Tropical Cyclone Wave Research Articles

Sensitivity of Offshore Tropical Cyclone Wave Simulations to Spatial Resolution in Wave Models

This study investigated and quantified the sensitivity of tropical cyclone (TC) wave simulations in the open ocean to different spatial resolutions ( 1 / 3 ∘ , 1 / 6 ∘ , 1 / 12 ∘ and 1 / 24 ∘ ) using two wave models, WAVEWATCH III (WW3) and Simulating WAves Nearshore (SWAN). Six idealized TCs of different radii of maximum winds (25 km and 50 km), and of different translation speeds (3 m/s, 6 m/s and 9 m/s) were prescribed to force these two wave models. Results from both models show that the coarsest resolution ( 1 / 3 ∘ ) introduces significant errors in both the significant wave height (SWH) and the mean wavelength. Moreover, results reveal that sensitivity to spatial resolution strongly depends on storm characteristics. Waves simulated under the small (25 km) and fast moving (9 m/s) TC show the largest sensitivity to the coarse spatial resolutions. With the 1 / 3 ∘ resolution, maximum SWH can be underestimated by as much as 6% in WW3 and 16% in SWAN compared to those with the 1 / 24 ∘ resolution. These findings from the idealized TC simulations are further confirmed by wave simulations under a historical storm. Our analysis also demonstrates that spatial smoothing of the input wind field with coarse grids is not the only reason for the errors in wave simulations.

Study of sampling methods for assessment of extreme significant wave heights in the South China Sea

Adequate knowledge of extreme wave events is crucial for the coastal and offshore engineering community. In this study, assessment of extreme significant wave heights is performed in the South China Sea (SCS). Significant wave heights from a 40-year (1975–2014) hindcast of tropical cyclone waves are adopted as the initial database. The annual maxima (AM) method with the Gumbel model, a conventional method, is used to assess extreme significant wave heights, which fits the annual maximal significant wave height for extrapolation. The peak over threshold (POT) method with the generalized Pareto distribution (GPD) model is applied to determine return significant wave heights with certain return periods by fitting the peak excesses over a sufficiently large value (the threshold). To select the suitable threshold for the POT method, the sensitivity of the return significant wave height to the threshold is analysed. Based on the sampling theory and the characteristic of hindcasted significant wave heights of tropical cyclone waves, applicability of two sampling methods in the SCS is investigated.

Coastal Hazards Caused by Different Extreme Storms in the Bohai Sea, China

Zhou, C.Y.; Xu, C.Y.; Zhang, J.S.; Fu, X.Y., and Yin, Y., 2018. Coastal hazards caused by different extreme storms in the Bohai Sea, China. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 816–820. Coconut Creek (Florida), ISSN 0749-0208.The Bohai Sea, a semi-enclosed epicontinental sea, suffers different storms frequently, mainly tropical cyclones in summer/autumn and cold waves in winter/spring. The extreme storms can cause severe coastal hazards such as flooding, coastal structures and ocean platforms failures. A numerical model is set up for the Bohai Sea using MIKE21 with coupled hydrodynamic and wave modules. Observed data of water levels, velocities and wave are used to make model calibration. Based on this model, three typical tropical cyclones and cold waves are simulated. Then the major characteristics of summer tropical cyclones and winter cold waves are discussed. Affected by the tropical cyclone, the water levels of Laizhou Bay and Bohai Bay increase and that of Liaodong Bay decreases. Influenced by the cold wave coupled with an extratropical cyclone, the water levels of Laizhou Bay and Bohai Bay decrease firstly and then increase, which is contrary to the variation trend of water level at Liaodong Bay. Under the single cold wave weather, the water level increases at Laizhou Bay, decreases at Liaodong Bay, and firstly increases then decreases at Bohai Bay. The maximum of surge level caused by cold wave coupled with extratropical cyclone is smaller than that induced by tropical cyclone and single cold wave weather.

Coral boulders on Melekeok reef in the Palau Islands: An indicator of wave activity associated with tropical cyclones

