Exploring Western North Pacific Tropical Cyclone Activity in the High‐Resolution Community Atmosphere Model

Abstract

High‐resolution climate models (∼28 km grid spacing) can permit realistic simulations of tropical cyclones (TCs), thus enabling their investigation in relation to the climate system. On the global scale, previous works have demonstrated that the Community Atmosphere Model (CAM) version 5 presents a reasonable TC climatology under prescribed present‐day (1980–2005) forcing. However, for the Western North Pacific (WNP) region, known biases in simulated TC genesis frequency and location under‐represent the basin's dominant share in observations. This study addresses these model biases in WNP by evaluating WNP TCs in a decadal simulation, and exploring potential improvements through nudging experiments. Among the major environmental controls of TC genesis, the lack of mid‐level moisture is identified as the leading cause of the deficit in simulated WNP TC genesis over the Pacific Warm Pool. Subsequent seasonal experiments explore the effect of constraining the large‐scale environment on TC development by nudging WNP temperature field toward reanalysis at various strengths. Temperature nudging elicits a significant response in TC genesis and intensity development, as well as in moisture and convection over the Warm Pool. These responses are sensitive to the choice of nudging timescale. Overall, the nudging experiments demonstrate that improvements in the large‐scale environment can lead to improvements in simulated TCs, suggesting future model developments in relation to model physics. In this way, the potential improvements in model fidelity will contribute to the understanding of how the mean state of current or future climates may give rise to extremes such as TCs.

Tropical cyclones in global high-resolution simulations using the IPSL model

“…. In fact, using nudging experiments, Wu et al (2022) recently highlighted that a similar TC deficit in CAM could be alleviated by correcting a humidity bias that resembles ours.…”

Tropical Cyclones in Global High-Resolution Simulations using the IPSL Model

“…It is well known that low vorticity and dry environments are both limiting factors for TC genesis, which suggests that these two biases may explain the reduced and northward shift of the TC's main development region in the WNP. Interestingly, Wu et al (2022) recently explored the origin of a similar humidity bias in CAM and showed that it could be alleviated by nudging the humidity to the observed climatology in their model. It would be interesting to explore whether this is also the case in the IPSL model using similarly nudged numerical experiments.…”