Hurricane Research Articles

Mortality caused by tropical cyclones in the United States

Natural disasters trigger complex chains of events within human societies1. Immediate deaths and damage are directly observed after a disaster and are widely studied, but delayed downstream outcomes, indirectly caused by the disaster, are difficult to trace back to the initial event1,2. Tropical cyclones (TCs)—that is, hurricanes and tropical storms—are widespread globally and have lasting economic impacts3–5, but their full health impact remains unknown. Here we conduct a large-scale evaluation of long-term effects of TCs on human mortality in the contiguous United States (CONUS) for all TCs between 1930 and 2015. We observe a robust increase in excess mortality that persists for 15 years after each geophysical event. We estimate that the average TC generates 7,000–11,000 excess deaths, exceeding the average of 24 immediate deaths reported in government statistics6,7. Tracking the effects of 501 historical storms, we compute that the TC climate of CONUS imposes an undocumented mortality burden that explains a substantial fraction of the higher mortality rates along the Atlantic coast and is equal to roughly 3.2–5.1% of all deaths. These findings suggest that the TC climate, previously thought to be unimportant for broader public health outcomes, is a meaningful underlying driver for the distribution of mortality risk in CONUS, especially among infants (less than 1 year of age), people 1–44 years of age, and the Black population. Understanding why TCs induce this excess mortality is likely to yield substantial health benefits.

Capturing Urban Heterogeneity Enhances Tropical Cyclones Simulation in Houston

AbstractUrbanization in the coastal region has increased socioeconomic losses from landfalling tropical cyclones (TCs). Although previous studies have explored the broad impacts of urbanization on TCs, the effect of heterogeneity caused by local intra‐urban variability has not been examined. To address this gap, this study utilized the urban Local Climate Zone (LCZ) to capture the urban landscape heterogeneity and the impacts of this representation on the simulation of the post‐landfall TCs characteristics in Houston. Taking the case of two recent TCs: Hurricane Harvey (occurred in 2017) and Tropical Storm Imelda (occurred in 2019), the study evaluated the impact of urban heterogeneity on 10‐m winds, 2‐m temperature, land surface temperature, and precipitation across Houston. The consideration of intra‐urban heterogeneity using LCZ can improve the 10‐m winds, 2‐m temperature, and spatial pattern of land surface temperature. Although the cumulative rainfall remained largely similar within the experiments (with and without LCZ), incorporating intra‐urban heterogeneity notably modified the spatial structure of urban rainfall, particularly in simulating heavy rainfall hot spots. These findings are consistent for both TCs and demonstrate the positive impact of incorporating intra‐urban heterogeneity on the landfalling TC simulations over the Houston area.

Propagation of underwater wave groups in a compressible ocean coupled with an elastic seafloor

The overall system of interest is an infinite half-space in which a compressible ocean is the top layer and an elastic seafloor (together with the crust beneath) forms a semi-infinite bottom layer. Whereas water-column compression waves and seafloor waves individually have received considerable attention, not much is known about their propagation as groups. This work utilizes the group behaviour of these waves to derive energy balance relations for wavenumber spectra for wave groups propagating through a mildly non-uniform water-column–seafloor system. Dispersion relations for the coupled system are derived using known kinematic and kinetic conditions at the interface, and free and forced wave solutions for the wavenumber spectra are obtained, with particular attention to the case when certain frequency–wavenumber combinations in the forcing excite the two-media system into resonance. Wavenumber spectra predicted using the theory for mildly non-uniform media are found to be close to those predicted assuming uniform media, though the effect of non-uniformity becomes more noticeable as the groups propagate farther from the generation area. Here, nonlinear interactions among stationary, random multi-directional surface-wave fields provide the forcing for groups of compression waves in the water and surface waves on the seafloor. The formulation includes the cumulative effect of multiple generation areas along the group propagation direction. Comparisons with observational data from a sensor array in the Atlantic Ocean indicate that the theory can be applied to reconstruct plausible combinations of generation areas and interaction times that are consistent with the measured data, for deriving approximate predictions at down-wave distances along the group propagation directions. Implications of this and other findings are discussed for (i) the potential for energy conversion from water-column compression waves on the seafloor, (ii) tracking of tropical cyclones from the seafloor, and (iii) quantification and comparative assessment of low-frequency mid-ocean ambient noise and microseism activity.

