Theoretical and Experimental Analysis of Vortex Origin

Several investigations refer to the issue of creation and identification of vortices in flows with different regime and presence of obstacles. Reasons have to do with the crucial role that vortices play in nature and industrial processes （sediment transport, mixing, radiation, noise, etc.）. Despite the contributions, further work is needed in order to perform more analysis of the mathematical arguments used to explain this phenomenon. In this idea order, the paper presents some advances in mathematical analysis and experimental results. In the first section, we do a description of the fluid motion from a fractional view through a sequence of three steps： Darcy＇s law, Navier-Stokes equations and Reynolds equations. Next, a representation of the temporal change of kinetic energy is found, which allows the possibility of the two signs. We obtain a description of the process of vortex creation. A length that represents the transition between flow and vortex intensity is found; then a succession of lengths is established that allows scaling from micro to macro. In the second section, experimental results are present; we consider vortex creation and its detection upstream of a bed form similar to that found in rivers, installed in an open channel, equipped with a water circulation system. For vortex detection, a methodology based on the particle image velocimetry PIV technique is proposed. So, we fulfill two objectives： vortex identification and its passage frequencies behind the bed form installed in the channel. Such procedure allows a computer process time reduction in vortices identification task.

A Climatological Investigation of the Activity of Summer Subtropical Vortices

By applying a new vortex detection method to the ECMWF 40-yr reanalysis （ERA40） data from 1985 to 2002, the climatology of summer vortices has been investigated in five subtropical regions, i.e., the northwestern Pacific, northeastern Pacific, northwestern Atlantic, northeastern Atlantic, and Australia- South Pacific, followed by validation with NCEP/NCAR reanalysis data. Results are as follows： （1） The spatial distributions of ERA40 vortex activities （VAC） were well consistent with those of NCEP/NCAR reanalysis （NRA） results in all regions, especially in northwestern Pacific. （2） Because of different model resolutions, both the number and intensity of vortices obtained from NRA were significantly weaker than ERA40＇s. （3） Vortices mainly cruised in coasts and the adjacent seas, from where to the land or the open sea vortex activities were gradually decreased. （4） There were two active centers in the northwestern Pacific： one was located in South China Sea and the other, as the largest center of the five regions, spread from the east side of the Philippines to Japan. （5） Over the northwestern Atlantic, most vortices occurred in Panama and its west-side offshore. （6） The spatial distributions of vortices were alike between the northeastern Pacific and northeastern Atlantic, both spreading from coasts to the west-side sea at 5°-20°N. （7） In the Australia-South Pacific, vortices were not as active as those in the other four regions, and mostly took place in the equator-side of near ocean areas. （8） Except the northwestern Pacific and northwestern Atlantic, the VAC interannual variations in the other three regions were different between ERA40 and NRA data. （9） In the northwestern Pacific and northwestern Atlantic, the VAC interannual variation could be separated to several distinct stages. （10） Since the mid 1980s, mean vortex intensity was getting increased in the northwestern Pacific, which was most significant in the subtropical areas on a global basis. In the western North Atlantic, there was a decreasing （increasing） trend of the mean vortex intensity before （after） the mid 1990s.