Cyclonic Wind Research Articles

Time Series Analysis of Congestive Heart Failure Discharges in Florida (USA) Post Tropical Cyclones.

The aim of this study was to analyze congestive heart failure (CHF) discharges in Florida (USA) post tropical cyclones from 2007 through 2017. This was a retrospective longitudinal time series analysis of hospital CHF quarterly discharges across Florida using the Healthcare Cost and Utilization Project (HCUP) database. The autoregressive integrated moving average (ARIMA) model was used with correlated seasonal regressor variables such as cyclone frequency, maximum cyclone wind speed, average temperature, and reports of influenza-like illness (ILI). A total of 3,372,993 patients were identified, with average age in each quarter ranging 72.2 to 73.9 years and overall mortality ranging 4.3% to 6.4%. The CHF discharges within each year peaked from October through December and nadired from April through June with an increasing overall time trend. Significant correlation was found between CHF discharge and the average temperature (P <.001), with approximately 331.8 less CHF discharges (SE = 91.7) per degree of increase in temperature. However, no significant correlation was found between CHF discharges and frequency of cyclones, the maximum wind speed, and reported ILI. This study suggests that with the current methods and the HCUP dataset, there is no significant increase in overall CHF discharges in Florida as a result of recent previous cyclone occurrences.

Uncertainty assessment and an improved CYGNSS cyclonic wind speed retrieval model for cyclones over North Indian Ocean

Uncertainty assessment and an improved CYGNSS cyclonic wind speed retrieval model for cyclones over North Indian Ocean

Estimating the tropical cyclone wind structure using physics-incorporated networks

Satellite-based remote sensing technology plays a significant role in identifying tropical cyclones (TCs), and most of the current research focuses on intensity estimation. However, analyzing the wind structure of TCs, which is directly related to the danger they bring, remains a challenge. By adding prior knowledge of TCs into the model, we propose a physics-incorporated network based on multi-task learning to estimate wind radii and intensity, whose layers can automatically extract rotation-invariant features related to the TC core from multichannel satellite imageries. In addition, we build a more comprehensive dataset, including global Statistical Hurricane Intensity Prediction Scheme (SHIPS) predictors, to tackle the structure task. We compare our model with existing methods, and it shows that our model gets better results in estimating 50-knot and 64-knot wind radii and achieves a 4.87-knot root-mean-squared error (RMSE) of intensity. By predicting probability density functions, our model quantifies the uncertainty of the result. The experimental results show that the incorporation of rotation equivariance into the layers can enhance TC structure estimation. By considering the feature importance of multi-source predictors, we find that our model pays attention to key predictors related to the TC structure. Specifically, the tangential wind speed at 500 km from the TC center and the radius of the 5-knot wind both greatly reduce the error of the estimated parameters. Finally, two case studies show that the proposed model performs well most of the time during TCs’ rapid intensification. However, when TCs’ system is not well organized, estimating the wind structure is challenging.

Anomalously fresh Chukchi Sea surface salinity in summer-autumn 2021

ABSTRACT The Chukchi Sea is a marginal sea in the Arctic with a mixed layer that is a few psu units saltier than ambient open Arctic water. Such higher salinity is maintained by salty and warm Pacific water inflow through the Bering Strait, implying that changes in inflow characteristics should affect the thermohaline properties of the Chukchi Sea. Recently, two additional controlling factors have been highlighted – the strength of boundary currents along the Siberian coast, and meridional exchanges due to wind-driven transport. In this note, we illustrate that anomalous fresh Chukchi Sea surface salinity in summer-autumn 2021 may be related to the anomalous southward shift of the ice edge and its meltwater source. These anomalous ice conditions occur concurrently with anomalously low Beaufort High, anomalous westerly cyclonic winds over ice-covered and open water Chukchi Sea, and related southward Ekman transport of late season meltwater. The September 2021 ice expansion was the largest in 1981–2021 detrended ice records.