Parameterization of Vertical Turbulent Transport in the Inner Core of Tropical Cyclones and Its Impact on Storm Intensification. Part II: Understanding TC Intensification in a Generalized Sawyer–Eliassen Diagnostic Framework

Abstract An analytical method for diagnosing the interaction between the primary and secondary circulations of a tropical cyclone (TC) and vortex intensification is developed. It includes a diagnostic equation describing the mean secondary circulation of a TC in an unbalanced framework by including the radial eddy forcing in the analytical system. It is an extension of the Sawyer–Eliassen equation (SEE) developed from the strict gradient-wind balance. This generalized SEE (GSEE) remediates some of the limitations of SEE and can be used to diagnose both balanced and unbalanced dynamical processes during the TC evolution. Using GSEE, this study investigates how the tangential and radial eddy forcing affects the TC intensification simulated by the Hurricane Weather Research and Forecasting Model (HWRF) with differently parameterized turbulent mixing. The diagnostic results show that the supergradient component of radial eddy forcing contributes positively to the acceleration of the peak tangential wind, whereas the subgradient component of the radial eddy forcing tends to lower the height of peak tangential wind. The relative importance of negative and positive effects of tangential eddy forcing on TC intensification varies depending on the details of turbulence parameterization. For a turbulent kinetic energy (TKE) scheme used in this study, a large sloping curvature of mixing length in the low troposphere causes the tangential eddy forcing to produce a net positive tangential wind tendency near the location of the peak tangential wind. In contrast, a small sloping curvature of mixing length generates a net negative tangential wind tendency at the peak tangential wind. Significance Statement The interaction between the primary and secondary circulations of a tropical cyclone (TC) plays a key role in TC evolution. Historically, the secondary circulation induced by turbulence and convection is often described by a so-called Sawyer–Eliassen equation (SEE). While SEE has provided much insight into the TC dynamics in the past, the assumption of gradient-wind balance used by SEE prevents it from understanding TC unbalanced dynamics. To remediate the limitation, we extended the analytical framework into the unbalanced regime by including radial eddy forcing in the analytical system and derived a generalized SEE (GSEE). Using GSEE, this study investigates how tangential and radial eddy forcing affects TC intensification. The result highlights the importance of multiple roles that turbulence plays in the intensification of TCs.

On the Size Dependence in the Recent Time-Dependent Theory of Tropical Cyclone Intensification

Abstract Previous observational studies have shown that the intensification rate (IR) of a tropical cyclone (TC) is often correlated with its real-time size. However, no any size parameter explicitly appears in the recent time-dependent theory of TC intensification, while the theory can still well capture the intensity evolution of simulated TCs. This study provides a detailed analysis to address how TC real-time size affects its intensification and why no size parameter explicitly appears in the theory based on the results from axisymmetric numerical simulations. The results show that the overall correlation between the TC IR and real-time size as reported in previous observational studies, in terms of both the radius of maximum wind (RMW) and the radius of 17 m s−1 wind (R17), is largely related to the correlation between the IR and intensity because the size and intensity are highly interrelated. As a result, the correlation between the TC IR and size for a given intensity is rather weak. Diagnostic analysis shows that the TC real-time size (RMW and R17) has two opposing effects on intensification. A larger TC size tends to result in a higher steady-state intensity but reduce the conversion efficiency of thermodynamic energy to inner-core kinetic energy or the degree of moist neutrality of the eyewall ascent for a given intensity. The former is favorable, while the latter is unfavorable for intensification. The two effects are implicitly included in the theory and largely offset, resulting in the weak dependence of the IR on TC size for a given intensity.

