The Role of Topography and Diabatic Heating in the Formation of Dipole Blocking in the Atmosphere

In this paper, the nonlinear stationary waves forced by topography and diabatic heating are investigated. It is pointed out that (1) the nonlinear interaction of different stationary waves forced only by topography might form dipole blocking in the atmosphere, this might explain the dipole blocking appeared in the Pacific and Atlantic regions; (2) the dipole blocking could not be caused by the nonlinear interaction of the different stationary waves forced by the diabatic heating alone; (3) the nonlinear interaction of the diffferent stationary waves forced by both topography and diabatic heating could initiate dipole blocking in the atmosphere. In winter, the dipole blocking mainly occurs in the west regions of the Pacific and the Atlantic, and the heat source over the western part of the two oceans is advantageous to the formation of dipole blocking in the west of two oceans. However, in summer, the dipole blocking could be formed in the east part of the two oceans, and the heat source over the eastern part of two continents is favourable for the formation of dipole blocking in the east regions of two oceans.

Study of the Optimal Precursors for Blocking Events

The precursors of dipole blocking are obtained by a numerical approach based upon a quasi-geostrophic barotropic planetary- to synoptic-scale interaction model without topography and with a localized synoptic-scale wave-maker. The optimization problem related to the precursors of blocking is formulated and the nonlinear optimization method is used to examine the optimal synoptic-scale initial field successfully. The results show that the prominent characteristics of the optimal synoptic-scale initial field are that the synoptic-scale wave train structures exist upstream of the incipient blocking. In addition, the large-scale low/high eddy-forcing pattern upstream of the incipient blocking is an essential precondition for the onset of dipole blocking.