Atmospheric impacts of local sea surface temperatures versus remote drivers during strong South China Sea winter cold tongue events

AbstractSea surface temperatures (SSTs) in the western part of the South China Sea (SCS) are cooler than in the eastern part in boreal winter, owing to a winter climatological cold tongue (CT). In this study, using a regional atmospheric model configured for the Maritime Continent, we assess the atmospheric impacts of local (or SCS) SSTs versus those from remote drivers (e.g., western tropical Pacific SSTs) during strong CT events with anomalously cool SSTs. In the local run, more rainfall is observed over the eastern SCS, but no significant atmospheric impacts are found over the CT region when SSTs associated with strong CT events are imposed within the SCS while climatological conditions are imposed elsewhere. SCS SST anomalies during strong CT events do not significantly modify the regional wind circulation. The lack of atmospheric response to SSTs over the CT region may be explained by the wintertime mean SSTs (i.e., &lt;27–28°C) over the CT region that are inadequate to trigger deep atmospheric convection, while eastern SCS SSTs are high enough. The increase of anomalous positive moist static energy (MSE) near the sea level over the eastern SCS indicates underlying warm eastern SCS SST anomalies could be influencing positive rainfall anomalies. In the remote run, imposing climatological SCS SSTs but remote SSTs and lateral boundary conditions linked to strong CT events results in cyclonic wind and positive rainfall anomalies over the eastern SCS and Philippines, which are a Matsuno–Gill response to the diabatic heating anomalies over the warm western tropical Pacific SST anomalies. Positive rainfall and cloud cover anomalies associated with the cyclonic wind anomalies are due to the anomalous positive MSE import into the eastern SCS by horizontal advection.

Tropical Cyclone Wind Direction Retrieval From Dual-Polarized SAR Imagery Using Histogram of Oriented Gradients and Hann Window Function

Accurate knowledge of wind directions plays a critical role in ocean surface wind retrieval and tropical cyclone (TC) research. Under TC conditions, apparent wind streaks induced by marine atmospheric boundary layer rolls can be detected in VV- and VH-polarized synthetic aperture radar (SAR) images. It suggests that though relatively noisy, VH signals may help enhance wind streak orientation magnitudes contained in VV signals and thus to achieve a more accurate wind direction estimation. The study proposes a new method for wind direction retrieval from TC SAR images. Unlike conventional approaches, which calculate wind directions from single-polarization imagery, the method combines VV and VH signals to obtain continuous wind direction maps across moderate and extreme wind speed regimes. The technique is developed based on the histogram of oriented gradient descriptor and Hann window function, accounting for the contribution of neighboring wind streak information (weighted by separation distances). As a case study, the wind directions over four TCs (Karl, Maria, Douglas, and Larry) are derived and verified by estimates from simultaneous dropsonde, ASCAT and ECMWF winds, showing a promising consistency. Furthermore, a more comprehensive statistical analysis is carried out with 14 SAR images, revealing that obtained wind directions have a correlation coefficient of 0.98, a bias of −6.07 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> and a RMSD of 20.24 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> , superior to estimates from VV (0.97, −7.84 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> , and 24.23 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> , resp.) and VH signals (0.96, −10.46 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> , and 29.53 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> , resp.). The encouraging results prove the feasibility of the technique in SAR wind direction retrieval.

Can lightning indicate genesis frequency of tropical cyclones over the South China Sea?

AbstractThe present study identifies a significant negative correlation of the South China Sea (SCS) summer–fall (JJASON) tropical cyclone (TC) genesis with the previous boreal spring (MAM) total lightning flash rate east of the Philippines during 1996–2013. The increased lightning flash rate east of the Philippines signifies an enhancement in deep convection, which induces cyclonic wind anomalies to the west via a Gill‐type atmospheric response and results in an increase in convection and cloud cover over the SCS during spring. The atmospheric changes lead to a decrease in sea surface temperature (SST) and ocean heat content (OHC) in the SCS by reducing downward short‐wave radiation and enhancing oceanic upwelling. The negative SST and OHC anomalies persist from spring to summer–fall and induce unfavourable thermodynamic anomalies, suppressing the SCS TC genesis during JJASON. Thus, the spring total lightning flash rate east of the Philippines, as an indicator of deep convection, may serve as a precursor of the SCS TC genesis.

