ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-10803-2010 Coarse, intermediate and high resolution numerical simulations of the transition of a tropical wave critical layer to a tropical storm Montgomery M. T. 1 Wang Z. 3 Dunkerton T. J. 1 2 Naval Postgraduate School, Monterey CA, USA NorthWest Research Associates, Bellevue WA, USA Department of Atmospheric Sciences, University of Illinois, Urbana, IL, USA 18 11 2010 10 22 10803 10827 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/10/10803/2010/acp-10-10803-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/10803/2010/acp-10-10803-2010.pdf

Recent work has hypothesized that tropical cyclones in the deep Atlantic and eastern Pacific basins develop from within the cyclonic Kelvin cat's eye of a tropical easterly wave critical layer located equatorward of the easterly jet axis. The cyclonic critical layer is thought to be important to tropical cyclogenesis because its cat's eye provides (i) a region of cyclonic vorticity and weak deformation by the resolved flow, (ii) containment of moisture entrained by the developing flow and/or lofted by deep convection therein, (iii) confinement of mesoscale vortex aggregation, (iv) a predominantly convective type of heating profile, and (v) maintenance or enhancement of the parent wave until the developing proto-vortex becomes a self-sustaining entity and emerges from the wave as a tropical depression. This genesis sequence and the overarching framework for describing how such hybrid wave-vortex structures become tropical depressions/storms is likened to the development of a marsupial infant in its mother's pouch, and for this reason has been dubbed the "marsupial paradigm". <br></br> Here we conduct the first multi-scale test of the marsupial paradigm in an idealized setting by revisiting the Kurihara and Tuleya problem examining the transformation of an easterly wave-like disturbance into a tropical storm vortex using the WRF model. An analysis of the evolving winds, equivalent potential temperature, and relative vertical vorticity is presented from coarse (28 km), intermediate (9 km) and high resolution (3.1 km) simulations. The results are found to support key elements of the marsupial paradigm by demonstrating the existence of a rotationally dominant region with minimal strain/shear deformation near the center of the critical layer pouch that contains strong cyclonic vorticity and high saturation fraction. This localized region within the pouch serves as the "attractor" for an upscale "bottom up" development process while the wave pouch and proto-vortex move together. <br></br> Implications of these findings are discussed in relation to an upcoming field experiment for the most active period of the Atlantic hurricane season in 2010 that is to be conducted collaboratively between the National Oceanic and Atmospheric Administration (NOAA), the National Science Foundation (NSF), and the National Aeronautics and Space Adminstration (NASA).

