2005: Tropical plumes and extreme precipitation in subtropical and tropical West Africa. Quart. J. Roy. Meteor. Soc., 131 , 23372365.

    • Search Google Scholar
    • Export Citation
  • Knippertz, P., , and J. E. Martin, 2007: The role of dynamic and diabatic processes in the generation of cut-off lows over Northwest Africa. Meteor. Atmos. Phys., 60 , 23372365.

    • Search Google Scholar
    • Export Citation
  • Knippertz, P., , L. Fröhlich, , and F. Meier, 2008: The development of potential vorticity intrusions over the tropical North Atlantic. Geophysical Research Abstracts, Vol. 10, Abstract 02307. [Available online at http://www.cosis.net/abstracts/EGU2008/02307/EGU2008-A-02307.pdf.].

  • Lafore, J. P., and Coauthors, 2005: The dry-run forecasting activities in Summer 05 for AMMA. AMMA Meeting: Process Scale Studies and Implementation, Biarritz, France, AMMA, 19 pp. [Available online at http://amma-international.org/meetings/thematicWorkshops/biarritz/docs/Biarritz2005_Dryrun.pdf.].

  • Majewski, D., 1998: The new global icosahedral–hexagonal grid point model GME of the Deutscher Wetterdienst. Proc. Seminar Developments in Numerical Methods for Atmospheric Modelling, Reading, United Kingdom, ECMWF, 173–201.

  • Majewski, D., and Coauthors, 2002: The operational global icosahedral–hexagonal gridpoint model GME: Description and high-resolution tests. Mon. Wea. Rev., 130 , 319338.

    • Search Google Scholar
    • Export Citation
  • Martin, J. E., , and J. A. Otkin, 2004: The rapid growth and decay of an extratropical cyclone over the central Pacific Ocean. Wea. Forecasting, 19 , 358376.

    • Search Google Scholar
    • Export Citation
  • Massacand, A. C., , H. Wernli, , and H. C. Davies, 2001: Influence of upstream diabatic heating upon an Alpine event of heavy precipitation. Mon. Wea. Rev., 129 , 28222828.

    • Search Google Scholar
    • Export Citation
  • McGregor, G. R., , and S. Nieuwolt, 1998: Tropical Climatology: An Introduction to the Climates of the Low Latitudes. Wiley and Sons, 352 pp.

    • Search Google Scholar
    • Export Citation
  • Montmerle, T., , J. Lafore, , L. Berre, , and C. Fischer, 2006: Limited-area model error statistics over Western Africa: Comparisons with midlatitude results. Quart. J. Roy. Meteor. Soc., 132 , 213230.

    • Search Google Scholar
    • Export Citation
  • Nicholson, S. E., and Coauthors, 2003: Validation of TRMM and other rainfall estimates with a high-density gauge dataset for West Africa. Part II: Validation of TRMM rainfall products. J. Appl. Meteor., 42 , 13551368.

    • Search Google Scholar
    • Export Citation
  • Nieto, R., and Coauthors, 2005: Climatological features of cutoff low systems in the Northern Hemisphere. J. Climate, 18 , 30853103.

  • Nieto, R., and Coauthors, 2007: Interannual variability of cut-off low systems over the European sector: The role of blocking and the Northern Hemisphere circulation modes. Meteor. Atmos. Phys., 96 , 85101.

    • Search Google Scholar
    • Export Citation
  • Pomroy, H. R., , and A. J. Thorpe, 2000: The evolution and dynamical role of reduced upper-tropospheric potential vorticity in intensive observing period one of FASTEX. Mon. Wea. Rev., 128 , 18171834.

    • Search Google Scholar
    • Export Citation
  • Sanders, F., , and J. R. Gyakum, 1980: Synoptic–dynamic climatology of the “bomb”. Mon. Wea. Rev., 108 , 15891606.

  • Schwierz, C., , M. Croci-Maspoli, , and H. C. Davies, 2004: Perspicacious indicators of atmospheric blocking. Geophys. Res. Lett., 31 .L06125, doi:10.1029/2003GL019341.

    • Search Google Scholar
    • Export Citation
  • Seck, A., 1962: Le Heug ou pluies de saison sèche au Sénégal. (The Heug or dry season rainfalls in Senegal). Ann. Géograph., 385 , 225246.

