A Numerical Study of a Mesoscale Convective System during TOGA COARE. Part II: Organization

Badrinath Nagarajan Department of Atmospheric and Oceanic Sciences, McGill University, Montreal, Quebec, Canada

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M. K. Yau Department of Atmospheric and Oceanic Sciences, McGill University, Montreal, Quebec, Canada

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Da-Lin Zhang Department of Meteorology, University of Maryland, College Park, College Park, Maryland

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Abstract

In Part I, the authors presented a successful numerical simulation of the life cycle of a warm-pool mesoscale convective system (MCS) that occurred on 15 December 1992 during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment. In this study, the simulation results of Part I are diagnosed to investigate the organization of the MCS and the convective onsets that occurred during the growing and mature stages of the MCS.

During the life cycle of the MCS, four convective onsets occur in the presence of large-scale ascent, convective available potential energy (CAPE), and surface potential temperature drop-off (SPTD). It is found that the first convective onset is caused by the existence of upward motion, CAPE, and SPTD in the model initial conditions. The second convective onset is regulated by the favorable occurrence of SPTD. The third and fourth convective onsets arise from the development of upward motion associated with the westward propagation of the quasi-2- day wave. The four mesoscale precipitation features clustered together to form the MCS in response to the evolution of the vertical motion field.

The organization of the MCS is characterized by the presence of a midtropospheric mesovortex situated near the position of the first convective onset. Analysis of the relative vorticity (RV) budget indicates that the mesovortex originates and intensifies largely from vortex stretching induced by deep convective heating. A decrease in RV above (below) the mesovortex arises because of the combined effects of the tilting and horizontal advection terms (the tilting, stretching, and solenoidal terms). Our results suggest that the mesovortex played little role in the subsequent onsets (i.e., second, third, and fourth) and that other warm-pool MCSs occurring near the transequatorial flow are likely to be associated with mesovortices.

Current affiliation: Abdus Salam International Centre for Theoretical Physics, Trieste, Italy

Corresponding author address: Dr. Badrinath Nagarajan, Abdus Salam International Centre for Theoretical Physics, PWC section, Strada Costiera 11, Trieste I-34014, Italy. Email: badrinath.nagarajan@elf.mcgill.ca

Abstract

In Part I, the authors presented a successful numerical simulation of the life cycle of a warm-pool mesoscale convective system (MCS) that occurred on 15 December 1992 during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment. In this study, the simulation results of Part I are diagnosed to investigate the organization of the MCS and the convective onsets that occurred during the growing and mature stages of the MCS.

During the life cycle of the MCS, four convective onsets occur in the presence of large-scale ascent, convective available potential energy (CAPE), and surface potential temperature drop-off (SPTD). It is found that the first convective onset is caused by the existence of upward motion, CAPE, and SPTD in the model initial conditions. The second convective onset is regulated by the favorable occurrence of SPTD. The third and fourth convective onsets arise from the development of upward motion associated with the westward propagation of the quasi-2- day wave. The four mesoscale precipitation features clustered together to form the MCS in response to the evolution of the vertical motion field.

The organization of the MCS is characterized by the presence of a midtropospheric mesovortex situated near the position of the first convective onset. Analysis of the relative vorticity (RV) budget indicates that the mesovortex originates and intensifies largely from vortex stretching induced by deep convective heating. A decrease in RV above (below) the mesovortex arises because of the combined effects of the tilting and horizontal advection terms (the tilting, stretching, and solenoidal terms). Our results suggest that the mesovortex played little role in the subsequent onsets (i.e., second, third, and fourth) and that other warm-pool MCSs occurring near the transequatorial flow are likely to be associated with mesovortices.

Current affiliation: Abdus Salam International Centre for Theoretical Physics, Trieste, Italy

Corresponding author address: Dr. Badrinath Nagarajan, Abdus Salam International Centre for Theoretical Physics, PWC section, Strada Costiera 11, Trieste I-34014, Italy. Email: badrinath.nagarajan@elf.mcgill.ca

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  • Bartels, D. L., and R. A. Maddox, 1991: Midlevel cyclonic vortices generated by mesoscale convective systems. Mon. Wea. Rev, 119 , 104188.

    • Search Google Scholar
    • Export Citation
  • Benoit, R., J. Cote, and J. Mailhot, 1989: Inclusion of a TKE boundary layer parameterization in the Canadian regional finite-element model. Mon. Wea. Rev, 117 , 17261750.

    • Search Google Scholar
    • Export Citation
  • Benoit, R., M. Desgagne, P. Pellerin, S. Pellerin, Y. Chartier, and S. Desjardins, 1997: The Canadian MC2: A semi-Lagrangian, semi- implicit wideband atmospheric model suited for finescale process studies and simulation. Mon. Wea. Rev, 125 , 23822415.

    • Search Google Scholar
    • Export Citation
  • Betts, A. K., 1986: A new convective adjustment scheme. Part I: Observational and theoretical basis. Quart. J. Roy. Meteor. Soc, 112 , 667691.