Modulation of Tropical Cyclogenesis by Convectively Coupled Kelvin Waves

Abstract Tropical cyclone numbers can vary from week to week within a hurricane season. Recent studies suggest that convectively coupled Kelvin waves can be partly responsible for such variability. However, the precise physical mechanisms responsible for that modulation remain uncertain partly due to the inability of previous studies to isolate the effects of Kelvin waves from other factors. This study uses an idealized modeling framework—called an aquaplanet—to uniquely isolate the effects of Kelvin waves on tropical cyclogenesis. The framework also captures the convective-scale dynamics of both tropical cyclones and Kelvin waves. Our results confirm an uptick in tropical cyclogenesis after the passage of a Kelvin wave—twice as many tropical cyclones form 2 days after a Kelvin wave peak than at any other time lag from the peak. A detailed composite analysis shows anomalously weak ventilation during and after (or to the west of) the Kelvin wave peak. The weak ventilation stems primarily from anomalously moist conditions, with weaker vertical wind shear playing a secondary role. In contrast to previous studies, our results demonstrate that Kelvin waves modulate both kinematic and thermodynamic synoptic-scale conditions that are necessary for tropical cyclone formation. These results suggest that numerical models must capture the three-dimensional structure of Kelvin waves to produce accurate subseasonal predictions of tropical cyclone activity. Significance Statement Anticipating active tropical cyclone periods several weeks in advance could help mitigate the loss of lives and property due to these phenomena. Recent studies suggest that a type of tropical cloud cluster—known as convectively coupled Kelvin waves—can promote tropical cyclone formation. Kelvin waves travel around the world and can be detected days to weeks in advance. We use a simplified numerical model to isolate the effects of Kelvin waves on tropical cyclone formation. Our unique approach confirms that tropical cyclones are more likely to form 2 days after a Kelvin wave than before the wave. We also demonstrate that—contrary to previous perception—the enhancement of tropical cyclogenesis is due to both more moisture and weaker wind currents following the waves.

Responses of surface ozone under the tropical cyclone circulations: Case studies from Fujian Province, China

The circulation of tropical cyclones (TCs) exerts a multifaceted influence on the spatial and temporal distribution of surface pollutants. This study investigates the response of surface ozone (O3) concentration to the TCs in Fujian Province from June to December 2022 by analyzing the contributions of atmospheric pollutants, meteorological conditions, and dynamical transports. Empirical orthogonal function (EOF) decomposition methods are used to analyze the spatio-temporal distribution patterns of affected O3, and a Gradient Boosting Regression Trees (GBRT) machine learning model is employed to estimate surface O3 concentration, quantifying the influence of each factor. The results indicate an anomaly increase in O3 concentration during this period, with photochemistry-related meteorological conditions being the primary influencer, accounting for 66.9% of O3 variations, elucidating the interpretability of the GBRT model for attributing changes in O3 concentration. Low relative humidity and high temperature conditions have been identified as pivotal factors influencing the rise in O3 concentrations. The presence of TC undermines this predominant influence, amplifying the role of transport factors and other atmospheric pollutants. In the case studies of TC (Muifa and Nanmadol, 2022), the slow or stagnant TCs triggered persistent downdrafts in its periphery and brought favorable meteorological conditions such as clear sky and warm temperature for photochemistry. TCs also enhances the impact of horizontal and vertical dynamic transport on O3 concentrations. This work provides vital insights into the complex interplay between TCs and surface O3 concentrations, highlighting the need for targeted environmental and air quality management strategies in regions frequently impacted by TCs.

The role of diabatic heating/cooling in outer rainbands in the secondary eyewall formation and evolution in a numerically simulated tropical cyclone

