Abstract
It is shown that the spectral density of vorticity of transient ultra-long waves in the frequency domain is proportional to the minus second power of the frequency in middle latitudes in winter season. In order to explain the physical background of the above result, the vorticity equation of transient ultra-long waves is examined if there is the possibility to rewrite: in the same form with Langevin's equation in Brownian motion. By making use of data in two winter seasons of 1971-1972 and 1975-1976, it is shown that the vorticity equation of ultra-long waves in middle latitudes in winter may be treated in the same way with Langevin's equation in Brownian motion.