Waves generated by tropical cyclones and tsunamis cause various impacts such as coastal erosion and damage to infrastructure. The intensity of tropical cyclones will probably increase in the near future as a result of global warming; therefore, predicting the likely impacts of these storms is a prime concern. Boulder deposits are one of the key proxies that assist our understanding of previous tropical cyclones and tsunamis, and are important if we are to accurately project their future impacts. In December 2012, Typhoon Bopha hit the Palau Islands and many boulders were probably deposited on the east coast of Babeldaob Island during the event. This area is one of the few locations where it is possible to distinguish between deposits that were generated by tropical cyclone waves and tsunamis. This study records the distribution of boulders from the shore to the reef crest at Melekeok reef on Babeldaob Island and evaluates the relationship between the movement of boulders and the hydraulic forces generated by the waves using a hydrodynamic model and wave calculations. In addition, this study projects the coastal impacts of tropical cyclone waves in the near future. Many boulders have been deposited on the reef crest within 100 m of the reef edge, and the maximum weight of the boulders is 2.2 tons. The boulders are composed of massive corals (e.g., Platygyra) and they originated from the upper reef slope. The results of the hydrodynamic modeling indicate that these boulders were transported and deposited by the waves generated by Typhoon Bopha (significant wave height = 8.7 m) or TCs with a similar intensity of Typhoon Bopha. Moreover, there are no boulder deposits at the shore, which implies that the reef has not been affected by tsunamis. Even if one or more tsunamis have inundated the reef, the associated hydraulic forces appear to have been lower than those of Typhoon Bopha. These findings indicate that Typhoon Bopha has probably generated the most intense wave event in recent times. However, it is likely that tropical cyclones more intense than Typhoon Bopha will affect the reef in the near future as the climate continues to warm through the 21st century. Consequently, the study site will probably face an increased risk of coastal erosion and destruction of property, if no plans are developed to reduce and manage such impacts.

Estimates of Surface Waves Using Subsurface EM-APEX Floats under Typhoon Fanapi 2010

AbstractSeven subsurface Electromagnetic Autonomous Profiling Explorer (EM-APEX) floats measured the voltage induced by the motional induction of seawater under Typhoon Fanapi in 2010. Measurements were processed to estimate high-frequency oceanic velocity variance associated with surface waves. Surface wave peak frequency fp and significant wave height Hs are estimated by a nonlinear least squares fitting to , assuming a broadband JONSWAP surface wave spectrum. The Hs is further corrected for the effects of float rotation, Earth’s geomagnetic field inclination, and surface wave propagation direction. The fp is 0.08–0.10 Hz, with the maximum fp of 0.10 Hz in the rear-left quadrant of Fanapi, which is ~0.02 Hz higher than in the rear-right quadrant. The Hs is 6–12 m, with the maximum in the rear sector of Fanapi. Comparing the estimated fp and Hs with those assuming a single dominant surface wave yields differences of more than 0.02 Hz and 4 m, respectively. The surface waves under Fanapi simulated in the WAVEWATCH III (ww3) model are used to assess and compare to float estimates. Differences in the surface wave spectra of JONSWAP and ww3 yield uncertainties of <5% outside Fanapi’s eyewall and >10% within the eyewall. The estimated fp is 10% less than the simulated before the passage of Fanapi’s eye and 20% less after eye passage. Most differences between Hs and simulated are <2 m except those in the rear-left quadrant of Fanapi, which are ~5 m. Surface wave estimates are important for guiding future model studies of tropical cyclone wave–ocean interactions.

Examining Tropical Cyclone–Kelvin Wave Interactions Using Adjoint Diagnostics

AbstractThe initial-state sensitivity and interactions between a tropical cyclone and atmospheric equatorial Kelvin waves associated with the Madden–Julian oscillation (MJO) during the DYNAMO field campaign are explored using adjoint-based tools from the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS). The development of Tropical Cyclone 5 (TC05) coincided with the passage of an equatorial Kelvin wave (KW) and westerly wind burst associated with an MJO that developed in the Indian Ocean in late November 2011. COAMPS 18-h adjoint sensitivities of low-level kinetic energy to changes in initial state winds, temperature, and water vapor are analyzed for both TC05 and the KW to document when the evolution of each system is sensitive to the other. Time series of sensitivity patterns confirm that TC05 and the KW low-level westerlies are sensitive to each other when the KW is to the southwest and south of TC05. While TC05 is not sensitive to the KW after this, the KW low-level westerlies remain sensitive to TC05 until it enters the far eastern Indian Ocean. Vertical profiles of both TC05 and KW sensitivity indicate lower-tropospheric maxima in temperature, wind, and moisture, with KW sensitivity typically 20% smaller than TC05 sensitivity. The magnitude of the sensitivity for both systems is greatest just prior to, and during, their closest proximity. A case study examination reveals that adjoint-based optimal perturbations grow and expand quickly through a dynamic response to decreased static stability. The evolution of moist-only and dry-only initial perturbations illustrates that the moist component is primarily responsible for the initial rapid growth, but that subsequent growth rates are similar.

A robust operational model for predicting where tropical cyclone waves damage coral reefs.