In this study, the role of diabatic heating/cooling in outer rainbands (ORBs) in the formation and evolution of the secondary eyewall of a numerically simulated tropical cyclone (TC) is investigated. This is done through a series of sensitivity experiments under idealized conditions using a high-resolution cloud-resolving atmospheric model. The results show that artificially increasing diabatic heating in rainbands enhances convective activities in ORBs and leads to an earlier secondary eyewall formation (SEF), and later the faster weakening and earlier dissipation of the primary eyewall. Reducing diabatic heating in ORBs weakens the rainbands and delays the SEF but prolongs the duration of the double eyewall structure if the SEF occurs. Reducing diabatic cooling in ORBs enhances convective activity in rainbands but has little effect on convection in the primary eyewall prior to the SEF. However, it results in a widened eyewall structure and a stronger TC after the eyewall replacement. Increasing diabatic cooling in ORBs largely suppresses convection in rainbands and prohibits the SEF. These results demonstrate that diabatic heating/cooling in ORBs plays important roles in the SEF and evolution. Since diabatic heating/cooling in rainbands is sensitive to the near-core environmental relative humidity, our results demonstrate the critical importance of large-scale environmental moist condition to the formation and evolution of secondary eyewall in TCs. In addition, it is also found that when the area-averaged diabatic heating rate in ORBs becomes similar in magnitude to that in the primary eyewall, the secondary eyewall forms. Plain language summaryPrevious studies have demonstrated the importance of diabatic heating/cooling in outer rainbands to the structure and intensity changes of tropical cyclones (TCs) with a single eyewall. It is unclear whether and how diabatic heating/cooling in outer rainbands may affect the formation and evolution of the secondary eyewall in TCs. These issues have been addressed based on a series of sensitivity experiments under idealized conditions using a high-resolution atmospheric model. Results show that diabatic heating in outer rainbands is favorable for the secondary eyewall formation (SEF). Increasing diabatic heating in outer eyewall can lead to faster weakening and thus earlier dissipation of the primary eyewall. Diabatic cooling in outer rainbands suppresses convection in outer rainbands and prohibits the SEF. Since diabatic heating/cooling in outer rainbands is sensitive to the near-core environmental relative humidity, our results demonstrate the importance of the large-scale environmental moist condition to the SEF of TCs. We also found that when the area-averaged diabatic heating rate in outer rainbands becomes similar in magnitude to that in the primary eyewall, the secondary eyewall would form, which can be considered as a measure of the SEF in TCs. Key points1.Increasing diabatic heating in outer rainbands leads to earlier SEF, and faster weakening and earlier dissipation of the primary eyewall.2.Increasing diabatic cooling in outer rainbands suppresses convective activity in outer rainbands and is unfavorable for the SEF.3.When the area-averaged diabatic heating rate in outer rainbands and the eyewall become similar in magnitude, the secondary eyewall forms.

A regional ocean–atmosphere coupled model using CMA-TRAMS and LICOM: Preliminary results for tropical cyclone gale prediction over the northern South China Sea

This paper provides a comparative analysis of the performance of a high-resolution regional ocean–atmosphere coupled model in predicting tropical cyclone (TC) gales over the northern South China Sea. The atmosphere and ocean components of the coupled system are represented by the China Meteorological Administration's Tropical Regional Atmosphere Model for the South China Sea (CMA-TRAMS) and the LASG/IAP Climate system Ocean Model (LICOM), respectively. The Ocean Atmosphere Sea Ice Soil VersionH 3 (OASIS3) software has been utilized for the exchange of momentum, heat, and freshwater fluxes between these two components. An assessment of the coupled model's three-day predictions for five TCs’ gales was conducted. Preliminary findings indicate that the predicted TC tracks show less sensitivity to oceanic influences than the predicted TC intensities. Significant improvement in predicting the surface TC gales has been achieved through coupling the ocean model. This improvement is attributed to the impact of the warmer ocean's effect on TC intensification, counteracting the cooling effect of the cold wake. In summary, coupling has enhanced the model's predictive capabilities for TC gales. A detailed assessment of the coupled model's performance in predicting other tropical weather phenomena is forthcoming.摘要本文对一个具有我国自主知识产权的高分辨率区域海气耦合模式在南海北部台风大风预报性能进行对比分析. 该耦合模式的大气和海洋部分分别为中国气象局南海台风模式 (CMA-TRAMS) 和中国科学院大气物理研究所的海洋模式 (LICOM), 并用OASIS耦合器实现海气界面动量, 热量和淡水通量的交换. 本文对海气耦合模式预报5个台风的24, 48和72小时大风的性能进行了检验评估. 初步结果表明, 预报的台风路径对海洋影响的敏感性低于台风强度. 耦合模式使预报台风大风的准确性得到显著提高, 这一改进归结于海气耦合模式更为准确的海表温度对台风增强的影响, 从而抵消了冷尾流的降温效应. 总而言之, 耦合模式增强了模式对台风大风的预报能力. 关于海气耦合模式在其他热带天气中的预报能力评估将在未来工作中展示.

