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

A. Protat Centre d'études des Environnements Terrestre et Planétaires, Velizy, France

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Y. Lemaître Centre d'études des Environnements Terrestre et Planétaires, Velizy, France

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Abstract

This paper, the second of a series, documents the precipitation, and kinematic and thermodynamic structure of a tropical mesoscale convective system observed by instrumented aircraft on 15 December 1992 during TOGA COARE. Radar-derived precipitation fields indicate that the studied system consists of two subsystems, S1 and S2, characterized by distinct internal dynamics and morphological structures. The retrieved kinematic and thermodynamic structures are compared in detail with the synoptic-scale characteristics described in Part I of this paper, so as to evaluate the scale interactions involved in the internal organization of this convective system. It is shown essentially that the synoptic-scale circulation governs the mesoscale and convective-scale motions and, therefore, determines the internal organization of the selected system. In particular, this study highlights the major role played by the synoptic-scale vertical wind shear in the internal structure of this tropical mesoscale system. Momentum flux calculations show that upward transport of horizontal momentum on the mesoscale is large and mostly carried out at a scale of motion larger than the mesoscale (i.e., by the mean component of the total momentum flux). The westerly rear inflow exhibits characteristics consistent with the density current theory. However, specific mesoscale and convective-scale processes linked to the presence of precipitation modulate this dominant synoptic-scale forcing. A mesoscale interaction between the two distinct subsystems S1 and S2 is identified. The apparition of a shallow density current resulting from the downward spreading of air at the ground within S1 is suspected to be the triggering mechanism for S2.

Corresponding author address: Dr. Alain Protat, CETP–UVSQ, 10–12 Avenue de l'Europe, 78140 Vélizy, France. Email: protat@cetp.ipsl.fr

Abstract

This paper, the second of a series, documents the precipitation, and kinematic and thermodynamic structure of a tropical mesoscale convective system observed by instrumented aircraft on 15 December 1992 during TOGA COARE. Radar-derived precipitation fields indicate that the studied system consists of two subsystems, S1 and S2, characterized by distinct internal dynamics and morphological structures. The retrieved kinematic and thermodynamic structures are compared in detail with the synoptic-scale characteristics described in Part I of this paper, so as to evaluate the scale interactions involved in the internal organization of this convective system. It is shown essentially that the synoptic-scale circulation governs the mesoscale and convective-scale motions and, therefore, determines the internal organization of the selected system. In particular, this study highlights the major role played by the synoptic-scale vertical wind shear in the internal structure of this tropical mesoscale system. Momentum flux calculations show that upward transport of horizontal momentum on the mesoscale is large and mostly carried out at a scale of motion larger than the mesoscale (i.e., by the mean component of the total momentum flux). The westerly rear inflow exhibits characteristics consistent with the density current theory. However, specific mesoscale and convective-scale processes linked to the presence of precipitation modulate this dominant synoptic-scale forcing. A mesoscale interaction between the two distinct subsystems S1 and S2 is identified. The apparition of a shallow density current resulting from the downward spreading of air at the ground within S1 is suspected to be the triggering mechanism for S2.

Corresponding author address: Dr. Alain Protat, CETP–UVSQ, 10–12 Avenue de l'Europe, 78140 Vélizy, France. Email: protat@cetp.ipsl.fr

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  • Alexander, G. D., and G. S. Young, 1992: The relationship between EMEX mesoscale precipitation feature properties and their environmental characteristics. Mon. Wea. Rev, 120 , 554564.

    • Search Google Scholar
    • Export Citation
  • Barnes, G. M., and K. Sieckman, 1984: The environment of fast- and slow-moving tropical mesoscale convective cloud lines. Mon. Wea. Rev, 112 , 17821794.

    • Search Google Scholar
    • Export Citation
  • Berry, F. A. Jr, E. Bollay, and N. R. Beers, 1945: Handbook of Meteorology,. McGraw-Hill, 1068 pp.

  • Biggerstaff, M. L., and R. A. Houze Jr., 1993: Kinematics and microphysics of the transition zone of a midlatitude squall line system. J. Atmos. Sci, 50 , 30913110.

    • Search Google Scholar
    • Export Citation
  • Braun, S. A., and R. A. Houze Jr., 1994: The transition zone and secondary maximum of radar reflectivity behind a midlatitude squall line: Results retrieved from Doppler radar data. J. Atmos. Sci, 51 , 27332755.

