Influence of air–sea coupling on Indian Ocean tropical cyclones

Premonsoon/Postmonsoon Bay of Bengal Tropical Cyclones Intensity: Role of Air‐Sea Coupling and Large‐Scale Background State

“…In observations, the two TC-prone periods (defined as months with more than 5% of the annual average TC-day count) are April-May and October-December (Figure 1b), and we will use those definitions in the following for the premonsoon and postmonsoon seasons. As already mentioned in previous papers Lengaigne et al, 2018), the model however strongly overestimates cyclogenesis in the BoB, with an average 11.1 TCs/year compared to 3.2 TCs/year in observations. The model seasonal TCs distribution in the BoB however displays some systematic biases compared to observations, including an overestimation of TCs occurrence during the summer monsoon (June-September) and an underestimation in November-December.…”

“…Lengaigne et al (2018) indeed demonstrated that comparing the statistics of simulated TCs in these twin experiments allows diagnosing the influence of air-sea coupling on TCs. While individual TC tracks are different in the two simulations, we will examine statistical differences in, for example, the number of cyclones or cyclone intensity distribution in the rest of the paper.…”

“…A 21-year coupled simulation (CPL) is first performed using the above 1989-2009 lateral boundary conditions. The two experiments have a very similar atmospheric background state over the BoB, in particular for variables that have a well-documented influence on TCs (supporting information Figure S1), so that the TC differences between the two experiments are dominated by the effects of air-sea coupling (also see Lengaigne et al, 2018). As a result, the FOR simulation does not account for any oceanic feedback on TCs.…”

“…In a recent study, Lengaigne et al (2018) investigated the influence of air-sea coupling on TC characteristics in both hemispheres of the Indian Ocean, comparing a one fourth degree regional coupled ocean- atmosphere model 20-year-long simulation with a twin forced atmospheric experiment. They found that coupling reduces the number of TCs and their intensity in both hemispheres, as the TC-induced cooling reduces the upward enthalpy fluxes under TCs.…”

“…TCs from both simulations are tracked using the same methodology as in Samson et al (2014) and Lengaigne et al (2018) using criteria similar to those considered in previous studies (Jourdain et al, 2011;Jullien et al, 2014): TCs from both simulations are tracked using the same methodology as in Samson et al (2014) and Lengaigne et al (2018) using criteria similar to those considered in previous studies (Jourdain et al, 2011;Jullien et al, 2014):…”