Abstract
An explosive cyclogenesis over the east coast of South America was simulated during the period from 28 to 30 May 1999, using a limited-area hydrostatic model with 100 km horizontal resolution. The simulations showed that surface heat flux had an important contribution in developing the explosive cyclogenesis, and that the latent heat flux (LHF) has a larger contribution than the sensible heat flux (SHF). In the absence of a total heat flux (THF, ie. LHF plus SHF), the cyclone was 6 hPa shallower than in the control simulation (with THF). Without LHF the cyclone was 4 hPa shallower, while without SHF the cyclone presented the same intensity as the control simulation. The sensitivity experiments show the following effects of surface heat fluxes: i) the magnitudes and extensions of the effects grew with simulation time; ii) the maximum effects appeared in the southeastern part of the cyclone (warm front sector); iii) the LHF effects were 2–3 times larger than the SHF ones; and iv) the LHF effects were observed in the neighborhood of the cyclone, while the SHF effects were more spread out over the domain. In the THF absent experiment, a drier and colder environment was generated, mainly in the lower troposphere over the ocean, decreasing the environmental potential instability, latent heat release and cyclone intensification. Although the THF effects became larger during the most rapid development phase, they must have been present before this period because they preconditioned the environment for explosive development. Thus, to simulate or forecast the explosive cyclogenes on the South American east coast, an adequate representation of the planetary boundary layer is necessary.
