Cyclonic Wind Research Articles

Tropical Cyclone Wind Speed Retrieval from Dual-Polarization Sentinel-1 EW Mode Products

AbstractRecent studies indicate that the cross-polarization synthetic aperture radar (SAR) images have the ability of retrieving high wind speed on ocean surface without wind direction input. This study presents a new approach for tropical cyclone (TC) wind speed retrieval utilizing thermal-noise-removed Sentinel-1 dual-polarization (VV + VH) Extra-Wide Swath (EW) Mode products. Based on 20 images of 9 TCs observed in the 2016 and 2018 and SAR-collocated European Centre for Medium-Range Weather Forecasts (ECMWF) fifth-generation reanalysis (ERA5) data and the National Oceanic and Atmospheric Administration (NOAA) Hurricane Research Division’s (HRD) Real-time Hurricane Wind Analysis System (H*Wind) data, a subswath-based geophysical model function (GMF) Sentinel-1 EW Mode Wind Speed Retrieval Model after Noise Removal (S1EW.NR) is developed and validated statistically. TC wind speed is retrieved by using the proposed GMF and the C-band model 5.N (CMOD5.N). The results show that the wind speeds retrieved by the S1EW.NR model are in good agreement with wind references up to 31 m s−1. The correlation coefficient, bias, and standard deviation between the retrieval results and reference wind speeds are 0.74, −0.11, and 3.54 m s−1, respectively. Comparison of the wind speeds retrieved from both channels suggests that the cross-polarized signal is more suitable for high–wind speed retrieval, indicating the promising capability of cross-polarization SAR for TC monitoring.

Extreme waves generated by cyclonic winds in the western portion of the South Atlantic Ocean

This article analyzes the spatial distribution of extreme waves generated by extratropical cyclones and studies the atmospheric conditions that lead to the most severe events in the Southwestern portion of the South Atlantic Ocean. Significant wave heights from the NCEP/WW3 hindcast and atmospheric fields from NCEP/CFSR are selected for the analysis that joins automatic tracking of the storms with visual analyses of the most relevant cases. The synoptic pattern of extreme events suggested that extreme waves can occur in three regions of the cyclones: (1) behind the cold front; (2) along the warm front; and (3) ahead of the cold front. The first pattern is widely reported in the literature, while the others are unexplored in the region and are first reported in this paper. It was also shown that the anticyclone position relative to the cyclone center plays an important role in the extreme waves in two ways: (1) due to the increase of horizontal pressure gradient and, consequently, surface wind speed; and (2) affecting the cyclone displacement speed, which determines the fetch positioning and the wave generation process. The novel features identified show that slow cyclones tend to promote longer events of extreme waves, with impact on larger areas.

Sensitivity analysis of the numerical aspect of the SWAN for the tropical cyclone wave simulations in the Gulf of Oman

The simulating waves nearshore (SWAN) model is designed for the wave simulations of nearshore areas. In the present study, this model has been applied for simulating tropical cyclone–generated waves in the Gulf of Oman. The wind and pressure field of the Gonu cyclone were reproduced by means of the cyclone wind generation (CWG) tool of the Mike DHI within multiple inputs, including the geographical location of the center of the cyclone, the radius of maximum wind speed, the pressure at the center of the cyclone, the neutral pressure, the start time of the cyclone period, and the maximum wind speed. The required specifications of the cyclone were obtained from the Joint US Typhoon Warning Center (JTWC) and introduced into the CWG module. With the purpose of achieving optimal settings of the model, a sensitivity analysis of the time step, grid resolution, and angle resolution has been conducted. Sensitivity analysis demonstrates that effects of time step have a significant impact on the results, while generally speaking angel and grid resolution are less impressive.

