• Alaka, G. J., and E. D. Maloney, 2012: The influence of the MJO on upstream precursors to African easterly waves. J. Climate, 25, 32193236.

    • Search Google Scholar
    • Export Citation
  • Arkin, P. A., and P. E. Ardanuy, 1989: Estimating climatic-scale precipitation from space: A review. J. Climate, 2, 12291238.

  • Duchon, C. E., 1979: Lanczos filtering in one and two dimensions. J. Appl. Meteor., 18, 10161022.

  • Foltz, G. R., and M. J. McPhaden, 2004: The 30-70 day oscillations in the tropical Atlantic. Geophys. Res. Lett., 31, L15205, doi:10.1029/2004GL020023.

    • Search Google Scholar
    • Export Citation
  • Grodsky, S. A., and J. A. Carton, 2001: Coupled land/atmosphere interactions in the West African monsoon. Geophys. Res. Lett., 28, 15031506.

    • Search Google Scholar
    • Export Citation
  • Gu, G., 2009: Intraseasonal variability in the equatorial Atlantic–West Africa during March–June. Climate Dyn., 32, 457471.

  • Gu, G., and R. F. Adler, 2004: Seasonal evolution and variability associated with the West African monsoon system. J. Climate, 17, 33643377.

    • Search Google Scholar
    • Export Citation
  • Han, W., P. J. Webster, J.-L. Lin, W. T. Liu, R. Fu, D. Yuan, and A. Hu, 2008: Dynamics of intraseasonal sea level and thermocline variability in the equatorial Atlantic during 2002–2003. J. Phys. Oceanogr., 38, 945967.

    • Search Google Scholar
    • Export Citation
  • Hendon, H. H., and M. L. Salby, 1994: The life cycle of Madden–Julian oscillation. J. Atmos. Sci., 51, 22252237.

  • Hoskins, B. J., and G.-Y. Yang, 2000: The equatorial response to higher-latitude forcing. J. Atmos. Sci., 57, 11971213.

  • Janicot, S., and B. Sultan, 2001: Intra-seasonal modulation of convection in the West African monsoon. Geophys. Res. Lett., 28, 523526.

    • Search Google Scholar
    • Export Citation
  • Janicot, S., F. Mounier, N. M. J. Hall, S. Leroux, B. Sultan, and G. N. Kiladis, 2009: Dynamics of the West African monsoon: Part IV: Analysis of 25–90-day variability of convection and the role of the Indian monsoon. J. Climate, 22, 15411565.

    • Search Google Scholar
    • Export Citation
  • Janicot, S., and Coauthors, 2011: Intraseasonal variability of the West African monsoon. Atmos. Sci. Lett., 12, 5866.

  • Jones, C., M. V. Carvalho, R. W. Higgins, D. E. Waliser, and J. K. E. Schemm, 2004: Climatology of tropical intraseasonal convective anomalies: 1979–2002. J. Climate, 17, 523539.

    • Search Google Scholar
    • Export Citation
  • Kiladis, G., and M. Wheeler, 1995: Horizontal and vertical structure of observed tropospheric equatorial Rossby waves. J. Geophys. Res., 100 (D11), 22 98122 997.

    • Search Google Scholar
    • Export Citation
  • Liebmann, B., and C. A. Smith, 1996: Description of a complete (interpolated), outgoing longwave radiation dataset. Bull. Amer. Meteor. Soc., 77, 12751277.

    • Search Google Scholar
    • Export Citation
  • Liebmann, B., C. A. Smith, L. M. V. Carvalho, C. Jones, C. S. Vera, I. Bladé, and D. Allured, 2009: Origin of convectively coupled Kelvin waves over South America. J. Climate, 22, 300315.

    • Search Google Scholar
    • Export Citation
  • Madden, R. A., and P. R. Julian, 1971: Detection of a 40–50 day oscillation in the zonal wind in the tropical Pacific. J. Atmos. Sci., 28, 702708.

    • Search Google Scholar
    • Export Citation
  • Madden, R. A., and P. R. Julian, 1972: Description of global-scale circulation cells in the tropics with a 40–50 day period. J. Atmos. Sci., 29, 11091123.

    • Search Google Scholar
    • Export Citation
  • Madden, R. A., and P. R. Julian, 1994: Observations of the 40–50-day tropical oscillation—A review. Mon. Wea. Rev., 122, 814837.

  • Maloney, E. D., and J. Shaman, 2008: Intraseasonal variability of the West African monsoon and Atlantic ITCZ. J. Climate, 21, 28982918.

    • Search Google Scholar
    • Export Citation
  • Maloney, E. D., D. B. Chelton, and S. K. Esbensen, 2008: Subseasonal SST variability in the tropical eastern North Pacific during boreal summer. J. Climate, 21, 41494167.

