• Betts, A. K., , and M. J. Miller, 1986: A new convective adjustment scheme. Part II: Single column tests using GATE wave, BOMEX, ATEX, and arctic air-mass data sets. Quart. J. Roy. Meteor. Soc., 112 , 693709.

    • Search Google Scholar
    • Export Citation
  • Betts, A. K., , and M. J. Miller, 1993: The Betts–Miller scheme. The Representation of Cumulus Convection in Numerical Models of the Atmosphere, Meteor. Monogr., No. 46, Amer. Meteor. Soc., 107–121.

    • Search Google Scholar
    • Export Citation
  • Chao, W. C., 2000: Multiple quasi equilibria of the ITCZ and the origin of monsoon onset. J. Atmos. Sci., 57 , 641652.

  • Chao, W. C., , and B. Chen, 2004: Single and double ITCZ in an aqua-planet model with constant sea surface temperature and solar angle. Climate Dyn., 22 , 447459.

    • Search Google Scholar
    • Export Citation
  • Chou, C., , and J. D. Neelin, 1996: Linearization of a longwave radiation scheme for intermediate tropical atmospheric models. J. Geophys. Res., 101 , 1512915145.

    • Search Google Scholar
    • Export Citation
  • Chou, C., , and J. D. Neelin, 1999: Cirrus detrainment–temperature feedback. Geophys. Res. Lett., 26 , 12951298.

  • Chou, C., , and J. D. Neelin, 2004: Mechanisms of global warming impacts on regional tropical precipitation. J. Climate, 17 , 26882701.

  • Chou, C., , J. D. Neelin, , and H. Su, 2001: Ocean–atmosphere–land feedbacks in an idealized monsoon. Quart. J. Roy. Meteor. Soc., 127 , 18691892.

    • Search Google Scholar
    • Export Citation
  • Gill, A. E., 1980: Some simple solutions for heat-induced tropical circulation. Quart. J. Roy. Meteor. Soc., 106 , 447462.

  • Hack, J. J., , W. H. Schubert, , D. E. Stevens, , and H-C. Kuo, 1989: Response of the Hadley circulation to convective forcing in the ITCZ. J. Atmos. Sci., 46 , 29572973.

    • Search Google Scholar
    • Export Citation
  • 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
  • Joly, A., , and A. J. Thorpe, 1990: Frontal instability generated by tropospheric potential vorticity anomalies. Quart. J. Roy. Meteor. Soc., 116 , 525560.

    • Search Google Scholar
    • Export Citation
  • Kirtman, B. P., , and E. K. Schneider, 2000: A spontaneously generated tropical atmospheric general circulation. J. Atmos. Sci., 57 , 20802093.

    • Search Google Scholar
    • Export Citation
  • Kuo, H. L., 1973: Dynamics of quasi-geostrophic flows and instability theory. Adv. Appl. Mech., 13 , 247330.

  • Lin, X., , and R. H. Johnson, 1996: Kinematic and thermodynamic characteristics of the flow over the western Pacific warm pool during TOGA COARE. J. Atmos. Sci., 53 , 695715.

    • Search Google Scholar
    • Export Citation
  • Magnusdottir, G., , and C-C. Wang, 2008: Intertropical convergence zones during the active season in daily data. J. Atmos. Sci., 65 , 24252436.

    • Search Google Scholar
    • Export Citation
  • Mechoso, C., and Coauthors, 1995: The seasonal cycle over the tropical Pacific in coupled ocean–atmosphere general circulation models. Mon. Wea. Rev., 123 , 28252838.

    • Search Google Scholar
    • Export Citation
  • Neelin, J. D., , and J-Y. Yu, 1994: Modes of tropical variability under convective adjustment and the Madden–Julian oscillation. Part I: Analytical results. J. Atmos. Sci., 51 , 18761894.

    • Search Google Scholar
    • Export Citation
  • Neelin, J. D., , and N. Zeng, 2000: A quasi-equilibrium tropical circulation model—Formulation. J. Atmos. Sci., 57 , 17411766.

  • Nieto Ferreira, R., , and W. H. Schubert, 1997: Barotropic aspects of ITCZ breakdown. J. Atmos. Sci., 54 , 261285.

  • Raymond, D. J., , G. B. Raga, , C. S. Bretherton, , J. Molinari, , C. López-Carrillo, , and Z. Fuchs, 2003: Convective forcing in the intertropical convergence zone of the eastern Pacific. J. Atmos. Sci., 60 , 20642082.

    • Search Google Scholar
    • Export Citation
  • Schubert, W. H., , P. E. Ciesielski, , D. E. Stevens, , and H-C. Kuo, 1991: Potential vorticity modeling of the ITCZ and the Hadley circulation. J. Atmos. Sci., 48 , 14931509.

    • Search Google Scholar
    • Export Citation
  • Sumi, A., 1990: Pattern formation of convective activity over the aqua-planet with globally uniform sea surface temperature. Meteorological Research Rep. 90-1, Division of Meteorology, Geophysical Institute, University of Tokyo, 124 pp.

    • Search Google Scholar
    • Export Citation
  • Wang, C-C., , and G. Magnusdottir, 2005: ITCZ breakdown in three-dimensional flows. J. Atmos. Sci., 62 , 14971512.

