Study of a cyclone wave in the Drake Passage region

Abstract

The evolution of a ridge-trough system that occurred in the periphery of the Antarctic in late July 1986 is examined. A cyclonic disturbance within the polarward side of a blocking anticyclone, developed into an intense closed circulation to the east of the Drake Passage. The maturity and decay of the system took place over the Weddell Sea, a location for cyclolysis according to the climatology. The eddy kinetic energy budget of this wave was evaluated, using 12-h ECMWF operational analyses, in order to identify the physical processes that contributed to its development. Particularly, attention was given to the role of the downstream baroclinic development process in the growth and decay of energy centers associated with the cyclonic wave. The initial growth of an eddy kinetic energy center near 90ºW was mastered by the convergence ofageostrophic geopotential fluxes, originated from a previous energy center in dissipation stage. The center developed in a region of relatively low baroclinicity and then the incidence of the baroclinic conversion process was not significant. As the center intensified, it produced strong radiation of energy downstream to the east of Drake Passage, where a deep cyclone developed, with a new associated eddy kinetic energy center. It was found that the convergence of ageostrophic geopotential fluxes and, in lesser extent, the baroclinic conversion were the most important physical processes during the early stage of growing. Finally, this last energy center decayed, mainly, by flux divergence.