• Ajayamohan, R. S., , B. Khouider, , and A. J. Majda, 2013: Realistic initiation and dynamics of the Madden–Julian oscillation in a coarse resolution aquaplanet GCM. Geophys. Res. Lett., 40, 62526257, doi:10.1002/2013GL058187.

    • Search Google Scholar
    • Export Citation
  • Ajayamohan, R. S., , B. Khouider, , and A. J. Majda, 2014: Simulation of monsoon intraseasonal oscillations in a coarse-resolution aquaplanet GCM. Geophys. Res. Lett., 41, 56625669, doi:10.1002/2014GL060662.

    • Search Google Scholar
    • Export Citation
  • Bellenger, H., , K. Yoneyama, , M. Katsumata, , T. Nishizawa, , K. Yasunaga, , and R. Shirooka, 2015: Observation of moisture tendencies related to shallow convection. J. Atmos. Sci., 72, 641659, doi:10.1175/JAS-D-14-0042.1.

    • Search Google Scholar
    • Export Citation
  • Cheng, M.-D., , and A. Arakawa, 1997: Inclusion of rainwater budget and convective downdrafts in the Arakawa–Schubert cumulus parameterization. J. Atmos. Sci., 54, 13591378, doi:10.1175/1520-0469(1997)054<1359:IORBAC>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Choudhury, A. D., , and R. Krishnan, 2011: Dynamical response of the South Asian monsoon trough to latent heating from stratiform and convective precipitation. J. Atmos. Sci., 68, 13471363, doi:10.1175/2011JAS3705.1.

    • Search Google Scholar
    • Export Citation
  • De La Chevrotiere, M., , B. Khouider, , and A. Majda, 2014: Calibration of the stochastic multicloud model using Bayesian inference. SIAM J. Sci. Comput., 36, B538B560, doi:10.1137/13094267X.

    • Search Google Scholar
    • Export Citation
  • Deng, Q., , B. Khouider, , and A. Majda, 2015: The MJO in a coarse-resolution GCM with a stochastic multicloud parameterization. J. Atmos. Sci., 72, 5574, doi:10.1175/JAS-D-14-0120.1.

    • Search Google Scholar
    • Export Citation
  • Dennis, J., , A. Fournier, , W. F. Spotz, , A. St-Cyr, , M. A. Taylor, , S. J. Thomas, , and H. M. Tufo, 2005: High-resolution mesh convergence properties and parallel efficiency of a spectral element atmospheric dynamical core. Int. J. High Perform. Comput. Appl., 19, 225235, doi:10.1177/1094342005056108.

    • Search Google Scholar
    • Export Citation
  • Dudhia, J., , and M. W. Moncrieff, 1987: A numerical simulation of quasi-stationary tropical convective bands. Quart. J. Roy. Meteor. Soc., 113, 929967, doi:10.1002/qj.49711347711.

    • Search Google Scholar
    • Export Citation
  • Emanuel, K. A., 1987: An air–sea interaction model of intraseasonal oscillations in the tropics. J. Atmos. Sci., 44, 23242340, doi:10.1175/1520-0469(1987)044<2324:AASIMO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Emanuel, K. A., 1994: Atmospheric Convection. Oxford University Press, 580 pp.

  • Feng, Z., , S. Hagos, , A. K. Rowe, , C. D. Burleyson, , M. N. Martini, , and S. P. de Szoeke, 2015: Mechanisms of convective cloud organization by cold pools over tropical warm ocean during the AMIE/DYNAMO field campaign. J. Adv. Model. Earth Syst., 7, 357381, doi:10.1002/2014MS000384.

    • Search Google Scholar
    • Export Citation
  • Ferguson, J., , B. Khouider, , and M. Namazi, 2009: Two-way interactions between equatorially trapped waves and the barotropic flow. Chin. Ann. Math., 30B, 539568, doi:10.1007/s11401-009-0102-9.

    • Search Google Scholar
    • Export Citation
  • Frenkel, Y., , A. J. Majda, , and B. Khouider, 2012: Using the stochastic multicloud model to improve tropical convective parameterization: A paradigm example. J. Atmos. Sci., 69, 10801105, doi:10.1175/JAS-D-11-0148.1.

