A Climatology of Waves in the Equatorial Region

Paul E. Roundy Department of Meteorology, The Pennsylvania State University, University Park, Pennsylvania

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William M. Frank Department of Meteorology, The Pennsylvania State University, University Park, Pennsylvania

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Abstract

Propagating anomalies of moisture and moist deep convection in the Tropics are organized into a variety of large-scale modes. These include (but are not limited to) the so-called intraseasonal oscillations, convectively coupled waves similar to those predicted by shallow water theory on the equatorial beta plane, and tropical-depression-type disturbances. Along with the annual and diurnal cycles, these modes act and interact to control much of the variance of tropical convection. Analyses of 10 yr of outgoing longwave radiation (OLR) and precipitable water (PW) data are carried out to develop comparative climatologies of these wavelike modes. The analysis relaxes the commonly used cross-equatorial symmetry constraints, which allows study of the portions of the wavelike processes that are asymmetric across the equator.

Mean background states are found for OLR and for PW as functions of day of the year. Examination of anomalies together with the background reveals much about how the waves are affected by their environments. Zonal wavenumber–frequency spectral analyses are performed on these anomalies. Following the spectral analyses, the OLR and the PW data are then filtered for specific regions of the wavenumber–frequency domain. Results show how variance generated by propagating modes is distributed in time and space, approximately illustrating the relative contributions of the wave modes to regional OLR and PW variability.

Corresponding author address: Paul Roundy, CIRES, University of Colorado, NOAA/Aeronomy Laboratory, 325 Broadway, Boulder, CO 80305-3328. Email: proundy@al.noaa.gov

Abstract

Propagating anomalies of moisture and moist deep convection in the Tropics are organized into a variety of large-scale modes. These include (but are not limited to) the so-called intraseasonal oscillations, convectively coupled waves similar to those predicted by shallow water theory on the equatorial beta plane, and tropical-depression-type disturbances. Along with the annual and diurnal cycles, these modes act and interact to control much of the variance of tropical convection. Analyses of 10 yr of outgoing longwave radiation (OLR) and precipitable water (PW) data are carried out to develop comparative climatologies of these wavelike modes. The analysis relaxes the commonly used cross-equatorial symmetry constraints, which allows study of the portions of the wavelike processes that are asymmetric across the equator.

Mean background states are found for OLR and for PW as functions of day of the year. Examination of anomalies together with the background reveals much about how the waves are affected by their environments. Zonal wavenumber–frequency spectral analyses are performed on these anomalies. Following the spectral analyses, the OLR and the PW data are then filtered for specific regions of the wavenumber–frequency domain. Results show how variance generated by propagating modes is distributed in time and space, approximately illustrating the relative contributions of the wave modes to regional OLR and PW variability.

Corresponding author address: Paul Roundy, CIRES, University of Colorado, NOAA/Aeronomy Laboratory, 325 Broadway, Boulder, CO 80305-3328. Email: proundy@al.noaa.gov

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  • Carlson, T. N., 1969: Some remarks on African disturbances and their progress over the tropical Atlantic. Mon. Wea. Rev, 97 , 716726.

  • Chang, C-P., and T. M. Piwowar, 1974: Effect of a CISK parameterization on tropical wave growth. J. Atmos. Sci, 31 , 12561261.

  • Dickinson, M., and J. Molinari, 2002: Mixed Rossby–gravity waves and western Pacific tropical cyclogenesis. Part I: Synoptic evolution. J. Atmos. Sci, 59 , 21832196.

    • Search Google Scholar
    • Export Citation
  • Dunkerton, T. J., and F. X. Crum, 1995: Eastward propagating 2- to 15-day equatorial convection and its relation to the tropical intraseasonal oscillation. J. Geophys. Res, 100 , 2578125790.

    • Search Google Scholar
    • Export Citation
  • Gu, G., and C. Zhang, 2001: A spectrum analysis of synoptic-scale disturbances in the ITCZ. J. Climate, 14 , 27252739.

  • Hayashi, Y., 1982: Space–time spectral analysis and its application to atmospheric waves. J. Meteor. Soc. Japan, 60 , 156171.

  • Hendon, H. H., and B. Liebmann, 1991: The structure and annual variation of antisymmetric fluctuations of tropical convection and their association with Rossby–gravity waves. J. Atmos. Sci, 48 , 21272140.

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

  • Hess, P. G., D. S. Battisti, and P. J. Rasch, 1993: Maintenance of the intertropical convergence zones and the large-scale tropical circulation on a water-covered earth. J. Atmos. Sci, 50 , 691713.

    • Search Google Scholar
    • Export Citation
  • Kemball-Cook, S., and B. Wang, 2001: Equatorial waves and air–sea interaction in the boreal summer intraseasonal oscillation. J. Climate, 14 , 29232942.