Parameterization of Vertical Turbulent Transport in the Inner Core of Tropical Cyclones and Its Impact on Storm Intensification. Part I: Sensitivity to Turbulent Mixing Length

Abstract In the inner core of a tropical cyclone, turbulence not only exists in the boundary layer (BL) but can also be generated above the BL by eyewall and rainband clouds. Thus, the treatment of vertical turbulent mixing must go beyond the conventional scope of the BL. The turbulence schemes formulated based on the turbulent kinetic energy (TKE) are attractive as they are applicable to both deep and shallow convection regimes in the tropical cyclone (TC) inner core provided that the TKE production and dissipation can be appropriately determined. However, TKE schemes are not self-closed. They must be closed by an empirically prescribed vertical profile of mixing length. This motivates this study to investigate the sensitivity of the simulated TC intensification to the sloping curvature and asymptotic length scale of mixing length, the two parameters that determine the vertical distribution of a prescribed mixing length. To tackle the problem, both idealized and real-case TC simulations are performed. The results show that the simulated TC intensification is sensitive to the sloping curvature of mixing length but only exhibits marginal sensitivity to the asymptotic length scale. The underlying reasons for such sensitivities are explored analytically based on the Mellor and Yamada level-2 turbulence model and the analyses of azimuthal-mean tangential wind budget. The results highlight the uncertainty and importance of mixing length in the numerical prediction of TCs and suggest that future research should focus on searching for physical constraints on mixing length, particularly in the low- to midtroposphere, using observations and large-eddy simulations. Significance Statement The parametric representation of subgrid-scale turbulent mixing is one of the major sources of uncertainty in numerical predictions of tropical cyclones (TCs). This study investigates how the numerical prediction of TC intensification is affected by the turbulent mixing length, a length scale that is required to close a turbulence scheme formulated based on the turbulent kinetic energy (TKE). The research highlights the uncertainty and importance of mixing length in numerical prediction of TCs and suggests that future research should focus on searching for physical constraints on the mixing length, particularly in the low- to midtroposphere, using observations and large-eddy simulations.

Impacts of Large-Scale Offshore Wind Farms on Tropical Cyclones: A Case Study of Typhoon Hato

Abstract With the rising global demand for renewable energy sources, a great number of offshore wind farms are being built worldwide, as well as in the northern South China Sea. There is, however, limited research on the impact of offshore wind farms on the atmospheric and marine environment, particularly tropical cyclones, which frequently occur in summertime in the South China Sea. In this paper, we employ the Weather Research and Forecasting (WRF) Model to investigate the impacts of large-scale offshore wind farms on tropical cyclones, using the case of Typhoon Hato, which caused severe damage in 2017. Model results reveal that maximum wind speeds in coastal areas decrease by 3–5 m s−1 and can reach a maximum of 8 m s−1. Furthermore, the wind farms change low-level moisture convergence, causing a shift in the precipitation center toward the wind farm area and causing a significant overall reduction (up to 16%) in precipitation. Model sensitivity experiments on the area and layout of the wind farm have been carried out. The results show that larger wind farm areas and denser turbine layouts cause a more substantial decrease in the wind speed over the coast and accumulated precipitation reduction, further corroborating our findings. Significance Statement This study holds significant implications for developing offshore wind farms in tropical cyclone-prone regions like the South China Sea. By focusing on Typhoon Hato as a case study, the research sheds light on the previously understudied relationship between large-scale offshore wind farms and tropical cyclones. The observed decrease in coastal wind speeds and altered precipitation patterns due to wind farm presence highlights the potential for mitigating cyclone-related risks in these regions. Additionally, the study’s sensitivity experiments underscore the importance of careful planning and design in optimizing wind farm layouts for maximum impact reduction. This research contributes vital insights into sustainable energy infrastructure development while minimizing environmental and meteorological risks in cyclone-prone areas.

