Are Special Processes at Work in the Rapid Intensification of Tropical Cyclones?

Abstract Probably not. Frequency distributions of intensification and dissipation developed from synthetic open-ocean tropical cyclone data show no evidence of significant departures from exponential distributions, though there is some evidence for a fat tail of dissipation rates. This suggests that no special factors govern high intensification rates and that tropical cyclone intensification and dissipation are controlled by statistically random environmental and internal variability.

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Detected climatic change in global distribution of tropical cyclones

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1922500117 ◽

2020 ◽

Vol 117 (20) ◽

pp. 10706-10714 ◽

Cited By ~ 7

Author(s):

Hiroyuki Murakami ◽

Thomas L. Delworth ◽

William F. Cooke ◽

Ming Zhao ◽

Baoqiang Xiang ◽

...

Keyword(s):

Tropical Cyclone ◽

Spatial Pattern ◽

Climatic Change ◽

Tropical Cyclones ◽

Volcanic Eruptions ◽

Internal Variability ◽

Global Scale ◽

Central Pacific ◽

The North ◽

Limited Length

Owing to the limited length of observed tropical cyclone data and the effects of multidecadal internal variability, it has been a challenge to detect trends in tropical cyclone activity on a global scale. However, there is a distinct spatial pattern of the trends in tropical cyclone frequency of occurrence on a global scale since 1980, with substantial decreases in the southern Indian Ocean and western North Pacific and increases in the North Atlantic and central Pacific. Here, using a suite of high-resolution dynamical model experiments, we show that the observed spatial pattern of trends is very unlikely to be explained entirely by underlying multidecadal internal variability; rather, external forcing such as greenhouse gases, aerosols, and volcanic eruptions likely played an important role. This study demonstrates that a climatic change in terms of the global spatial distribution of tropical cyclones has already emerged in observations and may in part be attributable to the increase in greenhouse gas emissions.

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The Effect of the Ocean Eddy on Tropical Cyclone Intensity

Journal of the Atmospheric Sciences ◽

10.1175/jas4051.1 ◽

2007 ◽

Vol 64 (10) ◽

pp. 3562-3578 ◽

Cited By ~ 105

Author(s):

Chun-Chieh Wu ◽

Chia-Ying Lee ◽

I-I. Lin

Keyword(s):

Tropical Cyclone ◽

Tropical Cyclones ◽

Mixed Layer ◽

Thermal Structure ◽

Critical Role ◽

Strong Mixing ◽

Rapid Intensification ◽

Tropical Cyclone Intensity ◽

Cyclone Intensity ◽

The Impact

Abstract The rapid intensification of Hurricane Katrina followed by the devastation of the U.S. Gulf States highlights the critical role played by an upper-oceanic thermal structure (such as the ocean eddy or Loop Current) in affecting the development of tropical cyclones. In this paper, the impact of the ocean eddy on tropical cyclone intensity is investigated using a simple hurricane–ocean coupled model. Numerical experiments with different oceanic thermal structures are designed to elucidate the responses of tropical cyclones to the ocean eddy and the effects of tropical cyclones on the ocean. This simple model shows that rapid intensification occurs as a storm encounters the ocean eddy because of enhanced heat flux. While strong winds usually cause strong mixing in the mixed layer and thus cool down the sea surface, negative feedback to the storm intensity of this kind is limited by the presence of a warm ocean eddy, which provides an insulating effect against the storm-induced mixing and cooling. Two eddy factors, FEDDY-S and FEDDY-T, are defined to evaluate the effect of the eddy on tropical cyclone intensity. The efficiency of the eddy feedback effect depends on both the oceanic structure and other environmental parameters, including properties of the tropical cyclone. Analysis of the functionality of FEDDY-T shows that the mixed layer depth associated with either the large-scale ocean or the eddy is the most important factor in determining the magnitude of eddy feedback effects. Next to them are the storm’s translation speed and the ambient relative humidity.

