Downstream development of baroclinic waves in the midlatitude jet induced by extratropical transition: A case study

Abstract

This study uses eddy kinetic energy analysis and a targeting method to investigate how an extratropical transition (ET) event induced downstream development (the modification of the midlatitude flow downstream of the ET system) in the midlatitude jet environment. The downstream development showed distinct characteristics of “coupling development” and being “boundary-trapped”. Eddies (potential disturbances) first developed at the upper levels, and these triggered lower-level eddy development, with all eddies decaying away from the tropopause and the surface. Thereafter, a lower-level eddy caught up with the upper-level eddy ahead of it, and they coupled to form a cyclone extending through the whole troposphere. Vertical ageostrophic geopotential flux may be a crucial dynamic factor throughout the eddy’s lower-level growth, boundary-trapping, and coupling development.