The Spatial Distribution of Ocean Waves in Tropical Cyclones

AbstractThe spatial structure of both the wind and wave fields within tropical cyclones is investigated using two large databases. The first of these was compiled from global overpasses of tropical cyclones by satellite altimeters. The second dataset consists of an extensive collection of North American buoy measurements during the passage of tropical cyclones (hurricanes). The combined datasets confirm the vortex structure of the tropical cyclone wind field with the strongest winds to the right (Northern Hemisphere) of the storm. The wave field largely mirrors the wind field but with greater right–left asymmetry that results from the extended fetch to the right of the translating tropical cyclone. The extensive in situ buoy database confirms previous studies indicating that the one-dimensional spectra are generally unimodal. The directional spectra are, however, directionally skewed, consisting of remotely generated waves radiating out from the center of the storm and locally generated wind sea. The one-dimensional wave spectra have many similarities to fetch-limited cases, although for a given peak frequency the spectra contain less energy than for a fetch-limited case. This result is consistent with the fact that much of the wave field is dominated by remotely generated waves.

Simulation and Prediction of Storm Surges and Waves Using a Fully Integrated Process Model and a Parametric Cyclonic Wind Model

AbstractThis paper presents a fully integrated coastal process model and a simple parametric cyclonic wind‐pressure model for simulation of wind, storm surges, waves, tidal currents, and river flows. By sharing one computational grid within all those process modules and no need for switching executable codes from one module to another, this full‐coupling feature eliminates possible errors and loss of information due to interpolation and extrapolation of variables between different grids. To generate better cyclonic wind speed and barometric pressure, this parametric wind model includes nonlinear decay effect on wind intensity after hurricane's landfall. By implementing a new wind energy source term, the wave action model is capable of computing wave growth, propagation, and deformation through a regional‐scale domain from deepwater to shallow waters. Model validation and model skill assessment were performed by hindcasting wind, storm surges, waves, and river flows during Hurricane Gustav (2008) by using a high‐resolution grid covering the northern Gulf Coast. With improved wind fields estimated by the new parametric wind model, this fully integrated process model produced high‐quality wavefields in deep and shallow waters and storm tidal levels in the northern Gulf Coasts. Because of computing efficiency provided by seamless integration of process modules and optimized numerical solution schemes, faster‐than‐real‐time predictions of storm surges for the advisories during Hurricane Isaac (2012) were achieved by running the validated model in a desktop computer.

Simulating tropical cyclone waves in the East China Sea with an event-based, parametric-adjusted model

Parametric cyclone wind models with storm characteristics derived from statistical representation do not agreeably delineate the wind field in the East China Sea, leading to uncertain errors in the numerical simulations of Typhoon waves. A new approach to adjust the cyclone wind field in the framework of the Holland model is proposed. The radius of maximum wind speed and the logarithmically varied shape parameter B from the Holland model are iterated out with in situ data and extended to the cyclone track in the East China Sea. This event-based Holland parametric assimilation scheme can model different kinds of unimodal wind profiles and deliver a significant improvement over the original Holland model. The simulated wind fields of three typhoon events, Typhoons Saomai (200608), Fitow (201312) and Maria (201808), are then used to drive the Simulating Waves Nearshore (SWAN) wave model, and wave fields during the three typhoon events show better agreement with the in situ observations. Compared with satellite scatterometer and altimeter products, the effectiveness of modelled typhoon events is largely limited by temporal changes of typhoon structure. This approach is recommended for typhoon events with small temporal changes. Overall, the approach to adjusting wind profiles with observations satisfactorily improves the simulation performances of cyclonic winds and wave heights at a low computation cost.

A case study of Chlorophyll a response to tropical cyclone Wind Pump considering Kuroshio invasion and air-sea heat exchange