Impact of Tropical Cyclone Wind Forcing on the Global Climate in a Fully Coupled Climate Model

Abstract Tropical cyclones (TCs) alter upper-ocean temperature and influence ocean heat content via enhanced turbulent mixing. A better understanding of the role of TCs within the climate system requires a fully coupled modeling framework, where TC-induced ocean responses feed back to the atmosphere and subsequently to the climate mean state and variability. Here, we investigate the impacts of TC wind forcing on the global ocean and the associated feedbacks within the climate system using the fully coupled Community Earth System Model version 1.3 (CESM1.3). Using the low-resolution version of CESM1.3 (1° atmosphere and ocean grid spacing) with no intrinsic TCs, we conduct a suite of sensitivity experiments by inserting TC winds extracted from a high-resolution (0.25° atmosphere grid spacing) TC-permitting simulation into the low-resolution model. Results from the low-resolution TC experiment are compared to a low-resolution control simulation to diagnose TCs’ impact. We found that the added TC winds can increase ocean heat content by affecting ocean vertical mixing, air–sea enthalpy fluxes, and cloud amount. The added TCs can influence mean SST, precipitation, ocean subsurface temperature, and ocean mixed layer depth. We found a strengthening of the wind-driven subtropical cells and a weakening of the Atlantic meridional overturning circulation due to the changes of surface buoyancy fluxes. TCs in the model cause anomalous equatorward ocean heat convergence in the deep tropics and an increase of poleward ocean heat transport out of the subtropics. Our modeling results provide new insights into the multiscale interactions between TCs and the coupled climate system.

Evaluating the Increasing Trend of Strength and Severe Wind Hazard of Philippine Typhoons Using the Holland-B Parameter and Regional Cyclonic Wind Field Modeling

For the Philippines, a country exposed to multiple natural hazards, such as severe winds, sustainable development includes resiliency. A severe wind hazard is raised by tropical cyclones in the Western Pacific, known as typhoons, which frequent the Philippines. Therefore, adequately evaluating wind hazards and their impact is crucial for sustainable building design. Acknowledging the effects of climate change on said hazards requires adaptation to their consequences, which necessitates a deeper understanding of the changing behavior of typhoons in recent years. For this study, detailed wind information from the Japanese Meteorological Agency from 1977 to 2021, the Holland-B parameter, and the radius of maximum wind speed for each typhoon, are determined for simulation of the regional cyclonic wind field. The analysis of the Holland-B parameters, which represent the steepness of the pressure gradient and tropical cyclone convection, suggests that the Holland-B parameters have been increasing since 2011. The evaluation of the maximum regional wind fields and the return period wind fields caused by typhoons also indicate an increasing trend in severe wind hazards. Seasonality for the location of severe wind hazards is also observed, with Visayas and Mindanao experiencing an increase (decrease) during the Northeast (Southwest) Monsoon season and Luzon experiencing an increase (decrease) during the Southwest (Northeast) Monsoon season.

Baroclinic Ocean Response to Climate Forcing Regulates Decadal Variability of Ice‐Shelf Melting in the Amundsen Sea

AbstractWarm ocean waters drive rapid ice‐shelf melting in the Amundsen Sea. The ocean heat transport toward the ice shelves is associated with the Amundsen Undercurrent, a near‐bottom current that flows eastward along the shelf break and transports warm waters onto the continental shelf via troughs. Here we use a regional ice‐ocean model to show that, on decadal time scales, the undercurrent's variability is baroclinic (depth‐dependent). Decadal ocean surface cooling in the tropical Pacific results in cyclonic wind anomalies over the Amundsen Sea. These wind anomalies drive a westward perturbation of the shelf‐break surface flow and an eastward anomaly (strengthening) of the undercurrent, leading to increased ice‐shelf melting. This contrasts with shorter time scales, for which surface current and undercurrent covary, a barotropic (depth‐independent) behavior previously assumed to apply at all time scales. This suggests that interior ocean processes mediate the decadal ice‐shelf response in the Amundsen Sea to climate forcing.