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Air-sea Interface Exchanges in Rapidly Intensifying Tropical Cyclones

10.5194/egusphere-egu2020-12109 ◽

2020 ◽

Author(s):

Alexander Soloviev ◽

Breanna Vanderplow ◽

Roger Lukas

Keyword(s):

Tropical Cyclone ◽

Tropical Cyclones ◽

Aerodynamic Drag ◽

Model Verification ◽

Intensity Change ◽

Rapid Decline ◽

Rapid Intensification ◽

Discrete Phase Model ◽

Momentum Exchange ◽

General Terms

Rapid intensification of tropical cyclones is a challenge for forecasters. In 2017, Hurricane Maria intensified to a Category 5 storm within 24 hours and devastated Puerto Rico. The official forecast and all computer models were unable to predict it. Hurricane Dorian had been predicted as a tropical storm; unexpectedly, it intensified into a Category 5 storm and destroyed the Bahamas. Soloviev et al. (2017) suggested that under the assumption of constant enthalpy exchange coefficient, rapid cyclone intensification and decay can be related to the drag coefficient dependence on wind speed including an &#8220;aerodynamic drag well&#8221; around 60 m/s. This concept is in general terms consistent with Emanuel&#8217;s (1988) theory of maximum potential intensity of a tropical cyclone and its extension by Lee et al. (2019). The influence of sea spray is still a significant uncertainty. In order to study the effect of spray on dynamics of tropical cyclones, we have implemented a Volume of Fluid to Discrete-Phase Model (VOF to DPM). This model re-meshes the areas with increased gradients or curvature, which are suspicious for the interface instability. The generated water particles that satisfy the condition of asphericity are converted into Lagrangian particles. The size distribution of spray measured in air-sea interaction facilities is used for the model verification. Due to dynamic remeshing, VOF to DPM resolves spray particle radius from ten micrometers to a few millimeters, which correspond to spume. Results of the numerical simulation show a dramatic increase of spume generation under major tropical cyclones. Though sub-micrometer and micrometer scale spray particles are not resolved in this simulation, they are likely less significant in the momentum exchange at the air-sea interface than spume. These results are expected to contribute to the parameterization and proper treatment of spray in forecasting models, including cases of rapid intensification and rapid decline of tropical cyclones. References: Emanuel, K. A. (1988). The maximum intensity of hurricanes. JAS 45, 1143&#8211;1155. Soloviev, A. V., Lukas, R., Donelan, M.A., Haus, B. K., Ginis, I. (2017). Is the state of the air-sea interface a factor in rapid intensification and rapid decline of tropical cyclones? JGR - Oceans 122, 10174-10183. Lee, W., Kim, S.&#8208;H., Chu, P.&#8208;S., Moon,I.&#8208;J., and Soloviev, A. V. (2019). An index to better estimate tropical cyclone intensity change in the western North Pacific. GRL 46, 8960-8968.

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Young Ocean Waves Favor the Rapid Intensification of Tropical Cyclones—A Global Observational Analysis

Monthly Weather Review ◽

10.1175/mwr-d-18-0214.1 ◽

2018 ◽

Vol 147 (1) ◽

pp. 311-328 ◽

Cited By ~ 4

Author(s):

Lin Zhang ◽

Leo Oey

Keyword(s):

Tropical Cyclone ◽

Surface Waves ◽

Tropical Cyclones ◽

Ocean Waves ◽

Surface Fluxes ◽

Moisture Convergence ◽

Intensity Change ◽

Upper Ocean ◽

Rapid Intensification ◽

Low Level

Abstract Identifying the condition(s) of how tropical cyclones intensify, in particular rapid intensification, is challenging, because of the complexity of the problem involving internal dynamics, environments, and mutual interactions; yet the benefit to improved forecasts may be rewarding. To make the analysis more tractable, an attempt is made here focusing near the sea surface, by examining 23-yr global observations comprising over 16 000 cases of tropical cyclone intensity change, together with upper-ocean features, surface waves, and low-level atmospheric moisture convergence. Contrary to the popular misconception, we found no statistically significant evidence that thicker upper-ocean layers and/or warmer temperatures are conducive to rapid intensification. Instead, we found in storms undergoing rapid intensification significantly higher coincidence of low-level moisture convergence and a dimensionless air–sea exchange coefficient closely related to the youth of the surface waves under the storm. This finding is consistent with the previous modeling results, verified here using ensemble experiments, that higher coincidence of moisture and surface fluxes tends to correlate with intensification, through greater precipitation and heat release. The young waves grow to saturation in the right-front quadrant as a result of trapped-wave resonance for a group of Goldilocks cyclones that translate neither too slowly nor too quickly, which 70% of rapidly intensifying storms belong. Young waves in rapidly intensifying storms also produce relatively less (as percentage of the wind input) Stokes-induced mixing and cooling in the cyclone core. A reinforcing coupling between tropical cyclone wind and waves leading to rapid intensification is proposed.

