Large-scale dynamics of tropical cyclone formation associated with ITCZ breakdown

Wang, Quan; Kieu, Chanh; Vu, The-Anh

doi:10.5194/acp-19-8383-2019

Cited by 8 publications

(10 citation statements)

References 42 publications

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“…Furthermore, the maximum number of the daily TC genesis events is not arbitrary but capped by a limit of approximately 10 genesis events at any given day. Such an upper bound in the daily TC genesis events for each episode is consistent with a recent theoretical estimation of the TC disturbances in the ITCZ breakdown model by Wang et al (2019), which showed that the maximum number of TC disturbances for any given day cannot be larger than 12 due to the internal constraint of the tropical dynamics.…”

Section: Resultssupporting

confidence: 89%

A Numerical Study of the Global Formation of Tropical Cyclones

Kieu

Chavas

et al. 2020

Preprint

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This study examines the large-scale factors that govern global tropical cyclone (TC) formation and an upper bound on the annual number of TCs. Using idealized simulations for an aquaplanet tropical channel, it is shown that the tropical atmosphere has a maximum capacity in generating TCs, even under ideal environmental conditions. Regardless of how favorable the tropical environment is, the total number of TCs generated in the tropical channel possesses a consistent cap across experiments. Analyses of daily TC genesis events reveal further that global TC formation is intermittent throughout the year in a series of episodes at a roughly 2-week frequency, with a cap of 8-10 genesis events per day. Examination of different large-scale environmental factors shows that 600-hPa moisture content, 850-hPa absolute vorticity, and vertical wind shear are the most critical factors for this global episodic TC formation. Specifically, both the 850-hPa absolute vorticity and the 600-hPa moisture are relatively higher at the onset of TC formation episodes. Once TCs form and move to poleward, the total moisture content and the absolute vorticity in the main genesis region subside, thus reducing large-scale instability and producing an unfavorable environment for TCs to form. It takes ∼2 weeks for the tropical atmosphere to remoisten and rebuild the large-scale instability associated with the Intertropical Convergence Zone before a new TC formation episode can occur. These results offer new insight into the processes that control the upper bound on the global number of TCs in the range of 80-100 annually. Plain Language Summary Understanding the mechanisms behind the upper bound on the global tropical cyclone (TC) number is important yet still elusive. Using TC simulations on an aquaplanet tropical channel, this study shows that the tropical atmosphere possesses a maximum capacity in producing TCs globally, regardless of how ideal the environmental conditions are. In particular, global TC formation does not occur throughout the year but in a series of episodes with a frequency of about 2 weeks, with ∼8-10 TCs per episode. Examination of the TC genesis index shows that midlevel moisture content and 850-hPa absolute vorticity associated with the ITCZ instability are key factors governing the episodic global TC formation.

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Section: Resultssupporting

confidence: 89%

A Numerical Study of the Global Formation of Tropical Cyclones

Kieu

Chavas

et al. 2020

Preprint

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“…From modeling perspectives, the simulation of TC genesis frequency is known to be sensitive to subgrid‐scale physical parameterizations (Bacmeister et al., 2014; Zarzycki & Jablonowski, 2015; Zhao et al., 2012), physics–dynamics coupling (e.g., X. Li et al., 2020), dynamical core (K. Reed et al., 2015), or choices in the tracking algorithm (Horn et al., 2014; Zarzycki & Ullrich, 2017). More broadly, various physical arguments have been proposed regarding the constraints of TC genesis frequency in models and observations (Hoogewind et al., 2020; Vu et al., 2021; Q. Wang et al., 2019). The investigation on modeled TC genesis frequency is deferred to future work.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

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

Xin

Reed

Callaghan

et al. 2021

Earth and Space Science

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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.

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“…As SST is uniform in these simulations, it should be thought of as analogous to global (or tropical) mean SST on a more realistic planet, not relative SST. The relevance of these rotating RCE simulations to Earth's climate can only be indirect, because the number of TCs in them depends on how many can fit in a tightly-packed configuration, while the number of TCs that exist in Earth's real climate is far less than the number that could fit within the global area that has a favorable environment (Hoogewind et al, 2020;Vu et al, 2020;Q. Wang, Kieu, & Vu, 2019).…”

Section: Idealized Modelingmentioning

confidence: 99%

Tropical Cyclone Frequency

et al. 2021

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Tropical cyclone frequency is the number of tropical cyclones occurring over a given time period and spatial domain. Here, we are most interested in the annual frequency over either the entire globe or individual basins, that is, particular distinct portions of the tropical oceans over which tropical cyclones occur (such as the North Atlantic, South Indian, etc.). Tropical cyclone frequency strongly controls the total hazard and risk from tropical cyclones, because no other aspect of a tropical cyclone matters if it does not occur. We are particularly interested in how tropical cyclone frequency is related to climate: what factors in the climate system determine the climatological frequency in the present and recent past, its natural variability, and its possible changes as a consequence of anthropogenic global warming.Other dimensions of the relationship between tropical cyclones and climate are understood with some confidence. Recent reviews indicate relatively high confidence that, on average, global warming increases the precipitation produced by tropical cyclones, and also intensifies their winds (e.g.

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Large-scale dynamics of tropical cyclone formation associated with ITCZ breakdown

Cited by 8 publications

References 42 publications

A Numerical Study of the Global Formation of Tropical Cyclones

A Numerical Study of the Global Formation of Tropical Cyclones

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

Tropical Cyclone Frequency

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