Tropical cyclone (TC) waves can severely damage coral reefs. Models that predict where to find such damage (the ‘damage zone’) enable reef managers to: 1) target management responses after major TCs in near-real time to promote recovery at severely damaged sites; and 2) identify spatial patterns in historic TC exposure to explain habitat condition trajectories. For damage models to meet these needs, they must be valid for TCs of varying intensity, circulation size and duration. Here, we map damage zones for 46 TCs that crossed Australia’s Great Barrier Reef from 1985–2015 using three models – including one we develop which extends the capability of the others. We ground truth model performance with field data of wave damage from seven TCs of varying characteristics. The model we develop (4MW) out-performed the other models at capturing all incidences of known damage. The next best performing model (AHF) both under-predicted and over-predicted damage for TCs of various types. 4MW and AHF produce strikingly different spatial and temporal patterns of damage potential when used to reconstruct past TCs from 1985–2015. The 4MW model greatly enhances both of the main capabilities TC damage models provide to managers, and is useful wherever TCs and coral reefs co-occur.

Effects of cyclone-generated disturbance on a tropical reef foraminifera assemblage.

The sedimentary record, and associated micropalaeontological proxies, is one tool that has been employed to quantify a region’s tropical cyclone history. Doing so has largely relied on the identification of allochthonous deposits (sediments and microfossils), sourced from deeper water and entrained by tropical cyclone waves and currents, in a shallow-water or terrestrial setting. In this study, we examine microfossil assemblages before and after a known tropical cyclone event (Cyclone Hamish) with the aim to better resolve the characteristics of this known signal. Our results identify no allochthonous material associated with Cyclone Hamish. Instead, using a swathe of statistical tools typical of ecological studies but rarely employed in the geosciences, we identify new, previously unidentified, signal types. These signals include a homogenising effect, with the level of differentiation between sample sites greatly reduced immediately following Cyclone Hamish, and discernible shifts in assemblage diversity. In the subsequent years following Hamish, the surface assemblage returns to its pre-cyclone form, but results imply that it is unlikely the community ever reaches steady state.

Evaluation of a Wind-Wave System for Ensemble Tropical Cyclone Wave Forecasting. Part II: Waves

Abstract A wind-wave forecast system, designed with the intention of generating unbiased ensemble wave forecasts for extreme wind events, is assessed. Wave hindcasts for 12 tropical cyclones (TCs) are forced using a wind analysis produced from a combination of the North American Regional Reanalysis (NARR) and a parametric wind model. The default drag parameterization is replaced by one that is more in line with recent studies where a cap at weak-to-moderate wind speeds is applied. Quadrant-based significant wave height (Hs) statistics are composited in a storm-relative reference frame and stratified by the radius of maximum wind, storm speed, and storm intensity. Improvements in Hs are gleaned from both downscaling the NARR winds and tuning the wave model. However, the paradigm whereby the drag coefficient depends solely on the wind speed is limiting. Results indicate that Hs is biased low in the right quadrants (for all statistical subcategories). Conversely, Hs is high biased in the left-rear quadrant even though the analysis wind field is underforecast there. At radii less than 100 nautical miles, the model peak wave direction is offset from the observed, with the model (buoy) peak more in line with (to the left of) the direction of the tropical cyclone motion. As a result, the predominant storm-relative wind direction, which is northwesterly in the left-rear quadrant, opposes that of the buoy peak wave direction, while the model peak is more crosswise with respect to the wind. This will likely reduce the magnitude of the wind stress in the model.

Evaluation of a Wind-Wave System for Ensemble Tropical Cyclone Wave Forecasting. Part I: Winds

Abstract A computationally efficient method of producing tropical cyclone (TC) wind analyses is developed and tested, using a hindcast methodology, for 12 Gulf of Mexico storms. The analyses are created by blending synthetic data, generated from a simple parametric model constructed using extended best-track data and climatology, with a first-guess field obtained from the NCEP–NCAR North American Regional Reanalysis (NARR). Tests are performed whereby parameters in the wind analysis and vortex model are varied in an attempt to best represent the TC wind fields. A comparison between nonlinear and climatological estimates of the TC size parameter indicates that the former yields a much improved correlation with the best-track radius of maximum wind rm. The analysis, augmented by a pseudoerror term that controls the degree of blending between the NARR and parametric winds, is tuned using buoy observations to calculate wind speed root-mean-square deviation (RMSD), scatter index (SI), and bias. The bias is minimized when the parametric winds are confined to the inner-core region. Analysis wind statistics are stratified within a storm-relative reference frame and by radial distance from storm center, storm intensity, radius of maximum wind, and storm translation speed. The analysis decreases the bias and RMSD in all quadrants for both moderate and strong storms and is most improved for storms with an rm of less than 20 n mi. The largest SI reductions occur for strong storms and storms with an rm of less than 20 n mi. The NARR impacts the analysis bias: when the bias in the former is relatively large, it remains so in the latter.

