Surface temperature dependence of tropical cyclone‐permitting simulations in a spherical model with uniform thermal forcing

Merlis, Timothy M.; Zhou, Wenyu; Held, Isaac M.; Zhao, Ming

doi:10.1002/2016gl067730

Cited by 57 publications

(56 citation statements)

References 22 publications

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“…Though other factors like surface relative humidity also affect the air‐sea disequilibrium, an increase with SST is the leading‐order behavior for radiatively forced climate changes and this, in turn, increases potential intensity [ Emanuel , ; Emanuel and Sobel , ]. In contrast, the influence of SST on TC genesis is still unclear, particularly at the basin scale [ Bengtsson et al , ; Emanuel et al , ; Sugi et al , ; Zhao et al , ; Knutson et al , ; Held and Zhao , ; Emanuel , ; Merlis et al , ; Zhao et al , ; Merlis et al , ; Knutson et al , ; Sugi et al , ; Walsh et al , ]. We emphasize that our analysis of SST G is a frequency‐independent statistic, and neither implies that a warmed SST environment favors nor disfavors TC genesis frequency.…”

Section: Warming Trends In Sst At Tc Genesismentioning

confidence: 99%

Observed warming trend in sea surface temperature at tropical cyclone genesis

Defforge

Merlis

2017

Geophysical Research Letters

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Tropical cyclone (TC) activity is influenced by environmental factors, and it is expected to respond to anthropogenic climate change. However, there is observational uncertainty in historical changes in TC activity, and attributing observed TC changes to anthropogenic forcing is challenging in the presence of internal climate variability. The sea surface temperature (SST) is a well‐observed environmental factor that affects TC intensity and rainfall. Here we show that the SST at the time of TC genesis has a significant warming trend over the three decades of the satellite era. Though TCs are extreme events, the warming trend at TC genesis is comparable to the trend in SST during other tropical deep convection events and the trend in SST in the TC main development regions throughout the TC season. This newly documented, observed signature of climate change on TC activity is also present in high‐resolution global atmospheric model simulations that explicitly simulate TCs.

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Section: Warming Trends In Sst At Tc Genesismentioning

confidence: 99%

Observed warming trend in sea surface temperature at tropical cyclone genesis

Defforge

Merlis

2017

Geophysical Research Letters

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“…TCs are among the most dangerous manifestations of organized convection, with several impacts including wind damage, storm surge, and potentially extreme rainfall. Studies of rotating RCE have shown that self‐aggregation can take the form of spontaneous tropical cyclogenesis (Bretherton et al, ; Boos et al, ; Davis, ; Held & Zhao, ; Khairoutdinov & Emanuel, ; Merlis et al, ; Muller & Romps, ; Nolan et al, ; Reed & Chavas, ; Shi & Bretherton, ; Wang et al, ; Wing et al, ; Zhou et al, , ). Idealized simulations in these studies led to TC formation from both a prescribed moist bubble or vortex and white noise random convection.…”

Section: Introductionmentioning

confidence: 99%

Tropical Cyclogenesis From Self‐Aggregated Convection in Numerical Simulations of Rotating Radiative‐Convective Equilibrium

