South Atlantic Ocean cyclogenesis climatology simulated by regional climate model (RegCM3)

Abstract

A detailed climatology of the cyclogenesis over the Southern Atlantic Ocean (SAO) from 1990 to 1999 and how it is simulated by the RegCM3 (Regional Climate Model) is presented here. The simulation used as initial and boundary conditions the National Centers for Environmental Prediction—Department of Energy (NCEP/DOE) reanalysis. The cyclones were identified with an automatic scheme that searches for cyclonic relative vorticity (ζ₁₀) obtained from a 10-m height wind field. All the systems with ζ₁₀ ≤ −1.5 × 10⁻⁵ s⁻¹ and lifetime equal or larger than 24 h were considered in the climatology. Over SAO, in 10 years were detected 2,760 and 2,787 cyclogeneses in the simulation and NCEP, respectively, with an annual mean of 276.0 ± 11.2 and 278.7 ± 11.1. This result suggests that the RegCM3 has a good skill to simulate the cyclogenesis climatology. However, the larger model underestimations (−9.8%) are found for the initially stronger systems (ζ₁₀ ≤ −2.5 × 10⁻⁵ s⁻¹). It was noted that over the SAO the annual cycle of the cyclogenesis depends of its initial intensity. Considering the systems initiate with ζ₁₀ ≤ −1.5 × 10⁻⁵ s⁻¹, the annual cycle is not well defined and the higher frequency occurs in the autumn (summer) in the NCEP (RegCM3). The stronger systems (ζ₁₀ ≤ −2.5 × 10⁻⁵ s⁻¹) have a well-characterized high frequency of cyclogenesis during the winter in both NCEP and RegCM3. This work confirms the existence of three cyclogenetic regions in the west sector of the SAO, near the South America east coast and shows that RegCM3 is able to reproduce the main features of these cyclogenetic areas.