  • Wang, C-C., , and G. Magnusdottir, 2006: The ITCZ in the central and eastern Pacific on synoptic time scales. Mon. Wea. Rev., 134 , 14051421.

    • Search Google Scholar
    • Export Citation
  • Webster, P. J., , V. O. Magaña, , T. N. Palmer, , J. Shukla, , R. A. Tomas, , M. Yanai, , and T. Yasunari, 1998: Monsoons: Processes, predictability, and the prospects for prediction. J. Geophys. Res., 103 , 1445114510.

    • Search Google Scholar
    • Export Citation
  • Yu, J-Y., , and J. D. Neelin, 1994: Modes of tropical variability under convective adjustment and the Madden–Julian oscillation. Part II: Numerical results. J. Atmos. Sci., 51 , 18951914.

    • Search Google Scholar
    • Export Citation
  • Yu, J-Y., , and J. D. Neelin, 1997: Analytic approximations for moist convectively adjusted regions. J. Atmos. Sci., 54 , 10541063.

  • Yu, J-Y., , C. Chou, , and J. D. Neelin, 1998: Estimating the gross moist stability of the tropical atmosphere. J. Atmos. Sci., 55 , 13541372.

    • Search Google Scholar
    • Export Citation
  • Zehnder, J. A., , and D. M. Powell, 1999: The interaction of easterly waves, orography, and the intertropical convergence zone in the genesis of eastern Pacific tropical cyclones. Mon. Wea. Rev., 127 , 15661585.

    • Search Google Scholar
    • Export Citation
  • Zeng, N., , J. D. Neelin, , and C. Chou, 2000: A quasi-equilibrium tropical circulation model–implementation and simulation. J. Atmos. Sci., 57 , 17671796.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 25 25 1
PDF Downloads 12 12 1

Breakdown and Reformation of the Intertropical Convergence Zone in a Moist Atmosphere

View More View Less
  • 1 Research Center for Environmental Changes, Academia Sinica, and Department of Atmospheric Sciences, Chinese Culture University, Taipei, Taiwan
  • 2 Research Center for Environmental Changes, Academia Sinica, and Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan
  • 3 Research Center for Environmental Changes, Academia Sinica, Taipei, Taiwan
© Get Permissions
Restricted access

Abstract

The effects of moisture on the intertropical convergence zone (ITCZ) over the eastern Pacific on the synoptic time scale are investigated using an intermediate complexity atmospheric circulation model, the quasi-equilibrium tropical circulation model (QTCM1), on an aquaplanet.

The dry simulation shows results consistent with those of simple dynamic models, except that a slightly stronger heating rate is needed owing to different model designs. In the moist simulations, the most important result is the formation of a tail southwest of a vortex during and after the ITCZ breakdown. This tail may extend zonally more than 60° longitude and last for more than two weeks in an idealized simulation. In the eastern North Pacific, this phenomenon is often observed in cases that involve easterly waves. In a sense, the formation of the tail suggests a possible mechanism that forms an ITCZ efficiently.

This study shows that the surface convergent flow induced by a disturbance initializes a positive wind–evaporation feedback that forms the tail. In the tail, the most important energy source is surface evaporation, and the latent heat is nicely balanced by an adiabatic cooling of the ascending motion. In other words, the energy is redistributed vertically by vertical energy convergence.

The lifespan of the tail is controlled by the propagation of tropical waves that modify the surface wind pattern, leading to a decrease in surface wind speed and corresponding surface fluxes. It may explain the absence of the tail in some of the events in the real atmosphere.

Corresponding author address: Chia-chi Wang, Department of Atmospheric Sciences, Chinese Culture University, 55 Hwa-Kang Road, Taipei, 111, Taiwan. Email: wang1794@rcec.sinica.edu.tw

Abstract

The effects of moisture on the intertropical convergence zone (ITCZ) over the eastern Pacific on the synoptic time scale are investigated using an intermediate complexity atmospheric circulation model, the quasi-equilibrium tropical circulation model (QTCM1), on an aquaplanet.

The dry simulation shows results consistent with those of simple dynamic models, except that a slightly stronger heating rate is needed owing to different model designs. In the moist simulations, the most important result is the formation of a tail southwest of a vortex during and after the ITCZ breakdown. This tail may extend zonally more than 60° longitude and last for more than two weeks in an idealized simulation. In the eastern North Pacific, this phenomenon is often observed in cases that involve easterly waves. In a sense, the formation of the tail suggests a possible mechanism that forms an ITCZ efficiently.

This study shows that the surface convergent flow induced by a disturbance initializes a positive wind–evaporation feedback that forms the tail. In the tail, the most important energy source is surface evaporation, and the latent heat is nicely balanced by an adiabatic cooling of the ascending motion. In other words, the energy is redistributed vertically by vertical energy convergence.

The lifespan of the tail is controlled by the propagation of tropical waves that modify the surface wind pattern, leading to a decrease in surface wind speed and corresponding surface fluxes. It may explain the absence of the tail in some of the events in the real atmosphere.

Corresponding author address: Chia-chi Wang, Department of Atmospheric Sciences, Chinese Culture University, 55 Hwa-Kang Road, Taipei, 111, Taiwan. Email: wang1794@rcec.sinica.edu.tw

Save