New evidences provided that the tropical cyclone (TC) Linfa in 2015 induced looping path of Kuroshio invasion into the northeastern South China Sea (NESCS) through the northwestern Luzon Strait (LS), based on the in-situ measurements, satellite data and model output data. This TC-enhanced Kuroshio invasion with low nutrients and denser waters suppressed the TC “Wind Pump” induced upwelling and nutrients uptake, and therefore inhibited the Chlorophyll a concentration (Chl-a) increase from surface to ~50 m in the open ocean of the NESCS. The TC-induced Kuroshio invasion promoted the generation of the strong cyclonic eddy to its left side where weak Ekman Pumping Velocity was observed. This enhancing cyclonic eddy then dominated the nutrients uplift and increased the surface and subsurface (0–50 m) Chl-a through eddy pumping rather than Ekman Pumping. The TC-declined anti-cyclonic eddy, which shoaled the Mixed Layer Depth (MLD), benefited to the nutrient uptake through TC-induced upwelling and thereby increased the surface Chl-a and raised the Chl-a Maximum Layer (CML) to ~20 m over the southwestern LS. The temporal Chl-a variations were also influenced by TC intensities and biochemical processes. The air-sea heat budget analysis indicated that, the air-sea heat exchange contributed to nearly 80% of the sea surface cooling (SST cooling) over the northwestern LS with Kuroshio invasion, while eddy-induced upwelling dominated the SST cooling over the western LS, and the wind-driven upwelling (and mixing) controlled the SST cooling over the southwestern LS. These different formations of SST cooling then played important role in Chl-a variations. This study is the first case of TC “Wind Pump” induced Chl-a variations considering air-sea heat exchange, Kuroshio invasion and mesoscale eddies over LS, which would help to evaluate the influence of TCs over the other major heat transport arteries of the world ocean: The Gulf Stream area.

Countering tropical cyclonic storm impacts on low-rise houses

PurposeThis study investigates the aerodynamics of the airflow over low-rise houses subjected to turbulent cyclonic winds along the South-eastern peninsular India, routinely afflicted by tropical cyclones. The purpose of this paper is to demonstrate how the power of modern computational fluid dynamics (CFD) and its engineering application accentuate decision-making at the planning stage of house designing in vulnerable areas.Design/methodology/approachThe Weather Research and Forecasting (WRF) model was used for first simulating the landfall of cyclone Hudhud, a real storm, and its effect in extant and new house designs. Results from the WRF model were utilized to configure further CFD simulations of airflow around house designs. The analyses yielded deep insights, often non-intuitive, into airflow patterns around these houses with disparate roof forms indicating new possibilities in redesigning houses along Indian coastal areas.FindingsThis study shows that storm-induced high TKE values warranted a fuller CFD-based study. The second major finding showed that for a 90° angle of attack, arguably the most destructive attack angle, a pitched roof (with a pitch angle of 10°) worked best – this is about half the recommended angle sourced from earlier empirical estimates dating back to the British Raj period. There is a thin layer of padded air cushion shielding the roof's vulnerable surface from the storm's most energetic parts.Originality/valueThe originality of this research lies in its discourse to systematically resolve the TKE distribution of a cyclone impacting a standalone house. In particular, the study presents a lucid demonstration of all the probable scenarios connecting cyclonic stresses with a roof response, inferred from a careful combination of results garnered from cyclonic storm modelling coupled with CFD analysis. Additionally, the paper also shows a graphic visual representation of the forces induced on different roof designs, presented as a checklist for the first time. This should serve as a ready reckoner for civic authorities involved in disaster management over cyclone-ravaged areas.

Estimation of tropical cyclone wind hazards in coastal regions of China

Abstract. Coastal regions of China feature high population densities as well as wind-sensitive structures and are therefore vulnerable to tropical cyclones (TCs) with approximately six to eight landfalls annually. This study predicts TC wind hazard curves in terms of design wind speed versus return periods for major coastal cities of China to facilitate TC-wind-resistant design and disaster mitigation as well as insurance-related risk assessment. The 10 min wind information provided by the Japan Meteorological Agency (JMA) from 1977 to 2015 is employed to rebuild TC wind field parameters (radius of maximum winds Rmax,s and shape parameter of radial pressure profile Bs) at surface level using a height-resolving boundary layer model. These parameters will be documented to develop an improved JMA dataset. The probabilistic behaviors of historical tracks and wind field parameters at the first time step within a 500 km radius subregion centered at a site of interest are examined to determine preferable probability distribution models before stochastically generating correlated genesis parameters utilizing the Cholesky decomposition method. Recursive models are applied for translation speed, Rmax,s and Bs during the TC track and wind field simulations. Site-specific TC wind hazards are studied using 10 000-year Monte Carlo simulations and compared with code suggestions as well as other studies. The resulting estimated wind speeds for northern cities (Ningbo and Wenzhou) under a TC climate are higher than code recommendations, while those for southern cities (Zhanjiang and Haikou) are lower. Other cities show a satisfactory agreement with code provisions at the height of 10 m. Some potential reasons for these findings are discussed to emphasize the importance of independently developing hazard curves of TC winds.