TC‐GEN: Data‐Driven Tropical Cyclone Downscaling Using Machine Learning‐Based High‐Resolution Weather Model

AbstractSynthetic downscaling of tropical cyclones (TCs) is critically important to estimate the long‐term hazard of rare high‐impact storm events. Existing downscaling approaches rely on statistical or statistical‐deterministic models that are capable of generating large samples of synthetic storms with characteristics similar to observed storms. However, these models do not capture the complex two‐way interactions between a storm and its environment. In addition, these approaches either necessitate a separate TC size model to simulate storm size or involve post‐processing to capture the asymmetries in the simulated surface wind. In this study, we present an innovative data‐driven approach for TC synthetic downscaling. Using a machine learning‐based high‐resolution global weather model (ML‐GWM), our approach can simulate the full life cycle of a storm with asymmetric surface wind that accounts for the two‐way interactions between the storm and its environment. This approach consists of multiple components: a data‐driven model for generating synthetic TC seeds, a blending method that seamlessly integrates storm seeds into the surrounding while maintaining the seed structure, and a model based on a recurrent neural network to correct for biases in storm intensity. Compared to observations and synthetic storms simulated using existing statistical‐deterministic and statistical downscaling approaches, our method shows the ability to effectively capture many aspects of TC statistics, including track density, landfall frequency, landfall intensity, and outermost wind extent. Leveraging the computational efficiency of ML‐GWM, our approach shows substantial potential for TC regional hazard and risk assessment.

Impact of the Fujiwhara effect from tropical cyclones Seroja and Odette on ocean dynamic in Southern Indonesia: Insights from argo data and model analysis

Tropical cyclone (TC) disturbances can cause changes in ocean dynamics before, during, and afterwards. We employed an Argo data and ocean model product of Copernicus Marine Environment Monitoring Service (CMEMS) to address the gap in observations of the ocean response from the severe TC Seroja and its interactions with the tropical low TC Odette, known as the rare Fujiwhara effect phenomenon. Our study in southern Indonesia seawater was conducted between March and April 2021, beginning with reconciling the deviation of the CMEMS ocean model product by assessing the model accuracy to the Argo float data to build confidence in using the model for further analysis. Comparison revealed that the temperature model datasets have a higher correlation coefficient (∼0.95) with the Argo observation than the salinity model datasets. Further, we investigated the temporal evolution of vertical profiles and upper ocean responses both inside and beyond the TCs route zone. We discovered that the upper ocean response results in a colder and saltier surface with a recovery time of more than 15 days. Furthermore, as a result of the strong surface cooling, mixed layers inside the Seroja track were rapidly thickening following the passage of TC. Our findings provide insights into how the TCs Seroja and Odette affect the ocean layers, especially the primary ocean features and behaviours (temperature and salinity), using the Argo and model datasets.

Relationship between the geopotential height anomalies induced by tropical cyclones and the meridional movement of the western Pacific subtropical high

The present study employs statistical analysis to investigate the relationship between the geopotential height anomalies induced by tropical cyclones (TCs) and the meridional movement of the western Pacific subtropical high (WPSH), as well as the mechanisms through which TCs can induce such geopotential height anomalies. Results show that TCs can cause the WPSH to move northward, and the meridional motion of the WPSH ridgeline is related with the geopotential height anomalies, which is better indicated by the relative geopotential height anomalies. In the process of TCs causing the WPSH to move northward, the TCs cause abnormal horizonal warm (cold) advection and abnormal ascending (descending) motion in the region south (north) of 40°N. Since the influence of the abnormal vertical motion is weaker, the abnormal temperature tendency eventually shows a more consistent phase distribution with the abnormal horizonal temperature advection, which is favorable for the temperature to abnormally increase near 40°N. Such an abnormal increase in temperature causes the geopotential height to abnormally increase under the static equilibrium constraint, which further changes the location of the centroid of the WPSH geopotential height, and hence the location of the WPSH ridgeline changes as well.

Distinct Features of Tropical Cyclone Landfall over East Asia during Various Types of El Niño

