Subtropical Cyclone Anita's Potential to Tropical Transition Under Warmer Sea Surface Temperature Scenarios

Abstract

On 6 March 2010, Anita, the first subtropical cyclone observed over the South Atlantic Ocean, formed near the southeastern coast of Brazil, and during its life cycle, Anita almost acquired a tropical structure. The potential of Anita to undergo tropical transition in scenarios of increased sea surface temperature (SST) was investigated through a set of numerical sensitivity experiments. The results show that, if the SST had been 2°C warmer throughout Anita's life cycle, the system would have undergone tropical transition in its maturity stage; however, if the SST had increased only during Anita's quasi‐stationary period, the tropical transition completion would have occurred only with higher values of SST (6°C).

Iba: The First Pure Tropical Cyclogenesis Over the Western South Atlantic Ocean

“…SST anomaly in Iba's genesis region overcame the threshold of +2.0°C that Reboita et al. (2019b) discussed that would be necessary for Anita subtropical cyclone to make the transition to tropical. In the Iba's genesis area the negative anomalies of top net thermal radiation (Figure 9d) indicate anomalous cloud cover associated with convective activity in the previous cyclogenesis environment.…”

“…Other anomalous features contributing to Iba's genesis are the warmer SST, with anomaly above +2.0°C over the genesis region (Figure 9a), the cyclonic relative vorticity (negative) anomaly at 850 hPa and that due to the horizontal wind shear at 925 hPa (Figure 9b and 9c). SST anomaly in Iba's genesis region overcame the threshold of +2.0°C that Reboita et al (2019b) discussed that would be necessary for Anita subtropical cyclone to make the transition to tropical. In the Iba's genesis area the negative anomalies of top net thermal radiation (Figure 9d) indicate anomalous cloud cover associated with convective activity in the previous cyclogenesis environment.…”

“…Although the environmental conditions over the SAO are less favorable for tropical cyclogenesis (Gray, 1968; Pezza & Simmonds, 2005), in certain situations the middle‐upper circulation provides adequate conditions for subtropical cyclogenesis as well as TT (da Rocha et al., 2019; Dias Pinto et al., 2013; Gozzo et al., 2014; McTaggart‐Cowan et al., 2006; Reboita et al., 2019a, 2019b). These conditions are propitiated, for example, by the presence of a small‐amplitude trough or a cut‐off low at mid‐levels, a weak vertical wind shear, and moisture flux convergence at lower levels.…”

Relationship between daily atmospheric circulation patterns and South Atlantic Convergence Zone (SACZ) events

“…9c) over the Atlantic Ocean, close to the South region of Brazil. This cyclone is usually not frontal and shows subtropical features (Evans and Braun, 2012;Brasiliense et al, 2018;Reboita et al, 2019). A real sequence of surface and altitude charts related to a CG pattern corresponds to 10-12 February 2007, when an extratropical cyclone developed over the Atlantic Ocean off the coast between SC and SP states (Fig.…”

Climatologia do Índice do Potencial de Gênese de Ciclones Tropicais nos Oceanos Adjacentes à América do Sul

“…Em alguns casos de ciclones extratropicais, os fluxos podem contribuir significativamente para o seu desenvolvimento inicial (Kuo et al 1991, Rogers & Bosart, 1991, antes da rápida redução da pressão, como nos ciclones explosivos (Bosart & Lin, 1984;Uccellini et al, 1987), ou na fase de rápido aprofundamento (Kuo & Reed, 1988;Chang et al., 1996). Outro exemplo é o caso do ciclone subtropical Anita, dado que este sistema poderia ter se transformado em tropical se os fluxos de calor latente e sensível tivessem sido mais intensos na região de atuação do sistema (Reboita et al, 2019c).…”