The Role of Land–Sea Topography in Blocking Formation in a Block–Eddy Interaction Model

Abstract

This paper is an extension of a theoretical study by Luo on the effect of large-scale land?sea contrast (LSC) topography on the formation of an eddy-driven blocking. It is found that the topography term can be included explicitly in the blocking evolution equation because of the inclusion of the higher-order wave?topography interaction. Although the blocking flow cannot be excited purely by the LSC topography, the LSC topography is found to be capable of enhancing the amplification of the dipole component in a blocking flow associated with upstream synoptic-scale eddies. In this case, a strong omega-type blocking high can be driven by the joint action of synoptic-scale eddies and LSC topography. This seems to provide an explanation of a difference in blocking intensity between the Northern and Southern Hemispheres. The most important finding of this paper is that in the presence of LSC topography the double jets that appear during the onset of an eddy-driven dipole block collapse into a strong single westerly jet that is within the south side of an omega-type blocking high, which is different from the result predicted by the theoretical model proposed in Luo?s previous work.