    • Search Google Scholar
    • Export Citation
  • Kleeman, R., 1989: A modeling study of the effect of the Andes on the summertime circulation of tropical South America. J. Atmos. Sci, 46 , 33443362.

    • Search Google Scholar
    • Export Citation
  • Kuo, H. L., 1975: Instability theory of large-scale disturbances in the tropics. J. Atmos. Sci, 32 , 22292245.

  • Liebmann, B., and H. H. Hendon, 1990: Synoptic-scale disturbances near the equator. J. Atmos. Sci, 47 , 14631479.

  • 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
  • Lindzen, R. S., 1967: Planetary waves on beta planes. Mon. Wea. Rev, 95 , 441451.

  • Lindzen, R. S., 1974: Wave-CISK in the Tropics. J. Atmos. Sci, 31 , 156179.

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

  • Matsuno, T., 1966: Quasi-geostrophic motions in the equatorial area. J. Meteor. Soc. Japan, 44 , 2543.

  • Pires, P., J-L. Redelsperger, and J-P. Lafore, 1997: Equatorial atmospheric waves and their association to convection. Mon. Wea. Rev, 125 , 11671184.

    • Search Google Scholar
    • Export Citation
  • Randel, D. L., T. H. Vonder Haar, M. A. Ringerud, G. L. Stephens, T. J. Greenwald, and C. L. Combs, 1996: A new global water vapor dataset. Bull. Amer. Meteor. Soc, 77 , 12331246.

    • Search Google Scholar
    • Export Citation
  • Roundy, P. E., and W. M. Frank, 2004a: Effects of low-frequency wave interactions on intraseasonal oscillations. J. Atmos. Sci., in press.

    • Search Google Scholar
    • Export Citation
  • Roundy, P. E., and W. M. Frank, 2004b: Applications of a multiple linear regression model to the analysis of relationships between eastward- and westward-moving intraseasonal modes. J. Atmos. Sci., in press.

    • Search Google Scholar
    • Export Citation
  • Straub, K. H., and G. N. Kiladis, 2002: Observations of a convectively coupled Kelvin wave in the eastern Pacific ITCZ. J. Atmos. Sci, 59 , 3053.

    • Search Google Scholar
    • Export Citation
  • Straub, K. H., and G. N. Kiladis, 2003a: Extratropical forcing of convectively coupled Kelvin waves during austral winter. J. Atmos. Sci, 60 , 526543.

    • Search Google Scholar
    • Export Citation
  • Straub, K. H., and G. N. Kiladis, 2003b: Interactions between the boreal summer intraseasonal oscillation and higher-frequency tropical wave activity. Mon. Wea. Rev, 131 , 945960.

    • Search Google Scholar
    • Export Citation
  • Straub, K. H., and G. N. Kiladis, 2003c: The observed structure of convectively coupled Kelvin waves: Comparison with simple models of coupled wave instability. J. Atmos. Sci, 60 , 16551668.

    • Search Google Scholar
    • Export Citation
  • Takayabu, Y. N., 1994: Large-scale cloud disturbances associated with equatorial waves. Part I: Spectral features of the cloud disturbances. J. Meteor. Soc. Japan, 72 , 433448.

    • Search Google Scholar
    • Export Citation
  • Takayabu, Y. N., and T. Nitta, 1993: 3–5 day disturbances coupled with convection over the tropical Pacific Ocean. J. Meteor. Soc. Japan, 71 , 221245.

    • Search Google Scholar
    • Export Citation
  • Wheeler, M., 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., G. N. Kiladis, and P. J. Webster, 2000: Large-scale dynamical fields associated with convectively coupled equatorial waves. J. Atmos. Sci, 57 , 613640.

    • Search Google Scholar
    • Export Citation
  • Wilks, D. S., 1995: Statistical Methods in the Atmospheric Sciences: An Introduction. International Geophysics Series, Vol. 59, Academic Press, 467 pp.

    • Search Google Scholar
    • Export Citation
  • Yanai, M., and M. Murakami, 1970: Spectrum analysis of symmetric and antisymmetric equatorial waves. J. Meteor. Soc. Japan, 48 , 186197.

    • Search Google Scholar
    • Export Citation
  • Zhang, C., and P. J. Webster, 1989: Effects of zonal flows on equatorially trapped waves. J. Atmos. Sci, 46 , 36323652.

  • Zhang, M., and M. A. Geller, 1994: Selective excitation of tropical atmospheric waves in wave-CISK: The effect of vertical wind shear. J. Atmos. Sci, 51 , 353368.

    • Search Google Scholar
    • Export Citation
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