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Assimilation of All-Sky Infrared Radiances from Himawari-8 and Impacts of Moisture and Hydrometer Initialization on Convection-Permitting Tropical Cyclone Prediction

Monthly Weather Review ◽

10.1175/mwr-d-17-0367.1 ◽

2018 ◽

Vol 146 (10) ◽

pp. 3241-3258 ◽

Cited By ~ 20

Author(s):

Masashi Minamide ◽

Fuqing Zhang

Keyword(s):

Tropical Cyclone ◽

Tropical Cyclones ◽

Inner Core ◽

Geostationary Satellite ◽

Rapid Intensification ◽

Moist Convection ◽

Brightness Temperatures ◽

Sensing Technology ◽

Infrared Radiances ◽

Cyclone Prediction

Abstract This study explores the impacts of assimilating all-sky infrared satellite radiances from Himawari-8, a new-generation geostationary satellite that shares similar remote sensing technology with the U.S. geostationary satellite GOES-16, for convection-permitting initialization and prediction of tropical cyclones with an ensemble Kalman filter (EnKF). This case studies the rapid intensification stages of Supertyphoon Soudelor (2015), one of the most intense tropical cyclones ever observed by Himawari-8. It is found that hourly cycling assimilation of the infrared radiance improves not only the estimate of the initial intensity, but also the spatial distribution of essential convective activity associated with the incipient tropical cyclone vortex. Deterministic convection-permitting forecasts initialized from the EnKF analyses are capable of simulating the early development of Soudelor, which demonstrates encouraging prospects for future improvement in tropical cyclone prediction through assimilating all-sky radiances from geostationary satellites such as Himawari-8 and GOES-16. A series of forecast sensitivity experiments are designed to systematically explore the impacts of moisture updates in the data assimilation cycles on the development and prediction of Soudelor. It is found that the assimilation of the brightness temperatures contributes not only to better constraining moist convection within the inner-core region, but also to developing a more resilient initial vortex, both of which are necessary to properly capture the rapid intensification process of tropical cyclones.

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Development and Nondevelopment of Binary Mesoscale Vortices into Tropical Cyclones in Idealized Numerical Experiments

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-15-0028.1 ◽

2016 ◽

Vol 73 (3) ◽

pp. 1223-1254 ◽

Cited By ~ 5

Author(s):

David A. Schecter

Keyword(s):

Tropical Cyclone ◽

Tropical Cyclones ◽

Potential Vorticity ◽

Numerical Experiments ◽

Separation Distance ◽

Rapid Intensification ◽

Tropical Cyclone Formation ◽

Vortex Separation ◽

Cloud Resolving Model ◽

Insight Into

Abstract The evolution of two symmetric midlevel mesoscale vortices situated above a warm ocean is examined with a basic cloud-resolving model. Idealized numerical experiments provide insight into how the evolution may vary with the initial vortex separation distance D and other parameters that influence the time scale for an isolated vortex to begin rapid intensification. The latter parameters include the ambient middle-tropospheric relative humidity (RH) and the initial midlevel wind speed of each vortex. At relatively low RH, there exists an interval of D where binary midlevel vortex interaction prevents tropical cyclone formation. While tropical cyclones generally develop at high RH, similar values of D can delay the process if the vortices are initially weak. Prevention or inhibition of tropical cyclone formation occurs in association with the outward expulsion of lower-tropospheric potential vorticity anomalies as the two vortices merge in the middle troposphere. It is proposed that the primary mechanism for midlevel merger and low-level potential vorticity expulsion involves the excitation of rotating misalignments in each vortex. An analog model based on this premise provides a good approximation for the range of D in which the merger–expulsion scenario occurs. Relatively strong vortices in high-RH environments promptly develop vigorous convection and begin rapid intensification. Differences between the interaction of such diabatic vortices and their adiabatic counterparts are briefly illustrated. In systems that generate tropical cyclones, the mature vortex properties (size and strength) are found to vary significantly with D.

