Atmospheric modes fiddling the simulated ENSO impact on tropical cyclone genesis over the Northwest Pacific

Abstract

The El Niño-Southern Oscillation (ENSO) is crucial to the interannual variability of tropical cyclone (TC) genesis over the western North Pacific (WNP). However, most state-of-the-art climate models exhibit a consistent pattern of uncertainty in the simulated TC genesis frequency (TCGF) over the WNP in ENSO phases. Here, we analyze large ensemble simulations of TC-resolved climate models to identify the source of this uncertainty. Results show that large uncertainty appears in the South China Sea and east of the Philippines, primarily arising from two distinct atmospheric modes: the Matsuno-Gill-mode (MG-mode) and the Pacific-Japan-like pattern (PJ-mode). These two modes are closely associated with anomalous diabatic heating linked to tropical precipitation bias in model simulations. By conditionally constraining either of the modes, we can significantly reduce model uncertainty in simulating the dipole structure of the TCGF anomalies, confirming that it is the atmospheric circulation bias in response to tropical precipitation bias that causes uncertainty in the simulated WNP TCGF.

Remote effect of tropical south Atlantic sea surface temperature anomalies on April–June accumulated cyclone energy over the western North Pacific

“…Given a significant inverse correlation between Niño-3.4 and TSA SSTAs (r = −0.32; p = 0.02), warm and cool TSA years are classified using a ±0.8 standard deviation threshold for the TSA SSTA index, while excluding El Niño and La Niña years with a magnitude of the Niño-3.4 SSTA index greater than 0.8 standard deviations. This threshold of 0.8 standard deviation has been used to select years in previous TC-related studies (e.g., Zhan et al 2011, Zhao et al 2023, Shi et al 2024. Our results remain relatively unchanged, if other thresholds (e.g., 0.6 or 1 standard deviation) are used (tables not shown).…”

Seasonal Cycle Delay of the Western North Pacific Tropical Cyclone Genesis Frequency in CMIP6 Simulations

“…That means uncertainty of the atmospheric internal variability may also influence the simulated TCGF biases. For instance, Zhao et al (2023) suggest that there is a large uncertainty in the TC genesis simulation over western WNP, which originates from the Gill-type response (Gill, 1980) and Pacific-Japan wave train (Nitta, 1989) excited by diabatic heating associated with the precipitation simulation bias, which in turn triggers a series of anomalies in the large-scale atmospheric circulation. Feng et al (2023) pointed out that the anomalous cyclonic circulation at 850 hPa and the weakening of the WNPSH, including the stronger connection between the tropics and the subtropics, are responsible for the bias in the simulation of the location of TC genesis over the WNP in high-resolution atmosphere-only models.…”

Distinct Modulations of Northwest Pacific Tropical Cyclone Precipitation by Atlantic Multidecadal Oscillation and Interdecadal Pacific Oscillation

“…). Previous studies have explained the extratropics-tropics interactions from intraseasonal to interannual time scales through the Pacific-Japan pattern (PJ mode; Kubota et al, 2016;Takemura & Mukougawa, 2020;Zhao, Zhan, et al, 2023) forced by tropical SST anomalies, which can be also projected to decadal time scale. However, this study does not extensively discuss extratropic feedback to SE TCP.…”