Abstract Numerous studies focus on the impacts of ENSO diversity on tropical cyclone (TC) activities in the western North Pacific (WNP). In recent years, there is a growing threat of landfalling and northward-moving TCs in East Asia, accompanying an increase in central Pacific (CP) El Niño. Here, we aim to discover variations in landfalling TCs during various types of CP El Niño (CP-I and CP-II El Niño). It is found that significant changes in landfalling and going northward TCs over East Asia north 20°N are modulated by CP-I El Niño. During CP-I El Niño, TCs tend to landfall more often over the mainland of China with longer duration, moving distance, and stronger power dissipation index (PDI) after landfall and increased TC-induced rainfall, due to favorable conditions (beneficial steering flow, weak vertical wind shear, increased specific humidity, increased soil moisture, and temperature), especially significant over the northeastern part. The situation over the mainland of China is reversed during eastern Pacific (EP) El Niño and CP-II El Niño, with a significant decrease in the characteristics with corresponding unfavorable environments. Over the Korean Peninsula and Japan, the frequency of TC landfalls, as well as the duration and the moving distance after landfall, exhibits greater levels during CP-I and CP-II El Niño than during EP El Niño due to favorable steering flow, and thus, TC-induced rainfall enhances correspondingly. Regarding the PDI over the Korean Peninsula and Japan, it remains relatively consistent across all El Niño types. However, a notable increase in the PDI during EP El Niño could be attributed to the higher intensity of TCs prior to landfall.

Study on whitecapping dissipation process for wave modelling during tropical cyclones

The atmosphere-wave interaction is an important physical process during tropical cyclones. Understanding and modelling of this process are of great significance for the technical and functional design of coastal and harbor structures. At the high wind velocities of tropical cyclones, foams and sprays that are blown away from the sea form a slip layer between the atmosphere and the sea surface. This slip layer makes the atmosphere-wave interaction exhibit different characteristics compared with that at low wind velocities. The significant effect of this layer on the atmosphere is the reduction of aero-dynamical surface roughness, which has been used to improve the expression of the drag coefficient. On this basis, the effect of the slip layer on the sea surface is further explored in this study. The whitecap coverage may reach a low limit at high wind velocities, and a modified numerical method of whitcapping dissipation for the wave spectrum model is proposed based on the classic field observations of whitecaps. According to these observations, when developing waves appear, the variation characteristics of whitecap coverage are different from those of developed waves with low wind velocities. Thus, the critical friction velocity of wave states should be defined, which can be expressed by the threshold steepness of developed waves due to the negative correlation between wave age and wave steepness. The dissipation mode is then modified to gradually reach the limit with the increase of friction velocities, which is validated during 24 tropical cyclones measured with 26 buoys. The negative Bias of the default mode generally decreases with the increase of friction velocity, even reaching −0.8 m, while the Bias of the modified mode is mostly maintained between 0.2 m and −0.2 m.

Prescribed fire regimes influence responses of fungal and bacterial communities on new litter substrates in a brackish tidal marsh.

Processes modifying newly deposited litter substrates should affect fine fuels in fire-managed tidal marsh ecosystems. Differences in chemical composition and dynamics of litter should arise from fire histories that generate pyrodiverse plant communities, tropical cyclones that deposit wrack as litter, tidal inundation that introduces and alters sediments and microbes, and interactions among these different processes. The resulting diversity and dynamics of available litter compounds should affect microbial (fungal and bacterial) communities and their roles in litter substrate dynamics and ecosystem responses over time. We experimentally examined effects of differences in litter types produced by different fire regimes and litter loads (simulating wrack deposition) on microbial community composition and changes over time. We established replicated plots at similar elevations within frequent tidal-inundation zones of a coastal brackish Louisiana marsh. Plots were located within blocks with different prescribed fire regimes. We deployed different measured loads of new sterilized litter collected from zones in which plots were established, then re-measured litter masses at subsequent collection times. We used DNA sequencing to characterize microbial communities, indicator families, and inferred ecosystem functions in litter subsamples. Differences in fire regimes had large, similar effects on fungal and bacterial indicator families and community compositions and were associated with alternate trajectories of community development over time. Both microbial and plant community compositional patterns were associated with fire regimes, but in dissimilar ways. Differences in litter loads introduced differences in sediment accumulation associated with tidal inundation that may have affected microbial communities. Our study further suggests that fire regimes and tropical cyclones, in the context of frequent tidal inundation, may interactively generate substrate heterogeneities and alter microbial community composition, potentially modifying fine fuels and hence subsequent fires. Understanding microbial community compositional and functional responses to fire regimes and tropical cyclones should be useful in management of coastal marsh ecosystems.