    • Search Google Scholar
    • Export Citation
  • Maloney, E. D., A. H. Sobel, and W. M. Hannah, 2010: Intraseasonal variability in an aquaplanet general circulation model. J. Adv. Model. Earth Syst., 2 (5), doi:10.3894/JAMES.2010.2.5.

    • Search Google Scholar
    • Export Citation
  • Matthews, A. J., 2000: Propagation mechanisms for the Madden–Julian oscillation. Quart. J. Roy. Meteor. Soc., 126, 26372651.

  • Matthews, A. J., 2004: Intraseasonal variability over tropical Africa during northern summer. J. Climate, 17, 24272440.

  • Milliff, R. F., and R. A. Madden, 1996: The existence and vertical structure of fast, eastward-moving disturbances in the equatorial troposphere. J. Atmos. Sci., 53, 586597.

    • Search Google Scholar
    • Export Citation
  • Molinari, J., K. Lombardo, and D. Vollaro, 2007: Tropical cyclogenesis within an equatorial Rossby wave packet. J. Atmos. Sci., 64, 13011317.

    • Search Google Scholar
    • Export Citation
  • Mounier, F., S. Janicot, and G. N. Kiladis, 2008: The West African monsoon dynamics. Part III: The quasi-biweekly zonal dipole. J. Climate, 21, 19111928.

    • Search Google Scholar
    • Export Citation
  • Nicholson, S. E., and J. P. Grist, 2003: The seasonal evolution of the atmospheric circulation over West Africa and equatorial Africa. J. Climate, 16, 10131030.

    • Search Google Scholar
    • Export Citation
  • Pan, L.-L. and T. Li, 2008: Interactions between the tropical ISO and midlatitude low-frequency flow. Climate Dyn., 31, 375388.

  • Park, C.-K., and S. D. Schubert, 1993: Remotely forced intraseasonal oscillations over the tropical Atlantic. J. Atmos. Sci., 50, 89103.

    • Search Google Scholar
    • Export Citation
  • Redelsperger, J.-L., A. Diongue, A. Diedhiou, J. P. Ceron, M. Diop, J. F. Gueremy, and J. P. Lafore, 2002: Multi-scale description of a Sahelian synoptic weather system representative of the West African monsoon. Quart. J. Roy. Meteor. Soc., 128, 12291257.

    • Search Google Scholar
    • Export Citation
  • Redelsperger, J.-L., C. D. Thorncroft, A. Diedhiou, T. Lebel, D. J. Parker, and J. Polcher, 2006: African Monsoon Multidisciplinary Analysis: An international research project and field campaign. Bull. Amer. Meteor. Soc., 87, 17391746.

    • Search Google Scholar
    • Export Citation
  • Shapiro, L. J., and S. B. Goldenberg, 1993: Intraseasonal oscillations over the Atlantic. J. Climate, 6, 677699.

  • Simmons, A., S. Uppala, D. Dee, and S. Kobayashi, 2007: ERA-Interim: New ECMWF reanalysis products from 1989 onwards. ECMWF Newsletter, No. 110, ECMWF, Reading, United Kingdom, 25–35.

  • Sultan, B., and S. Janicot, 2003a: The West African monsoon dynamics. Part I: Documentation of intraseasonal variability. J. Climate, 16, 33893406.

    • Search Google Scholar
    • Export Citation
  • Sultan, B., and S. Janicot, 2003b: The West African monsoon dynamics. Part II: The “preonset” and “onset” of the summer monsoon. J. Climate, 16, 34073427.

    • Search Google Scholar
    • Export Citation
  • Taylor, C. M., 2008: Intraseasonal land–atmosphere coupling in the West African monsoon. J. Climate, 21, 66366648.

  • Taylor, C. M., and Coauthors, 2011: New perspectives on land–atmosphere feedbacks from the African Monsoon Multidisciplinary Analysis. Atmos. Sci. Lett., 12, 3844, doi:10.1002/asl.336.

    • Search Google Scholar
    • Export Citation
  • Thorncroft, C. D., and Coauthors, 2003: The JET2000 project: Aircraft observations of the African easterly jet and African easterly waves. Bull. Amer. Meteor. Soc., 84, 337351.

    • Search Google Scholar
    • Export Citation
  • Ventrice, M. J., C. D. Thorncroft, and P. E. Roundy, 2011: The Madden–Julian oscillation’s influence on African easterly waves and downstream tropical cyclogenesis. Mon. Wea. Rev., 139, 27042722.

    • Search Google Scholar
    • Export Citation
  • Waliser, D., and Coauthors, 2009: MJO simulation diagnostics. J. Climate, 22, 30063030.