    • Search Google Scholar
    • Export Citation
  • Brandes, E. A., and C. L. Ziegler, 1993: Mesoscale downdraft influences on vertical vorticity in a mature mesoscale convective system. Mon. Wea. Rev, 121 , 13371353.

    • Search Google Scholar
    • Export Citation
  • Chen, S. S., and R. A. Houze, 1996: Multiscale variability of deep convection in relation to large-scale circulation in TOGA COARE. J. Atmos. Sci, 53 , 13801409.

    • Search Google Scholar
    • Export Citation
  • Chen, S. S., and R. A. Houze, 1997: Diurnal variation and life-cycle of deep convective systems over the tropical Pacific warm pool. Quart. J. Roy. Meteor. Soc, 123 , 357388.

    • Search Google Scholar
    • Export Citation
  • Chong, M., and O. Bousquet, 1999: A mesovortex within a near- equatorial mesoscale convective system during TOGA COARE. Mon. Wea. Rev, 127 , 11451156.

    • Search Google Scholar
    • Export Citation
  • Crook, N. A., 1996: Sensitivity of moist convection forced by boundary layer processes to low-level thermodynamic fields. Mon. Wea. Rev, 124 , 17671785.

    • Search Google Scholar
    • Export Citation
  • Crook, N. A., and M. W. Moncrieff, 1988: The effect of large-scale convergence on the generation and maintenance of deep moist convection. J. Atmos. Sci, 45 , 36063624.

    • Search Google Scholar
    • Export Citation
  • Davies, C. A., and M. L. Weisman, 1994: Balanced dynamics of mesoscale vortices produced in simulated convective systems. J. Atmos. Sci, 51 , 20052030.

    • 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 , 926967.

    • Search Google Scholar
    • Export Citation
  • Errico, R. M., 1985: Spectra computed from a limited area grid. Mon. Wea. Rev, 113 , 15541562.

  • Fairall, C. W., E. F. Bradley, D. P. Rogers, J. B. Edson, and G. S. Young, 1996: Bulk parameterization of air–sea fluxes for Tropical Ocean-Global Atmosphere Coupled-Ocean Atmosphere Response Experiment. J. Geophys. Res, 101 , 37473764.

    • Search Google Scholar
    • Export Citation
  • Garand, L., and J. Mailhot, 1990: The influence of infrared radiation on numerical weather forecasts. Proc. Seventh Conf. on Atmospheric Radiation, San Francisco, CA, Amer. Meteor. Soc., J146–J151.

    • Search Google Scholar
    • Export Citation
  • Jabouille, P., J. L. Redelsperger, and J. P. Lafore, 1996: Modification of surface fluxes by atmospheric convection in the TOGA COARE region. Mon. Wea. Rev, 124 , 816837.

    • Search Google Scholar
    • Export Citation
  • Johnson, R. H., and D. L. Bartels, 1992: Circulations associated with a mature-to-decaying midlatitude mesoscale convective system. Mon. Wea. Rev, 120 , 13011320.

    • Search Google Scholar
    • Export Citation
  • Johnston, E. C., 1981: Mesoscale vorticity centers induced by mesoscale convective complexes. M.S. thesis, Dept. of Meteorology, University of Wisconsin—Madison, 54 pp.

    • Search Google Scholar
    • Export Citation
  • Kain, J. S., and J. M. Fritsch, 1990: A one-dimensional entraining/ detraining plume model and its application in convective parameterization. J. Atmos. Sci, 47 , 27842802.

    • Search Google Scholar
    • Export Citation
  • Keenan, T. D., and S. A. Rutledge, 1993: Mesoscale characteristics of monsoonal convection and associated stratiform precipitation. Mon. Wea. Rev, 121 , 352374.

    • Search Google Scholar
    • Export Citation
  • Kingsmill, D. E., and R. A. Houze, 1999: Kinematic characteristics of air flowing into and out of precipitating convection over the west Pacific warm pool: An airborne Doppler radar survey. Quart. J. Roy. Meteor. Soc, 125 , 11651207.

    • Search Google Scholar
    • Export Citation
  • Kong, F. Y., and M. K. Yau, 1997: An explicit approach to microphysics in MC2. Atmos.–Ocean, 35 , 257291.

  • Leary, C. A., and R. A. Houze, 1979: The structure and evolution of convection in a tropical cloud cluster. J. Atmos. Sci, 36 , 437457.

    • Search Google Scholar
    • Export Citation
  • LeMone, M. A., E. J. Zipser, and S. B. Trier, 1998: The role of environmental shear and thermodynamic conditions in determining the structure and evolution of mesoscale convective systems during TOGA COARE. J. Atmos. Sci, 55 , 34933518.

    • Search Google Scholar
    • Export Citation
  • Mapes, B. E., 1993: Gregarious tropical convection. J. Atmos. Sci, 50 , 20262037.

