Climatology of Tropical Cyclone Seed Frequency and Survival Rate in Tropical Cyclones

Abstract

Elucidating the mechanism that determines the number of tropical cyclones (TCs) is fundamental for understanding variations in TC activity and predicting future changes. An average of about 80 TCs form each year around the world, with the exact number varying interannually and seasonally (Gray, 1968;Schreck et al., 2014;Webster et al., 2005). Although these variations have been described in relation to large-scale environmental fields represented by a genesis potential index (Emanuel & Nolan, 2004;Gray, 1975;Murakami & Wang, 2010;Tippett et al., 2011), such a relationship does not necessarily hold for future global warming conditions (Camargo et al., 2014). Davis et al. (2008) proposed focusing on pre-TC vortices to clarify how large-scale conditions affect cyclogenesis efficiency. The modulation of TC frequency by the Madden-Julian Oscillation (MJO) is more attributed to tropical depression (TD) frequency than to the probability of TDs intensifying in the western Pacific and the Indian Ocean (Duvel, 2015;Liebmann et al., 1994), though TDs are relatively mature. Recent studies considered TC frequency as the product of the number of weak pre-TC vortices (TC seeds) and the percentage of TC seeds that develop to TCs (survival rate), and proposed that this framework could help to uncover the mechanism behind the variation in TC frequency (Sugi et al., 2020;Vecchi et al., 2019;Yamada et al., 2021). To determine the change in TC frequency due to global warming, for example, it has been suggested that the change in TC seed frequency is most important (Sugi et al., 2020;Vecchi et al., 2019). However, an analysis of results from multiple high-resolution models showed that the contribution of survival rate to TC frequency cannot be ignored (Yamada et al., 2021). Such analyses of TC frequency have more

Model Spread in the Tropical Cyclone Frequency and Seed Propensity Index Across Global Warming and ENSO‐Like Perturbations

“…We have shown that SPI describes the propensity to generate convective weak vorticies, which is a simple definition of seeds based only on the precipitation and vorticity fields. Alternatively, seeds are defined in some studies by using a weaker vorticity threshold in the TC tracking algorithm (Ikehata & Satoh, 2021; Sugi et al., 2020; Vidale et al., 2021; Yamada et al., 2021). Our definition and the alternative definition of seeds have similar spatial distributions and transition probability to TCs (Hsieh, Vecchi, et al., 2020).…”

“…In the transition stage, a seed evolves into a TC with a probability that depends on the ventilation index, which is a function of the environmental potential intensity, saturation deficit, and vertical wind shear (Hoogewind et al., 2020; Hsieh, Vecchi, et al., 2020; Tang & Camargo, 2014; Vecchi et al., 2019; Yang et al., 2021). The transition probability is less important to explain the response of TC frequency to climate change (Hsieh, Vecchi, et al., 2020), but it is important to explain the response to the annual cycle (Yang et al., 2021) and to the interannual variability (Ikehata & Satoh, 2021).…”

Prediction of Tropical Cyclogenesis Based on Machine Learning Methods and Its SHAP Interpretation

“…To filter out weak TC seeds, a tropical disturbance needs to have a lifetime of at least 3 days, and for at least 4 six‐hourly time steps, along with a smoothed 850 hPa vorticity that is greater than 2 × 10 −5 s −1 . These requirements are modified from those in Ikehata and Satoh (2021). A final criterion is the mean precipitation in a centered box of 5 × 5° need to exceed 0.5 mm/hr also for more than 4 time steps, in order to remove any dry vortex.…”

The Role of Precursor Disturbances on the Modulation of Western Pacific Tropical Cyclogenesis by the Madden‐Julian Oscillation

“…In contrast, studies have suggested that the variation of TCPD has a negligible impact on TC frequency (Danso et al., 2022; Emanuel, 2022; Ikehata & Satoh, 2021; Patricola et al., 2018), suggesting that the large‐scale environment controls TC frequency mainly through the transition or survival rate of TCPDs. Recent modeling studies have shown that the number of simulated TCs in the Atlantic basin is unaffected by the complete removal of African Easterly Waves (AEWs), the basin's primary source of TCPDs (Danso et al., 2022; Patricola et al., 2018).…”