Tropical cyclone Wind Pump induced chlorophyll-a enhancement in the South China Sea: A comparison of the open sea and continental shelf

The continental shelf and open sea region have different ocean physical and environmental responses to tropical cyclones (TC). The present study firstly compared the grid-based maximum response (GMR) of sea surface chlorophyll a (Chl-a) to TCs Wind Pump between the continental shelf (depths 50-200m) and open sea (depths&amp;gt;200 m) region in the South China Sea (SCS) during 1998-2020, using multiple-satellite data. For all TC events, the average Chl-a increases by 0.13 mg/m3. The comparisons between the pre- and post-TC periods show that Chl-a increases by 0.18 mg/m3 (115%) in the continental shelf and 0.07 mg/m3 (57%) in the open sea region, respectively. In both areas, TC-induced Chl-a enhancement (Chl_en) strongly depends on TC maximum wind speed and translation speed. The strong and fast-moving TCs and weak and slow-moving TCs both induce the maximum Chl_en in the continental shelf region. While in the open sea, the maximum Chl_en was induced by the strong and slow-moving TCs. Overall, our results reveal that the TC wind pump’s effects on Chl-a enhancement are stronger in the continental shelf region than in the open sea.

Site- and building height-dependent design extreme wind speed vertical profile of tropical cyclone

Tropical cyclone (TC) wind is one of the dominant loadings in the design of building structures. The radial distance-dependent vertical profile and prominent jet structure or super gradient of TC winds make the conventional terrain-dependent design profile inadequate for describing TC wind loadings along the height. Herein, a stochastic simulation-based algorithm is developed to determine the design extreme wind speed vertical profile of TC using a quasi-3D TC wind field model. The wind field model is first described and validated by comparing the vertical wind speed profiles with the upper-level dropsonde data and lower-level tower observation results. The evolution of the wind profile during the passage of historical real storms is reproduced by introducing optimal fitting results for the wind field parameters. Ten-thousand-year synthetic tracks are simulated to obtain the design extreme wind speeds for several coastal cities. The design extreme wind speed composite profile and structure height-dependent outer envelope profile (OEP) are proposed, which are applicable to a certain height of interest and buildings with different heights, respectively. These profiles also depend on terrain exposure, return period, and location of the site of interest. The code-suggested profiles are confirmed to underestimate the TC-induced wind loadings along the height, especially at sites with lower roughness lengths. The power law profile is still applicable, but larger power coefficients should be utilized, and the design extreme wind speed at 10m should be increased with an increase in the structure height. This study provides a forward step towards the rational estimation of TC-induced wind loadings for high-rise structures. • The radial distance-dependent vertical profile and prominent jet structure of tropical cyclone winds are reproduced. • The design extreme wind speed composite profile and structure height-dependent outer envelope profile (OEP) for tropical cyclone are proposed. • The inadequacy of current code-suggested wind speed vertical profiles to tropical cyclone winds is discussed. • The design extreme wind speed vertical profiles of tropical cyclone in several coastal cities are developed.

A Bias Correction Scheme with the Symmetric Cloud Proxy Variable and Its Influence on Assimilating All-Sky GOES-16 Brightness Temperatures