How fringe cyclone experience affects predictions of damage severity

PurposeThis paper aims to understand how experience with the fringe effects of a cyclone influences perception of cyclone severity. Understanding how certain types of experience influences risk perception should help to clarify why there is an unclear link between experience and risk perception within the existing literature.Design/methodology/approachA total of 155 respondents with fringe cyclone experience were recruited to fill in a closed-ended question survey. The survey was designed to assess perceptions of a previous cyclone and future cyclone severity.FindingsMost respondents who had experienced the fringe effects of a cyclone overestimated the wind speed in their location. Respondents who overestimated previous cyclone wind speed also predicted less damage from future Category 5 cyclones.Research limitations/implicationsThis research indicates that overestimating the severity of past cyclones can have a detrimental effect on how people predict damage due to high category cyclones.Practical implicationsThe findings suggest that people with fringe cyclone experience need additional information to help reshape their perceptions of cyclone severity.Originality/valueThis paper provides a unique perspective on the relationship between experience and risk perception by demonstrating that experience on the fringe of a cyclone has a negative influence on risk perception.

Causal Interactions between Southern Ocean Polynyas and High-Latitude Atmosphere–Ocean Variability

AbstractWeddell Sea open-ocean polynyas have been observed to occasionally release heat from the deep ocean to the atmosphere, indicating that their sporadic appearances may be an important feature of high-latitude atmosphere–ocean variability. Yet, observations of the phenomenon are sparse and many standard-resolution models represent these features poorly, if at all. We use a fully coupled, synoptic-scale preindustrial control simulation of the Energy Exascale Earth System Model (E3SMv0-HR) to effectively simulate open-ocean polynyas and investigate their role in the climate system. Our approach employs statistical tests of Granger causality to diagnose local and remote drivers of, and responses to, polynya heat loss on interannual to decadal time scales. First, we find that polynya heat loss Granger causes a persistent increase in surface air temperature over the Weddell Sea, strengthening the local cyclonic wind circulation. Along with responding to polynyas, atmospheric conditions also facilitate their development. When the Southern Ocean experiences a rapid poleward shift in the circumpolar westerlies following a prolonged negative phase of the southern annular mode (SAM), Weddell Sea salinity increases, promoting density destratification and convection in the water column. Finally, we find that the reduction of surface heat fluxes during periods of full ice cover is not fully compensated by ocean heat transport into the high latitudes. This imbalance leads to a buildup of ocean heat content that supplies polynya heat loss. These results disentangle the complex, coupled climate processes that both enable the polynya’s existence and respond to it, providing insights to improve the representation of these highly episodic sea ice features in climate models.

Morphodynamic response of sand waves in the Taiwan Shoal to a passing tropical storm

Data from three repeated multi-beam echo-sounder surveys of pre-storm, post-storm, and one year after the storm were used to study the response of sand waves in the Taiwan Shoal to the tropical storm, Talim. The measurements showed significant decreases in wave height of giant sand waves between post-storm and pre-storm, and moderate increases in one year period after the storm. The maximum decrease in wave height is more than 2 m and the averaged decrease is 1.2 m along the measured profile. The linear regression analysis shows an increasing trend of wave height changes from northwest to southeast along the profile. The uneven evolution pattern was possibly caused by the asymmetry of the currents induced by the cyclone winds. The analysis based on the Morlet wavelet function showed that the storm smeared out small-scale sand waves and eroded the giant sand wave crests, and recovery of bedforms after the storm. Two-dimensional features of storm effects were analyzed using the imagery of a Digital Terrain Model processed in a 2D survey area for pre-storm, post-storm and one year after the storm. The analysis revealed sand wave migration processes during the storm and the growing-back feature of the eroded wave crests after the storm.