    • Search Google Scholar
    • Export Citation
  • Frenkel, Y., , A. J. Majda, , and B. Khouider, 2013: Stochastic and deterministic multicloud parameterizations for tropical convection. Climate Dyn., 41, 15271551, doi:10.1007/s00382-013-1678-z.

    • Search Google Scholar
    • Export Citation
  • Gillespie, D. T., 1975: An exact method for numerically simulating the stochastic coalescence process in a cloud. J. Atmos. Sci., 32, 19771989, doi:10.1175/1520-0469(1975)032<1977:AEMFNS>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Gillespie, D. T., 1977: Exact stochastic simulation of coupled chemical reactions. J. Phys. Chem., 81, 23402361, doi:10.1021/j100540a008.

    • Search Google Scholar
    • Export Citation
  • Grabowski, W. W., , and M. W. Moncrieff, 2004: Moisture–convection feedback in the tropics. Quart. J. Roy. Meteor. Soc., 130, 30813104, doi:10.1256/qj.03.135.

    • Search Google Scholar
    • Export Citation
  • Hagos, S., , Z. Feng, , K. Landu, , and C. N. Long, 2014: Advection, moistening, and shallow-to-deep convection transitions during the initiation and propagation of Madden–Julian oscillation. J. Adv. Model. Earth Syst., 6, 938949, doi:10.1002/2014MS000335.

    • Search Google Scholar
    • Export Citation
  • Han, Y., , and B. Khouider, 2010: Convectively coupled waves in a sheared environment. J. Atmos. Sci., 67, 29132942, doi:10.1175/2010JAS3335.1.

    • Search Google Scholar
    • Export Citation
  • Hohenegger, C., , and B. Stevens, 2013: Preconditioning deep convection with cumulus congestus. J. Atmos. Sci., 70, 448464, doi:10.1175/JAS-D-12-089.1.

    • Search Google Scholar
    • Export Citation
  • Holloway, C. E., , and J. D. Neelin, 2009: Moisture vertical structure, column water vapor, and tropical deep convection. J. Atmos. Sci., 66, 16651683, doi:10.1175/2008JAS2806.1.

    • Search Google Scholar
    • Export Citation
  • Holloway, C. E., , and J. D. Neelin, 2010: Temporal relations of column water vapor and tropical precipitation. J. Atmos. Sci., 67, 10911105, doi:10.1175/2009JAS3284.1.

    • Search Google Scholar
    • Export Citation
  • Houze, R. A., 1997: Stratiform precipitation in regions of convection: A meteorological paradox? Bull. Amer. Meteor. Soc., 78, 21792196, doi:10.1175/1520-0477(1997)078<2179:SPIROC>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Hung, M.-P., , J.-L. Lin, , W. Wang, , D. Kim, , T. Shinoda, , and S. J. Weaver, 2013: MJO and convectively coupled equatorial waves simulated by CMIP5 climate models. J. Climate, 26, 61856214, doi:10.1175/JCLI-D-12-00541.1.

    • Search Google Scholar
    • Export Citation
  • Jakob, C., , and C. Schumacher, 2008: Precipitation and latent heating characteristics of the major tropical western Pacific cloud regimes. J. Climate, 21, 43484364, doi:10.1175/2008JCLI2122.1.

    • Search Google Scholar
    • Export Citation
  • Johnson, R. H., , T. M. Rickenbach, , S. A. Rutledge, , P. E. Ciesielski, , and W. H. Schubert, 1999: Trimodal characteristics of tropical convection. J. Climate, 12, 23972418, doi:10.1175/1520-0442(1999)012<2397:TCOTC>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Khouider, B., 2014: A coarse-grained stochastic multi-type particle interacting model for tropical convection: Nearest neighbour interactions. Commun. Math. Sci., 12, 13791407, doi:10.4310/CMS.2014.v12.n8.a1.