 References Bister, M. and Emanuel, K. A.: The genesis of Hurricane Guillermo: TEXMEX analyses and a modeling study, Mon. Weather Rev., 125, 2662–2682, 1997. Bui, H. H., Smith, R. K., Montgomery, M. T., and Peng, J.: Balanced and unbalanced aspects of tropical cyclone intensification, Q. J. Roy. Meteorol. Soc., 135, 1715–1731, 2009. Braun, S. A., Montgomery, M. T., Mallen, K. J., and Reasor, P. D.: Simulation and interpretation of the genesis of tropical storm GERT~(2005) as part of the NASA tropical cloud systems, J. Atmos. Sci., 67, 999-1025, 2010. Cram, T. A., Montgomery, M. T., and Hertenstein, R. F. A.: Early Evolution of Vertical Vorticity in a Numerically Simulated Idealized Convective Line, J. Atmos. Sci., 59, 2113–2127, 2002. Davis, C. A. and Trier, S. B.: Cloud-Resolving Simulations of Mesoscale Vortex Intensification and Its Effect on a Serial Mesoscale Convective System. Mon. Wea. Rev., 130, 2839–2858, 2002. Dunkerton, T. J., Montgomery, M. T., and Wang, Z.: Tropical cyclogenesis in a tropical wave critical layer: easterly waves, Atmos. Chem. Phys., 9, 5587–5646, 2009. Emanuel, K. A., Neelin, J. D., and Bretherton, C. S.: On largescale circulations in convecting atmosphere, Qu. J. Roy. Meteor. Soc., 120, 1111–1143, 1994. Emanuel, K. A.: Divine Wind: The History and Science of Hurricanes, Oxford University Press, New York, USA, 285~pp., 2005. Eliassen, A. and Lystad, M.: The Ekman layer of a circular vortex: A numerical and theoretical study, Geophys. Norv., 31, 1-16, 1977. Guinn, T. A. and Schubert, W. H.: Hurricane spiral bands, J. Atmos. Sci., 50, 3380–3403, 1993. Hall, N. M. J., Kiladis, G. N., and Thorncroft, C. D.: Three-dimensional structure and dynamics of African easterly waves. Part II: dynamical modes, J. Atmos. Sci., 63, 2231–2245, 2006. Halverson, J., Black, M., Braun, S., et al.: NASA's Tropical Cloud Systems and Processes Experiment, B. Am. Meteor. Soc., 88, 867–882, 2007. Haynes, P. H. and McIntyre, M. E.: On the evolution of vorticity and potential vorticity in the presence of diabatic heating and frictional or other forces, J. Atmos. Sci., 44, 828–841, 1987. Holton, J. R.: An Introduction to Dynamic Meteorology, 3rd edn., Academic Press, San Diego, 511~pp., 1992. Hong, S. -Y. and Lim, J.-O.: The WRF Single-moment 6-class microphysics scheme (WSM6), J. Korean. Meteor. Soc., 42, 129–151, 2006. Houze Jr., R. A.: Mesoscale convective systems, Rev. Geophys., 42, RG4003, doi:10.1029/2004RG000150, 2004. Houze, R. A., Lee, W.-C., and Bell, M. M.: Convective Contribution to the Genesis of Hurricane Ophelia (2005), Mon. Weather Rev., 137, 2778–2800, 2009. Kurihara, Y. and Bender, M. A.: Use of a Movable Nested-Mesh Model for Tracking a Small Vortex, Mon. Weather Rev., 108, 1792–1809, 1980. Kurihara, Y. and Tuleya, R. E.: A Numerical Simulation Study on the Genesis of a Tropical Storm, Mon. Weather Rev., 109, 1629–1653, 1981. %Marín, J. C., Raymond, D. J., and Raga, G. B.: Intensification of %tropical cyclones in the GFS model, Atmos. Chem. Phys., 9, 1407–1417, 2009. Marín, J. C., Raymond, D. J., and Raga, G. B.: Intensification of tropical cyclones in the GFS model, Atmos. Chem. Phys., 9, 1407–1417, doi:10.5194/acp-9-1407-2009, 2009. McWilliams, J. C.: The emergence of isolated coherent vortices in turbulent flow, J. Fluid Mech., 140, 21–43, 1984. Montgomery, M. T. and Enagonio, J.: Tropical Cyclogenesis via Convectively Forced Vortex Rossby Waves in a Three-Dimensional Quasigeostrophic Model, J. Atmos. Sci., 55, 3176–3207, 1998. Montgomery, M. T., Nicholls, M. E., Cram, T. A., and Saunders, A. B.: A vortical hot tower route to tropical cyclogenesis, J. Atmos. Sci., 63, 355–386, 2006. Montgomery, M. T., Nguyen, V. S., Smith, R. K., and Persing, J.: Do tropical cyclones intensify by WISHE?, Q. J. Roy. Meteorol. Soc., 135, 1697–1714, 2010. Molinari, J., Vollaro, D., and Corbosiero, K. L.: Tropical cyclone formation in a sheared environment: a case study, J. Atmos. Sci., 61, 2493–2509, 2004. Nolan, D. S.: What is the trigger for tropical