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Some Implications of Core Regime Wind Structures in Western North Pacific Tropical Cyclones

Weather and Forecasting ◽

10.1175/2010waf2222420.1 ◽

2011 ◽

Vol 26 (1) ◽

pp. 61-75 ◽

Cited By ~ 12

Author(s):

Delia Yen-Chu Chen ◽

Kevin K. W. Cheung ◽

Cheng-Shang Lee

Keyword(s):

Tropical Cyclone ◽

Tropical Cyclones ◽

Quantitative Measure ◽

Small Region ◽

Rapid Intensification ◽

Maximum Wind ◽

Convective Structures ◽

Tangential Wind ◽

Strong Convection ◽

Infrared Brightness

Abstract In this study, a tropical cyclone (TC) is considered to be compact if 1) the radius of maximum wind or the maximum tangential wind is smaller than what would be expected for an average tropical cyclone of the same intensity or the same radius of maximum wind, and 2) the decrease of tangential wind outside the radius of maximum wind is greater than that of an average TC. A structure parameter S is defined to provide a quantitative measure of the compactness of tropical cyclones. Quick Scatterometer (QuikSCAT) oceanic winds are used to calculate S for 171 tropical cyclones during 2000–07. The S parameters are then used to classify all of the cases as either compact or incompact according to the 33% and 67% percentiles. It is found that the early intensification stage is favorable for the occurrence of compact tropical cyclones, which also have a higher percentage of rapid intensification than incompact cases. Composite infrared brightness temperature shows that compact tropical cyclones have highly axisymmetric convective structures with strong convection concentrated in a small region near the center. Low-level synoptic patterns are important environmental factors that determine the degree of compactness; however, it is believed that compact tropical cyclones maintain their structures mainly through internal dynamics.

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Effects of Vertical Wind Shear on the Predictability of Tropical Cyclones

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-12-0133.1 ◽

2013 ◽

Vol 70 (3) ◽

pp. 975-983 ◽

Cited By ~ 120

Author(s):

Fuqing Zhang ◽

Dandan Tao

Keyword(s):

Tropical Cyclone ◽

Tropical Cyclones ◽

Small Amplitude ◽

Wind Shear ◽

Random Noise ◽

Vertical Wind Shear ◽

Vertical Wind ◽

Small Scale ◽

Rapid Intensification ◽

Moist Convection

Abstract Through cloud-resolving simulations, this study examines the effect of vertical wind shear and system-scale flow asymmetry on the predictability of tropical cyclone (TC) intensity during different stages of the TC life cycle. A series of ensemble experiments is performed with varying magnitudes of vertical wind shear, each initialized with an idealized weak TC-like vortex, with small-scale, small-amplitude random perturbations added to the initial conditions. It is found that the environmental shear can significantly affect the intrinsic predictability of tropical cyclones, especially during the formation and rapid intensification stage. The larger the vertical wind shear, the larger the uncertainty in the intensity forecast, primarily owing to the difference in the timing of rapid intensification. In the presence of environmental shear, initial random noise may result in changes in the timing of rapid intensification by as much as 1–2 days through the randomness (and chaotic nature) of moist convection. Upscale error growth from differences in moist convection first alters the tilt amplitude and angle of the incipient tropical storms, which leads to significant differences in the timing of precession and vortex alignment. During the precession process, both the vertical tilt of the storm and the effective (local) vertical wind shear are considerably decreased after the tilt angle reaches 90° to the left of the environmental shear. The tropical cyclone intensifies immediately after the tilt and the effective local shear reach their minima. In some instances, small-scale, small-amplitude random noise may also limit the intensity predictability through altering the timing and strength of the eyewall replacement cycle.

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