A General Viscous Model for Some Aspects of Tropical Cyclonic Winds

Abstract A previous investigation found that the existence of double exponential terms is a reason for rapid intensification of cyclonic winds with the assumption of a linearised form of viscosity. Here, we consider viscosity of general type and still get similar terms. A perturbation technique is applied to the solution. The domain of analysis is split into two regions: an inner one that experiences updraft, and an outer one that possesses no vertical component of velocity but does have azimuthal and radial components. It is observed that the radial pressure difference between an arbitrary radial distance and the point of the maximum wind diminishes with height, time, and Reynolds number. The azimuthal velocity, close to the ground, in region 1 increases fast with time, but its dependence diminishes at a height a little above the ground. At a considerable height, time ceases to be a factor, and further, above that, trends reverse. Perturbation terms behave almost identically with the terms without perturbation. The significance of their contribution depends on the magnitude of the Reynolds number and, hence, the viscosity. Trends for region 2 are qualitatively similar to those in region 1 but differ quantitatively. It is also observed that the central pressure drop decreases with time.

Spatial variation of climate change issues using remote sensing technique

The assessment of climate change can be carried out by analysing rainfall variability, temporal climatic changes, spatial interpolation of climatic factors and climatic risking. The climatic changes have consequences on precipitation pattern changes, temperature variation, and crop growing season alteration, increase of sea ice and grounded ice sheets. This has implications on ecosystem, human health, settlement and agriculture. Some of the repercussions attributed to temperature and precipitation increase is an increase of Cyclonic activities with increase of cyclonic wind speeds, Increase in Extreme Precipitation events like floods and droughts, agricultural yield is projected to decrease and negative impact on subsistence agriculture. The Tropical Cyclones intensifying in eastern Indian Ocean and crossing the coasts of Indian subcontinent year after year is a major cause of concern. The Latent Heat Release (LHR) of cyclones of Bay of Bengal carried out using advanced sensors like SSM/I (Special Sensor Microwave/Imager) on-board DMSP satellites (Defence Meteorological Satellite Program of US) for assessing spatial distribution of precipitation since LHR is responsible for maintenance and intensification of tropical cyclones and LHR can also enable measurement of brightness temperatures of atmospheric/ocean surfaces. The images of the clouds in visible and infrared region provide information about cloud aerial extent, type, and growth/decay. The raining clouds have high visible band reflectance and are tall due to upward motion indicating deep convection. These issues pertaining to climate changes through Remote sensing techniques is discussed in the paper.

Design Tropical Cyclone Wind Speed when Considering Climate Change

AbstractThis paper investigated the evolution of tropical cyclone (TC) wind threat from the past into the future and discussed its implications for the building code specifications for two vulnerab...

Delft Dashboard: a quick set-up tool for hydrodynamic models

AbstractThe open-source program Delft Dashboard (DDB) is a graphical user interface designed to quickly create, edit input parameters and visualize model inputs for a number of hydrodynamic models, using private or publicly available local and global datasets. It includes a number of toolboxes that facilitate the generation of spatially varying inputs. These include new model schematizations (grids, bathymetry, boundary conditions, etc.), cyclonic wind fields and initial tsunami waves. The use of DDB can have significant benefits. It can save modellers considerable time and effort. Furthermore, the automated nature of both data collection and pre-processing within the program reduces the likelihood of errors that could occur when setting up models manually. Three case studies are presented: simulation of tides in the North Sea, storm surge and wave modelling under tropical cyclone conditions and the simulation of a tsunami. The test cases show that models created with DDB can be set up efficiently while maintaining a predictive skill that is only slightly lower than that of extensively calibrated models.

Interannual Variability of the Outflow of Weddell Sea Bottom Water

AbstractThe Weddell Sea Bottom Water (WSBW) export from 1999 to 2019 displays distinct seasonal and interannual variability. From 2014 into 2017 a marked salinity decrease was recorded, with the lowest salinity, 34.615, attained in early 2016. The reduced salinity is derived from the V‐shaped trough formed by a double front along the shelf break of the Weddell Gyre's western boundary, which is filled with a blend of surface water and modified Weddell Deep Water. We estimate that when the V‐shaped apex attains a depth of greater than ~700 m, the thermobaric effect promotes its descent into the WSBW. We propose that this occurred during anomalously strong cyclonic wind stress curl over the Weddell Gyre from 2014 into 2017, which increased the intensity of the gyre and its western boundary current, deepening the V‐shape trough. The WSBW salinity increased to its prior to 2014 values as the wind stress relaxed in 2018.