  • Wheeler, M. C., and G. N. Kiladis, 1999: Convectively coupled equatorial waves: Analysis of clouds and temperature in the wavenumber–frequency domain. J. Atmos. Sci., 56, 374399.

    • Search Google Scholar
    • Export Citation
  • Wheeler, M. C., and H. H. Hendon, 2004: An all-season real-time multivariate MJO index: Development of an index for monitoring and prediction. Mon. Wea. Rev., 132, 19171932.

    • Search Google Scholar
    • Export Citation
  • Xie, P., and P. A. Arkin, 1996: Analyses of global monthly precipitation using gauge observations, satellite estimates, and numerical model predictions. J. Climate, 9, 840858.

    • Search Google Scholar
    • Export Citation
  • Yu, W., W. Han, E. D. Maloney, D. Gochis, and S. Xie, 2011: Observations of eastward propagation of atmospheric intraseasonal oscillations from the Pacific to the Atlantic. J. Geophys. Res., 116, D02101, doi:10.1029/2010JD014336.

    • Search Google Scholar
    • Export Citation
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Influence of the Madden–Julian Oscillation and Intraseasonal Waves on Surface Wind and Convection of the Tropical Atlantic Ocean

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  • 1 Research Applications Laboratory, National Center for Atmospheric Research, Boulder, Colorado
  • | 2 Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, Colorado
  • | 3 Research Applications Laboratory, National Center for Atmospheric Research, Boulder, Colorado
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Abstract

Atmospheric intraseasonal variability in the tropical Atlantic is analyzed using satellite winds, outgoing longwave radiation (OLR), and reanalysis products during 2000–08. The analyses focus on assessing the effects of dominant intraseasonal atmospheric convective processes, the Madden–Julian oscillation (MJO), and Rossby waves on surface wind and convection of the tropical Atlantic Ocean and African monsoon area. The results show that contribution from each process varies in different regions. In general, the MJO events dominate the westward-propagating Rossby waves in affecting strong convection in the African monsoon region. The Rossby waves, however, have larger contributions to convection in the western Atlantic Ocean. Both the westward- and eastward-propagating signals contribute approximately equally in the central Atlantic basin. The effects of intraseasonal signals have evident seasonality. Both convection amplitude and the number of strong convective events associated with the MJO are larger during November–April than during May–October in all regions. Convection associated with Rossby wave events is stronger during November–April for all regions, and the numbers of Rossby wave events are higher during November–April than during May–October in the African monsoon region, and are comparable for the two seasons in the western and central Atlantic basins. Of particular interest is that the MJOs originating from the Indo-Pacific Ocean can be enhanced over the tropical Atlantic Ocean while they propagate eastward, amplifying their impacts on the African monsoon. On the other hand, Rossby waves can originate either in the eastern equatorial Atlantic or West African monsoon region, and some can strengthen while they propagate westward, affecting surface winds and convection in the western Atlantic and Central American regions.

Corresponding author address: Wei Yu, Research Applications Laboratory, National Center for Atmospheric Research, Boulder, CO 80301. E-mail: weiyu@ucar.edu

Abstract

Atmospheric intraseasonal variability in the tropical Atlantic is analyzed using satellite winds, outgoing longwave radiation (OLR), and reanalysis products during 2000–08. The analyses focus on assessing the effects of dominant intraseasonal atmospheric convective processes, the Madden–Julian oscillation (MJO), and Rossby waves on surface wind and convection of the tropical Atlantic Ocean and African monsoon area. The results show that contribution from each process varies in different regions. In general, the MJO events dominate the westward-propagating Rossby waves in affecting strong convection in the African monsoon region. The Rossby waves, however, have larger contributions to convection in the western Atlantic Ocean. Both the westward- and eastward-propagating signals contribute approximately equally in the central Atlantic basin. The effects of intraseasonal signals have evident seasonality. Both convection amplitude and the number of strong convective events associated with the MJO are larger during November–April than during May–October in all regions. Convection associated with Rossby wave events is stronger during November–April for all regions, and the numbers of Rossby wave events are higher during November–April than during May–October in the African monsoon region, and are comparable for the two seasons in the western and central Atlantic basins. Of particular interest is that the MJOs originating from the Indo-Pacific Ocean can be enhanced over the tropical Atlantic Ocean while they propagate eastward, amplifying their impacts on the African monsoon. On the other hand, Rossby waves can originate either in the eastern equatorial Atlantic or West African monsoon region, and some can strengthen while they propagate westward, affecting surface winds and convection in the western Atlantic and Central American regions.

Corresponding author address: Wei Yu, Research Applications Laboratory, National Center for Atmospheric Research, Boulder, CO 80301. E-mail: weiyu@ucar.edu
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