    • Search Google Scholar
    • Export Citation
  • Khouider, B., , and A. J. Majda, 2006: Model multi-cloud parameterizations for convectively coupled waves: Detailed nonlinear wave evolution. Dyn. Atmos. Oceans, 42, 5980, doi:10.1016/j.dynatmoce.2005.12.001.

    • Search Google Scholar
    • Export Citation
  • Khouider, B., , and A. J. Majda, 2008: Multicloud models for organized tropical convection: Enhanced congestus heating. J. Atmos. Sci., 65, 895914, doi:10.1175/2007JAS2408.1.

    • Search Google Scholar
    • Export Citation
  • Khouider, B., , and M. Moncrieff, 2015: Organized convection parameterization for the ITCZ. J. Atmos. Sci., 72, 30733096, doi:10.1175/JAS-D-15-0006.1.

    • Search Google Scholar
    • Export Citation
  • Khouider, B., , J. Biello, , and A. J. Majda, 2010: A stochastic multicloud model for tropical convection. Commun. Math. Sci., 8, 187216, doi:10.4310/CMS.2010.v8.n1.a10.

    • Search Google Scholar
    • Export Citation
  • Khouider, B., , A. St-Cyr, , A. J. Majda, , and J. Tribbia, 2011: The MJO and convectively coupled waves in a coarse-resolution GCM with a simple multicloud parametrization. J. Atmos. Sci., 68, 240264, doi:10.1175/2010JAS3443.1.

    • Search Google Scholar
    • Export Citation
  • Kiladis, G. N., , K. Straub, , and P. Haertel, 2005: Zonal and vertical structure of the Madden–Julian oscillation. J. Atmos. Sci., 62, 27902809, doi:10.1175/JAS3520.1.

    • Search Google Scholar
    • Export Citation
  • Kiladis, G. N., , M. C. Wheeler, , P. T. Haertel, , K. H. Straub, , and P. E. Roundy, 2009: Convectively coupled equatorial waves. Rev. Geophys., 47, RG2003, doi:10.1029/2008RG000266.

    • Search Google Scholar
    • Export Citation
  • Kim, D., and et al. , 2009: Application of MJO simulation diagnostics to climate models. J. Climate, 22, 64136436, doi:10.1175/2009JCLI3063.1.

    • Search Google Scholar
    • Export Citation
  • Lappen, C.-L., , and C. Schumacher, 2014: The role of tilted heating in the evolution of the MJO. J. Geophys. Res. Atmos., 119, 29662989, doi:10.1002/2013JD020638.

    • Search Google Scholar
    • Export Citation
  • Lin, J.-L., , B. Mapes, , M. Zhang, , and M. Newman, 2004: Stratiform precipitation, vertical heating profiles, and the Madden–Julian oscillation. J. Atmos. Sci., 61, 296309, doi:10.1175/1520-0469(2004)061<0296:SPVHPA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Lin, J.-L., and et al. , 2006: Tropical intraseasonal variability in 14 IPCC AR4 climate models. Part I: Convective signals. J. Climate, 19, 26652690, doi:10.1175/JCLI3735.1.

    • Search Google Scholar
    • Export Citation
  • 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, doi:10.1175/1520-0469(1996)053<0695:KATCOT>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Majda, A. J., 2007: New multiscale models and self-similarity in tropical convection. J. Atmos. Sci., 64, 13931404, doi:10.1175/JAS3880.1.

    • Search Google Scholar
    • Export Citation
  • Majda, A. J., , and M. Shefter, 2001: Models for stratiform instability and convectively coupled waves. J. Atmos. Sci., 58, 15671584, doi:10.1175/1520-0469(2001)058<1567:MFSIAC>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Majda, A. J., , B. Khouider, , G. N. Kiladis, , K. H. Straub, , and M. G. Shefter, 2004: A model for convectively coupled tropical waves: Nonlinearity, rotation, and comparison with observations. J. Atmos. Sci., 61, 21882205, doi:10.1175/1520-0469(2004)061<2188:AMFCCT>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Mapes, B. E., 1993: Gregarious tropical convection. J. Atmos. Sci., 50, 20262037, doi:10.1175/1520-0469(1993)050<2026:GTC>2.0.CO;2.

