Diagnosis of Pre-Depression Large-Scale Vortex Instability in the Tropical Atmosphere

An approach is proposed [1] for determining the precise time of the start of tropical cyclogenesis, which includes a combined analysis of data from cloud-resolving numerical modeling and GOES Imagery. The approach is based on the similarity of patterns in the fields of vertical helicity (numerical simulation) and temperature (satellite data), allowing for the localization of intense rotating convective clouds known as the Vortical Hot Towers. As a theoretical ground, we applied a hypothesized (to date) interpretation of tropical cyclogenesis as a large-scale instability caused by the mechanism of the turbulent vortex dynamo in the atmosphere [1,2], and with bearing in mind the crucial role of Vortical Hot Towers in providing the dynamo-effect [2]. In this context, birth of a hurricane is considered as an extreme threshold event in the helical atmospheric turbulence of a vorticity-rich environment of a pre-depression cyclonic recirculation zone. Helical turbulence is characterized by the broken mirror symmetry and permits an existence of inverse energy cascade in three-dimensional cases. In order to trace and analyze processes of self-organization in the tropical atmosphere, that span scales from convective clouds with horizontal dimensions of 1-5 km to mesoscale vortices of hundreds of kilometers, we used the post-processing [1-3] of data from cloud-resolving numerical simulations [4].  Implementation of the proposed approach revealed that large-scale vortex instability can begin a few hours, or even dozens of hours, before the formation of the Tropical Depression. This work was supported by the research project “Monitoring” No. 01200200164.

References

[1] Levina, G. V., 2020. Birth of a hurricane: early detection of large-scale vortex instability. J. Phys.: Conf. Ser., 1640  012023,  doi:10.1088/1742-6596/1640/1/012023

[2] Levina, G. V., 2018. On the path from the turbulent vortex dynamo theory to diagnosis of tropical cyclogenesis. Open J. Fluid Dyn., 8, 86–114,  https://doi.org/10.4236/ojfd.2018.81008

[3] Levina, G. V. and M. T. Montgomery, 2015. When will Cyclogenesis Commence Given a Favorable Tropical Environment?  Procedia IUTAM, 17, 59–68, https://doi.org/10.1016/j.piutam.2015.06.010

[4] Montgomery, M. T., M. E.  Nicholls, T. A. Cram, and A. B. Saunders, 2006: A vortical hot tower route to tropical cyclogenesis. J. Atmos. Sci., 63, 355–386,  https://doi.org/10.1175/JAS3604.1