A study of helicity and helicity flux in the Gonu tropical storm

In the study of atmospheric phenomena, different types of parameters are generallyconsidered. The type of parameter applied depends mostly on the scale and severity of the phenomena under consideration. Weather systems with fast rotating wind, such astropical storms or tornadoes, are among the most destructive weather-related phenomenon. Study of these kinds of phenomena and recognition of the causes of theirintensification or weakening are very important. Quantities that are measured in this typeof system vary and the calculations yield different results and properties depending on themethod used. There is a direct relationship between type of system and severity to thethermodynamic instability of the atmosphere in the region of the occurrence. It is typicalto use certain parameters for studying atmospheric instabilities, such as vorticity,potential vorticity. However, these parameters are gauges for measuring the power of asystem related to the value of the instability of a system suitable for a straight flow. Tomeasure the energy of activity of system with a severely rotating flow it is suggested touse another quantity, that of helicity. Thus, surveying sources and sinks of helicity ishighly important in dealing with vortices and hurricanes and rotating systems in general.Besides helicity, helicity flux is also a very valuable tool for studying rotating flows. Themathematical relationship between helicity and helicity-flux are presented in this study.Also, a new method of computing helicity flux is discussed and the values of helicity intwo methods are compared.In theory, the dissipation of helicity occurs in the boundary layer. In fact, thedissipation aspect of helicity involved in the frictional process in the boundary layer ismuch higher than the production of it in buoyancy process. Consequently, there is aseparating surface in the boundary layer above the surface of which the production ishigher than the loss by friction effect, and below it the friction is much higher than thatproduced by buoyancy. The helicity produced in the upper layer moves downward intothe area wherein the turbulent viscose force of the surface is dissipated due to friction.Since the stationary condition of the vortex is used in calculating helicity,, the downwardflux of helicity is a highly accurate parameter of the stationary turbulent vortex.This study calculates the downward helicity flux, sources and sinks of helicity of thehurricane Gonu. Data of hurricane Bonnie were utilized as both a comparison andreference for the study of hurricane Gonu. The results show that dynamical buoyancy isthe main factor in producing helicity and surface friction and the main dissipating factor.Therefore, an increase in dynamical buoyancy or reduction in dissipative friction resultsin the regeneration or enhancement of a rotating system. Furthermore, the increase (ordecrease) of the magnitude of helicity results in an increase (or decrease) in the height ofthe layer at which the maximum helicity flux occurs. It is suggested that the maximumhelicity flux occurs at the top of viscous turbulence boundary layer.