  • Mapes, B. E., 2000: Convective inhibition, subgrid-scale triggering energy, and stratiform instability in a toy tropical wave model. J. Atmos. Sci., 57, 15151535, doi:10.1175/1520-0469(2000)057<1515:CISSTE>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Mapes, B. E., , S. Tulich, , J. Lin, , and P. Zuidema, 2006: The mesoscale convection life cycle: Building block or prototype for large-scale tropical waves? Dyn. Atmos. Oceans, 42, 329, doi:10.1016/j.dynatmoce.2006.03.003.

    • Search Google Scholar
    • Export Citation
  • Matthews, A. J., 2008: Primary and successive events in the Madden–Julian oscillation. Quart. J. Roy. Meteor. Soc., 134, 439453, doi:10.1002/qj.224.

    • Search Google Scholar
    • Export Citation
  • Matthews, A. J., , J. M. Slingo, , B. J. Hoskins, , and P. M. Inness, 1999: Fast and slow Kelvin waves in the Madden–Julian oscillation of a GCM. Quart. J. Roy. Meteor. Soc., 125, 14731498, doi:10.1002/qj.49712555702.

    • Search Google Scholar
    • Export Citation
  • Moncrieff, M. W., 1981: A theory of organized steady convection and its transport properties. Quart. J. Roy. Meteor. Soc., 107, 2950, doi:10.1002/qj.49710745103.

    • Search Google Scholar
    • Export Citation
  • Moncrieff, M. W., 2010: The multiscale organization of moist convection and the intersection of weather and climate. Climate Dynamics: Why Does Climate Vary?, Geophys. Monogr., Vol. 126, Amer. Geophys. Union, 3–26, doi:10.1029/2008GM000838.

  • Moncrieff, M. W., , and E. Klinker, 1997: Organized convective systems in the tropical western Pacific as a process in general circulation models: A TOGA COARE case-study. Quart. J. Roy. Meteor. Soc., 123, 805827, doi:10.1002/qj.49712354002.

    • Search Google Scholar
    • Export Citation
  • Nair, R. D., , H.-W. Choi, , and H. Tufo, 2009: Computational aspects of a scalable high-order discontinuous Galerkin atmospheric dynamical core. Comput. Fluids, 38, 309319, doi:10.1016/j.compfluid.2008.04.006.

    • Search Google Scholar
    • Export Citation
  • Nakazawa, T., 1988: Tropical superclusters within intraseasonal variations over the western Pacific. J. Meteor. Soc. Japan, 66, 777786.

    • Search Google Scholar
    • Export Citation
  • Neelin, J. D., , I. M. Held, , and K. H. Cook, 1987: Evaporation–wind feedback and low-frequency variability in the tropical atmosphere. J. Atmos. Sci., 44, 23412348, doi:10.1175/1520-0469(1987)044<2341:EWFALF>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Neelin, J. D., , O. Peters, , J. W.-B. Lin, , K. Hales, , and C. E. Holloway, 2008: Rethinking convective quasi-equilibrium: Observational constraints for stochastic convective schemes in climate models. Philos. Trans. Roy. Soc. London, A366, 25792602, doi:10.1098/rsta.2008.0056.

    • Search Google Scholar
    • Export Citation
  • Parker, M. D., , and R. H. Johnson, 2004: Structures and dynamics of quasi-2D mesoscale convective systems. J. Atmos. Sci., 61, 545567, doi:10.1175/1520-0469(2004)061<0545:SADOQM>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Peters, K., , C. Jakob, , L. Davies, , B. Khouider, , and A. Majda, 2013: Stochastic behavior of tropical convection in observations and a multicloud model. J. Atmos. Sci., 70, 35563575, doi:10.1175/JAS-D-13-031.1.

    • Search Google Scholar
    • Export Citation
  • Peters, O., , A. Deluca, , A. Corral, , J. D. Neelin, , and C. E. Holloway, 2010: Universality of rain event size distributions. J. Stat. Mech.: Theory Exp., 2010, P11030, doi:10.1088/1742-5468/2010/11/P11030.