cyclogenesis?, Aust. Meteorol. Mag., 56, 241–266, 2007. Phillips, N. A.: A coordinate system having some special advantages for numerical forecasting, J. Meteorol., 14, 184–185, 1957. Raymond, D. J., López-Carrillo, C., and López Cavazos, L.: Case-studies of developing east Pacific easterly waves, Q. J. Roy. Meteorol. Soc., 124, 2005–2034, 1998. Raymond, D. J. and Sessions, S. L.: Evolution of convection during tropical cyclogenesis, Geophys. Res. Lett., 34, L06811, doi:10.1029/2006GL028607, 2007. Reasor, P. D., Montgomery, M. T., and Boast, L. F.: Mesoscale observations of the genesis of Hurricane Dolly~(1996), J. Atmos. Sci., 62, 3151–3171, 2005. Ritchie, E. A. and Holland, G. J.: Scale interactions during the formation of Typhoon Irving, Mon. Weather Rev., 125, 1377–1396, 1997. Rotunno, R. and Emanuel, K. A.: An Air-Sea Interaction Theory for Tropical Cyclones. Part II: Evolutionary Study Using a Nonhydrostatic Axisymmetric Numerical Model, J. Atmos. Sci., 44, 542–561, 1987. Skamarock, W. C., Klemp, J. B., Dudhia, J., Gill, D. O., Barker, D. M., Wang, W., and Powers, J. G.: A description of the Advanced Research WRF Version 2. NCAR Tech. Note/TN-468+STR, 88~pp., 2005. Smith, R. K., Montgomery, M. T., and Nguyen, V. S.: Tropical cyclone spin up revisited, Q. J. Roy. Meteorol. Soc., 135, 1321–1335, 2009. Srivastava, R.: A model of intense downdrafts driven by the melting and evaporation of precipitation, J. Atmos. Sci., 44, 1752-1773, 1987. Tao, W. K., Simpson, J., Sui, C. H., Ferrier, B., Lang, S., Scala, J., Chou, M. D., and Pickering, K.: Heating, Moisture, and Water Budgets of Tropical and Midlatitude Squall Lines: Comparisons and Sensitivity to Longwave Radiation, J. Atmos. Sci., 50, 673–690, 1993. Thorncroft, C. D. and Hoskins, B. J.: An idealized study of African easterly waves. I: a linear view, Q. J. Roy. Meteorol. Soc., 120, 953–982, 1994. Tory, K. J. and Montgomery, M. T.: Internal influences on tropical cyclone formation. Topic 2.2 in Sixth International Workshop on Tropical Cyclones, San Jose, Costa Rica, World Meteorological Organization, 22~pp., 2006. Tory, K. J., Montgomery, M. T., and Davidson, N. E.: Prediction and diagnosis of tropical cyclone formation in an NWP system. Part I: the critical role of vortex enhancement in deep convection, J. Atmos. Sci., 63, 3077–3090, 2006a. Tory, K. J., Montgomery, M. T., Davidson, N. E., and Kepert, J. E.: Prediction and diagnosis of tropical cyclone formation in a NWP system. Part II: a diagnosis of tropical cyclone Chris formation, J. Atmos. Sci., 63, 3091–3113, 2006b. Tory, K. J., Davidson, N. E., and Montgomery, M. T.: Prediction and diagnosis of tropical cyclone formation in an NWP system. Part III: diagnosis of developing and non-developing storms, J. Atmos. Sci., 64, 3195–3213, 2007. Tory, K. J. and Montgomery, M. T.: Tropical cyclone formation: A synopsis of the internal dynamics, AMS 28th Conference on Hurricanes and Tropical Meteorology, Orlando, FL, 2008. Wang, Z., Montgomery, M. T., and Dunkerton, T. J.: Genesis of Pre-hurricane Felix (2007). Part I: The Role of the Easterly Wave Critical Layer, J. Atmos. Sci., 67, 1711–1729, 2010. Wang, Z., Montgomery, M. T., and Dunkerton, T. J.: Genesis of Pre-hurricane Felix (2007). Part II: Warm core formation, precipitation evolution and predictability, J. Atmos. Sci., 67, 1730-1744, 2010. Weisman, M. L. and Davis, C. A.: Mechanisms for the Generation of Mesoscale Vortices within Quasi-Linear Convective Systems, J. Atmos. Sci., 55, 2603–2622, 1998.