    • Search Google Scholar
    • Export Citation
  • Sprenger, M., 2007: Numerical piecewise potential vorticity inversion: A user guide for real-case experiments. ETH Zurich, 87 pp. [Available from the Institute for Climate and Atmospheric Science, ETH Zurich, CH-8092 Zurich, Switzerland.].

  • Thorncroft, C. D., , B. J. Hoskins, , and M. E. McIntyre, 1993: Two paradigms of baroclinic–wave life–cycle behaviour. Quart. J. Roy. Meteor. Soc., 119 , 1755.

    • Search Google Scholar
    • Export Citation
  • Tiedtke, M., 1989: A comprehensive mass flux scheme for cumulus parameterization in large-scale models. Mon. Wea. Rev., 117 , 17791800.

    • Search Google Scholar
    • Export Citation
  • Waugh, D. W., , and L. M. Polvani, 2000: Climatology of intrusions into the tropical upper troposphere. Geophys. Res. Lett., 27 , 38573860.

    • Search Google Scholar
    • Export Citation
  • Wernli, H., , and M. Sprenger, 2007: Identification and ERA-15 climatology of potential vorticity streamers and cutoffs near the extratropical tropopause. J. Atmos. Sci., 64 , 15691586.

    • Search Google Scholar
    • Export Citation
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Dynamics and Predictability of a Heavy Dry-Season Precipitation Event over West Africa—Sensitivity Experiments with a Global Model

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  • 1 Institute for Atmospheric Physics, Johannes Gutenberg University, Mainz, Germany
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Abstract

In January 2002 the Cape Verde region in tropical West Africa was hit by an exceptionally heavy precipitation event. Rain rates of up to 116 mm (48 h)−1 caused harmful impacts on the local population. The rainfall was triggered by a series of two upper-level disturbances penetrating from the extratropics to the West African coast. This study investigates the dynamics and predictability of this event on the basis of simulations with the global model Global Model Europe (GME) of the German Weather Service [i.e., Deutscher Wetterdienst (DWD)] initialized by the European Centre for Medium-Range Weather Forecasts (ECMWF) analysis data. Free forecasts satisfactorily reproduce the upper-level disturbances and the precipitation up to a lead time of 7 days. Several sensitivity experiments are conducted to unveil the reasons for this comparably high predictability and to identify dynamical precursors. The relevance of the upper-level wave structure in the extratropics is examined by modifications of the initial conditions using a quasigeostrophic potential vorticity (PV) inversion technique. While a reservoir of high PV over the North Atlantic and a PV ridge over Europe are found to be crucial for the upper-level wave amplification and the rainfall over West Africa, latent heating over the North Atlantic affects the event rather little in contrast to previous case studies. Surface properties like orography and sea surface temperature anomalies modify the precipitation quantity, but appear not to be essential for the occurrence of the extreme event on the simulated time scale.

Corresponding author address: Florian Meier, Institute for Atmospheric Physics, Johannes Gutenberg University, Becherweg 21, D-55099 Mainz, Germany. Email: meierf@uni-mainz.de

Abstract

In January 2002 the Cape Verde region in tropical West Africa was hit by an exceptionally heavy precipitation event. Rain rates of up to 116 mm (48 h)−1 caused harmful impacts on the local population. The rainfall was triggered by a series of two upper-level disturbances penetrating from the extratropics to the West African coast. This study investigates the dynamics and predictability of this event on the basis of simulations with the global model Global Model Europe (GME) of the German Weather Service [i.e., Deutscher Wetterdienst (DWD)] initialized by the European Centre for Medium-Range Weather Forecasts (ECMWF) analysis data. Free forecasts satisfactorily reproduce the upper-level disturbances and the precipitation up to a lead time of 7 days. Several sensitivity experiments are conducted to unveil the reasons for this comparably high predictability and to identify dynamical precursors. The relevance of the upper-level wave structure in the extratropics is examined by modifications of the initial conditions using a quasigeostrophic potential vorticity (PV) inversion technique. While a reservoir of high PV over the North Atlantic and a PV ridge over Europe are found to be crucial for the upper-level wave amplification and the rainfall over West Africa, latent heating over the North Atlantic affects the event rather little in contrast to previous case studies. Surface properties like orography and sea surface temperature anomalies modify the precipitation quantity, but appear not to be essential for the occurrence of the extreme event on the simulated time scale.

Corresponding author address: Florian Meier, Institute for Atmospheric Physics, Johannes Gutenberg University, Becherweg 21, D-55099 Mainz, Germany. Email: meierf@uni-mainz.de

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