Carstens

Wing

2020

J Adv Model Earth Syst

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In a modeled environment of rotating radiative-convective equilibrium (RCE), convective self-aggregation may take the form of spontaneous tropical cyclogenesis. We investigate the processes leading to tropical cyclogenesis in idealized simulations with a three-dimensional cloud-permitting model configured in rotating RCE, in which the background planetary vorticity is varied across f -plane cases to represent a range of deep tropical and near-equatorial environments. Convection is initialized randomly in an otherwise homogeneous environment, with no background wind, precursor disturbance, or other synoptic-scale forcing. We examine the dynamic and thermodynamic evolution of cyclogenesis in these experiments and compare the physical mechanisms to current theories. All simulations with planetary vorticity corresponding to latitudes from 10 • -20 • generate intense tropical cyclones, with maximum wind speeds of 80 m s −1 or above. Time to genesis varies widely, even within a five-member ensemble of 20 • simulations, indicating large stochastic variability. Shared across the 10 • -20 • group is the emergence of a midlevel vortex in the days leading to genesis, which has dynamic and thermodynamic implications on its environment that facilitate the spin-up of a low-level vortex. Tropical cyclogenesis is possible in this model at values of Coriolis parameter as low as that representative of 1 • . In these experiments, convection self-aggregates into a quasicircular cluster, which then begins to rotate and gradually strengthen into a tropical storm, aided by strong near-surface inflow that is already established days prior. Other experiments at these lower Coriolis parameters instead self-aggregate into a nonrotating elongated band and fail to undergo cyclogenesis over the 100-day simulation. Plain Language SummaryDespite decades of research on tropical cyclones, we still do not have a universal agreement on how they form. Current theories agree that some sort of disturbance must exist beforehand, but our knowledge of the processes leading to a surface-based cyclone remains limited. To address this, we examine idealized numerical simulations in which convection is allowed to spontaneously cluster together on its own due to interactions between clouds, moisture, and radiation. Using this framework, we obtain a complete view of the tropical cyclone formation process, including the formation of the precursor disturbance. New to this study is the use of lower values of background rotation to simulate the formation of hurricanes at lower latitudes. Overall, simulations are run to represent latitudes from 0.1 • -20 • . Every simulation corresponding to latitudes between 10 • and 20 • produces a major hurricane, a few days after a vortex emerges a few kilometers aloft and affects its surrounding environment. Some simulations at 1 • and 2 • lead to formation of a weaker tropical cyclone, after cloud s have first organized into one circular cluster. In other low-latitude cases, this cluster of storms is instead a long band and fa...

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“…These projections are obtained using high-resolution global climate models [e.g., Murakami et al, 2012;Zhao and Held, 2012], high-resolution idealized experiments [Rappin et al, 2010;Merlis et al, 2016], as well as using dynamical downscaling using regional climate models [Knutson et al, 2008;Bender et al, 2010]. For instance, Knutson et al [2015] considered storms produced by a global model, but then used a higher-resolution model in order to simulate the most intense storms.…”

Section: Introductionmentioning

confidence: 99%

Dynamical downscaling of tropical cyclones from CCSM4 simulations of the Last Glacial Maximum

Yoo

Galewsky

Camargo

et al. 2016

J Adv Model Earth Syst

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Dynamical downscaling of simulations of the Last Glacial Maximum (LGM) and late twentieth century (20C) were conducted using the Weather Research and Forecasting (WRF) model with the aim of (1) understanding how the downscaled kinematic and thermodynamic variables influence simulated tropical cyclone (TC) activity over the western North Pacific during the LGM and the 20C periods and (2) to test the relevance of TC genesis factors for the colder LGM climate. The results show that, despite the lower temperatures during the LGM, the downscaled TC climatology over the western North Pacific in the LGM simulation does not differ significantly from that in the 20C simulation. Among the TC environmental factors, the TC potential intensity, mid‐tropospheric entropy deficit, and vertical wind shear during the LGM were consistent with previous analyses of TC genesis factors in LGM global climate model simulations. Changes in TC genesis density between the LGM and the 20C simulations seem to be well represented by the ventilation index, a nondimensional measure of the combined effects of vertical wind shear, and thermodynamic properties, suggesting the potential applicability of those factors for TC activity evaluation during the LGM and possibly other climates.

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Surface temperature dependence of tropical cyclone‐permitting simulations in a spherical model with uniform thermal forcing

Cited by 57 publications

References 22 publications

Observed warming trend in sea surface temperature at tropical cyclone genesis

Observed warming trend in sea surface temperature at tropical cyclone genesis

Tropical Cyclogenesis From Self‐Aggregated Convection in Numerical Simulations of Rotating Radiative‐Convective Equilibrium

Dynamical downscaling of tropical cyclones from CCSM4 simulations of the Last Glacial Maximum

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