Nonlinear Impacts of Surface Exchange Coefficient Uncertainty on Tropical Cyclone Intensity and Air‐Sea Interactions

AbstractTropical cyclone maximum intensity is believed to result from a balance between the surface friction, which removes energy, and a temperature/moisture (enthalpy) difference between the sea surface and the air above it, which adds energy. The competing processes near the air‐sea interface are controlled by both the near surface wind speed and the surface momentum (Cd) and enthalpy (Ck) exchange coefficients. Unfortunately, these coefficients are currently highly uncertain at high wind speeds. Tropical cyclone winds also apply a force on the ocean surface, which results in ocean surface cooling through vertical mixing. Using coupled atmosphere‐ocean and uncoupled (atmosphere only) ensemble simulations we explore the complex influence of uncertain surface exchange coefficients on storm‐induced ocean feedback and tropical cyclone intensity. We find that the magnitude of ocean cooling increases with storm intensity and Cd. Additionally, the simulated maximum wind speed uncertainty does not necessarily decrease when ocean feedback are considered.

Coastal inundation due to tropical cyclones along the east coast of India: an influence of climate change impact

Coastal inundation due to storm tides is computed using ADvanced CIRCulation (ADCIRC) model along the east coast of India. Inland inundation due to storm tides is calculated every 10 km along the coast by using synthetic tracks as described in Rao et al. (Nat Hazards, 2019. https://doi.org/10.1007/s11069-019-03804-z). The cyclonic winds are computed using a maximum pressure drop of the cyclone based on a 100-year return period. The coast is mapped for the maximum possible extent of inland inundation with water levels at the district level. The influence of climate change impact as a result of global warming on the coastal inundation is evaluated by enhancing the intensity of the cyclones. Peak water levels of about 10–12 m are found along the north of Odisha coast. The most vulnerable region in terms of coastal inundation in the present scenario is found in the districts of West Bengal; however, they are the least affected by about 5–6% due to climate change scenario (CCS). The most affected inundated districts by more than 50% due to CCS are observed in the Godavari deltaic region in Andhra Pradesh. Though the water levels in the Ramanathapuram District in Tamil Nadu reach more than 8 m in any scenario, the region is unaffected by the coastal inundation due to high local topography. By examining the inundated area of different water levels, it is revealed that more than 75% of the total area is inundated with greater than 2 m water levels in the northern districts of Odisha and Ramanathapuram District in Tamil Nadu.

On the joint tropical cyclone wind and wave hazard

A simulation-based framework to estimate tropical cyclone (TC) induced wind and wave hazards is proposed by considering the TC tracks, wind field model, and significant wave height model. The proposed approach is applied to several offshore sites located near the coastline of mainland China. Both the block maximum analysis and event-based analysis are carried out. It was concluded that the marginal distribution of the annual maximum wind speed and of annual maximum significant wave height could be modelled using the generalized extreme value distribution. Plots of paired samples in terms of probability of the annual maximum wind speed (significant wave height) and of its companion significant wave height (wind speed) suggested that they could be characterized using Gumbel copula. The ranked correlation coefficient (i.e., Kendall’s tau) varies from about 0.4 to 0.7, depending on the considered paired random variable and site. The implication of the results in assigning the load combination factor for combined TC wind and wave load effect is discussed. The deaggregation results indicate that the identified most likely event causing p-quantile of the annual maximum wind speed differs from that identified from p-quantile of the annual maximum significant wave height. Therefore, for the reliability analysis, risk modelling, and emergency preparedness, it is recommended that two sets of hazard characterizations are be considered: one based on the maximum of wind speed and its companion wave height, and the other based on maximum wave height and its companion wind speed.