    • Search Google Scholar
    • Export Citation
  • Savarin, A., , S. S. Chen, , B. W. Kerns, , C. Lee, , and D. P. Jorgensen, 2012: Convective cold pool structure and boundary layer recovery in DYNAMO. 2012 Fall Meeting, San Francisco, CA, Amer. Geophys. Union, Abstract A13A-0211.

  • Schumacher, C., , and R. A. Houze Jr., 2003: Stratiform rain in the tropics as seen by the TRMM precipitation radar. J. Climate, 16, 17391756, doi:10.1175/1520-0442(2003)016<1739:SRITTA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Sharma, S., , M. Konwar, , D. K. Sarma, , M. C. R. Kalapureddy, , and A. R. Jain, 2009: Characteristics of rain integral parameters during tropical convective, transition, and stratiform rain at Gadanki and its application in rain retrieval. J. Appl. Meteor. Climatol., 48, 12451266, doi:10.1175/2008JAMC1948.1.

    • Search Google Scholar
    • Export Citation
  • Stechmann, S. N., , and A. J. Majda, 2009: Gravity waves in shear and implications for organized convection. J. Atmos. Sci., 66, 25792599, doi:10.1175/2009JAS2976.1.

    • 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, doi:10.1175/1520-0469(2002)059<0030:OOACCK>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Tao, W.-K., , S. Lang, , X. Zeng, , S. Shige, , and Y. Takayabu, 2010: Relating convective and stratiform rain to latent heating. J. Climate, 23, 18741893, doi:10.1175/2009JCLI3278.1.

    • Search Google Scholar
    • Export Citation
  • Taylor, M., , J. Tribbia, , and M. Iskandarani, 1997: The spectral element method for the shallow water equations on the sphere. J. Comput. Phys., 130, 92108, doi:10.1006/jcph.1996.5554.

    • Search Google Scholar
    • Export Citation
  • Tiedtke, M., 1993: Representation of clouds in large-scale models. Mon. Wea. Rev., 121, 30403061, doi:10.1175/1520-0493(1993)121<3040:ROCILS>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Tokay, A., , D. A. Short, , C. R. Williams, , W. L. Ecklund, , and K. S. Gage, 1999: Tropical rainfall associated with convective and stratiform clouds: Intercomparison of disdrometer and profiler measurements. J. Appl. Meteor., 38, 302320, doi:10.1175/1520-0450(1999)038<0302:TRAWCA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Tompkins, A. M., 2001: Organization of tropical convection in low vertical wind shears: The role of water vapor. J. Atmos. Sci., 58, 529545, doi:10.1175/1520-0469(2001)058<0529:OOTCIL>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Waite, M. L., , and B. Khouider, 2010: The deepening of tropical convection by congestus preconditioning. J. Atmos. Sci., 67, 26012615, doi:10.1175/2010JAS3357.1.

    • 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, doi:10.1175/1520-0469(1999)056<0374:CCEWAO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Zhang, C., , and S. M. Hagos, 2009: Bi-modal structure and variability of large-scale diabatic heating in the tropics. J. Atmos. Sci., 66, 36213640, doi:10.1175/2009JAS3089.1.

    • Search Google Scholar
    • Export Citation
  • Zhang, C., , J. Gottschalck, , E. Maloney, , M. Moncrieff, , F. Vitart, , D. Waliser, , B. Wang, , and M. Wheeler, 2013: Cracking the MJO nut. Geophys. Res. Lett., 40, 12231230, doi:10.1002/grl.50244.

    • Search Google Scholar
    • Export Citation
  • Zhang, G. J., , and N. A. McFarlane, 1995: Sensitivity of climate simulations to the parameterization of cumulus convection in the Canadian Climate Centre General Circulation Model. Atmos.–Ocean, 33, 407446, doi:10.1080/07055900.1995.9649539.