Abstract All-sky assimilation of brightness temperatures (BTs) from GOES-16 infrared water vapor channels is challenging, primarily because these channels are sensitive to cloud ice that causes large nonlinear errors in the forecast and forward models. Thus, bias correction (BC) for all-sky assimilation of GOES-16 BTs is vital. This study examines the impacts of different BC schemes, especially for a scheme with a quartic polynomial of cloud predictors (the ASRBC4 scheme), on the analysis and WRF Model forecasts of tropical cyclones when assimilating the all-sky GOES-16 channel-8 BTs using the NCEP GSI-based 3D ensemble–variational hybrid data assimilation (DA) system with variational BC (VarBC). Long-term statistics are performed during the NASA Convective Processes Experiment field campaign (2017). Results demonstrate that the ASRBC4 scheme effectively reduces the average of all-sky scaled observation-minus-backgrounds (OmBs) in a cloudy sky and alleviates their nonlinear conditional biases with respect to the symmetric cloud proxy variable, in contrast to the BC schemes without the cloud predictor or with a first-order cloud predictor. In addition, adopting the ASRBC4 scheme in DA decreases the positive temperature increments at 200 hPa and the accompanying midlevel cyclonic wind increments in the analysis of Tropical Storm (TS) Cindy (2017). Applying the ASRBC4 scheme also leads to better storm-track predictions for TS Cindy (2017) and Hurricane Laura (2022), compared to experiments with other BC schemes. Overall, this study highlights the importance of reducing nonlinear biases of OmBs in a cloudy sky for successful all-sky assimilation of BTs from GOES-16 infrared water vapor channels.

Relative accuracy of HWRF reanalysis and a parametric wind model during the landfall of Hurricane Florence and the impacts on storm surge simulations

Prediction and reanalysis of storm surge rely on wind and pressure fields from either parametric tropical cyclone wind models or numerical weather model reanalysis, and both are subject to large errors during landfall. This study assesses two sets of wind/pressure fields for Hurricane Florence that made landfall along the Carolinas in September 2018 and appraises the impacts of differential structural errors in the two suites of modeled wind fields on the predictive accuracy of storm surge driven thereby. The first set was produced using Holland 2010 (H10), and the second set is the Hurricane Weather Research and Forecasting (HWRF) reanalysis created by the NWS National Centers for Environmental Prediction (NCEP). Each is validated using a large surface data set collected at public and commercial platforms and then is used as input forcing to a 2-D coastal hydrodynamic model (Delft3D Flexible Mesh) to produce storm surge along the Carolina coasts and major sounds. Major findings include the following. First, wind fields from HWRF are overall more accurate than those based on H10 for the periphery of the storm, though they exhibit limitations in resolving high wind speeds near the center. Second, applying H10 to the best track data for Florence yields an erroneously spike in wind speed on September 15th when the storm reduced to a tropical depression. Third, HWRF wind fields exhibit a progressively negative bias after landfall, likely due to deficiencies of the model in representing boundary layer processes, and to the lack of assimilation of surface product after landfall for compensating for these deficiencies. Fourth, using HWRF reanalysis as the forcings to Delft3D yields more accurate peak surges simulations, though there is severe underestimation of surge along the shoreline close to the track center. The peak surge simulations by Delft3D are biased low when driven by H10, even though over several locations the H10 model clearly overpredicts surface wind speeds. This contrast highlights the importance of resolving wind fields further away from the center in order to accurately reproduce storm surge and associated coastal flooding.

SAR and ASCAT Tropical Cyclone Wind Speed Reconciliation

Wind speed reconciliation across different wind sources is critically needed for extending available satellite wind records in Tropical Cyclones. The deviations between wind references of extremes, such as the moored buoy data and dropsonde wind estimates for guidance on geophysical model function development, are one of the main causes of wind speed differences for wind products, for instance, the overestimation of Synthetic Aperture Radars (SARs) relative to ASCAT winds. The study proposes a new wind speed adjustment to achieve mutual adjustment between ASCAT CMOD7 winds and simultaneous SAR wind speeds. The so-called CMOD7D-v2 adjustment is constructed based on the statistical analysis of SAR and ASCAT Tropical Cyclone acquisitions between 2016 and 2021, showing a satisfactory performance in wind speed reconciliation for winds with speeds higher than 14 m/s. Furthermore, the error characteristics of the CMOD7D-v2 adjustment for Tropical Cyclone winds are analyzed using the Triple Collocation analysis technique. The analysis results show that the proposed wind adjustment can reduce ASCAT wind errors by around 16.0% when adjusting ASCAT winds to SAR wind speeds. In particular, when downscaling SAR winds, the improvement in ASCAT wind errors can be up to 42.3%, effectively alleviating wind speed differences across wind sources. Furthermore, to avoid the impacts of large footprints by ASCAT sensors, wind speeds retrieved from SAR VV signals (acting as a substitute for ASCAT winds) are adjusted accordingly and compared against SAR dual-polarized winds and collocated Stepped Frequency Microwave Radiometer (SFMR) observations. We find that the bias values of adjusted winds are lower than products from other adjustment schemes by around 5 m/s at the most extreme values. These promising results verify the plausibility of the CMOD7D-v2 adjustment, which is conducive to SAR and ASCAT wind speed comparisons and extreme wind analysis in Tropical Cyclone cases.

