Energetics of southeastern Pacific cut-off lows

Abstract

The existence of cut-off lows (COLs) over South Pacific and South America is often associated with adverse weather events such as intense precipitation over the central region of South America, frost episodes in southern Brazil and the development of Andes lee cyclones and intense cyclones over the southern coast of Brazil. Despite this importance, the formation and maintenance mechanisms of the COLs are not well understood. To detail the significant variability in terms of the eddy kinetic energy equation for fifty cases of COLs that formed over the southeastern Pacific Ocean is the aim of this study. Only the cases of COLs that formed over the ocean and remained there during most of their life were chosen. The main terms of the equation [ageostrophic flux convergence (AFC), baroclinic conversion (BRC) and barotropic conversion (BRT)] were calculated using the 6-hourly gridded data from the National Centers for Environmental Prediction/Department of Energy reanalysis. The formation mechanism of the COLs was associated with BRC and AFC. During the midlife period, the BRC term converted eddy kinetic energy to eddy potential energy and the AFC had a positive contribution until 6 h after the midlife point. In the dissipation phase, the BRC term remained positive and AFC became negative. The BRT extracted kinetic energy from the COL during the entire life cycle. The AFC term was the most important in all phases of the cut-off lifetime, and it was the responsible for extending the cut-off lifetime while the others terms were negatives.