    • Search Google Scholar
    • Export Citation
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Effect of Stratiform Heating on the Planetary-Scale Organization of Tropical Convection

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  • 1 Center for Prototype Climate Modeling, New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
  • | 2 Department of Mathematics and Statistics, University of Victoria, Victoria, British Columbia, Canada
  • | 3 Department of Mathematics, and Center for Atmosphere Ocean Science, Courant Institute of Mathematical Sciences, New York University, New York, New York, and Center for Prototype Climate Modeling, New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
  • | 4 Center for Prototype Climate Modeling, New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
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Abstract

It is widely recognized that stratiform heating contributes significantly to tropical rainfall and to the dynamics of tropical convective systems by inducing a front-to-rear tilt in the heating profile. Precipitating stratiform anvils that form from deep convection play a central role in the dynamics of tropical mesoscale convective systems. The wide spreading of downdrafts that are induced by the evaporation of stratiform rain and originate from in the lower troposphere strengthens the recirculation of subsiding air in the neighborhood of the convection center and triggers cold pools and gravity currents in the boundary layer, leading to further lifting. Here, aquaplanet simulations with a warm pool–like surface forcing, based on a coarse-resolution GCM of approximately 170-km grid mesh, coupled with a stochastic multicloud parameterization, are used to demonstrate the importance of stratiform heating for the organization of convection on planetary and intraseasonal scales. When the model parameters, which control the heating fraction and decay time scale of the stratiform clouds, are set to produce higher stratiform heating, the model produces low-frequency and planetary-scale MJO-like wave disturbances, while parameters associated with lower-to-moderate stratiform heating yield mainly synoptic-scale convectively coupled Kelvin-like waves. Furthermore, it is shown that, when the effect of stratiform downdrafts is reduced in the model, the MJO-scale organization is weakened, and a transition to synoptic-scale organization appears despite the use of larger stratiform heating parameters. Rooted in the stratiform instability, it is conjectured here that the strength and extent of stratiform downdrafts are key contributors to the scale selection of convective organizations, perhaps with mechanisms that are, in essence, similar to those of mesoscale convective systems.

Corresponding author address: Dr. Boualem Khouider, Department of Mathematics and Statistics, University of Victoria, P.O. Box 3045, STN CSC, Victoria BC V8W 3P4, Canada. E-mail: khouider@math.uvic.ca

Abstract

It is widely recognized that stratiform heating contributes significantly to tropical rainfall and to the dynamics of tropical convective systems by inducing a front-to-rear tilt in the heating profile. Precipitating stratiform anvils that form from deep convection play a central role in the dynamics of tropical mesoscale convective systems. The wide spreading of downdrafts that are induced by the evaporation of stratiform rain and originate from in the lower troposphere strengthens the recirculation of subsiding air in the neighborhood of the convection center and triggers cold pools and gravity currents in the boundary layer, leading to further lifting. Here, aquaplanet simulations with a warm pool–like surface forcing, based on a coarse-resolution GCM of approximately 170-km grid mesh, coupled with a stochastic multicloud parameterization, are used to demonstrate the importance of stratiform heating for the organization of convection on planetary and intraseasonal scales. When the model parameters, which control the heating fraction and decay time scale of the stratiform clouds, are set to produce higher stratiform heating, the model produces low-frequency and planetary-scale MJO-like wave disturbances, while parameters associated with lower-to-moderate stratiform heating yield mainly synoptic-scale convectively coupled Kelvin-like waves. Furthermore, it is shown that, when the effect of stratiform downdrafts is reduced in the model, the MJO-scale organization is weakened, and a transition to synoptic-scale organization appears despite the use of larger stratiform heating parameters. Rooted in the stratiform instability, it is conjectured here that the strength and extent of stratiform downdrafts are key contributors to the scale selection of convective organizations, perhaps with mechanisms that are, in essence, similar to those of mesoscale convective systems.

Corresponding author address: Dr. Boualem Khouider, Department of Mathematics and Statistics, University of Victoria, P.O. Box 3045, STN CSC, Victoria BC V8W 3P4, Canada. E-mail: khouider@math.uvic.ca
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