Tropical cyclone waves detected with infrasound sensor array

The strong winds of a tropical cyclone whip up the sea surface, driving ocean waves a dozen meters high. When one such ocean wave runs into another wave that has an equal period but is traveling in the opposite direction, the interaction produces low‐frequency sound waves that can be detected thousands of kilometers away. The infrasound signals produced by interacting ocean surface waves—known as microbarom—have typical frequencies around 0.2 hertz. Researchers previously determined that as a hurricane travels along its track, early waves generated by the storm will interact with those generated later on, producing a strong microbarom signal in the storm's wake. Researchers also found, however, that microbarom signals are produced by regular surface ocean behavior, including swell, surface waves, and nontropical cyclone storms.

Reply to Comment on: Coarse clast ridge sequences as suitable archives for past storm events? Case study on the Houtman Abrolhos, Western Australia

Prehistoric storm records are relatively scarce in most parts of the world. This article presents storm records derived from coral rubble-based geological archives of the Houtman Abrolhos Archipelago located off the west coast of Australia, where the southernmost coral reefs of the Indian Ocean are found. Winter storm swell from the circum-Antarctic ‘Brave Westerlies’, as well as tropical cyclone waves, have left numerous ridge systems on dozens of islands of the archipelago, all composed of coral rubble from adjacent reefs. At three islands, seven ridge systems were dated by three different methods: U-series (68 dates), radiocarbon (64 dates), electron spin resonance (7 dates); 139 radiometric dates span the last 5500 years of the Holocene. In contrast to the geomorphological interpretation, the age sequences show ‘inversions’, hiatuses and different ages for the same ridge, all pointing to complicated ridge formation processes. Time gaps, some exceeding 1000 years, are interpreted as phases of erosion and not as phases without storm activity.

Atmospheric infrasound from nonlinear wave interactions during Hurricanes Felicia and Neki of 2009

Monitoring stations around the globe routinely detect microbarom signals with a dominant frequency of ∼0.2 Hz from regions of marine storminess. International Monitoring System (IMS) infrasound array IS59 in Kailua‐Kona, Hawaii recorded clear signals in close proximity of Hurricanes Felicia and Neki of 2009 for a first‐hand investigation of the detailed source mechanism through a hindcast analysis. A spectral wave model describes the tropical cyclone and ambient sea states through a system of two‐way nested grids with forcing from a blended data set of global, regional, and cyclonic winds. The computed wave conditions are validated with altimetry measurements and utilized in an acoustic model to estimate the intensity and spatial distribution of the microbarom source. The model results elucidate origins of infrasound signals from the tropical cyclone waves as well as their interactions with the ambient conditions consisting of swells, wind seas, and storm waves from nearby systems. The positive correlation between the IS59 observations and the theoretical microbarom estimates, and the saturation of recorded signals from high‐energy sources support the use of infrasound signals for inference of tropical cyclone waves.

Coarse clast ridge sequences as suitable archives for past storm events? Case study on the Houtman Abrolhos, Western Australia

AbstractPrehistoric storm records are relatively scarce in most parts of the world. This article presents storm records derived from coral rubble‐based geological archives of the Houtman Abrolhos Archipelago located off the west coast of Australia, where the southernmost coral reefs of the Indian Ocean are found. Winter storm swell from the circum‐Antarctic ‘Brave Westerlies’, as well as tropical cyclone waves, have left numerous ridge systems on dozens of islands of the archipelago, all composed of coral rubble from adjacent reefs. At three islands, seven ridge systems were dated by three different methods: U‐series (68 dates), radiocarbon (64 dates), electron spin resonance (7 dates); 139 radiometric dates span the last 5500 years of the Holocene. In contrast to the geomorphological interpretation, the age sequences show ‘inversions’, hiatuses and different ages for the same ridge, all pointing to complicated ridge formation processes. Time gaps, some exceeding 1000 years, are interpreted as phases of erosion and not as phases without storm activity. Copyright © 2012 John Wiley & Sons, Ltd.