    • Search Google Scholar
    • Export Citation
  • Caniaux, G., J-P. Lafore, and J-L. Redelsperger, 1995: A numerical study of the stratiform region of a fast-moving squall line. Part II: Relationship between mass, pressure, and momentum fields. J. Atmos. Sci, 52 , 331352.

    • Search Google Scholar
    • Export Citation
  • Chong, M., P. Amayenc, G. Scialom, and J. Testud, 1987: A tropical squall line observed during the COPT 81 experiment in West Africa. Part I: Kinematic structure inferred from dual-Doppler radar data. Mon. Wea. Rev, 115 , 670694.

    • Search Google Scholar
    • Export Citation
  • Dou, X. K., G. Scialom, and Y. Lemaître, 1996: MANDOP analysis and airborne Doppler radar for mesoscale studies. Quart. J. Roy. Meteor. Soc, 122 , 12311261.

    • Search Google Scholar
    • Export Citation
  • Fovell, R. G., and Y. Ogura, 1988: Numerical simulation of a midlatitude squall line in two dimensions. J. Atmos. Sci, 45 , 38463879.

  • Gal-Chen, T., 1978: A method for the initialization of the anelastic equations: Implications for matching models with observations. Mon. Wea. Rev, 106 , 587606.

    • Search Google Scholar
    • Export Citation
  • Hane, R. B., and P. S. Ray, 1985: Pressure and buoyancy fields derived from Doppler radar in a tornadic thunderstorm. J. Atmos. Sci, 42 , 1835.

    • Search Google Scholar
    • Export Citation
  • Hane, R. B., and D. P. Jorgensen, 1995: Dynamic aspects of a distinctly three-dimensional mesoscale convective system. Mon. Wea. Rev, 123 , 31943214.

    • Search Google Scholar
    • Export Citation
  • Hardy, K. R., 1963: The development of raindrop-size distributions and implications related to the physics of precipitation. J. Atmos. Sci, 20 , 299312.

    • Search Google Scholar
    • Export Citation
  • Hildebrand, P. H., 1998: Shear-parallel moist convection over the tropical ocean: A case study from 18 February 1993 TOGA COARE. Mon. Wea. Rev, 126 , 19521976.

    • Search Google Scholar
    • Export Citation
  • Hildebrand, P. H., and C. K. Mueller, 1985: Evaluation of meteorological airborne Doppler radar. Part I: Dual-Doppler analyses of air motions. J. Atmos. Oceanic Technol, 2 , 362380.

    • Search Google Scholar
    • Export Citation
  • Houze, R. A. Jr, . 1993: Cloud Dynamics. International Geophysics Series, Vol. 53, Academic Press, 572 pp.

  • Jorgensen, D. P., P. H. Hildebrand, and C. L. Frush, 1983: Feasability test of an airborne pulse-Doppler meteorological radar. J. Climate Appl. Meteor, 22 , 744757.

    • Search Google Scholar
    • Export Citation
  • Jorgensen, D. P., M. A. LeMone, and S. B. Trier, 1997: Structure and evolution of the 22 February 1993 TOGA COARE squall line: Aircraft observations of structure, circulation, and surface energy fluxes. J. Atmos. Sci, 54 , 19611985.

    • Search Google Scholar
    • Export Citation
  • Keenan, T. D., and R. E. Carbone, 1992: A preliminary morphology of precipitation systems in tropical northern Australia. Quart. J. Roy. Meteor. Soc, 118 , 283326.

    • Search Google Scholar
    • Export Citation
  • Lafore, J-P., J-L. Redelsperger, and G. Jaubert, 1988: Comparison between a three-dimensional simulation and Doppler radar data of a tropical squall line: Transport of mass, momentum, heat, and moisture. J. Atmos. Sci, 45 , 521544.

    • Search Google Scholar
    • Export Citation
  • Lemaître, Y., and J. Testud, 1986: Observation and modelling of tropical squall lines observed during the “COPT 79” experiment. Ann. Geophy, 4B , 2136.

    • Search Google Scholar
    • Export Citation
  • LeMone, M. A., 1983: Momentum transport by a line of cumulonimbus. J. Atmos. Sci, 40 , 18151834.

  • LeMone, M. A., and D. P. Jorgensen, 1991: Precipitation and kinematic structure of an oceanic mesoscale convective system. Part II: Momentum transport and generation. Mon. Wea. Rev, 119 , 26382653.

