Coarse, intermediate and high resolution numerical simulations of the transition of a tropical wave critical layer to a tropical storm 1Naval Postgraduate School, Monterey CA, USA
2NorthWest Research Associates, Bellevue WA, USA
3Department of Atmospheric Sciences, University of Illinois, Urbana, IL, USA
Received: 14 March 2009 – Published in Atmos. Chem. Phys. Discuss.: 08 December 2009 Abstract. 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".
Revised: 29 August 2010 – Accepted: 09 September 2010 – Published: 18 November 2010
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.
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).
Citation: Montgomery, M. T., Wang, Z., and Dunkerton, T. J.: Coarse, intermediate and high resolution numerical simulations of the transition of a tropical wave critical layer to a tropical storm, Atmos. Chem. Phys., 10, 10803-10827, doi:10.5194/acp-10-10803-2010, 2010.