  • Mapes, B. E., and R. A. Houze, 1993: Cloud clusters and superclusters over the oceanic warm pool. Mon. Wea. Rev, 121 , 13981415.

  • Miller, M., and J. M. Fritsch, 1991: Mesoscale convective complexes in the western Pacific region. Mon. Wea. Rev, 119 , 29782992.

  • Nagarajan, B., M. K. Yau, and D-L. Zhang, 2001: A numerical study of a mesoscale convective system during TOGA COARE. Part I: Model description and verification. Mon. Wea. Rev, 129 , 25012520.

    • Search Google Scholar
    • Export Citation
  • Numaguti, A., 1995: Characteristics of 4-to-20-day period disturbances observed in the equatorial Pacific during the TOGA COARE IOP. J. Meteor. Soc. Japan, 73 , 353377.

    • Search Google Scholar
    • Export Citation
  • Protat, A., and Y. Lemaitre, 2001a: Scale interactions involved in the initiation, structure, and evolution of the 15 December 1992 MCS observed during TOGA COARE. Part I: Synoptic-scale processes. Mon. Wea. Rev, 129 , 17571778.

    • Search Google Scholar
    • Export Citation
  • Protat, A., and Y. Lemaitre, 2001b: Scale interactions involved in the initiation, structure, and evolution of the 15 December 1992 MCS observed during TOGA COARE. Part II: Mesoscale and convective-scale processes. Mon. Wea. Rev, 129 , 17791808.

    • Search Google Scholar
    • Export Citation
  • Ramage, C. S., 1971: Monsoon Meterology. Vol. 15,. Academic Press, 296 pp.

  • Raymond, D. J., 1995: Regulation of moist convection over the west Pacific warm pool. J. Atmos. Sci, 52 , 39453959.

  • Rickenbach, T. M., and S. A. Rutledge, 1998: Convection in TOGA COARE: Horizontal scale, morphology, and rainfall production. J. Atmos. Sci, 55 , 27152729.

    • Search Google Scholar
    • Export Citation
  • Rogers, R. F., and J. M. Fritsch, 2001: Surface cyclogenesis from convectively driven amplification of midlevel mesoscale convective vortices. Mon. Wea. Rev, 129 , 605637.

    • Search Google Scholar
    • Export Citation
  • Takayabu, Y. N., K-M. Lau, and C-H. Sui, 1996: Observation of a quasi-2-day wave during TOGA COARE. Mon. Wea. Rev, 124 , 18921913.

  • Tollerud, E. I., and S. K. Esbensen, 1985: A composite life cycle of nonsquall mesoscale convective systems over the tropical ocean. Part I: Kinematic fields. J. Atmos. Sci, 42 , 823837.

    • Search Google Scholar
    • Export Citation
  • Verlinde, J., and W. R. Cotton, 1990: A mesovortex couplet observed in the trailing anvil of a multicellular convective complex. Mon. Wea. Rev, 118 , 9931010.

    • Search Google Scholar
    • Export Citation
  • Webster, P. J., and R. Lukas, 1992: TOGA COARE: The Coupled Ocean Atmosphere Response Experiment. Bull. Amer. Meteor. Soc, 73 , 13771416.

    • Search Google Scholar
    • Export Citation
  • Webster, P. J., C. A. Clayson, and J. A. Currie, 1996: Clouds, radiation, and the diurnal cycle of sea surface temperature in the tropical western Pacific. J. Climate, 9 , 17121730.

    • Search Google Scholar
    • Export Citation
  • Yuter, S. E., R. A. Houze, F. Smull, F. D. Marks, J. R. Daugherty, and S. R. Brodzik, 1995: TOGA COARE aircraft mission summary images: An electronic atlas. Bull. Amer. Meteor. Soc, 76 , 319328.

    • Search Google Scholar
    • Export Citation
  • Zhang, D-L., 1992: The formation of a cooling-induced mesovortex in the trailing stratiform region of a midlatitude squall line. Mon. Wea. Rev, 120 , 27632785.

    • Search Google Scholar
    • Export Citation
  • Zhang, D-L., and J. M. Fritsch, 1987: Numerical simulation of the meso-β- scale structure and evolution of the 1977 Johnstown flood. Part II: Inertially stable warm-core vortex. J. Atmos. Sci, 44 , 25932612.

    • Search Google Scholar
    • Export Citation
  • Zhang, D-L., and N. Bao, 1996: Ocean cyclogenesis as induced by a mesoscale convective system moving offshore. Part I: A 90-h real- data simulation. Mon. Wea. Rev, 124 , 14491469.

    • Search Google Scholar
    • Export Citation
  • Zhang, D-L., E-Y. Hsie, and M. W. Moncrieff, 1988: A comparison of explicit and implicit predictions of convective and stratiform precipitating weather systems with a meso-β-scale numerical model. Quart. J. Roy. Meteor. Soc, 114 , 3160.

    • Search Google Scholar
    • Export Citation
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