Satellite based analysis of rapid intensification of Super Cyclone Amphan

Tropical Cyclones (TCs) are formidable natural hazards with destructive impacts on life and property along the tropical belt. TCs are responsible for multiple hazards such as riverine and urban floods, extreme winds, and lightning, storm surge significantly amplifying the threats they pose. Rapid Intensification (RI), defined as a sudden increase in Maximum Sustained Winds (MSWs) by 30 kt or more in 24 h, has been a growing concern. These events, characterized by a swift escalation in MSW are challenging to the forecasters and remain a considerable operational challenge, amplifying risks for coastal communities. Numerical modeling also struggles to predict RI, with limitations in describing inner core convective scale processes cited as a major limitation. Monitoring and assessing TCs heavily rely on satellite-based observations due to the absence of adequate in-situ measurements over the ocean. In the present study, we examine Super Cyclonic Storm (SuCS) Amphan, the first Super Cyclone of this century, that formed over the Bay of Bengal in 2020 using satellite imagery and derived products available in near-real time to monitor and identify the early signatures for the RI. It is observed that the intensification is intricately tied to substantial expansions in both the outer and inner core sizes along with its symmetricity before the RI. Notably, no significant alterations in size are observed between the very severe cyclonic storm (VSCS) and SuCS stages. The convection characteristics of TCs are found to provide crucial markers of their intensification, with a particular emphasis on polar satellite-based passive microwave imagery for analyzing embedded convection and early eye detection. Key observations indicate that inner convective ring patterns, identified through 37Ghz microwave imagery in lower-level convection, act as precursors to rapid intensification. Concurrently, the outer ring pattern observed during the mid-life course is found to permit further intensification of the system.

Natural hazard induced coastal vulnerability in Indian Sundarbans: A village-level study by using geospatial and statistical techniques

The Sundarbans, an area with a history dating back to the dawn of civilization, has faced numerous environmental hazards that have remarkably affected the lives and livelihoods of its natives. Strom surge and Tropical cyclones are the most substantial natural hazards, causing severe damage to local communities by affecting food security, the economy, shelter and health. By defining vulnerability as a function of exposure, sensitivity, and resilience capacity, we calculated a composite vulnerability index (CVI) using equal weight method (EWM) to assess the vulnerability of mouzas (small administrative units) to natural hazards in the Sundarbans, India. The vulnerability map has been drawn based on composite value of CVI which shows 30.50% of villages falling into the high vulnerability category and 12.06% in the very high vulnerability category. The mouza-level analysis also indicates that 22.62% of Sundarbans's villages are highly exposed to natural hazards and 19.70 % of villages are classified as being at Very high sensitive. Only 7.07% villages have very high adopted capacity against these natural hazards. Villages in the southern parts and along the coast were found to be more vulnerable to storm surges. Conversely, those situated at higher elevations in the central area exhibited lower vulnerability. In the northern part of the region, several villages faced high to very high vulnerability due to low-lying, waterlogged wetlands. This study offers vital insights for decision-makers, government planners, and disaster management professionals, assisting in the identification of high-risk populations and areas that require immediate preservation efforts.

Analysis of the annual number of tropical cyclones over Japan using the extreme value theory

We predicted the extreme value of the annual number of typhoons, tropical cyclones over the western North Pacific, approaching typhoons, and landing typhoons for 1951–2019 over Japan and the minimum central pressure for 1987–2020 using the extreme value theory. The generalized extreme value (GEV) distribution was used to fit the extreme indices. Various diagnostic plots for assessing the accuracy of the GEV model fitted to the annual number of typhoons, approaching typhoons, and landing typhoons are shown, and all four diagnostic plots support the fitted GEV model. The shape parameter ξ for the annual number of typhoons and approaching typhoons is negative, and the number of typhoons has a finite upper limit. The calculated upper limits were 44.5 and 23.2 for the annual number of typhoons and approaching typhoons, respectively. However, ξ in the number of landing typhoons was zero; therefore, the number of landing typhoons did not have a finite upper limit, and there was a possibility that a significant risk would occur. The number of typhoons increased for 1951–2019. The minimum central pressure of typhoons estimated using geostationary satellite images decreased for 1987–2020, and the number of strong typhoons increased. The annual number of violent typhoons ( 54 m/s) increased in the 2010s. The calculated limit of the minimum central pressure of the typhoon is 877 hPa. When the Pacific Decadal Oscillation (PDO) index is positive, more violent typhoons tend to occur.