Dynamics of Tropical Cyclones
Final Report Abstract
We carried out idealized, high resolution numerical simulations to investigate the dynamics of formation (or genesis) of tropical cyclones and their subsequent intensification starting from a prescribed, weak, cloud-free initial vortex in thermal wind balance in a quiescent environment. The findings provide strong support for the hypothesis of Montgomery and Smith (2011) that the processes of tropical cyclogenesis and tropical cyclone intensification are the same, involving the concentration of absolute vorticity in the lower troposphere by convergence induced by the collective action of deep cumulus convection. The basic cyclogenesis process, which is intrinsically asymmetric, can be captured in a model where deep convection is modelled as a warm rain process only, although the inclusion of ice microphysics leads first to the development of a mid-level vortex. The ultimate low-level vortex that forms has a much smaller radial scale than the mid-level vortex and is largely uninfluenced by the latter. Moreover, there is considerable organization of the low level vertical vorticity field prior to genesis, defined as the point where rapid intensification begins. The findings provide a new perspective on tropical cyclogenesis, which traditionally has been treated as a separate topic from tropical cyclone intensification, the implication being that the processes of genesis and intensification are in some way different. While much previous work has emphasized the crucial nature of the mid-level vortex, we have shown this feature to be incidental to the formation of the ultimate low-level vortex. Our work has demonstrated also the important role of the frictional boundary layer in focusing deep convection, even at comparatively low wind speeds before genesis has taken place. Based mainly on European Centre for Medium Range Forecasts Analyses, we have shown that tropical lows that intensify over land have similar dynamics to tropical cyclones, the main difference being the more restricted moisture supply from the land surface compared with a water surface.
Publications
- 2015: Tropical low formation during the Australian monsoon: the events of January 2013. Aust. Meteor. Ocean. Journl., 65, 318- 341
R. K. Smith, M. T. Montgomery, G. Kilroy, S. Tang, and S. Müller
(See online at https://doi.org/10.22499/2.6503.003) - 2016: A case study of a monsoon low that intensified over land as seen in the ECMWF analyses. Quart. J. Roy. Meteor. Soc., 142, 2244-2255
G. Kilroy, R. K. Smith, M. T. Montgomery, B. Lynch and C. Earl-Spurr
(See online at https://doi.org/10.1002/qj.2814) - 2016: Numerical study of the spin up of a tropical low over land during the Australian monsoon. Quart. J. Roy. Meteor. Soc., 142, 2021-2032
S. Tang, R. K. Smith, M. T. Montgomery and M. Gu
(See online at https://doi.org/10.1002/qj.2797) - 2016: Understanding hurricanes. Weather, 71, 219-223
R. K. Smith, and M. T. Montgomery
(See online at https://doi.org/10.1002/wea.2776) - 2017 The effects of initial vortex size on hurricane genesis and intensification. Quart. J. Roy. Meteor. Soc., 143, 2832-2845
G. Kilroy, R. K. Smith
(See online at https://doi.org/10.1002/qj.3134) - 2017: A unified view of tropical cyclogenesis and intensification. Quart. J. Roy. Meteor. Soc., 143, 450-462
G. Kilroy, R. K. Smith, M. T. Montgomery
(See online at https://doi.org/10.1002/qj.2934) - 2017: Recent developments in the fluid dynamics of tropical cyclones. Annu. Rev. Fluid Mech., 49, 541-574
M. T. Montgomery and R. K. Smith
(See online at https://dx.doi.org/10.1146/annurev-fluid-010816-060022) - 2017: The role of boundary layer friction on tropical cyclogenesis and intensification. Quart. J. Roy. Meteor. Soc., 143, 2524-2536
G. Kilroy, M. T. Montgomery, and R. K. Smith
(See online at https://doi.org/10.1002/qj.3104) - 2017: Tropical low formation and intensification over land as seen in ECMWF analyses. Quart. J. Roy. Meteor. Soc., 143, 772-784
G. Kilroy, R. K. Smith, M. T. Montgomery
(See online at https://doi.org/10.1002/qj.2963) - 2018: The role of heating and cooling associated with ice processes on tropical cyclogenesis and intensification. Quart. J. Roy. Meteor. Soc., 144, 99-114.
G. Kilroy, R. K. Smith, M. T. Montgomery
(See online at https://doi.org/10.1002/qj.3187)
