Numerical Simulation of the Blocking Process

[摘要] The geostrophic system of equations with both the effects of orography and heat contrast corresponding to land-sea distribution is integrated with respect to time by using the spectral method. The computed results show the appearance of reasonable blocking situation and a corre-sponding double jet stream in the latitudinal distribution of the zonally averaged zonal wind.The budgets of heat, angular momentum and energy for the period characterized by the predominant double jet stream are compared with those for another period to clarify the dynamical properties concerning blocking. The results of comparison are summarized as follows :1. As a result of the unusual poleward transport of heat, the meridional circulation has a 4-cell structure for the period during which the double jet stream predominates.2. In the upper layer, the angular momentum is transferred to high latitudes to compensate for the destruction of angular momentum due to the direct polar meridional circulation, forming a 4-cell structure during this period. This angular momentum contributes to the formation and development of the north branch of the double jet stream.3. The poleward transports of heat and angular momentum are performed mainly by the disturbance of wave number 2 which shows a large growth when the predominant double jet stream appears.4. In the upper layer, this disturbance is fed by conversion of available potential energy into kinetic energy through the baroclinic process and by transport of kinetic energy from the lower layer through the pressure force; while, in the lower layer, mainly by the transformation from zonal to eddy kinetic energy through the effect of mountains.5. The difference between the diabatic heatings of the oceans and the continents becomes smaller during the predominant blocking situation.

[学科分类] 大气科学