Variability of Heat Content and Eddy Kinetic Energy in the Southeast Indian Ocean: Roles of the Indonesian Throughflow and Local Wind Forcing

Abstract Prominent interannual-to-decadal variations were observed in both heat content and mesoscale eddy activity in the southeast Indian Ocean (SEIO) during 1993–2020. The 2000–01 and 2008–14 periods stand out with increased 0–700-m ocean heat content (OHC) by ∼4.0 × 1021 J and enhanced surface eddy kinetic energy (EKE) by 12.5% over 85°–115°E, 35°–12°S. This study provides insights into the key dynamical processes conducive to these variations by analyzing observational datasets and high-resolution regional ocean model simulations. The strengthening of the Indonesian Throughflow (ITF) and anomalous cyclonic winds over the SEIO region during the two periods are demonstrated to be the most influential. While the ITF caused prevailing warming of the upper SEIO, the cyclonic winds cooled the South Equatorial Current and attenuated the warming in the subtropical SEIO by evoking upwelling Rossby waves. The EKE increase exerts significant influence on OHC only in the Leeuwin Current system. Dynamical instabilities of the Leeuwin Current give rise to high EKEs and westward eddy heat transport in climatology. As the Leeuwin Current was enhanced by both the ITF and local winds, the elevated EKEs drove anomalous heat convergence on its offshore flank. This process considerably contributes to the OHC increase in the subtropical SEIO and erases the wind-driven cooling during the two warm periods. This work highlights the vital role of eddies in regional heat redistribution, with implications for understanding time-varying ocean heat storage in a changing climate.

Interannual variations and their dynamic mechanisms of wintertime temperature inversions in the Gulf of Alaska

Using the Simple Ocean Data Assimilation Version 2.2.4 dataset from 1950 to 2010, we analyzed the interannual variations in wintertime temperature inversions in the Gulf of Alaska (GOA), and the linkages to the Aleutian Low are also examined. The results show that the climatological wintertime temperature inversions is predominantly distributed in the northwestern GOA (NWGOA) and northern GOA (NGOA), in which it is stronger in the NWGOA than in the NGOA. Interannual variations in the temperature difference (∆T) are pronounced and are mainly controlled by the temperature minimum (Tmin) of the inversions layer. The temperature inversions layer became warmer and shallower during 1950–2010, among Tmin and the temperature maximum (Tmax) was notably warming, and the upper edge depth (Dmin) and lower edge depth (Dmax) revealed significant shoaling. ∆T decreased by 0.12 °C from 1950 to 2010 in the NWGOA but had no trend in the NGOA. The interannual variations in wintertime temperature inversions are controlled by the mixed-layer temperature anomalies and are closely correlated with the changes in the Aleutian Low. The weakened (deepened) Aleutian Low during strong (weak) ∆T winters could cause the weakening (enhancement) of the cyclone wind field in the North Pacific subarctic region, which is conducive to slowing down (spinning up) the flow of the Alaskan Gyre and the transportation of warm air into the GOA. Thus, a negative (positive) Tmin anomalies within the mixed layer is larger than Tmax anomalies, resulting in a larger (smaller) ∆T; meanwhile, the strong (weak) cooling effect leads to a deeper (shallower) Dmax. The interannual variations in the wintertime temperature inversions could be influenced by net heat flux and advection anomalies in the NWGOA, but only caused by net heat flux anomalies in the NGOA.

