The Role of Latent and Sensible Heat Fluxes in an Explosive Cyclogenesis over the South American East Coast

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.

Synoptic climatology of warm fronts in Southeastern South America

“…MSLP anomaly minimum is deeper in winter, besides being located farther north (Figure (c)). Other researchers related this MSLP anomaly pattern to cyclogenesis over Uruguay, mainly in winter (Gan and Rao, ; Funatsu et al , ; Dal Piva et al , ). The 850‐hPa wind anomalies on day +1 form a stream from Bolivia to eastern SESA, where the wind drastically shifts at the warm front.…”

Driving Roles of Tropospheric and Stratospheric Thermal Anomalies in Intensification and Persistence of the Arctic Superstorm in 2012

“…The relatively stable and widely extended Arctic front along the Eurasian Arctic coast supported the storm development for a longer intensification period, a total of 4 days from 3 to 6 August in this superstorm. Second, surface energy flux plays important roles in the midlatitude intense or "bomb" storms (e.g., Heo et al, 2015;Piva et al, 2011;Yoshida & Asuma, 2004). However, the Arctic storm lived most time over the cold ice-covered surface and in a dry atmospheric environment; no obvious diabatic heating is available to support the development of Arctic storms (Simmonds & Rudeva, 2012).…”

Climatologia de ciclones explosivos para a área ciclogenética da América do Sul

“…Roebber (1984) sugere que a maioria dos CEx possuam origem em mecanismos provocados pela instabilidade baroclínica. Entretanto, de acordo com os resultados encontrados por Piva et al (2008Piva et al ( , 2011, obtidos a partir de simulações numéricas, os fluxos de calor latente e sensível no Oceano Atlântico Sul, próximos à costa do sul do Brasil e Uruguai, possuem influência decisiva na intensidade dos ciclones. De acordo com Piva et al (2008Piva et al ( , 2011, as trocas de energia entre o oceano e a atmosfera nessa região ciclogenética da América do Sul são importantes antes da fase de mais rápido desenvolvimento do ciclone, preparando o ambiente, através da maior disponibilidade de energia e umidade, para uma ciclogênese mais intensa.…”

“…Smith (2000) mostrou que a distribuição horizontal do aquecimento é importante para o desenvolvimento de ciclones. Essa distribuição do aquecimento, quando caracteriza-se por altos gradientes horizontais de temperatura, tais como 0,3 ºC km -1 , conforme encontrado por Pezzi et al (2009) na confluência das correntes Brasil-Malvinas, tem relação com os fluxos de calor latente e sensível entre a superfície oceânica e a atmosfera, os quais contribuem para o desenvolvimento de ciclones (Nuss e Anthes, 1987;Davis e Emanuel, 1988;Crescenti e Weller, 1992;Neiman e Shapiro, 1993;Saraiva, 1996;Piva, 2001 e Piva et al, 2008Piva et al, e 2011. Além disso, há a influência da Cordilheira dos Andes (Satyamurty et al, 1980;Gan e Rao, 1994;Sinclair, 1995;Seluchi et al, 1998;Seluchi e Saulo, 1998;Vera et al, 2002;Miky-Funatsu et al, 2004;Hoskins e Hodges, 2005;Mendes et al, 2007), visto que a vorticidade ciclônica associada com o distúrbio transiente perde intensidade ao se aproximar dos Andes devido a redução da coluna atmosférica (Hoskins, 1997), voltando a se intensificar após ultrapassar a cordilheira.…”