    • Search Google Scholar
    • Export Citation
  • LeMone, M. A., and M. W. Moncrieff, 1994: Momentum and mass transport by convective bands: Comparisons of highly idealized dynamical models to observations. J. Atmos. Sci, 51 , 281305.

    • Search Google Scholar
    • Export Citation
  • LeMone, M. A., G. M. Barnes, and E. J. Zipser, 1984: Momentum fluxes by lines of cumulonimbus over the tropical oceans. J. Atmos. Sci, 41 , 19141932.

    • 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
  • Lin, Y., T. C. Wang, R. W. Pasken, H. Shen, and Z. S. Deng, 1990:: Characteristics of a subtropical squall line determined from TAMEX dual-Doppler data. Part II: Dynamic and thermodynamic structure and momentum budgets. J. Atmos. Sci, 47 , 23822399.

    • Search Google Scholar
    • Export Citation
  • Marécal, V., S. Houée, P. Amayenc, T. Tani, and J. Testud, 1996: Radar attenuation in TOGA-COARE systems: Estimation and interpretation from microphysical data. Proc. 12th Conf. on Clouds and Precipitation, Zurich, Switzerland, Int. Commission on Clouds and Precipitation and Int. Association of Meteorology and Atmospheric Science, 204–207.

    • Search Google Scholar
    • Export Citation
  • Marécal, V., T. Tani, P. Amayenc, C. Klapisz, E. Obligis, and N. Viltard, 1997: Rain relations inferred from microphysical data in TOGA COARE and their use to test a rain profiling method from radar measurements at Ku-band. J. Appl. Meteor, 36 , 16291646.

    • Search Google Scholar
    • Export Citation
  • Matejka, T., and M. A. LeMone, 1990: The generation and redistribution of momentum in a squall line. Preprints, Fourth Conf. on Mesoscale Processes, Boulder, CO, Amer. Meteor. Soc., 196–197.

    • Search Google Scholar
    • Export Citation
  • Protat, A., and Y. Lemaître, 2001: 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., Y. Lemaître, and G. Scialom, 1997: Retrieval of kinematic fields using a single-beam airborne Doppler radar performing circular trajectories. J. Atmos. Oceanic Technol, 14 , 769791.

    • Search Google Scholar
    • Export Citation
  • Protat, A., Y. Lemaître, and G. Scialom, 1998: Thermodynamic analytical fields from Doppler radar data by means of the MANDOP analysis. Quart. J. Roy. Meteor. Soc, 124 , 16331669.

    • Search Google Scholar
    • Export Citation
  • Rotunno, R., and J. B. Klemp, 1982: The influence of the shear induced pressure gradient on thunderstorm motion. Mon. Wea. Rev, 110 , 136151.

    • Search Google Scholar
    • Export Citation
  • Roux, F., 1998: The oceanic mesoscale convective system observed with airborne Doppler radars on 9 February 1993 during TOGA-COARE: Structure, evolution and budgets. Quart. J. Roy. Meteor. Soc, 124 , 585614.

    • Search Google Scholar
    • Export Citation
  • Schlesinger, R. E., 1984: Mature thunderstorm cloud-top structure and dynamics: A three-dimensional numerical simulation study. J. Atmos. Sci, 41 , 15511570.

    • Search Google Scholar
    • Export Citation
  • Scialom, G., and Y. Lemaître, 1990: A new analysis for the retrieval of the three-dimensional wind field from multiple Doppler radars. J. Atmos. Oceanic Technol, 7 , 640665.

    • Search Google Scholar
    • Export Citation
  • Szeto, K. K., and H-R. Cho, 1994: A numerical investigation of squall lines. Part II: The mechanics of evolution. J. Atmos. Sci, 51 , 425433.

    • Search Google Scholar
    • Export Citation
  • Webster, P. J., and R. Lukas, 1992: TOGA COARE: The Coupled Ocean–Atmosphere Response Experiment. Bull. Amer. Meteor. Sci, 73 , 13771415.

    • Search Google Scholar
    • Export Citation
  • Weisman, M. L., 1992: The role of convectively generated rear-inflow jets in the evolution of long-lived mesoconvective systems. J. Atmos. Sci, 49 , 18261847.

    • Search Google Scholar
    • Export Citation
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