Seeking expert answers: the physical meaning of vorticity

Vorticity correlation technology is the main technical means to measure CO2 flux between vegetation and atmosphere by FLUXNET, but most CO2 flux observation stations are under atypical ideal conditions, which can not fully meet the basic assumptions of vorticity correlation technology, thus leading to uncertainty in estimating CO2 exchange capacity of vegetation/atmosphere clean ecosystem based on vorticity correlation technology. The basic theoretical formula and the types and characteristics of errors are discussed. The main sources of uncertainty in flux measurement are emphasized, such as the physical limitations of the instrument itself, two-dimensional and three-dimensional airflow movement, data processing methods and underestimation of night flux. On this basis, some suggestions on the priority problems in flux observation and research are put forward. It is considered that data quality control and analysis and error evaluation are the key issues to be considered in the process of comparing and comprehensively analyzing the results of different flux stations around the world.

Commonly used is the vorticity of horizontal wind, that is, the vertical component of vorticity. Vorticity correlation technique is a direct method to measure net CO2, water vapor and heat flux between vegetation and atmosphere. Vorticity correlation refers to the vertical flux of a substance, that is, the oblique variance of its concentration and its vertical velocity. Vorticity correlation technology can measure the long-term or short-term environmental variables of the ecosystem, so that human beings can quantitatively understand the exchange process of water and carbon dioxide in the ecosystem and deeply understand the impact of climate change on the ecosystem.

Suppose there is a massless particle in the flow field, so the position of a particle at different time or different arc segments can be determined. Therefore, by solving the equation and expressing it in graphic form, the trajectory of particles can be obtained, which is the traditional particle trajectory method; When the traces of countless particles are expressed, a simulated flow field will appear. In this process, in view of its complexity, it is necessary to solve the equation by numerical integration. When given, the numerical integration method directly determines the quality of simulation results. Taking a specific system as an example, this factor affecting the simulation effect is discussed in detail. Velocity field of the system

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The model is similar to a two-dimensional vortex with the intensity of 2πb, and the intensity source of 2πa is superimposed at the beginning, but the influence of 1/r is not considered. When a =-0.5 and b = 2.0, the particle trajectories corresponding to the analytical solution are in the range of | x | ≤ 4.5 and | y | ≤ 4.5.