Source of microbaroms from tropical cyclone waves

[1] Microbaroms are continuous infrasonic signals with a dominant frequency around 0.2 Hz produced by ocean surface waves. Monitoring stations around the globe routinely detect strong microbaroms in the lee of tropical cyclones. We utilize a parametric wind model and a spectral wave model to construct the tropical cyclone wave field and a theoretical acoustic source model to describe the intensity, spatial distribution, and dynamics of microbarom sources. This approach excludes ambient wave conditions and facilitates a parametric analysis to elucidate the source mechanism within the storm. A stationary tropical cyclone produces the strongest microbarom signals at the center, where the waves generated by the cyclonic winds converge. As the tropical cyclone moves forward, the converging wave field becomes less coherent and lags and expands behind the storm center. The models predict a direct relation between the storm forward speed and the location of maximum microbarom source intensity consistent with the infrasonic observations from Hurricane Felicia 2009 in the North Central Pacific.

Modeling Tropical Cyclone Wave Population of the Great Barrier Reef

Wave information is generated for the population of tropical cyclones that affects the Great Barrier Reef region. Several models are combined to create a wave database at 150,000 locations at a resolution of 1,500 m throughout this large and remote region. An autoregressive time series model, based on historical data, generated time series of position and central pressure for a very large ensemble of synthetic tropical cyclones. An empirical model was used to create the wind field throughout the wave generating area. The wind field had three components: The primary cyclone vortex, a secondary vortex used to model the low-pressure trough in which a cyclone is often embedded, and the external synoptic scale wind field created between the cyclone and the mid latitude high-pressure systems. WAMGBR, a wave generation model especially adapted for conditions in the Great Barrier Reef, was used to simulate a very large ensemble of storms on a nested grid system in transformed spherical coordinates. The results of the study are significant wave heights, peak periods, and mean directions for return periods between 20 and 1,000 years.

A wave model for the Great Barrier Reef

A new wind wave generation model, WAMGBR, is presented that has been adapted from WAM especially for use in the complex geometry of the Great Barrier Reef. A technique (reef parameterization) has been presented that incorporates sub-grid scale dissipation caused by coral reefs. Three other improvements to WAM have been proposed. An explicit/implicit finite difference scheme has been implemented that allows for more efficient modelling (longer time steps) while maintaining diffusive characteristics that are at least as good as those of WAM. An offset in discrete angles creates more uniform diffusive characteristics. And, a transformed spherical coordinate system allows for more efficient grid sizes and smaller grid dependent refraction. Comparisons between modelling techniques and between model and measured data show that WAMGBR produces very good results in the difficult challenge of modelling both non-cyclonic and tropical cyclone waves in the geographically complex environment of the Great Barrier Reef.

Measurement and modelling of tropical cyclone waves in the Great Barrier Reef

Recorded wave data from four wave measuring instruments located at various points within a section of the Great Barrier Reef during the passage of a tropical cyclone are presented. A spectral wave prediction model is used as an aid to the interpretation of the data. The tropical cyclone generated significant wave heights of approximately 10 m seaward of the reef complex. The many scattered reefs, however, act to reduce this value to approximately 6 m landward of the reef complex. Individual reefs appear to act as complete barriers to waves at typical oceanic periods, even at high tide. In a scattered reef complex such as the Great Barrier Reff, wave energy can penetrate the inter-reef gaps. Although such inter-reef gaps may appear large in comparison to the sizes of individual reefs, wave attenuation is still significant.

Effects of tropical cyclone waves on ecological and geomorphological structures on the Great Barrier Reef

Damage to coral reefs caused by Tropical Cyclone Ivor (March 1990) on 46 sites over 150 km of the Great Barrier Reef was patchily distributed within 50 km of the path, while at distances 50km from the eye, it was uniformly low. These distances suggest that local wind-generated waves, not ocean swells, may be the major cause of destruction. Wind component incident on each site, U N, was therefore hindcast from tropical cyclone circulation models. The sum of hourly U N explained about 82% of the variance in an index of total damage and 90% of the destruction of a veneer of dense coral growth up to 1.5 m in thickness. This correlation is consistent with an “attrition” model, in which cyclone waves exfoliate reefs, chunk by chunk, over the period of storm waves.

WIND WAVES GENERATED BY TROPICAL CYCLONES AND HURRICANES

Tropical cyclone wave spectra in deep water have been put in a universal form similar to the JONSWAP spectra. Average spectral shape parameters were defined from values obtained in the open literature. Spectral level, peak frequency and significant wave height correlations with dimensionless fetch were obtained from Gulf of Mexico hurricanes Camille 1969, Eloise 1975, Edith 1971 and Felice 1970 and compared to tropical cyclone waves in the Eastern and Western Pacific. The data indicates that the correlations obtained can be useful for climatological studies of deep water tropical cyclone waves.