Influence of sea surface wave-dependent roughness on summer precipitation over the Southeastern United States

To study the influence of ocean surface roughness on summer precipitation over the southeastern United States, we perform singular value decomposition (SVD) analysis between the mean summer precipitations and the significant wave height from 1979 to 2017 over the Gulf of Mexico (GOM). The first dominant mode shows that the swell energy in the northern GOM is larger than that in the southern GOM, especially over the region adjacent to the southeastern United States (SE-US). Meanwhile, the precipitation in the SE-US is much heavier than the other regions. Composite analysis shows that when the first pattern takes place, the wind speed is small near the region of the SE-US, swell dominates. There is a cyclonic wind anomaly at 850 hPa over the SE-US, which results in strong upward motion, therefore heavy rainfall in this region. To further study the effect of the swell on the precipitation in the SE-US, we also design two numerical experiments using the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) Modelling System. In the control (CTL) experiment, the popular Charnock aerodynamical roughness length parameterization is adopted. In the other experiment, a wave-dependent roughness scheme is used. The precipitation in the SE-US is better simulated in the wave-dependent roughness experiment than in the CTL experiment. In summer, the 10-m wind speed is weak in the northeastern Gulf of Mexico, and that means the swell is dominant in this region. The wave-dependent surface roughness strengthens the wind, which means that the momentum is transferred from the wave to the atmosphere under swell dominant conditions. The increase of the shear term and the cyclonic wind anomaly in the lower layers of the atmosphere leads to a stronger upward motion which drives heavier rainfall in the SE-US.

Fragility assessment for new and deteriorated portal framed industrial buildings subjected to tropical cyclone winds

Low-rise portal framed industrial buildings are widely used as warehouses, workshops and storage facilities. Damage surveys following severe tropical cyclones have shown that both structural and non-structural damage can occur to these buildings. While non-structural damage to the building envelope of portal framed industrial buildings are considered by several existing fragility models, almost none exist that include structural failures in the wind fragility assessment. This study develops a fragility assessment method for portal framed industrial buildings that accounts for wind-induced damage to both structural (steel portal frame and end wall frame) and non-structural (metal cladding system and fenestration) building components. Fragility curves are developed for a prototype industrial building located on the cyclone-prone east coast of Australia considering four damage states with increasing damage severity. A Monte Carlo simulation incorporating probabilistic models of the spatio-temporal variable wind pressures, wind-induced demands and component capacities is employed to conduct the fragility assessment for both individual building components and the building system under critical failure modes. It was found that the fragility of structural framing is non-negligible when wind speed exceeds 80% of the design level. Structural framing failure is a major contributor to the most severe damage state and is a necessary inclusion in the fragility assessment for this type of building. A sensitivity analysis also showed that fastener corrosion can significantly increase the fragility of deteriorated buildings near to coastlines, particularly for low levels of damage.

Investigation of Tropical Cyclone Wind Models With Application to Storm Tide Simulations

AbstractThe hazards induced by tropical cyclones (TCs), for example, high winds, extreme precipitation, and storm tides, are closely related to the TC surface wind field. Parametric models for TC surface wind distribution have been widely used for hazards and risk analysis due to their simplicity and efficiency in application. Here we revisit the parametric modeling of TC wind fields, including the symmetrical and asymmetrical components, and its applications in storm tide modeling in the North Atlantic. The asymmetrical wind field has been related to TC motion and vertical wind shear; however, we find that a simple and empirical background‐wind model, based solely on a rotation and scaling of the TC motion vector, can largely capture the observed surface wind asymmetry. The implicit inclusion of the wind shear effect can be understood with the climatological relationship between the general TC motion and wind shear directions during hurricane seasons. For the symmetric wind field, the widely used Holland wind profile is chosen as a benchmark model, and we find that a physics‐based complete wind profile model connecting the inner core and outer region performs superiorly compared to a wind analysis data set. When used as wind forcing for storm tide simulations, the physics‐based complete wind profile integrated with the background‐wind asymmetry model can reproduce the observed storm tides with lower errors than the often‐used Holland model coupled with a translation‐speed‐based method.