Evaluation of the contribution of tropical cyclone seeds to changes in tropical cyclone frequency due to global warming in high-resolution multi-model ensemble simulations

Abstract

Previous projections of the frequency of tropical cyclone genesis due to global warming, even in terms of sign of the change, depends on the chosen model simulation. Here, we systematically examine projected changes in tropical cyclones using six global atmospheric models with medium-to-high horizontal resolutions included in the sixth phase of the Coupled Model Intercomparison Project/High-Resolution Model Intercomparison Project. Changes in the frequency of tropical cyclone genesis could be broken down into the contributions from (i) the tropical cyclone seed, a depression having a closed contour of sea level pressure with a warm core and (ii) the survival rate, the ratio of the frequency of tropical cyclone genesis to that of tropical cyclone seeds. The multi-model ensemble mean indicates that tropical cyclone genesis frequencies are significantly decreased during the period 1990–2049, which is attributable to changes in tropical cyclone seeds. Analysis of the individual models shows that although most models project a more or less decreasing trend in tropical cyclone genesis frequencies and seeds, the survival rate also contributes to the result in some models. The present study indicates the usefulness of decomposition into the frequency of the tropical cyclone seeds and the survival rate to understand the cause of uncertainty in projected frequencies of tropical cyclone genesis.

Why is the Hurricane Season So Sharp?

“…By taking into account seed variability, we demonstrate that the new framework reproduces the hurricane annual cycle much more consistently than the probability alone, and in particular, is able to capture the sharp hurricane season. It also provides a unified framework to view TC annual cycles from various basins, sources (both observations and model simulations), and numerical experiments.Previous studies have shown that the probability and seed framework could help explain diverging responses of TC frequency to radiative climate forcing induced by greenhouse gases(3,11,21,22). Here we test and validate that the new framework also works in a different scenario: climatological variations driven by the annual cycle radiative forcing.…”

Impact of the Boreal Summer Intraseasonal Oscillation on Typhoon Tracks in the Western North Pacific and the Prediction Skill of the ECMWF Model

“…Yoshida and Fudeyasu (2020) found that the frequency of the easterly wave flow pattern, which often transforms into tropical depressions, is the highest in October. Considering the small number of tropical disturbances that transform into TCs, we need to understand how the activity of seeds of TC and their survival rate (the fraction of TC formation to tropical disturbances; Lee et al., 2020; Sugi et al., 2020; Yamada et al., 2021) are modulated by the BSISO and improve the model performance of TC genesis predictions based on this understanding.…”